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SECTION 1CODE DIVISION MULTIPLE ACCESS
Section Introduction
The CDMA frequency band Frequency Allocation in CDMA Understanding the DSSS Codes and their functions in CDMA Generation of Codes Spreading And Despreading with Codes
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CDMA
WELCOME TO CDMA OVERVEIW
INTRODUCTION TO CDMA RADIOINTERFACE
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Guten Tag
Time division Frequency division!
CHAOS
Hello
Buenos Dias
Bonjour
Shalom
The SYMPHONY!
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GSM Vs CDMA
FREQUENCY REUSE IN CDMA & TDMA
TYPICAL TDMA SYSTEMEACH CELL USESDIFFERENT FREQUENCY
THE PATTERN ISREPEATED FOR THE NEXTSET OF CELL SITES
TYPICAL CDMA SYSTEMEACH CELL USES SAMEFREQUENCY
F 1
F 1
F 1F 1
F 1
F 1F 1
F 1
F 2
F 5
F 4F 6
F 7 F 3
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Frequency Re-use
f 7
f 7 f 2
f 2
7 cell re-use pattern
f 6
f 6
f 1 f 5 f 3
f 4 f 1
f 5 f 3
f 4
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CDMA Frequency Reuse
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Frequency Reuse
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Spread Spectrum Concept
1800 MHz 1850 MHz 1910 MHz 1930 MHz 1990 MHz 2000 MHz
Mobile Tx Cell Tx
In GSM small time slots of the spectrum (200 kHz) are used by different users as channels.
Spread spectrum uses much larger slice (1.25 MHz) of the available bandwidth.Same slice is used for all user with no time multiplexing but each user isassigns with a different code to uniquely identify them.
User 1User 2User 3User 4
User n
Code 1Code 2Code 3Code 4
Code n
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The Cellular CDMA Channel
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The Cellular CDMA Channel
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CDMA Cellular Spectrum
846.5MHz
825MHz
824MHz
835MHz
845MHz
849MHz
A A A B B Reverse link
891.5MHz
870MHz
869MHz
880MHz
890MHz
894MHz
A A A B B Forward link
2 - 7
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DSSS AND THE PROCESSING GAIN
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DIRECT SEQUENCE SPREAD SPECTRUM
A System is said to be using DSSS if it follows the two basic rules mentioned
The Bandwidth of the Carrier frequency must be much larger than theBandwidth of the baseband Signals to be transmitted. The same codes that are used for coding the signal must also be used for
decoding the signals.
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TYPES OF SPREAD SPECTRUMMODULATION
The types of spread spectrum modulation commonly used in
communication systems are classified as:
Direct Sequence Frequency HoppingCDMA is a direct sequence system .
In direct sequence modulation the carrier frequency is fixed and thebandwidth of the transmitted signal is larger and independent of thebandwidth of the information signal.
The carrier frequency is varied and the bandwidth of the transmitted signal iscomparable to the bandwidth of the information signal. Information ismodulated on top of a rapidly changing carrier frequency.
Direct Sequence
Frequency Hopping
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PROCESSING GAIN
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PROCESSING GAIN
Chip Rate (Rc): The Chip Rate is the rate at which the PN sequence is generated. ForCDMA, IS95, the chip rate is 1.2288 * 10 ^ 6 cps (chips per second).
Bit Rate (Rb): The bit rate is base band user information (i.e. user voice/data) rate. InCDMA, voice is digitized at different rates depending on the speech activity level. Thesystem parameters presented in this discussion are based on a maximum bite rate of 9.6kbps and 14.4 kbps per IS95For CDMA (IS95A/B):
Ex.Rc = 1.2288 Mcps, Rb = 14.4 kbps (max), resulting in a Processing Gain of 85.33 (19.3
dB).
Processing Gain is a term common to all direct sequence spread spectrumsystems.
Process gain is defined as the ratio of the Chip Rate (Rc) to theinformation bit rate (Rb).
This provides a measure of ``spreading'' in the system.
Processing Gain = Rc / Rb
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The Processing Gain and Capacity Relation
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SOFT CAPACITY IN CDMA
YOU CAN ALWAYS ADD JUST ONE MORE CALLER TO A CDMACHANNEL AT THE COST OF QUALITY. CDMA SYSTEM CAPACITY IS A COMPROMISE BETWEEN THE NUMBER OF USERS AND QUALITY OF SERVICE .
