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WCDMA Wireless Principle
ZTE University
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Multi-path characteristics of radio channel
n Electromagnetic propagation:--direct radiationreflectiondiffraction and scattering
n Signal attenuation:
l Path loss Loss of electromagnetic waves in large scope
of the spread reflects the trend of the received signal in the
spreading
l Slow fadingLoss because of being blocked by the
building and hill in the propagation path
l Fast fadingElectromagnetic signals rapidly decline in a
few dozens wavelength ranges
n Description of Fast fading distribution
l Rayleigh distributionnon line-of sight(NLOS)transmission
l Rician distributionline-of sight(LOS) transmission
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Multi-Path Effects
receiving signaleceiving signaltimetime
strengthstrength
00
sending signalending signal
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Frequency off-set caused by the movement of mobilethat is Doppler effect
FrequencyFrequencyoffoff--setsetcaused by the movement of mobilecaused by the movement of mobilethat is Doppler effectthat is Doppler effect
Sending signal Accepting signal
InterferenceInterference
0dB
Sending signal
-25dB
Accepting signal
fadingfading
0 +
Sending signal Accepting signal
delaydelay
0 2 3 +
Sending signal Accepting signal
ditheringdithering
Characteristics of Radio Propagation
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Content
The Basic Principles of WirelessCommunication
Radio Propagation Characteristics
Spreading Technology
Channel Coding
Interleave Technology
Modulation
WCDMA Radio mechanism
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SHANON Formula
C = Blog2(1+S/N)C = Blog2(1+S/N)
Spread Spectrum Principles
n Where,
C is capacity of channel, b/s
B is signal bandwidth, Hz
S is average power for signal, W
N is average power for noise, W
n It is the basic principle and theory for spread spectrum
communications.
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Spread Spectrum Principles
1.25 MHz
30 KHz
Power is Spread Over a Larger Bandwidth
MATHHAMMER
MATHHAMMER
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radio channel
ReceiverTransmitter
Spreading
Despreading
Noise
Spread Spectrum Principles
n User information bits are spread over a widebandwidth by multiplying high speed spreadcode(chip)
n Spread signal bandwidth W wider than originalsignal bandwidth Rb
n For WCDMA, W=3.84Mchip/s Rb(voice)=12kbit/s
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f
Sf
f0
Before spreading
signal
Sf
ff0
After spreading
signal
Sf
ff0
After despreading
signal
White noise
f
Sf
f0
Before despreading
signal
White noise
signal interference White noise
Spread Spectrum Principles
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Spreading Mode
n
Direct sequence spread spectrum
DS-SS
l Base band data is spread by multiplication of pseudo-noisesequence and base-band pulse, the pseudo-noisesequence generated by the pseudo-noise generator
l BER subject to Multiple Access Interference and near-fareffect
l Power control can overcome the near-far effect, but it islimited by power detection accuracy
l WCDMA uses DS-SS
n Frequency hopping spread spectrumFH-SS
l Data is transmitted in the random channel by the carrierfrequency hopping
l Before FH again, data is transmitted using traditionalnarrowband modulation
l No near-far effect
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DS-SS communication system
n A technology of transmission after spreading signalspectrum.
FastSpreadingSequence
Slow
InformationSent
TX
Slow
InformationRecovered
RX
FastSpreadingSequence
WidebandSignal
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Spread Spectrum Principles
Many code channels are individuallyspread and then added together to
create a composite signal
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Unwanted Power fromOther Resoures
Spread Spectrum Principles
n Any Code Channel can be extracted from thereceived composite signal by using the rightorthogonal code
n Energy for transmitting signal can be lower than
interference and noise
Processing Gain
BroadbandInterference
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Concept of orthogonal code
n Orthogonal
the result of multiplying
and sum is 0
-1 -1 +1 -1 +1 +1 -1 +1Mul
0Sum
Orthogonal
-1 +1 +1 -1 -1 +1 +1 -1Code2
+1 -1 +1 +1 -1 +1 -1 -1Code1
+1 -1 -1 -1 +1 -1 -1 +1Mul
-2Sum
Non-orthogonal
+1 +1 -1 +1 -1 -1 +1 -1Code2
+1 -1 +1 -1 -1 +1 -1 -1Code1
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-1 1 -11-1 -11 1 -1 -1 11-1 1-1 1MUL
-1 1 -11-1 -11 1
1 -1 1 -1
-4 4
0 0J u d g e
-1 1
1 -1 1 -1
-1 1MUL
Integral
1 1 1 1-1 -1 -1 -1
Example of orthogonal code
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S1S1
S2S2
S1xC1S1xC1
S2XC2S2XC2
WWSpreading
Despreading
(S1xC1)+(S2xC2)(S1xC1)+(S2xC2)
Air InterfaceAir Interface
[S1xC1+S2xC2]xC2[S1xC1+S2xC2]xC2
==S2S2
[S1xC1+S2xC2]xC1[S1xC1+S2xC2]xC1
==S1S1NN
SS
C1xC2=0,C1,C2,orthogonal
Direct spread technique
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Spreading code =
1 -1 -1 1 -1 1 1 -1
( SF = 8 )
Symbol
Spreading
Despreading
1-1
1-1
1
-1
1-1
1-1
Data=010010
Spreading code
Spread signal= Data code
Data =Spread signalSpreading code
Chip
Sketch map of Spreading and Despreading
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Characteristics of Spreading Communication
n
High anti-multi-path- interference capabilityn Anti-sudden-pulse
n High security
n Lower transmitting power
n Easy to implement large-capacity Multiple Access
Communication
n Occupy band wide
n Complex realization
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Content
The Basic Principles of WirelessCommunication
Radio Propagation Characteristics
Spreading Technology
Channel Coding
Interleave Technology
Modulation
WCDMA Radio mechanism
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Purpose of Channel Coding
n
By adding redundant information in the original datastream, receivers can detect and correct the errorsignal, and improve data transmission rates.
