Performance of space-time coding for 3GPP HSDAPA service under flat and frequency selective fading conditions

There is little doubt that an important feature of Third Generation (3G) mobile systems will be the ability to send and receive large volumes of data at high speed. The Third Generation Partnership Project (3GPP) is currently considering suitable systems for the High-Speed Downlink Packet Access (HSDPA) services, which will provide the required data throughput. One of the systems currently under consideration is a Space-Time Coding (STC) architecture using the Vertical-Bell-labs- Layered-Space-Time (VBLAST) system on the Downlink-Shared Channel (DSCH), which will allow simultaneous transmissions over multiple channels destined for a single user. Although link level results for flat fading channels indicate significant performance advantages over the conventional single antenna systems it is only under frequency selective fading conditions that we are able to make a realistic analysis. In this paper we simulate the system and obtained its performance in frequency selective fading environments. Our results show severe system performance degradation in comparison to a flat fading channels. This loss in performance is due to the loss of orthogonality between spreading codes induced by such channels. This leads us to the conclusion that changes in the structure of the system will be necessary in order that this issue may be overcome.