TABLE OF CONTENTS CDMA is a multiple-access technique, where multiple users can share the same time and frequency domains while remaining distinct in the code domain (e.g., applying the orthogonality principle). Let us consider the case when we have two users occupying the same frequency channel and transmitting at the same time. For TDMA systems, this can be a nightmare! For our CDMA system, each user has a different PN code sequence. The users will be able to become separable with the use of the statistical properties of the PN code. This can be accomplished in two ways:
Use physically different PN sequence-generator polynomials. Here we must assure the cross-correlation between C 1( t) and C 2( t) is minimal or 0 for the orthogonal case, in order to reduce the MAI.
Use the same PN generator polynomials, but have the two users start spreading at different points in time of the chip sequence period. We rely on good autocorrelation properties of the PN sequence generator to reduce multiple user interference.
In fact, we can quickly draw the analogy of the above two ways to how the North American CDMA system (IS-95) operates [6]. Specifically, the first way parallels the downlink spreading and the second way parallels the uplink spreading. Let us discuss this in more detail in the following subsections.
Let us consider a simple example of two users, with their information signals given by b 1
