Search

In this paper we consider a wireless network composed of a base station and a number of clients, with the goal of scheduling real-time traffic. Even though this problem has been extensively studied in the literature, the impact of delayed acknowledgment has not been assessed. Delayed feedback is of increasing importance in systems where the round trip delay is much greater than the packet transmission time, and it has a significant effect on the scheduling decisions and network performance. Previous work considered the problem of scheduling real-time traffic with instantaneous feedback and without feedback. In this work, we address the general case of delayed feedback and use Dynamic Programming to characterize the optimal scheduling policy. An optimal algorithm that fulfills any feasible minimum delivery ratio requirements is proposed. Moreover, we develop a low-complexity suboptimal heuristic algorithm which is suitable for platforms with low computational power. Both algorithms are evaluated through simulations., National Science Foundation (U.S.) (CNS-1217048), United States. Office of Naval Research (Grant N00014-12-1-00640, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

We consider the problem of transmitting multicast flows with hard deadlines over unreliable wireless channels. Every user in the network subscribes to several multicast flows, and requires a minimum throughput for each subscribed flow to meet the QoS constraints. The network controller schedules the transmissions of multicast traffic based on the instant feedback from the users. We characterize the multicast throughput region by analyzing its boundary points, each of which is the solution to a finite-horizon dynamic programming problem over an exponentially large state space. Using backward induction and interchange arguments, we show that the dynamic programming problems are solved by greedy policies that maximize the immediate weighted sum throughput in every slot. Furthermore, we develop a dynamic throughput-optimal policy that achieves any feasible throughput vector by tracking the running performance received by the users.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013., Cataloged from PDF version of thesis., Includes bibliographical references (pages 81-82)., Today wireless networks are increasingly used to perform applications with Quality of Service constraints (QoS) such as delay, delivery ratio, and channel reliability. Especially, as demand for real-time transmissions increases, transmitting packets with hard delivery deadlines poses an important network control problem. In this thesis, we propose a framework for characterizing feasibility regions and finding an optimal scheduling policy in various wireless networks. First, we start with a wireless network with multiple unicast flows. We investigate how delay in feedback information decreases the feasibility region. Second, we consider time-varying channels and how delay in network state information decreases the feasibility region. Third, we characterize the feasibility region of a wireless network with multiple multicast flows. In each case, we characterize the feasibility region, prove that a max-weight policy is a feasibility optimal policy and present the results of simulation studies verifying the theoretical studies., by Kyu Seob Kim., S.M.