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WR_BT02_E1_1WCDMA Wireless Principle
ZTE University
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Content
The Basic Principles of Wireless Communication
» Radio Propagation Characteristics
» Spreading Technology
» Channel Coding
» Interleave Technology
» Modulation
WCDMA Radio Mechanism
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Multi-path characteristics of radio channel
n Electromagnetic propagation:
--direct radiation, reflection, diffraction and scattering
n Signal attenuation:
„ Path loss: Loss of electromagnetic waves in large scope of the spread
reflects the trend of the received signal in the spreading
„ Slow fading: Loss because of being blocked by the building and hill in the
propagation path
„ Fast fading: Electromagnetic signals rapidly decline in a few dozens
wavelength ranges
n Description of Fast fading distribution
„ Rayleigh distribution: non line-of –sight(NLOS) transmission
„ Rician distribution: line-of –sight(LOS) transmission
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Multi-Path Effects
receiving signaleceiving signal
timetime
strengthstrength
00
sending signalending signal
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Frequency off-set caused by the movement of mobile ,
that is Doppler effect
Frequency Frequency off off - - set set caused by the movement of mobile caused by the movement of mobile ,
that is Doppler effect that is Doppler effect
Sending signal Accepting signal
InterferenceInterference
0dB
Sending signal
-25dB
Accepting signal
fadingfading
0 τ σ σ+ τ
Sending signal Accepting signal
delaydelay
0 τ 2τ 3τ σ σ+ τ
Sending signal Accepting signal
ditheringdithering
Characteristics of Radio Propagation
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Contents
The Basic Principles of Wireless Communication
» Radio Propagation Characteristics
» Spreading Technology
» Channel Coding
» Interleave Technology
» Modulation
WCDMA Radio mechanism
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SHANON Formula
C = B*log2(1+S/N)C = B*log2(1+S/N)
Where,
C is capacity of channel, b/sB is signal bandwidth, HzS is average power for signal, WN is average power for noise, W
It is the basic principle and theory for spread spectrum
communications.
Spread Spectrum Principles
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Spread Spectrum Principles
1.25 MHz30 KHz
Power is “Spread” Over a Larger Bandwidth
M AT H H AM M E R
MATHHAMMER
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radio channel
ReceiverTransmitter
Spreading
Despreading
Noise
„ User information bits are spread over a wide bandwidth by
multiplying high speed spread code(chip)
„ Spread signal bandwidth W wider than original signal
bandwidth Rb
„ For WCDMA, W=3.84Mchip/s, Rb(voice)=12kbit/s
Spread Spectrum Principles
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f
S(f)
f0
Before spreading
signal
S(f)
ff0
After spreading
signal
S(f)
ff0
After despreading
signal
White noise
f
S(f)
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)„ Base band data is spread by multiplication of pseudo-noise (PN)
sequence and base-band pulse, the pseudo-noise sequence
generated by the pseudo-noise generator
„ BER subject to Multiple Access Interference and near-far effect
„ Power control can overcome the near-far effect, but it is limited by
power detection accuracy
„ WCDMA uses DS-SS
n Frequency hopping spread spectrum(FH-SS)
„ Data is transmitted in the random channel by the carrier frequency
hopping
„ Before FH again, data is transmitted using traditional narrowband
modulation
„ No near-far effect
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DS-SS communication system
n A technology of transmission after spreading signal
spectrum.
Fast Spreading Sequence
Slow
Information Sent
TX
Slow
Information Recovered
RX
Fast Spreading Sequence
WidebandSignal
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Spread Spectrum Principles
Many code channels are individually“ spread ” and then added together to
create a “composite signal”
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Unwanted Power fromOther Resources
Spread Spectrum Principles
Processing Gain
BroadbandInterference
„ Any Code Channel can be extracted from the received composite
signal by using the “ right ” orthogonal code
„ Energy for transmitting signal can be lower than interference and
noise
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Eb =Signal Power
Bit Rate=
S
R
E / t
B / t= N0 =
Noise Power
Bandwidth=
N
W
Eb
N0
=
S
R
N
W
=S
RX
W
N=
S
NX
W
R
Signal to Noise
Processing Gain
The relation between Eb/N0 and PG
扩频通信原理
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f
P
W
ProcessingGain
Rb
Despreading
n PG=Wc /Rb (Wc : Chip rate , Rb : Service bit rate)
„ Transmitter/receiver can obtain gain after spread/despread
„ The narrower original signal bandwidth, the larger PG, the better
Processing Gain
The higher PG, the more anti-interference capability system has.
b
c
R
WGainProcessing =
WCDMA Radio mechanism
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Question
n PG=10lg(Wc/Rb) , dB units
„ Wc: 3.84Mchip/s
„ Rb: 12.2kbps
n So for voice service,
„ PG=10lg(3.84*106 /12.2*103)= 25 dB
What’s the Processing Gain for voice service in WCDMA
system?
