OWA200003 WCDMA Radio Interface_Physical Layer (With Comment) ISSUE 1.0(Fr)
01 Principles of the WCDMA System-20080715-A-1.0
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Transcript of 01 Principles of the WCDMA System-20080715-A-1.0
HUAWEI TECHNOLOGIES CO., LTD.
www.huawei.com
Huawei Confidential
Internal
Principles of the WCDMA System
HUAWEI TECHNOLOGIES CO., LTD. Page 2Huawei Confidential
Preface
Now, the most popular term in the mobile
communication field is WCDMA!
What is WCDMA? And what is its benefit?
Today, let’s go to know about WCDMA!
HUAWEI TECHNOLOGIES CO., LTD. Page 3Huawei Confidential
Objectives
Know the basic knowledge of the CDMA system.
Master advantages of the CDMA technology comparing with other multiple access technologies.
Know technical features of WCDMA FDD.
After studying this course, you should be able to:
HUAWEI TECHNOLOGIES CO., LTD. Page 4Huawei Confidential
Contents
Chapter 1 WCDMA Principle
Chapter 2 Technical Features of WCDMA
FDD
HUAWEI TECHNOLOGIES CO., LTD. Page 5Huawei Confidential
Overview of CDMA Principles
Radio Propagation EnvironmentRadio Propagation Environment
Multiple Access Technology and Multiple Access Technology and Duplex TechnologyDuplex Technology
CDMA Principles and Rake ReceiverCDMA Principles and Rake Receiver
HUAWEI TECHNOLOGIES CO., LTD. Page 6Huawei Confidential
Multipath Environment
Time
Strength of the received signal
Transmitted
signal
HUAWEI TECHNOLOGIES CO., LTD. Page 7Huawei Confidential
FadingTransmitted data
-40
-35
-30
-25
-20
-15
-10
-5
0
dB
Received data
HUAWEI TECHNOLOGIES CO., LTD. Page 8Huawei Confidential
Fading
Distance (m)
Rx power (dBm)
10 20 30
-20
-40
-60
Slow fading
Fast fading
HUAWEI TECHNOLOGIES CO., LTD. Page 9Huawei Confidential
Frequency-Selective Fading
NarrowbandSystem
NarrowbandSystem
Fading
Transmit Signal Received Signalff
P(f) P(f)
Fading
Transmit Signal Received Signalff
P(f) P(f)
BroadbandSystem
BroadbandSystem
HUAWEI TECHNOLOGIES CO., LTD. Page 10Huawei Confidential
Classification of Typical Radio Mobile Channels
Static channel
Pedestrian channel in typical urban areas (TU3)
Vehicle mounted channel in typical urban areas (TU30)
Vehicle mounted channel in rural areas (RA50)
Vehicle mounted channel on the highway (HT120)
HUAWEI TECHNOLOGIES CO., LTD. Page 11Huawei Confidential
Overview of CDMA Principles
Radio Propagation EnvironmentRadio Propagation Environment
Multiple Access Technology and Multiple Access Technology and
Duplex TechnologyDuplex Technology
CDMA Principles and Rake ReceiverCDMA Principles and Rake Receiver
HUAWEI TECHNOLOGIES CO., LTD. Page 12Huawei Confidential
Duplex Technology – Distinguish User’s UL and DL Signal – FDD
Frequency division duplex (FDD) : Distinguish the uplink and
downlink according to the frequencies. Adopted by the WCDMA, CDMA2000 and GSM
Advantage: It can be easily implemented.
Disadvantage: The spectrum utilization is low when the uplink and
downlink services (mainly the data services) are asymmetrical.
HUAWEI TECHNOLOGIES CO., LTD. Page 13Huawei Confidential
Duplex Technology – Distinguish User’s UL and DL Signal – TDD
Time division duplex (TDD) : Distinguish the uplink and downlink
according to the timeslots. Adopted by the TD-SCDMA
Advantage: The uplink and downlink can be allocated with different numbers
of timeslots when the uplink and downlink services are asymmetrical.
Therefore, the spectrum utilization is high.
Disadvantage:
− It cannot be easily implemented and needs precise synchronization. In the CDMA
system, GPS synchronization is needed.
