Overloading Cellular DS-CDMA: A Bandwidth-Efficient Scheme for Capacity Enhancement

摘要

Overloading is a technique to accommodate more number of users than the spreading factor N. This is an efficient way to increase the number of users in a fixed bandwidth, which is of practical interest to mobile system operators. In this paper we have reviewed the different overloading schemes proposed in the literature for the DS-CDMA systems. The performance of an Orthogonal/Orthogonal (O/O) overloading scheme, using two sets of orthogonal codes (O/s-O) has been evaluated. Iterative multistage detector (IMSD) is used to reduce the multiple access interference between the users of two sets. The BER performance of IMSD is evaluated with hard and soft decisions functions using Monte-Carlo simulations. It is found that, this scheme provides 19% and 11% channel overloading for synchronous DS-CDMA system in an AWGN channel, with a SNR degradation of less than 0.5 dB at a BER of 10~(-5) compared to single user bound for N=16 and 64 respectively.