Ad Hoc网络中基于距离的机会频谱接入方案

本论文研究ad hoc网络中的机会频谱接入(OSA)技术,建立一种既能够抑制次用户对主用户的干扰,又能够在非合作次用户间进行公平、无冲突的资源共享的接入机制.解决了在自组织的多用户ad hoc网络中,主次用户以及次用户之间共享频谱资源,次用户选择最佳频谱接入,并确保抑制对主用户的干扰以及自身性能优化的问题.为此,建立次...     

HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.     

Effects of Location Awareness on Concurrent Transmissions for Cognitive Ad Hoc Networks Overlaying Infrastructure-Based Systems

Through wide-band spectrum sensing, cognitive radio (CR) can identify the opportunity of reusing the frequency spectrum of other wireless systems. However, wide-band spectrum sensing requires energy consumption processes. In this paper, we aim to relieve the burden of spectrum scanning in a CR system by means of location awareness. We investigate to what extent a CR system with location awareness capability can establish a scanning-free region where a peer-to-peer connection of the secondary CR users can coexist with an infrastructure-based connection of the primary user. We compute the concurrent transmission probability of a peer-to-peer connection and an infrastructure-based connection in a system based on the carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol. It has been shown that the frequency band of the legacy system can be reused up to 45% by the overlaying cognitive ad hoc network if certain location techniques help CR users locate primary and other secondary users. In summary, a CR system equipped with location awareness techniques can dramatically reduce the need of spectrum sensing thanks to the capability of identifying the concurrent transmission region in a hybrid infrastructure-based and ad hoc overlaying systems. Hence, from another aspect, the issue of wide-band spectrum sensing in CR systems is resolved fundamentally.     

A distributed network coded control channel for multihop cognitive radio networks

Designing a solution for multihop cognitive radio networks poses several challenges such as the realization of the control channel, the detection of primary users, and the coordination of secondary users for dynamic spectrum access purposes. In this article we discuss these challenges and propose a solution that aims to meet most of them. The proposed solution is completely distributed, and does not need dedicated spectrum resources for control purposes, but rather leverages on a virtual control channel that is implemented by having users exchange control information whenever they meet in a particular channel, using network coding techniques for better dissemination performance. Due to these aspects, our proposal represents a significant improvement over existing dynamic spectrum access and multichannel MAC solutions. We discuss the effectiveness of our scheme in multihop cognitive ad hoc networks, where secondary users need to opportunistically access the spectrum at those locations and times at which it is not used by primary users. Finally, we report the results of an evaluation study assessing the performance of the proposed scheme with respect to different system and scenario parameters.     

Ad hoc认知无线网络的主用户感知定位方案

为了对频谱资源进行合理的运用,在认知无线Ad hoc网络中,各次用户必须准确地对主用户信号进行感知,以防止恶意攻击者发起的模仿授权用户攻击。本文基于对信号的波达方向(DOA)估计,提出了一种存在系统误差下对主用户的感知定位算法,仿真证明,该方案能准确地对主用户信号进行定位;当信道环境恶劣、信噪比较低时,本文通过引入环境系数,提出了一种灵活性较好的协作加权检测策略。该策略中每个次用户都可以做出对主用户信号的最终判决,解决了以往协作感知方案中由于权力过分集中而引起的潜在安全性问题。     

A unified spectrum sensing and throughput analysis model in cognitive radio networks

Cognitive radio (CR) is a newly developed technology for increasing spectral efficiency in wireless communication systems. In the CR networks, there exist two traditional spectrum‐sharing technologies called spectrum overlay and spectrum underlay. A new hybrid overlay/underlay paradigm has also been discussed in the literature. In this work, we create a unified spectrum sensing and throughput analysis model, which is suitable for overlay, underlay, and hybrid overlay/underlay paradigms in the CR networks. In the proposed model, the energy detection scheme is employed for the spectrum sensing in the network in which the co‐channel interference is present among primary users and secondary users (SUs). The SUs' throughput in the proposed CR system model is then analyzed. The simulations are also carried out for demonstrating the performance of overlay, underlay, and hybrid overlay/underlay paradigms. Copyright © 2013 John Wiley & Sons, Ltd.     