− When it is used with the CDMA technology, it is difficult to control interference
between the uplink and the downlink.
HUAWEI TECHNOLOGIES CO., LTD. Page 14Huawei Confidential
Traffic channels: different users are assigned unique code and transmitted over the same frequency band, for example, WCDMA and CDMA2000
Traffic channels: different frequency bands are allocated to different users,for example, AMPS and TACS
Traffic channels: different time slots are allocated to different users, for example, DAMPS and GSM
Multiple Access Technology - Distinguish Different Users
FrequencyTime
Power
FDMA
User
User
User User
User
FrequencyTime
Power
TDMA
Power
Time Frequency
CDMA
HUAWEI TECHNOLOGIES CO., LTD. Page 15Huawei Confidential
Characteristics of CDMA System
High Spectral Efficiency
Frequency multiplex coefficient is 1.
Soft capacity
Quality
Coverage
Interference
Self-interference system
A UE transmission power is interference for another UE.
Wideband system
HUAWEI TECHNOLOGIES CO., LTD. Page 16Huawei Confidential
Overview of WCDMA Principles
Radio Propagation EnvironmentRadio Propagation Environment
Multiple Access Technology and Multiple Access Technology and
Duplex TechnologyDuplex Technology
CDMA Principles and Rake ReceiverCDMA Principles and Rake Receiver
HUAWEI TECHNOLOGIES CO., LTD. Page 17Huawei Confidential
Questions
Why does the WCDMA system have enhanced anti-
interference performance?
Why is the WCDMA system more secure?
Why are the WCDMA handsets more environment protective?
HUAWEI TECHNOLOGIES CO., LTD. Page 18Huawei Confidential
Common Terms Bit, symbol and chip
Bit (bps): the data that is obtained upon source coding and contains
information.
Symbol (sps): the data obtained upon channel coding and interleaving.
Chip (cps): the data obtained upon final spreading.
− The spreading rate of WCDMA is: 3.84 Mcps
Processing gain
It refers to the ratio of the final spreading rate to the bit rate (cps/bps).
In the WCDMA system, the processing gain depends on the specific
service.
HUAWEI TECHNOLOGIES CO., LTD. Page 19Huawei Confidential
Spreading Factor and Service Rate
Chip rate = symbol rate spreading factor
For WCDMA, if the chip rate is 3.84 MHz and the spreading factor is 4, the
symbol rate is 960 Kbps.
For CDMA2000-1x, if the chip rate is 1.2288 MHz and the spreading factor is
64, the symbol rate is 19.2 Kbps.
Symbol rate = (service rate + check code) × channel code ×repetition
or punching rate
For WCDMA, if the service rate is 384 Kbps and the channel code is 1/3
Turbo, the symbol rate is 960 Kbps.
For CDMA2000-1x, if the service rate is 9.6 Kbps and the channel code is
1/3 convolutional code, the symbol rate is 19.2 Kbps.
HUAWEI TECHNOLOGIES CO., LTD. Page 20Huawei Confidential
Basic Diagram of the WCDMA System
Source coding
Channel coding and interleaving
ScramblingSpreading ModulationRF
transmission
Source decoding
deinterleavingChannel
decoding and de-interleaving
De-scramblingDe-spreading DemodulationRF
reception
Radio link
HUAWEI TECHNOLOGIES CO., LTD. Page 21Huawei Confidential
Source Coding in WCDMA
The WCDMA system adopts the adaptive multi-rate (AMR) speech coding. A total of eight coding modes are available. The coding rate ranges from 12.2
Kbps to 4.75 Kbps.
Multiple voice rates are compatible with the coding modes used by current mainstream mobile communication systems. This facilitates the design of multi-mode terminals.
The system automatically adjusts the voice rate according to the distance between the user and the NodeB, thus reducing the number of handovers and call drop.
The system automatically decreases the voice rate of some users according to
the cell load, thus saving power and containing more users.
Source coding
InterleavingChannel coding and interleaving
ScramblingSpreading ModulationRF
transmission
HUAWEI TECHNOLOGIES CO., LTD. Page 22Huawei Confidential
Channel Coding in WCDMA
Channel coding can enhance symbol correlation to recover
signals in the case of interference.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Code type
Voice service: Convolutional code (1/2 and 1/3).
