Mathematical Modelling and Analysis of Spatially Correlated Heterogeneous and Vehicular Networks - A Stochastic Geometry Approach

Heterogeneous Cellular Networks (HCNs) and vehicular communications are two key ingredients of future 5G communication networks, which aim at providing high data rates on the one former case and high reliability on the latter one. Nevertheless, in these two scenarios, interference is the main limiting factor, which makes achieving the required performance, i.e., data rate or reliability, a challenging task. Hence, in order to cope with such issue, concepts like uplink/downlink (UL/DL) decoupling, Interference-Aware (IA) strategies or cooperative communications with Cloud Radio Access Networks (CRANs) has been introduced for new releases of 4G and future 5G networks. Additionally, for the sake of increasing the data rates, new multiple access schemes like Non-Orthogonal Multiple Access (NOMA) has been proposed for 5G networks. All these techniques and concepts require accurate and tractable mathematical modelling for performance analysis. This analysis allows us to obtain theoretical insights about key performance indicators leading to a deep understanding about the considered techniques. Due to the random and irregular nature that exhibits HCNs, as well as vehicular networks, stochastic geometry has appeared recently as a promising tool for system-level modelling and analysis. Nevertheless, some features of HCNs and vehicular networks, like power control, scheduling or frequency planning, impose spatial correlations over the underlying point process that complicates significantly the mathematical analysis. In this thesis, it has been used stochastic geometry and point process theories to investigate the performance of these aforementioned techniques. Firstly, it is derived a mathematical framework for the analysis of an Interference-Aware Fractional Power Control (IAFPC) for interference mitigation in the UL of HCNs. The analysis reveals that IAFPC outperforms the classical FPC in terms of Spectral Efficiency (SE), average transmitted power, and mean and variance of the interference. Then, it is investigated the performance of a scheduling algorithm where the Mobile Terminals (MTs) may be turned off if they cause a level of interference greater than a given threshold. Secondly, a multi-user UL model to assess the coverage probability of different MTs in each cell is proposed. Then, the coverage probability of cellular systems under Hoyt fading (Nakagami-q) is studied. This fading model, allows us to consider more severe fading conditions than Rayleigh, which is normally the considered fading model for the sake of tractability. Thirdly, a novel NOMA-based scheme for CRANs is proposed, modelled and analyzed. In this scheme, two users are scheduled in the same resources according to NOMA; however the performance of cell-edge users is enhanced by means of coordinated beamforming. Finally, the performance of a decentralized Medium Access Control (MAC) algorithm for vehicular communications is investigated. With this strategy, the cellular network provides frequency and time synchronization for direct Vehicle to Vehicle (V2V) communication, which is based on its geographical information. The analysis demonstrates that there exists an operation regime where the performance is noise-limited. Then, the optimal transmit power that maximizes the Energy Efficiency (EE) of the system subject to a minimum capture probability constraint is derived

Cognitive Radio Systems

Cognitive radio is a hot research area for future wireless communications in the recent years. In order to increase the spectrum utilization, cognitive radio makes it possible for unlicensed users to access the spectrum unoccupied by licensed users. Cognitive radio let the equipments more intelligent to communicate with each other in a spectrum-aware manner and provide a new approach for the co-existence of multiple wireless systems. The goal of this book is to provide highlights of the current research topics in the field of cognitive radio systems. The book consists of 17 chapters, addressing various problems in cognitive radio systems

Integrated cellular and device-to-device networks

textDevice-to-device (D2D) networking enables direct discovery and communication between cellular subscribers that are in proximity, thus bypassing the base stations (BSs). In principle, exploiting direct communication between nearby mobile devices will improve spectrum utilization, overall throughput, and energy consumption, while enabling new peer-to-peer and location-based applications and services. D2D-enabled broadband communication technology is also required by public safety networks that must function when cellular networks are not available. Integrating D2D into cellular networks, however, poses many challenges and risks to the long-standing cellular architecture, which is centered around the BSs. This dissertation identifies outstanding technical challenges in D2D-enabled cellular networks and addresses them with novel models and fundamental analysis. First, this dissertation develops a baseline hybrid network model consisting of both ad hoc nodes and cellular infrastructure. This model uses Poisson point processes to model the random and unpredictable locations of mobile users. It also captures key features of multicast D2D including multicast receiver heterogeneity and retransmissions while being tractable for analytical purpose. Several important multicast D2D metrics including coverage probability, mean number of covered receivers per multicast session, and multicast throughput are analytically characterized under the proposed model. Second, D2D mode selection which means that a potential D2D pair can switch between direct and cellular modes is incorporated into the hybrid network model. The extended model is applied to study spectrum sharing between cellular and D2D communications. Two spectrum sharing models, overlay and underlay, are investigated under a unified analytical framework. Analytical rate expressions are derived and applied to optimize the design of spectrum sharing. It is found that, from an overall mean-rate perspective, both overlay and underlay bring performance improvements (vs. pure cellular). Third, the single-antenna hybrid network model is extended to multi-antenna transmission to study the interplay between massive MIMO (multi-input multiple-output) and underlaid D2D networking. The spectral efficiency of such multi-antenna hybrid networks is investigated under both perfect and imperfect channel state information (CSI) assumptions. Compared to the case without D2D, there is a loss in cellular spectral efficiency due to D2D underlay. With perfect CSI, the loss can be completely overcome if the number of canceled D2D interfering signals is scaled appropriately. With imperfect CSI, in addition to pilot contamination, a new asymptotic underlay contamination effect arises. Finally, motivated by the fact that transmissions in D2D discovery are usually not or imperfectly synchronized, this dissertation studies the effect of asynchronous multicarrier transmission and proposes a tractable signal-to-interference-plus-noise ratio (SINR) model. The proposed model is used to analytically characterize system-level performance of asynchronous wireless networks. The loss from lack of synchronization is quantified, and several solutions are proposed and compared to mitigate the loss.Electrical and Computer Engineerin

