Enhanced Soft-Handover for DS-CDMA Systems using Complementary Error Correction Codes

In order to enhance soft-handover performance in the downlink of DS-CDMA systems, we propose to use different codes at the base stations in the active set to encode the information sequence targeted to a mobile station. For reliable information recovery, in case all links except one happen to be simultaneously in deep fade, self-decodable complementary punctured convolution codes, inspired from Hybrid ARQ III, are used. When turbo-decoding is feasible at the mobile station, new complementary codes, using different interleavers followed by a common systematic recursive convolutional encoder, are proposed for an additional enhancement in performance. Experimental evaluation of the enhancement in performance provided by complementary coding is carried for both Gaussian and multipath Rayleigh fading channels. The proposed coding schemes can provide very significant gains. In some cases, gains around 4 dB can be achieved.