We develop a framework that exploits network coding (NC) and multiple-input/multiple-output (MIMO) techniques, jointly together, to improve throughput of downlink broadcast channels. Specifically, we consider a base station (BS) equipped with multiple transmit antennas that serves multiple mobile stations (MSs) simultaneously by generating multiple signal beams. Given the large number of MSs and the small number of transmit antennas, the BS must decide, at any transmission opportunity, which group of MSs it should transmit packets to, in order to maximize the overall throughput. We propose two algorithms for grouping MSs that take advantage of NC and the orthogonality of user channels to improve the overall throughput. Our results indicate that the proposed techniques increase the achievable throughput significantly, especially in highly lossy environments.

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Limited bandwidth and high packet loss rate pose a serious challenge for video streaming applications over wireless networks. Even when packet loss is not present, the bandwidth fluctuation, as a result of an arbitrary number of active flows in an IEEE 802.11 network, can significantly degrade the video quality. This paper aims to enhance the quality of video streaming applications in wireless home networks via a joint optimization of video layer-allocation technique, admission control algorithm, and medium access control (MAC) protocol. Using an Aloha-like MAC protocol, we propose a novel admission control framework, which can be viewed as an optimization problem that maximizes the average quality of admitted videos, given a specified minimum video quality for each flow. We present some hardness results for the optimization problem under various conditions and propose some heuristic algorithms for finding a good solution. In particular, we show that a simple greedy layer-allocation algorithm can perform reasonably well, although it is typically not optimal. Consequently, we present a more expensive heuristic algorithm that guarantees to approximate the optimal solution within a constant factor. Simulation results demonstrate that our proposed framework can improve the video quality up to 26% as compared to those of the existing approaches.

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Providing Quality of Service (QoS) is one of significant issues for multimedia traffic. One approach to achieve the requested QoS is to characterize the traffic flows and guarantee their committed throughput. In a typical multi-hop wireless ad hoc network, determining the feasibility for a given set of flow characteristics is challenging due to the multi-user interference problem. To that end, this paper presents the following contributions. First, we describe a simple Aloha-like Medium Access Control (MAC) protocol that enables each flow to maintain its requested bandwidth, and thus is suitable for multimedia traffic. Second, we propose a bandwidth feasibility algorithm based on the Variable Elimination (VE) technique. The bandwidth feasibility algorithm determines whether or not a given network can support a set of flows of certain bit rates. Simulations indicate that our solution can precisely control the bit rates over all hosts while providing the throughput guarantees.