Performance of UMTS packet service over dedicated channels (DCH)

The provision of high speed packet data services in an efficient way is probably the most important challenge for UNITS since this can give an advantage with respect to second generation systems. The efficiency mainly depends on the radio interface and since it is characterized by a great flexibility it is of utmost importance to investigate the effect of different configurations on the system performance. In this paper we evaluate the performance of packet data services over downlink dedicated channels (DCH) by means of detailed simulations. Due to the traffic variability, ARQ mechanism and dosed loop power control the system behavior is quite complex and not so easily predictable as with constant rate services such as voice. We study the effect of several parameters (spreading factor, code rate, channel setup delay, etc.) on the system capacity by means of the delay-throughput curves. We show that the setting of parameters may be critical for system capacity and stability. For this reason we propose a flow control mechanism which is able to guarantee stability and to make the system capacity almost independent of channel rates.