Delay spread effects on BER performance of single code and multi-code WCDMA signalling schemes for high rate data transmission

In this paper, the bit-error-rate (BER) performance of two signalling schemes for high rate data transmission in the 3rd generation direct-sequence, wide-band code-division-multiple-access (DS/WCDMA) systems are compared. The transmission channel is frequency selective with Rician and Rayleigh fading, and a RAKE receiver is employed to achieve diversity gain with maximal ratio combining (MRC). In the first scheme, referred to as the single code scheme, high rate data transmission is achieved by using a single spreading pseudo-noise (PN) code with varying processing gain (PG) that might be as low as 4. In the other scheme, called the multi-code scheme, the high rate data stream is split into several low rate substreams. Each substream is spread by a concatenated Walsh/PN sequence and all the substreams are then transmitted in parallel. It is shown that notable performance improvement can be achieved by using multi-code scheme in the multipath fading channel when the channel delay spread is small