Common packet channel (CPCH): the optimum wireless Internet mechanism in W-CDMA

Abstract

Wideband packet CDMA was introduced to the 3GPP process in February of 1999. GBT championed the specification of common packet channel (CPCH), which was the main distinguishing feature of WP-CDMA, the RTT submitted to the ITU. In this paper, the CPCH mechanism in W-CDMA is compared with the dedicated channel (DCH) and the random access channel (RACH) mechanisms for bursty packet data transfer. CPCH is the most efficient wireless Internet mechanism in W-CDMA. It operates at all rates including 384 kbps and could also support 2.048 Mbps, if the entire cell were dedicated to packet data services. The CPCH is more spectrum efficient as compared to the DCH mode of operation in the uplink and downlink directions. We show that the CPCH offers 25% and 11.2% more capacity in the uplink and downlink direction, respectively. We specifically compared the CPCH with the stop and resumption control of the DCH. Other proposed methods, such as the gating method for DCH, are even less efficient from a spectrum efficiency perspective than the stop and resumption control. In the gating method for DCH, the MS generates even more interference than the stop and resumption control. The CPCH requires 5-10 times less channel cards in the base node, which leads to a significant reduction in base node complexity. This has been shown in a comparative study of circuit mode versus packet mode of operation. The use of the CPCH leads to a decrease of 24% in power consumption in the MS as compared to DCH. In consequence, this will increase the talk time by 24%. The CPCH operates in closed loop power control as compared to the random access channel, which operates in open loop power control, this leads to a 2-4 capacity ratio of CPCH over RACH.