Multiservice/multirate pure CDMA for mobile communications

Future mobile communication systems should be able to support a wide range of services with different bit rates. Spread-spectrum code-division multiple-access (CDMA) techniques have attracted much attention to be employed in such a system. Different techniques of CDMA could be used to map low-, medium-, and high-bit rates data into the same allocated bandwidth, including pure or wide-band CDMA, FDM/FH/CDMA, TDM/TH/CDMA, or a hybrid of these techniques. This paper investigates multirate pure CDMA using multiuser interference statistics derived for both Gaussian and Rayleigh fading channels. Approximation of multiuser/multipath interference, in general, helps in the theoretical approach to error performance evaluation and, in particular, is quite useful for simulation approach in a fading channel. Some results of a multirate pure CDMA system with two services (low- and high-bit rates), for both BPSK and DPSK modulation schemes, are presented and compared.