Performance of downlink shared channels in WCDMA radio networks

In order to avoid downlink channelization code shortage, a downlink shared channel (DSCH) has been specified for WCDMA systems. On DSCH, many packet data users with bursty traffic can share a single channelization code. However, since DSCH is transmitted from only one access point it provides no macro-diversity gain, as the dedicated channels (DCH) do via soft handover. A scheme that combines high rate DSCH and medium rate DCH is proposed. Basically, users close to the base stations are allocated DSCH in order to save channelization codes, whereas users close to the cell boarders are allocated DCH to conserve base station transmission power. The scheme is compared with other packet data channel allocation schemes. The simulation results show that DSCH provides high packet data bit rates due to less channelization code blocking. This is however at the cost of high transmission power, due to lack of soft handover gain. The proposed scheme achieves equally good packet data bit rate as the pure DSCH scheme, but with considerably less base station transmission power.