Energy-efficient multicast with deadlines in wireless networks via lazy rate scheduling

In this paper, we consider the problem of providing QoS (Quality of Service) guaranteed data download services in wireless networks with high energy-efficiency. To guarantee the QoS, a transmission deadline is set for each request, before which the whole data should be received by the user. To attain high energy-efficiency, multicast technique is adopted. Traditionally, the multicast rate is constant and independent of the number of users served in one session. However, we show that when we change the transmission rate dynamically according to current state, such as user numbers, more transmission energy can be saved. We design the optimal rate scheduling algorithm for the offline case when non-causal information about user arrivals is available. We show that the optimal rate scheduling scheme can save energy by 15%. For the online scheduling problem when only causal information is available, we propose several heuristic lazy transmission schemes based on DP (Dynamic Programming) results. Simulation results show that with these heuristic schemes, up to 10% transmission energy can be saved.