Transcript CDMA2000-1x宣讲资料

Contents
 World
Trends
 The Cellular Concept and Multiple Access
Techniques
 Principles of CDMA
 CDMA Major Features
 Comparison with Other Technologies
GSM and CDMA Coverage
Evolution of CDMA
Technologies of Mobile Communications
Projected Subscribers by Standard
(Calendar Year 2005)
2%13%
1%
4%
1%
18%
2%
59%
Analogue
CDMA
W-CDMA
GSM
PDC
PDC-800
iDEN
US TDMA
CDMA: Past, Present, and Future
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The origins of spread spectrum are in military field and navigation
systems
In 1949, John Pierce wrote a technical memorandum where he
described a multiplexing system in which a common medium
carries coded signals that need not be synchronized. This system
can be classified as a time hopping spread spectrum multiple
access system
In 1949, Claude Shannon and Robert Pierce introduced the basic
ideas of CDMA by describing the interference averaging effect and
the graceful degradation of CDMA
In 1950, De Rosa-Rogoff proposed a direct sequence spread
spectrum system and introduced the processing gain equation and
noise multiplexing idea
CDMA: Past, Present, and Future
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In 1956, Price and Green filed for the anti-multipath "RAKE"
patent . Signals arriving over different propagation paths can be
resolved by a wideband spread spectrum signal and combined by
the RAKE receiver.
In 1961 ,The near-far problem (i.e., a high interference
overwhelming a weaker spread spectrum signal) was first
mentioned by Magnuski
For cellular application spread spectrum was suggested by Cooper
and Nettleton in 1978
During the 1980s Qualcomm investigated DS-CDMA techniques,
which finally led to the commercialization of cellular spread
spectrum communications in the form of the narrowband CDMA
IS-95 standard in July 1993
Commercial operation of IS-95 systems started in 1996.
CDMA: Past, Present, and Future
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Multiuser detection (MUD) has been subject to extensive
research since 1986 when Verdu formulated an optimum
multiuser detection for the additive white Gaussian noise
(AWGN) channel, maximum likelihood sequence
estimator (MLSE)
During the 1990s ,wideband CDMA techniques with a
bandwidth of 5 MHz or more have been studied
intensively throughout the world, and several trial
systems have been built and tested
Based on the above description, the CDMA era is divided
into three periods:
1. the pioneer CDMA era
2. the narrowband CDMA era
3. the wideband CDMA era
Table 1. CDMA era
Pioneer Era
1949
John Pierce: time hopping spread spectrum
1949
Claude Shannon and Robert Pierce: basic ideas of CDMA
1950
De Rosa-Rogoff: direct sequence spread spectrum
1956
Price and Green: antimultipath "RAKE" patent
1961
Magnuski: near-far problem
1970s
Several developments for military field and navigation systems
Narrowband CDMA Era
1978
Cooper and Nettleton: cellular application of spread spectrum
1980s
Investigation of narrowband CDMA techniques for cellular applications
1986
Formulation of optimum multiuser detection by Verdu
1993
IS-95 standard
Wideband CDMA Era
Europe:FRAMES FMA2
Japan: Core-A
1995
USA :cdma2000
Korea :TTA I TTA II
2000s
WCDMA
Commercialization of wideband CDMA systems
Evolution of Mobile communication system
N-BAND
Analog
Digital
W-BAND
Evolution from 2G to 3G
WCDMA
GSM
GPRS
TD-SCDMA
EDGE
cdma2000-3x
IS-95A
cdma2000-1x
1X-EVDV
IS-95B
HRPD
CDMA Concepts
- Multiple Access Techniques
- Description of CDMA
- Two Types of CDMA
- How does CDMA work?
- DSSS Spreading: Time-Domain View
- Spreading from a Frequency-Domain View
- CDMA Spread Spectrum Payoff
- CDMA’s Nested Spreading Sequences
Multiple Access Techniques
FDMA
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FDMA:Frequency division multiple access
Feature:each user is allocated a unique frequency
Power
band or channel
TACS AMPS
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TDMA:Time Division Multiple Access
Feature:Radio spectrum is divided into time
slots,and in each slot only one user is allowed to
either transmit or receive.
GSM DAMPS
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TDMA
Power
CDMA:Code division multiple access
Feature:In CDMA each user is assigned a unique CDMA
code sequence it uses to encode its informationbearing signal
Power
IS-95/CDMA2000 /WCDMA/TD-SCDMA
Description of CDMA
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The spreading signal is a pseudo-noise code sequence
that has a chip rate which is greater than the data rate
of the message.
All CDMA users occupy the same frequency at the
same time! Frequency and time are not used as
discriminators.
In cdma systems,the narrowband message signal is
multiplied by a very large bandwidth signal called the
spreading signal.
CDMA operates by using CODING to
discriminate between users.
Each user has its own pseudorandom codeword which
is approximately orthogonal to all other codewords.
CDMA interference comes mainly from
Time
nearby users
The receiver performs a time correlation operation to
detect only the specific desired codeword.All other
codewords appear as noise due to decorrelation.
Code
Chnannel1
Chnannel2
Chnannel3
Chnannel4
Frequency
ChnannelN
Two Types of CDMA
How does CDMA work?
 Sender combines data with a fast spreading
sequence, transmits spread data stream
 Receiver intercepts the stream, uses same
spreading sequence to extract original data
Direct Sequence CDMA
For example:
Data rate 240 kb/s
Spreading factor 16
Chip rate 3.84
Mchip/s
Data signal: bit
Code signal: chip
DSSS Spreading: Time-Domain View
Spreading from a Frequency-Domain View
CDMA Spread Spectrum Payoff
CDMA’s Nested Spreading Sequences
Principle of spread-spectrum multiple access
- Code signal consists of
a number of code bits
called "chips" that can be
either +1 or 1.
- Chip rate of the code
signal must be much
higher than the rate of
the information signal.
- In this figure, 10 code
chips per information
symbol are transmitted
(the code chip rate is 10
times the data rate) so the
processing gain is equal
to 10.
Block diagram of a DS-SS transmitter
Generation of a BPSK-modulated SS signal
Spreading the Spectrum
Original narrowband bit
rate information
Fc: Carrier frequency
rb: Bit rate
Encoded wideband signal
at symbol rate
rc: Chip rate
Frequen
cy
Fc
Fc + rc
Fc + rb
Receiver of a DS-SS signal
Receiver of a DS-SS signal
- The receiver uses coherent demodulation to despread the SS signal, using a
locally generated code sequence.
- To be able to perform the despreading operation, the receiver must not only
know the code sequence used to spread the signal, but the codes of the
received signal and the locally generated code must also be synchronized.
- This synchronization must be accomplished at the beginning of the
reception and maintained until the whole signal has been received.
- The code synchronization/tracking block performs this operation
- After despreading a data modulated signal results, and after demodulation
the original data can be recovered.
Spreading Sequences
Code sequence #1
ACF
Code sequence #2
CCF
Sequence properties:
• High ACF peak
• Low ACF sidelobe 
inter-symbol interference (ISI)
• Low CCF 
multi-user interference (MUI)
Block of DS-SS communication system
A
b(t)
Spreading
Modulation
Information
Modulation
B
C
Despreading
Information
Demodulati
on
C(t)
PN
A Point
fc
Interference PN
B Point
C Point
fc
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Spreading spectrum Sequences(PN)
- Property of PN
- m-sequences
-Walsh Code
Property of PN
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Correlation - The Rule of Sequence design
The ideal Sequence:
The side peak value of auto-correlation(ACF) is
zero
The value of cross-correlation(CCF) is zero
Ideal Sequence can eliminate co-channel
Auto-correlation Function
interference(MAI)
Unfortunately,We can’t find the ideal sequence

