جــــــــامـــــعة المســــــتقبل
كلـية الهندسـة والتكنولوجــيا
FUE - Future University in Egypt
Faculty of Engineering and Technology
Electrical Engineering Department
Direct Sequence Spread Spectrum (DSSS)
Communication System Simulation in
Simulink
Spread spectrum techniques can be used to transmit multiple message signals simultaneously in
the same frequency band. Such techniques, referred to as code-division multiple access
(CDMA), are often used in mobile phone communications. This is made possible by assigning
each user a unique spreading code from a set of codes. Then, multiple spread-spectrum signals
can be transmitted in the same frequency band, and the messages can be decoded at each receiver
using the unique (and properly synchronized) spreading code.
It is required to Design a CDMA communication system in Simulink consisting of a
transmitter, channel, and receiver. Start by opening a new Simulink model and defining the
system parameters in Model Properties → Callbacks → InitFcn as follows:
1. fs = 1e4; % sampling frequency
2. Ts = 1/fs; % sample time
3. Tb = 0.1; % bit time
4. Tc = 0.0125; % chip time
5. frame Size = 1000; % size of each frame in source blocks
The Transmitter section generates source signals for User 1 and User 2, spreading each signal
using unique Walsh-Hadamard codes of length 8. Set code length=8, sample time=8, frame
size=8 and stop time=10s
The channel introduces noise by adding an AWGN (Additive White Gaussian Noise) block,
modeling real-world communication conditions.
The Receiver section includes separate paths for User 1 and User 2. Each user’s receiver
correlates the incoming signal with their respective spreading code to despread and recover the
original signal. The system is designed to ensure that each user can accurately retrieve their data
despite interference and noise.
Delivered:
1. Include screen captures of the designed system
2. Based on the parameters specified above, what is the spreading factor of the DSSS
system?
3. Use MATLAB to compute the autocorrelation function for the sequence generated in the
transmitter
4. In the Transmitter, use Time Scope and Spectrum Analyzer blocks to observe the inputs
to and the output of the Add block. That is, observe the User 1 and User 2 DSSS signals,
and their sum. Include screen captures and comment on what you observe.
5. Use a Time Scope block to display the User 1 and User 2 messages in the transmitter, and
the User 1 and User 2 messages recovered in the receiver. Submit screen captures for
simulations where the AWGN noise variance is 0, 1, and 10. Comment on the results
6. Repeat the previous problem, however now change the User 2 Receiver sequence to [1 -1
1 -1 1 -1 -1 -1]
7. Find In phase and Quadrature components of the modulation signal
