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Effect of Antenna Configurations
on Soft Handoff and Coverage Performance
of Wireless CDMA Systems
Harry W. Liu
-4 thesis submit ted in conformity with the requirements
for the clegree of Master of -4pplied Science
Graduate Department of Electrical and Computer Engineering
University of Toronoto
@Copyright by Harry W. Liu 2000
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Effect of Antenna Configurations on Soft Handoff and
Coverage Performance of Wireless CDMA Systems
Harry W. Liu
Master of -4pplied Science, 2000
Depart ment of Electrical and Corn puter Engineering
Uiiiversi ty of Toronto
Abstract
An analytical model of base station antenna configurations for wireless CDMA sys-
tems is proposed. By both numerical evaluation and simulations we investigate the
effect of antenna pattern, antenna downtilting, azimuth configuration, and ce11 lay-
out on soft handoff and forward link coverage performance. The investigation shows
that antenna patterns with different characteristics should be properly selected based
on different system configurations. For three-sectorized systern, pattern with 65'
beamwidt h gives best performance. .4nd non-interleaving configuration, or antenna
orientation of within IO0: is rational. For six-sectorized system, antenna with 33"
bearnwidth a t 15' orientation is preferred. Its corresponding total handoff percent-
age is comparable to the selections for three-sectorized case. Antenna downtilting
can substantially affect the handoff and coverage probability distributions but their
percentage variations are ncjt significant. This model provide a basic building block
for future development of the software tool for planning and optimizing the forward
link of cellular CDM-4 network.
Acknowledgement s
1 a m so grateful to my wonderful parents and granny for their love and care. -4nd
thanks for my sister for her valuable input.
1 would like to thank rny supervisor, Prof. E. Sousa. for his excellent guidance,
support. and understandings throughou t the course of my graduate study.
1 also want express rny gratitude to Mr. Dragan Nerandzic of Bell Mobility for
tiis invaluable ideas and numerous suggestions.
Thanks to my cornmittee members: Professor R. Kwong, Professor K. Plataniotis,
and Professor 1. Katzela for their careful reading of the thesis and supportive advice.
Special thanks to my colleague, Chris Gao, for his friendship and great comments.
1 am also indebted to Sarah Cherian, Judith Levene, Diane Silva, Susan Grant and
Debie Stewart for their help and kindly assitance.
Last but not least, 1 gratefully acknowledge the financial support 1 received from
the Natural Sciences and Engineering Research Council of Canada (NSERC).
Contents
Abstract
Acknowiedgements
Table of Contents
List of Tables
List of Figures
iii
vii
viii
1 Introduction 1
1.1 The CDM-4 System Link Structure . . . . . . . . . . . . . . . . . . .- 5
1.2 The Handoffs in CDW4 System . . . . , . . . . . . . . . . . . . - . . 7
1.2.1 Handoff Types . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2.2 Set Main1;enance . . . . . . . . . . . . . . . . . . . . . . . . . I O
1.2.3 The Handoff Process . . . . . . . . . . . . . . . . . . . . - . . 11
1.3 Motivations and Objectives . . . . . . . . . . . . . . . . . . . . . . . 13
1.4 ThesisOutline. . . . . . . . . . . . . . . . . - . . . . . . . . . . . . . 14
2 Analysis of Handoffs and Coverage in CDMA Mobile Systems 16
2.1 Introduction . . . . . . . . . . . . . . . . - . . - . . . . - . . . . . . 16
2.2 System Mode1 and .4ssumptions . . . . . . . . . . . . . . . . . . . . . 17
2.3 Handoff and Coverage Analysis . . . . . . . . . . . . . . . . . . - . . 19
2 .3.1 Fonvard Link Coverage -4nalysis . . . . . . . . . . . . . . . . .
2.3.2 Soft Handoff Probability and Percentage . . . . . . . . . . . . 2.3.3 Softer Handoff Probability and Percentage . . . . . . . . . . .
2.3.4 Coverage Hole Probability Distribution i4nalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Conclusion
Effect of Antenna Patterns on HandoEs and Coverage
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Introduction
3.2 Effect of the Antenna Beamwidth . . . . . . . . . . . . . . . . . . . .
3.2.1 Hypothetical Antenna Pattern . . . . . . . . . . . . . . . . . .
3.2.2 Performance Evaluations Model . . . . . . . . . . . . . . . . .
3.2.3 Soft, Softer Handoff and Coverage Probabilities Under Different
. . . . . . . . . . . . . . . . . . . . . . . . . . . . Beamwidth
. . . . . . 3.2.4 Determining the Handoff and Coverage Percentage
. . . . . . . . . . . . . . . . . . . . . . . . 3.2.5 Simulation Results
. . . . . . . . . . . . . . . . . . . . . . . . 3.3 Real Antenna Evaluations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Conclusion
4 Effect of Antenna Tilting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 -4ntenna Downtilting
. . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Performance Evaluations
4.3.1 Performance of Downtilting N-eighbour Cell Sites' .4 ntennas .
4.3.2 Performance of Downtiiting the Central Base Stations . . . . .
4.3.3 Performance of Downtilting -411 Base Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Conclusion
5 Effect of Cell Site Configuration
. . . . . . . . . . . . . . . . 5.1 Effect of -4ntenna Azimuth Configuration
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Introduction
5.1.2 -4zimu th Orientations . . . . . . . . . . . . . . . . . . . . . . . 75
5.1.3 Performance Results . . . . . . . . . . . . . . . . . . . . . . . 76
5.1.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.2 Further Sectorization . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.2.1 Corn parison between Six-Sectorization and
Three-Sectorization. . . . . . . . . . . . . . . . . . . . . . . . 85
5.2.2 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6 Thesis Summary and Future Work 89
6.1 Tliesis Surnmary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
6.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
A Pattern Data for DB982H33-M
B Pattern Data for DB982H65
C Pattern Data for DB978H9û-M
Bibliography
List of Tables
3.1 .41itenna gain vs. azirnuth angle of the patterns with different sector
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . crossovers 34
3.2 Soft, softer handoff and coverage probability at some locations with
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . the central ceIl 37
3.3 Handoff and coverage percentages for different real antennas under
different handoff threshoids . . . . . . . . . . . . . . . . . . . . . . . 50
4.1 Soft, softer handoff and coverage probability at boundary locations
with 5" downtilting the neighbour cells . . . . . . . . . . . . . . . . . 64
4.2 Soft, softer handoff and coverage probability a t ce11 boundary locations
with 9" downtilting the neighbour cells . . . . . . . . . . . . . . . . . 65
S.1 Handoff and coverage percentages of the real patterns for six-sectorized
non-interleaving ce11 configuration . . . . . . . . . . . . . . . . . . . . 83
5.2 Handoff and coverage percentages of the real patterns for six-sectorized
. . . . . . . . . . . . . . . . . . . . . . interleaving ce11 configuration 83
vii
List of Figures
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Handoff process
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 The systenl layout
3.1 Tlie beam pattern definition . . . . . . . . . . . . . . . . . . . . . . .
3.2 3dB beamwidth vs . sector crossover for the hypothetical antenna pat-
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . tern mode1
3.3 Hypothetical directional antenna horizontal radiation patterns . . . .
3.4 Coverage probability distributions of the base station in sectaroo . . .
3.5 Soft and softer handoff probabili ty distributions . . . . . . . . . . . . .
3.6 Intracell and intercell coverage hole probability distributions . . . . .
3 Coverage hole probabili ty distributions . . . . . . . . . . . . . . . . .
3.8 The soft, softer handoff and coverage hole area percentages vs . proba-
bility distributions for the assumed antenna mode1 . . . . . . . . . . .
3.9 Handoff and coverage percentages vs . sector crossover gain . . . . . .
3.10 Coverage hole percentage vs . sector crossover gain . . . . . . . . . . .
3.11 The intracell and intercell coverage hole percentages for different sector
crossovers for the hypothetical antenna mode1 . . . . . . . . . . . . . 3.12 Simulation resuits for no-hancioff: softer and two-way soft under differ-
ent antenna sec tor crossovers . . . . . . . . . . . . . . . . . . . . . . .
3.13 Simulation results for softsofter,thre e-way soft: and coverage hole under
differen t antenna sector crossovers . . . . . . . . . . . . . . . . . . . .
viii
3.14 Handoff and coverage percentage comparisons between simulation and
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . analysis
3.15 Antenna mode1 DB978H90-h4 . . . . . . . . . . . . . . . . . . . . . . 3.16 Antenna Mode1 DB982H65 . . . . . . . . . . . . . . . . . . . . . . . . 3.17 -4ntenna Mode1 DB982H33-M . . . . . . . . . . . . . . . . . . . . . . 3.18 Comparisons of handoff and coverage percentages of the real antennas
3.19 Handoff: coverage and coverage hole percentages of antenna model
. . . . . . . . . . . . . DB982H65 under different handoff thresholds
. . . . . . . 3.20 Probability distributions for antenna model DB978H90-$1
. . . . . . . . 3.21 Probability distributions for antenna model DB982H65
. . . . . . . 3-32 Probability distributions for antenna model DB982H33-M
-4ntenna pattern downtilting scheme . . . . . . . . . . . . . . . . . .
Hypothetical horizontal and vertical base station bearn patterns . . . antenna downtilting co.ordinate . . . . . . . . . . . . . . . . . . . . . .
Horizontal beam patterns under different downtilting angles . . . . .
The composite horizontal antenna pattern beamwidth under different
downtilting angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Probability distributions under 5" downtilting of the neighbour ce11
base stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Probability distributions iinder 9' downtilting of the neighbour ceil
base stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Handoff and coverage percentages under different angles' of downtil ting
of al1 neighbour base stations . . . . . . . . . . . . . . . . . . . . . .
Probability distributions for under 5" dowritilting of the central ce11
base stations orily . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Probability distributions under 9" downtilting of the centrai ce11 base
stations onlv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1 1 Soft handoff probability distributions of downtilting the central ce11
base stations only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12 Handoff and coverage percentages under different angles' of downtilting
of only central ce11 base stations . . . . . . . . . . . . . . . . . . . . . 4.13 Probability distributions under 5 O downtilting of al1 base stations . .
4.14 Probability distributions under 9" downtilting of al1 base stations . . 4.15 Soft handoff probability distribution meshes under different angles of
downtilting of al1 base stations . . . . . . . . . . . . . . . . . . . . . . 4.16 Handoff and coverage percentages under different angles of downtilting
of al1 base stations . . . . . . . . . . . . . . . . . . . . . . . . . . . .
-4zimuth orientations . . . . . . . . . . . . . . . . . . . . . . . . . . . Probability distributions for interleaving configuration . . . . . . . . .
Probability distributions for 45" azimuth orientations . . . . . . . . . Probability distributions for 60' aïimuth configuration . . . . . . . . Handoff and coverage probabilities at ce11 corner for different azimuth
configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Haiidoff and coverage probabilities at ce11 boundary for different az-
imuth configuration . . . . . - . . . . . . . . . . . . . . . . . . . . . . Handoff and coverage percentages vs. azimuth orientation angle . . . Six sectorized azimuth configuration . . . . . . . . . . . . . . . . . . . Handoff and coverage percentages of different antenna azimuth config-
urations for six-sectorized ce11 layout . . . . . . . . . . . . . . . . . .
5.10 The hando. coverage and coverage hole percentages for antenna mode1
DB982H33-M with 15' antenna orientation under different handoff
t hresholds in siu-sectorized ce11 layout . . . . . . . . . . . . . . . . . .
5.11 Total handoff percentage vs. handoff threshold for different sectorized
antenna patterns under different azirnuth configurations . . . . . . . .
Chapter 1
Introduction
The market for cellular and personal communication system (PCS) services has ex-
periericed tremendous growth in the recent years. To satisfy the increasing demand
for higher capacity, systems based on Direct Sequence-Code Division Multiple -4ccess
(DS-CDhl1.4) standard have been deployed by many service providers in numerous
cellular and PCS markets around the world.
Using the idea of suppressing interference by employing Direct Sequence Spread
Spectrum (DS-SS) modulation. the DS-CDM-4 system offers some unique features
suc11 as cochannel interference suppression, soft hancioff: frequency reuse factor of
one. simplified frequency planning, and easy cellular systern deployment[7][8][13].
In general, the typical cellular system consists of mobile stations, base stations,
and niobile switching centre(hl1SC). One of the major concerns for CDMA service
providers is to use minimum resources to provide the best service coverage.
In the following, Ive will briefly introduce some of the factors in the cellular envi-
ronment that affect the coverage of the system.
The Mobile Radio Environment
Between the antenna of the base station and the antenna of the mobile station, the
propagated radio signal varies witli time and position due to user movement and
changing environment. The mobile received radio signal power in the direct path
between the niobile and the base station attenuates slowly as the mobile user moves
away from the base station. Puth loss is a mathematical model usecl to characterize
this phenomenon. It describes how the mean signal power strength decays with
distance from the transmitter. However, the direct signd path sometimes can be
blocked by objects such as trees, building, hill, or moving trucks. This blocking can
cause occasional drops in the received signal power. The phenomenon caused by this
irregular terrain contour between the transmit ter and the receiver is called shadowing,
or slow /adkg due to relatively slow signal variation. Shadowing is usudly rnodelled
by log-normal distribution with mean power and standard deviation between 6dB
and 12dB, hence it's also often referred to as log-normal fading.
Sometimes the transmit ted waves are reflected by receiver's surrounding ob jects,
the mobile unit will receive signals arrived at different tirne: with different amplitude
and different phase. The sum of this group of reflections (multipath waves) might
cause severe signal fading. This phenomenon is cailed multipath fading, or fast fading
due to the fact tliat the rate of change of the received amplitude and phase occurs
very rapidly. Multipath fading may behave according to Rayleigh model or Rician
niodel depending on the relative signal strength between the paths.
Ce11 Planning and Coverage
The need to accommodate large numbers of mobile subscribers using limited spectral
resources led to the concept of cellular radio[6]. Under this concept. system capacity
can be improved by jrequency reuse ' and ce11 splitting '. Ce11 splitting can be realized by reducing the current base station coverage and
adding new base stations into the service area. .4nother way is to sectorize the
ceIls/sec tors into smaller sectors by changing the base station antenna radiation foot-
'the reuse of the spectra in more than one geographical section (cell) of a larger service area
t hrough careful control of transmitter (base station) powers. %the division of cells into smaiier cells
print. These techniques are usually performed in the high traffic area during system
optimization phase. MTithin the sectorized cell, the transceiver is able to transmit or
receive signals over certain range. Therefore, both intercell and intracell interference
can be suppressed to some extent, thus the capacity can be improved.
The effective coverage area is the geographical region in which the mobile re-
ceived signal power exceeds certain minimum level. Theoretically, the coverage area
is fornied by circles and their overlaps. In actual practice, the coverage area of a
particular base station is a function of its power, antenna pattern, system layout and
paranieter settings, and the characteristics of the mobile radio signal propagation in
the service region. Because of this irregularity of the radio environment? uniform
coverage is impossible. There exist weak spots called coverage holes within the ser-
vice region. Users located in the coverage holes will not be able transmit or receive
correct signal messages. Since 100 percent ce11 coverage of an area is not attainabIe?
the base stations must be engineered so that the holes are very small or located in
the low-traffic regions.
Antenna and Antenna Pattern
An antenna is a device for transmit ting or receiving electromagnetic radio signals.
-4ntennas can be classified by the directions in which they transmit or receive. They
can be isotropic, omnidirectional, or directional. An isotropic antenna is a hypothet-
ical antenna that radiates uniformly in al1 directions so that the electric field at any
point on the sphere, centred by the antenna, lias the same magnitude. An omnidirec-
tional antenna radiates uniformly in one plane. -4 directional antenna racliates most
of its power in one particular direction.
