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Beamforming Techniques for Millimeter Wave Relay Networks
[Thesis]. Manchester, UK: The University of Manchester; 2017.
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Abstract
The energy and data rate requirements for the next generation cellular networks urge the need for innovative solutions. Inspired by its massive bandwidth, millimeter wave (mmWave) band is thought-out to be one of the key elements to meet the aspirations. However, mmWave links are known to have short coverage distance due to the propagation losses introduced at high frequencies. The proposed solutions to overcome the transmission challenges include using large arrays with improved directivity, adopting smaller cells, and relying on cooperative networks to extend the mmWave link and avoid shadowing areas. This work aims to improve the connectivity of the mmWave link in the outdoor environments. One of the cost effective methods is to increase the array gain by using Analogue Beamforming (ABF). The performance of the ABF system in the presence of phase quantization error has been analytically investigated. The study also includes comparing three different channel sounding techniques, namely: exhaustive search, side-to-side search, and n-tier search. The time overhead related to each method and their energy consumption are calculated. The numerical results assist in determining the optimum search period to obtain a reasonable spectral efficiency using minimal power consumption. The results also help identify the minimum number of quantization bits required to produce about ninety percent of the optimistic results. In order to extend the coverage further, relay networks are considered an essential component in mmWave communications. The performance of a single hybrid beamforming full-duplex relay system and multi-relay networks were investigated. The design algorithms for the processors in the network are proposed based on the greedy pursuit approach. The performance of the proposed algorithms is analysed under various scenarios. The analysis highlights the influence of the array size, the number of RF chains, and the length of the channel sounding period. The performance of the proposed systems is compared from both the spectral efficiency and power consumption prospects. The results also establish that the number of antennas at the source and the relay receiver arrays have a superior impact on the system performance than the sizes of the array at the destination and the relay transmitter.