Digital Cellular Systems (CDMA)


Chapter 4

[1]  Introduction
[2]  Spreading Spectrum Characteristics
[3]  Mobile Radio Environment
[4]  Key Elements in Designing Cellular
[5]  Multiple Access Schemes
[6]  Ten Top Advantages Using CDMA

Introduction

In recent years, Entirely new opportunities such as wireless LAN's; personal communication networks; and, all over, digital cellular radios have created the need for research on how spread spectrum systems can be optimized at the best possible, in order to get more efficient use in these commercial applications.

Taking advantage of the noise-like characteristics of the signal waveform, spread spectrum technique gets important efficiency improvements in the system. This technique has achieved a high bandwidth efficiency in the world of mobile and personal portable communications. Talking about the specific case of digital systems, there are three basic multiple access schemes:

Frecuency Division Multiple Access (FDMA);

Time Division Multiple Access (TDMA) used in GSM; and

Code Division Multiple Access (CDMA).

In theory, regardless the scheme choosen, the capacity provided from these three multiple access techniques is the same. However, in cellular systems, we can find that CDMA is better than the other two. A very nice characteristic of CDMA is its universal frequency reuse (That is: the fact that many users, regardless their physical location, can use, simultaneosly, a common frequency spectrum allocation).