01 wr bt1002 e01_1 wcdma wireless principle-49
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Transcript of 01 wr bt1002 e01_1 wcdma wireless principle-49
WCDMA Wireless Principle
ZTE University
Content
The Basic Principles of Wireless Communication
Radio Propagation Characteristics
Spreading Technology
Channel Coding
Interleave Technology
Modulation
WCDMA Radio mechanism
Multi-path characteristics of radio channel
Electromagnetic propagation:
--direct radiation、reflection、diffraction and scattering
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
Description of Fast fading distribution
Rayleigh distribution:non line-of –sight(NLOS) transmission
Rician distribution:line-of –sight(LOS) transmission
Multi-Path Effects
receiving signal
time
strength
0
sending signal
Frequency off-set caused by the movement of mobile ,that
is Doppler effect
Sending signal Accepting signal
Interference
0dB
Sending signal
-25dB
Accepting signal
fading
0 +
Sending signal Accepting signal
delay
0 2 3 +
Sending signal Accepting signal
dithering
Characteristics of Radio Propagation
Content
The Basic Principles of Wireless Communication
Radio Propagation Characteristics
Spreading Technology
Channel Coding
Interleave Technology
Modulation
WCDMA Radio mechanism
SHANON Formula
C = Blog2(1+S/N)
Spread Spectrum Principles
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
It is the basic principle and theory for spread spectrum
communications.
Spread Spectrum Principles
1.25 MHz
30 KHz
Power is “Spread” Over a Larger Bandwidth
radio channel
ReceiverTransmitter
Spreading
Despreading
Noise
Spread Spectrum Principles
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
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
Spreading Mode
Direct sequence spread spectrum(DS-SS) Base band data is spread by multiplication of pseudo-noise
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
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
DS-SS communication system
A technology of transmission after spreading
signal spectrum.
FastSpreadingSequence
SlowInformation
Sent
TX
SlowInformationRecovered
RX
FastSpreadingSequence
WidebandSignal
Spread Spectrum Principles
Many code channels are individually
“spread” and then added together to
create a “composite signal”
Unwanted Power from
Other Resoures
Spread Spectrum Principles
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
Processing Gain
Broadband
Interference
Concept of orthogonal code
Orthogonal—
the result of multiplying
and sum is 0
Code1 +1 -1 +1 +1 -1 +1 -1 -1
Code2 -1 +1 +1 -1 -1 +1 +1 -1
Mul -1 -1 +1 -1 +1 +1 -1 +1
Sum 0
Orthogonal
Code1 +1 -1 +1 -1 -1 +1 -1 -1
Code2 +1 +1 -1 +1 -1 -1 +1 -1
Mul +1 -1 -1 -1 +1 -1 -1 +1
Sum -2
Non-orthogonal
-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 0Judge -1 1
1 -1 1 -1
-1 1MUL
Integral
1 1 1 1-1 -1 -1 -1
Example of orthogonal code
S1
S2
S1xC1
S2XC2
WSpreading
Despreading
(S1xC1)+(S2xC2)
Air Interface
[S1xC1+S2xC2]xC2
=S2
[S1xC1+S2xC2]xC1
=S1N
S
C1xC2=0,
C1,C2,orthogonal
Direct spread technique
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
Characteristics of Spreading Communication
High anti-multi-path- interference capability
Anti-sudden-pulse
High security
Lower transmitting power
Easy to implement large-capacity Multiple Access
Communication
Occupy band wide
Complex realization
Content
The Basic Principles of Wireless Communication
Radio Propagation Characteristics
Spreading Technology
Channel Coding
Interleave Technology
Modulation
WCDMA Radio mechanism
Purpose of Channel Coding
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 ~ 10-2Can not satisfy
the communication
Convolutional coding:BER<10-3Can satisfy the
speech communication
Turbo coding: BER<10-6Can satisfy the
data communication
Principle of Channel Coding
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
Content
The Basic Principles of Wireless Communication
Radio Propagation Characteristics
Spreading Technology
Channel Coding
Interleave Technology
Modulation
WCDMA Radio mechanism
Principle of Interleave Technology
advantage
Interleave is to change the sequence of data to random the
unexpected errors
Advance the correcting validity
disadvantage:
Increase the processing delay
Especially, Several independent random errors may intertwined for
the unexpected error .
x1 x6 x11 x16 x21
x2 x7 … x22
x3 x8 … x23
x4 x9 … x24
x5 x10 … x25
Data input
A = (x1 x2 x3 x4 x5 … x25)
Data output
A’= (x1 x6 x11 x16… x25)
e.g.
