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.

/pdf/relay-based-deployment-concepts-for-wireless-and-mobile-4js7u1daca.pdf

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.

/pdf/securing-vehicular-ad-hoc-networks-4sgegi8hgk.pdf

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

First (A) and second (B) radio stations have a layer structure with a physical layer (PL), a security layer (DLL), a network layer (NL) and higher layers (HL), i.e. a basic structure of protocol layers. Data is transmitted from A to B via geocast. Data is addressed by means of an address that contains geographical information and is on a security layer.

Method for radio transmission using geographical addressing

The method involves transmitting using a Time Division Multiple Access method with a temporal frame structure and transmitting information using different modulations and/or codings with variable transmission power in a given time span of the frame structure. The modulation and/or coding are selected within a time span so that the transmit time for the information being transmitted approximates to the length of the time span. AN Independent claim is also included for the following: a radio communications system with at least one base station and at least one user station.

Channel-adapted transmission of information in a radio communication system

OFDM-based multi-carrier systems combined with a hybrid multiple access scheme, MC-CDMA/FDMA, are able to provide high flexibility and granularity for the synchronized downlink transmission. In combination with a new resource allocation scheme, referred to as adaptive sub-band allocation (ASBA), the sub-carriers are assigned to the users in order to maximise the overall system capacity based on the channel knowledge. In a time-variant channel the channel knowledge for ASBA should be updated and an estimate of the channel is supposed to be obtained by measuring the pilots periodically inserted in the uplink (UL) under the assumption of TDD (Time Division Duplex) operation mode. This paper analyzes different channel estimation methods and the signalling overhead due to pilot transmission. An optimized updating period for ASBA is derived based on the simulation results such that the performance in terms of system throughput is maximized. It is shown that when a proper updating period is selected, ASBA has a considerable gain even at a velocity of 200 km/h.

https://ieeexplore.ieee.org/iel5/5755254/5755255/05755273.pdf

Signaling Overhead for ASBA in an MC-CDMA System

Die Erfindung betrifft ein Verfahren zur Kommunikation in einem Funkkommunikationssystem umfassend eine Mehrzahl von Funkstationen (A, B, C), wobei in dem Funkkommunikationssystem Nachrichten (MESSAGE) von Funkstation (A, 3, C) zu Funk station (A, B, C) direkt oder uber eine oder mehrere die Nachrichten (MESSAGE) weiterleitende Funkstationen (A, B, C). unter Verwendung von Funkressourcen gesendet werden, und wobei fur die Versendung der Nachrichten (MESSAGE) eine dezentrale Zuordnung von Funkressourcen zu Funkstationen (A, B, C) erfolgt. Erfindungsgemass versendet mindestens eine Funkstation (B) Informationen (INFO) uber die fur die Versendung von mindestens einer Nachricht (MESSAGE) an die mindestens eine Funkstation (B) verwendeten ersten Funkressourcen, wobei die Versendung der Informationen (INFO) uber die ersten Funkressourcen unter Verwendung von der mindestens einen Funkstation (B) zugeordneten zweiten Funkressourcen erfolgt. Weiterhin betrifft die Erfindung eine Funkstation (A, B, C) zur Durchfuhrung des Verfahrens.

Verfahren zur kommunikation in einem adhoc-funkkommunikationssystem

The method involves one of the stations (WT,AP,APT1-5) participating in the system informing at least one station outside its associated cell (Z) about its capacity requirements when required by sending at least one message and/or information. The messages are received and/or relayed by stations in the form of subscriber-side stations or network stations. AN Independent claim is also included for the following: a station for implementing the method.

Matthias Lott

Papers

Method for radio transmission using geographical addressing

Channel-adapted transmission of information in a radio communication system

Signaling Overhead for ASBA in an MC-CDMA System

Verfahren zur kommunikation in einem adhoc-funkkommunikationssystem

Method and device for a station to access a common transmitting medium