When transmitting or receiving signals, the antenna responds t o an outgoing or
incoming wave from a given direction according to the pattern value in that direc-
31ntercell interference is generated from the transceivers in other cells. The interference from the
users nithin the same ce11 is called intraceii interference. ''Usually, the cluster of hexagonal cells are assurned for flexible and convenient anaiysis.
tion. Hence, the radiation pattern represents a very important characteristic of the
antenna. The radiation pattern of an antenna is related to the type of antenna and its
electrical chaïacteristics as well as its physical dimensions. For Iand-based antennas,
the antenna pattern is characterized in two principal pianes, the azimuth and ele-
vation planes, or usually called the horizontal and vertical planes: respectively. The
angles in the horizontal plane are conventionally denoted by 4: and in the vertical
plane by 0. The intersection of the two principal planes is the antenna boresight. In
general: the antenna radiation patterns are different in the two planes.
-4ntenna pattern is usually graphed in terms of relative power against the angle
tFom the boresight direction. The relative power can be evaluated by normalizing the
measured powver at a constant distance in the far field of the antenna to the power
a t boresight also measured a t the same distance. The radiation pattern is often posi-
tioned so that its boresight coincides with the zero angular position of the graph. The
main lobe of an antenna is in the direction of the maximum radiation power. The peak
of the main lobe is a t the boresight of the antenna. Therefore, the power a t boresight
is usually plotted a t OdB, while the power a t al1 other directions appear as a nega-
tive value. The main Iobe is quantified tlirough its haif-power bearnwidth(HPBW), or
3dB bearnvidth 5 , which is the angular separation of the points on each side of the
main bearn with the radiated power 3dB below the boresight gain. The sidelobes are
lobes in any direction other than that of the main lobe. They are characterized by
their level below the boresight gain and their angular position relative to the bore-
sight. The sidelobe gain is usually quite small cornpared to the boresight gain. The
Ir-ont-to-back ratio is a measure of the ability of a directional antenna to concentrate
the beam in the required fonvard direction. It is defined as the ratio of the antenna
boresight power to the back lobe power.
Ideally, directional antenna does not have side lobes. Its main lobe pattern gain is
independent of the azimuth angles. If the horizontal pattern coincides with the shape
5For antenna with very narron- beams, tOdB beamwidth is also used
of the sector of a cell: this is called perfectly sectorized antenna pattern. However,
in practice the realization of this antenna pattern is impossible. The pattern gains
are related to the radiation directions. and the side lobes are inevitable but can be
restrained to a certain degree. Thus, the shape of the antenna main lobe is very
important in deterrnining the base station coverage.
-4ntenna footprint can be affected by antenna tilting, which is normdly referring to
mechanically or electronically dowrrtiltiny the main beam of the base station antenna.
The antenna vertical pattern and the downtilting angle together with the horizontal
pattern are used in j ustifying the resulting downtilting pattern. Downtilting can
change the received signal strength and cause the variation of the beamwidth of the
riew pattern. It can be used to reduce the cochannel interference and enhance the
weak spots in the cell.
In cellular systems, the effect of antenna vertical pattern is not significant in
system design and optimization analysis. In most cases the horizontal pattern is the
only one to be considered. -4ntennas for mobile terminals have an omnidirectional
radiation pattern in the horizontal plane. However, the base station antennas are not
always omnidirectional. They can be directional in order to conform to the pattern
of specified zones in the horizontal plane. The base station antennas are very critical
elements that can either enhance or constrain system performance. Depending on
the size and shape of the service area and the nurnber of cells, base station antenna
configurations can greatly affect the cellular network design and system optimization.
Tberefore: the base station antennas are carefully chosen for use according to their
characteristics and system requirements.
1.1 The CDMA System Link Structure
Wireless CDMA system is unique in that its forward and reverse links have different
link structure [l]. This is necessary to accommodate the requirements of a land-mobile
communication system. The forward link, the channel from the base station to the
mobile user, consists of four types of logical channels: pilot' sync, paging, and traffic
channels. There is one pilot channel, one sync channel, up to seven paging channels,
and several trafEc channels. Each of the logic channels on the forward link is identified
by its assigned Walsh function[l]. Each of these fonvard-link channels is first spread
orthogonally by its NTaish function: then it's spread by a quadrature pair of short
PN codes 6 . -411 channels are added together to form the composite spread spectrum
signal to be transmitted on the forward link. The pilot channel provides the mobile
wit h timing and phase references the sync cliannel carries information about systcm
synchroni'tation and parameters: the paging channels are used for sending overhead
information to notify the mobile of important system configuration parameters J The
traffic channel is for transmitting data, voice and signalling messages.
The reverse link. on the other hand, supports only two types of logical channels:
access channels and traffic channels. Long P N sequences are used for channelization.
The access channel is used by the mobile to communicate with the base station for
cal1 origination and responding t o pagings. The function of the reverse link trafEc
channel is the same as the forward counterpart.
The Pilot Channel
In CDM.4 system. each sector is distinguished from one another by the pilot channel
of that sector. The pilot channel serves as a " beacon" for the sector and aids the
mobile in acquiring other logical channels of the same sector. There is no information
contained in the pilot other the short P N code with a specified offset '. The pilot
channel is identified by the Walsh function O. The channel itself contains no baseband
information. The baseband sequence is a strearn of O s tha t are spread by Walsh
function O? which is also a sequence of al1 Os. The resulting sequence is then multiplied
6Pseudorandom Noise Codes, generated from specialiy constructed linear feedback shift registers,
is used in CDMA channelization. 7Used to identie the particular sector that is transrnitting the pilot signai.
by a pair of quadrature PX sequences. Therefore, the pilot channel is effectively the
PX sequence itself. Since there is no baseband information contained in the pilot
channel, the pilot is not despread and bits are not recovered.
The pilot channel is transmitted continuously by the base station sector. A special
term is used to describe the Signal-to-Noise Ratio (SNR) of the pilot channel: Energy
per chip per interference density, or EJ&. &/Io gives an indication of which is
the strongest serving sector of that mobile. It represents the signai strength of the
pilot channel. The mobile continuously measures the EJio and compares it against
different threshold, sucli as the pilot detection threshold, T-4DD, and pilot drop
threshold. TDROP. The results of these comparisons are reported back to the base
station so that the base station can make a determination of whether of not the
mobile should be handed off from one base station to the next. Thus the EJI0 plays
a prominent role in determining whether or not a mobile is within the coverage area
of a base station. Furthermore, the pilot signai is transmitted by a base station at
a relatively higher power than those of other foward-link logical channels to ensure
the initial system acquisition. ,4 cal1 cannot be set up without the mobiles successful
reception of the pilot channel, Liecause, along with other functions, the pilot channel
serves as a coherent carrier phase reference for demodulation of other logical channels
on the forward link. Therefore, the EJI0 effectively determines the handoffs and
forward link coverage area of a ce11 or sector. and one has to ensure that the fonvard
link EJI0 strength is sufficient.
1.2 The Handoffs in CDMA System
In cellular systems, rnobility causes dynamic variations in link quality and interference
levels. sometimes? a particular user may be required to change its seming base station.
This change is known as handofi. Handing off from ce11 to ce11 is fundamentally the
process of transferring the mobile unit that has a cal1 in progress on a particular
voice channel to another voice channel without interrupting the call. Handoffs can
occur between adjacent cells or sectors of the same ce11 site. The neecl for a handoff
is usually determined by the actual quality of the RF signal received from the mobile
into the ce11 site. In CDMA network: this is determined by the strength of &/Io.
1.2.1 Handoff Types
In cellular CDMA systems, there are mainly three different types of handoffs '; namely
soft handoff, softer handoff, and hard handoff. Each of the handoff scenarios is a result
of the particular system configuration and of where the subscriber unit is located in
the network.
Hard Handoff
The hard handoff process is rneant to enable a subscriber unit to hand off from a
CDM-4 call to an analog call or to another CDM.4 call with different frequency band
or frame offset. The process is functionally a break-before-make and is implemented
in areas where there is on longer CDM-4 service for the subscriber to utilize while
on a current c d , o r there are two distinct CDM.4 channels which are operating on
diffemnt frequencies. The continuity of the radio link is not rnaintained during the
liard handoff.
Soft Handoff
The capability of using the same frequency spectrum throughout the service area
makes the soft handoff operations unique ir? a CDM-4 cellular systeni. Combined
witli micro diversity and reverse link power control, soft handoff can be implemented
to lower the requirement on the mobile's transmit power in the handoff region, thus?
'There are also handoffs involving the combinations of soft and softer handoffs, e-g., softsofter
handoffs, where three links are involveci with two From the sectors in the same cell, one for the sector
of another cell.
increase the coverage range and improve the handoff reliability[8]. Soft handoff can
also reduce the number of dropped calls and alleviate the ping pong effect [24], which
occurs when the mobile user hovers around the boundary of the ce11 and is handed
back and forth several times between different base stations due to signal variation.
The soft handoff involves an intercell handoff and is a make-before-break connec-
tion. It can occur only when the old and new base stations are operating on the same
CDhl-4 frequency channel. During the process, the connection between the mobile
unit and the base station could be maintained by several base stations, Depending
on how many base stations involved, there could be 2-way, 3-way, o . . , or n-way soft
liaiidoffsg. On the for\vxd link, the mobile uses the rake receiver to demodulate
separate signals from different base stations. The signals are combined to yield a
composite signal of better quality. On the reverse link, the mobile's transmit signal is
received by several base stations. The base stations demodulate the signal separately
and send the demodulated frarnes back to the M C . The MSC contains a selector
tliat selects the best frame out of the two that are sent back.
Softer Handos
The CDM-4 softer handoff is an intracell handoff occurring between sectors of a ce11
site and is also a make-before-break type. On the forivard link, the mobile perforrns
the same kinct of combining process as that of soft handoff. In this case, the mobile
uses its rake receiver to combine signals received from different sectors, normally two
sectors. On the reverse link, however, two sectors of the same ce11 simultaneously
receive two signals from the mobile. The signals are demodulated and cornbined
inside the cell, and only one frame is sent back to the MSC. Tlius it only aeeds one
channel element to process the signal.
'In this thesis, the tenn soft handoff is only used for general representation of simultaneous link
connections
1.2.2 Set Maintenance
In 1s-95, once the mobile acquired the link. i t rvill constantly notify the base station
regarding the local propagation condition. The base station makes use of this infor-
mation to make handoff decisions. The scheme that the mobile makes a measurement
of forward link EJI0 and reports the measurement result to the base station is c a l l d
mobile assisted handoff(M.4HO). Since each base station transmits its own pilot on
different P N the EJIo of a pilot gives a good indication of whether or not
the particular sector should be the serving sector for the mobile.
In managing the liandoff process, the mobile maintains in its memory four exclu-
sive lists of base station sectors. The sectors are stored in the form of pilot P N offsets
of those sectors. These lists are also called sets. The mobile station can obtain four
sets of pilot channels: active set: candidate set- neighbour sets, and remaining sel[l].
The active set contains the pilots of those sectors that are actively communicating
rvith the mobile on traffic channels. If the active set contains only one pilot, then the
mobile is covered but not in soft handoff. However, if the active set contajas more
than one pilot, then the mobile is maintaining connections with al1 those sectors on
separate traffic channeIs. The base station controls the handoff process because a pilot
can only be added to the active set if the base station sends the mobile a handoff
direction message, which contains message about that particular pilot to be added to
the active set. In 1s-95, the active set can contain a t least six pilots.
The candidate set holds those pilots that are not in the active set but their EJIOs
are sufficient to make them become handoff candidates. Usually if the Ec/ro of a
particular pilot is greater than the pilot detection threshold, T,4DD, then that pilot
will be added to the candidate set. A pilot is removed from this set and placed in
the neighbour set if the strength of that pilot drops below the pilot drop threshold,
TDROP, for more than the duration specified by the hando8 drop t imer expiration
value, T-TDROP.
''In 1s-95, the minimum separation between different base station's PN codes is ô4 chips
10
The neighbour set consists of those pilots that are in the neighbour list of the m e
biles current serving sector. The mobile's neighbour set is updated by the neighbour
list message from the serving base station. The mobile aiso keeps an ageing counter
for each pilot, in order to keep current for ail the pilots in the this set,
The remaining set contains al1 possible pilots in the current system for the current
CDMA frequency assignment, excluding pilots that are in active, candidate, and
neighbour sets.
In addition, for each of the above pilots sets, the base station specifies the search
windows in which the mobile station is to search for usabie multipath cornponents of
the pilots in the set.
1.2.3 The Handoff Process
The handoff process is handled by passing special messages between the mobile station
and the base stations. The typical handoff process begins when a mobile unit detects
a pilot signai that is significantly stronger than any of the fonvard traffic channels
assigned to it. When the mobile detects the stronger pilot channel, it will send
a pilot strength measurement message to the base station instructing it to initiate
the handoff process. The base station then sends a handoff direction message to
the mobile station! directing it to perform the handoff. Upon the execution of the
handoff direction message the mobile sends out a handoff completion message on the
new reverse traffic channel.
The typical 2-way soft handoff process from the source ce11 to the target ceil is
examined in details in the following example as described in [Il. Figure 1.1 presents
the case when a mobile is moving from the coverage area of source ce11 A to the
coverage area of target ce11 B. The two curves represents the variations of the pilot
signal's &/Io . As the mobile user moves away from its current senring base station,
the mobile measured &-/Io decreases. The following is a sequence of events occurring
during this transition:
Figure 1.1: Handoff process
1. The mobile station is initially assumed being served by the base station from
ce11 -4 only. The mobile's active set, therefore? contains only the PN offset of
pilot A. The mobile continuouslÿ mesures pilot A Ec/Io and the neighbours'
E,-/Io, such as pilot Bk. When it's getting closer to the ce11 boundarÿ! it will
find EJIo to be greater than T-4DD. The mobile sends out a pilot strength
measurement message and moves pilot B from its neighbour set to the candidate
set.
2. The mobile receives a handoff direction message from the base statior, of ce11 -4.
The message directs the mobile to s tar t cornmunicating on a new t r a c channel
with ce11 B The message contains the P N offset of ce11 B and the Walsh code
of the newly assigned t r a c channels.
3. The mobile moves pilot B from the candidate set to the active set. -4fter ac-
quiring the fonvard trafic channel specified in the handoff direction message,
the mobile sends a handoff completion message. Now the active set contains
two piiots and the mobiie is in 2-way soft handoff.
4. The mobile detects that the strength of pilot -4 has now dropped below TDROP.
The mobile starts the drop timer.
5. The drop timer reaches T-TDROP. The mobile sends a pilot strength rneasure-
ment message.
6. The mobile receives a handoff direction message. The message contains only
the P N offset of ce11 B. The P N offset of cell.4 is not included in the message.
7. The mobile moves pilot -4 from the active set to the neighbour set, and sends
out a handoff completion message.
The above scenario implies that the mobile is in 2-way soft handoff within time
interval between distance (3) and (7).
1.3 Motivations and Objectives
Soft Iiandofi is known to be one of the key features that differentiates CDM4 tech-
nolog-y compared to the others. Theoretically? soft hancloff can yield substantial
gains in performance in terms of increctsed capacity aiid coverage, and reduced cal1
drop rates[24]. However, in practice. the realization of soft Iiandoff is much cornpli-
cated. Soft handoff requires large amoiint of information processing ability from the
MSC. During soft hando. redundant information passed by the base stations to the
kESC might create extra system load and consume excessive resources of the network.