1 0 1
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 N 1
N
So,our target is to find such sequence:
Cross-correlation Function
The smaller of the side peak value of autocorrelation and the value of cross-correlation ,the
better of the sequence.
N
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1
0
1
n 1
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Definition of ACF and CCF
Periodic sequence ( x0 , x1 ,...........xN 1 ),( y0 , y1 ,...........yN 1 )
The Periodic ACF:
The Periodic CCF:
R x (l ) 
R y (l ) 
N 1
x x
i 0
i
i l
N 1
y
i 0
N 1
i
yi  j
R xy (l )   xi yi l
i 0
m-sequences
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Good periodic ACF properties
Bad periodic CCF properties
CDMA operates by using different offset of the same
m-sequence to discriminate between users for the bad
periodic CCF properties
In IS-95 and IS2000 standard ,two kinds of msequences are used:
short code (2 1)chips and long code (2  1)chips
The m-sequences are generated using shift register
The normative ACF of m-sequence:
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N
Rx (l )   xi xi l  
i 0
 1
N 1
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l  0(modN )
0  l  N (modN )
Spreading / Despreading
Despreading
of mobile 1
Terminal transmission
Base station reception
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Interference Rejection
Before despreading
After despreading
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An Example of periodic ACF of m-sequence
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length 15 m-sequence (- - - -+ - + - - + + - + + +)
here , - means 1,+means -1
m-sequence:N=15
- - - - + - + - - + + - + + +

