Coding strategies that exploit node cooperation are developed for relay networks. Two basic schemes are studied: the relays decode-and-forward the source message to the destination, or they compress-and-forward their channel outputs to the destination. The decode-and-forward scheme is a variant of multihopping, but in addition to having the relays successively decode the message, the transmitters cooperate and each receiver uses several or all of its past channel output blocks to decode. For the compress-and-forward scheme, the relays take advantage of the statistical dependence between their channel outputs and the destination's channel output. The strategies are applied to wireless channels, and it is shown that decode-and-forward achieves the ergodic capacity with phase fading if phase information is available only locally, and if the relays are near the source node. The ergodic capacity coincides with the rate of a distributed antenna array with full cooperation even though the transmitting antennas are not colocated. The capacity results generalize broadly, including to multiantenna transmission with Rayleigh fading, single-bounce fading, certain quasi-static fading problems, cases where partial channel knowledge is available at the transmitters, and cases where local user cooperation is permitted. The results further extend to multisource and multidestination networks such as multiaccess and broadcast relay channels.

Cooperative strategies and capacity theorems for relay networks

In recent years, there has been an upsurge of interest in multihop-augmented infrastructure-based networks in both the industry and academia, such as the seed concept in 3GPP, mesh networks in IEEE 802.16, and converge extension of HiperLAN/2 through relays or user-cooperative diversity mesh networks. This article, a synopsis of numerous contributions to the working group 4 of the wireless world research forum and other research work, presents an overview of important topics and applications in the context of relaying. It covers different approaches to exploiting the benefits of multihop communications via relays, such as solutions for radio range extension in mobile and wireless broadband cellular networks (trading range for capacity), and solutions to combat shadowing at high radio frequencies. Furthermore, relaying is presented as a means to reduce infrastructure deployment costs. It is also shown that through the exploitation of spatial diversity, multihop relaying can enhance capacity in cellular networks. We wish to emphasize that while this article focuses on fixed relays, many of the concepts presented can also be applied to systems with moving relays.

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Relay-based deployment concepts for wireless and mobile broadband radio

Vehicular networks are very likely to be deployed in the coming years and thus become the most relevant form of mobile ad hoc networks. In this paper, we address the security of these networks. We provide a detailed threat analysis and devise an appropriate security architecture. We also describe some major design decisions still to be made, which in some cases have more than mere technical implications. We provide a set of security protocols, we show that they protect privacy and we analyze their robustness and efficiency.

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Securing vehicular ad hoc networks

Cognitive radio is an exciting emerging technology that has the potential of dealing with the stringent requirement and scarcity of the radio spectrum. Such revolutionary and transforming technology represents a paradigm shift in the design of wireless systems, as it will allow the agile and efficient utilization of the radio spectrum by offering distributed terminals or radio cells the ability of radio sensing, self-adaptation, and dynamic spectrum sharing. Cooperative communications and networking is another new communication technology paradigm that allows distributed terminals in a wireless network to collaborate through some distributed transmission or signal processing so as to realize a new form of space diversity to combat the detrimental effects of fading channels. In this paper, we consider the application of these technologies to spectrum sensing and spectrum sharing. One of the most important challenges for cognitive radio systems is to identify the presence of primary (licensed) users over a wide range of spectrum at a particular time and specific geographic location. We consider the use of cooperative spectrum sensing in cognitive radio systems to enhance the reliability of detecting primary users. We shall describe spectrum sensing for cognitive radios and propose robust cooperative spectrum sensing techniques for a practical framework employing cognitive radios. We also investigate cooperative communications for spectrum sharing in a cognitive wireless relay network. To exploit the maximum spectrum opportunities, we present a cognitive space-time-frequency coding technique that can opportunistically adjust its coding structure by adapting itself to the dynamic spectrum environment.

/pdf/cooperative-communications-for-cognitive-radio-networks-48j13lw4r8.pdf

Cooperative Communications for Cognitive Radio Networks

Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogenous network deployment based on micro, pico and femtocells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a "green" cellular network technology.

Green Cellular Networks: A Survey, Some Research Issues and Challenges

The method involves adjusting the transmission power (S) depending on positional information (O) relating to the mobile station (MS1). The positional information is dependent upon the geographic position of the mobile station. It can depend upon the type of environment in which the mobile station is located. AN Independent claim is also included for the following: a radio system with a mobile station and a mobile station for a radio system.

Adjusting transmission power of mobile station in radio system involves adjusting transmission power depending on positional information relating to mobile station

Radio stations in a radio communication system send messages from one radio station to another either directly or via one or several radio stations forwarding the messages by using radio resources. The radio resources are allocated in a decentralized manner to radio stations to send the message. At least one radio station sends information about first radio resources used for sending at least one message to the at least one radio station, the information about the first radio resources being sent by using second radio resources that are allocated to the at least one radio station.

Method for communicating in an ad-hoc radio communication system

In a radio communications network, the time is divided into a succession of frames for conducting data communications with subscriber stations located within a coverage area of two central stations of the network In a first broadcast phase of each frame, a first central station (AP1) transmits first frame format information (BCH), which defines a first downlink phase of the frame (DL phase) and a first uplink phase (UL phase) In the same frame, a second central station transmits, on the same frequency, second frame format information (BCH), which defines a second downlink phase and a second uplink phase for the communication of subscriber stations (MS) with the second central station (AP2), whereby the phases within a frame do not overlap

Method for conducting data communications with subscriber stations, and radio communications network for implementing said method

The current era of mobile communication is passing through the days of rapidly changing technologies. A technology which holds promise to bring surprise to the future users is ad hoc networks. The multiple access procedure in ad hoc networks is not error prone till now, although significant researches are going on in its MAC layer. The communications in ad hoc networks are adversely affected by the neighborhood capture problem along with some other problems like hidden station problem, exposed station problem as well as channel capture problem. This paper will characterize the adverse effect of neighborhood capture problem with two views of a remedy and some analytical results

Characterization of the adverse effect of neighborhood capture in MANET and on the way to a remedy

A medium access control protocol for a wireless multihop network is described and evaluated. The network is able to guarantee the bandwidth contracted to a connection in a hidden station environment and to most efficiently use the spectrum capacity by providing a mechanism for dynamic channel allocation to services. Both channel and packet switched services are supported, based on real channel connections. Ad-hoc networks without a central control node can be realized due to the ability of any station to route connections according to the current meshing of the network. Channels are established and used for the duration of a so called train of data packets, released when the train ends and reestablished when the next train arrives. To guarantee available capacity of the network for the reestablishment of a connection, connection admission control is applied and new connections are accepted only if spare capacity is available. The traffic performance of the proposed protocol is given by means of a simulation study in an example scenario.

Matthias Lott

Papers

Adjusting transmission power of mobile station in radio system involves adjusting transmission power depending on positional information relating to mobile station

Method for communicating in an ad-hoc radio communication system

Method for conducting data communications with subscriber stations, and radio communications network for implementing said method

Characterization of the adverse effect of neighborhood capture in MANET and on the way to a remedy

Protocols for a wireless-ATM multihop network