Cross-Layer Design for QoS Support in Multihop Wireless Networks

Due to such features as low cost, ease of deployment, increased coverage, and enhanced capacity, multihop wireless networks such as ad hoc networks, mesh networks, and sensor networks that form the network in a self-organized manner without relying on fixed infrastructure is touted as the new frontier of wireless networking. Providing efficient quality of service (QoS) support is essential for such networks, as they need to deliver real-time services like video, audio, and voice over IP besides the traditional data service. Various solutions have been proposed to provide soft QoS over multihop wireless networks from different layers in the network protocol stack. However, the layered concept was primarily created for wired networks, and multihop wireless networks oppose strict layered design because of their dynamic nature, infrastructureless architecture, and time-varying unstable links and topology. The concept of cross-layer design is based on architecture where different layers can exchange information in order to improve the overall network performance. Promising results achieved by cross-layer optimizations initiated significant research activity in this area. This paper aims to review the present study on the cross-layer paradigm for QoS support in multihop wireless networks. Several examples of evolutionary and revolutionary cross-layer approaches are presented in detail. Realizing the new trends for wireless networking, such as cooperative communication and networking, opportunistic transmission, real system performance evaluation, etc., several open issues related to cross-layer design for QoS support over multihop wireless networks are also discussed in the paper.     

无线通信的跨层优化

传统的OSI分层结构无法适应无线网络环境，随着越来越多无线应用的出现，人们提出了跨层设计，其主要内容就是通过在协议栈的各层之间（主要是应用层、传输层、网络层、链路层和物理层）传递特定的信息，使协议栈能够根据无线环境的变化来实现对资源的自适应优化配置，从而更有效的利用无线网络资源，提高系统的性能。     

Cross-layer feedback architecture for mobile device protocol stacks

Applications using traditional protocol stacks (e.g., TCP/IP) from wired networks do not function efficiently in mobile wireless environments. This is primarily due to the layered architecture and implementation of protocol stacks. One mechanism to improve the efficiency of the stack is cross-layer feedback, that is, making information from within one layer available to another layer of the stack. For example, TCP retransmissions can be reduced by making it aware of network disconnections or handoff events. We highlight the need for a cross-layer feedback architecture and identify key design goals for an architecture. We present our ECLAIR architecture, which satisfies these design goals. We describe a prototype implementation that validates ECLAIR. We also discuss other cross-layer architectures and provide a cross-layer design guide.     

下一代无线网络中的跨层设计

下一代无线通信系统必须能够与互联网实现信息交互,这就需要利用通信协议来实现系统与其他通信系统间的互连互通。但是,现有通信协议基于OSI标准,其协议栈按照严格的分层方式工作,很难适应快速变化的无线通信环境。通过对现有协议栈进行改进,加入跨层设计方案则有助于改善下一代无线系统性能。文章简要分析了分层协议栈局限性,讨论了跨层设计原理,并系统地阐述了跨层设计时物理层、链路层、网络层、传输层和应用层协议应考虑的因素。     

Application-driven cross-layer optimization for video streaming over wireless networks

Mobile multimedia applications require networks that optimally allocate resources and adapt to dynamically changing environments. Cross-layer design (CLD) is a new paradigm that addresses this challenge by optimizing communication network architectures across traditional layer boundaries. In this article we discuss the relevant technical challenges of CLD and focus on application-driven CLD for video streaming over wireless networks. We propose a cross-layer optimization strategy that jointly optimizes the application layer, data link layer, and physical layer of the protocol stack using an application-oriented objective function in order to maximize user satisfaction. In our experiments we demonstrate the performance gain achievable with this approach. We also explore the trade-off between performance gain and additional computation and communication cost introduced by cross-layer optimization. Finally, we outline future research challenges in CLD.     

Cross-Layer Architecture for Adaptive Video Multicast Streaming Over Multirate Wireless LANs

Multicast video streaming over multirate wireless LANs imposes strong demands on video codecs and the underlying network. It is not sufficient that only the video codec or only the underlying protocols adapt to changes in the wireless link quality. Research efforts should be applied in both and in a synchronized way. Cross layer design is a new paradigm that addresses this challenge by optimizing communication network architectures across traditional layer boundaries. This paper presents cross-layer architecture for adaptive video multicast streaming over multirate wireless LANs where layer-specific information is passed in both directions, top-down and bottom-up. The authors jointly consider three layers of the protocol stack: the application, data link and physical layers. The authors analyze the performance of the proposed architecture and extensively evaluate it via simulations. The results show that the real-time video quality of the overall system can be greatly improved by cross-layer signaling.     

