Coverage PlanningFree space propagation 3
Diffraction loss 4
Long term fading 8
Quality of service 9
GSM900 band 13
GSM1800/1900 band 17
Microcell models 18
Walfisch-Ikegami model 18
CW measurements 21
Required received level 24
Reference sensitivity level 24
Fade margin 35
Feeder losses 36
Hierarchical cell structures 38
Combined indoor / outdoor site 40
Indoor repeater 41
Micro BTS 41
Minimise network cost
Maximise service quality
power density decreases with distance
isotropic receiving antenna with aperture A (A=2/(4)) will receive power
Assume transmitting and receiving antennae Gt and Gr respectively and rearranging
Path loss for isotropic antennae
Observations:
s
One direct path and one ground reflection
Approximation for perfect reflections and d >> hT, hR
For isotropic antennae
d
ht
hr
s
Diffraction Loss
Fresnel zones
the space bounded by an ellipsoid, which has the foci at the transmitter and receiver
nth Fresnel zone:
path transmitter receiver via any point on the ellipse is n/2 longer than d
shadowing occurs if an obstruction lies within the first Fresnel zone
d+n/2
for point-to-point links most 1st Fresnel
zone should be clear (at least 55 %)
diffraction parameter
d1
d2
h
T
R
-2
-1
0
1
2
3
20
16
12
8
4
0
s
log-normal distribution
Rician distribution (direct + reflected components)
“Local mean”
Received signal is a combination of several reflected components - multipath components
each multipath wave has
strengthening of composite signal
weakening of composite signal
signal strength constant
signal strength varies
+
=
Rayleigh fading
frequency hopping provides diversity
Coherence bandwidth
range of frequencies which are affected about the same way by the channel
Frequency
With Rayleigh fading required S/N increases for a given BER
GMSK demodulator,
BT = 3
Synchronous demodulator
log-normal distribution
determined by ,
Typical values
At cell edge: Cell Edge Location Probability
Log-normal
distribution
i
n
Area coverage probability
Cell edge location probability
probability that at cell edge signal will be greater than or equal to a specified value
determines fade margin (FM)
z is taken from tables for the normal distribution function
Min_Rx_Level (x% loc. prob.) = Min_Rx_Level_median + z(x%) * standard deviation
FM
z
sufficient coverage
Use “Jakes curves”
example of channel impulse response
Channel changes
bitstreams received at different time shifts interfere with each other
Mean delay spread
typical values (from Lee)
GSM requirement: Should be able to handle time dispersion up to 16 sec
Solutions:
Related to coherence bandwidth
speed v
signal arrives at angle a relative to direction of movement
frequency will experience a Doppler shift
maximum Doppler shift
each with different Doppler shift
Frequency dispersive channel
Doppler baseband spectrum example
Illustration of Doppler effect
General structure of most path loss models
L: Loss in dB B: propagation index (loss per decade), typical range 30-40
A: unit loss (at 1 km) d: distance MS - BS (km)
L = A + B*log(d[km])
L(dB)
A
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Macrocell Models - GSM900 Band
Free Space Path Loss
Near the base station antenna Line of Sight (LOS) conditions can be expected
near free space path loss conditions
Remote hill with LOS and no reflections or over water
near free space conditions
s
Hata model for urban areas
Lurban=69.55 + 26.16* log(f[MHz]) - 13.82*log(HBS)-a(HMS) + {44.9 - 6.55*log(HBS)*log(d[km])
Lurban=147.14 - 13.82* log(HBS) - a(HMS) + {44.9-6.55*log(HBS)*log(d[km]) for f=925MHz
small city: a(HMS) = (1.1*logf[MHz] - 0.7)* (HMS) - (1.56*logf[MHz] - 0.8)
