Biased Adaptive Modulation/Coding to Provide VoIP QoS over HSDPA

The High-speed Downlink Packet Access (HSDPA) of the Universal Mobile Telecommunication System (UMTS) provides a flexible and efficient packet transmission platform, and has been attracting operators to integrate a diverging variety of services. We studied the possibilities of delivering conversational speech traffic in the form of voice over IP (VoIP), over HSDPA. To provide the VoIP QoS typified by severe delay requirements, the adaptive modulation/coding of HSDPA is biased to achieve lower error rates, thereby reducing the number of hybrid-ARQ retransmissions and the transfer delay. Each radio frame is transmitted either with a higher power or using a lower rate modulation/coding scheme, depending on the available power at NodeB. Simulation results show that the proposed scheme effectively improves VoIP QoS consuming a trifle of extra power, and substantially increases the system capacity. The results show that VoIP deliveries over HSDPA is feasible.