基于LTE-A技术无线资源管理的跨层联合博弈

提出了一种在LTE-A(long term evolution advanced,长期演进技术增强)技术下的无线资源管理跨层模型,阐述了模型的基本功能特征。以博弈论为依据,分析了无线网络资源的分配方式,并根据无线网络资源和系统协议栈中各层之间的联系,通过设计跨层结构,使各层博弈的目标统一。提出的理论模型面向多种无线网络资源,涉及多个无线网络协议栈层,实现了无线资源的综合管理以及各层之间的联合优化。     

Enhanced performance based on cross-layer design from physical to transport layers for multihop wireless networks

This paper puts forward a novel cognitive cross-layer design algorithms for multihop wireless networks optimization across physical,mediam access control(MAC),network and transport layers.As is well known,the conventional layered-protocol architecture can not provide optimal performance for wireless networks,and cross-layer design is becoming increasingly important for improving the performance of wireless networks.In this study,we formulate a specific network utility maximization(NUM)problem that we believe is appropriate for multihop wireless networks.By using the dual algorithm,the NUM problem has been optimal decomposed and solved with a novel distributed cross-layer design algorithm from physical to transport layers.Our solution enjoys the benefits of cross-layer optimization while maintaining the simplicity and modularity of the traditional layered architecture.The proposed cross-layer design can guarantee the end-to-end goals of data flows while fully utilizing network resources.Computer simulations have evaluated an enhanced performance of the proposed algorithm at both average source rate and network throughput.Meanwhile,the proposed algorithm has low implementation complexity for practical reality.     

Cross-layer design of ad hoc networks for real-time video streaming

Cross-layer design breaks away from traditional network design where each layer of the protocol stack operates independently. We explore the potential synergies of exchanging information between different layers to support real-time video streaming. In this new approach information is exchanged between different layers of the protocol stack, and end-to-end performance is optimized by adapting to this information at each protocol layer. We discuss key parameters used in the cross-layer information exchange along with the associated cross-layer adaptation. Substantial performance gains through this cross-layer design are demonstrated for video streaming.     

Modeling and Optimization of Transmission Schemes in Energy-Constrained Wireless Sensor Networks

We consider a wireless sensor network with energy constraints. We model the energy consumption in the transmitter circuit along with that for data transmission. We model the bottom three layers of the traditional networking stack - the link layer, the medium access control (MAC) layer, and the routing layer. Using these models, we consider the optimization of transmission schemes to maximize the network lifetime. We first consider the optimization of a single layer at a time, while keeping the other layers fixed. We make certain simplifying assumptions to decouple the layers and formulate optimization problems to compute a strategy that maximizes the network lifetime. We then extend this approach to cross-layer optimization of time division multiple access (TDMA) wireless sensor networks. In this case, we construct optimization problems to compute the optimal transmission schemes to an arbitrary degree of accuracy and efficiently. We then consider networks with interference, and propose methods to compute approximate solutions to the resulting optimization problems. We give numerical examples that illustrate the computational approaches as well as the benefits of cross-layer design in wireless sensor networks.     

UPS: Universal Protocol Stack for emerging wireless networks

Recent devices developed for emerging wireless networks, such as 4G cellular networks, wireless mesh networks, and mobile ad hoc networks, support multiple communication substrates and require execution of multiple protocols within a layer, which cannot be supported efficiently by traditional, layered protocol stack approaches. While cross-layer approaches can be designed to support these new requirements, the lack of modularity makes cross-layer approaches inflexible and hence difficult to adapt for future devices and protocols. Thus, there is a need for a new protocol architecture to provide universal support for cross-layer interactions between layers, while also supporting multiple communication substrates and multiple protocols within a stack. In this paper, we propose Universal Protocol Stack (UPS), which provides such support in a modular way through packet-switching, information-sharing and memory management. To show that UPS is realizable with very low overhead and that it enables concurrent and independent execution of protocols of the same stack layer, first, we present a wireless sensor network test-bed evaluation, where UPS is implemented in TinyOS and installed on individual sensor motes. Two cross-layer routing protocols are implemented and evaluated with UPS and without UPS. We also implemented UPS in the OPNET simulator, where the IP (e.g., Routing Information Protocol (RIP)) and AODV routing protocols are executed concurrently to support networks with both static and mobile wireless nodes. Our implementation shows that the overhead incurred to implement UPS is very low, and little or no modification is required to adapt existing protocols to the UPS framework. Both studies also show the advantage of enabling concurrent protocol execution within a stack layer, improving the successful packet delivery ratio or the total number of packets sent for the investigated scenarios.     