Tfierefore, in current industruv, number of base stations involved in soft handoff tends
to be controlled to its minimum. However, this minimization might bring sorne side
effect to the network coverage.
Soft handoff control, therefore, becomes very critical for system optimization and
capacity improvement. Currently, the approach in industry is by base station power
coritrol~ pilot search-window size adjustment, or handoff threshold alteration IL. In
t his thesis, we will approach it by concentrating on base station antenna configuration.
Since the base station antenna radiation footprint on the ground is closely related to
its antenna pattern, and the degree of the overlap of the footprints determines soft
handoff percentage and nurnber of links involved in soft handoff? by selecting different
base station antenna pattern under different system layout, we can analyse the effect
on handoff and coverage percentage.
Several other studies related to sectorized antenna anci soft handoff have been con-
ducted. By predefining the overlapping footpnnt, Lee and Steele[29] categorized the
soft handoff zones into different types of soft handoff subzones to analyze the effect
of soft and softer handoff on the system capacity. Wang and WTang[30] approached i t
by running simulations with the application of a hypothetical antenna pattern to find
soft liandoff percentages by the types. But, none of the above considered different
antenna configuration. Therefore, the objective of this study is to develop an ana-
lytical model to study the performance of antenna configuration on soft handoff and
coverage under different system layout. It usually takes an engineer enormous tirne on
simulations to choose a suitable base station antenna for a particular CDh4.4 system
laj.out. The proposed simple mode1 can help to Save sorne efforts on determining and
evaluating different base station antenna patterns.
1.4 Thesis Outline
The thesis is organiïed as follows: Chapter 2 will setup the model and construct the
analytical relationship between antenna pattern and soft, softer handoff and coverage
statistics. The mode1 is then applied as described in three different chapters: Chap-
ter 3 analyzes the soft, softer handoff and coverage by considering different antenna
beamwidth and applying the method on selecting suitable real antennas for a partic- - -
l l This approach is normally avoided since that would greatly affect the overall system.
ular system. Handoff parameter settings are d s o investigated. Chapter 4 focuses on
the effect of antenna downtilting on handoff and coverage percentages under different
downtilting angles. Chap ter 5 investigates different system configurations. Details
on different azimuth configurations and further system sec torixation and ce11 spli t ting
are discussed. Chapter 6 summarizes the work? and further research topic will be
identified.
Chapter 2
Analysis of Handoffs and Coverage
in CDMA Mobile Systems
2.1 Introduction
Ideally, sectorization in cellular CDM.4 systerns increases tlie capacity in proportion
to the number of sectors per cell. -4 directional antenna is mounted at each base
station to cover the sector. For a perfectly sectorized antenna pattern, where there
are no antenna footprint overlaps, soft and softer handoff canriot be applied. In
practice, the antenna patterns do not fit the sector area perfectly. Tliere are overlaps
aiid coverage holes betweeii tlie sectors. The shape of the sectorized antenna pattern,
thus, has great impact on soft. softer handoff and coverage distributions.
Iu tliis chapter, the system mode1 will first be constructeci. The CDM.4 fonvard
link pilot's EJI0 will be expresseci in terms of antenna pattern, handoff thresholds,
and radiation power. The analy tical expressions between handoffs? coverage s tatistics
and antenna pattern can then be derived based on Ec/Io. This chapter serves the
purpose of setting u p the basic mode1 for the work to be followed in the rest of the
thesis.
2.2 System Mode1 and Assumptions
In order to analyze the effect of antenna pattern on handoffs and coverage, the fol-
lowing assumptions are made for the basic system model- Detailed characteristics
of the model will be added and described in each of the later sections for different
situations.
System geometry consists of a regular cluster of cells in a hexagonal grid with
the same size. Cells are sectorized iuto sectors, as shown in Fig. 2.1.
a Provided with ornni-directional antennas. mobile users are assumed stationary
or with very low speed and uniformly distributed within eacli sector.
Tlie base station antenna for each sector is assumed witli the same height but
not necessarily with the same radiation pattern
Tlie initial cal1 admission is based on pilot's Ec/&. Mobile station will be
covered by a certain sector's base station which has the most strongest pilot
signal. Each mobile station in the system must have i ts own home base station
to wliich it initially communicates when the mobile is turned on.
Pilot's Ec/Io from al1 tiers of cells are considered. For equally loaded sectors,
the transmitting power of each base station is assumed to be the sarne.
Log-linear path loss and log-normal shadowing with zero mean and standard
deviation of 5 dB are considered in the propagation model. The effect of mul-
tipath fading is not included since only the short terrn average of pilot power is
of interest.
Within a sectorized cell, the shadowing statistics from al1 the base station an-
tennas of the ce11 to a given mobile station are assumed to be the same.
The voice activity factor is ignored .
Ec/& is the energy per chip per interference density measured on the pilot channel.
Baçed on the above assumptionso without considering sectorization, a mobile user's
received EJIo from the base station of ce11 i , in general, can then be expressed as:
where
0, is the angle between the main beam of antenna of ce11 i and direction to mo-
bile. P , ( O i ) is the iM base station's composite Effective Radiation Power(ERP),
including pilot, paging, sync and traffic powers in the direction 8 to the mobile
user. The ERP depends on the base station antenna pattern, which is a func-
tion of direction 6. Pz can be expressed as SiGi (Oi), where Si is the maximum
average composite power of the BTS Power -4mplifier located in RF Front End
(RFFE) : auci Gi(Oi) is the Base Station Transceiver (BTS) antenna radiation
pattern gain in direction Bi for base station i. The antenna gain depends on the
area intended to be serviced by the base station.
a, is the fraction of the i'" base station's ERP allocated to its pilot signal.
a L, represents the gain due to path loss from the ith base station to the mobile.
expressed as
L, = r,-l' (2.2)
where, r, is the distance from the ilh ce11 site to the mobile user, and p is the
path loss esponent with typical value range from 3 to 5.
0 10e'/10 models the lognormal fading, where <, is a Gaussian random variable
with zero mean and standard deviation, 6, typical of 8 dB.
G, is the mobile user's receive antenna gain.
Ih, the forward link intracell interference, stands for the total power received by
the moble from the ich base station, and can be described as
In, the forward Iink intercell intederence, is the sum of the power from the ce11
site i's neighbour base stations, expresseci as:
where c is the number of base stations' Pj is the jth base station's ERP, 0, is the
mobile user's direction to the ce11 site j: and L, is the users% path lost relative
to the jth base station.
!V = N0W = kTW, is the total thermal noise power within bandwidth IV: where
k is Boltzman's constant (k = 1.38 x IO-~~J/K) and T is the temperature in
Kelvins.
a 14,' and R are tlie signal's bandwidth and transmission rate. In IS-95: the pilot
chanriel doesn't contain any user information, therefore, W=R.
2.3 Handoff and Coverage Analysis
.4ssunle a CDM-4 system with c cell, each ce11 is equally split by s sectors. -4 mobile is
receiving the pilot signal from sector u of the ce11 u, denoted by sedor,,, as shown in
Fig.2.1. In the analysis, we will follow notations according to the following manner:
when a parameter is followed by two subscripts, the first one represent the ce11 index
and tlie second is for sector. For example, Bij represents the angle to the base station
of sector j of ce11 i. Therefore, based on (2.1): the received &/Io from the base station
of sector,, a t sorne mobile location is:
Lire further assume that the users are equally distributed over sectors. The transmit ted
power, S: can be reasonably assumed the same for al1 of the base stations within the
system. By dividing S from both the numerator and the denominator, we can let Gi
be the total antenna pattern gain from al1 three sectors of ce11 site i: that is,
And let G, represent the antenna gain for sector j of ce11 i. Gi and Glj are functions
of mobile angular directions. Therefore, (2.5) can be rewritten ast
where,
' t x, is a function of the mobilek location to the ce11 site i. And cl and eu are independent
Gaussian random variables for ce11 i and u respectively. Since the thermal noise is
very srnall compared to the signal power and we are more interested in the central
cell, where intercell interference is the major concern, by neglectiag the background
noise, equation (2.7) becomes:
I', is related to the intercell interference. It is the sum of ind epend ent lognormally
distributed random variables, it could be approximated as a lognormal random vari-
able[l]. The first two moments of ï,, can be obtained as[18]:
where: X is a constant given by X = ln 10/10. Since ru is a lognormal random variable.
we could define Zu = IO loglo ru be a Gaussian variable with mean rnzu and variance
ofu pi-. by:
Therefore, Equation (2.9) can be written as,
2.3.1 Forward Link Coverage Analysis
The fonvard link coverage of a base station from a sector is the geographical area in
which a mobile unit may receive sufficient signal level from the base station trans-
mitter to satisfy the service requirement. In CDMA, the forward link coverage region
depends on the pilot signal to interference value: Ec/Io, rcceived by the mobile from
the corresponding base station. -4s described early in Fig.l.1, the handoff parameter,
TDROP (along with the use of the drop timer T-TDROP), determines when to re-
move a base station from mobile's -4ctive Set. Therefore, the probability of a mobile
user a t any location, (0: r) expressed in polar co-ordinates, being covered by the pilot
[rom sector,, can Le approxirnated as:
P&(O, r ) = Prob[[E,/ l~] , , 2 T D R O P ]
P,',(O, r ) = Pr 2, 5 10 log,, ( T D R O P
where,
(S. 14)
The iunction P:, (8, r ) act ually reprcsents the coverage probability density funct ion
for pilot,, in terms of the mobile locations. Therefore, the probability of a user in a
region, e.g. cell,, being covered by pilotuvl or the average coverage percentage of a
region for pilot,,, would be,
where -4 is the area of the analyzed region, and within this region, the users are
uniforrnly distributed.
2.3.2 Soft Handoff Probability and Percentage
-4s rnentioned previously, the mobile continuously measures its received EJI0 and
compares it against different thresholds, such as the pilot detection t breshold, T A D D,
aiid the pilot drop threshold, TDROP. The results of these cornparisons are reported
back to the base station so that the base station can make an appropriate decision
on whether o r not the mobile should be handed off from one base station to another,
or stay in connections with both base stations.
Assume that a mobile is initially communicating with base station u. Since, the
pilot clrop threshold, TDROP: determines when to drop the mobile, therefore, the
mobile's received E,/Io irorn u has to be greater than TDROP. Now, in order for
this mobile to be in soft handoff with another base station: i: the received Ec/Io from
2 lias to be greater than the handoff parameter TADD: so that base station i could
be added orito the mobile's -4ctive Set. Therefore, for a mobile a t a location initially
coverecl by pilot,,, its probability of heing in soft handoff with, for example, sector,,,
caIi be approximated by,
The above expression can also be explained by the handoff process described in
Fig.l.1 from Chapter One. Based on Fig.l.1, the mobile is in soft handoff only
bctween Location (3) and Location ('7) when its Active Set contains trvo pilots. For
slow moving users, the distance from Location (1) to Location (3) and from Location
(4) to Location (7) are negligible since the transmission of the handoff messages is
estremely fast. Thus: the distance between Location (3) and Location (7) c m be
closely approximated by the distance from Location (1) to Location (4). For the
stationary users, on the other hand, the soft handoff occurs only when they are
located between Location (3) and Location (7) if they are initially covered by cell
site -4. By the same reasoning, this can also be approximated by the locations from
Location (1) to Location (4). Hence both cases lead to Equation 2.18.
N7ith the substitution of (2.13): (2.18) becomes
Since 2, and Zi
correlation betrveen
are related to their own intercell interference respectively. The
2, and 2, is very srnall. Simulations have shown that the nor-
malized correlation between 2, and Zi is almost 0[18]. Therefore, by approximating
the independence and let
the probability for the mobile being in two way soft handoff between sector,, and
can be obtained as:
In general, for a mobile located a t (O, r ) initially covered by the pilot from sector,,,
the prohabiiity of being in soft handoff with any number of the neighbouring sectors
witliin the systern is,
Substitute (2.13): hence.
P O r = Pr[& 5 10 log,, - G.) y
Let = rnax[R]:? - - 7 R T ~ - ' ) ] : silrnilar to equation (2.21. equation (2.23) be-
cornes,
The function Pi,(B! r ) clepends on the mobileos location. It describes the soft
liandoff probability distributions due to pilot,, and al1 of its neighbour pilots. There-
fore. the average soft handoff percentage wi~.iin the c d u due to the coverage of
l~ilot,, and any of the other neiglibour pilots would be.
where -4 is the area of the ce11 u.
2.3.3 Softer Handoff Probability and Percentage
The softer handoff occurs when a mobile is able to receive strong pilots between sectors
of the same cell. Again, assume a mobile is initially covered by pilot,,. In order for
tliis mobile also to be in communicating with a pilot from, for example, ~ e c t c r , ~
where j = O. ..., c - 1: and j # v ! the ~ l o t u j has to be added onto the mobile's
.Active Set. Therefore, based on the analysis on soft handoff from last section ' , the
probability for this mobile to be in softer handoff with sedor, , can be given by:
Note, in general, sector,, and sectmUj are normally adjacent to each other. Due to
the assumption that a mobile's received signal will incur the same lognormal fading
from the base stations of al1 sectors of a cell, by substitute (2.13)
= Pr[Zu < 10 log,, (T_DR~P - G> :
Hence,
Now for a mobile at location (8: r) within sedor,,, the probability of being in
softer handoff with the other sectors within the ce11 u is,
Hence,
s-1
U Z. 5 i O log,, (;A",.; j=Oj#v
- GU) 1
(-y(-') min[C!g, m ~ ~ + ~ [ O i ~ ~ -----.: - - A ]] - m, = 1 - Q [ 1 (2.30)
02,
'Based on the handoff process in Fig.l.1, for softer handoff, ce11 site A and ce11 site B are co-
Iocated.
The fuiiction P&,(O, r) is the softer handoff probability density function in terrns of
mobile location. The average softer handoff percentage within the ce11 u due to the
coverage from sedaru, and any of the other sectors within u would be:
where 4 represents the area of the ce11 u., or the andyzed region.
2.3.4 Coverage Hole Probability Distribution Analysis
The coverage hole is the area where mobile user is not able to receive any of the
pilots of the system with enough signal power. That is, the user is not covered by
any pilots. Since in our rnodel, we assume the user is initially covered by a base
station, if a user is not covered any more: the pilot's P N Offset has to be dropped
from the users -4ctive Set and other pilots are not able to be added ont0 the Set.
Therefore: a location within tell, is defined as a possible coverage hole caused by the
pilot from sector,, if a mobile a t this location is not able to receive pilot,,'s Ec/Io
strong enough, and at the same time the mobile is not in soft(er) handoff with any of
the other sectors within the cluster. In other words, pilot,, has to be dropped from
the mobile's Active Set, and the pilots from rest of the sectors are not strong enough
in order to be acided on to the mobile's -4ctive Set. Hence, at any location within
cell,, t he coverage hole probability caused by pilot,, can be represented as following,
Hence,
Since Zi =
. . .
j = O j # v i=Oi#u j = O
2, : t herefore,
Similady. the function P& (0: T) is the coverage hole probability density function?
therefore, the coverage hole percentage resulted by pilot,, and its neighbour pilots
can t.hen be evaluated.
where -4 is the area of the analyzed ce11 u.
2.4 Conclusion
In this chapter, a sectorized CDhlI.4 network mode1 was set up and the coverage, soft
hancloff: softer handoff and coverage hole probabilities were defined and analyzed for
the systern. The probability density functions in terms of locations: antenna pattern,
handoff thresholds, and relative pilot signal strength for handoffs and coverage were
presented respectively. Based on the probabili ty density functions, the corresponding
handoff and coverage percentages were also expressed statistically. The percentages
are closely relakd to the base station antenna bearn pattern. This chapter serves as
the basis for the later analysis.