Data service: Turbo code (1/3).
Source coding
InterleavingChannel coding interleaving
ScramblingSpreading ModulationRF
transmission
HUAWEI TECHNOLOGIES CO., LTD. Page 23Huawei Confidential
Interleaving Interleaving is used to damage symbol correlation and reduce the impact caused by fast
fading and interference of the channel.
1 2 3 4 5 6 7 8 ... ... 452 453 454 ……1 2 3 4 5 6 7 8 ... ... 452 453 454 ……
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.... ....
B0 B1 B2 B3 B4 B5 B6 B7
{A4,B0} {A5,B1} {A6,B2} {A7,B3} {B4,C0} {B5,C1} {B6,C2} {B7,C3}{A4,B0} {A5,B1} {A6,B2} {A7,B3} {B4,C0} {B5,C1} {B6,C2} {B7,C3}
Ist interleaving
2nd interleaving
HUAWEI TECHNOLOGIES CO., LTD. Page 24Huawei Confidential
Self Correlation and Mutual Correlation of Code Words
Different users adopt different spreading code words,
such as x1(t) , x2(t) ….
Self correlation determines multipath interference.
Mutual correlation determines multiple access
interference.
Self-correlation function
R(τ) =<x1(t) , x1(t+τ) >
Mutual-correlation function
V(τ) =<x1(t) , x2(t+τ) >
Note: <x1(x) , x2(y)> =1, when x1=x2 , and x = y
0, others
HUAWEI TECHNOLOGIES CO., LTD. Page 25Huawei Confidential
Users who need to send information: UE1, UE2 and UE3
UE1 uses c1 for spreading: UE1 x c1
UE2 uses c2 for spreading: UE2 x c2
UE3 uses c3 for spreading: UE3 x c3
c1, c2 and c3 are orthogonal to each other
Information sent: UE1 x c1 + UE2 x c2 + UE3 x c3
Spreading Principle
Source coding
InterleavingChannel coding and interleaving
ScramblingSpreading ModulationRF
transmission
HUAWEI TECHNOLOGIES CO., LTD. Page 26Huawei Confidential
UE1 uses c1 for de-spreading.
(UE1 x c1 + UE2 x c2 + UE3 x c3) x c1
= UE1 x (c1 x c1) + UE2 x (c2 x c1) + UE3 x (c3 x c1)
= UE1 x 1 + UE2 x 0 + UE3 x 0
= UE1
In the same way, UE2 uses c2 for de-spreading and UE3
uses c3 for de-spreading to get their own signals.
De-spreading Principle
HUAWEI TECHNOLOGIES CO., LTD. Page 27Huawei Confidential
____________
UE1: +1 -1 1 _____________
UE2: -1 +1
c1: +1 -1 +1 -1 +1 -1 +1 -1
c2: +1 +1 +1 +1 +1 +1 +1 +1
UE1xc1: +1 -1 +1 -1 -1 +1 -1 +1
UE2xc2: -1 -1 -1 -1 +1 +1 +1 +1
UE1xc1 + UE2xc2: 0 -2 0 -2 0 +2 0 +2
Spreading Principle
HUAWEI TECHNOLOGIES CO., LTD. Page 28Huawei Confidential
UE1×c1 + UE2×c2 : 0 -2 0 -2 0 +2 0 +2
De-spreading Principle
Question: How to generate those orthogonal codes like c1 and c2?
UE1 de-spreading with c1: +1 -1 +1 -1 +1 -1 +1 -1
De-spreading result: 0 +2 0 +2 0 -2 0 -2
Integral: +4 -4
Decision: +4/4 = +1 -4/4 = -1
UE2 de-spreading with c2: +1 +1 +1 +1 +1 +1 +1 +1
De-spreading result: 0 -2 0 -2 0 +2 0 +2
Integral: -4 +4
Decision : -4/4 = -1 +4/4 = +1
HUAWEI TECHNOLOGIES CO., LTD. Page 29Huawei Confidential
OVSF & Walsh
OVSF codes (Walsh) are completely orthogonal and their mutual correlation is zero.