= 0 for HMS = 1.5m and f=925MHz
large city: a(HMS) = 3.2*(log(11.75*HMS))2-4.97
= 0 for HMS = 1.5m and f=925MHz
Lsuburban= Lurban- 2*(log(f[MHz/28))2 - 5.4
= Lurban- 10.0 for f=925MHz
Lquasi open= Lurban- 4.78*(log(f[MHz))2 + 18.33*log(f[MHz) - 35.94
= Lurban- 23.6 for f = 925MHz
Adjustment factors, or “clutter factors”
s
f = 150 - 1500 MHz
not valid for GSM1800
HBS = 30 - 200 m
d = 1 - 20 km
not valid for microcell
Valid for urban areas,
Lother area = Lurban + Kcl
From link budget, obtain max permissible path loss, Lmax
Rearrange the above formula to derive distance as a function of path loss for urban area
For other areas the path losses have to be corrected by the clutter factors, Kcl, i.e,
From this area per base station can be estimated
can estimate roughly the no. of BTS’s to cover an area of a given type
d[km] = 10 (Lmax - 147.14 +13.82 * log (HBS) + a(HMS) ) / (44.9 - 6.55 * log (HBS))
d[km] = 10 (Lmax -Kcl -147.14 +13.82 * log (HBS) + a(HMS) ) / (44.9 - 6.55 * log (HBS))
PS! Max range for GSM (without extended cell) = 35 km (due to timing advance)
s
% Cell border 90 %
Urban 3 7 20 4
Suburban 9.5 6 15 3
0
km
3
1
2
s
Tornado general propagation model
factors K1, K2, K3 and K5 can be derived from the Hata model
simplify Hata model inserting the frequency and convert format to derive K factors
PS! d is in meters for Tornado / Planet format
clutter correction factors must be specified separately
Tornado / Planet also calculate diffraction losses
L=K1+K2log(d[m])+K3log(HBS-eff)+K4*Diffraction
+K5log(H BS-eff)log(d[m])+K6HMS-eff+Kclutter
s
COST231-Hata model(GSM1800) for urban area
Valid for f = 1500 - 2000 MHz (validity ranges for HBS, HMS and d are the same as for Hata model)
Unit loss increases with frequency (about 10 dB higher than GSM), decreases with BTS antenna height
Loss per decade is independent of frequency, decreases with BTS antenna height
clutter factors will be different from GSM
L=46.3+33.9* log(f[MHz])-13.82*log(HBS)-a(HMS)+{44.9-6.55*log(HBS)}*log(d[km])
L=156.65-13.82* log(HBS)-a(HMS)+{44.9-6.55*log(HBS)}*log(d[km]) for f=1800MHz
a(HMS) = 0 for HMS = 1.5m, f = 1800 MHz
s
Frequency 1800 MHz
% Cell border 90 %
Urban 3 7 20 4
Suburban 13 6 15 3
Indoor Suburban
Indoor Urban
Microcell Models
Objective: High capacity by large number of cells serving a given area with high frequency reuse
Typical diameter of microcell: 200-400 m
BTS antenna typically mounted below roof tops
Two main type of coverage
line-of-sight (LOS) - free space propagation and reflection
non line-of-sight (NLOS) inside road - diffraction mainly around corners and to some extent around roof tops
Path loss in the Tornado tool is based on vector street data
New models available using 3-D array tracing
s
Compensates for building heights - no clutter correction factors used
valid for
If no LOS
The rooftop-to-street diffraction and scatter loss is given by:
where,
and:
where:
for medium sized cities and suburban centres with moderate tree density
for metropolitan centres
COST231 Outdoor to Indoor Model
Valid for when the mobile is inside the building and the BS is outdoors-with line-of-sight from base station to outer wall.
where:
WGe= extra loss in the outer wall at =0 (dB)
Wi = loss in the inner walls (dB)
p = number of inner walls
= loss inwards in the building in dB/m,
used when there are no inner walls
Outer wall We
Inner wall Wi
Typical figures:
We: 4 - 10 dB, concrete with large windows: 7 dB
WGe: about 20 dB
: about 0.6 dB/m
This model has shown good results. However, it is highly dependent on parameter setting.
