无线多跳混合路由视频传输

提出了一种同时利用机会路由和传统路由进行跨层优化的实时视频传输方法,通过将I帧和P帧分别利用不同路由进行传输,获得了比单独利用传统路由或机会路由更好的性能。     

无线多跳网络的自适应容量感知优化与控制技术

In wireless multimedia communications, it is extremely difficult to derive general end-to-end capacity results because of decentralized packet scheduling and the interference between communi-cating nodes. In this paper, we present a state-based channel capacity perception scheme to provide sta-tistical Quality-of-Service (QoS) guarantees under a medium or high traffic load for IEEE 802.11 wire-less multi-hop networks. The proposed scheme first perceives the state of the wireless link from the MAC retransmission information and extends this information to calculate the wireless channel capaci-ty, particularly under a saturated traffic load, on the basis of the interference among flows and the link state in the wireless multi-hop networks. Finally, the adaptive optimal control algorithm allocates a net-work resource and forwards the data packet by tak-ing into consideration the channel capacity deploy-ments in multi-terminal or multi-hop mesh net-works. Extensive computer simulations demonstrate that the proposed scheme can achieve better per-formance in terms of packet delivery ratio and net-work throughput compared to the existing capacity prediction schemes.     

Cross-Layer Optimized Conditions for QoS Support in Multi-Hop Wireless Networks with MIMO Links

Recent advances in antenna technology made it possible to build wireless devices with more than one antenna at affordable costs. Because multiple antennas offer wireless networks a potential capacity increase, they are expected to be a key part of next-generation wireless networks to support the rapidly emerging multimedia applications characterized by their high and diverse QoS requirements. This paper developed methods that exploit the benefits of multiple antennas to enable multi-hop wireless networks with flow-level QoS capabilities. The authors first propose a cross-layer table-driven statistical approach that allows each node to determine the amount of spatial reuse and/or multiplexing, offered by the multiple antennas that are available to it. The authors then use the developed statistical approach to derive sufficient conditions under which flow rates are guaranteed to be feasible. The derived conditions are multi-layer aware in the sense that they account for cross-layer effects between the PHY and the MAC layers to support QoS at higher layers. The authors evaluate and compare the derived sufficient conditions via extensive simulations. The authors show that the conditions result in high flow acceptance rates when used in multi-hop wireless networking problems such as QoS routing and multicommodity flow problems. The authors also demonstrate the importance and the effect of considering cross-layer couplings into the development of flow acceptance methods.     

Performance Modeling and Analysis of a Class of ARQ Protocols in Multi-Hop Wireless Networks

This paper models and analyzes the performances of a class of ARQ (automatic repeat request) protocols in a multi-hop wireless data network. The performance metric here is the number of transmissions required for successful delivery of a packet over a multi-hop path. By using a discrete-time Markov model, the distribution for the total required number of transmissions is modeled as phase type distribution. The effects of different network parameters-such as packet error rate in each hop, maximum number of allowable retransmissions at each hop and retransmission probability at each hop-on the required total number of transmissions are investigated. The novelty of this model is that the probability mass function (pmf) for the number of transmissions required for successful end-to-end delivery of a packet can be easily obtained under different hop-level error control policies. Using the pmf, the tradeoff between transmission energy and percentage of data delivery (i.e., reliability) in a multi-hop path can be analyzed. The analytical model is validated by simulations. While the proposed analytical framework is general enough to capture the impact of any MAC (medium access control) mechanism at each hop, we specifically present typical performance results under IEEE 802.11 DCF (distributed coordination function) MAC     

