Abstract
In cellular wireless communication systems, the current and future networks are promising to provide multimedia services at the cell edges and beyond the cell boundaries efficiently and cost effectively. The relay assisted MIMO networks have got much attraction to meet the requirements by providing high capacity, link reliability and high quality of service. The performance of the relay assisted networks is maximized by making the use of beamforming design at the relay nodes. This chapter describes the recent developments in relay beamforming design for Amplify-and-Forward (AF) relay networks and introduces a new beamforming scheme to improve the network performance in terms of ergodic capacity. The chapter contributes in introduction to basic MIMO channel, various relaying strategies and introduction to relay assisted network topologies. It is followed by critical literature review on AF beamforming techniques. This leads towards the novel and efficient relay beamforming design, its performance evaluation and validity by comparing with various available beamforming techniques.
TopBackground
The main application scenario of the relaying transmission is found in cellular wireless communication systems for capacity and coverage extension. Mostly the wireless communication networks experience three fundamental problems interdependently which are coverage, capacity and interference (Dohler & Li, 2010). In terms of capacity and endorsed transmit power, a limited amount of resources are assigned to a base station to serve a pre-defined number of users. However, with the growing number of users, the offered capacity becomes inadequate and results in unsatisfactory service. The limitation on transmit power causes inadequate power at the cell edge. The users at cell edge are suffered from neighbouring interference users and cells. The relays have proved to be the best and cost effective solution to alleviate these problems other than micro base station concept of solving the problems of capacity and coverage.
Key Terms in this Chapter
MIMO Precoding: It is designed to maximize signal power to the target user while minimizing the interference power to other co-channel users.
Amplify-and-Forward Relay: A simple and less complex relaying transmission protocol, that simply multiply amplifying matrix with the received signal and forward it to the destination.
SINR: Signal to interference and noise ratio; defined as the ratio of desired signal power to the interference plus noise.
Distributed Array Gain: The gain obtained using multiple relay nodes in the dual-hop network.
SLNR: Signal to noise and leakage ratio; defined as the ratio of intended signal power to the leakage interference plus noise.
Beamforming: A signal processing technique in MIMO that helps to optimize the resources.
Leakage Interference: The interference due to the leakage signal from the intended antenna that causes interference to the neighbouring antenna in the MIMO system.
Co-Channel Interference: The interference among multiple data streams.
Channel State Information: The knowledge of channel that is used for beamforming design in MIMO system.
Ergodic Capacity: The expectation of the instantaneous mutual information between the source and the destination.