Enhancing the performance of W-CDMA downlink in mobile satellite systems for Web traffic

In this paper, we attempt to enhance the performance of W-CDMA downlink for third generation (3G) land mobile satellite communication systems for Web traffic. It has been shown that Web traffic requires very low bit error rate (BER) in order to avoid severe degradation in its throughput over satellite links. In Hijres et al. (1999), it has been shown that power control errors can seriously degrade the performance of the downlink in W-CDMA mobile satellite systems. Hence, we focus on the combined effect of using the radio link protocol (RLP) and macrodiversity (space diversity) to improve the performance of turbo coded downlink under power control errors for Web traffic. The macrodiversity is employed at the mobile Web terminal rather than at the satellite, due to satellite space limitation. Simulation results demonstrate that the combined effect of using RLP and macrodiversity is essential in reducing the frame error rate to a very low level in order to support Web traffic over W-CDMA mobile satellite links. This very low frame error rate has been achieved at very low Eb/No, e.g. FER ≈10^-5 has been achieved at Eb/No=1 dB for downlink which suffers from large power control error with standard deviation (σ_s) of 4 dB. It is extremely important to operate downlinks of mobile satellites at very low Eb/No in order to preserve satellite capacity, as mobile satellites are power limited.