Advanced Relay Technologies in Next Generation Wireless Communications
2: Wolfson School of Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough, UK
Cooperative networks/relaying is a fundamental design approach that has been used to reduce path-loss and fading effects in conventional wireless communication systems. This book describes the use of this approach in new and emerging telecommunications technologies and new application areas. Topics covered include spatial modulation for cooperative networks; relaying for massive MIMO; relaying for outdoor to indoor in mmWave communications; precoding techniques for relaying with interference; relaying in full-duplex radio communication systems; relay selection in modern communication systems; relaying in green communications systems; energy-efficient relaying; cognitive radio with relaying; relaying in non-ideal conditions; relaying and physical layer secrecy; relaying technologies for smart grid; simultaneous wireless and power transfer for interference relay channel; relaying in visible light communication systems; and on-ground and on-board signal processing for multibeam. With contributions from an international panel of experts, this book is essential reading for researchers and advanced students in academia and industry working in telecommunications system design.
Inspec keywords: radiofrequency interference; telecommunication security; energy conservation; next generation networks; relay networks (telecommunication); radiofrequency power transmission; MIMO communication; cooperative communication; free-space optical communication; telecommunication power management; antenna arrays
Other keywords: massive MIMO system; simultaneous wireless information and power transfer; energy-efficient relaying; spatial modulation; cooperative relay; relay interference channel; physical layer security; green communication system; multiantenna relaying system; optical wireless communication
Subjects: Antenna arrays; Textbooks; General topics, engineering mathematics and materials science; Radio links and equipment; Telecommunication systems (energy utilisation); Free-space optical links; Electromagnetic compatibility and interference
- Book DOI: 10.1049/PBTE068E
- Chapter DOI: 10.1049/PBTE068E
- ISBN: 9781785610035
- e-ISBN: 9781785610042
- Format: PDF
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Front Matter
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1 Spatial modulation for cooperative networks
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In this chapter, Distributed Spatial Modulation (DSM) and Distributed Spatially Modulated Space-Time Block Code (DSM-STBC) are elaborately described. DSM and DSM-STBC are two new cooperative wireless protocols for multi-relay networks, which are based on the principle of Spatial Modulation (SM). The distinguishable feature of DSM lies in improving the reliability of the source via distributed diversity and by increasing the aggregate throughput of the cooperative network, since new data is transmitted during each transmission phase. This is achieved by encoding the data transmitted from the source into the spatial positions of the available relays and by exploiting the signal domain for transmitting the data of the relays. In DSM-STBC, SM and Space-Time-Block-Codes (STBCs) are synergistically combined for a distributed scenario. The distinguishable feature of DSM-STBC lies in offering throughput enhancement, by achieving the same order of diversity and having to activate the same number of relay nodes as conventional distributed STBC schemes. At the destination, demodulators robust to demodulation errors at the relays are developed, and their end-to-end error probability and achievable diversity are studied. With the aid of Monte Carlo simulations, DSM and DSM-STBC are compared against state-of-the-art cooperative protocols, and they are shown to provide better performances.
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2 Relaying for massive MIMO
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Multi-user massive MIMO relaying is a cost-effective, pragmatic solution to one of the fundamental bottlenecks of the wireless physical layer, namely, the low-area spectral efficiency. Specifically, a combination of massive MIMO and wireless relaying techniques can potentially be exploited for improving the trade-off between spectral efficiency and coverage, thereby substantially improving the achievable area spectral efficiency. To this end, in this chapter, system configurations, transmission frame structures, CSI acquisition techniques and signal processing aspects for multi-user massive MIMO relay networks have been presented. Moreover, the corresponding channel models and favourable propagation conditions have been reviewed, and thereby, a generalized end-to-end signal model has been developed. First, the performance analysis techniques and the underlying mathematical tools have been presented, and then, they have been used for deriving basic performance metrics including asymptotic SINR and achievable sum rate expressions. Finally, important insights have been drawn by using these performance metrics, and thereby, the validity and viability of the proposed system, channel and signal models can be ascertained.
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3 SUDAS: mmWave relaying for 5G outdoor-to-indoor communications
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In this chapter, we have proposed a novel SUDAS with the objective of achieving the 10 Gbit/s data rate goal set by 5G for indoor UEs. The proposed SUDAS exploits the benefits of the licensed and unlicensed frequency bands simultaneously. In particular, it translates the spatial multiplexing in the licensed bands into frequency multiplexing in the unlicensed bands for boosting the end-to-end data rate via VMIMO. It is expected that the proposed SUDAS can further enhance the system performance when advanced resource allocation technique is employed. Besides, we have also discussed some potential application scenarios where deployment of SUDAS appears to be beneficial. Also, we have investigated different potential realizations of SUDAS and the corresponding implementation challenges. It is expected that the proposed SUDAS is able to bridge the gap between the current technology and the high data rate requirement of the next generation communication systems.