Improving handoff performance by utilizing ad hoc links in multi-hop cellular systems

Handoff performance is a critical issue for mobile users in wireless cellular networks, such as GSM networks, 3G networks, and next generation networks (NGNs). When ad hoc mode is introduced to cellular networks, multi-hop handoffs become inevitable, which brings in new challenging issues to network designers, such as how to reduce the call dropping rate, how to simplify the multi-hop handoff processes, and how to take more advantage of ad hoc mode for better resource management, and most of these issues have not been well addressed as yet. In this paper, we will address some of the issues and propose a scheme, Ad-hoc-Network–Embedded handoff Assisting Scheme (ANHOA), which utilizes the self-organizing feature of ad hoc networks to facilitate handoffs in cellular networks and provide an auxiliary way for mobile users to handoff across different cells. Moreover, we also propose a scheme enabling each BS to find the feasible minimum reservation for handoff calls based on the knowledge of adjacent cells’ traffic information. Due to the use of multi-hop connections, our scheme can apparently alleviate the reservation requirement and lower the call blocking rate while retaining higher spectrum efficiency. We further provide a framework for information exchange among adjacent cells, which can dynamically balance the load among cells. Through this study, we demonstrate how we can utilize ad hoc mode in cellular systems to significantly improve the handoff performance.     

Wireless ATM LAN with and without infrastructure

We consider wireless ATM concepts for small LANs, especially for SOHO and future consumer applications. We describe a wireless ATM LAN framework architecture that supports wireless ATM communications in environments with and without fixed ATM infrastructure. For the configuration with an ATM infrastructure, a distributed ATM switched backbone is proposed, which enables a smart ATM switching element to be embedded in every wireless and fixed access point. For bandwidth efficiency and ease of operation (place-and-play), we also propose an ad hoc wireless ATM LAN concept based on the same 5 GHz wireless ATM air interface as is currently under standardization in the ETSI/BRAN and ATM Forum. Unlike CSMA-based ad hoc systems such as HIPERLAN and IEEE802.11, our ad hoc wireless ATM system makes QoS management feasible in an infrastructureless environment by using resource reservation and scheduled medium access protocol. Since cost scalability is essential throughout our system design, we consider forwarding between ad hoc subnets and interworking with the fixed network as important but optional features     

An efficient heterogeneous key management approach for secure multicast communications in ad hoc networks

In a mobile wireless ad hoc network, mobile nodes cooperate to form a network without using any infrastructure such as access points or base stations. Instead, the mobile nodes forward packets for each other, allowing communication among nodes outside wireless transmission range. As the use of wireless networks increases, security in this domain becomes a very real concern. One fundamental aspect of providing confidentiality and authentication is key distribution. While public-key encryption has provided these properties historically, ad hoc networks are resource constrained and benefit from symmetric key encryption. In this paper, we propose a new key management mechanism to support secure group multicast communications in ad hoc networks. The scheme proposes a dynamic construction of hierarchical clusters based on a novel density function adapted to frequent topology changes. The presented mechanism ensures a fast and efficient key management with respect to the sequential 1 to n multicast service.     

Local data control and admission control for QoS support in wireless ad hoc networks

Wireless ad hoc networks consist of nodes having a self-centrically broadcasting nature of communication. To provide quality of service (QoS) for ad hoc networks, many issues are involved, including routing, medium-access control (MAC), resource reservation, mobility management, etc. Carefully designed distributed medium-access techniques must be used for channel resources, so that mechanisms are needed to efficiently recover from inevitable frame collisions. For ad hoc wireless networks with a contention-based distributed MAC layer, QoS support and guarantee become extremely challenging. In this paper, we address this challenging issue. We first consider MAC and resource-reservation aspects for QoS support in one-hop ad hoc wireless networks. We propose two local data-control schemes and an admission-control scheme for ad hoc networks with the IEEE 802.11e MAC standard. In the proposed fully distributed local data control schemes, each node maps the measured traffic-load condition into backoff parameters locally and dynamically. In the proposed distributed admission-control scheme, based on measurements, each node makes decisions on the acceptances/rejections of flows by themselves, without the presence of access points. The proposed mechanisms are evaluated via extensive simulations. Studies show that, with the proposed schemes, QoS can be guaranteed under a clear channel condition while maintaining a good utilization. Discussions on applying the proposed schemes into multihop ad hoc networks are also included.     