Smart-Aloha for Multi-Hop Wireless Networks

This paper presents a novel slotted ALOHA-based protocol for use in ad hoc networks where nodes are equipped with adaptive array smart antennas. The protocol relies on the ability of the antenna and DoA (Direction of Arrival) algorithms to identify the direction of transmitters and then beamform appropriately to maximize SINR (Signal to Interference and Noise Ratio) at the receiver. The performance of the protocol is evaluated using analytical modeling as well as detailed simulation in OPNET and Matlab where we demonstrate the benefits of using smart antennas. The impact of using different number of antenna elements is also studied for this environment.This work is funded by the NSF under grant ANIR-0125728.Harkirat Singh is a PhD candidate in Computer Science at Portland State University. He holds Master in Computer Science from Portland State University and B. E. in Electrical Engineering from Indian Institute of Technology (IIT), Roorkee, India. After his under graduation he joined Automation division of Siemens AG. He has research interests in next-generation TCP/IP networking, Mobile Wireless Computing, Ad-hoc networking, and low-power lost-cost sensor networks.Suresh Singh received his B. Tech. Degree in Computer Science from the Indian Institute of Technology (IIT) Kanpur in 1984 and his Ph.D. degree in 1990 from the University of Massachusetts at Amherst, both in Computer Science. His areas of research include energy-efficient protocols for wireless networking, sensor networks, cellular networking with a focus on 3g standards, and performance evaluation. His work has been funded by several federal agencies such as NSF, DARPA, and ONR and by a variety of industries. He is a member of the ACM and IEEE.     

Asynchronous Congestion Control in Multi-Hop Wireless Networks With Maximal Matching-Based Scheduling

We consider a multi-hop wireless network shared by many users. For an interference model that constrains a node to either transmit to or receive from only one other node at a time, and not to do both, we propose an architecture for fair resource allocation that consists of a distributed scheduling algorithm operating in conjunction with an asynchronous congestion control algorithm. We show that the proposed joint congestion control and scheduling algorithm supports at least one-third of the throughput supportable by any other algorithm, including centralized algorithms.      

Characterizing Achievable Rates in Multi-Hop Wireless Mesh Networks With Orthogonal Channels

This paper considers the problem of determining the achievable rates in multi-hop wireless mesh networks with orthogonal channels. We classify wireless networks with orthogonal channels into two types, half duplex and full duplex, and consider the problem of jointly routing the flows and scheduling transmissions to achieve a given rate vector. We develop tight necessary and sufficient conditions for the achievability of the rate vector. We develop efficient and easy to implement Fully Polynomial Time Approximation Schemes for solving the routing problem. The scheduling problem is a solved as a graph edge-coloring problem. We show that this approach guarantees that the solution obtained is within 50% of the optimal solution in the worst case (within 67% of the optimal solution in a common special case) and, in practice, is close to 90% of the optimal solution on the average. The approach that we use is quite flexible and can be extended to handle more sophisticated interference conditions, and routing with diversity requirements.     

Optimization of Hybrid ARQ for IP Packet Transmission

This paper presents, optimizes, and analyzes the performance of a novel hybridSelective Repeat/Multi Copy(SR/MC) Automatic Repeat Request (ARQ) scheme for transmitting fragmentedInternetProtocol (IP) packets. The ARQ scheme works in the SR mode until the last IPpacket fragment istransmitted. If a fragment is negatively acknowledged after the last fragmentis transmitted, then the system goes into theMC mode. In the MC mode, multiple copies of the erroneous fragment aretransmitted. After the IPfragments are received without error, the system returns to the SR mode.The optimization of the ARQ is done in terms of two parameters: fragment sizeand the optimum number of packetsto be transmitted in the MC mode, M. Optimum values for both parameters arecalculated for Bit ErrorRate (BER), throughput, IP packet size, and delay. The fragment size is alsocalculated for actual datathroughput for a given IP packet size, both with and without Forward ErrorCorrection (FEC). Then,the performance of the proposed scheme is evaluated in terms of BER andIP packet size with theoptimum M and fragment size. Performance results are obtained with and withoutBose ChaudhuriHocquenghem (BCH) error correction codes under Additive White Gaussian Noise(AWGN) as wellas Flat Rayleigh Fading channels. The ARQ scheme gives optimum performance forM equal to 10fragments and fragment size of 75 bytes. Under the AWGN channel, a throughputof 0.9 is achieved for any IPpacket size and at higher BER conditions compared to the Selective Repeat +Stutter Scheme 2 (SR + ST 2).An 8 dB improvement is achieved under the flat Rayleigh fading channel usingBCH(63, 51, 2) for a throughputof 0.9.     