Figure 2.2: The system Iayout
Chapter 3
Effect of Antenna Patterns on
Handoffs and Coverage
3.1 Introduction
The forward link CDM-4 system capacity is normally represented by number of mo-
bile users in simultaneous communication with the base station. Each mobile user
occupies a t least one fonvard traffic channel. MThen a mobile is in soft(er) handofl
state, it will maintain the communication link with more than one base stations.
Therefore, the mobile will receive same information on several channels. The MSC
will also receive sarne information fonvarded by the base stations involved in soft
Ilandoff. -41 t hough this might result a bet ter communication quaii ty, additional net-
work resources are used. .4nd these resources (forward links) become unavailable to
be used elsewhere[l8]. Therefore, from the network point of view, uiider the satisfac-
tion of certain coverage requirements, extra soft(er) handoffs should be reduced. In
general, the more soft(er) handoffs, the greater the coverage, and the less coverage
hole. Reducing the soft(er) handoffs might bring the rise of coverage hole. Therefore,
to obtain a minimum soft(er) handofI percentage and a minimum coverage hole, an
optimum solution is expected.
From the previous analysis, the handoff and coverage percentages are closely re-
lated to the antenna beam patterns. Therefore, it is be very important to investigate
what effect the antenna beam pattern could create on controlling the soft(er) handoffs
and coverage: and how to find the optimal antenna pattern for a certain ce11 Iayout.
In this chapter, the effect of antenna beamwidth will be analyzed by applying the
proposed model constructed in the previous chapter. The model will then be used on
rea1 antenna selections.
3.2 Effect of the Antenna Bearnwidth
-4ntenna beamwidth is one of the main parameters in defining an antenna pattern.
Normally an antenna beamwidth is defined as the angle wbich has a gain of 3dB less
than the pattern's boresight gain. In this section, a hypothetical horizontal antenna
pattern is used to analyxe the handoff and coverage issues caused by different antenna
beamwidth. Evaluations of handoff and coverage probabilities and percentage and
simulations will be both conducted.
3.2.1 Hypothetical Antenna Pattern
The base station antenna radiation pattern for the three-sectorized ce11 can be a p
prosimated by a parabola in power gain, with a sinusoidal backside gain as follows ' [XI:
'This model is adopted mainly due to the easiness of changing the antenna beamwidth while
maintaining the same boresight gain.
Tlie parameters 8: b. L? k and e are used to control the pattern as shown in Fig.
3.1. 8 controls the maximum main lobe beam width; b(dB) is the gain at the sector
cros~over(S.C)~ which is closely related to th antenna beamwidth. L and E are the
parameters for the sidelobes. L is the sidelobe gain, and k is related to the bearnwidth
of the sidelobes, ivhile E represents the nul1 depth.
Figure 3.1: The beam pattern definition
Based on this antenna model, we can define a particular antenna pattern by
setting the pattern parameters. 8 = 2 ~ / 3 is chosen for the three sectorized cell. c
is typically cliosen to be -40 dB. The bearn shape factor, n: is chosen to be 3. k is
equal to 2.5/(n - 0,) -4 set of antennas witti different antenna beamwidth is created
ly varying 6 in a reasonable range from -2 dB to -9 dB, while maintaining a constant
boresight gain of 1: Fig.3.2 depicts the relationship between the 3dB beamwidth and
the sector crossover gain, b, for this set of antenna patterns.
Fig. 3.3 displays some of the horizontal anterina patterns of the set. In this
analysis, the 3dB horizontal beamwidth range from around 100° for b=-9dB to 130°
for b=-2dB. Notice that the boresight gain for al1 the patterns at different sector
crossovers are the same. Table 3.1 summarizes the pattern gains for the selected
95 - -9 8 -7 d -5 -4 -3 -2
Scror C-r (de)
Figure 3.2: 3dB bearnwidth vs. sector crossover for the hypothetical antenna pattern
niodel. (n = 3: 8 = 3 ~ / 2 )
patterns shown in Fig.3.3.
3.2.2 Performance Evaluations Mode1
Based on the previously defined network mode1 in Chapter 2: we now assumed that
tlrere me 19 cells in the cluster. Each ce11 is three sectorized wit-h non-interleaving
azimut11 configuration as shown in Fig. 2.1. Pilot's &/Io from two tiers of cells are
considered. The users are assumed stationary and uniformly distributed within each
sector. -411 the sectors are assumed equally loaded. Again, the transmitting power of
each sector is assumed to be the sarne. The allocated power ratio, a: to the pilot of
each sector is dso the same. It's reasonably assumed that 20% of the BTS ERP is
assigned to the pilot signal[lô][l]. Path loss euponent, p, for the log-linear path loss
'Each boresight of the sectorized base station antenna points to the base station of i t s closest
neighbour cell- Details wiil be discussed in Chapter 5.
Figure 3.3: Hypothetical directional antenna horizontal radiation patterns, (n=3,
8 = 3i1/2, r = -40dB: Sector Crossover b=-2,-4,-8 dB)
is assigned to be 4. For the log-normal shadowing, the standard deviation, 6: is equal
to 8dB. In 1s-95, the typical threshold parameters T-4DD and TDROP are about
2dB difference in order t o give the mobile a chance to search for another base station
before the cal1 drop [28]. This can also eliminate the Ping-pong effect and delay the
liandoff requests due t o fast signal variations. The typical values for the pair cari
be (-13dB, -15dB) or (-14dBI -16dB). For general purpose, the handoff and coverage
probabilities are analyzed for a sector in the central ce11 of the assumed cluster. This
sector is narned as s e d m o as shown in Fig. 2.1.
In order to find the handoff and coverage percentages within the central ce11 for
pilotoo, Ive will need t o find the corresponding probabilities at each location of the
cell. By applying equations (2.15), (2 .24): (2.28): and (2.34) respectively, the results
can then be obtained.
1 -4ntenna Gain II Azimuth -4ngle (degree) for -4ntenna Pattern with 1
Table 3.1: -4ntenna gain vs. azimuth angle of the selected patterns with different
sector crossovers in Fig.3.3. (S.C. Gain=-2dB, S.C. Gain=-4dB, and S.C. Gain=-
8dB)
(dB) 1 -- 2
- I
-2
-3
-3
-8
-10
-20
-30
-40
3.2.3 Soft , Softer Handoff and Coverage Probabilities Under
Different Bearnwidth
In this section, we will find the coverage and coverage hole probabilities and soft,
softer handoff probabilities for a user at any location within the central cell. This
involves findings for each point in the cell the values of the antenna pattern gains and
the interference statistics to the mobile from al1 the pilots of the sectors within the
cluster.
For sector crossover gain, e.g., -4 dB, Fig. 3.4 depicts the particular coverage
probability distribution for the pilot from sectoroo. The probability of a spot within
cello being covered by the pilot from s e c t m is higher near the ce11 site due to the
strong signal strength and less interference. It drops as the distance and the azirnuth
S.C. Gain=-2dB
39.9
49.4
60.0
66.3
70.6
79.0
80.8
83.4
83.6
1 83.6 II
S.C. Gain=-4dB
33.9
41 -9
5 1 .O
56.4
60.0
67- 1
68.6
70.8
71.0
71.1
S.C. Gain=-8dB
30.3
37.5
45.6
50.4
53.7
60.0
61.4
63.3
63.5
63.6 l
angle to the ce11 site raised. Table 3.2 sumrnarizes the coverage probability results
for some locations on the boundary of the sedoroa. -4s the user moves from azimuth
angle of O0 to 60°, the probability of being covered by pilotoo drops about 45 percent.
The main reason is because of the base station antenna pattern. Table 3.1 shows that
at GO0 of the horizontal angle, the antenna gain is 4dB lorver than the boresight gain.
Noticed that there are sharp drops around the sector crossovers.
Fig. 3.5 depicts the typical soft and softer handoff probability distributions for a
mobile user a t any location within cella due to the coverage of the pilots from sectwroo
and its neighbours. The softer handoff is the region on both side of the sector, the
soft handoff region, on the other hand, is mainly located near the ce11 boundary. The
probability of being in soft handoff is rising as a user moves from the centre of the ce11
site to the sector border, whereas the softer handoff probability drops. There is a drop
Figure 3.4: Coverage probability distributions of the base station in sectoroo.
(Td4DD=-13dB: TDROP=-l fidB, b=-4dB)
Figure 3.5: Soft and softer handoff probability distributions. (T4DD=-13dB,
TDROP=-15dB, b=-4dB)
zone for the soft handoff around azimuth angle of zero degree, even the user a t that
location is able to receive the antenna boresight gain from pilotoo, and with a strong
coverage probability(3.4). This is due to the fact that this part of the area receives
neighbour pilot signals with less antenna gains under this particular non-interleaving
ce11 site configuration3. For this particular ceIl layout: ive can see from Table 3.1, the
antenna gains contributed from the two nearest base stations to the user located a t
the azimuth angle of O" of sedoroo is -4dB. Table 3.2 summarizes the results a t sorne
locations near the boundary for antenna pattern with sector crossover of -4 dB. If the
mobile user is a t where the boresight of the antenna horizontal pattern covers and
located right on the hexagonal ce11 boundary, the chance that a soft handoff will occur
3The effect due to other ce11 site configurations will be considered in details in Chapter 5.
Softer Handoff Coverage Hole Coverage
Prob. % Prob. % Prob. % -
Table 3.2: Probability of having a soft or softer handoff and coverage probability a t
some locations within sectoroo for the anterina model with sector crossover of -4dB1
TT-4DD=-13dB and TDROP=-l5dB
for tliis user% call is about 5 percent. If the user is making a call on the corner of the
intrasector boundaries, 60" to the antenna boresight direction, the call will be having
about 50 percent chance, ten times higher, in soft handoff with the sectors from the
neighbour cells. The chances for softer handoff: on the other hand, will be much lower
in most of the area except near the intrasector boundary, where the antenna bearns
of the two adjacent sectors of the ce11 overlap. On this direction, there are over 87
percent chance for the user in softer handoff at 0.8R from the base station. -4 further
increment in the distance will result significant drop in probability. There are only
slightly over 4 percent chance for the mobile to be in softer Iiandoff if it's located on
the ce11 boundary.
The coverage hole is defined as the spot not being able to be covered by any of
the base stations. -4s shown in (2.34): the cause for coverage hole can be reasoned
by two factors: one is due to the intracell coverage (sectors within the same cell); the
otlier is due to the intercell coverage (sectors from neighbour cells). Fig. 3.6(a) and
Fig. 3.6(b) depict the intracell and intercell coverage hole probability distributions
for the antenna model with sector crossover of -8dB respectively. The higher coverage
(a) Intraceu (b) intercell
Figure 3.6: Intracell and intercell coverage hole probability distributions for pattern
with sector crossover of 8dB, Td4DD=-13dB and TDROP=-15dB
hole probabilities due to the lack of intracell coverage is mainly located a t the ce11
corners. -4s the users move cioser to the center of the cella, the received pilot signal
st rengt h froni the neighbour ce11 site decreases. Therefore, the intercell coverage
hole probability rises a t the boundary and reaches to the maximum inside the cell.
Notice that the intercell coverage hole is very low on the ce11 boundary a t both
+GO0 and -60" azimuth angles. This is due to non-interleaving cell configuration.
Users at those locations are facing the antenna boresights of the closest neighbour
cells. These users will be able to receive strong pilot signals from them. The two
cornpeting factors, intercell and intracell covorage: determine how the final coverage
hole probability distributes. Fig. 3.7 depicts the coverage hole probability density
distributions. Since the locations inside the ce11 are able to be covered by pilotoo, the
high coverage hole probabilities mainly exist near the ce11 corners. The coverage hoIe
probabilities at those locations are much lower than the evaluated intercell coverage
hole probabilities. This is due to the rnitigation effect brought by the intercell coverage
at those locationes.
Figure 3.7: Coverage hole probability distributions. (T-4DD=-L3dB: TDROP=-
15dBr b=-4dB)
Fig 3.8 summarizes the soft, softer liandoff and coverage hole percentages with
respect to the cumulative probability distribution for the antenna mode1 wi th sector
crossover gain of -4dB. For each caser it shows the percentage of the ce11 area in which
the mobiles will have a probability of less or equal to the probability values on the
x - a i s due to the coverage of pilotoo and its neighbour pilots. For instance: for the
soft liandoff. there are about 90% area within cella with probability of less than IO-'.
From the curve, the softer handoff curve tends to becorne flat for probability of less
than or equal to IO-': hence: we can conclude that there are about 15 percent of the
area will have probabilty of more than IO-'. Rest of the area has very low softer
handoff probability. There are about 2 percent of the ce11 area with coverage hole
probability over 10-'.
Figure 3.8: The soft, softer handoff and coverage hole area percentages vs. probability
distributions for the assumed antenna model. (b=-4dB: n=3, 8 = 3n/2, E = -4OdB)?
with T,4DD=-13dB and TDROP=-15dB
3.2.4 Determining the Handoff and Coverage Percentage
In last section, we have evaluated the handoff and coverage probabilities a t each loca-
tion within the central cell. Since the user are assumed uniformly distributed within
each sector: therefore, the average handoff and coverage percentages can be evaluated
by applying (2.15). (2.24): (2.28): and (1.34) respectively. The soft (er) handoff and
coverage, coverage hole area percentages are evaluated for the hypothetical antenna
pattern niodel with different sector crossovers as depicted in Fig.3.9. Note, the term
- -- Total-Handoffs
ab# - ---- Çofter ---A soft
Figure 3.9: Handoff and coverage percen tages for patterns with different sec tor
crossovers. (T,4DD=-13dB, TDROP=-15dB)
total handoff is the total handoff percentage for al1 three base stations of the central
cell. Notice that as the sector crossover (or beamwidth) decreases, the total hand-
off and coverage percentages are decreasing significantly. Since the pattern's sector
crossover mainly affects the pattern gains of regions over the sector crossover bound-
aies , the soft handoff is relatively stable: while softer handoff percentage rises with
larger sector crossovers.
Fig.3.10 characterizes the coverage hole percentage for this set of antenna pattern
wi t li differen t sector crossovers. The coverage hole percentage increases as the sector
crossover gain increases. -4s stated previously, there are two factors: intracell and
Figure 3.10: Coverage hole percentage vs. sector crossover gain for the hypothetical
antenna mode1 with Td4DD=-13dB and TDROP=-15dB
intercell coverage, affecting the coverage hole distributions, i t's necessary to consider
the intercell and intracell coverage hole percentages. Fig. 3.11 lists the evaluation
results for these two factors under different sector crossovers. For this particular set
of antenria patterns, as sector crossover decreases, there are less overlaps between
int race11 sectors. Therefore, the intracell coverage hole percentage increases. But
the intercell coverage hole. on the other hand, decreases as the beamwidth decreases,
despite that the decremerit is not very significant. This could be explaineci by the fact
that as the base station pattern gain increases a t some mobile location, the mobile's
received pilot signal strength increases, but a t the same time, the total interference
Figure 3.11: Intracell and intercell coverage hole percentages for different sector
crossovers for the hypothetical antenna mode1 with T-4DD=-13dB and TDROP=-
is also increased. Tliereforet EJI0 changes depending on the variations of tlie signal
strength and total interference. Since the neighbour ce11 pilots incur more signal losses
due to longer travelling distance, consequently, as the beam widtli getting a bit wider,
the total interference increases much more than the strength of the pilots from the
neighbour cells. Therefore, EC/& of the neighbour sectors are getting srnaller. Thus,
a t that location, tlie mobile will be gettirig less chance of being covered by the pilots
from ot her cells.