PS: Metal glazed windows will affect this strongly.
s
Verification of critical and borderline coverage areas
Measurements
Lee criterion
Averaging intervals:
40 outdoor
20 indoor
Gain of antenna: 8.0 dB
__________________________________________
Test Transmitter
42.4 dBm
38.4 dBm
sufficient number of test sites
measurements in all representative environments (clutter types)
measurements which deviate considerably should not be taken into account if reason for deviation is known (e.g. underpass)
database (digitised maps) must represent environment accurately
avoid measurements near measuring equipment sensitivity limit
s
Standard Propagation Model
+ K5log (Heff)log (d) + K6(Hmeff) + KCLUTTER
Task: Set appropriate values for K1, K2, K3, K4, K5, K6, KCLUTTER
Compare predicted values with measurements
Criterion: Minimise
mean error
s
Deinter-
leaver
Inter-
leaver
De-
cryption
Encryption
Block
decoder
Block
encoder
Viterbi-
decoder
Convolution
encoder
Modulator
Radio-
channel
De-
modulator
Traffic
or
control
channel
Transmitter
Receiver
Two cases:
Low traffic areas (e.g. rural): No co-channel interference
Design according to maximum range constraints
RxLev > reference sensitivity level
B: System interference limited
RxLev > level determined by C/I criteria
s
Normal BTS (GSM900 and GSM1800): -104 dBm (minimum requirement)
GSM1800 MS (class 1,2): -100 dBm (most common)
GSM1800 MS (class 3): -102 dBm
GSM900 small MS: -102 dBm (most common)
Other GSM900 MS: -104 dBm
Degradation of sensitivity level in presence of interference
RSL = RSL0 + IDM
s
= -121 dBm + C/N + F
Example I
BTS receiver noise figure (F): 8 dB (from GSM specifications, SBS is better)
Receiver noise bandwidth: B = 200 kHz = 53 dBHz
BTS receiver noise level:
= -174 dBm/Hz + 53 dBHz + 8 dB = -113 dBm
k = Boltzmann’s constant
10log{C/(N+I)} > 9dB (basic system requirement)
Assume C/I is large and C/N = 9 dB
C (BTS) = -113 + 9 = -104 dBm = RSL0
s
C = received carrier power
N = received noise power
I = received interference power
IDM = 0 dB
2. C/I = 12 dB => C/N > 12 dB => C/(N+I) > 9 dB
IDM = 3 dB
state of the art is much better than 8 dB
Diversity included?
Some suppliers state receiver sensitivities including diversity gain (e.g. 4 dB)
C/N and C/I required
9 dB is a conservative figure - includes effect of Raileigh fading
can be reduced significantly if one assumes stationary subscriber located in a “non-faded” location
GPRS / HSCSD: Sacrifice coding security for enhanced capacity
require higher C/N and C/I
PS! When comparing
receiver sensitivity figures
Diversity
Principle: Redundancy by receiving replicas of the same signal which have been affected differently by the propagation medium
Purpose: Combat fading
of total signal energy
significant CIR
efficiency
CIR
Time
Antenna Space Diversity
Nearly uncorrelated fading
provided spacing between antennas is sufficient, signals received at the two branches will experience nearly uncorrelated fading
the chances of both signals being faded simultaneously are small
Diversity gain
Diversity
Combiner
The one with highest signal to noise ratio (SNR) preferred
Branch 1
Branch 2
Signals are simply added
If one branch has very poor SNR this can degrade performance compared with best input
Branch 1
Branch 2
Best performance with uncorrelated noise
s
Definition:
Maximum allowed attenuation between transmitter (Tx) and receiver (Rx) to obtain the specified grade of quality
Calculation
P[dBm] = 10*log(P[mW])
s
- TX_Antenna_Cable_Loss + TX_Antenna_Gain
TRX
MS
Cable
RX-Antenna
Interferer
Carrier
s
EiRP = MS_Power_Output - TX_Antenna_Cable_Loss + TX_Antenna_Gain
+ Interference_degradation_margin + Body_Loss
Example: Min_RX_Level_median = -109dBm - 0dB + 3dB - 0dB - 15dBi - 4dB + 3dB + 3dB = -119dBm
BTS
Cable
RX1-Antenna
Interferer
Carrier
Cable
RX2-Antenna
TMPA
TMPA
s
Uplink / downlink
Unbalanced System
Lmax = EiRP - Min_RX_Level_median
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Data Applications (HSCSD / GPRS)
Data applications in general require better received signal levels than voice applications
higher requirements for BER / FER
better C/N and C/I needed to satisfy BER / FER requirements
receiver sensitivity stated by supplier is sufficient to achieve requirements
For HSCSD / GPRS less efficient channel coding schemes are used in order to enhance bit rates
better signal to S/N and S/I needed for a given BER / FER
the system will have worse receiver sensitivity
HSCSD / GPRS: Need correction factors for link budget!