No correct coding: BER
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Principle of Channel Coding
n Channel coding
l Error-correcting ability obtains by adding redundancy in the
original data
l Convolutional coding and Turbo coding1/21/3 arewidely applied.
l Increase noneffective load and transmission time
l Suitable to correct few non-continuous errors
W C D M A
T U R B O
S P E A K
W W C C D D M M A A
T T U U R R B B O O
S S P P E E A A K K
W ? C C D D M M A A
T T ? U R R B B O O
S S P P E E A ? K K
Decoding
Encoding
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Content
The Basic Principles of WirelessCommunication
Radio Propagation Characteristics
Spreading Technology
Channel Coding
Interleave Technology
Modulation
WCDMA Radio mechanism
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Principle of Interleave Technology
n advantage
l Interleave is to change the sequence of data to random the
unexpected errors
l Advance the correcting validity
n disadvantage
l Increase the processing delay
l Especially, Several independent random errors mayintertwined for the unexpected error .
x1 x6 x11 x16 x21x2 x7 x22x3 x8 x23x4 x9 x24x5 x10 x25
Data inputA = (x1 x2 x3 x4 x5 x25)
Data outputA= (x1 x6 x11 x16 x25)
e.g.
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Encoding and Interleaving
W C D M A
T U R B O
S P E A K
W W C C D D M M A A
T T U U R R B B O O
S S P P E E A A K K
W T S W T S
C U P C U P
D R E D R E
M B A M B A
A O K A O K
W ? ? C D D M M A ?
T ? ? U R ? ? B O O
S ? ? P ? E A A K K
Encoding Interleaving
W T S ? ? ?
? ? ? C U P
D R ? D ? EM ? A M B A
A O K ? O K
DeinterleavingDecoding
Encoding+ Interleaving can correct both
continuous and non-continuous errors
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Content
The Basic Principles of WirelessCommunication
Radio Propagation Characteristics
Spreading Technology
Channel Coding
Interleave Technology
Modulation
WCDMA Radio mechanism
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Principle of Modulation
n
Definitionl Modulation is the process where the amplitude,
frequency, or phase of an electronic or optical signalcarrier is changed in order to transmit information.
l Using symbol stand for one or more bits to improvecommunication effectiveness
n Classification
l Analog Modulation
l Digital Modulation
SymbolbitModulation
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Analog Modulation
n The purpose of analog modulation is to impressan information-bearing analog waveform onto a
carrier for transmission.
l Common analog modulation methods include:
n Amplitude modulation (AM)
n Frequency modulation (FM)
n Phase modulation (PM)
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Digital Modulation
n
The purpose of digital modulation is to convert aninformation-bearing discrete-time symbol sequenceinto a continuous-time waveform (perhapsimpressed on a carrier).
l Basic analog modulation methods include
n
Amplitude shift Keying (ASK)n Frequency shift Keying (FSK)
n Phase shift Keying (PSK)
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Content
The Basic Principles of WirelessCommunication
WCDMA Radio mechanism
WCDMA Data transmission Procedure
Channel Coding of WCDMA
Spreading Technology of WCDMA
Modulation of WCDMA
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WCDMA Data transmission Procedure
RF ReceivingDemodulationDespreading
Decoding &De-inteleaving
UE Data
UE Data Spreading
RF Transmitting
Modulation
Basebanddemodulation
Baseband
modulation
Encoding &
Interleaving
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Content
The Basic Principles of WirelessCommunication
WCDMA Radio mechanism
WCDMA Data transmission Procedure
Channel Coding of WCDMA
Spreading Technology of WCDMA
Modulation of WCDMA
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Convolutional Code
n Characteristics
l Mainly used in the voice channel and control signalchannel
l Coding rate : 1/2 & 1/3
l Channel bit error rate is 10-3 magnitude
l
Easy decodingl Short delay
l Suitable for realtime service
n e.g. speech and video service.
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Turbo Code
n Characteristicsl Used in Data service channel
l Code Rate is 1/3
l Channel bit error rate is 10-6 magnitude
l Can be implemented in the transmission for large block and
long delay servicesl Complex decoding, needs cycle iterative calculation
l Very suitable for non-realtime package service which is
BER sensitive & delay insensitive
n e.g. WWW, FTP, E-mail , multimedia transmission .