Given: Voice data rate = 12.2kbps
WCDMA Radio mechanism
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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 -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
Example of orthogonal code
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1 1 1 1
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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 signal×Spreading code
Chip
Sketch map of Spreading and Despreading
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Characteristics of Spreading Communication
n High anti-multi-path interference capability
n 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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Contents
The Basic Principles of Wireless Communication
» 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 data stream,receivers can detect and correct the error signal, and
improve data transmission rates.
No correct coding: BER<10-1 ~ 10-2 Can not satisfythe communication
Convolutional coding:BER<10-3Can satisfy the
speech communication
Turbo coding: BER<10-6
Can satisfy the
data communication
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C
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Principle of Channel Coding
n Channel coding
„ Error-correcting ability obtains by adding redundancy in the original data
„ Convolutional coding and Turbo coding(1/2,1/3) are widely applied.
„ Increase noneffective load and transmission time
„ 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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Contents
The Basic Principles of Wireless Communication
» Radio Propagation Characteristics
» Spreading Technology
» Channel Coding
» Interleave Technology
» Modulation
WCDMA Radio mechanism
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Th B i P i i l f Wi l C i ti
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Principle of Interleave Technology
n advantage
„ Interleave is to change the sequence of data to random the unexpected
errors
„ Advance the correcting validity
n disadvantage:
„
Increase the processing delay
„ Especially, Several independent random errors may intertwined for the
unexpected error .
x1 x6 x11 x16 x21
x2 x7 … x22x3 x8 … x23
x4 x9 … x24
x5 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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Contents
The Basic Principles of Wireless Communication
» Radio Propagation Characteristics
» Spreading Technology
» Channel Coding» Interleave Technology
» Modulation
WCDMA Radio mechanism
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Principle of Modulation
n Definition
„ Modulation is the process where the amplitude, frequency, or
phase of an electronic or optical signal carrier is changed in
order to transmit information.
„ Using symbol stand for one or more bits to improve
communication effectiveness
n Classification
„ Analog Modulation
„ Digital Modulation
Symbol bit Modulation
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Analog Modulation
n The purpose of analog modulation is to impress an
information-bearing analog waveform onto a carrier
for transmission.
„ Common analog modulation methods include:
Ÿ Amplitude modulation (AM)
Ÿ Frequency modulation (FM)
Ÿ Phase modulation (PM)
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Digital Modulation
n The purpose of digital modulation is to convert an
information-bearing discrete-time symbol
sequence into a continuous-time waveform
(perhaps impressed on a carrier).
„ Basic modulation methods include
Ÿ Amplitude shift Keying (ASK)
Ÿ Frequency shift Keying (FSK)
Ÿ Phase shift Keying (PSK)
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Contents
The Basic Principles of Wireless Communication
WCDMA Radio mechanism
» WCDMA Data Transmission Procedure
» Channel Coding of WCDMA» Spreading Technology of WCDMA
» Modulation of WCDMA
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WCDMA Radio mechanism
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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
C ad o ec a s
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Contents
The Basic Principles of Wireless Communication
WCDMA Radio mechanism
» WCDMA Data transmission Procedure
» Channel Coding of WCDMA» Spreading Technology of WCDMA
» Modulation of WCDMA
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WCDMA Radio mechanism
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Convolutional Code
n Characteristics
„ Mainly used in the voice channel and control signal
channel
„
Coding rate : 1/2 & 1/3
„ Channel bit error rate is 10-3 magnitude
„ Easy decoding
„ Short delay
„ Suitable for realtime service
Ÿ e.g. speech and video service.
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WCDMA Radio mechanism
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Turbo Code
n Characteristics
„ Used in Data service channel
„ Code Rate is 1/3
„ Channel bit error rate is 10-6 magnitude
„ Can be implemented in the transmission for large block and long
delay services
„ Complex decoding, needs cycle iterative calculation
„ Very suitable for non-realtime package service which is BER
sensitive & delay insensitive
Ÿ e.g. WWW, FTP, E-mail , multimedia transmission .
