Wireless digital point to multipoint link utilizing wideband CDMA

Abstract

One of the proposed techniques for multiple access communications for the third generation is code division multiple access (CDMA). This has been shown to be a viable alternative to both TDMA and FDMA. While there does not appear to be a single multiple accessing technique that is superior to others in all situations, there are characteristics of CDMA that give it a distinct advantage over the other multiple access techniques. In CDMA each user is provided with an unique, orthogonal code. If these K codes are orthogonal and uncorrelated with each other, than K independent users can transmit at the same time and in the same radio bandwidth. The receivers decorrelate the information and regenerate the original transmitted signal. It must be noted that the term "Wideband CDMA" is used comparatively to the only existing commercial CDMA system, IS-95 which uses a spectral bandwidth of only 1.2288 MHz. This thesis examines and evaluates a good set of orthonormal codes (orthogonal and normalized to have equal power) and their application to providing accessing for a point to multipoint (PMP) stationary system. The correlation properties, design and constellation properties of these codes are investigated. The system model is then simulated using Systemview and then evaluated in terms of it's bit error rate, user capacity and Erlang with addition of users to the system.