SF = 1 SF = 2 SF = 4
Cch,1,0 = (1)
Cch,2,0 = (1,1)
Cch,2,1 = (1,-1)
Cch,4,0 =(1,1,1,1)
Cch,4,1 = (1,1,-1,-1)
Cch,4,2 = (1,-1,1,-1)
Cch,4,3 = (1,-1,-1,1)
HUAWEI TECHNOLOGIES CO., LTD. Page 30Huawei Confidential
Why CDMA system is a self interference system?
Since all the users use orthogonal code, where does the self
interference come from?
Comes from the code error during the transfer.
If there are some code error on one user’s information, it
misses some orthogonal to others. Then interference comes.
HUAWEI TECHNOLOGIES CO., LTD. Page 31Huawei Confidential
UE1xc1 + UE2xc2 : 0 -2 0 -2 0 +2 0
+2
UE1xc1 + UE2xc2 error : 2 -2 0 -2 1 +2 0 +2
Sample of code error
C2 +1 +1 +1 +1 +1 +1 +1 +1
Result: 2 -2 0 -2 0 +2 0 +2
Integral: -2 +4
Decision: -2/4=-0.5 +4/4=1
c1: +1 -1 +1 +1 +1 -1 +1 -1
Result: 2 +2 0 +2 0 -2 0 -2
Integral: +6 -4
Decision: +6/4 = 1.5 -4/4=-1
HUAWEI TECHNOLOGIES CO., LTD. Page 32Huawei Confidential
Scrambling in the WCDMA System
Downlink: Different cells have different downlink scrambling codes.
Each cell is configured with a unique downlink scramble. The UE
identifies a cell based on the scramble.
The OVSF code is used to distinguish different users in a cell.
Uplink: Scrambles are used to distinguish different users.
In one cell, each user is configured with a unique uplink scrambling
code.
The OVSF code is used to distinguish the services of a user.
Source coding
InterleavingChannel coding and interleaving
ScramblingSpreading ModulationRF
transmission
HUAWEI TECHNOLOGIES CO., LTD. Page 33Huawei Confidential
Spreading and Scrambling
Symbols
OVSF code Scrambling code
Chips after spreading
and scrambling
3.84M3.84Mcps
3.84Mcps
xx sps
HUAWEI TECHNOLOGIES CO., LTD. Page 34Huawei Confidential
Code Generation Technologies in CDMA Random sequence (Bernoulli sequence)
It consists of 0’s and 1’s only, with the number of 0’s equal to that of 1’s.
The probability of continuous 1 or 0 is as follows: 1/2 for one continuous 0 or 1, 1/4
for two continuous 0 or 1, 1/8 for three continuous 0 or 1….
One half of the shift sequence is the same as the original sequence and the other
half is different.
m sequence - scrambling code used in the CDMA2000 system It is generated by the shift register.
As the longest linear shift register sequence, its period is 2n-1, where “n” stands for
the length of the shift register.
When the delay is 0, the self-correlation function has a maximum value. In other
cases, the function value is always -1.
It meets the Bernoulli sequence.
Its disadvantages are: Only one sequence is available and different users are
distinguished by different phases. So it has a high requirement for synchronization.
HUAWEI TECHNOLOGIES CO., LTD. Page 35Huawei Confidential
Gold Sequence — Scrambling Code in the WCDMA System Gold sequence
It consists of two preferred m sequences on the Exclusive-OR
basis.
Its self-correlation function has multiple values, which is worse
than the m sequence.
It exceeds the m sequence in quantity.
The Gold sequence is used to distinguish the cells and users
in the WCDMA system owing to its good self correlation.
Good self correlation determines the Gold sequences can be
used to distinguish users, thus the multiple access function is
realized.
HUAWEI TECHNOLOGIES CO., LTD. Page 36Huawei Confidential
Advantages and Disadvantages of the Gold Sequence
Advantages: The Gold sequence needs no GPS synchronization
and features high system flexibility and security.
The NodeB can work in asynchronous mode.
It is easy to realize indoor coverage.
Disadvantages: The Gold sequence has greater inter-code
interference than the m sequence.