s
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Link Budget for GPRS
Same link budget as for other applications may be used, except
correction factors as shown below
body loss (typically 3 dB) may be omitted
Note! Link budget in some cases better for GPRS than for voice
Only gradual degradation of performance as received signal goes below minimum requirement. Therefore communication may still be possible at “voice cell border”
GSM 900
Coding Scheme
Channel model
This table is based on GSM05.05 ver. 7.0.0, table 1a
s
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Link Budget for HSCSD
Same link budget as for other applications may be used, except
correction factors as shown below
again body loss may be omitted
More rapid degradation of performance as received signal goes below minimum requirement than for GPRS. At “voice cell border” TCH/F14.4 throughput will be less than for TCH/F9.6
GSM 900 and GSM 1800
Bearer mode
Channel model
0 dB
0 dB
2 dB
2 dB
0 dB
0 dB
5 dB
5 dB
3 dB
3 dB
0 dB
0 dB
3 dB
3 dB
1 dB
1 dB
< 0 dB
< 0 dB
Note:
This table is based on information contained in Tdoc SMG2 176/97
Note 1:
Note 2:
Note 3:
Note 4:
Certain real time applications operated on a transparent HSCSD bearer may require such BER values, e.g. video
s
Add fade margin to increase confidence level
Propagation index = 3.5
Calculate composite standard deviation
Calculate composite fading margin
Add median penetration loss
indoor = 7 dB
outdoor = 6 dB
then
Note:
indoor penetration loss
valid for GSM900
Feeder Type
Feeder Losses
Calculation Example
3,85 dB is very high high. Reduce by changing feeder to 1 1/4"
Source: Erring
2 connectors jumper antenna-feeder
2 connectors feeder
Total 6 connectors
= 0,60 dB
0,18 dB x 2,5m
= 2,80 dB
= 3,85 dB
35.0
50.0
2.0
W
-100.0
-102.0
-127.1
dBm
Miscellaneous
In-car penetration loss
Max path loss (50%)
Max path loss (50%)
Max path loss (50%)
Link Budget
35.0
50.0
2.0
W
-100.0
-102.0
-127.1
dBm
Downlink
Downlink
Uplink
Unit
Miscellaneous
In-car penetration loss
Max path loss (50%)
Max path loss (50%)
s
improve indoor coverage
pedestrians / slow moving
Combined indoor / outdoor site
Pico BTS
Leaky cable
BTS
Difficult to cover top floors in urban areas
s
Low cost
Long feeders possible
applications (e.g.elevator shafts)
Normally too expensive
Hata Model in Tornado/Planet Format
Converting Hata’s formula, the following constants are derived (one piece model)
K1 = -12.8
K2 = -44.9
K3 = -5.8
K5 = 6.55
K6 = 0 (not used)
Eff. Antenna height(HBS-eff)
normally “base height”(slope height only in special cases, when BTS is on mountain or in a valley)
Some typical clutter correction factors
dense urban(metropolitan,10 floors,narrow roads) 0 dB
normal urban 3 dB
suburban (4-5 floors, medium to wide roads) 8 - 11 dB
village 14 - 17 dB
quasi open (bushes, single small houses) 18 - 22 dB
open 25 dB
Converting the Cost-231-Hata formula, the following constants are derived (one piece model):
K1 = -25
K2 = -44.9
K3 = -5.8
K5 = 6.55
K4 = Multiplying factor for diffraction loss prediction (typically 0.5 - 0.7 depending on terrain undulations)
K6 = 0 (not used)
Eff. Antenna height (HBS-eff)
normally “base height”(slope height only in special cases, when BTS is on mountain or in a valley)
Some typical clutter correction factors
dense urban (metropolitan,10 floors,narrow roads) 0 dB
normal urban 3 dB
suburban (4-5 floors, medium to wide roads) 11 - 15 dB
village (open type 16 - 20 dB
forest (tropical) 5 - 10 dB
quasi open (bushes, single small houses) 20 - 27 dB
open (flat) 25 - 30 dB
s
Outdoors-no line-of-sight
Simple recursive model valid in city streets where houses are much higher than the antennas.See figure below.Nodes(j=0,j=1 etc.) are at TX and RX as well as break points caused by street corners.
