Saurabh Mathur

Cooperative Recovery in Heterogeneous Mobile Networks

In multicast/broadcast services over infrastructure- based/cellular wireless networks (e.g. 3G cellular networks, WiMax, DVB), data is transmitted to multiple recipients from an access point/base station. Multicast greatly improves the network efficiency to distribute data to multiple recipients as compared to multiple unicast sessions of the same data to each receiver individually, by taking advantage of the shared nature of the wireless medium. However it is difficult to guarantee the reception reliability of multiple multicast/broadcast recipients because the wireless medium is error prone and each receiver experiences different channel conditions. An additional difficulty is that multicast/broadcast services in many networks such as 3G multimedia multicast services do not provide a reverse communications channel for the receivers to request the retransmission of lost data packets. This research proposes a novel method to provide QoS support by using an assistant network to recover the loss of multicast data in the principal network. Wireless devices are connected to the principal network to receive the multicast data. A wireless device may lose some of the multicast data sent over the principal network. The wireless devices form an assistant network to recover the lost multicast data cooperatively from their peers. The performance of this recovery mechanism has been investigated using extensive simulation experiments.

Supporting Video Streaming Services in Infrastructure Wireless Mesh Networks: Architecture and Protocols

In this paper, we present UPAC, a unified peer-to-peer (P2P) and cache framework for high quality video-on-demand services over infrastructure multi-hop wireless mesh networks. Streaming video in multi-hop wireless networks faces many challenges, e.g., the varying available path bandwidth, interference due to shared medium, the impact of multiple relay nodes, etc. To increase the capacity of streaming services and ensure high video quality, in UPAC, the video content is cached at selected wireless mesh access points (MAPs) inside the mesh network. Furthermore peers help each other on video downloading in a best effort manner to reduce the workload imposed on the servers and networks. This unified framework has the advantages of both the content distribution network approach and peer-to-peer network approach. To obtain optimal video quality, a user device can form the P2P relationship with MAP content cache servers and other user devices. Meanwhile, the client-server relationship is established between the device and the MAP content cache servers. In addition, we propose and compare several methods to select the content cache servers for serving a device and to establish the end-to-end routes between the device and the selected servers. Our preliminary simulation results show that the proposed framework increases the number of users that can be concurrently served in the infrastructure wireless mesh network and improves the received video quality.

Implementation Experience of a Prototype for Video Streaming over Wireless Mesh Networks

Streaming video over wireless mesh networks is an attractive and challenging technology. It is important to select an appropriate metric in the routing algorithm to improve the video delivery quality. In this paper, we report the design, implementation, and evaluation of a prototype for video streaming over a wireless mesh network. In order to select the best path dynamically to improve the multimedia performance, Ad Hoc On-Demand Distance Vector (AODV) routing protocol is enhanced with a new radio and bandwidth aware routing metric, better route request/reply message process rules and periodic route refreshment and maintenance. A metric quantization method is also proposed to maintain the route stability while achieving quick response to the network dynamics. In addition, we implemented a proxy function in the mesh access point so that the stations can access the mesh through the access point without any modification to themselves. Using the prototype, we prove the concept that our approach can significantly improve the video quality over the traditional AODV routing protocol in a real system implementation.

A Staggered FEC System for Seamless Handoff in Wireless LANs: Implementation Experience and Experimental Study

We report the implementation experience and experimental evaluation of a staggered adaptive forward error correction (FEC) system for video multicast over wireless LANs. In the system, the parity packets generated by a cross-packet FEC code are transmitted at a time delay from the original video packets, i.e. staggercasting video stream and FEC stream in different multicast groups. The delay provides temporal diversity to improve the robustness of video multicast, especially to enable the clients to correct burst packet loss using FEC and to achieve seamless handoff. A wireless client dynamically joins the FEC multicast groups based upon its channel conditions and handoff events. We have implemented the system including the streaming server and client proxy. A novel software architecture is designed to integrate the FEC functionality in the clients without requirement for changing the existing video player software. We conduct extensive experiments to investigate the impact of FEC overhead and the delay between the video stream and FEC stream to the video quality under different interference levels and mobile handoff durations. The efficacy of staggered adaptive FEC system on improving video multicast quality is demonstrated in real system implementation.

Feasibility Study of Video Distribution over WLANs in Dense Deployment

emerging technologies such as orthogonal frequency division multiplexing (OFDM) and multiple in multiple out (MIMO) has significantly increased the bandwidth of a wireless channel. A potential application of these technologies is to distribute digital video content over wireless in a home environment. However, video streaming is bandwidth demanding, and the number of interference free wireless channels is limited, selecting the best operating channel is critical to guarantee the quality of viewers experience. We study the feasibility of transmitting video over WLANs in a multi-dwelling unit environment; design a centralized channel selection algorithm that satisfies each clients demand, at the same time, takes the fairness and residual bandwidth into consideration. We use directed edge-weighted graph to model the interference between different basic service systems and classify APs into cooperative APs and non cooperative APs. Our simulation results show that using existing 802.11a channels, a feasible channel allocation scheme for video streaming over WLANs in a dense deployment can be found in most cases.