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1
Introduction to WCDMA and
WCDMA Dimensioning for UMTS
2
Third generation services2M
384K
64K
32K
16K
9.6K
2.4K
1.2K
point to point multipoint
bidirectional unidirectional multicast
video
conference
video
conference
remote
medical
service video
catalogue
shopping
video
on
demand
mobile
TV
inte
rn
et
telephone
conference
telephone
voice
electronic
newspaper ISDN
electronic
publishing
FAX
distribution
services
(data)
mobile
radio
distribution
services (voice)
pager
4
UTRAN (UMTS Terrestrial Radio Access
Net) Architecture
Core Network
RNC RNC
Site Contr
BTS BTS BTS
Site Contr
BTS BTS BTS
Site Contr
BTS BTS BTS
Site Contr
BTS BTS BTS
RNS
UTRAN
RNS
Iub IubIub Iub
Iur
IuIu
B-node B-node B-node B-node
5
Access techniques for mobilecommunications
P - Power
T - Time
F - Frequency
P
T
P
T
F
P
T
F
FDMA (TACS)
TDMA,FDMA (GSM)
CDMA (UMTS)
F
6
W-CDMA (Wide Band CDMA)
Key features
• Improved capacity and coverage (over second generation); thus, backward compatible
• High degree of service flexibility: multiple, parallel services per connection; efficient pkt access
7
Basics of Spread Spectrum
and CDMA
8
Overview
• Why consider Spread Spectrum ?
• What is Spread Spectrum & CDMA ?
• Frequency Hopping Spread Spectrum
– Impact of channel
– Current systems
• Direct Sequence Spread Spectrum
– Spreading Codes
– Analytical Performance Model
– Rake Processing
– Near Far Effect (Power Control)
– Handover
9
Why Consider Spread Spectrum ?
• Spread Spectrum has been adopted as the air
interface standard for 3rd Generation Mobile
Systems (IMT2000):
– Europe (ETSI): UMTS (W- CDMA )
– Japan (ARIB): Wideband CDMA
– USA (TIA TR45. 5) CDMA 2000
• 2nd Generation standard deployed in US and Korea
– IS95 (Qualcomm CDMA)
10
What is spread spectrum?
Narrow Band
Message
Narrow Band
Message
Wideband
Message
11
Frequency Hopping Spread
Spectrum
12
• Classification of Spread Spectrum
Systems
• Frequency Hopping (FH)
• Narrow band message signal is
modulated with a carrier frequency which
is rapidly shifted . The hop frequency is
indicated by a spreading function.
• This spreading function is also available
at the receiver and enables it to retune to
the correct channel for each ‘hop’.
13
Hop rates in an FH system
• Fast frequency hopping
• – Data symbol spread over several hop frequencies
• –Symbol diversity
• – Very resistant to jamming and interference, often used in military systems
• Slow frequency hopping
• – Several data symbols on each hop frequency
• –Codeword diversity with interleaving
– Less complex
14
Direct Sequence Spread
Spectrum
15
Classification of Spread Spectrum
Systems
• Direct Sequence (DS)
– Secondary modulation in the form of pseudo-
noise is applied to an already modulated
narrowband message, thereby spreading the
spectrum.
– At the receiver, the incoming waveform is
multiplied by an identical synchronized
spreading waveform in order to recover the
message.
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Direct sequence spread spectrum
D(t)
C(t)fc fc C(t)
S(t)
Narrow Band
Message Narrow Band
Message
Wide Band
Pseudo Random
Noise
Up conversion
To fixed carrier
frequency
Down
conversionWide Band
Pseudo Random
Noise
17
Data
Signal
Code
Signal
Multiplication
18
Spreading codes
• Maximal length sequences
– good auto- and cross- correlation
Gold codes and Kasami sequences are
derived from M- sequences with similar
• correlation properties, and a larger code
set.
