The delayed symbol combining interference canceller for multi-rate DS-CDMA

In mobile and personal radio, direct sequence code division multiple access (DS-CDMA) systems are attracting attention because of their inherently high capacity. Furthermore, the DS-CDMA system is a flexible system which can accommodate various user rates easily. As many user will occupy the same frequency band simultaneously, the traffic capacity of a DS-CDMA system is determined by the interference power. Interference cancellation is one of the important techniques in decreasing the interference power and increasing the traffic capacity. We propose the delayed symbol combining interference canceller which can suppress the interference from various users sending at different information rates. Its performance is calculated by computer simulations from the viewpoint of bit-error-rate (BER). In the flat fading environment, it is found that the E_b/N_o degradation by the interference is suppressed to 3 dB at a BER of 10^-3 with 24 users. In the frequency selective fading environment, it is found that the required E_b/N_o of the frequency selective fading canceller is about 11 dB better than that of the flat fading canceller to establish the BER of 10^-3