Internet Protocol Television (IPTV) has become the application that drives the Internet to a new height. However, challenges still remain in IPTV in-home distribution. The high-quality video streaming in IPTV services demands home networks to deliver video streaming packets with stringent Quality-of-Service (QoS) requirements. Currently, most service providers recommend Ethernet-based broadband home networks for IPTV. However, many existing houses are not wired with Ethernet cables and the rewiring cost is prohibitively expensive. Therefore, wireless solutions are preferred if their performance can meet the requirements. IEEE 802.11 wireless local area networks (WLANs) are pervasively adopted in home networks for their flexibility and affordability. However, through our experiments in the real environment, we found that the conventional single-hop infrastructure mode WLANs have very limited capacity and coverage in a typical in-door environment due to high attenuation and interference. The single-hop wireless networks cannot provide support for high-quality video streaming to the entire house. Multi-hop wireless networks are therefore used to extend the coverage. Contrary to the common believes that adding relay routers in the same wireless channel should reduce the throughput, our experiment, analysis and simulation results show that the multi-hop IEEE 802.11 WLANs can improve both the capacity and coverage in certain scenarios, and sufficiently support high-quality video streaming in a typical house. In this research, we analyzed and evaluated the performance of H.264-based video streaming over multi-hop wireless networks. Our analysis and simulation results reveal a wide spectrum of coverage-capacity tradeoff of multi-hop wireless networks in generic scenarios. More- over, we discuss the methods of how to further improve video streaming performance. This research provides the guidance on how to achieve the optimal balance for a given scenario, which is of great i.
Internet Protocol Television (IPTV) has become the application that drives theInternet to a new height. However, challenges still remain in IPTV in-home distribution. The high-quality video streaming in IPTV services demands home networks to deliver video streaming packets with stringent Quality-of-Service (QoS) requirements. Currently, most service providers recommend Ethernet-based broadband home networks for IPTV. However, many existing houses are not wired with Ethernet cables and the rewiring cost is prohibitively expensive. Therefore, wireless solutions are preferred if their performance can meet the requirements. IEEE 802.11 wireless local area networks (WLANs) are pervasively adopted in home networks for their flexibility and affordability. However, through our experiments in the real environment, we found that the conventional single-hop infrastructure mode WLANs have very limited capacity and coverage in a typical in-door environment due to high attenuation and interference. The single-hop wireless networks cannot provide supportfor high-quality video streaming to the entire house. Multi-hop wireless networksare therefore used to extend the coverage. Contrary to the common believes that adding relay routers in the same wireless channel should reduce the throughput, our experiment, analysis and simulation results show that the multi-hop IEEE 802.11 WLANs can improve both the capacity and coverage in certain scenarios, and sufficiently support high-quality video streaming in a typical house. In this research, we analyzed and evaluated the performance of H.264-based video streaming over multi-hop wireless networks. Our analysis and simulation results reveal a wide spectrum ofcoverage-capacity tradeoff of multi-hop wireless networks in generic scenarios. More-over, we discuss the methods of how to further improve video streaming performance. This research provides the guidance on how to achieve the optimal balance for a givenscenario, which is of great importance when deploying end-to-end IPTV services withQoS guarantee.
Multimedia networking applications and, in particular, the transport of c- pressed video are expected to contribute signi?cantly to the tra?c in the future Internet and wireless networks. For transport over networks, video is typically encoded (i. e., compressed) to reduce the bandwidth requirements. Even compressed video, however, requires large bandwidths of the order of hundred kbps or Mbps. In addition, compressed video streams typically - hibit highly variable bit rates (VBR) as well as long range dependence (LRD) properties. This, in conjunction with the stringent Quality of Service (QoS) requirements (loss and delay) of video tra?c, makes the transport of video tra?covercommunicationnetworksachallengingproblem. Asaconsequence, in the last decade the networking research community has witnessed an - plosion in research on all aspects of video transport. The characteristics of video tra?c, video tra?c modeling, as well as protocols and mechanisms for the e?cient transport of video streams, have received a great deal of interest among networking researchers and network operators and a plethora of video transport schemes have been developed. For developing and evaluating video transport mechanisms and for - search on video networking in general, it is necessary to have available some characterizationofthevideo. Generally, therearethreedi?erentwaystoch- acterize encoded video for the purpose of networking research: (i)video tra?c model, (ii) video bit stream, and (iii) video tra?c trace.
