Guaranteeing QoS in network coded TDD satellite broadcast systems with hard delivery deadline

In this paper, we consider the problem of guaranteeing the quality of service (QoS) in delay sensitive network coded broadcast systems over time division duplex (TDD) satellite channels. We adopt feedback-less systematic random linear network coding (RLNC) and our goal is to design the system such that the required QoS is guaranteed. We focus on two classes of QoS requirements that necessitate the minimum/mean throughput of the users be higher than a threshold with a predefined probability and at the same time the packet drop rates (PDR) of the users be minimized within the delivery deadline requirements of the system. To this end, we start with formulating the probability and cumulative density functions (PDF and CDF) of users´ throughputs. Then by utilizing the calculated functions, the optimum system design parameters that meet the QoS requirements can be obtained. The achieved results on the PDF and CDF of users´ throughputs offer good insights about the performances of different users with different packet erasure conditions, and more importantly provide design guidelines for TDD satellite broadcast systems. Furthermore, the results show that the proposed feedback-less scheme performs nearly as well as an idealistic scheme using immediate and perfect feedbacks.