-4s stated above, the intracell and intercell coverage factors affect the coverage liole
percentage. Their effects are on the opposite directions as the antenna beamwidth
varies. The coverage hole percentage improves as the antenna sector crossover, or
3-dB beamwidth, decreases to a certain degree due to less interference form other
sectors. However: as the sectorized antenna beamwidth reduces, the sector coverage
may shrink as shown in Fig. 3.9. Therefore the sector antenna beamwidth can not
be chosen arbitrarily small. Hence, for a particular set of pattern shape, there might
exiçt an optimum beamwidth to have the least coverage hole while maintaining a
satisfactory percentages of coverage and sort (er) handoff percentages.
3.2.5 Sirnuiation Results
The Monte Carlo simulations are performed to further verify the above evaluation
results. ünder the same condition with the variations of the antenna sector crossover
gain, the simulations are conducted by randomly assigning a mobile station into a
large number of equally distributed locations within the central cell. .4t each location,
total of 56 pilots' &/&, are evaluated and compared with the handoff threshold,
T-ADD, while EJIo of the pilot from sectmoo is compared with TDROP. Based on
the strength of these pilots' Eb/lo, handoff types can be categorized. By running the
procedure numerous times: the distribution of the different handoff types can then be
obtained.
Fig. 3.12 gives the percentage results for two-way soft: softer, and the case when
rio handoff occurs. Fig. 3.13 characterizes the cases for softsofter, three-way soft: and
coverage hole. The figure doesn't display the curves for soft handoffs with four-way
and above. The simulation results show that under the handoff thresholds, Td4DD=-
13dB and TDROP=-l5dB, the percentage is negligible. This indirectly indicate that
the mobile station can have three demodulators to provide acceptable performance in
soft handoffs without sacrificing the diversity advantages of soft haadoff. .As shown
in Fig.3.12, when the antenna sector crossover gain increases, there are more users
involved in handoffs, mostly two-way-softer handoffs, and the percentage of users
witli no handoffs are getting les . For the two-way soft handoffs, it actudly slightly
decreases as the antenna beam width increases. This is due to the variations of the
Iiandoff types. .As sliown in Fig.3.13, there a re twvo-way soft handoff users becoming
softsofter or three-way soft after the beamwid t h changes. Bot h softsofter and t hree-
Figure 3.12: Simulation results for no-handoff, softer and two-way soft under different
antenna sec tor crossovers. T,4DD=-13dB and TDROP=- l5dB
way soft percentage will increase as the beamwidth increases. Soft handoffs with three
way or above occupy a very smal1 portions and don't have significant changes due to
beamwid t 11 variations. The simulation also verifies that coverage hole increases wi t h
large sector crossover as indicated in the previous analysis.
Fig, 3.14 compares the percentage results for both the analysis and tlie simulation.
1x1 the graph, the solid lines represent analytical results, while the dashdotted curves
represent the simulation outcornes. Note the term totalhandoffs is different from the
totallmndofis defined in Fig. 3.9, where it repreçents the estimated total handoff
percentage for al1 three base stations of the central cell. The term here is for one base
station in the central ce11 only. The simulation result is very close to the result from
analytical evaluations. -4gain, the percentage of totd handoff and coverage region for
pilotoo is increasing as the sector crossover: or beam width? increases. This is mainly
due to the increment of the softer handoff percentage, which is greatly coupled with
Figure 3.13: Simulation results for softsofter, three-way soft, and coverage hole under
different antenna sector crossovers. Td4DD=-13dB and TDROP=-1SdB
the overlaps of the antenna footprint between the adjacent sectors. The soft handoff
percentage, On the other hand, remains constantly around 5 percent as the beam
width changes. The simulation result, again, proves that the antenna beamwidth
variation affects more on the softer handoffs.
For a riormally loaded onini-network, the total handoff percentage which accounts
for the hardware overhead can be bounded to approximately 20 percent to 30 per-
cent. Tlierefore, for a three sectorized network, we wvould assume the total handoff
percentage are between 7 percent to 10 percent for each sector. Since during our
investigation, ive are only considering one sector: this leads to the evaluations of
two-sided region for softer handoff. Therefore, by half-dividing the softer handoff
percentage, and adding it with the soft handoff percentage, then multiplying it by
number of sectors, the total handoff percentage for the ce11 can be estimated. Both
Fig. 3.9 and Fig. 3.14 indicate that under current handoff thresholds, the patterns
Figure 3.14: Handoff and coverage percentage cornparisons between simulation and
analysis under differeat antenna sector crossovers. T-4DD=-13dB and TDROP=-
l5dB
with sector crossover between -3dB and -5dB are within the handoff requirements of
the network.
3.3 Real Antenna Evaluat ions
W've used our proposed mode1 to analyze handoff and coverage probabilities and
percentages due to antenna beamwidth variations. The results indicate tIiat there
esists some optimum beam pattern whose beamwidtii will result a minimum cov-
mage hole percentage while maintaining an acceptable coverage and soft(er) liandoff
pcrcentages. In this section, Ive wiil apply the same method on real antenria patterns.
We will rneasure and compare different patterns in order to find the suitable one for
our modelled three sectorized CDh4.4 system.
Three directional antennas DB978H90-M, DB982H65, and DB982H33-AI: with dif-
ferent beam width and pattern gain irom Allen Telecom are chosen for evaluations.
The detail specifications of the antennas and their patterns are attached in -4ppendiu
.A-C. Fig. 3-15, Fig. 3.16, and Fig. 3.17 describe the corresponding horizontal and
vertical antenna patterns for the three antenna models respectively. The correspond-
ing antenna boresight gains are clifferent for each of the antenna model, Notice that
(a) Horizontal (b) Vertical
Figure 3.15: .4ntenna model DB978H90-hi
aa - = = - -- LI0
(a) Horizontal (b) Verticai
Figure 3.16: Antenna Mode1 DB982H65
(a) Horizontal (b) Vertical
Figure 3.17: .btenna Mode1 DB982H33-M
t hese patterns are not symmetric. Neither DB978H90-M and DB982HG5 model have
sigriificant side lobes for their horizontal patterns. .And the backside lobe gains are
very small. There are large side lobe gains for antenna model DB982W33-hl. This
side lobe effect will be discussed in coverage and handoff probability distributions.
For al1 of the vertical patterns, the pattern shapes are very irregular.
Fig. 3.20, Fig. 3.21 and Fig. 3.22 portray the coverage, handoffs, and coverage
liole probability distributions for the antenna rnodels respectively. For antenna model
DB982H33-MI particularly, the side lobe effect is very obvious as shown in Fig. 3.22.
Besides the coverage due to main beam lobe: there are also high coverage probabilities
due to the side lobes. The side lobes thus have some effects on the softer and coverage
probability distributions. Notice there are higher coverage hole probabilities locateù
within the ce11 area. The notcli between the main lobe and the side lobe creates the
gaps in the softer handoff distribution meshes.
Table 3.3 lists the evaluation results for handoffs and coverage percentages under
different handoff threshoids.
Fig. 3.18 shows the handoff and coverage percentages for the selected real antennas
under handoff threshold of T,4DD=-14dB, TDROP=-16dB. The soft(er) handoff
Table 3.3: Handoff and coverage percentages for different real antennas under different
handoff t hresholds
and coverage percentages are decreasing as the beamwidth decreases.
-4 low handoff threshold cari be assigned to a ce11 to keep the mobile units in
the ce11 longer or a higher handoff threshold level is adjusted to request a handoff
earlier. Variations in handoff thresholds can lead to the changes of the coverage and
soft (er) handoff percentages. Fig. 3.19 shows the handoffs, coverage, and coverage
hole percentages for the 65O beamwidth antenna pattern, DB982H65, under different
handoff thresholds, respectively. AS the handoff thresholds increase: there are less
pilots being able to be received by the mobile. Therefore, the handoff thresholds are
the important parameters used to control handoffs and coverage percentages. The
graph shows that the relationship between coverage, soft and softer handoff percentage
ancl the handoff threshold is almost linear. -4 1 dB drop in T-4DD leads to over 3
ri
TADD
(dB)
-15
-15
-15
-14
-14
Antenna
Mode1
DB978H90-A4
DB982H65
DB982H33-?VI
DB978H90-ICI
DB982H65
TDROP
(dB)
-17
-17
-17
-16
-16
DB982H33-.II -16 -14
Soft
Handoff %
13.1
12.4
9.6
8.9
8.9
-
Coverage
Hole %
0.05
0.02
O. 15
0.53
0.27
r
Softer
Handoff %
17.2
9.0
6.3
13.5
6.9
6.9 0.58 4.7 7
DB978H90-hl1
DB982H65
DB982H33-hl
DB978H90-?VI
DB982H65
DB982H33-?VI
4.9
5.4
4.4
1.9
2.4
2.3
28.1 1
Coverage
%
43.7
38.1
29.9
41.5
36.4
38.9
34.4
26.2
36.0
32.3
24.6
-
-13
-13
-13
-12
-12
-12 i
9.9
5.0
3.3
6.6
3.3
2.1
-15
-15
-15
-14
-14
-14
2.75
1.66
1.67
8.74
5.85
4.20
Figure 3.18: Cornparisons of handoff and coverage percentages of the real antennas
urider handoff threshold of TADD = -14dB, T D R O P = -1GdB
percent rise in soft, 2 percent in coverage and softer handoff. The coverage hole rises
wi t h higher t hresholds.
For the three sectorïzed CDkI.4 system with handoff threshold, Td4DD=- 13 dB,
TDROP=-15 dB, the 65 degree bearnwidth antenna pattern, DB982H65, is a very
suitable antenna model. Despite that the 33" bearnwidth pattern, DB982H33-M, has
least percentages in soft and softer handoffs, but it's coverage is a bit small, below
1/3 of the area. The DB978H90-M model has a large coverage percentage, but the
handoff and coverage hole percent is a bit high. The DB982H65, on the other hand,
has a reasonable coverage percentage: 34 percent, and a small amount of handoff'
and coverage hole. In fact, the 65" beaniwidth pattern has already been chosen by
most service providers for the three sectorized CDMA ce11 layout.
30 -
-- Coverage *- Soft
25- 3- 7 Softer E % -_ - CoverageHole
g 20- Q)
2 Q> n
15
Figure 3.19: Handoff, coverage and coverage hole percentages of antenna mode1
DB982H63 under di fferent handoff t hresholds
3.4 Conclusion
We have provided a quantitative measure of the effect of the antenna beamwidth
on handoff and coverage performance. Based on the analysis from Chapter 1, a
hypothetical antenna mode1 has been constructed and used to andyze the effect of
antenna beamwidth on soft, softer handoffs, coverage and coverage hole percentages
by considering antennas with same boresight gains but different sector crossover gains.
The investigation started by evaluating the soft, softer handoff9 coverage and
coverage hole probabilities under one sectorized antenna pattern at any location of the
central cell. The results indicated that the soft handoff and coverage hole probability
increased significantly near the ce11 boundary. and varied with user's a n y l a r location.
The liigh softer handoff probability mainly exits near the sector crossovers. The
coverage probability drops near the ce11 boundary but the value varies with different
azimuth angles. It has been verified by both numerical evaluation and simulation
that the antenna bearnwidth variations has significant effect on coverage and softer
handoff. The soft handoff, on the other hand, does not appear to be much influenced
by antenna bearnwidth. The coverage hole is also analyzed by considering factors from
both intracell coverage and intercell coverage. It's shown that these two factors are the
two competing factors. As the aatenna sector crossover gain increases, the intracel1
coverage hole decreases, but the interceH coverage hoIe increases. For the chosen
antenna rnodel, the coverage hole improves as the sector crossover gain decreases.
However as sector crossover decreases, the coverage also shrinks. The beamwidth c m
not be arbitrarily small. The investigation also leads to a conclusion that there exists
a suitable antenna pattern with the beamwidth which results the least percentages
of soft (er) handoffs and coverage hole and at the same time sustaining a satisfactory
coverage. In addition. the simulations indicate tbat under the handoff t hreshold
T,\DD=-13 and TDROP=-15, the mobile station should have three demodulators
to efficiently combine signals from al1 base stations involved in handoff.
This proposed evaluation method is then applied to real antenna patterns with
different beamwidth. By considering different handoff thresholds, the results indi-
cate that the threshold variations and the handoff and coverage percentages have a
close to linear relationship. For our model, IdB drop in threshold leads to about
3 percent increase in soft liandoff percentage, and corresponding 2 percent increase
for coverage and softer handoff percentages. It again verified that a decreasing in
handoff thresholds improves the system coverage and less coverage bole, but will lead
more users to soft or softer handoffs, thus create more system load and result Iower
spectrum efficiency. For a three-sectorized CDA4.4 systeni with the liandoff thresh-
olds, T,\DD=-13 dB and TDROP=-15 dB, the 65" bearnwidth antenna pattern,
DB982H65, is cliosen to be the most suitable antenna model for the base station.
With this pattern. we can have the least coverage hole percentage with low soft and
softer handoff percentage, and rcach good coverage percentage. The result coincide
wi t h the choice determineci by service provider's simulations and engineering mea-
surernents.
. .. . m. 1 .. : 1". II : II: Ib- : L a 4
12. * J : *' . . - . . . a. u - u - U -
-- -- --
(a) Coverage (b) Handoffi (c) Coverage Hole
Figure 3.20: Probability distributions for antenna mode1 DB978H90-!LI
(a) Coverage (b) Hando& (c) Coverage Hole
Figure 3.21: Probability distributions for antenna model DB982H65
(a) Coverage (b) Handofi (c) Coverage Hole
Figure 3.22: Probability distributions for antenna model DB982H33-h4
Chapter 4
Effect of Antenna Tilting
4.1 Introduction
In cellular CDM.4 network. the capacity is directly d e c t e d by interference. Less
CO-channel interference will lead to a higher system capaci ty. -4ntenna til ting causes
the signal strength to be less for the mobile station on the sector boundary than
that without tilting. By tilting the neighbouring cells, the fonvarci link intercell in-
terference can be reduced. Hence, this technique is commonly used for CO-channel
interference reduction[2]. Depending on the degree of downtilting base station an-
tenna, the mobile station on the sector boundary might not be able to receive strong
pilot signal from the base station. The mobile rnight release its communication link
with it. Therefore, the cal1 might be dropped or switched to access the adjacent
sectors wi t h s trong pilot signal strength. Coilsequently, downtil ting can be used for
coverage control. It can also be used as a technique for hot-spot traffic relieql'?]. Since
antenna tilting can change the antenna coverage footprint, it would be necessary to
investigate hotv does it affect the system coverage quantitatively, and what impact it
will have on soft handoff performance.
In this cliapter, we will analyze antenna tilting effect by considering hypothetical
antenna patterns. UTe will first construct a hypothetical vertical antenna pattern
in addition to the horizontal pattern (3.1) used in the previous sections. Based on
the earlier introduced handoff and coverage analytical model, by finding the tilted
antenna composite gain, the performance results can be evaluated.
