Heterogeneous Cellular Networks Mixed with LoS and NLoS Transmissions

In the last decades, the rapid increase of user traffc demand for better user experience has pushed the traditional macrocell-only networks being evolving to modern heterogeneous networks(HetNets) with a multi-tier structure. The dense deployment of small-cell base stations (BSs) implies short distances between BSs and users. It is therefore likely that users will see line-of-sight (LoS) links from its serving BS and even nearby interfering BSs, which has not been considered in performance analysis for multi-tier HetNets yet. In this thesis, the dense multi-tier HetNet with LoS and non-line-of-sight (NLoS) transmissions based on a multi-slope path loss model is analyzed. The spatial locations of BSs of any given network tier and those of mobile users are modeled as independent spatial Poisson point processes (PPPs). The expressions of downlink coverage probability are divided for a multi-tier HetNet, based on that the calculations of the area spectral effciency (ASE) and energy effciency (EE) are further proposed. The results demonstrate that in an extremely dense HetNet, both the ASE and EE of the HetNet will drop quickly with further increase of the small-cell density due to the dominance of LoS interfering small-cell links. Following that, the investigation is moved to the probabilistic events of LoS and NLoS transmissions. Four transmission scenarios are simulated with different path loss models, including a linear LoS probability function, a suburban area, a millimetre wave transmission and a 3D path loss model. Accordingly, a user-centric BS clustering strategy is proposed for a non-coherent joint transmissions (JTs) in dense small-cell networks, based on the idea of grouping the BSs with their LoS probabilities to such user above a predefined threshold. The proposed BS clustering strategy is evaluated in the above four transmission environments. Our simulation results show that the coverage probability and spectrum effciency (SE) achieved by the proposed user-centric BS clustering strategy achieve a rapid growth rate with the increasing BS density, and even at extremely high BS densities in all four considered environments. Lastly, following the proposed BS clustering strategy above, a further developed clustering strategy called multi-BS multi-user-equipment (UE) clustering is proposed to allow multiple BSs to serve multiple UEs simultaneously. The main idea of this clustering strategy is to boost network performance in terms of coverage probability and SE at high BS density without sacrificing the ASE. Utilizing stochastic geometry, the closed form expressions of the network performance in terms of coverage probability, SE, ASE and EE are derived in a downlink small-cell network. The results show that the proposed clustering strategy achieves high coverage probability and linear increasing SE and ASE in ultra dense networks at same time

5G Ultra-dense networks with non-uniform Distributed Users

User distribution in ultra-dense networks (UDNs) plays a crucial role in affecting the performance of UDNs due to the essential coupling between the traffic and the service provided by the networks. Existing studies are mostly based on the assumption that users are uniformly distributed in space. The non-uniform user distribution has not been widely considered despite that it is much closer to the real scenario. In this paper, Radiation and Absorbing model (R&A model) is first adopted to analyze the impact of the non-uniformly distributed users on the performance of 5G UDNs. Based on the R&A model and queueing network theory, the stationary user density in each hot area is investigated. Furthermore, the coverage probability, network throughput and energy efficiency are derived based on the proposed theoretical model. Compared with the uniformly distributed assumption, it is shown that non-uniform user distribution has a significant impact on the performance of UDNs.Comment: 14 pages, 10 figure

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