A Dynamic Resource Allocation Scheme for the Downlink Heterogeneous Traffic of Internet Protocol (IP) Based OFDM networks

Radio Resource management mechanisms such as physical-centric radio resource allocation and medium access control (MAC)—centric packet scheduling are expected to play a substantial role in the performance of orthogonal frequency division multiplexing (OFDM) based wireless networks. OFDM provide fine granularity for resource allocation since they are capable of dynamically assigning sub-carriers to multiple users and adaptively allocating transmit power. The current layered networking architecture, in which each layer is designed and operated independently, results in inefficient resource use in wireless networks due to the nature of the wireless medium, such as time-varying channel fading. Thus, we need an integrated adaptive design across different layers, allowing for a cross-layer design. In this paper, a scheduling scheme is proposed to dynamically allocate resources for the downlink data transmission of internet protocol based OFDM networks. Generally to maximize the capacity and user satisfaction improvements in packet data admission, scheduling and policing are necessary. Of the three, efficient scheduling has the greatest impact on increased system capacity or effective spectrum usage. In addition, proper scheduling can greatly improve user satisfaction. The contribution of this work is twofold: first we evaluate current allocation schemes by exploiting the knowledge of channel sate information (CSI) and traffic characteristics in terms of queue state information (QSI) to acquire the system performance on a real time network. Second, the resource allocation scheme is extended by incorporating MAC layer information as well as opportunistic packet scheduling in the time-domain-based on minimum weight cost function. The key factors that affect the overall system performance in terms of system average throughput and delay are identified, evaluated and discussed.     

A Generic Framework for Cross-Layer Optimisation in Wireless Personal Area Networks

Wireless Personal Area Networking (WPAN) is introduced as a new concept for next generation wireless systems. WPANs are short-range wireless systems operating in the direct surrounding of the user. A reference architecture for short-range wireless communications has been designed covering the end-to-end system design. Traditional protocol stack implementations based on layering do not function efficiently in wireless environments due to inefficiency, inflexibility and suboptimality of the functionalities in the different layers. Specifically in WPAN and other short-range wireless systems the performance benefits from a cross-layer design strategy, supporting adaptability and optimizing the use of resources over multiple layers of the protocol stack. In this paper we advocate cross-layer optimisation for WPAN systems and introduce a centralised control structure for interaction between different layers in master or leader devices. The control structure adapts the link characteristics to the channel state and user requirements. Allowing for the support of heterogeneous services, each with their own quality-of-service demands, in wireless environments.     

Cross-Layer Multi-Packet Reception Based Medium Access Control and Resource Allocation for Space-Time Coded MIMO/OFDM

In this paper, a cross-layer design framework for multi-input multi-output (MIMO)/orthogonal frequency division multiplexing (OFDM) based wireless local area networks (WLANs) is proposed. In contrast to conventional systems where the medium access control (MAC) and physical (PHY) layers are separately optimized, our proposed methodology jointly designs a multi-packet reception (MPR) based protocol with adaptive resource allocation. Specifically, a realistic collision model is employed by taking into consideration the PHY layer parameters such as channel information, space-time coded beamforming and multiuser detection, as well as sub-carrier, bit, and power allocation. The allocation problem is formulated, so as to maximize the system throughput, subject to the constraints from both the MAC and PHY layers. These constraints depend on the results of access contention, data packets? length, users? spatial correlation and the quality of channel feedback information. An iterative algorithm is then provided to obtain the optimal solution. Simulation results will show that our proposed approach achieves significant improvement in system performance such as average throughput and packet delay, compared with conventional schemes where cross-layer design and optimization is not used.     