Efficient Cache Placement in Multi-Hop Wireless Networks

In this paper, we address the problem of efficient cache placement in multi-hop wireless networks. We consider a network comprising a server with an interface to the wired network, and other nodes requiring access to the information stored at the server. In order to reduce access latency in such a communication environment, an effective strategy is caching the server information at some of the nodes distributed across the network. Caching, however, can imply a considerable overhead cost; for instance, disseminating information incurs additional energy as well as bandwidth burden. Since wireless systems are plagued by scarcity of available energy and bandwidth, we need to design caching strategies that optimally trade-off between overhead cost and access latency. We pose our problem as an integer linear program. We show that this problem is the same as a special case of the connected facility location problem, which is known to be NP-hard. We devise a polynomial time algorithm which provides a suboptimal solution. The proposed algorithm applies to any arbitrary network topology and can be implemented in a distributed and asynchronous manner. In the case of a tree topology, our algorithm gives the optimal solution. In the case of an arbitrary topology, it finds a feasible solution with an objective function value within a factor of 6 of the optimal value. This performance is very close to the best approximate solution known today, which is obtained in a centralized manner. We compare the performance of our algorithm against three candidate cache placement schemes, and show via extensive simulation that our algorithm consistently outperforms these alternative schemes.     

Performance Analysis for Asynchronous Requests in Wireless Networks with Multiple Packet Reception Capability

Wireless Personal Communications - Fifth generation (5G), the currently evolving communication standard, promises better performance in terms of capability, capacity, speed, latency, etc. than...     

Content-Aware Resource Allocation and Packet Scheduling for Video Transmission over Wireless Networks

A cross-layer packet scheduling scheme that streams pre-encoded video over wireless downlink packet access networks to multiple users is presented. The scheme can be used with the emerging wireless standards such as HSDPA and IEEE 802.16. A gradient based scheduling scheme is used in which user data rates are dynamically adjusted based on channel quality as well as the gradients of a utility function. The user utilities are designed as a function of the distortion of the received video. This enables distortion-aware packet scheduling both within and across multiple users. The utility takes into account decoder error concealment, an important component in deciding the received quality of the video. We consider both simple and complex error concealment techniques. Simulation results show that the gradient based scheduling framework combined with the content-aware utility functions provides a viable method for downlink packet scheduling as it can significantly outperform current content-independent techniques. Further tests determine the sensitivity of the system to the initial video encoding schemes, as well as to non-real-time packet ordering techniques.     

无线数据传输中的混合ARQ

本文针对无线数据传输中的混合ARQ,介绍了混合ARQ的基本概念和技术,重点分析评述了用于混合ARQ系统中的各种包合并方案和相关的纠错编码技术,并对混合ARQ的相关研究工作进行了展望.     

Efficient Partial Relaying Protocol for Wireless Multi-Hop Transmission

We propose a multi-hop transmission protocol suitable for the reverse link of cellular systems. The proposed protocol, referred to as cooperative multiplexing with partial relaying (CM-PR), is based on relaying of partial information bits followed by cooperative multiplexing. The CM-PR protocol provides path loss reduction and spatial diversity gain without any loss in the spectral efficiency, in contrast to the conventional decode-and-forward protocol or its variants that cause bandwidth expansion to attain such benefits. Simulation results confirm that the CM-PR protocol significantly outperforms the direct transmission in terms of the bit error rate, especially when a relay is close to the source.     

Optimal Transmit Power in Wireless Sensor Networks

Power conservation is one of the most important issues in wireless ad hoc and sensor networks, where nodes are likely to rely on limited battery power. Transmitting at unnecessarily high power not only reduces the lifetime of the nodes and the network, but also introduces excessive interference. It is in the network designer's best interest to have each node transmit at the lowest possible power while preserving network connectivity. In this paper, we investigate the optimal common transmit power, defined as the minimum transmit power used by all nodes necessary to guarantee network connectivity. This is desirable in sensor networks where nodes are relatively simple and it is difficult to modify the transmit power after deployment. The optimal transmit power derived in this paper is subject to the specific routing and medium access control (MAC) protocols considered; however, the approach can be extended to other routing and MAC protocols as well. In deriving the optimal transmit power, we distinguish ourselves from a conventional graph-theoretic approach by taking realistic physical layer characteristics into consideration. In fact, connectivity in this paper is defined in terms of a quality of service (QoS) constraint given by the maximum tolerable bit error rate (BER) at the end of a multihop route with an average number of hops.     

