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Code Division Multiple Access (CDMA) Transmission Technology EE578 Assignment #5 Abdul-Aziz .M Al-Yami November 8 th 2010
Code Division Multiple Access (CDMA) Transmission Technology
EE578 Assignment #5
Abdul-Aziz .M Al-Yami
November 8th 2010
Contents
Multiple Access Schemes Code Division Multiple Access
(CDMA) CDMA Protocols Direct Sequence Code Division
Multiple Access (DS-CDMA) Matlab Results
Multiple Access Schemes
For radio systems there are two resources: frequency and time.
Division by frequency, so that each pair of communicators is allocated part of the spectrum for all of the time, results in Frequency Division Multiple Access (FDMA).
Division by time, so that each pair of communicators is allocated all (or at least a large part) of the spectrum for part of the time results in Time Division Multiple Access (TDMA).
In Code Division Multiple Access (CDMA), every communicator will be allocated the entire spectrum all of the time. CDMA uses codes to identify connections.
Multiple Access Schemes (cont)
Code Division Multiple Access (CDMA)
A digital method for simultaneously transmitting signals over a shared portion of the spectrum by coding each distinct signal with a unique code.
CDMA is a wireless communications technology that uses the principle of spread spectrum communication.
Advantages Multiple access capability Protection against multipath interference Privacy Interference rejection Ant jamming capability Low probability of interception
CDMA Protocols
Direct Sequence Code Division Multiple Access (DS-CDMA)o Characteristics:
o All users use same frequency and may transmit simultaneously.
o Narrowband message signal multiplied by wideband spreading signal, or codeword
o Each user has its own pseudo-codeword (orthogonal to others).
o Receivers detect only the desired codeword. All others appear as noise.
o Receivers must know transmitter’s codeword.
Direct Sequence Code Division Multiple Access (DS-CDMA) System
Direct Sequence Code Division Multiple Access (DS-CDMA) System (cont)
Signal transmission consists of the following steps:
1. A pseudo-random code is generated, different for each channel and each successive connection.
2. The Information data modulates the pseudo-random code (the Information data is “spread”).
3. The resulting signal modulates a carrier. 4. The modulated carrier is amplified and broadcast.
Signal reception consists of the following steps:
1. The carrier is received and amplified. 2. The received signal is mixed with a local carrier to recover the spread digital
signal. 3. A pseudo-random code is generated, matching the anticipated signal. 4. The receiver acquires the received code and phase locks its own code to it. 5. The received signal is correlated with the generated code, extracting the
Information data.
Parameters
sr = 256000.0; % symbol rateml = 2; % number of modulation levelsbr = sr * ml; % bit ratend = 100; % number of symbolebn0 = 3; % Eb/No %************************** Filter initialization ************************** irfn = 21; % number of filter tapsIPOINT = 8; % number of oversamplealfs = 0.5; % roll off factor[xh] = hrollfcoef(irfn,IPOINT,sr,alfs,1); % T FILTER FUNCTION[xh2] = hrollfcoef(irfn,IPOINT,sr,alfs,0);
AWGN
Transmitter
Data
0 2 4 6 8 10 12 14 16 18 20-1.5
-1
-0.5
0
0.5
1
1.5data
After QPSK modulation
1 2 3 4 5 6 7 8 9 10-1.5
-1
-0.5
0
0.5
1
1.5
(symbol index)
Am
plitu
de
Transmission I-channel
1 2 3 4 5 6 7 8 9 10-1.5
-1
-0.5
0
0.5
1
1.5
(symbol index)
Am
plitu
de
Transmission Q-channel
Spread data
0 50 100 150 200 250-1.5
-1
-0.5
0
0.5
1
1.5
(symbol index)
Am
plitu
de
Transmission I-channel
0 50 100 150 200 250-1.5
-1
-0.5
0
0.5
1
1.5
(symbol index)
Am
plitu
de
Transmission Q-channel
Transmitted data
0 50 100 150 200 250-1.5
-1
-0.5
0
0.5
1
1.5
(symbol index)
Am
plitu
de
Transmission I-channel
0 50 100 150 200 250-1.5
-1
-0.5
0
0.5
1
1.5
(symbol index)
Am
plitu
de
Transmission Q-channel
Receiver
AWGN addition
0 50 100 150 200 250-1.5
-1
-0.5
