An Analytic Model of IEEE 802.16e Sleep Mode Operation with Correlated Traffic

We propose and analyse a discrete-time queueing model for the evaluation of the IEEE 802.16e sleep mode operation in wireless access networks. This mechanism reduces the energy consumption of a mobile station (MS) by allowing it to turn off its radio interface (sleep mode) when there is no traffic present at its serving base station (BS). After a sleep period expires, the MS briefly checks the BS for data packets and switches off for the duration of another sleep period if none are available. Specifically for IEEE 802.16e, each additional sleep period doubles in length, up to a certain maximum. Clearly, the sleep mode mechanism can extend the battery life of the MS considerably, but also increases the delay at the BS buffer. For the analysis, we use a discrete-time queueing model with general service times and multiple server vacations. The vacations represent the sleep periods and have a length depending on the number of preceding vacations. Unlike previous studies, we take the traffic correlation into account by assuming a D-BMAP arrival process. The distribution of the number of packets in the queue is obtained at various sets of time epochs, as well as the mean packet delay and the mean number of consecutive vacations. We apply these results to the IEEE 802.16e sleep mode mechanism with downlink traffic. By means of some examples, we show the influence of both the configuration parameters and the traffic correlation on the delay and the energy consumption.