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

Amplify-and-Forward (AF) is a simple but effective relaying concept for multihop networks that combines transparency regarding modulation format and coding scheme with ease of implementation. Conventional AF, however, does not take into account the transfer function of the first and the second hop channels. For OFDM based systems, this appears to be sub-optimum. In this paper an AF relaying scheme is proposed that adapts to the transfer functions of both channels. The relay estimates the transfer functions and rearranges the subcarriers in each OFDM packet such that an optimum coupling between subcarriers of the first and the second hop channels occurs. Additionally, a signaling scheme is developed that allows for an efficient transfer of the necessary information. Simulations show that the proposed relaying scheme achieves significant SNR gains over conventional OFDM relaying.

A Chunk Based OFDM Amplify-and-Forward Relaying Scheme for 4G Mobile Radio Systems

About the Editors. Preface. Acknowledgements. Abbreviations. List of Contributors. 1 Introduction. 1.1 Development and Status of Mobile and Wireless Communications. 1.2 Expectations of Data Traffic Growth. 1.3 Development Towards IMT-Advanced. 1.4 Global Research Activities. 1.5 WINNER Project. 1.6 Future Work. References. 2 Usage Scenarios and Technical Requirements. 2.1 Introduction. 2.2 Key Scenario Elements. 2.3 Service Classes and Service Requirements. 2.4 Requirements for System Capabilities. 2.5 Terminal Requirements. 2.6 Performance Requirements. 2.7 Spectrum Requirements. 2.8 Dependency of Requirements. 2.9 Conclusion. Acknowledgements. References. 3 WINNER II Channel Models. 3.1 Introduction. 3.2 Modelling Considerations. 3.3 Channel-Modelling Approach. 3.4 Channel Models and Parameters. 3.5 Channel Model Usage. 3.6 Conclusion. Acknowledgements. References. 4 System Concept and Architecture. 4.1 Introduction. 4.2 Design Principles and Main Characteristics. 4.3 Logical Node Architecture. 4.4 Protocol and Service Architecture. 4.5 Conclusion. Acknowledgements. References. 5 Modulation and Coding Techniques. 5.1 Introduction. 5.2 Basic Modulation and Coding Scheme. 5.3 Coding Schemes. 5.4 Link Adaptation. 5.5 Link Level Aspects of H-ARQ. 5.6 Conclusions. References. 6 Link Level Procedures. 6.1 Introduction. 6.2 Pilot Design. 6.3 Channel Estimation. 6.4 Radio Frequency Impairments. 6.5 Measurements and Signalling. 6.6 Link Level Synchronisation. 6.7 Network Synchronisation. 6.8 Conclusion. Acknowledgements. References. 7 Advanced Antennas Concept for 4G. 7.1 Introduction. 7.2 Multiple Antennas Concept. 7.3 Spatial Adaptation. 7.4 Spatial Schemes. 7.5 Interference Mitigation. 7.6 Pilots, Feedback and Measurements. 7.7 MIMO Aspects in Relaying. 7.8 Conclusion. Acknowledgements. References. 8 Layer-2 Relays for IMT-Advanced Cellular Networks. 8.1 Introduction. 8.2 Motivation for Layer-2 Relays and Prior Work. 8.3 Relay-based Deployments. 8.4 Design Choices for Relay-based Cellular Networks. 8.5 System and Network Aspects. 8.6 System-level Performance Evaluation. 8.7 Conclusion. Acknowledgements. References. 9 Multiple Access Schemes and Inter-cell Interference Mitigation Techniques. 9.1 Introduction. 9.2 Multiple Access Schemes. 9.3 Inter-cell Interference Mitigation Schemes. 9.4 Conclusion. Acknowledgements. References. 10 Radio Resource Control and System Level Functions. 10.1 Introduction. 10.2 IPCL Layer. 10.3 Radio Resource Control. 10.4 Centralised, Distributed and Hybrid RRM Architecture. 10.5 System-Level Performance Results. 10.6 Conclusion. Acknowledgements. References. 11 Sharing and Flexible Spectrum Use Capabilities. 11.1 Introduction. 11.2 Spectrum Technologies Framework. 11.3 Detailed Design of a Spectrum Assignment Negotiation Mechanism. 11.4 Spectrum Assignment Enabling Mechanisms. 11.5 WINNER Sharing with FSS. 11.6 Performance Evaluation of Spectrum Assignment Mechanisms. 11.7 Conclusion. Acknowledgements. References. 12 ITU-R Spectrum Demand Calculation for IMT-Advanced. 12.1 Introduction. 12.2 ITU-R Work on Spectrum Requirements of IMT-Advanced. 12.3 ITU-R Spectrum Calculation Methodology. 12.4 Software Implementation of Methodology. 12.5 Estimated Spectrum Requirements of IMT-Advanced. 12.6 Conclusion. Acknowledgements. References. 13 System Model, Test Scenarios, and Performance Evaluation. 13.1 Introduction. 13.2 Performance Assessment of Wireless Networks. 13.3 Interface between Link and System Simulations. 13.4 Test Scenarios. 13.5 Spectral Efficiency and Number of Satisfied Users under QoS Constraints. 13.6 End-to-End Performance Evaluation. 13.7 Conclusion. Acknowledgements. References. 14 Cost Assessment and Optimisation for WINNER Deployments. 14.1 Introduction. 14.2 Cost Assessment Framework and Assumptions. 14.3 Cost Components. 14.4 Cost Assessment Models. 14.5 Reference Deployment Scenarios and Cost Assessments. 14.6 Conclusion. Acknowledgements. References. Index.

Radio technologies and concepts for IMT-Advanced

This paper presents a new analytical framework for the analysis of inter-cellular timeslot allocation over TDMA (time division multiple access) based air-interfaces using TDD (time division duplexing). The analysis is used to evaluate the delay- throughput performance of an adaptive decentralized inter- cell interference mitigation technique that exploits the inherent channel reciprocity of TDD. The main principle is that receivers upon successful transmission of a packet transmit a busy burst on a succeeding minislot. Potential transmitters in neighboring cells sense the minislot prior to signal transmission. With this mechanism, inter-cell interference to the existing link is avoided. The performance of this MAC (medium access control) protocol is compared against blind timeslot allocation. The new MAC protocol is shown to facilitate network self-organization, offering superior delay and throughput compared to the state of the art, with modest overhead and complexity requirements.

Analysis of TDD Cellular Interference Mitigation Using Busy-Bursts

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.

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

Research activities on systems beyond third generation mobile communication started already around 1999. The major drivers for these systems are the increasing demand for personal mobile communications with respect to performance, applications, traffic, and ease of use including communications involving machines. Cost reduction in terms of more bits for the same money is a major requirement to enable the economic success of future systems. From the user perspective increasing personal mobility enforces mobile communications in business and the private sector. ITU-R WP8F, ITU-T SSG and bodies like WWRF are currently working on the vision of systems beyond IMT-2000 on a global basis, and are defining basic requirements. New elements of these systems for the mobile access (up to 100 Mbps peak cell capacity) and the nomadic/wireless local area access (up to 1 Gbps peak cell capacity) are being discussed. These requirements result in a significant reduction of the covered range and, thereby, in the cell size compared to the third generation. In addition, a huge amount of spectrum is required to enable these requirements. The impact on attainable range and spectrum demand for a new mobile broadband access element is investigated. The nomadic/wireless local area access is not considered.

R. Luder

Papers

Data rate estimates, range calculations and spectrum demand for new elements of systems beyond IMT-2000