Optimal Joint Diversity and Power Control for Wireless Networks

We propose in this paper an efficient method to derive the optimal feasible power and weight for joint diversity and power control. Instead of solving a constrained optimization problem where both the variables of power and the variables of weight are involved, this method simply solves a set of equations where only the variables of power are involved. It is proven that the power and weight obtained from the proposed method can minimize the power consumption. To reduce the computational complexity, we further propose another method where the number of equations can be reduced from the number of users to the number of base stations.

Correlated Link Shadow Fading in Multi-Hop Wireless Networks

Accurate representation of the physical layer is required for analysis and simulation of multi-hop networking in sensor, ad hoc, and mesh networks. Radio links that are geographically proximate often experience similar environmental shadowing effects and thus have correlated shadowing. This paper presents and analyzes a non-site-specific statistical propagation model which accounts for the correlations that exist in shadow fading between links in multi-hop networks. We describe two measurement campaigns to measure a large number of multi-hop networks in an ensemble of environments. The measurements show statistically significant correlations among shadowing experienced on different links in the network, with correlation coefficients up to 0.33. Finally, we analyze multi-hop paths in three and four node networks using both correlated and independent shadowing models and show that independent shadowing models can underestimate the probability of route failure by a factor of two or greater.     

面向路径的无线多跳网络端-端吞吐量分析

基于802.11 DCF机制的无线多跳网络性能深受MAC层的介质访问机制和上层路由机制相互作用的影响.本文面向自组织网络路径,给出了端-端最优吞吐量的模型以及计算其上下界的方法.本文的研究更加注重无线多跳网络的实际特性:分组调度可以任意方式调度,节点的载波侦听范围大于其传输范围.研究发现路径的端到端吞吐量与路径长度、分组发送速率和分组调度策略等因素密切相关.本文还分析了其他因素对端-端带宽的影响程度.本文从面向路径的分析模拟工作中得出的一些独特结论相信将有助于上层应用程序以及路由协议的研究.     

Delay Aware Link Scheduling for Multi-Hop TDMA Wireless Networks

Time division multiple access (TDMA) based medium access control (MAC) protocols can provide QoS with guaranteed access to the wireless channel. However, in multi-hop wireless networks, these protocols may introduce scheduling delay if, on the same path, an outbound link on a router is scheduled to transmit before an inbound link on that router. The total scheduling delay can be quite large since it accumulates at every hop on a path. This paper presents a method that finds conflict-free TDMA schedules with minimum scheduling delay. We show that the scheduling delay can be interpreted as a cost, in terms of transmission order of the links, collected over a cycle in the conflict graph. We use this observation to formulate an optimization, which finds a transmission order with the min-max delay across a set of multiple paths. The min-max delay optimization is NP-complete since the transmission order of links is a vector of binary integer variables. We devise an algorithm that finds the transmission order with the minimum delay on overlay tree topologies and use it with a modified Bellman-Ford algorithm, to find minimum delay schedules in polynomial time. The simulation results in 802.16 mesh networks confirm that the proposed algorithm can find effective min-max delay schedules.     