Multimedia applications like video streaming and video conferencing are increasing rapidly over wireless networks. Video data is delay-sensitive and requires more bandwidth to be sent. Wireless channel has limited bandwidth and is prone to errors due to time-varying signal strength, which limits the availability of bandwidth for these applications. Hence, video compression techniques are crucial for video applications. The H.264/AVC video coding standard is widely used for streaming applications due to its high coding efficiency and the network friendly features. Loss of different packets in a video stream induces different amounts of distortion to the video quality; therefore, video bit stream should be prioritized. The basic IEEE 802.11 MAC protocol does not provide quality of service support to the users and cannot be used as the main access mechanism for transmitting prioritized video. In this thesis, we design a cross-layer and priority aware packet fragmentation scheme which transmits pre-encoded compressed H.264 video on IEEE 802.11e EDCA based MAC layer to enhance the video quality over error-prone wireless networks. Data fragmentation modifies the packet size by adapting to the varying channel conditions and improves successful video transmission. We also study the optimal packet size to maximize the weighted goodput for different number of users and channels bit error rates.
As development of wireless networking technologies continues, it has been increasingly expected to support content-rich multimedia communications (e.g., video) in such networks. In this dissertation, we study the important problems of enhancing QoS support for video applications in wireless mesh networks and LTE networks. We begin our investigation with a video performance evaluation study in a wireless mesh test-bed. The goal is to clearly understand the nature of video streaming and its performance in wireless mesh networks. By extensive experiments in various scenarios we analyze the network parameters and settings which impact video performance. Compared with simulation or network-layer statistics based approaches, our investigation is directly focused on video quality in multi-hop scenarios. The experimental results better represent the characteristics of real networks and reveal the interesting aspects of video performance in mesh networks, which may benefit the design of efficient QoS solutions for multimedia services in wireless mesh networks. Next, we explore the interference issue in wireless mesh networks, and propose an interference-aware admission control and QoS routing scheme, towards enhancing video streaming experience in wireless mesh networks. Interference is characterized using a conflict graph based model. Nodes exchange their flow information periodically and compute their available residual bandwidth based on the local maximal clique constraints. Admission decision is made based on the residual bandwidth at each node. An on-demand routing scheme is implemented to explicitly incorporate the interference model in the route discovery process. By avoiding the "hot-spots" with severe interference, it discovers the routes with less interference and enhances video performance significantly. We also leverage MAC layer retransmission counts to design a combined queuing and routing scheme which achieves better video quality than the existing approaches. A case study is performed focusing on MAC layer retransmission, which helps us better understand the impacting factors on video quality in multi-hop mesh networks. Our scheme is proposed from a cross-layer perspective which leverages the information across network (routing) layer and link (MAC) layer. MAC layer retransmission count is exploited to guide the interface queue management for video packets as well as a metric to construct a retransmission-aware QoS routing scheme. In our approach, the upper layers are aware of the dynamic network status via retransmission count, so timely QoS decision can be made to enhance video quality effectively. For LTE networks, our focus is radio resource management. We first investigate the important problem of downlink resource allocation in recently enhanced LTE-Advanced systems where a newly added feature, carrier aggregation, provides more flexibility in resource allocation in addition to the existing resource block level packet scheduling. The resource allocation problem is formulated as a complex combinatorial problem with multiple constraints. We decompose this highly complex optimization problem and construct a two-tier resource allocation framework which incorporates dynamic component carrier assignment and novel backlog based scheduling schemes with intelligent link adaptation based on weighted CQI. The proposed schemes offer both better throughput and delay performance as well as user fairness. Finally, we address the downlink scheduling problem in LTE networks by directly optimizing video quality. Unlike the conventional scheduling rules which exploit network layer metrics, our scheme is directly targeted on optimizing application-layer video quality. Video quality optimized scheduling is formulated as a complex combinatorial optimization problem, and solved by exploiting a GA (genetic algorithm) based metaheuristic approach. The intrinsic strength of population based solution of GA offers a superior advantage for this type of scheduling problems. Simulation results demonstrate the effectiveness of GA based scheduling scheme compared with the well-known M-LWDF scheduling rule and the simulated annealing method. It can offer better video quality at the receiver within the required delay bound.
While there are countless books on wireless networks, few actually quantify the key performance-limiting factors of wireless local area networks (WLANs) and describe various methods for improving WLAN performance. Fulfilling these needs, Improving the Performance of Wireless LANs: A Practical Guide provides both theoretical background and empirical
Although the existing layering infrastructure--used globally for designing computers, data networks, and intelligent distributed systems and which connects various local and global communication services--is conceptually correct and pedagogically elegant, it is now well over 30 years old has started create a serious bottleneck. Using Cross-Layer Techniques for Communication Systems: Techniques and Applications explores how cross-layer methods provide ways to escape from the current communications model and overcome the challenges imposed by restrictive boundaries between layers. Written exclusively by well-established researchers, experts, and professional engineers, the book will present basic concepts, address different approaches for solving the cross-layer problem, investigate recent developments in cross-layer problems and solutions, and present the latest applications of the cross-layer in a variety of systems and networks.
