Effects of discontinuous transmission on the performance of a WCDMA cellular system

In this paper, we investigate some side effects of discontinuous transmission (DTX) on the performance of a wide-band code-division multiple-access (WCDMA) radio interface with signal-to-interference-ratio-based closed-loop power control. More precisely, we study how the DTX mechanism affects the transmission of some user signals. It is shown that the mobile terminals, when they turn on their data channels after some frames without any data to transmit, can cause a sudden increase of the interference level, leading, for some neighboring users, to a temporary performance degradation that lasts until the power control has completely reacted to this event. The main parameters that characterize the dynamics of the DTX mechanism are described and the tradeoffs in the choice of their values are evaluated; we also propose a suitable variation to the DTX mechanism that reduces the unwanted effects. For our investigation, a suitable simulation tool, which integrates the system-level and link-level analysis, has been developed, including most of the actual details and features of the WCDMA physical layer.