Energy Efficiency and Capacity for TCP Traffic in Multi-Hop Wireless Networks

We study the performance metrics associated with TCP-regulated traffic in multi-hop, wireless networks that use a common physical channel (e.g., IEEE 802.11). In contrast to earlier analyses, we focus simultaneously on two key operating metrics—the energy efficiency and the transport-layer (TCP) throughput. Using analysis and simulations, we show how these metrics are strongly influenced by the radio transmission range of individual nodes. Due to tradeoffs between the individual packet transmission energy and the likelihood of retransmissions, the total energy consumption is a convex function of the number of hops (and hence, of the transmission range). On the other hand, the throughput of a single TCP session decreases with a decrease in the transmission range. The overall achievable TCP throughput in an ad-hoc network thus involves a tradeoff between the reduced throughput of an individual flow and the greater degree of spatial reuse possible. As a consequence of this tradeoff, the overall network capacity turns out to be a concave function of the transmission range. We analyze how parameters such as the node density and the radio transmission range affect the overall network capacity under different operating conditions. Our analysis shows that capacity metrics at the TCP layer behave quite differently from the capacity results previously presented in literature. We then extend the work and examine the sensitivity of the TCP-layer capacity to the speed of the nodes and the number of TCP connections in an ad hoc network. By incorporating the notion of a minimal acceptable QoS metric (loss) for an individual session, we show why the QoS-compliant capacity is a more accurate metric for studying the capacity of TCP traffic in an ad hoc network. Finally, we study the dependence of capacity on the source application (Telnet or FTP traffic) and on the choice of the ad hoc routing protocol (AODV, DSR or DSDV). Sorav Bansal is a graduate student in the Electrical Engineering Department at Stanford University,where he is currently working on Participation Incentives inMobile Networks. His primary research interests lie in Mobile Computing, Embedded Devices and Sensor Networks. Sorav holds a B.Tech. in Computer Science from Indian Institute of Technology, Delhi, and spent a summer interning at IBM Almaden Research Center. Rajeev Shorey is a research staff member at the IBM India Research Laboratory, New Delhi since March 1998. He received the Bachelor of Engineering (B.E) degree in Computer Science from the department of Computer Science and Automation, Indian Institute of Science, Bangalore, India in 1987. He received the M.S and Ph.D degrees in Electrical Communication Engineering from the Indian Institute of Science, Bangalore, India, in 1990 and 1996 respectively. Since March 1998, he is a Research Staff Member at the IBM India Research Laboratory, Indian Institute of Technology, New Delhi, India. His research interests include wireless LANs and wireless PANs, Internet protocols, performance modeling and analysis of wireline and wireless networks. Dr. Shorey has published numerous papers in international journals and conferences. He has to his credit one IBM US patent and around 8US patents that are pending, all in the area of networking. He serves on the technical program committee of several international conferences in networking, namely, IEEE Infocom 2004 and IEEE ICC 2004. In the past, hewas serving in the technical program committee for Infocom 2003 and Infocom 2002, Globecom 2002 and Globecom 2001 and ICC 2003. He is an adjunct faculty in the department of Computer Science and Engineering, Indian Institute of Technology, New Delhi where he actively teaches and guides undergraduate and graduate students. He is a senior member of IEEE. Archan Misra is currently a Research Staff Member with the Pervasive Security and Networking Department at the IBM TJ Watson Research Center, Hawthorne, NY. He is presently working on services and mobility protocols for next-generation (4G) wireless networks, middleware for location and context-aware data composition, scalable infrastructure for on-demand distributed computing and MAC/routing protocols for energy-efficient, high-performance wireless networks. Before joining IBM in March 2001, Archan spent 3 1/2 years at Telcordia Technologies (formerly called Bellcore), where he was responsible for several initiatives in the areas of IP-based mobility management, congestion control, QoS architectures and autoconfiguration of heterogeneous networks. As part of his research efforts, Archan co-invented the IDMP mobility management and the DCDP autoconfiguration protocols. He has published over fifty papers in the areas of wireless networking, congestion control and mobility management and received the Best Paper awards in ACMWOWMOM 2002 and IEEE MILCOM 2001. Archan received his Ph.D. in Electrical and Computer Engineering from the University of Maryland at College Park in May, 2000, and his B.Tech in Electronics and Communication Engineering from IIT Kharagpur, India in July 1993.     

Asymptotically Optimal Transmission Policies for Large-Scale Low-Power Wireless Sensor Networks

We consider wireless sensor networks with multiple gateways and multiple classes of traffic carrying data generated by different sensory inputs. The objective is to devise joint routing, power control and transmission scheduling policies in order to gather data in the most efficient manner while respecting the needs of different sensing tasks (fairness). We formulate the problem as maximizing the utility of transmissions subject to explicit fairness constraints and propose an efficient decomposition algorithm drawing upon large-scale decomposition ideas in mathematical programming. We show that our algorithm terminates in a finite number of iterations and produces a policy that is asymptotically optimal at low transmission power levels. Furthermore, we establish that the utility maximization problem we consider can, in principle, be solved in polynomial time. Numerical results show that our policy is near-optimal, even at high power levels, and far superior to the best known heuristics at low power levels. We also demonstrate how to adapt our algorithm to accommodate energy constraints and node failures. The approach we introduce can efficiently determine near-optimal transmission policies for dramatically larger problem instances than an alternative enumeration approach