Mobility support in wireless Internet

The tremendous advancement and popularity of wireless access technologies necessitates the convergence of multimedia (audio, video, and text) services on a unified global (seamless) network infrastructure. Circuit-switched proprietary telecommunication networks are evolving toward more cost-effective and uniform packet-switched networks such as those based on IP. However, one of the key challenges for the deployment of such wireless Internet infrastructure is to efficiently manage user mobility. To provide seamless services to mobile users, several protocols have been proposed over the years targeting different layers in the network protocol stack. In this article we present a cross-layer perspective on the mobility protocols by identifying the key features of their design principles and performance issues. An analysis of the signaling overhead and handoff delay for some representative protocols in each layer is also presented. Our conclusion is that although the application layer protocol is worse than the protocols operating in the lower layers, in terms of handoff delay and signaling overhead, it is better suited as a potential mobility solution for the next-generation heterogeneous networks, if we consider such factors as protocol stack modification, infrastructure change, and inherent operational complexity.     

仿真研究无线多跳网络跨层协议设计的优劣

为了改善无线多跳网络的性能，很多研究表明跨层协议设计比OSI模型更适合无线网络。本文分析了无线多跳网络的特征及对各协议层的影响，给出了跨层协议设计对网络性能的改善以及它可能带来的问题，并针对速率自适应MAC协议和网络层路由协议之间的相互影响给出了仿真实例，结果证明跨层协议设计要充分考虑不同协议之间的相互影响，合理规划、谨慎实施，否则网络的性能不升反降。     

A cross-layer framework for multiobjective performance evaluation of wireless ad hoc networks

In this paper we address the problem of finding the optimal performance region of a wireless ad hoc network when multiple performance metrics are considered. Our contribution is to propose a novel cross-layer framework for deriving the Pareto optimal performance bounds for the network. These Pareto bounds provide key information for understanding the network behavior and the performance trade-offs when multiple criteria are relevant. Our approach is to take a holistic view of the network that captures the cross-interactions among interference management techniques implemented at various layers of the protocol stack (e.g. routing and resource allocation) and determines the objective functions for the multiple criteria to be optimized. The resulting complex multiobjective optimization problem is then solved by multiobjective search techniques. The Pareto optimal sets for an example sensor network are presented and analyzed when delay, reliability and energy objectives are considered.     

A Cross-Layer Architecture of Wireless Sensor Networks for Target Tracking

We propose the Low Energy Self-Organizing Protocol (LESOP) for target tracking in dense wireless sensor networks. A cross-layer design perspective is adopted in LESOP for high protocol efficiency, where direct interactions between the Application layer and the Medium Access Control (MAC) layer are exploited. Unlike the classical Open Systems Interconnect (OSI) paradigm of communication networks, the Transport and Network layers are excluded in LESOP to simplify the protocol stack. A lightweight yet efficient target localization algorithm is proposed and implemented, and a Quality of Service (QoS) knob is found to control the tradeoff between the tracking error and the network energy consumption. Furthermore, LESOP serves as the first example in demonstrating the migration from the OSI paradigm to the Embedded Wireless Interconnect (EWI) architecture platform, a two-layer efficient architecture proposed here for wireless sensor networks     

A Tutorial on Cross-Layer Optimization in Wireless Networks

This tutorial paper overviews recent developments in optimization-based approaches for resource allocation problems in wireless systems. We begin by overviewing important results in the area of opportunistic (channel-aware) scheduling for cellular (single-hop) networks, where easily implementable myopic policies are shown to optimize system performance. We then describe key lessons learned and the main obstacles in extending the work to general resource allocation problems for multihop wireless networks. Towards this end, we show that a clean-slate optimization-based approach to the multihop resource allocation problem naturally results in a “loosely coupled” cross-layer solution. That is, the algorithms obtained map to different layers [transport, network, and medium access control/physical (MAC/PHY)] of the protocol stack, and are coupled through a limited amount of information being passed back and forth. It turns out that the optimal scheduling component at the MAC layer is very complex, and thus needs simpler (potentially imperfect) distributed solutions. We demonstrate how to use imperfect scheduling in the cross-layer framework and describe recently developed distributed algorithms along these lines. We conclude by describing a set of open research problems.     

ad hoc网络中跨层设计方法的研究

ad hoc网络与传统有线和无线蜂窝网络有着显著的区别,基于传统的分层协议栈的设计方法不再适合ad hoc网络,而应采用一种新型的跨层协议栈和跨层设计方法.本文首先阐述了ad hoc网络的特点和传统的分层协议栈的弊端,介绍了跨层设计的概念.然后,详细分析了ad hoc网络中跨层设计的方法,包括策略、体系结构和信令交互方式,探讨了跨层设计的相关技术和面临的挑战.最后,总结了全文并指出了今后的工作方向.