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Contents
The Basic Principles of Wireless Communication
WCDMA Radio mechanism
» WCDMA Data transmission Procedure
» Channel Coding of WCDMA» Spreading Technology of WCDMA
» Modulation of WCDMA
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WCDMA Radio mechanism
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Symbol rate× SF = Chip rate=3.84Mcps
For WCDMA, SF of uplink channelization code:4~256
SF of downlink channelization code: 4~512OVSF: 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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WCDMA Radio mechanism
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Channelization Code
n Adopt OVSF code
„ Definition: Cch,SF,k, describe channelization code, where
SF : spread factor, k : code number, 0 < k≤SF-1
SF = 1 SF = 2 SF = 4
C ch,1,0 = (1)
C ch,2,0 = (1,1)
C ch,2,1 = (1,-1)
C ch,4,0 =(1,1,1,1)
C ch,4,1 = (1,1, -1, -1)
C ch,4,2 = (1, -1 ,1, -1)
C ch,4,3 = (1, -1, -1, 1)
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WCDMA Radio mechanism
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nWCDMA Scrambling code is pseudo random binary sequence (PN code)
„ It has similar noise array character, seemingly random but with regularity.
„ Can make the user data further random, strengthened by scrambling code
to keep secret the user data, at the same time easy to carry out multiple
access communication.
Scrambling Code
n WCDMA scrambling code is generated from Gold sequence
„ Gold sequence has excellent self-correlation.
„ Cross-correlation is very weak between two codes.
„ 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, used to distinguish different
cells
„ Scrambling codes usually used are the first 8192 codes, which are code
0 ,1,……,8191. They are divided into 512 aggregations ,each
aggregation has 1 primary scrambling code ( PSC ) and 15 secondary
scrambling codes ( SSC ).
„
The 512 primary scrambling codes are divided further into 64 primaryscrambling code groups , with 8 primary scrambling codes in each group.
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WCDMA Radio mechanism
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Numbering rule for Downlink Scrambling
Codes
…
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 )
8176:
PSC8177:SSC
…
8191:SSC
81768177
8191
No. 511 Scrambling Code
Group
8160:主扰码
8161:辅扰码
…
8175:辅扰码
8160
8161
8175
No. 510 Scrambling Code
Group
8064:主扰码
8065:辅扰码
…
8079:辅扰码
8064
8065
8079
No. 504 Scrambling Code
Group …
8176:PSC
8177:辅扰码
…
8191:辅扰码
112
113
127
No. 7 Scrambling Code
Group
16:PSC
17:SSC
…
31:SSC
16
17
31
No. 1 Scrambling Code
Group
0:PSC
1:SSC
…
15:SSC
0
1
15
No. 0 Scrambling Code
Group
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 Pr i ma r y S c r a mb l i n g Co d e Gr o u p
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WCDMA Radio mechanism
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Code Functions
„ Channelization code ---- for separation of physical channels
in the uplink and separation of users in the downlink
„
Scrambling code ---- for separation of users/terminals in theuplink and cells/sectors in the downlink.
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WCDMA Radio mechanism
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Air Interface
2chc
3chc
1chc
scramblingc
Modulation
Spreading code & scrambling code
„ Cch:spread code
Ÿ Relative to service rate,extended to 3.84Mchips/s
Ÿ A kind of orthogonal code
„ Cscrambling:scrambling code
Ÿ Have no effect on signal bandwidth
Ÿ downlink for identifier cell,uplink identifier terminal
Ÿ A pseudo-random sequence
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WCDMA Radio mechanism
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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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Contents
The Basic Principles of Wireless Communication
WCDMA Radio mechanism
» WCDMA Data transmission Procedure
»Channel Coding of WCDMA
» Spreading Technology of WCDMA
» Modulation of WCDMA
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WCDMA Radio mechanism
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Modulation Methods in WCDMA
n BPSK (Binary Phase Shift Keying) in Uplink channels
n QPSK (Quadrature Phase Shift Keying) in Downlink channels
n 16QAM (16-state Quadrature Amplitude Modulation) in HSDPA
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WCDMA Radio mechanism
8/8/2019 1_WCDMA Wireless Principle 49
http://slidepdf.com/reader/full/1wcdma-wireless-principle-49 49/49
Summary
n Principle of WCDMA
„ All users are simultaneously transmitted in the same frequency band
„ Users interfere with each other
„ Adjacent cells use the same frequency
„ Cells, users (terminals), and physical channels are separated by codes
n Channel coding
„ Convolutional code
„ Turbo code
n Codes
„ Channelization code
„ Scrambling code
n Modulation
„
BPSK„ QPSK
„ 16QAM
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