Statistical evaluation of code performance for Multi-rate CDMA system

Direct-sequence code division multiple-access (DS/CDMA) has for some years been considered as a candidate for future personal and mobile communications. The reasons are mainly the properties of universal frequency reuse and the multi-path mitigation. Generally, the focus has been on low rate services such as speech, and very little has been done on evaluating the performance for a system that can support many types of services, such as speech, fax, image and data transmission. In this context, the objective of this paper is to evaluate the statistic performance of UMTS network in multi-rate DS-CDMA systems using multi processing gain in term of the number of simultaneous users. We have developed analytical expressions for the cross-correlation between users at unequal bit rates. Thanks to these expressions; we use the mean and the standard deviation to calculate the confidence intervals for the BER (bit error rate) in the place of the use of the theoretical lower and upper limits. The multi-rate scheme that we consider is a multiprocessing gain system (constant chip rate) with spreading codes of length 127, 255 and 511 that will provide data rates of 100Mb/s, 50Mb/s and 25Mb/s respectively. The transmitter power for each data rate will be different so that the energy per bit (Eb) remains constant. In this work we evaluate the performance of deterministic pseudorandom code sequences (Gold, Kasami). The parameter of interest is the average interference to be used in a preliminary system design analysis