Analysis of VoIP over HSDPA Performance with Discontinuous Reception Cycles

The aim of this paper is to evaluate how Discontinuous Reception (DRX) cycles and related timers take effect to Voice over IP (VoIP) performance when High Speed Downlink Packet Access (HSDPA) networks are in question. DRX cycles limit the scheduling freedom of users and increase battery saving opportunities in the User Equipment (UE) by allowing it to turn its receiver circuitry off for some periods of time. Prior work has concentrated mainly on optimizing the usage of radio resources when small bit rate delay critical services, like VoIP, are considered. However, the battery life of small handheld devices might become a limiting factor in providing satisfactory user experience. Thus, this paper evaluates the performance also from the battery life perspective when DRX cycles together with VoIP are considered. The performance is evaluated with a fully dynamic system level tool in which the mobility of the users, radio resource management functionalities and the interactions between them are explicitly taken into account. The study indicated that the longer the DRX cycle is the higher are the battery saving opportunities but at the same time VoIP over HSDPA capacity can be compromised. Capacity degeneration in pure VoIP traffic simulations was, however, possible to be mitigated by using an adequately long inactivity timer. In mixed traffic scenarios including both VoIP and Best Effort (BE) traffic, higher cell throughput was achieved by allowing more scheduling time for BE users with adequately long DRX cycle and a short inactivity timer.