Mingquan Wu

Exploiting Multiple Antennas in Cooperative Cognitive Radio Networks

Recently, a new paradigm for cognitive radio networks has been advocated, where primary users (PUs) recruit secondary users (SUs) to cooperatively relay the primary traffic and in return grant the SUs the right to access the channel. However, all existing studies on such cooperative cognitive radio networks (CCRNs) operate in the temporal domain only, which limits the performance of both PUs and SUs. On the other hand, multiple-input-multiple-output (MIMO) enables transmission of multiple independent data streams in the spatial domain to improve capacity. Taking advantage of the MIMO technique in CCRNs is an unexplored area that we investigate in this paper. We propose a novel MIMO-CCRN framework, which enables the SUs to utilize MIMO techniques to cooperatively relay the traffic for the PUs, while concurrently accessing the same channel to transmit their own traffic. Specifically, we consider two typical network scenarios. For the case of a general PU link and multiple SUs, we provide theoretical analysis for the link rates and then formulate an optimization model based on a Stackelberg game to maximize the utilities of PUs and SUs. In addition, we extend our analysis to a practical cellular network with multiple MIMO-empowered femtocells, and provide an algorithm to find a stable matching of the PUs and SUs. Evaluation results show that high utility gains are achieved by both PUs and SUs by leveraging MIMO spatial cooperation in our proposed framework.

On Wide Area Network Optimization

Applications, deployed over a wide area network (WAN) which may connect across metropolitan, regional or national boundaries, suffer performance degradation owing to unavoidable natural characteristics of WANs such as high latency and high packet loss rate. WAN optimization, also known as WAN acceleration, aims to accelerate a broad range of applications and protocols over a WAN. In this paper, we provide a survey on the state of the art of WAN optimization or WAN acceleration techniques, and illustrate how these acceleration techniques can improve application performance, mitigate the impact of latency and loss, and minimize bandwidth consumption. We begin by reviewing the obstacles in efficiently delivering applications over a WAN. Furthermore, we provide a comprehensive survey of the most recent content delivery acceleration techniques in WANs from the networking and optimization point of view. Finally, we discuss major WAN optimization techniques which have been incorporated in widely deployed WAN acceleration products - multiple optimization techniques are leveraged by a single WAN accelerator to improve application performance in general.

On Accelerating Content Delivery in Mobile Networks

Owing to the imminent fixed mobile convergence, Internet applications are frequently accessed through mobile devices. Given limited bandwidth and unreliable wireless channels, content delivery in mobile networks usually experiences long delay. To accelerate content delivery in mobile networks, many solutions have been proposed. In this paper, we present a comprehensive survey of most relevant research activities for content delivery acceleration in mobile networks. We first investigate the live network measurements, and identify the network obstacles that dominate the content delivery delays. Then, we classify existing content delivery acceleration solutions in mobile networks into three categories: mobile system evolution, content and network optimization, and mobile data offloading, and provide an overview of available solutions in each category. Finally, we survey the content delivery acceleration solutions tailored for web content delivery and multimedia delivery. For web content delivery acceleration, we overview existing web content delivery systems and summarize their features. For multimedia delivery acceleration, we focus on accelerating HTTP-based adaptive streaming while briefly review other multimedia delivery acceleration solutions. This paper presents a timely survey on content delivery acceleration in mobile networks, and provides a comprehensive reference for further research in this field.

Network-embedded FEC for optimum throughput of multicast packet video☆

Forward error correction (FEC) schemes have been proposed and used successfully for multicasting realtime video content to groups of users. Under traditional IP multicast, application-level FEC can only be implemented on an end-to-end basis between the sender and the clients. Emerging overlay and peer-to-peer (p2p) networks open the door for new paradigms of network FEC. The deployment of FEC within these emerging networks has received very little attention (if any). In this paper, we analyze and optimize the impact of network-embedded FEC (NEF) in overlay and p2p multimedia multicast networks. Under NEF, we place FEC codecs in selected intermediate nodes of a multicast tree. The NEF codecs detect and recover lost packets within FEC blocks at earlier stages before these blocks arrive at deeper intermediate nodes or at the final leaf nodes. This approach significantly reduces the probability of receiving undecodable FEC blocks. In essence, the proposed NEF codecs work as signal regenerators in a communication system and can reconstruct most of the lost data packets without requiring retransmission. We develop an optimization algorithm for the placement of NEF codecs within random multicast trees. Based on extensive H.264 video simulations, we show that this approach provides significant improvements in video quality, both visually and in terms of PSNR values.