Sn=physical distance between node points
an=angle between streets
where dn = “imaginary” distance between Rx and Tx given by
The initial values are k1=1 and d0=0
q is a parameter which depends on a. For a = 90, q = 0.5.
The model may be adapted to special situations and expanded.
s
Can be used both for detecting and correcting bit errors
The ability to detect errors is greater than the ability to correct them
The 50 most important bits in each speech block are block-encoded
(53,50) block code - only used for error detection
can detect at least one bit error (in most cases also two)
FACCH, SACCH, BCCH, PCH, AGCH, SDCCH use Fire code
special shortened (224, 184) cyclic block code
can correct bit error bursts of up to 12 bits
can detect all error patterns which are not code words
s
d3 d2 d1 d0 p2 p1 p0
dn = databits (the actual information is contained in 4 databits)
pn = parity bits, e.g.
p0 = d0 d2 d3, p1 = d0 d1 d2, p2 = d1 d2 d3
one code word consists of 7 coded bits
only some code word combinations are allowed
error correction capability t < (dmin-1)/2 (in this case 1)
dmin = the minimum distance of the code (in this case 3)
s
The coder has a memory of previous databits (shift registers)
Different convolutional coders used for different channels
Example of a simple convolutional encoder
Bit sequence in
Coded sequence out
Decode sequences of bits, not individual bits
Compare the received sequence with allowed sequences
Choose the allowed sequence which looks most like the received sequence => the sequence with minimum distance from received seq.
Illustration: Calculate the shortest route: London - Vienna
10
9
8
8
10
13
7
8
London
Amsterdam
Munich
Vienna
Paris
Basel
s
Error correction cannot cope
put them back in order in the receiver
bursts of errors will be spread out in time
error correction coder may cope (especially if channel changes fast)
works better if user moves fast (channel changes fast) than if he moves slowly (channel nearly stationary)
disadvantage: Interleaver causes time delay
b8
b7
b6
b5
b4
b3
b2
b1
b16
b15
b14
b13
b12
b11
b10
b9
b24
b23
b22
b21
b20
b19
b18
b17
b32
b31
b30
b29
b28
b27
b26
b25
b40
b39
b38
b37
b36
b35
b34
b33
b48
b47
b46
b45
b44
b43
b42
b41
b56
b55
b54
b53
b52
b51
b50
b49
b64
b63
b62
b61
b60
b59
b58
b57
constant amplitude => can use class C amplifier
Gaussian frequency and impulse response filter
good compromise between bandwidth and pulse duration in time
BT = 0.3
s
Noise Figure Reduction
Consider amplifiers in cascade with gain Ki and noise figure Fi
Overall noise figure of system:
Ftot = F1 + (F2-1)/K1 + (F3-1)/(K1K2) …
Conclusion:
By using low noise pre-amplifier (LNA) with small F1 and large K1 the overall noise figure of the system is reduced (dominated by F1)
K1, F1
From antenna
K2, F2
K3, F3
" 47.033.0dBm
2
2
i
1
S
D
In-car penetration loss7.07.0dB
Link budget (in-car coverage)
2
2
This table is based on GSM05.05 ver. 7.0.0, table 1a
GSM 900 and GSM 1800
Bearer mode
Channel model
3 dB
3 dB
1 dB
1 dB
< 0 dB
< 0 dB
Tdoc SMG2 176/97
Note 2:
Note 3:
Note 4:
bearer may require such BER values, e.g. video
Feeder Type
2 connector
2 connector
=
0,18 dB x 2,5m
=