2. Content
The Basic Principles of Wireless Communication
» Radio Propagation Characteristics
» Spreading Technology
» Channel Coding
» Interleave Technology
» Modulation
WCDMA Radio mechanism
3. Multi-path characteristics of radio channel
n Electromagnetic propagation:
--direct radiation、reflection、diffraction and scattering
n Signal attenuation:
„ Path loss： Loss of electromagnetic waves caused because of distance。
„ Slow fading：Loss because of being blocked by some objects 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
The Basic Principles of Wireless Communication
5. Frequency off-set caused by the movement of mobile ，
that is Doppler effect
FrequencyFrequency offoff--setset caused by the movement of mobilecaused by the movement of mobile ，，
that is Doppler effectthat is Doppler effect
Sending signal Accepting signal
InterferenceInterference
0dB
Sending signal
-25dB
Accepting signal
fadingfading
0 t s s+ t
Sending signal Accepting signal
delaydelay
0 t 2t 3t s s+ t
Sending signal Accepting signal
ditheringdithering
Characteristics of Radio Propagation
The Basic Principles of Wireless Communication
6. Contents
The Basic Principles of Wireless Communication
» Radio Propagation Characteristics
» Spreading Technology
» Channel Coding
» Interleave Technology
» Modulation
WCDMA Radio mechanism
7. SHANON Formula
C = Blog2(1+S/N)C = Blog2(1+S/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
It is the basic principle and theory for spread spectrum
communications.
Spread Spectrum Principles
The Basic Principles of Wireless Communication
8. Spread Spectrum Principles
5 MHz
30 KHz
Power is “Spread” Over a Larger Bandwidth
MATHHAMMER
MATH
HAMMER
The Basic Principles of Wireless Communication
9. 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)=12.2kbit/s
Spread Spectrum Principles
The Basic Principles of Wireless Communication
11. Spreading Mode
n 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
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
The Basic Principles of Wireless Communication v
12. 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
Wideband
Signal
The Basic Principles of Wireless Communication
13. Spread Spectrum Principles
Many code channels are individually
“spread” and then added together to
create a “composite signal”
The Basic Principles of Wireless Communication
14. Unwanted Power from
Other Resoures
Spread Spectrum Principles
Processing Gain
Broadband
Interference
„ 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
The Basic Principles of Wireless Communication
15. 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
The Basic Principles of Wireless Communication
16. -1 1 -11-1 -11 1 -1 -1 11-1 1-1 1
MU
-1 1 -11-1 -11 1
1 -1 1 -1
-4 4
0 0
Judg
-1 1
1 -1 1 -1
-1 1
MU
Integral
1 1 1 1-1 -1 -1 -1
Example of orthogonal code
The Basic Principles of Wireless Communication
18. 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
The Basic Principles of Wireless Communication
19. Characteristics of Spreading Communication
n High anti-multi-path- interference capability (Rake receiver)
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
The Basic Principles of Wireless Communication
20. Contents
The Basic Principles of Wireless Communication
» Radio Propagation Characteristics
» Spreading Technology
» Channel Coding
» Interleave Technology
» Modulation
WCDMA Radio mechanism
21. 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. Ensure the integrality of
DATA.
No correct coding: BER<10-1 ~ 10-2
Can not satisfy
the communication
Convolutional coding：BER<10-3
Can satisfy the
speech communication
Turbo coding： BER<10-6
Can satisfy the
data communication
The Basic Principles of Wireless Communication
22. 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
The Basic Principles of Wireless Communication
23. Contents
The Basic Principles of Wireless Communication
» Radio Propagation Characteristics
» Spreading Technology
» Channel Coding
» Interleave Technology
» Modulation
WCDMA Radio mechanism
24. 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 … 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.
The Basic Principles of Wireless Communication
25. 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
The Basic Principles of Wireless Communication
26. Contents
The Basic Principles of Wireless Communication
» Radio Propagation Characteristics
» Spreading Technology
» Channel Coding
» Interleave Technology
» Modulation
WCDMA Radio mechanism
27. 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
Symbolbit
Modulation
The Basic Principles of Wireless Communication
28. 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)
The Basic Principles of Wireless Communication
29. 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 analog modulation methods include
Ÿ Amplitude shift Keying (ASK)
Ÿ Frequency shift Keying (FSK)
Ÿ Phase shift Keying (PSK)
The Basic Principles of Wireless Communication
30. 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
31. WCDMA Data transmission Procedure
RF ReceivingDemodulationDespreading
Decoding &
De-inteleaving
UE Data
UE Data Spreading
RF Transmitting
Modulation
Baseband
demodulation
Baseband
modulation
Encoding &
Interleaving
WCDMA Radio mechanism
32. 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
33. 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.
WCDMA Radio mechanism
34. 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 .
WCDMA Radio mechanism
35. 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
36. 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
WCDMA Radio mechanism
37. 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)
WCDMA Radio mechanism
38. 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 a
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.
WCDMA Radio mechanism
39. 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 primary
scrambling code groups , with 8 primary scrambling codes in each group.
WCDMA Radio mechanism
40. Numbering rule for Downlink Scrambling
Codes
…
2
18
-1 Downlink Scrambling Codes in all
(0..262142)
8176：PSC
8177：SSC
…
8191：SSC
8176
8177
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.63 Primary Scrambling Code Group
… …
No.0 Primary Scrambling Code Group
WCDMA Radio mechanism
41. 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.
WCDMA Radio mechanism
42. Air Interface
2ch
c
3ch
c
1ch
c
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
WCDMA Radio mechanism
43. f
P
W
Processing
Gain
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
W
GainProcessing =
WCDMA Radio mechanism
44. 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
45. Despreading procedure
n Method of despreading
Input signal
Local PN code
When T=Ts, judge
Output after despreading
integral
0
Ts
(*)dt
WCDMA Radio mechanism
46. 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
47. 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
WCDMA Radio mechanism
48. 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
WCDMA Radio mechanism
