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Combining TDMA with Slotted Aloha for delay constrained traffic over lossy links

Reliability and real-timeliness of wireless communications are the major concerns that hamper the wide deployment of wireless technologies for mission- and time-critical applications. This paper investigates the problem of maximizing transmission reliability of delay constrained traffic in a single-hop network by exploring the advantages of TDMA and Slotted Aloha. In our scheme, each time slot is either exclusively allocated to a dedicated node or shared by a group of nodes. All nodes sharing the same time slot operate based on the Slotted Aloha protocol. The key problem we address is: given a delay constraint, how to construct the transmission schedule by allocating the dedicated and shared slots in such a way that the probability that all packets are received at the destination is maximized. We show that the optimal schedules have some good structures, and propose both optimal and heuristic scheduling schemes. Numerical simulation results demonstrate that our schemes significantly outperform the traditional TDMA scheduling scheme in which time slots are all exclusively allocated. Moreover, our heuristic scheme can construct schedules with success probability coming very close to the optimal schedules at much more modest computational cost.