0
0.5
1
1.5
(symbol index)
Am
plitu
de
Transmission I-channel
0 50 100 150 200 250-1.5
-1
-0.5
0
0.5
1
1.5
(symbol index)
Am
plitu
de
Transmission Q-channel
Despread data
1 2 3 4 5 6 7 8 9 10-10
-8
-6
-4
-2
0
2
4
6
8
10
(symbol index)
Am
plitu
de
Transmission Q-channel
1 2 3 4 5 6 7 8 9 10-10
-8
-6
-4
-2
0
2
4
6
8
10
(symbol index)
Am
plitu
de
Transmission I-channel
Demodulated Data
Noe2=00 2 4 6 8 10 12 14 16 18 20
-1.5
-1
-0.5
0
0.5
1
1.5demodata
Direct Sequence Code Division Multiple Access (DS-CDMA) System
Advantages:oIncreased capacityoImproved voice qualityoEliminating the audible effects of multipath fadingoEnhanced privacy and securityoReduced average transmitted poweroReduced interference to other electronic devices
Disadvantages:oWide bandwidth per user required
oPrecision code synchronization needed
GOLD CODES – FADING CHANNEL
0 2 4 6 8 10 12 14 16 18 2010
-3
10-2
10-1
100
Gold Codes - BER Vs Eb/N0
Eb/N0
BE
R
Flat FadingAmplitude And Phase Distortion
ORTHOGONAL GOLD CODES – FADING CHANNEL
0 2 4 6 8 10 12 14 16 18 2010
-3
10-2
10-1
100
Orthogonal Gold Codes - BER Vs Eb/N0
Eb/N0
BE
R
Flat FadingAmplitude And Phase Distortion
M Sequences | Gold Codes Autocorrelation
-30 -20 -10 0 10 20 300
2
4
6
8
10
12
14
16
18
20Autocorrelation Functions -- Stages = 5 | Register 1 Taps = [1 3] ...| Register 1 Taps = [2 3]
M SequenceGold Sequence
GOLD CODES – CROSS CORRELATION
-30 -20 -10 0 10 20 300
2
4
6
8
10
12
14
16
18
20Gold Sequences : Autocorrelation & Crosscorrelation -- regi1=[1 0 1 1 1]|regi2=[1 0 1 0 1]|ptap1=[2 4 5]
AutocorrelationCrosscorrelation
DS-CDMA Performance under AWGN Environment for different sequences (1 user)
0 2 4 6 8 10 12 1410
-6
10-5
10-4
10-3
10-2
10-1
Eb/N0 [dB]
BE
RDS-CDMA Different Code Generation Schemes
M-sequenceGoldOrthognal Gold
DS-CDMA Performance under Rayleigh Environment for different sequences (1 user)
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
RDS-CDMA Different Code Spreading Schemes
M-sequenceGoldOrthognal Gold
DS-CDMA Performance under AWGN Environment for different sequences (5 users)
0 2 4 6 8 10 12 14 16 18 2010
-6
10-5
10-4
10-3
10-2
10-1
Eb/N0 [dB]
BE
RDS-CDMA Different Code Generation Schemes
M-sequenceGoldOrthognal Gold
DS-CDMA Performance under Rayleigh Environment for different sequences (5 users)
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
RDS-CDMA Different Code Spreading Schemes
M-sequenceGoldOrthognal Gold
1 user
0 2 4 6 8 10 12 1410
-6
10-5
10-4
10-3
10-2
10-1
Eb/N0 [dB]
BE
R
DS-CDMA Different Code Generation Schemes
M-sequenceGoldOrthognal Gold
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
R
DS-CDMA Different Code Spreading Schemes
M-sequenceGoldOrthognal Gold
AWGN Rayleigh
5 users
0 2 4 6 8 10 12 14 16 18 2010
-6
10-5
10-4
10-3
10-2
10-1
Eb/N0 [dB]
BE
R
DS-CDMA Different Code Generation Schemes
M-sequenceGoldOrthognal Gold
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
R
DS-CDMA Different Code Spreading Schemes
M-sequenceGoldOrthognal Gold
AWGN Rayleigh
DS-CDMA Performance under Rayleigh Environment using M-sequence
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
RDS-CDMA Over Different Number of Users
1 user4 users7 users
DS-CDMA Performance under Rayleigh Environment using Gold Sequence
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
RDS-CDMA Over Different Number of Users
1 user4 users7 users
DS-CDMA Performance under Rayleigh Environment using Orthogonal Gold Sequence
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
RDS-CDMA Over Different Number of Users
1 user4 users7 users
DS-CDMA Performance under Rayleigh Environment (Comparison)
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
R
DS-CDMA Over Different Number of Users
1 user4 users7 users
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
R
DS-CDMA Over Different Number of Users
1 user4 users7 users
M-sequence
Gold Sequence
0 5 10 15 20 25 30 35 4010
-5
10-4
10-3
10-2
10-1
100
Eb/N0 [dB]
BE
R
DS-CDMA Over Different Number of Users
1 user4 users7 users
Orthogonal Gold Sequence