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 ? E
M ? A M B A
A O K ? O K
DeinterleavingDecoding
Encoding + Interleaving can correct both
continuous and non-continuous errors
Content
The Basic Principles of Wireless Communication
Radio Propagation Characteristics
Spreading Technology
Channel Coding
Interleave Technology
Modulation
WCDMA Radio mechanism
Principle of Modulation
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
Classification
Analog Modulation
Digital Modulation
SymbolbitModulation
Analog Modulation
The purpose of analog modulation is to impress
an information-bearing analog waveform onto a
carrier for transmission.
Common analog modulation methods include:
Amplitude modulation (AM)
Frequency modulation (FM)
Phase modulation (PM)
Digital Modulation
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 analog modulation methods include
Amplitude shift Keying (ASK)
Frequency shift Keying (FSK)
Phase shift Keying (PSK)
Content
The Basic Principles of Wireless Communication
WCDMA Radio mechanism
WCDMA Data transmission Procedure
Channel Coding of WCDMA
Spreading Technology of WCDMA
Modulation of WCDMA
WCDMA Data transmission Procedure
RF ReceivingDemodulationDespreading
Decoding &
De-inteleavingUE Data
UE Data Spreading
RF Transmitting
Modulation
Baseband
demodulation
Baseband
modulation
Encoding &
Interleaving
Content
The Basic Principles of Wireless Communication
WCDMA Radio mechanism
WCDMA Data transmission Procedure
Channel Coding of WCDMA
Spreading Technology of WCDMA
Modulation of WCDMA
Convolutional Code
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
e.g. speech and video service.
Turbo Code
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
e.g. WWW, FTP, E-mail , multimedia transmission .
Content
The Basic Principles of Wireless Communication
WCDMA Radio mechanism
WCDMA Data transmission Procedure
Channel Coding of WCDMA
Spreading Technology of WCDMA
Modulation of WCDMA
Symbol rate × SF = Chip rate=3.84Mcps
For WCDMA,SF of uplink channelization code:4~256
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
Channelization Code
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)
Scrambling Code
WCDMA 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 a code to keep secret the user data, at the same time easy to carry out multiple access communication.
WCDMA scrambling code is generated from Gold sequence Gold sequence has excellent self-correlation.
Cross-correlation is very week between two codes.
It is used to identify cell and user for multiple access.
Characteristic of Scrambling code
There are 224 Uplink Scrambling Codes, they are
used to distinguish different users in one cell.
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 primary scrambling code groups , with 8 primary
scrambling codes in each group.
Numbering rule for Downlink Scrambling
Codes
…
218
-1 Downlink Scrambling Codes in all
(0..262142)
No. 511 Scrambling Code
Group
8176
8177
8191
8176:PSC
8177:SSC
…
8191:SSC
No. 510 Scrambling Code
Group
8160
8161
8175
8160:主扰码
8161:辅扰码
…
8175:辅扰码
No. 504 Scrambling Code
Group
8064
8065
8079
8064:主扰码
8065:辅扰码
…
8079:辅扰码
…
No. 7 Scrambling Code
Group
112
113
127
8176:PSC
8177:辅扰码
…
8191:辅扰码
No. 1 Scrambling Code
Group
16
17
31
16:PSC
17:SSC
…
31:SSC
No. 0 Scrambling Code
Group
0
1
15
0:PSC
1:SSC
…
15:SSC
No.63 Primary Scrambling Code Group… …
No.0 Primary Scrambling Code Group
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 the uplink and cells/sectors in
the downlink.
Air Interface
2chc
3chc
1chc
scramblingc Modulation
Spreading code & scrambling code
Cch:spread code
Relative to service rate,extended to 3.84Mchips/s
A kind of orthogonal code
Cscrambling:scrambling code
Have no effect on signal bandwidth
downlink for identifier cell,uplink identifier terminal
A pseudo-random sequence
f
P
W
Processing
Gain
Rb
Despreading
Processing Gain
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
The higher PG, the more anti-interference capability system has.
b
c
R
WGain Processing
Question
What’s the Processing Gain for voice service in
WCDMA system?
Given: Voice data rate = 12.2kbps
PG=10lg(Wc/ Rb) , dB units
Wc: 3.84Mchip/s
Rb: 12.2kbps
So for voice service,
PG=10lg(3.84* 106 /12.2* 103)= 25 dB
Despreading procedure
Method of despreading
Input signal
Local PN code
When T=Ts, judge
Output after despreading
integral
0
Ts
(*)dt
Content
The Basic Principles of Wireless Communication
WCDMA Radio mechanism
WCDMA Data transmission Procedure
Channel Coding of WCDMA
Spreading Technology of WCDMA
Modulation of WCDMA
Modulation Methods in WCDMA
BPSK (Binary Phase Shift Keying) in Uplink channles
QPSK (Quadrature Phase Shift Keying) in Downlink channels
16QAM (16-state Quadrature Amplitude Modulation) in HSDPA
summary
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
Channel coding
Convolutional code
Turbo code
Codes
Channelization code
Scrambling code
Modulation
BPSK
QPSK
16QAM