Antenna Downt ilt ing
Downtiiting the base station antenna is an effective technique for controlling the
radiation pattern. Basically, there are two ways of tilting an antenna: electronic
til ting and mechanical tilting. Electrical tilting is using an N-element phase-array
antenna. %y changing the N values of the phase differences and the space differences,
a desired pattern a t a given down tilting angle can be obtained. Mechanical tilting,
or1 the other liand, is by physically tilting an antenna as shown in Fig. 4.1. Since
Figure 4.1: -4ntenna pattern downtil ting scheme
-4ntenna pattern downtiltirig scherne: seen on the XZ plane
niechanicai tilt ing generally allows for rnuch greater flexibili ty in the adj ustment of
downtiiting angles, it will be mainly considered in rest of the chapter.
The collinear array antenna: widely used in mobile communication industry, is
assumed here to be used. In general, the primaxy concem is the resulting horizontal
antenna pattern after the antenna is titled down by an angle 23 in the vertical plane.
In addition to the horizontal pattern, if the vertical antenna pattern is known, the
resulting horizontal antenna pattern with angle 6 tilted can be obtained. We as-
surrie that the normalized vertical antenna pattern of the main lobe can be expressed
approximately by[17]
where a = Jm 0 is the angle to the vertical plane and increasing up to a&. In
the analysis, the angle, O,, is assumed to be IO0, 7 is -10 dB, hence' a = 3/m.
The modified horizontal pattern with some predetermined parameters is shown
below:
[ 1 - ,1413 if Idl < di: Gh(d =
L E otherwise;
-Again, the parameters b and E are the attenuation at the sector crossover and the
sideiobe gain respectively. e is chosen to be -40 dB. Fig. 4.2 shows the hypothetical
horizontal and the vertical patterns for this particular case.
U'hen an antenna is downtilted by an angle of 19: the relationship between the
observed direction (8: 4) and the effective direction (8, @) is a rotation of the angle
23 dong the Y-axis. as shown in Fig.4.3 .
The formulas for calculating the effective vertical angle 8 and the effective hori-
zontal angle are shown below[23]:
8 = arccos(cos 0 cos 19 + sin 0 cos # sin 6) sin 8 sin 4
= arctan( sin 8 cos 4 cos 6 - cos 8 sin 19 1
Since we are oniy interested in the gain a t the horizontal plane! therefore, 0 = n/2.
Figure 4.2: Hypothetical horizontal and vertical base station bearn patterns
Figure 4.3: antenna downtilting CO-ordinate.
Hence. (4.4) becomes:
8 = arccos(cos 8 cos 9) tan 4 = arctan(-) cos 6
The composite antenna gain in dB at direction (€9: a) is the sum of the horizontal
aiid vertical gains, therefore, the observeci horizontal gain will be
wIiere. Go is the antenna boresight gain in dB? e V ( @ ) and Gh(@) are the antennas
\vertical and horizontal radiation pattern respectively.
Fig. 4.4 depicts some of the resuiting horizontal antenna patterns under different
dowrrtilting angles for the Iiypothetical patterns. It can be uoticed that the pattern
Figure 4.4: Horizontal bearn patterns under downtilting angles of 0": 3". 7": 8": and
9"
shrinks? and the antenna gain drops as the downtilting angle increases. m e n the
antenna downtilted to about 7O: a little notch a t the center of the resulting horizontal
beam pattern is appearing. Further downtilting results even severe notches as shown
for 8 O and go downtilting. This can be explaineci by the fact that the effective vertical
gain. G, (8): and the effective horizontal gain, Gh(@): are the two competing factors
in determining the composite gain. The vertical gain increases as the effective vertical
angle O increases. The horizontal gain, on the other hand, decreases as the effective
horizontal angle increases. It's also noticed that 8 and both increase as the
horizontal observe angle 4 increases. Under certain downtilting angle, G,(9) would
out-run Gh(<P). then G ( f , 4) will increase as 4 increases to certain angle. Therefore,
a notch will appear. This notch is used to effectively reduce interference in the
CO-channel cells[23]. CVe can further observe that, the beamwidth of the patterns
are increasing as the downtilting continues. Fig. 4.5 illustrates this phenornenon.
Therefore, antenna downtilting has an equivalent effect of widening the beamwidth
of an antenna. UTe also notice that the pattern gain over the sector crossovers are
almost not changed with downtilting. The impact of it will be shown in the handoff
evaluations in the next section.
4.3 Performance Evaluat ions
The evaluations will be based on the previously constructed system model. Wit h
three sectorized CDhlI-4 system, the users are assumed to be uniformly distributed
wit,hin each sector. This implies the base station ERP is the same for al1 sectors. We
Further assume that the antenna pattern for each sector's base station is the same
before the tilting started. However, the pattern for tilted and non-tilted antennas
are different as modelled in the last section. Based on these assumptions, Ive will
consider three different performances iridividually ': downtilting al1 neighbour ce11
base stations, and downtilting only the three base stations of the central ce11 (cella),
lLn practise, it w o d d be i m p o s s i b l ~ ~ determine which base station is the centrai one, and which
are the neighbour ones within a network. Therefore, the f h t two cases are only usai as way of
testing the model.
H'"'
Figure 4.5: The composite horizontal antenna pattern bearnwidth under different
downtilting angles, for horizontal pattern sector crossovers gain of -4dB and -6dB
and downtilting di base stations.
4.3.1 Performance of Downtilting Neighbour Ce11 Sites' An-
tennas
First we will consider the case of downtilting of al1 neighbour base stations7 except
the ones in the central ce11 (celloo) of the nineteen ce11 cluster. Fig.J.6 and FigA.7
depict the IiandoHs and coverage probability distributions for 5 O and go tilting of the
neighbour ce11 sites7 antennas respectively. Downtilting neighbour ce11 sites' antennas
is equivalent to reduce the intercell interference. Therefore. the user received E c / l o
fron pilotoo is higher than without downtilting. This can be verified by cornparing
the 3-D coverage probabilities meshes in Fig. 3.4, Fig. 4.6(a) and Fig. 4.7(a), and the
(a) Coverage (b) HandoEs (c) Coverage Hole
Figure 4.6: Probability distributions under 5" downtilting of the neighbour cell base
stations
(a) Coverage (b) Handoffs (c) Coverage Hole
Figure 4.7: Probability distribut ions under 9" downtilting of the neighbour ce11 base
stations
coverage hole meshes in Fig.3.7: Fig.4.61~) and Fig.4.7(c) respectively. The curves of
the coverage probabilities on the analysed sector edge is flatter in Fig. 4.7(a) than in
Fig. 4.6(a) and Fig. 3.4. The coverage hole probability spikes a t the corner of the
ce11 are seen getting less as the antenna downtilted more.
Due to the loss of fonvard pilot signal strength from the neighbour ce11 sites:
the soft handoff probability mesh also shrinlis as the downtilting continues if we
compare Fig.3.5: Fig.4.6(b) and Fig. 4.7(b). The softer handoff mesh seems not
having significant changes in its width.
Table 4.1 and Table 4.2 summarize the probabilities a t sorne locations near the
central ce11 boundary for 5" and 9" downtilting as a continuity of Table 3.2 without
downtilting.
- - - -- - - -
Table 4.1: Probability of having a soft or softer handoff and coverage probability
at boundary locations within sectoroo for the antenna rnodel with 5" downtilting,
Td4DD=-13dB and TDROP=-15dB
-
J
The lia~idoff and coverage percentages are also evaluated for different downtilting
angles as presented in Fig. 4.8. -4s we can see the changes of the percentage curves
are not significant when the antenna is within 4 O downtilting. An 1" downtilting
leads only 0.02% drop in soft handoff and coverage hole percentage, 0.01% in softer
liandoff increment and 0.02% decreasing in coverage hole, and total of .4s the antenna
downtilting continues, the curves start to vary more. The significant changes occur
wlien the notch is developed There are about 1% rise of softer handoff percentage and
2% decrease in soft handoff percentage when the riotch appears around 7" downtilting.
This results total of 5% handoff perceatage drop for the central cell. The coverage
and coverage hole percentages, on the other hand, both have a little bit less than 1%
gain. At 9" downtilting, the coverage hole percentage is almost disappeared, while
Theta Soft Handoff
Prob. %
Radius
R = &/2 1
-
Softer Handoff
Prob. %
0.00
0.00
0.00
0.00
95.23
12.35
0.8R
R
0.8
L
0.8R
R
O"
30"
60"
0.00
5.50
3.14
46.24
3.71
64.54
Coverage Hole
Prob. %
0.00
69.92
0 .O0
3.35
0.02
3.32
Coverage
Prob. %
100.00
99.93
100.00
93.36
99.98
73.98
Theta Radius
Table 4.2: Probability of having a soft or softer handoff and coverage probability at
cell boundary locations within sectoroo for the antenna mode1 with 9" downtilting,
T4DD=-13dB and TDROP=-1SdB
R = fi/2
0.8R
Figure 4.8: Handoffs and coverage percentages under different angles' of downtilting of
al1 neiglibour base stations with the hypothetical antenna patterns. (Td4DD=-13dB,
TDROP=-15dB)
Soft Handoff
Prob. %
0.00
Softer Handoff Coverage Hole Coverage
Prob. %
0.00
Prob. %
0.00
Prob. %
100.00
the coverage percentage nse only about 1.3%. The total handoff percentage for al1
three base stations within the central ce11 drops 10% to 15%.
4.3.2 Performance of Downtilting the Central Base Stations
Downt il t ing the central base stations has the equivaient effec t of lowering the signal
strength but leave the intercell interference unchanged. .4s seen in Fig. 3.4, Fig.
4.9(a) and Fig. 4.10(a).
(a) Coverage (b) HandoEs ( c ) Coverage Hole
Figure 4.9: Probability distributions for under 5" downtilting of the central cell base
stations only
The downtilting causes significant drops for the coverage probabilities near the ce11
boundaries, especially a t 9" downtilting. Consequently, the coverage hole probability
meslies also shows large spikes as downtilting continues. To have a closer observe
of the soft handoff mesh, a 60" top view of soft handoff probability rnesh is shown
in Fig. 4.11 for O", 5" and 9" downtilting respectively. .b we can see, the soft
handoff meshes on the central ce11 boundaries are getting lower as the antennas are
downtilted more. This implies that downtilting causes the soft handoff probabilities
on the boundaries getting lower, since the signal strength is decreased. However,
the soit handoff probabilities a bit more inside the boundaries, for instance, those
(a) Coverage (b) Handoffs (c ) Coverage Hole
Figure 4.10: Probability distributions under 9" downtilting of the centra1 ce11 base
stations only
Figure 4.11: Soft handoff probability distributions of downtilting the central ce11 base
stations for the hypothetical antenna mode1 with different downtil ting angles of the
central ce11 base stations only
locations with distance less than 0.8, are showing opposite effect. We can see that
as we clowntilt the central base stations more: the soft handoff probabilities a t those
locations are actually increased. Calculations have shown that at azimuth angle of 30"
with distance of 0.8 from the base station? when it's 9 O downtilted, the soft handoff
probability is 27.46%: while 5" is 9.62%: about 3 times lower. For the case without
downtilting as shown in Table 3.2, the probability is only 6.18%. This opposite effect
is because the signal strength from the pilot in central sectors is getting smaller
when downtilting it. This leads to the reduction of the intercell interference to the
neighbour ce11 pilots. The neighbour ce11 pilot signal strength, on the other hand?
remaigs the same, since they are not downtilted. Therefore, for the users inside the
central cell: their received pilets' Ec/Io from the neighbour cells are getting higher.
Since the coverage loss effect for sedoroo is not significant for those in-ce11 locations
far from the boundaries (Fig. 4.9(a) and Fig. 4.10(a)). the soft handoff probabilities,
tlius. is increased.
Fig. 4.12 depicts the handoffs, coverage and coverage hole percentage resul ts
uncler different downtil ting angles. The coverage percentage decreases very lit tle for
a - 920
Total-Handoffs . ,
a -- Softer - --a-
B soft - 15. Coverage - CoverageHole .
IO-
Figure 4.12: HandoEs and cowrage percentages under different angles' of downtil ting
of only central ce11 base stations wi th the hypothetical antenna patterns. (Td4DD=-
13dB1 TDROP=-15dB)
downtilting of up to Gd, where the percentage drop is about 0.7% compare to the case
without downtilting. The decrement starts to be significant when the notch appears
around 7 O . 4 t the same time coverage hole percentage increases as the antenna
is downtilted more. -4t go downtilting, there is about 5.2% increase of coverage
hole percentage from 1.5% when downtilting is not conducted. The softer handoff
percentage curve is relatively Bat, since the intercell interference remains the sarne,
and the gain a t the sector crossover also remains almost constant as irnplied by
Fig.4.5. The soft handoff percentage curve, on the other hand, rises and reaches to
its maximum of slightly over 7% a t ïO where the notch appears. It then starts to
drop as the downtilting continues. As mentioned before, downtilting of the central
ce11 base stations has effect of increasing soft handoff probabilities inside the cell. and
decreasiug the probabili ties on the boundaries. Therefore the soft handoff percentage
is the results of these two competing effects. Under small degree of downtilting,
the coverage loss is very small. Therefore the incrernent of the probabilities for the
locations iriside ce11 outruns the decrement of the ones near the boundaries. Hence,
the soft handoff percentage increases under srnaIl angle downtilting. -4s downtilting
continues, the coverage loss is getting large, the soft handoff probabilities near the
boundaries decreases more. This leads to the declining of the soft handoff percentage
curve. As a result, the estirnated total handoff curve also rises and then drops as the
downtilting getting large. The maximum increment is about 3% for the whole central
cell.
4.3.3 Performance of Downtilting All Base Stations
In this section we will consider the case when al1 base stations of the cluster are
downtilted a t the same degree. For comparisons, Fig. 4.13 and Fig. 4.14 describe the
probability distributions for downtilting angles of 5" and 9" respectively.
By comparing Fig. 4.13(a) and Fig. 4.14(a), we can see that the coverage prob-
abilities near the ce11 boundary a t azimuth angle of 0" for 9" tilting is lower due
to significant loss of home sector pilot signal strength a t this direction. The softer
(a) Coverage (b) Handoffs (c) Coverage Hole
Figure 4.13: Probability distributions under 5" downtilting of dl base stations
(a) Coverage (b) Handoffs (c) Coverage HoIe
Figure 4.14: Probability distributions under 9" downtilting of al1 base stations
handoff meshes exhibit higher probabilities near the ce11 boundacy if more downtilt-
ing is made. The shape of soft handoff rneshes are different for different downtilting
angle. Fig. 4.15 depicts the soft handoff probability meshes viewed from the fiont
with 30° above the ground plane. Each of the soft handoff probability mesh has deep
notch in the middle of the graph a t O0 azimuth angle, where the pilot signals the
user will receive from the two closed neighbour sectors have low antenna gains. This
low antenna gain makes those two signals have small signal strength. Consequently,
the soft handoff probability is lower there. In the graph, notice that there are lobes
Figure 4.15: Soft handoff probability distribution meshes under different angles of
downtilting of al1 base stations
around 130° and *CO0 for 0" and 5" downtilting and the lobes show up only a t *30°
for 9" downtil ting. These lobes represent higher soft handoff probabili ties. The non-
interleaving configuration leads users at those locations to receive higher signal power
from neighbour cell. For instance: a user on the boundary at azimuth angle of 60" will
receive the pilot signal with maximum gain from its closest neighbour sector if the
antenna is not downtilted. If downtilted and the notch appears, then the user there
will receive a very small pilot signal power from that neighbour sector. This is the
case for 9" downtilting as shown in Fig. 4.15(c), where the soft handoff probability is
very high a t 30°: b u t low at CO0.
