R. Pabst

Bio: R. Pabst is an academic researcher from RWTH Aachen University. The author has contributed to research in topics: Wireless & Relay. The author has an hindex of 11, co-authored 25 publications receiving 2147 citations.

Relay-based deployment concepts for wireless and mobile broadband radio

Abstract: 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.

Performance evaluation of a fixed relay concept for next generation wireless systems

Abstract: This work presents a concept and the related performance evaluation for a wireless broadband system based on fixed relay stations acting as wireless bridges. The system is intended for dense populated areas as an overlay to cellular radio systems. A short introduction is given to the general topic of fixed relaying, the proposed extension to a MAC-frame based access protocol like IEEE 802.11e, 802.15.3, 802.16a and HIPERLAN2 is outlined. A possible deployment scenario is introduced and the simulative traffic performance in a Manhattan-like dense urban environment is presented. It is established that the fixed relaying concept is well suited to substantially contribute to provide high capacity cellular broadband radio coverage in future (NG) cellular wireless broadband systems.

Fixed Relays for Next Generation Wireless Systems

Abstract: This chapter presents a concept and the related performance evaluation for a wireless broadband system based on fixed relay stations acting as wireless bridges. The system is equally well-suited for both dense populated areas and wide-area coverage as an overlay to cellular radio systems. A short introduction is given to the general topic of fixed relaying. The proposed extension to a Medium Access Control-frame based access protocol like IEEE802.11e, 802.15.3, 802.16a and HIPERLAN2 is outlined. A possible deployment scenario is introduced and the simulative traffic performance in a Manhattan-like dense urban environment and a wide-area open-space environment is presented. It is established that the fixed relaying concept is well suited to substantially contribute to provide high capacity cellular broadband radio coverage in future (NG) cellular wireless broadband systems.

Capacity of a relaying infrastructure for broadband radio coverage of urban areas

Abstract: Owing to the difficult propagation conditions in the frequency range of future cellular broadband radio systems, very small cell sizes and high attenuation through obstacles (sufficient C/I ratio only in direct line of sight (LoS)) are expected to constitute a major challenge for the development of such systems. Thus, complete coverage of urban areas using a conventional (one-hop) cellular infrastructure is expected to be very costly due to the high number of base stations and fixed network connections needed. For this reason, the introduction of relaying is widely accepted to be an essential element in the development of future cellular broadband radio networks. This paper presents a methodology to quantify the influence of relaying on the capacity of a single base station. We define the capacity as the aggregate downlink throughput that is achieved by all users in the cell. Inspired by the recently proposed wireless media system (WMS) architecture [B. Walke, et al., Apr. 2003], we compare the capacity of a conventional one-hop cellular architecture with the capacity of a configuration consisting of one base station and four regenerative fixed relay stations (FRS) that together cover the same area like five base stations in a conventional cellular architecture. The presented methodology allows exploring the parameter space, which is spanned by system parameters like antenna gain, scenario geometry, and noise and transmitting power.

System Level Performance of Cellular WiMAX IEEE 802.16 with SDMA-enhanced Medium Access

Abstract: Recent years have witnessed an ever-increasing interest in smart antenna technologies to boost the capacity of existing and future wireless systems. As one of the first standards the wireless metropolitan area network IEEE 802.16 (WiMAX) provides means to support these techniques. This paper investigates the potential of smart antenna beamforming and space division multiple access (SDMA) in the context of a cellular IEEE 802.16 deployment. It presents the system level performance evaluation of a joint TDMA/SDMA scheduling approach taking into account the influence of intra- and inter-cell interference generated by concurrent SDMA transmissions. The performance of single- and multi-user beamforming is compared with the non-beamforming reference case.

Cooperative strategies and capacity theorems for relay networks

Abstract: 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.

Relay-based deployment concepts for wireless and mobile broadband radio

Abstract: 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.

IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems Draft Amendment: Management Information Base Extensions

Abstract: This document provides updates to IEEE Std 802.16's MIB for the MAC, PHY and asso- ciated management procedures in order to accommodate recent extensions to the standard.

Cooperative Communications for Cognitive Radio Networks

Abstract: 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.

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

Abstract: 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.