HUAWEI TECHNOLOGIES CO., LTD. Page 37Huawei Confidential
Allowed maximum interference level of the system
Demodulation threshold
Spreading/De-spreading Principle — Explanations for Frequency Domain
Power spectrum
Power that all the users can share
a2Tbit = Ebit
Gain
Interference signals from other users
Echip
Eb / No = Ec / Io gain
HUAWEI TECHNOLOGIES CO., LTD. Page 38Huawei Confidential
The CDMA broadband spreading technology effectively avoids frequency-selective fading of radio channels.
Spreading code
Spreading code
Signal combination
Spectrum Change in CDMA
Narrowband signal
f
P(f)
Broadband signal
P(f)
f
Noise
P (f)
f
Noise + broadband signal
P (f)
f
Separation of signals and noise
P (f)
f
HUAWEI TECHNOLOGIES CO., LTD. Page 39Huawei Confidential
Rake ReceiverRake Receiver
Receive set
Correlator 1
Correlator 2
Correlator 3
Searcher correlator
Calculate the time delay and signal strength
CombinerThe
combined signal
tt
s(t) s(t)
RAKE receiver help to overcome on the multi-path fading and enhance the receive performance of the system
HUAWEI TECHNOLOGIES CO., LTD. Page 40Huawei Confidential
Summary - Advantages of CDMA RAKE receiver is adopted
The time diversity effect generated by channel coherence time is efficiently used.
Frequency diversity
Wideband frequency spectrum
Higher interference tolerance and security performance
Low signal transmission power
Great flexibility in carrying multiple services with largely different bit rate and QoS requirement.
Different spreading factors for different services with different data rates
High spectral efficiency
All users can share the same frequency spectrum simultaneously.
Supporting soft handover and softer handover.
HUAWEI TECHNOLOGIES CO., LTD. Page 41Huawei Confidential
Contents
Chapter 1 WCDMA Principle
Chapter 2 Technical Features of WCDMA
FDD
HUAWEI TECHNOLOGIES CO., LTD. Page 42Huawei Confidential
Characteristics of WCDMA FDD
Channel bandwidth: 5MHz
Chip rate: 3.84Mcps
Frame length: 10ms
Voice coding: AMR (Adaptive Multi-Rate)
Uplink and downlink modulation: QPSK/QPSK
Coherence demodulation aided with pilot
Fast closed loop power control: 1500Hz
Handover: soft/hard handover
Support synchronous and asynchronous NodeB
operation
HUAWEI TECHNOLOGIES CO., LTD. Page 43Huawei Confidential
Characteristics of WCDMA FDD
Satisfy the minimum performance requirement of IMT2000
Compatible with GSM-MAP core network
Comparatively steady version R99 has been released
Support open loop and closed loop transmit diversity mode
Support Common Packet Channel(CPCH) and Downlink
Share Channel, adapt to Internet data access mode
Support macro diversity, selection diversity of NodeB
location
Support different fast power control algorithms and open
loop, out loop power control
Fully support UE locating services
HUAWEI TECHNOLOGIES CO., LTD. Page 44Huawei Confidential
Differences Between the WCDMA and GSM on the Air Interface
WCDMA GSM
Carrier spacing 5 MHz 200 KHz
Frequency reuse coefficient 1 1-18
Power control frequency 1500 Hz 2 Hz or lower
QoS control Through the RRM algorithmThrough network planning
(frequency planning)
Frequency diversity
The 3.84 MHz bandwidth
enables the air interface to use
the rake receiver for multipath
diversity.
Frequency hopping
Packet data Load-based packet scheduling Timeslot-based scheduling
in GPRS
Downlink transmit diversity Supported by the protocol to
improve downlink capacity
Not supported by the
standard but can be applied.
HUAWEI TECHNOLOGIES CO., LTD. Page 45Huawei Confidential
Conclusion This course describes the WCDMA system.
This course first describes some key technologies. Then,
describes the basic principles of CDMA and the WCDMA
FDD mode.
After studying this course, we can have a preliminary
understanding of WCDMA, thus laying a good foundation for
subsequent study.
Thank You !www.huawei.com