- - - - - - -
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Introduction of the short code
Introduce of the long code
Walsh Code- orthogonal sequence
Walsh codes are generated by applying Hadamard transform
upon 0 repeatedly. Hadamard transform is given by
H 1  0
00
H2   
01
0000
0101
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
H4  

0011
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0110
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H 2N
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H N H N 
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
 
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H N H N 

 most important feature: Orthogonal
Walsh Sequence is Orthogonal when synchronized.
ACF and CCF of Walsh Sequence are not ideal when not synchronized.
 Walsh function Set is self-contained.
r
Walsh Sequence with Length n= 2 can constitute n= 2 r Sequences
orthogonal one another.
Features of CDMA
- Multiple Access Capability
- Protection Against Multipath Interference
- Privacy
- Interference Rejection
- Anti-Jamming Capability, Especially
Narrowband Jamming
- Low Probability of Interception(LPI)
Multiple Access Capability
If multiple users transmit a spread-spectrum signal at the same time,
the receiver will still be able to distinguish between the users
provided each user has a unique code that has a sufficiently low
cross-correlation with the other codes.
 Correlating the received signal with a code signal from a certain user
will then only despread the signal of this user, while the other spreadspectrum signals will remain
spread over a large bandwidth.
 Within the information bandwidth
the power of the desired user will be
larger than the interfering power
provided there are not too many
interferers, and the desired signal
can be extracted.
 At the receiver 1 only the signal of
user 1 is "despread" and the data Principle of spread-spectrum multiple access
recovered.
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Protection Against Multipath Interference
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The signals of the different paths
are all copies of the same transmitted
1
signal but with different amplitudes, Tx
0
phases, delays, and arrival angles.
Adding these signals at the receiver
3
2
will be constructive at some of the
frequencies and destructive at others. In the time domain,
this results in a dispersed signal.
If the code sequence has an ideal autocorrelation function,
then the correlation function is zero outside the interval [Tc,Tc], where Tc is the chip duration. This means that if the
desired signal and a version that is delayed for more than
2Tc are received, coherent demodulation will treat the
delayed version as an interfering signal, putting only a
small part of the power in the information bandwidth.
Rx
Privacy
 Privacy
-- The transmitted signal can only
be despread and the data recovered if the
code is known to the receiver.
Interference Rejection
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Cross-correlating the code
signal with a narrowband
signal will spread the power of
the narrowband signal thereby
reducing the interfering power
in the information bandwidth.
The spread-spectrum signal (s)
receives a narrowband
interference (i). At the receiver
the SS signal is "despread"
while the interference signal is
spread, making it appear as
background noise compared to
the despread signal.
Interference rejection
Anti-Jamming Capability
 This
is more or less the same as interference
rejection except the interference is now
willfully inflicted on the system. It is this
property, together with the next one-LPI,
that makes spread-spectrum modulation
attractive for military applications.
Low Probability of Interception(LPI)
S（f）
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Because of its
low power
density, the
spreadspectrum
signal is S（f）
difficult to
detect and
intercept by a
hostile listener.
Signal
Signal
f0
Signal Frequency Before SS
f0
f
f
Signal Frequency after SS
S（f）
Signal
Noise
Noise
Signal
f0
f
Signal Frequency Before Decoding
Signal
Pulse Noise
f0
f
Signal Frequency After Decoding
Other Noise
Features of cdma2000-1X
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Reverse Pilot Support:
Function:Phase reference,Coherent demodulation
For each cdma2000 user, either Turbo or Convolutional
codes can be used.
Fast 800 Hz forward and reverse link power control.The
reverse power control subchannel can be divided into two
independent power control channel,the power control rate
can be 400/400bps or 200/600bps for FCH/SCH.
Double the capacity vs. IS-95-A/B
Provide higher data rates more efficiently (up to 307.2
kbps)
Features of cdma2000-1X
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Support for Quasi Orthogonal Functions (QOF)
increasing available forward channels
Quick paging channel. This allows the mobile to wake
up for a shorter period of time before entering sleep
mode, thereby increasing the standby time of phones.
OTD(Orthogonal Transmit Diversity) and STS(Space
Time Spreading) transmit diversity
Power Control
Near-far ambiguity
Transmit just enough power to achieve min. SIR
Open loop : path loss and shadow fading
Inner closed loop: fast adjustment to achieve target SIR,
compensates some fast fading (Rayleigh) and lower required SIR
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Soft and Softer Handovers
CDMA has
Soft
handover
region
Freq1
the ability to talk to
multiple cells simultaneously… a
“soft handover*”
 When you’re in a soft
handover, it’s likely that there’s
at least one good link into the
system… nice!
* “Softer” handover is when a terminal
talks to two sectors of the same cell
Freq1
Question: What two
characteristics of CDMA make
this possible?
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Answer: Universal Frequency Reuse and Rake Receivers
Soft/ Softer Handover
 Soft
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Handover
The terminal is connected to (at least) two cells
The signals are combined in the RNC by means of
e.g. selection combining using CRC
 Softer
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
Handover
The terminal is connected to two sectors within one
cell
More efficient combining in the uplink is possible like
maximum ratio combining (MRC) in the BTS.
Soft Handover Principle
soft handover
area
NodeB 2
NodeB 1 UE
Measurement
Quantity
CPICH 1
CPICH 2
Link to 1
Link to 1 & 2
Link to 2
time
Multipath and Fading
Multipath
signals can cancel each
other, causing “fading”
Two receive antennas largely takes
care of this problem because
different places have different fading
profiles
 Fine for the uplink, but you’ve still
got a problem on the downlink