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4 Linear processing techniques for multi-antenna relaying systems with interference
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This paper reviewed recent advances of linear processing techniques for multi-antenna relaying systems with interference. This paper showed that with simple linear processing schemes such as MRC/MRT, ZF/MRT, or MMSE/MRT, multiple antennas can be efficiently exploited to suppress or cancel CCI in dual-hopAF relaying systems. The performance of these schemes depend on the SNR operation point of the system. Specifically, the MMSE/MRT scheme achieves the best outage performance, and the ZF/MRT scheme outperforms the MRC/MRT scheme in the low-SNR regime, while becomes inferior to the MRC/MRT scheme in the high-SNR regime. Moreover, increasing the number of antennas at the relay and using advanced linear processing schemes such as ZF/MRT or MMSE/MRT are effective solutions to mitigate the effect of interference.
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5 Relaying in full-duplex radio communication systems
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As explained in many chapters of this book, relaying in principle means indirect data transmission from a source node to a destination node via intermediate relay nodes (RNs), e.g., not so unlike repeaters, gap-fillers, or signal boosters do in old-fashioned wireless systems. On the other hand, the field of information theory has addressed many classical questions related to the performance of idealistic relay links. Relay transceivers in these original research areas conventionally operate in a full-duplex (FD) mode, while later studies on cooperative communication deemed it impossible to begin with and focused almost invariably on half-duplex (HD) relaying. However, modern relay transceivers such as those assumed in the context of this chapter are much more advanced than simple analog amplifiers in terms of their processing capabilities so that, e.g., they can be made robust to interference. Time has thus become right for us to return to the origins of relaying by promoting FD operation as a practical and highly efficient design choice whose technical difficulties can be now overcome. With this background, this chapter provides an overview of essential aspects to be considered when introducing FD operation into relaying systems. Two particular contributions are central for this development, namely introducing transmit power control for FD relaying and comparing the performance of FD relay links to that of their HD counterparts. The main focus herein is on infrastructure relaying although the considered systems have their relatives with cable-connected distributed antennas and mobile relays instead. Thus, the considered relay transceivers are fixed nodes and belong to infrastructure deployed by a network operator. This scope choice differs from earlier mainstream literature which is inclined toward ad hoc mobile relaying by user terminals. When discussing cellular systems, the link elements may be referred to as a base station (BS), a RN, and a user equipment (UE). The BS and RNs form a “backhaul link” while UEs are always connected to a “service link”. There is typically only one relay per each group of destinations (except for special hand-over situations) while backhaul links may involve multihop relaying. Furthermore, the study is formulated in an implicit context to concern a single subcarrier within orthogonal frequency-division multiplexing (OFDM) transmission.
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6 Relay selection in modern communication systems
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This chapter presents relay selection policies under different communication scenarios and applications. Specifically, the chapter focuses on the benefits and efficiency of relay selection in the context of full-duplex (FD) enabled relays (Section 6.2), relays with buffers (Section 6.3) and relays with wireless power transfer (WPT) capabilities (Section 6.4). These scenarios show that relay selection is an efficient PHY layer tool for the design of modern communication networks.
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7 Relaying in green communication systems
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This chapter has discussed energy efficiency issues and comparisons among relay protocols. A widely applicable system model has been introduced along with relevant energy efficiency metrics. In addition, the importance of using models that can compute the overall energy consumption (not just the transmitted radio-frequency power) has been emphasized. We have discussed in detail the energy efficiency optimization of different relay protocols includingAF,DF and CF. Mathematical methods including a general fractional programming framework to minimize the energy consumption ratio have been presented and the best energy efficiency regions for deploying relays have also been presented. This chapter has also studied the benefits of using relaying to form VMIMO network configurations. The performance trade-offs for different relay protocols in this scenario have been discussed and compared. The spectral and energy efficiency comparisons of different relay setups with varying numbers of antennas have also been discussed.
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8 Energy-efficient relaying
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The next generations of wireless cellular communications will deploy flexible heterogeneous architectures including smart relays, femto, and macro base stations [28]. It is expected that 50 billion connected devices will operate by 2020, and that a lot of new services will be implemented including e-health, e-banking, e-learning, and so on. This requires both the data rates to grow by a factor of 1000 and the communication latency to be drastically reduced [8]. These requirements are to be realized with similar or even lower energy consumption as in current wireless communications. Therefore, we need an energy-efficient design of relay-assisted cellular networks.
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9 Cognitive relaying for information and energy cooperation
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The rapidly growing wireless networks come with great challenges such as fading degradation, spectrum scarcity and energy constraints. This chapter introduces advanced relaying techniques in cognitive radio networks in which the primary and the secondary systems actively seek for cooperation opportunities, that can deal with these challenges in an effective way. We focus on cooperation at both information level and energy level, such that the primary users' (PUs) performance can be boosted, the secondary users (SUs) have much higher chance for spectrum access, and energy flow is optimized to benefit both systems.