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Content
The Basic Principles of WirelessCommunication
WCDMA Radio mechanism
WCDMA Data transmission Procedure
Channel Coding of WCDMA
Spreading Technology of WCDMA
Modulation of WCDMA
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Symbol rate SF = Chip rate=3.84McpsFor WCDMASF of uplink channelization code4~256
SF of downlink channelization code: 4~512
OVSF: Orthogonal Variable Spreading Factor
OVSF Code Scrambling Code
Data Spread Data
Spreading Process of WCDMA
Symbol Chip
3.84Mcps
3.84Mcps
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Channelization Code
n Adopt OVSF code
l Definition: Cch,SF,k, describe channelization code,where
SF : spread factor k : code number, 0 < k
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Scrambling Code
n WCDMA Scrambling code is pseudo random binary
sequence (PN code)
l It has similar noise array character, seeminglyrandom but with regularity.
l Can make the user data further random ,strengthened by scrambling a code to keep secret theuser data, at the same time easy to carry out multipleaccess communication.
n WCDMA scrambling code is generated from Goldsequence
l Gold sequence has excellent self-correlation.
l Cross-correlation is very week between two codes.
l It is used to identify cell and user for multiple access.
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Characteristic of Scrambling code
n There are 224 Uplink Scrambling Codes, they are
used to distinguish different users in one cell.
n There are 218-1 Downlink Scrambling Codes, usedto distinguish different cells
l Scrambling codes usually used are the first 8192
codes, which are code 0
1
8191. They aredivided into 512 aggregationseach aggregation has1 primary scrambling code (PSC) and 15 secondaryscrambling codes (SSC).
l The 512 primary scrambling codes are divided furtherinto 64 primary scrambling code groups , with 8
primary scrambling codes in each group.
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N mbering r le for Do nlink Scrambling
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Numbering rule for Downlink ScramblingCodes
21 8
- 1 Do wn l i n k Sc r a mb l i n g Co d e s i n a l l( 0 . . 2 6 2 1 4 2 )
8176PSC
8177SSC
8191SSC
8176
8177
8191
No. 511 Scrambling CodeGroup
8160
8161
8175
8160
8161
8175
No. 510 Scrambling CodeGroup
8064
8065
8079
8064
8065
8079
No. 504 Scrambling CodeGroup
8176PSC
8177
8191
112
113
127
No. 7 Scrambling CodeGroup
16PSC
17SSC
31SSC
16
17
31
No. 1 Scrambling CodeGroup
0PSC
1SSC
15SSC
0
1
15
No. 0 Scrambling CodeGroup
No . 6 3 P r i ma r y S c r a mb l i n g Co d e Gr o u p
No . 0 P r i ma r y S c r a mb l i n g Co d e Gr o u p
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Code Functions
n Channelization code ---- for separation of physical
channels in the uplink and separation of users in thedownlink
n Scrambling code ---- for separation of
users/terminals in the uplink and cells/sectors in thedownlink.
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Air Interface
2chc
3chc
1chc
scramblingc
Modulation
Spreading code & scrambling code
l Cchspread code
n Relative to service rateextended to 3.84Mchips/sn A kind of orthogonal code
l Cscramblingscrambling code
n Have no effect on signal bandwidth
n downlink for identifier celluplink identifier terminaln A pseudo-random sequence
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f
P
W
ProcessingGain
Rb
Despreading
Processing Gain
n PG=Wc/Rb (Wc : Chip rate , Rb : Service bit rate)
l Transmitter/receiver can obtain gain afterspread/despread
l The narrower original signal bandwidth, the larger Pg ,the better
The higher PG, the more anti-interference capability system has.
b
c
R
WGainProcessing =
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Question
n Whats the Processing Gain for voice service in
WCDMA system?
n Given: Voice data rate = 12.2kbps
n PG=10lg(Wc/ Rb) , dB units
l Wc: 3.84Mchip/s
l Rb: 12.2kbpsn So for voice service,
l PG=10lg(3.84* 106 /12.2* 103)= 25 dB
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Despreading procedure
n Method of despreading
Input signal
Local PN code
When T=Ts, judge
Output after despreading
integral
0
Ts
(*)dt
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Content
The Basic Principles of WirelessCommunication
WCDMA Radio mechanism
WCDMA Data transmission Procedure
Channel Coding of WCDMA
Spreading Technology of WCDMA
Modulation of WCDMA
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Modulation Methods in WCDMA
n BPSK (Binary Phase Shift Keying) in Uplink channles
n QPSK (Quadrature Phase Shift Keying) in Downlink channels
n 16QAM (16-state Quadrature Amplitude Modulation) in HSDPA
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summary
n Principle of WCDMA
l All users are simultaneously transmitted in the samefrequency band
l Users interfere with each other
l Adjacent cells use the same frequency
l Cells, users (terminals), and physical channels areseparated by codes
n Channel coding
l Convolutional code
l Turbo coden Codes
l Channelization code
l Scrambling coden Modulation
l BPSKl QPSK
l 16QAM
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