Millimetre wave frequency band as a candidate spectrum for 5G network architecture : a survey

In order to meet the huge growth in global mobile data traffic in 2020 and beyond, the development of the 5th Generation (5G) system is required as the current 4G system is expected to fall short of the provision needed for such growth. 5G is anticipated to use a higher carrier frequency in the millimetre wave (mm-wave) band, within the 20 to 90 GHz, due to the availability of a vast amount of unexploited bandwidth. It is a revolutionary step to use these bands because of their different propagation characteristics, severe atmospheric attenuation, and hardware constraints. In this paper, we carry out a survey of 5G research contributions and proposed design architectures based on mm-wave communications. We present and discuss the use of mm-wave as indoor and outdoor mobile access, as a wireless backhaul solution, and as a key enabler for higher order sectorisation. Wireless standards such as IEE802.11ad, which are operating in mm-wave band have been presented. These standards have been designed for short range, ultra high data throughput systems in the 60 GHz band. Furthermore, this survey provides new insights regarding relevant and open issues in adopting mm-wave for 5G networks. This includes increased handoff rate and interference in Ultra-Dense Network (UDN), waveform consideration with higher spectral efficiency, and supporting spatial multiplexing in mm-wave line of sight. This survey also introduces a distributed base station architecture in mm-wave as an approach to address increased handoff rate in UDN, and to provide an alternative way for network densification in a time and cost effective manner

Millimeter Wave Hybrid Beamforming Systems

The motivation for this thesis is the design of millimetre wave (mmWave) hybrid beamforming systems for supporting high user density. mmWave systems with hybrid digital-to-analogue beamforming (D-A BF) have the potential to fulfil 5G traffic demands. However, the capacity of mmWave systems is severely limited as each radio frequency (RF) transceiver chain in current sub-array mmWave base station (BS) architectures support only a particular user. Therefore, two new algorithms have been proposed for broadband mmWave systems. The algorithms operate on the principles of selection combining (SC) and principal component (PC). SC is a spatio-temporal hybrid D-A BF which has been designed to exploit multipath diversity, which is a characteristic feature of broadband propagation at mmWave. A novel low-complexity variant of SC, called low-complexity selection combining (LC-SC) has also been proposed for supporting high user density for such sub-array mm-Wave BS. mmWave lens-antenna systems are an emergent beamforming technology. They are novel because they eliminate the requirement of traditional analog beamformers. In this context, a low-complexity beam allocation (LBA) algorithm, proposed in an earlier research, has been applied to solve the challenging problem of maximizing sum data-rates in switched-beam mmWave systems. However, there are practical limitations, such as restrictions in the number of available RF chains at the BS, sensitivity to sidelobe interference and the beam generation techniques. Using generalized beam-patterns, the maximum sum data-rates achievable in switched-beam mmWave systems is compared to fixed-beam systems by applying LBA. Then, the impact on maximum sum data-rates of actual beam-patterns, obtained from a practical mmWave lens-antenna, which have higher and non-uniform sidelobes compared to the theoretical beams, is assessed. Non-orthogonal multiple access (NOMA) relay with hybrid digital-to-analog precoding (D-A P) as a promising solution for supporting high user densities in overloaded millimeter wave (mmWave) systems is investigated. To support high user densities in current mmWave hybrid D-A P systems, an idea based on exploiting the concept of NOMA relay to support 2K users per RF chain is proposed, where 2K M. To design the hybrid D-A P systems, the SC and PC algorithms are combined with NOMA relay to support significantly higher user densities. In future research, performance impairments in beamforming assistedmmWaveNOMA systems due to far-user's angle-of-departure (AoD) divergence with respect to the near-user is being investigated. This investigation is novel since most literature in NOMA considers both the near-user and far-user pairs static with respect to one another