A hybrid multi-rate scheme for WCDMA

Different kinds of multi-rate communication systems are considered for accommodating information sources with different data rates. Direct-sequence code-division multiple access (DS/CDMA) techniques have attracted much attention for use in such systems. In this paper three multi-rate transmission schemes in a WCDMA system are compared. Both AWGN and multipath Rayleigh fading channels are considered. It is shown that for high data rates the spreading factor in the variable spreading factor scheme will be very small and thus the performance will be significantly degraded due to intersymbol interference. Thus variable spreading factors are used for the low and medium high data rates, and combined with multicode transmission for the highest data rates. Simulation result shows that hybrid multi-rate transmission scheme is suitable for WCDMA.