Transmitter
Receiver
Power
received
RX Ant0
RX Ant1
Distance
Base
Station
Combiner
To receiver
RAKE Receiver for CDMA
Correlator 2
Combiner
Correlator 1
To De-Interleaver,
Viterbi Decoder
Correlator 3
Multipath Delay
Components
( 150 ms > Dt > 1ms)
Search Correlator
Rake receiver can isolate multipath spaced > 1 chip length.
Should one path fade for a short while, another is probably still available
CDMA Advantages —— Vast Coverage
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The coverage radius is 2
times of standard GSM.
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Coverage of 1000 km2: GSM
needs 200 BSs, while CDMA
requires only 50.
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Under the same coverage
conditions, the number of
BSs is greatly decreased.
CDMA Advantages —— Full Use of Spectrum
Spectrum of 10MHz (5MHz for transmitting, and 5MHz for receiving)
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Parameter
Bandwidth
Number of CF
Frequency reuse
Effective CF
Voice call/CF
Voice call/cell
Sector/cell
Voice call/sector
Erlangs/sector***
CDMA WLL
1.25MHz
3
1
3/1=3
25 to 40+
75 to 120+
3
75 to 120+
64 to 107E
FIXED GSM
0.20MHz
25*
4
25/4=6.25
7.25**
7.25×6.25=45
3
45/3=15
9.01E
5 times of
GSM!
*Optimal situation, no guard band for GSM and AMPS;
**0.75 fewer than 8 voice call/CF, which is used for overhead (e.g.,
control/pilot);
***Based on 2% of air block
CDMA Advantages —— High Quality Voice
Voice quality
64k
8k
present
13k 8k EVRC
PCM GSM CDMA CDMA CDMA
CDMA Advantages —— Green handset
Low transmission
power: Accurate power
control, handoff control,
voice activation
Systems
GSM
CDMA
Mean
transmission
power
125 mW
2 mW
Max
transmission
power
2W
200mW
Power absorbed in the body is 2dB (0.4 mW in CDMA and 25mW in GSM)