Experimental study on wireless multicast scalability using Merged Hybrid ARQ with staggered adaptive FEC

We report the design, implementation and evaluation of Merged Hybrid ARQ with staggered FEC (MHARQ) system for video multicast over wireless LANs. MHARQ combines the advantages of receiver-driven staggered FEC and hybrid ARQ schemes to compensate the large dynamic range of WLAN channels and to achieve high reliability, scalability and wireless bandwidth efficiency for video multicast. The FEC packets generated by a cross-packet FEC code are divided into multiple streams according to the pre-configured overhead and are transmitted in different multiple IP multicast groups. Certain FEC streams are delayed from the original video stream. The receivers dynamically join/leave the FEC multicast groups based on the channel conditions. For efficient utilization of WLAN bandwidth, FEC data for a multicast group would not be transmitted by the APs in wireless networks if no receiver joins this group. The time shift between the video stream and the FEC streams introduces temporal diversity and compensates for the client join delay and handoff interruption. In addition, when delayed FEC packets are not enough to recover the lost packets, the receivers can send a hybrid ARQ request to the video server. We design a channel estimation algorithm for a receiver to dynamically determine the delayed FEC multicast groups to join and/or send ARQ NACK to request for retransmission. Using the ORBIT radio grid testbed, we have investigated the performance of the proposed MHARQ system with various numbers of users per AP and different number of APs per video server. It is demonstrated via real system implementation on ORBIT that MHARQ improves wireless bandwidth efficiency and scalability for reliable video multicast, compared with existing reliable multicast schemes.

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.

Network embedded FEC (NEF) for video multicast in presence of packet loss correlation

Network embedded forward error correction (NEF) framework is a paradigm shift from a conventional approach of providing forward error correction (FEC) only on an end-to-end basis. Previous work on NEF has shown promise in greatly improving the decodable probability, message throughput and video quality available to the end receiver. However the utility of NEF for video applications in presence of packet loss correlation has not been evaluated as yet. In practice, packet losses are often correlated and occur in bursts. The distortion in video can be sensitive to the bursty nature of the losses. Thus in this paper we analyze the performance of NEF within random multicast distribution trees that exhibit losses-with-memory over their branches. We utilized the Gilbert model for packet losses over each link. We quantify the performance improvement of NEF over conventional end-to-end FEC in terms of improvement in video quality in presence of packet loss correlation. Embedding NEF codecs can impact the sensitivity of video quality to packet loss correlation. We explicitly evaluate as to how NEF can alter the dependence of video quality on packet loss burstiness. Finally we show that in addition to an average improvement in video quality, NEF can improve the performance in terms of quality guarantees also.

Software defined network-enabled multicast for multi-party video conferencing systems

Providing well-satisfactory multi-party video conferencing service is remarkably challenging, which demands not only high bandwidth but also low latency. Current commercial implementations typically use one or multiple multipoint control units (MCUs) as the central points for distributing video bit-streams to all participants in the conferencing session. Such MCU-based solution has limited control on quality of service (QoS), which may cause large delay, single-point malfunction and communication bottleneck for entire system. Recent years have witnessed the emergence of a new paradigm in networking, software defined networking (SDN), which advocates separating data plane and control plane, making network switches in the data plane simple packet forwarding devices and leaving a logically centralized controller to manipulate network behaviors. SDN provides the flexibility of changing underlying infrastructure and makes it possible to radically provide service/flow-aware QoS guarantee. In this paper, we propose a novel architecture for multi-party video conferencing by utilizing SDN-enabled multicasting, where SDN controller helps media controller to buildup multicast trees for video flows originated at video parties. To realize the architecture, we correspondingly propose a novel multicast construction and packing method, in which multiple source-based multicast trees are constructed and integrated to maximize system-wide utility while guaranteeing an end-to-end delay bound. Extensive simulations demonstrate that it could provide better video delivery compared to the conventional MCU-based solution in terms of video rate and delay in both sparsely and densely distributed networks.

End-to-End Performance Aware Association in Wireless Municipal Mesh Networks

In wireless municipal mesh (muni mesh) networks, a client station needs to associate with a mesh access point (MAP) in order to access the network. The end-to-end performance of a station depends on the access link quality between the station and the associated MAP as well as the multi-hop path quality from the associated MAP to the Internet gateway. However conventional association mechanisms used for single-hop WLANs assume that the wireless access link is the bottleneck and do not take the backhaul conditions into account, which may result in poor performance in muni mesh networks. In this paper, we propose a new joint MAP association mechanism for muni mesh networks to achieve optimal end-to-end communication performance from the station to the gateway. A station associates to one of its nearby MAPs by jointly considering the transmission capability of the access link and the backhual path. In addition, we design a new metric, called CAETT, to measure the access link quality. Different from previously proposed link metrics, CAETT takes into account the impact of 802.11 MAC layer contention on bandwidth sharing among the stations with multi-rate capability. It yields more accurate link throughput estimation. Furthermore, in order to reduce the association time, we develop an analytical model and propose a hybrid measurement/estimation method to enable a station to quickly determine the CAETT. We evaluate the performance of our system through simulations and demonstrate that the proposed joint association mechanism with the CAETT metric can greatly improve the end-to-end performance for the stations.