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10 Relaying in non-ideal conditions
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Wireless relaying has been proposed as a promising technology to achieve either diversity gain via a distributed multiple-input multiple-output setting or extended network coverage without the need for extra infrastructure. In practice, this is often performed under non-ideal channel and signal conditions. In this chapter, the effects of various non-ideal conditions on the performance of wireless relaying will be examined. We focus on amplify-and-forward (AF) relaying, where the relay node amplifies and forwards the signal received from the source node to the destination node without any decoding. The examined non-ideal conditions include feedback delay, link correlation, non-Gaussian interference, and wireless power.
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11 Relaying and physical layer security
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In this chapter, we investigate the problem of physical-layer security in wireless networks with cooperative relays. In Sections 11.2 and 11.3, we study the notion of deaf cooperation to reinforce security of transmission in wireless relay networks. We distinguish between two main approaches to deaf cooperation, namely, the cooperative jamming (CJ) approach and the noise forwarding (NF) approach. In a CJ scheme, a helping interferer transmits Gaussian noise when it can hurt the eavesdropper more than it can hurt the legitimate receiver, and hence improves the achievable secure information rate. The idea of introducing artificial noise in a Gaussian wiretap channel by a helper node was introduced in References 5-7. In relay networks with secrecy constraints, the role of CJ was further investigated, e.g., in References 8-10. References 11-13 proposed CJ strategies for multiple-antenna relay networks. On the other hand, in the NF scheme which was introduced in Reference 14, the relay node sends a dummy (context-free) codeword drawn at random from a codebook that is known to both the legitimate receiver and the eavesdropper to introduce helpful interference that would hurt the eavesdropper more than the legitimate receiver.
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12 Relaying technologies for smart grid
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In this chapter, an introduction of communication networks and relaying strategies for SGs is presented, together with a discussion of how to improve spectral efficiency and coverage in relay-based ICT infrastructure for SG applications. Considering communication channel medium, there are two sets of networks in SGs, i.e., wired and wireless communication networks. Special attention is paid to the use of various relaying strategies in power line communication (PLC) and wireless communication networks.
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13 Simultaneous wireless information and power transfer in relay interference channels
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In this chapter, we extend our previous works [24, 25] to a more general scenario of relay interference channels with energy harvesting relays equipped with multiple antennas. It is worth pointing out that implementing multiple antennas at the relays is particularly appealing in practice since it can not only boost the amount of harvesting energy at the relay in the first hop but also enhance the strength of the received signal at the destination by exploiting the transmit diversity technique in the second hop. The power splitting technique is assumed to implement at relays. Specifically, each relay node splits the signal received from all sources into two parts according to a power splitting ratio: one part is sent to the information processing unit, and the rest is used to harvest energy for forwarding the received information in the second time slot. We consider that each link's performance is characterized by its achievable rate and thus regard the sum-rate of all links as a network-wide performance metric. However, the network-wide sum-rate maximization problem of the considered system is shown to be analytically non-tractable due to its complexity and non-convexity. Motivated by this, we propose a heuristic two-stage network optimization approach. Specifically, considering the energy harvesting feature of the relays, we first figure out that the maximum ratio combining/maximal ratio transmission (MRC/MRT) scheme would be a particularly appropriate signal processing technique for the relays in practice owing to its low complexity and light requirement of channel state information (CSI). In the second stage, we optimize the power splitting ratios of the relays with the selected MRC/MRT technique.
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14 Relaying in optical wireless communication
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Co-located MIMO systems might not be realisable for all applications and this encourages the implementation of distributed MIMO systems with widely separated nodes cooperating to provide spatial diversity. Such systems, which are also known as cooperative or relay-assisted communication, have been extensively investigated in the context of RF wireless communication. Multi-hop transmission is an alternative relay-assisted scheme, which employs multiple relays in serial configuration. RF multi-hop systems do not offer any diversity gain but they are typically employed to extend the coverage of communication networks. This chapter will investigate the application of distributed MIMO and relaying strategies as efficient solutions to overcome atmospheric degradations in OWC channels.
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15 Multibeam joint processing satellites: cooperative relays, high above
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The main goal of this chapter has been to introduce the reader to the most recent research developments on joint processing multibeam satellite communications. Since a joint processing enabled multibeam satellite constitutes a cooperative amplify-and-forward relay, these developments are closely related to the cooperative relaying literature. Nevertheless, as in detail described herein, the inherent nature of the satellite channel emanates fundamental differentiations in the proposed signal processing methods. Three main practical limitations have been overviewed. First, the need to jointly process signals over a fixed framing structure, coined as framed-based precoding. Second, the proper consideration of the non-idealities of real amplifiers and the effect they can have on precoded signals. Finally, but equally important, the detailed design of receivers that can operate in an interference-limited environment and adequately estimate the channel state of each user, so that precoding at the transmitter can be ultimately performed. If a single take home lesson needs to be gained from this overview would be that cooperative satellite relaying from high above is a mature technology from a research perspective and has reached the doorstep of practical demonstration and implementation.
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Back Matter
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