Management of cognitive radio ad hoc networks using a congestion‐based metric

In this paper, we propose a new network management protocol to address the unique challenges of managing cognitive radio ad hoc networks that have distributed, multihop architectures with dynamic spectrum availability. We focus on performance management for these networks, and address the problem of network congestion for secondary users, because of its significant impact on data throughput. Specifically, we define a performance metric, the average congestion level of the network, and derive it analytically as a function of the primary users’ activities and the secondary users’ strategy. For practical implementation, we further propose a cluster‐based management architecture that utilizes a designated central manager and cluster heads that function as distributed managers. The cluster heads collect information from multiple layers of the protocol stack using new MIB (management information base) variables to capture the characteristics of cognitive radio ad hoc networks, such as the location‐dependent spectrum availability. The objective of the management action is to utilize a network‐level view of the congestion situation in the network by directing the secondary users to select the highest‐quality links available and avoid congested clusters. This hierarchical networkmanagement design allows us to take advantage of its scalability to achieve near‐real‐time management. Numerical results demonstrate the effectiveness of the proposed scheme. Copyright © 2013 John Wiley & Sons, Ltd.     

A flow-based network monitoring framework for wireless mesh networks

As an extension of wireless ad hoc and sensor networks, wireless mesh networks recently were developed as a key solution to provide high-quality multimedia services and applications, such as voice, data, and video, over wireless personal area networks, wireless local area networks, and wireless metropolitan area networks. A WMN has a hybrid network infrastructure with a backbone and an access network and usually is operated in both ad hoc and infrastructure modes with self-configuration and self-organization capabilities. In this article, we review security challenges, attacks, and countermeasures in the physical, medium access control (MAC), and network layers of wireless mesh backbone and access networks. We then extend the concept of traffic flow from IP networks and define meshflow in wireless mesh networks. Based on this new concept, we propose a comprehensive framework to realize network monitoring, user and router profiling, application and service balancing, and security protection in wireless mesh backbone networks. Practical issues and design trade-offs for implementing the proposed framework in real systems also are discussed.     

Power Control for Cognitive Radio Networks: A Game Theoretic Approach

In communication industry one of the most rapidly growing area is wireless technology and its applications. The efficient access to radio spectrum is a requirement to make this communication feasible for the users that are running multimedia applications and establishing real-time connections on an already overcrowded spectrum. In recent times cognitive radios (CR) are becoming the prime candidates for improved utilization of available spectrum. The unlicensed secondary users share the spectrum with primary licensed user in such manners that the interference at the primary user does not increase from a predefined threshold. In this paper, we propose an algorithm to address the power control problem for CR networks. The proposed solution models the wireless system with a non-cooperative game, in which each player maximize its utility in a competitive environment. The simulation results shows that the proposed algorithm improves the performance of the network in terms of high SINR and low power consumption.

     

感知无线电ad hoc网络基于干扰的路由

感知无线电技术作为一种新兴技术,通过时间和空间维度上的频谱空洞的利用能很好地提高频谱利用率。感知无线电的路由不同于传统的路由度量,因为次用户从时间和空间上都不能对主用户造成干扰。在感知无线电ad hoc网络环境下,选取了干扰作为路由的度量,并将干扰分为系统内干扰(次用户自身之间的干扰)和系统间干扰(次用户对主用户的干扰)。在已有的ad hoc网络干扰路由协议的基础上对干扰权重做出改进,并提出新的基于系统间路由干扰(对主用户干扰最小化)和基于联合系统内和系统间干扰的路由协议。仿真结果表明,该干扰模型符合感知无线电移动ad hoc网络的特性。     

Traffic load metrics for multihomed mobile IP and global connectivity

Support for host mobility an essential and necessary feature for roaming users who connect to wireless networks via access points. Access points may have different capabilities, be connected to different networks and be installed by different providers. A mobile host will discover multiple access points in this environment. In such an environment, a mobile host should be able to use the best available connection to communicate with a correspondent host and perhaps use multiple connections for different hosts. In areas with wireless local area network access, pockets with limited or no coverage could exist. Such restricted connectivity could be compensated by neighbor hosts who form an ad hoc network and relay packets until they reach an access point. This paper describes and discusses a proposed solution towards enabling and supporting connectivity in wireless networks. In the proposed solution the network layer software will evaluate and decide which wireless network connections to use. A Running Variance Metric (RVM) and a Relative Network Load(RNL) are used to measure the traffic load of access points in wireless access networks. RVM and RNL can be efficiently used for both infrastructure networks and ad hoc networks. Multihomed Mobile IP (M-MIP) is an extension of Mobile IP that enables mobile hosts to use multiple care-of addresses simultaneously. The extension enhances network connectivity by enabling the mobile host, the home agent and correspondent hosts to evaluate and select the best connection. A proposed gateway architecture using M-MIP that integrates wired IP networks with ad hoc networks is described. The M-MIP and gateway architecture using the RVM and RNL metrics have been validated with simulation studies and results are presented.     