CDMAUSERS
USERTRAFFIC
QUALITYTOTALBANDWIDTH
QUALITY IS ANALOGOUS TO PROCESSING GAIN
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Comparison of Coverage due to change in traffic(5% to 80% of capacity)
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CDMA s Nested Spreading Sequences
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Spreading : What We Do, We Can Undo
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Shipping and Receiving via CDMA
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U1 = 0110010101001000
C1 ( 100110.10110010) *
=U1C1 ( 1001100000)
U1C1 ( 10011000000)
U1 = 0110010101001000
C1 ( 100110.10110010) *
=
UnCn
U4C4
U3C3
U2C2
UnCn*C1 = 0, UnCn*Cn = Un
U4C4*C1 = 0, U4C4*C4 = U4
U3C3*C1 = 0, U3C3*C3 = U3U2C2*C1 = 0, U2*C2*C2 = U2
C1*C1 = 1, C2*C2 = 1. Cn*Cn = 1 BUT C1*C2 = 0C1*Cn = 0
DSSS Spreading/ Despreading
Th Th CDMA S di
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The Three CDMA SpreadingTechniques
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Orthogonal Sequences Definition:Orthogonal functions have zero correlation. Two binary sequencesare orthogonal if the process of XORing them results in an equalnumber of 1s and 0s. Example:
0000(XOR) 0101
------0101 Generation Sequence:
- Seed 0 0
0 1- Repeat: right & below
- Invert: diagonally
0 0
0 1
0 0
0 1
0 0
0 1
1 1
1 0
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Walsh Codes
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 00 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 00 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 00 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 00 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 0
0 0 0 00 1 0 10 0 1 1
0 1 1 00 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 00 1 0 10 0 1 10 1 1 0
0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 6 6 6 60 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
0 0 0
0 0 0 0 0 0 0 0 1 1 1 1
1 1 1 1 1 2 2 2 2 2 2 2
2 2 2
3 3
6 6 6 6
0 1 2
3 4
5 6 7
8 9 0 1 2
3 4
5 6 7
8 9 0 1 2
3 4
5 6
7 8 9 0 1 ... 0 1 2
3
ORTHOGONALITY OF WALSH CODES
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ORTHOGONALITY OF WALSH CODES
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Orthogonal Spreading
1
0110011010011001100110010110011010011001011001100110011010011001
1001100101100110011001101001100101100110100110011001100101100110
Walsh Function #59
Pattern to be Transmitted
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Orthogonal Spreading
0
0 1 1 0
0
0 1 1 0
1
0 1 1 0
1
0 1 1 0
1
0 1 1 0
1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1
+1
-1
+1
-1
User Data
OrthogonalSequence
Tx Data
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Decoding Using a Correct Code
0
0 1 1 0
0
0 1 1 0
1
0 1 1 0
1
0 1 1 0
1
0 1 1 0
1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1
+1
-1
CorrectFunction
Rx Data
0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 11 1 1 1
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?
0 1 0 1
?
0 1 0 1
?
0 1 0 1
?
0 1 0 1
?
0 1 0 1
1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1IncorrectFunction
Rx Data
0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 01 1 0 0
Decoding Using a Incorrect Code
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Example: Spreading
+1
-1
+1
-1
+1
-1
+1
-3
Spread Waveform Representation ofUser As signal
Analog Signal Formed by the Summationof the Three Spread Signals
Spread Waveform Representation ofUser Cs signal
Spread Waveform Representation ofUser Bs signal
A=00Walsh Code for
A = 0101
B=10
Walsh Code forB = 0011
C=11Walsh Code for
C = 0000
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Despreading
Received Composite Signal
Walsh Code for User A = 0101
Product
+1
-3
+1
-1
+3
-1
Average=(5-1)/4=1 Average=(5-1)/4=1
0 0
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Pseudorandom Noise (PN) Codes
Two Short Codes (215
= 32,768)Termed I and Q codes (different taps )
Used for Quadrature Spreading
Unique offsets serve as identifiers for a Cell or a Sector
Repeat every 26.67 msec (at a clock rate of 1.2288Mcps )
One Long Code (2 42= 4400 Billion) Used for spreading and scrambling
Repeats every 41 days (at a clock rate of 1.2288Mcps )
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PN Code Generation
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PN Code Generation
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Masking
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Lookup Table for PN Offsets
Mask
001
010
011
100
101
110111
Offset (in chips)
7
6
4
5
1
32
Transmitted Sequence
1001011
0010111
1011100
0101110
1100101
01110011110010
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Quadrature Spreading
To BasebandFilter
I
Q
1011000010110
0100011101011
0110111001011
Symbols Spread byWalsh Chips
0110111001011
0110111001011 1101111011101
0010100100000
Offset I PN Code
Offset Q PN Code
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Phase Shift Keying (PSK)
-sinw ct(logic 0)
sinw ct(logic 1)
1
0
1
DigitalSignal
Bipolar PSK Quadrature PSK
00
0111
10
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Orthogonal QPSK
I-ChannelInput Data
tbb 0 b 1 b 2 b 3 b 4
Q-Channel
Input Data
tb
a0
a1
a2
a3
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QPSK MODULATION USING PN-SHORT CODE
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PN Offset - Cell Identification
Quick and Easy Cell Acquisition Reuse Walsh Codes
100101001100111010111001010100
100101001100111010111001010100
1001010011001110101110010Offset inincrementsof 64 chips
#1
#2
#3
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CDMA AIR INTERFACE ARCHTECTURE
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FORWARD & REVERSE LINK CODES
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Coherent / Non-Coherent
Detection
