Jiancong Chen

Multipath routing for video delivery over bandwidth-limited networks

The delivery of quality video service often requires high bandwidth with low delay or cost in network transmission. Current routing protocols such as those used in the Internet are mainly based on the single-path approach (e.g., the shortest-path routing). This approach cannot meet the end-to-end bandwidth requirement when the video is streamed over bandwidth-limited networks. In order to overcome this limitation, we propose multipath routing, where the video takes multiple paths to reach its destination(s), thereby increasing the aggregate throughput. We consider both unicast (point-to-point) and multicast scenarios. For unicast, we present an efficient multipath heuristic (of complexity O(|V|/sup 3/)), which achieves high bandwidth with low delay. Given a set of path lengths, we then present and prove a simple data scheduling algorithm as implemented at the server, which achieves the theoretical minimum end-to-end delay. For a network with unit-capacity links, the algorithm, when combined with disjoint-path routing, offers an exact and efficient solution to meet a bandwidth requirement with minimum delay. For multicast, we study the construction of multiple trees for layered video to satisfy the user bandwidth requirements. We propose two efficient heuristics on how such trees can be constructed so as to minimize the cost of their aggregation subject to a delay constraint.

Mixed-mode WLAN: the integration of ad hoc mode with wireless LAN infrastructure

In the traditional IEEE 802.11 wireless LAN using infrastructure mode, all users share the same channel and all packets are forwarded by an access point (AP). As a result, as the number of users in the cell increases, the throughput for each user degrades substantially. If there are users communicating with each other within the cell (as in conferencing or file exchange applications), such throughput degradation could be relieved by making these users communicate through ad hoc connections without going through the AP. The advantages are multi-fold. First, the traffic load at the AP is reduced, hence relieving the contention. Second, ad hoc connections are single-hop, hence improving the channel efficiency. Moreover, ad hoc connections could use different channels, hence multiplying the system bandwidth. In this paper, we propose to integrate the infrastructure mode and the ad hoc mode in a wireless network so as to achieve these advantages. We present a framework for such mixed-mode wireless LAN (termed M/sup 2/-WLAN). In such a network, a node can dynamically switch between the infrastructure mode and the ad hoc mode according to the instruction of the AP, and hence the switching is transparent to the users. Using simulations, we show that M/sup 2/-WLAN can indeed improve system throughput substantially without users manual configuration.

Multipath routing for video unicast over bandwidth-limited networks

Video applications, such as video-on-demand systems, in general have bandwidth and delay constraints. Such QoS requirements can no longer be guaranteed when video is transmitted with the traditional shortest-path routing over a bandwidth-limited network such as the Internet. We propose multipath routing algorithms for video unicast so as to meet a certain bandwidth requirement with minimum start-up delay (and hence low user buffer requirement). We first formulate the problem which in its most general form is difficult to solve. However, for the special case where the network links are of unit capacity, we present an exact solution using a k-shortest-disjoint paths algorithm with video rescheduling in the source. For the most general case, we propose an efficient heuristic based on max-flow and shortest path algorithms. The complexity of such an algorithm is only O(|V|/sup 3/), where |V| is the number of nodes in the network. Extensive simulation results show that the multipath approach meets the bandwidth requirement with a delay close to that of shortest-path routing.

A Framework to Relieve Wireless Hot-Spot Congestion by Means of Ad Hoc Connections

In recent years, wireless public networks have been widely deployed to provide high-speed Internet access to mobile users. Due to the dynamic and uneven distribution of user requests, some access points (the so-called “hot-spots”) may be congested by many users. In order to alleviate such congestion, we introduce an ad hoc relaying wireless LAN framework in this paper. A user can be served by a neighboring access point through an ad hoc connection in such a network. We propose a framework to establish such ad hoc connections. Using simulations, we show that the framework is efficient to reduce the service failure rate as well as to improve channel utilization in hot-spot networks.

A distributed power adaptation algorithm for multimedia delivery over ad hoc networks

There has been an increasing interest in recent years to deliver multimedia services over wireless ad hoc networks. Due to the existence of hidden terminal and absence of central control, the MAC protocol as used in the ad hoc networks may lead to channel capture, where some flows monopolize the channel while others suffer from starvation. This greatly degrades system throughput and fairness. After showing that static power control leads to channel capture, we propose and study a distributed dynamic power control scheme to break the capture. Our power control algorithm offers much higher fairness without compromising system throughput by better spatial reuse.