Multicasting with Localized Control in Wireless Ad Hoc Networks

This paper investigates how to support multicasting in wireless ad hoc networks without throttling the dominant unicast flows. Unicast flows are usually congestion-controlled with protocols like TCP. However, there are no such protocols for multicast flows in wireless ad hoc networks and multicast flows can therefore cause severe congestion and throttle TCP-like flows in these environments. Based on a cross-layer approach, this paper proposes a completely-localized scheme to prevent multicast flows from causing severe congestion and the associated deleterious effects on other flows in wireless ad hoc networks. The proposed scheme combines the layered multicast concept with the routing-based congestion avoidance idea to reduce the aggregated rate of multicast flows when they use excessive bandwidth on a wireless link. Our analysis and extensive simulations show that the fully-localized scheme proposed in this paper is effective in ensuring the fairness of bandwidth sharing between multicast and unicast flows in wireless ad hoc networks.     

Cross-Layer Scheduling and Power Control Combined With Adaptive Modulation for Wireless Ad Hoc Networks

Efficient resource management is a major challenge in the operation of wireless systems, especially energy-constrained ad hoc networks. In this paper, we propose a cross-layer optimization framework to jointly design the scheduling and power control in wireless ad hoc networks. We study the system performance by combining scheduling, power control, and adaptive modulation. Specifically, the transmitted power and constellation size are dynamically adapted based on the packet arrival, quality of service (QoS) requirements, power limits, and channel conditions. A key feature of the proposed method is that it facilitates a distributed implementation, which is desirable in wireless ad hoc networks. The performance of our proposed methodology will be investigated in ad hoc networks supporting unicast as well as multicast traffic. Simulation results will show that the proposed scheme achieves significant gains in both the single-hop throughput and power efficiency compared with the existing method, which implements the scheduling through a central controller, and adopts power control with fixed modulation     

A Cluster-Based MAC Protocol for Cognitive Radio Ad Hoc Networks

The cognitive radio (CR) technology is an efficient approach to share the spectrum. But how to access the idle channels effectively is a challenging problem. To solve this problem, we propose a MAC protocol for cluster-based CR ad hoc networks, with the aim of making cluster structure more robust to the primary users’ channel re-occupancy activities, so that the CR users can use the idle spectrum more efficiently. Under this framework, a cluster formation algorithm based on available channels, geographical position and experienced statistics is proposed to maximize the network throughput and maintain the cluster topology stability. The schemes for new CR user joining a cluster and cluster maintenance are also designed. An experience database is proposed to store the experienced statistics which are obtained from spectrum occupancy history. Such a database can be used to support the acts of nodes, such as neighbor discovery and cluster forming. Simulation results reveal that our proposed framework not only outperforms conventional CR MAC protocols in terms of throughput and packet delay, but also generates a smaller number of clusters and has more stable cluster structure with less reclustering time.     

CRAHNs: Cognitive radio ad hoc networks

Cognitive radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum-aware communication paradigm in wireless communications. CR networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse quality-of-service (QoS) requirements. Specifically, in cognitive radio ad hoc networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, intrinsic properties and current research challenges of the CRAHNs are presented. First, novel spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. A particular emphasis is given to distributed coordination between CR users through the establishment of a common control channel. Moreover, the influence of these functions on the performance of the upper layer protocols, such as the network layer, and transport layer protocols are investigated and open research issues in these areas are also outlined. Finally, a new direction called the commons model is explained, where CRAHN users may independently regulate their own operation based on pre-decided spectrum etiquette.     

基于图着色的无线自组网极小连通支配集算法

基于连通支配集算法的虚拟主干网技术对于无线自组网的路由优化、能量保护和资源分配都具有重要的作用。通过引入极大独立集和极小支配集概念,基于图着色思想提出一种新的适合于无线自组网的极小连通支配集算法,从理论上证明了该算法的正确性和高效性,也通过仿真实验分析了该算法在多种情况下的实际性能,仿真结果表明新算法在簇头和主干节点数目方面具有较好的性能,特别在节点密集的网络环境中更加突出。