Multi-point Cooperative Communication Systems: Theory and Applications

This chapter gives an introduction of this book. First, we begin with a large picture by reviewing the fast development of wireless communication in the past half century with the emphasis on the cellular network. Second, we discuss the future and key technologies of the enhanced fourth generation (4G) international telecommunication network based on analysis of challenges and requirements in the next decade. Third, among the discussed key technologies, we focus on the multipoint cooperative communication and present its background to readers. Finally, we indicate the scope and outline of this book to complete this introduction.

In this chapter, we address the existing work related to multipoint cooperative communication technologies. First, we discuss the fundamentals of wireless digital communication as a preparation for the following in-depth investigations on plenty of new concepts and technologies. Second, we review several selected topics that have laid the foundation for cooperative communication, for example, the orthogonal frequency-division multiplexing (OFDM) transmission, the multiple-input multiple-output (MIMO) system, the MIMO relay network, the multiuser (MU) MIMO theory, and channel state information (CSI) feedback methods. Third, we perform a thorough survey on the state of the researches of multipoint cooperative communication technology by classifying all the existing schemes into eight categories according to three factors, that is, whether data sharing is conducted, whether CSI sharing is allowed, and whether time-frequency synchronized transmission or reception (TFSTR) is operated. In this chapter, we present a large technical picture about the history and new development in each area of multipoint cooperative communication, which helps to show the positions of the topics to be treated in the following chapters.

For the sixth category of multipoint cooperative communication technology, we address the relay/antenna selection schemes for the amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network in this chapter. First, we discuss the system model of an AF MIMO relay network as well as the value of relay/antenna selection when joint relay precoding cannot be operated. Second, we review the existing relay/antenna selection algorithms and present our motivations of improving the existing schemes. Third, we propose three greedy relay/antenna selection algorithms, that is, doubly zero-forcing (ZF) greedy capacity maximization (DZF-GCM), greedy capacity maximization (GCM), and greedy mean square error (MSE) minimization (GMM) algorithms, to optimize the system based on various performance metrics. The effectiveness of the proposed schemes is corroborated by our simulation results followed by comprehensive discussions on the performance comparison of various algorithms to provide more insights on this topic.

For the seventh category of multipoint cooperative communication technology, we investigate the interference coordination schemes for the uplink frequency division multiple access (FDMA) cellular network in this chapter. First, we elaborate on the topology of a cellular system and show the interference problem in the uplink FDMA network. Second, we discuss the hard, fractional, and soft frequency reuse schemes, and then we address our motivations to improve the static implementation of soft resource reuse scheme with minimum intercell CSI exchanges. Third, we propose an advanced interference coordination scheme that consists of six steps with the key design lying in the enhanced user equipment (UE) categorization and resource-access control policies. In order to verify the effectiveness of the proposed scheme, we resort to the approach of system-level simulation, the methodology and implementation of which are addressed in great details. From the simulation results, it can be observed that compared with the conventional schemes, the proposed scheme can largely increase the efficiency of the trade-off between the cell-edge throughput and the overall throughput, thus showing high values in the study of interference coordination and application for the uplink FDMA cellular network.

For the eighth category of multipoint cooperative communication technology, we discuss joint precoding schemes with ideal backhaul conditions for the downlink cellular network in this chapter. First, we introduce some of the well-known precoding schemes for joint transmission (JT), that is, the global precoding (GP), local precoding (LP), weighted local precoding (WLP), and single-frequency network precoding (SFNP) schemes. Second, we propose an enhanced SFNP scheme with smart antenna selection (AS) operated at the cooperating base stations (BSs), which is named AS-SFNP scheme. Third, for single-antenna UEs, both analytical lower bounds and simulation results are provided to show that both the proposed AS-SFNP scheme and the WLP scheme achieve performance close to that of the optimal GP scheme in terms of average signal-to-interference-plus-noise ratio (SINR). For multi-antenna UEs, simulation results demonstrate that the proposed AS-SFNP scheme can achieve a larger capacity than the LP, WLP, and SFNP schemes in high-SNR regime. Furthermore, from a system-level simulation of a practical cellular network, the AS-SFNP scheme with a low feedback overhead and low-complexity implementation shows comparable performance of the cell-edge spectral efficiency with the WLP and GP schemes.

For the eighth category of multipoint cooperative communication technology, we discuss the sequential and incremental precoding scheme with nonideal backhaul conditions for the downlink joint transmission (JT) network in this chapter. First, we address the system model of JT and describe the backhaul impairments. Second, we discuss the conventional autonomous global precoding (AGP) scheme, which may suffer from severe performance degradation in the event of partial JT and single-BS transmission (ST) resulted from imperfect backhaul communications. Third, we propose a sequential and incremental precoding (SIP) scheme to overcome the drawbacks of the existing schemes. The objective of our design is to minimize the maximum of the sub-stream mean square errors (MSE), which dominates the average bit error rate (BER) performance of the system. The key problem is first illustrated and solved with a two-BS JT system, and the results are then generalized to multi-BS JT systems. Simulations show that, under the practical backhaul link conditions, our scheme significantly outperforms the AGP scheme in terms of BER performance.

In this chapter, the application of multipoint cooperative communication in the 4G networks, that is, the coordinated multipoint (CoMP) system, is addressed from a variety of aspects. First, we review the development of CoMP in the standardization of Long-Term Evolution-Advanced (LTE-A) networks and analyze the reason of its preclusion from the LTE Release 10 specification. Second, we discuss the renewed campaign of CoMP in LTE Release 11, including the downlink transmission and uplink reception schemes of CoMP, as well as the related specification works. Third, we analyze the simulation results from the 3GPP CoMP study item to show the advantages of CoMP system in practical cellular networks.

In this chapter, we address the common feedback framework (CFF) for downlink coordinated multipoint (CoMP) transmissions in Long-Term Evolution (LTE) Release 11 networks. First, we introduce the work item of CoMP in LTE Release 11 and the ambitious goal of standardizing a CFF to support all interested CoMP schemes. Second, we discuss four candidates of CFF options, with the emphases on feedbacks of co-phase information (CFF option 2) and aggregated CQI (CFF option 3). From system-level simulation results, it can be observed that both CFF options 2 and 3 are able to offer considerable cell-edge throughput gains compared with the non-CoMP scheme. Third, we review the relevant standardization activities and explain why it is another CFF option that will eventually be adopted in LTE Release 11. Finally, some concluding remarks are provided to forecast the further development of CoMP CFF in the future.

In this chapter, we summarize the key points of this book and look forward to the future of multipoint cooperative communication technologies. It is pointed out that multipoint cooperative communication with new features will continue to be one of the key technologies in the future 5G cellular networks.