19
Orthogonal spreading Codes
• Walsh and Hadamard sequences
– zero correlation between codes when aligned
– cross- correlation non- zero when time shifted
– fixed spreading factor (codes of different length are not orthogonal)
• Orthogonal Variable Spreading Factor (OVSF) codes
– permit orthogonal codes for different rate services
• Both types of code lose orthogonality when shifted due to channel dispersion
– e. g. 40% loss of orthogonality in a large macrocell
Orthogonal Variable Spreading Factor
c4,1
= (1,1,1,1)
c2,1 = (1,1)
c4,2 = (1,1,-1,-1)
c4,3 = (1,-1,1,-1)c2,2 = (1,-1)
c4,4 = (1,-1,-1,1)
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22
23
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DS-SS Application for CDMA
Mod.
g1(t)
S1(t)
Coswt
S1(t)g1(t)
S2(t)g2(t)
g1(t)
SN(t)gN(t)
X1(t)
25
Theoretical CDMA capacity
• DS- CDMA capacity is inversely proportional to the energy per bit per noise power density which is tolerated
• A standard DS- CDMA system is interference limited by
- intra- cell interference
- Therefore increase capacity by:
- voice activity detection
- antenna sectorisation
- adaptive antennas
- interference cancellation
26
The Multipath Environment
• The received signal
is made up of a sum
of attenuated, phase-
shifted and time
delayed versions of
the transmitted signal.
• Propagation modes
include diffraction,
transmission and
reflection.
27
Path diversity in the multipath Path
diversity
• Path diversity can be exploited by
separating out the multipath components,
co- phasing and summing them.
• Number of paths resolved (Lm) depends
on the total multipath delay (Tm) and the
chip period (Tc) Lm< Tm/Tc +1
28
RAKE Receiver
• One method of realising path diversity is with a RAKE and a bank of correlators
tc tc tc
Int. Int Int
Diversity Combiner
Out
Put
C(t) C(t-tc) C(t-LTc)
29
Diversity and diversity combinig
• Diversity: providing multiple versions of the transmitted signal. Commonly:
– multiple antennas
– multiple paths
• Diversity combining
–selection: best branch is chosen
–equal gain: equal combining: all branch summed
–maximal ratio: branches summed and weighted
depending on their quality
30
The near-far effect in CDMA
• Everyone on same
• frequency at the same
• time.
• A MS close to the BS will “drown out” other MSs unless it reduces it’s power.
• Power control is required.
31
CDMA Power Control
• Power control required on uplink, desired on
• downlink.
• Open loop control can be used to remove shadowing (as the channel is reciprocal).
• Closed loop control is required to remove the
• fast fading
– BS receives MS signal and calculates the SIR
– BS sends MS a transmit power control (TPC)
• signal to increase or decrease its power
• TPC issues include rate and step size
32
Uplink closed loop power
control algorithms
• Sigma- delta scheme used
• Command rate must be sufficient to track
channel changes
• Trade- off in step size between tracking
and accuracy
33
Handover and Mobility
BS1 BS2
34
W-CDMA in UMTS
• W- CDMA is used in FDD mode in UMTS
• On the downlink it is possible to use orthogonal
reading codes to reduce interference. A
scrambling code is used to separate the cells
• On the uplink, low cross correlation codes are
used to separate the mobiles. A single mobile
can use multi-code transmission: each service is
mapped onto several bearers, each of which is
spread by an orthogonal code.
35
WCDMA Air Interface
36
RLCRLC
LACLAC
Radio Interface - protocol
architecture
RLC
RRC
LAC
MAC
Physical Layer
L3
L2/LAC
L2/MAC
L1
C-plane U-plane
Logicalchannels
Transportchannels
RLC
37
Layer 1 - up link physical
channels
(W-CDMA example)Data
Pilot
Dedicated PhysicalData Channel
Dedicated PhysicalControl Channel
Transmitpower control
Transportformat ind.
