Introduction

As cell phones became more accessible, and analog cellular networks began to reach their capacities, several digital technologies have been introduced to alleviate problems associated with increased traffic on the airwaves. One digital transmission scheme that is currently being highly researched is Code Division Multiple Access (CDMA).

Project Abstract

In this exploration of CDMA, we modeled the entire CDMA transmission scheme using Matlab.

The forward link refers to signal transmission between the transmission tower and the user phone. This was modeled using 8 bit Walsh codes.

The reverse link refers to signal transmission between the user phone and the transmission tower. This was modeled using 21 bit psuedo-random Gold codes.

In addition, we also discovered some interesting features of CDMA that indicate potential for it to be a more efficient means of wireless transmission than FDMA or TDMA, two other means of transmission.

FDMA v. TDMA v. CDMA

Sending and Receiving in CDMA

In general, the transmission process works by multiplying the data
signal with a digital code, or a "chip", that consists of a series of
positive and negative pulses and is of a higher frequency than the
data signal. 
 
The encoded nature of CDMA requires that the receiver be synchronized
with the transmitted signal. However, since it is almost impossible to
synchronize signals coming from multiple phones, the transmission
implementation is different for each direction. 
 

One interesting aspect of CDMA is the asymmetric nature of the forward and reverse links.

 

Forward Link

 

Reverse Link

 

Features

 

Data and Conclusions

 

Group Members

 

Bibliography

 

2001 Kyle Bryson, Alison Chen, and Allen Wan