The handoff and coverage percentages are also evduated for different downtilting
angles as presented in Fig. 4.16. -4s the curves disclosed, except the curve for softer
ha~idoff~ there are not significant percentage changes under different downtilting an-
gles, even though we notice ttiat difference arnong their probability meshes. One of
the reason could be that percentage evaluation is an aggregate process. The drops
and the increment might be balanced out. Hence: in this case the percentage result
miglit not be a good indicator for the downtilting effect. Mre 'evould suggest to evaluate
the variations of number of links iristead. However, from 0" downtilting to 9 O down-
Figure 4.16: Handoffs and coverage percentages uner different angles' of downtilt-
ing of ail base stations with the hypothetical antenna patterns. (Td4DD=-13dB.
TDROP=-lad%)
tilting, softer handoff percentage increases 2%. -4s Fig. 4.5 shows, due to bearnwidth
exparision effect. For this particular antenna pattern, the antenna gain over the sec-
tor crossover doesn't change much. therefore: the signal strengt h at those locations
remain almost same, but the intercell interference reduced. Therefore: this increasing
in softer haridoff percentage is mainly due to the intercell interference reduction.
4.4 Conclusion
We have investigated the effect of antenna downtilt ing on handoffs and coverage.
We've used hypothetical vertical and horizontal antenna patterns to find the effective
horizontal antenna patterns after the antenna is downtilted. The resulting horizontal
antenna pattern is then applied to our systern mode1 with three different scenarios:
downtil t ing the neighbour tells:! downtilting only the central ones, and downtil ting
al1 base stationso. For different scenarios: antenna downtil ting has varied effects on
controlling liandoff and coverage for CDM.4 networks.
Due to signal strength reduction from neighbouring cells: the first case leads to
both upward Cumes for coverage and softer handoff percentages, while the downward
curves for soft handoff and coverage hole percentages. -4 small angle of downtilting the
neighbour ce11 base stations does not have significant effect on handoff percentages.
For the second case, when only the central ones are downtilted, it is equivalent to the
reduction of EJlo from the central ceil pilots, and a relative increment of EJi , of the
pilots from the neighbour cells. The downtilting in this case: created more coverage
lioles. The softer handoff does riot fluctuate mucli. The soft handoff percentage CUI-ve
displays a maximum point when the notch appears. For large downtilting angles,
coverage percentage will have as rnuch as 5% loss. In tlie last case! where al1 base
station antennas are downtilted, the performance shows that there are significant
changes on the probability meshes but not on the percentage resul ts.
-4s a conclusion, downtilting causes changes on antenna radiation footprint. When
downtilting degree is increased, especially when the notch is developed, tlie impact
becornes significant. Generally tbis should be avoided due to poor coverage perfor-
mance. Small degrees of downtilting do not affect coverage and handoff percentage
much. There are about less than 1% variations. Since the perceotage evaiuation is an
aggregate process, the decrement and the increment of the individual contributions
might be balanced out. -4 better indicator for measuring the downtilting effect on
soft handoff is to investigate the changes in number of links during soft handoff.
Chapter 5
Effect of Ce11 Site Configuration
During CDMA network design and system optirnization phase, ce11 site configuration
analysis is about how to plan the systern layout and configure the base stations to
rmet coverage objectives and achieve higher capacity. Since ce11 site configuration can
influence system coverage, it would be necessary to explore the quantitive impact and
study the performance on soft handoff. In this chapter, Ive will apply our proposecl
mode1 to exam sectorized CDM4 systerns for two cases: base station antenna azimuth
orientation and further sectori~ation.
5.1 Effect of Antenna Azimut h Configuration
5.1.1 Introduction
For sectorized CDM-4 systerns, one of the issues they might have to consider is tliat
wliat is the suitable antenna azimuth orientations, or in other words, under what
directions should the antennas point to, in order to achieve maximum coverage per-
formance and have the least interference. In our previous analysis, it is assumed
that the cells are three-sectorized with non-interleaving azimuth configuration, where
each of the antenna points to one of its closest neighbouring antenna. But in the
real world, i t niight not be possible to have such configuration when setting up the
base stations, e-g., property reasons: and this configuration might not the optimum
one. Therefore, i t would be necessary to investigate i ts orientation variation effects
on soft handoff and coverage performauce, and determine the optimum orientation
in terrns of handoff and coverage percentages. B a d on our proposed rnodel, this
section provides an analytical method for evaluating the effect of different azimuth
configuration on coverage and handoffs.
5.1.2 Azimuth Orientations
In most sectorized cellular analysis, a typical secterized iayout with interleaving az-
imu t h configuration is assumed(2J [l3], where the antenna boresight pointing to i ts
neighbouring antenna of next tier. The non-iaterleaving azimuth configuration, on
the other hand, is mostly adaptec! in industry. One of the reasons for that is that a
mobile at the ce11 corner might use less numbers of fonvard links during soR handoff
than tlie case in interleaving one. This will decrease the nurnber of voice circuits
required at each base station and have less resource consumption. This situation can
be explained by cornparing the boundary points Ak, Br, and 4: k = a,b, in Fig.
5.l(a) and Fig. 5.l(b) respectively. Note, Aa represents point -4 in Fig. 5.l(a): tlie
non-interleaving configuration, while Ab is for point -4 in Fig. 5.l(b) showing the
interleaving case. For the non-interleaving, by direct observation: tliere are at most
t h e e sectors intersecting at the ce11 boundary. Point A,: Ba: and Ca are the locations
wliere the maximum lies. For the interleaving case, on the other hand, the maximum
number of intersected sectors is a t point Ab? where a mobile user niight be able to
receive rip to six pilot signais from the surrounding sectors during soft handoff. User
located at point Cb will have a chance of getting three pilot signals, while at Bb, or
on the boundary and between point Ab and point Cb, only two strong pilots can be
acquired. Note, al1 these intuitive observations are made by assuming that for each
sector, the base station has a perfect antenna beam pattern covering it. Since prac-
ticalIy we will not be able to obtain such an antenna pattern, the number of polits
(a) Non-interieaving (b) Interleaving
Figure 5.1: k i r n u t h orientations
received during soft handoffs a t t hose boundary and corner points might be different.
But in general, this observation does give us some clue. In the next section, we will
apply our proposed model to analyze the effect with realistic antenna systematically.
5.1.3 Performance Results
Based on the same model set up previously, we will consider rotating the antenna az-
imuth angle of each sector in the cluster. The rotation starts with the non-interleaving
configuration (Fig. 5. l(a)) , which is assunieci O", and continues to the left and right
passing 30' and -30": representing the interleaving case (Fig. 5.l(b)) and ends with
GO0 and -60". The antenna model we used is DB982H65, since it was shown to have
the preferred pattern for a three-sectorized ce11 layout based on previous analysis.
Fig. 5.2, Fig. 5.3, and Fig. 5.4 depict the coverage, coverage hole and handoff
probability distributions for 30": 45": and 60" azimuth configuration complementary
to the non-interleaving one shown in Fig. 3.21. by comparing the coverage distri-
butions: ive could see tha t the graphs are symmetric about 30" for interleaviog, and
sy mmetric around 60° for 60" non-interleaving configuriation. The 45" azimut h con-
figuration is asymmetric on the ce11 boundary due to the geometric layout. The softer
(a) Coverage (b) Handoffs ( c ) Coverage Hole
Figure 5.2: Probability distributions for 30° azimuth configuration (interleaving) with
the real antenna mode1 DB982H65. (TADD=-13dB: TDROP=-15dB)
(a) Coverage (b) Handoffs ( c ) Coverage Hole
Figure 5.3: Probability distributions for 4 5 O azimuth orientations with the real an-
tenna mode1 DB982H65. (TA4DD=-13dB, TDROP=-15dB)
liandoff distribution meshes seem to be not affected much by azirnuth orientations.
However: the effect on the soft handoff distribution meshes is different. The maximum
soft handoff probability for non-interleaving is at point C: while for interleaving, i t
is at point B. The 30" azimuth configuration lias higher coverage hole probability on
the ce11 corners.
Fig.5.5 and Fig.5.6 summarize the handoff and coverage probabilities for some
(a) Coverage (b) HandofEi (c) Coverage Hole
Figure 5.4: Probability distributions for 60" azimuth configuration (non-interleaving)
witli the real antenna mode1 DB982H65. (T,4DD=-13dB, TDROP=-15dB)
particulas locations ori the central ceIl boundaries. In both figures, 0" represents the
non-interleaving configuration, a positive angle represents the antenna direction is
turning counterclockwise, and a negtive angle is for clockwise. The softer handoff
is not shown since its probability is very smalI a t those locations. In Fig. 5.5, the
curves picture the soft hando. coverage, and coverage hole probabilities a t the ce11
corner, e.g. point -4 or point C as shown in Fig. 5.1. As Fig. 5.5 reveals, the
maximum soft handoff probability occurs when the interleaving configuration (at
+30° representing point C of Fig.s.l(b)) is adopted. It is about 25% higher than
the non-interleaving counterpart. The minimum occurs at the negative rotation,
when the antenna backlobe facing the spot(point -4): despite that a t that point, it
might be able to receive up to six forward link signds from the surrounding sectors.
.4t that instance, the coverage hole probability actually reaches to its maximum.
The maximum coverage probability also occurs a t the interleaving case, when the
bciresights of the three surrounding sector's antenna mainlobe are pointing to it.
Fig. 5.6 describes the probabilities of point B of Fig.Ei.1 under different azimuth
configuration. Its soft handoff probability also reaches to the maximum a t both
30° and -30" aaimuth rotating angles. .4t non-interleaving case, the soft handoff
Figure 5.5: Handoff and coverage probabilities a t ceIl corner (point -4) for different
azimuth configurations with the real antenna mode1 DB982H65. (T-kDD=-13dB,
TDROP=-15dB)
probability drops to the lowest: since the signal strength from the two closed facing
sectors are very small even though the coverage probability is a t the maximum a t the
tirne. In addition, a 10° change in azimuth direction a t this instance does not affect
mucli on both coverage and soft hanoff probabilities. In al1 the cases, the coverage
hole probability a t point B is very low.
Fig. 5.7 presents the handoff and coverage percentage evaluation results of the
central ce11 under different azimuth angles. Notice that the softer handoff percentage
is very stable when the antenna azimuthal angle changes, since the orientation does
not affect the coverage overlaps between sectors within a same cell. Despite that
non-interleaving configuration seerns to have Iess chance of getting more links when
a mobile involved in soft handoff and have lower soft handoff probability a t some
boundary points (Fig.5.5 and Fig.5.6): on average, it actually has a bit higher per-
Figure 5.6: Handoff and coverage probabilities a t ce11 boundary (point B) for different
azirnutli configuration with the real antenna mode1 DB982H65. (T-4DD=-13dB:
TDROP=-l5dB)
centage in soft handoff. The resitlts show that it would have about 0.3% more users
involved in soft handoffs for non-interleaving than the interleaving case. Fluctuation
for coverage percentage is within about 1% around 35% The coverage hole percent-
age, on the other hand, is affected the most. The percentage increases from 1.6% a t
non-interleaving up to 7.5% at interleaving. We also notice that a &1O0 rotation from
non-interleaving configuration has very I i t tle impact on both coverage and hando.
percent agies.
5.1.4 Conclusion
In this section examed effect of antenna azirnuth configuration on coverage and soft
handoff performance in terms of t heir probabili ty distributions and percentages. UTe
. -A-- soft - CoverageHole , a--> Total-Handoffs
Figure 5.7: Handoff and coverage percentages vs. azirnuth orientation angle with the
real antenna mode1 DB982H65. (T,4DD=-13dB, TDROP=-15dB)
evaluated the handoff and coverage probabilities at some particular locations on ce11
boundaries and ce11 corners. The results indicated that a t both ce11 corner and ce11
boundary: soft tiandoff probability will reach to its maximum with interleaving con-
figuration. We further evahated the average percentages for handoffs, coverage and
coverage hole. The results showed that for three sectorized system, the soft handoff:
softer haadoff and coverage percentage were not significantly influenced by azimuth
configuration. The coverage hole percentage, on the ot her hand: apparently fluctuated
with different azimuth orientations. I t reached to the minimum a t non-interleaving
configuration. Based on the analysis: we conclude that the non-interleaving con-
figuration is a preferred selection when deciding base station orientations. If non-
interleaving configuration is not possible, an azimuth rotation of within z i l O O is also
acceptable.
5.2 Furt her Sectorizat ion
In cellular CDMA system, sectorization is one of the optimization techniques for
interference reduction and capacity improvement. When three sectori~ed cells reach
to their full capacity, further sectorization is desired. One of the simplest approaches
is to half divide the already three-sectorized cells into sk-sectorized layout. Fig. 5.8
displays t hree possible ways of six-sectorizing the three-sectorized ce11 layou t. In the
(a) Non-interteaving (b) 15" Rotation ( c ) Knterleaving
Figure 5.8: Six sectorized azimuth configuration
previous analysis, we have proposed non-interleaving azimuth configuration for three-
sectorized layout. Therefore? by half-dividing it: we will get six-sectorized interleaving
configuraton as shown in Fig. Fj.S(c). By rotating the base station antenna directions.
different ce11 site orientation can be obtained. Fig. S.8(b) shows the configuration with
15" rotation. -4 30" rotation of the antenna in six-sectorized interleaving configuration
leads to a non-interleaving layout as shown in Fig. 5.8(a). In this section we will apply
our method to order to choose a suitable antenna pattern for six-sectorized ce11 layout
wi t h consideration of different azimut h configuration.
First we will apply differeat antenna mode1 to the typical ce11 layouts, interleaving
and non-interleaving respectively. Table 5.1 and Table 5.2 summarize the hand-
off and coverage percentages of different antenna patterns for six-sectorized nori-
interleaving and interleaving ce11 configuration.
Coverage II -4ntenna Mode1
DB982H33-M
DB982H65
DB978H9û-M
Table 5.1: Handoff and coverage percentages of the real patterns for six-sectorized
non-interleaving ce11 configuration. (Td4DD=-13dB, TDROP=-15dB)
So ft
Handoff %
3.84
1.38
0.44
Softer
Handoff %
0.95
9.94
15.61
-4ntenna Mode1
Table 5.2: Handoff and coverage percentages of the real patterns for sk-sectorized
+
interleaving ce11 configuration. (T14DD=- l3dB, TDROP=-15dB)
Total
Handoff %
25.89
38.1
49.47
Both tables indicate that the soft handoff percentage decreases as the antenna
Coverage
Hole %
8.16
12.35
20.39
Soft
DB982H33- hl1
DB982H65
DB978H90-b1
bcamwid t h increases. Hoivever, the softer handoff percentage signi ficant ly increases
Softer
due to large amount of overlaps of the adjacent antenna footprint. Both coverage hole
Coverage Total
Handoff %
1.43
0.98
0.27
and coverage percentages increase with Iarge beamwidth. The tables show that the
Coverage
DB982H33-M antenna mode1 has about 1/6 of the ce11 coverage percentage? while the
Hôndoff %
1.18
10.52
15.9
otlier two models have a bit higher percentage due to footprint overlaps. The coverage
Iiole percentage is relatively low for DB982H33-hl in both configurations. The total
handoff percentage for DB982H33-M is also reasonable(1ess than 30%). Based on
above facts, under the criterion of acceptable coverage and minimum handoff and
coverage hole percentage, we can conclude that DB982H33-M antenna mode1 with
Handoff %
12.12
37.44
49.32
33" beamwidth is the most suitable one for both interleaving and non-interleaving
six-sectorized ce11 layouts.