Slot#1Slot#2 Slot#i Slot#15
Frame#1Frame#2 Frame#i Frame#72
0.667 ms
10 ms
Feedbackindicator
38
Layer 1 - down link physical
channels
(W-CDMA example)
Data
Slot#1Slot#2 Slot#i Slot#15
Frame#1Frame#2 Frame#i Frame#72
Pilot TPC TFI
DPCCH DPDCH
frame
superframe
0.667 ms
10 ms
39
Transport channels (example)
• Dedicated Channel (DCH): fast change of bit rate (10ms)fast power controlinherent MS addressing
• Random Access Channel (RACH) - up link: collisionopen loop power controlexplicit MS addressing
• Broadcast Control Channel (BCH) - down link
• Forward Access Channel (FACH) - down link: slow power controlexplicit MS addressing
• Paging Channel (PCH) - down link: use of sleep modes
40
Multiplexing transport channels onto
physical channels
DCH
DCH
DCH
DCH
cod
ing
inte
rle
avin
g
cod
ing
inte
rle
av
ing
rate
m
atc
hin
gra
te
matc
hin
g
inte
rle
avin
gin
terle
av
ing
ra
te
ma
tch
ing
inte
rle
av
ing
mu
ltip
lexin
g
inter frameinterleaving
intra frameinterleaving
static
dynamic(up link)
trasport channelsmultiplexing
41
MAC Services and Functions
mapping
phy ch phy ch
DCHDCHDCH
Coding and
multiplexing
mapping
phy ch
DCH DCH
Coding and
multiplexing
• set-up, release of logical channels• data transfer service on logical channels• allocation/re-allocation of radio resources• measurement report
• Selection of the transport format
• Handling of priority within one user/between users
• Scheduling of control messages (broadcast, paging,
notification)
• Multiplexing/de-multiplexing of higher layers PDUs
on/from common or dedicated transport channels
• Contention control on the random access channel
Functions
42
Radio Network planning And
Dimensioning Procedures
• Preparation
• Estimation No. of Cells
• Detailed Planning
43
Preparation
• 1-Targets of Capacity and Coverage
• 2-Strategy of Network Planning
44
Estimation No. of Cells
Population of Region
Influence
percentage
No of UsersTraffic/User
Offered Traffic Capacity/Cell Cell Rangr
No of Cells
45
Estimation Capacity of Cell
• Principle Factors :
1. Data Rate
2. Traffic characteristics (variation Rates,..)
3. Requirements (delays, BER)
4. Disconnect Probability
5. Sectorized Effect
6. Load Effect
46
Cell RangeLink Budget
A Chip Rate 3.84 Mchip/s
B Information Rate 12.2 Kbit/s
C Processing Gain
(10log(A/B))
24.98 dB
47
D Mobile transmit power 21.0 dBm
E Mobile antenna gain 2.0 dBi
F Body Loss 3.0 dB
G Mobile EIRP (D+E-F) 20.0 dBm
48
H Base Station antenna Gain 14.0 dBi
I Thermal noise density -174.0 dBm/Hz
J Base Station Noise density -108.2 dBm
K Base Station Noise Figure 5.0 dB
L Target Eb/N0 5.5 dB
M Base Station Sensivity -122.68 dBm
49
N Cable Loss 3.0 dB
O Lognormal shadowing margin 9.0 dB
P Noise Rise (intracell) 3.0 dB
Q Noise Rise (intercell) 2.0 dB
R Soft handoff gain 4.0 dB
Maximum path loss=G+H-M-N-O-P-Q+R= 143.68 dB
50
UMTS Dimensioning
Operators required
(QOS,Capacity,
Coverage)
Condition of
Radio
Propagaiton
Estimation The
Number of
users
Available
Techniques
Dimensioning Process
Estimation of required equipments and arrangment of network array
Optimization
51
UMTS RAN Dimensioning Process
Node B Dimensioning
RNC Dimensioning
Interface Dimensioning
Offering prepare topology for RAN
52
• Required Data for each phase of
Network development
1. Radio coverage (regions, subregions,
region classifications)
2. Traffic ( Frequency spectrum, customers
Density in each region, customers
profile)
3. QOS (coverage probability, Blocking
prob. , service level in each region)
53
Node B Dimensioning
• Up Link
1. Considering a radius for cell r1
2. Estimation average traffic inside cell
3. Estimation no. of channels for peak traffic
service
4. Considering a Statistical method for calculating
accumulated noise
54
Up Link
5. Calculating Maximum path loss then cell
range r2
6. Continuing till r1 = r2
7. Cell bar test
55
Down Link
1. Considering a cell range r1
2. From input traffic, estimate average cell traffic
3. Estimation no. of channels for peak traffic service
4. Calculation of One user required power for each service
5. Calculating transmit accumulated power in Node B
56
Down Link
• Calculating Cell range r2
• Continue till r1=r2
57
RNC Dimensioning Process Steps
1. Knowing No. of Node Bs then By Considering
Management Limitations ,Estimate minimum
RNC, RNC1
2. By considering input average traffic and traffic
limitations , Estimate minimum RNC that
needs for traffic handling , RNC2
3. Average traffic for each RNC is known, then
peak traffic for each RNC must be calculated
4. Max(RNC1,RNC2)=No. of RNC
58
RNC Dimensioning Process
Efficient factors for RNC Dimensioning
Process are:
1. Traffic Limitations
2. Management Limitations
3. Communications Limitations
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