Hole %
10.52
10.74
20.53
%
16.65
23.39
26.58 -
In previous analysis n e notice that there are some percentage difference with
different azimuth orientations for three-sectorized layout. From Table 5.1 and Ta-
ble 5.3: we also notice there are haadoff and coverage percentage variations for
six-sectorized layoii t with different azimut h configurations. Therefore, it's necessary
to further investigate what's a suitable azimuth configuration for the six-sectorized
cluster. Since DB982H33-bl antenna model was chosen as the most suitable one
for the six-sectorized ce11 layout, the following analysis will be conducted mainly on
this antenna model. Fig.5.9 depicts the handoff and coverage percentages of dif-
ferent anteiina asimuth configuration for the six-sectorized cell layou t with the real
antenna model DB982H33-h4. Notice that the coverage percentage is maintaining
.- Coverage -- Çoiîer A-_-- soft
CoverageHde Lf--- Total-Handoffs - -
Figure 5.9: Handoff and coverage percentages of different antenna azimuth config-
urations for six-sectorized ce11 layout with the real antenna model DB982H33-M.
(Td4DD=-13dB: TDROP=-15dB)
around 16.5% a t al1 azimuth orientation angles. The softer handoff percentage is also
very stable. The soft hando. on the other hand, has a bell-shaped curve. It reaches
to the minimum a t 30°, the interleaving azimuth configuration, and increased to the
niaxirnum at non-interleaving case. This is because for six-sectorized non-interleaving
ce11 layout, the antenna boresights of the two close sectors from different ceils are fac-
ing each other. Thus the users a t those locations will have much higher soft handoff
probabilities. Therefore the total hancloff percentage is very high for this configura-
tion. The coverage hole percentage possesses an W-shaped curve. The minimum is
around 15". And it reaches mavimum of 11% a t 30' orientation. ,4t O0 orientation:
the coverage Iiole is also very high, around 8%. Frorn Fig. 5.9 Ive can see that in
order to have a acceptable coverage 1ioIe and handoff percentages, the 15" antenna
orientation (Fig. 5.8(b) is the optimum ciloice for the six-sectorized ceIl layout.
5.2.1 Cornparison between Six-Sectorization and
Three-Sectorization
Now wc'd like to compare the effect of six-sectorization to our previously analyzed
tliree-sectorization network. Fig. 5.10 shows the result of the optimum choice for
six-sectorized system. under different handoff thresholds as a comparison to Fig.
3.19, the optimum choice for three-sectorized system. I t depicts the handoffs, cover-
age, and coverage hole percentages for chosen 3 3 O bearnwidth aatenna pattern rnodel,
DB982H33-M, under 15" azimuth orientation. These curves further verify the linear
relat ionships between handoff t hreshold and handoff and coverage percentages. The
coniparison indicates that the coverage hole percentage from DB982H33-hl for six-
sectorized is large tlian DB982H65 for three-sectorized layout under different thresh-
olds.
Wien changing from three-sector to six-sector ce11 site configuration, one of the
main concerns is number of links involved in soft(softer) handoff or the handoff per-
centages. In this section, we will compare the impact of sectorization on CDhll.4
liandoff percentages. Fig 5.11 compares the total handoff percentages for the real an-
tenna models wit h different azimu th configuration under varying Iiandoff t hresholds.
Coverage Soft
l2 .- I
- Softer - - Coverage-Hole ~~~1 IL- -- '&
- -7 - - - 0.- -- ---- -Pb-
-15 -14.5 -14 -13.5 -1 3 -12.5 -12 Handoff lhreshold. 1-AD0 (dB)
Figure 5.10: The handoff, coverage and coverage hole percentages for antenna model
DB982H33-A4 with 15" antenna orientation under different handoff thresholds in siu-
sectorized cell layout
In tlie figure, the dashed lines are for three-sectorized antennas! while the solid lines
are representing six-sectorized antennas. For each legend, the first part represents
tlie antenna model specified by the bearnwidth, the second part is for different sec-
torization, and the last one is for antenna orientation. For both the three-sectorized
and six-sectorized cases, the total handoff percentage drops with antennas of less
beamwidth. If ive choose 65" bearriwidth antenna for each base station of the three
sectori~ed non-interleaving ce11 layout as indicated from previous analysis, after apply-
ing six-sectorization. tlie resulted six-sectorized interleaving configuration will lead to
significant increase in total handoff percentage. Therefore we will have to use antenna
with 3 3 O beamwidth. With 15" azimuth orientation, the total handoff percentage sig-
Figure 5.11: Total handoff percentage vs. handoff threshold for different sectorized
antenna patterns under different azimut h configurations
xiificantly drops. From the figure we can see that the total fiandoff percentage curve
is very close to the one for the three-sectorized layout.
5.2.2 Conclusion
III this part of work: we further applied our proposed method on choosing suitable
antenna patterns for six-sectorized CDM.4 network. The results indicated that the
DB982H33-M antenna mode1 with 33' beamwidth is the most suitable antenna pat-
terri to be used for six-sectorized ce11 layout. In addition, the 33" beamwidth pattern
was used t o 6nd the optimum azimuth configuration for the network. The evaluation
leads to a conclusion that in order to have a minimum coverage hole percentage and
acceptable handoff performance, the 15" antenna orientation is an optimum choice
for the six-sectorized ce11 layout. We also made cornparisons of the total handoff
percentages between six-sectorization and three-sectorization ce11 layout. The result
point out that with appropriate choice of antenna pattern and azirnuth configura-
tion: in this case, 15" orientation of antenna DB982H33-M, six-sectorization can be
conducted wi th acceptable handoff percentage.
Chapter 6
Thesis Summary and Future Work
6.1 Thesis Summary
In this thesis, we have proposed a simple analytical mode1 used for analyzing the
effect of antenna pattern on coverage, soft and softer handoff performance for cellular
CDhll-4 systems. The model was extended further on analyzing effects due t o cellular
system configuration and cell layouts.
In Chapter 2: a sectorized CDM-4 network model was set up. The fonvard link
Ec/Io was arialyzed and its relationships rvith the base station transmitting power,
antenna pattern. path loss, fading: and interference were defined. Based on the
generally modelled handoff process, tlie relationsliips betweeri anterina pat terri and
coverage, soft hando. softer liandoff and coverage hole probabilities were derived re-
spec tively for any location wit hin the system. These handoff and coverage probabili ty
clensity functions were also presented in terrns of mobile locations, handoff thresh-
olds, arià relative pilot signal strength. Based on the probability density functions,
the corresponding handoff and coverage percentages were expressecl statistically. The
expressions indicate tliat these percentages were closely related to the base station
antenna beam pattern.
Based on the model and relationships constructed in Chapter 2, Cbapter 3 served
as a particular case. In Chapter 3: three sectorized cells of a nineteen-cell-cluster with
non-interleaving configuration were assumed. The quantitative measurement was first
applied to investigate the effect of the antenna beamwidth on handoffs and coverage
performance. Both the numerical evaluation and simulation agreed to some extend.
Both results from probability and percentage evaluations indicated that the antenna
beamwidth variations had significant effect on coverage and softer handoff but not
much on soft handoff. Coverage hole was also analyzed by considering factors from
botli competing factors: intracell coverage and intercell coverage. The investigation
irnplied that there esisted a suitable antenna pattern with the beamwidth which
resulted the least percentages of soft(er) liandoffs and coverage hole and at the same
t h e sustaining a satisfactory coverage.
The proposed model was then applied on selecting real antenna patterns with
different bearnwidth for the base station. The model was first used to investigate the
relationsliips between different handoff thresholds and handoff and coverage percent-
ages. It verified that a decreasing in handoff thresholds improves the system coverage
and results less coverage hole. but will lead more users to soft or softer handoffs, thus
create more system load and lower spectrum efficiency. The analysis provided a quan-
t i tat ive rneasure of tliis relat ionshi p. The mode1 concluded t hat for a t hree-sectorized
CDM-4 systeni with the liandoff thresholds. Td4DD=-13 dB and TDROP=-15 dB,
the 65" beamwidth antenna pattern was the rnost suitable antenna mode1 for the
base station. The evaluation prediction matches well with the the actual system
performance from the commercially deployed CDM-4 systems.
In Cliapter 4, We have investigated the effect of antenna downtilting on hand-
offs and coverage performance. Downtilting antenna can cause changes in antenna
radiation footprint. Based on the mat hematical relationships! hypothetical vertical
and horizontal antenna patterns were constructed and used in evaluatiag the effective
horizontal antenna pattern with different downtilting angles. The results showed that
the effective antenna pattern has a larger beamwidth but. Iess antenna pattern gain.
The notch effect was also analyzed in details. The resulting horizontal antenna pat-
tern was then applied to the system mode1 by considering three different scenarios:
dorvntil ting the neighbour celts', downtilting only the central ones, and downtilting
dl base stations'. The results from probability distribution meshes indicated that
antenna dowiitilting can be used for coverage and handoff control. Bu t the corre-
sponding percentage results showed that downtilting was not d e c t i n g coverage and
soft handoff much. With small degrees of downtilting, coverage and handoff percent-
ages varied less than 1%. When downtilting degree vas increased, especially when
the notch was developeci. the impact became a bit significant. But, generally, notch
should be avoided due to poor coverage. The investigation concluded tha t handoff
and coverage percentage was not a very effective performance indicator for analyzing
downtilting. A better one is needed.
In Chapter 5: the proposed mode1 was extended to analyze effect of ce11 site con-
figurations. The investigation was first on analyzing antenna azimut h configuration
by dianging the base station antenna orientations in a three-sectorixed systern. Lo-
cations on the ce11 boundary and ce11 corners were chosen to show that soft liandoff
probabili ties would reach to t heir maximum wit h interleaving configuration. The
coverage hole percentage was more affected by different antenna azimuth directions
than soft handoff percentage. The non-interleaving configuration led to t;he minimum
coverage hole percentage. The analysis concluded that the non-interleaving configu-
ration was preferred when selecting different azimuth configurations The results also
indicated that if non-interleaving was not possible' an azimuth rotation of within
f IOo was also acceptable.
The proposed method was further applied on choosing suitable base station an-
tenna patterns for six-sectorized CDh1.4 networks. The evaluations indicated t hat
the 33" beamwidth antenna patt.ern was the most suitable one for six-sectorized ce11
Iayout. In addition, the 33" beamwidth pattern was used to find the optimum u-
imuth configuration for the systern. The evaluation led to a conclusion tha t in order
to have a acceptable coverage hole and haadoff percentages, 1 5 O antenna orienta-
tion was an optimum choice for the six-sectorized ce11 layout. Cornparisons between
six-sectorization and three-sectorization ce11 layout were also made on coverage aod
soft handoff percentages. The result indicated that with the same antenna pattern
applied to both configurations: six-sectorized network tvill result more handoff per-
centages. But, with appropriate choice of antenna pattern and azimuth configuration,
sis-sectorization can be conducted wi th acceptable handoff percentage.
6.2 Future Work
In Chapter 4: the effect of antenna tilting was analÿzed. We can also analyze the
effect of antenna height. Antenna height can be another parameter to affect base
station antenna footprint. By applying different height to the antenna of the base
station, the effect on coverage and soft handoff can also be analyzed.
The model can be further applied to analyze the effect of adding new base stations
cw a continuity of the work in Chapter 5. -4dding new base stations is another way of
combating coverage holes. But it also brings the potentials of more soft handoffs. By
adjusting the base station transmit ting power and doing sorne modifications on the
ce11 layout geometry: this model can be easily used to give an in-depth investigation
in this perspective.
-4s suggested in Chapter 4: a better indicator for measuring the downtilting effect
on soft handoff is neecled. A good candidate could be the percentage of number of links
involved in soft handoff. .4ctually, it would be a great interest for the service provider
to know a t any location within the coverage, how many fonvard links are involved
in soft handoff, and how do the links distribute. This can provide the designers the
information of where the heavily used links are. With proper modifications of the
model, this could be a very useful indicator.
In conclusion, this mode1 provides an basic scheme for service providers and RF
engineers on designing and optimizing wireless CDM.4 networks. -4 software tool
can be designed and implemented based on this mode1 as an efficient and economic
solution to the most time consuming aspect of CDhL4 optimization of the forward
Iink performance tuning.
Appendix A
Pattern Data for DB982H33-M
ALLEN TELECOM
DB982H33-M
20.00
33.00
4 .O0
25.00
1850.00
1990.00
250.00
50.00
1-50
9 .O0
0.55
260.00
2
3
182.90
30.50
7.10
manufacturer (REQ)
mode1 (REQ)
maximum antenna gain (dBd) (REQ)
horizontal beamwidt h (deg) (REQ)
vert i d beamwid t h (deg) (REQ)
front-to-back ratio (dB) (OPT)
minimum operat ing frequency (MHz) (REQ)
maximum operating frequency (MHz) (REQ)
maximum input power (W) (OPT)
input impedance (Ohms) (OPT)
voltage standing wave ratio (OPT)
weight (kg) (OPT)
wind area (sq m) (OPT)
max wind speed (kph) (OPT)
polarizat ion (O:unknown, 1 :horz, 2:vert) - (OPT
downtilt (O:unknown, h o n e , 2:elec, 3:mech) (OPT)
height (cm) (OPT)
width (cm) (OPT)
depth (cm) (OPT)
Hotironrd Pnttcrn
Appendix B
Pattern Data for DB982H65
ALLEN TELECOM 11 DB982H61
rnanufac t urer (REQ)
mode1 (REQ)
maximum antenna gain (dBd) (REQ)
horizontal beamwidth (deg) (REQ)
vertical beamwidth (deg) (REQ)
front-to-back ratio (dB) (OPT)
minimuni operat ing frequency (MHz) (REQ)
maximum operating fiequency (MHz) (REQ)
maximum input power (W) (OPT)
input impedance (Ohms) (OPT)
voltage standing wave ratio (OPT)
weight (kg) (OPT)
wind area (sq m) (OPT)
max wind speed (kph) (OPT)
polarization (O:unknown, 1 : horz, 2:vert) (OPT)
downtilt (O:unknown, l:none, 2:elec, 3:mech) (OPT)
connecter type (OPT)
height (cm) (OPT)
width (cm) (OPT)
depth (cm) (OPT)
100
10 1
102
1 O3
1 O4
1 OS
1 O6
107
1 O8
109
110
III
112
Il3
114
Appendix C
Pattern Data for DB978H90-M
ALEN TELECOM
DB978H90-M
14.00
90.00
6.50
25.00
1850.00
1990.00
250.00
50.00
1.50
3.30
O. 19
260.00
2
3
121.90
15.50
7.10
PVC
manufacturer ( REQ)
mode1 (REQ)
maximum antenna gain (dBd) (REQ)
horizontal beamwidt h (deg) (REQ)
vertical beamwidt h (deg) (REQ)
front-to-back ratio (dB) (OPT)
minimum operat ing frequency (MHz) (REQ)
maximum operating frequency (MHz) (REQ)
maximum input power (W) (OPT)
input impedance (Ohms) (OPT)
voltage standing wave ratio (OPT)
weight (kg) (OPT)
wind area (sq m) (OPT)
max wind speed (kph) (OPT)
polarization (O:unknown, l:horz, 2:vert) (OPT)
downt ilt (O:unknown, 1 :none, 2:elec: 3:mech) (OPT)
height (cm) (OPT)
width (cm) (OPT)
depth (cm) (OPT)
radome type (OPT)
Horizontal Pattern Vertical Patcrn
ZOT
O L ' t C
O t ' O t .
01' 1 t.
0 t ' S C -
0 8 ' 1 C-
0 0 ' i C -
0 0 - I C -
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Bibliography
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[ï] R. Pickholtz, L. Hulstein: and D. Schilling, "Spread Spectrum for Mobile Com-
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