Efficient Device to Device Communications Underlaying Heterogeneous Networks

Device-to-Device communications have the great potential to bring significant performance boost to the conventional heterogeneous network by reusing cellular resources. In cellular networks, Device-to-Device communication is defined as two user equipments in a close range communicating directly with each other without going through the base station, thus offloading cellular traffic from cellular networks. In addition to improve network spectral efficiency, D2D communication can also improve energy efficiency and user experience. However, the co-existence of D2D communication on the same spectrum with cellular users can cause severe interference to the primary cellular users. Thus the performance of cellular users must be assured when supporting underlay D2D users. In this work, we have investigated cross-layer optimization, resource allocation and interference management schemes to improve user experience, system spectral efficiency and energy efficiency for D2D communication underlaying heterogeneous networks. By exploiting frequency reuse and multi-user diversity, this research work aims to design wireless system level algorithms to utilize the spectrum and energy resources efficiently in the next generation wireless heterogeneous network

Performance analysis of mmWave vehicle-to-vehicle communications : a stochastic geometry approach

Advanced sensory systems are the driving force behind autonomous vehicles. They have led to such vehicles producing and processing much more content-intensive visual data. It is foreseen that traffic consisting solely of autonomous vehicles will enable people and goods to travel more safely. Using millimetre wave (mmWave) frequencies for wireless communication between vehicles is a rising research topic, both to enhance safety and reliability of autonomous vehicles and to meet the data rate required by the content-intensive data-set produced by their advanced sensory systems. The main goal of this thesis is to make a stochastic analysis of the signal quality that can be achieved by vehicles when using mmWave frequencies for the wireless communication between them. To address this issue, the tools of stochastic geometry is used in this thesis. Firstly, stochastic geometry provides advanced mathematical properties to model the system fairly accurate and tractable. Secondly, resulting analytical model helps system designers to develop insights to understand relationships between system parameters. The first academic contribution of this thesis is a two-fold probabilistic connectivity analysis of an autonomous vehicle fleet for a single-lane road. In other words, it stochastically models the connectivity probability of the sensory data of the head and tail vehicles of the fleet shared over intermediate fleet vehicles by using a Poisson point process and geometric probability tools. The proposed model takes into account both the threshold of the obtained Signal-to-interference-plus-noise ratio in terms of the critical distance requirements and the beam misalignment issues caused by the lateral displacement of the vehicles in the lane. The second contribution of this thesis is a mean interference analysis for a typical receiver if the vehicles employ in-lane and closest vehicle routing schemes for a two-lane road. By comparing these two routing schemes, a strategy is proposed for different antenna beam widths and vehicle densities. Additionally, the distribution of autonomous vehicular traffic, that is modelled by the shifted Poisson point process, gains more realism by taking into account platooning-based headway distance requirements. The third contribution of this thesis is a derivation of the coverage probability and road spectral efficiency for multi-lane vehicle-to-vehicle communications, by taking into account the blockage impact of adjacent lane vehicles and antenna-placement dependent path loss behaviour under an in-lane routing scheme. Finally, all the analytical models are verified by Monte Carlo simulations

マクロセルにオーバーレイするスモールセルのための層間干渉低減に関する研究

The huge number of mobile terminals in use and the radio frequency scarceness are the relevant issues for future wireless communications. Frequency sharing has been considered to solve the problem. Addressing the issues has led to a wide adoption of small cell networks particularly femtocells overlaid onto macrocell or small cells implemented with the support of distributed antenna systems (DASs). Small cell networks improve link quality and frequency reuse. Spectrum sharing improves the usage efficiency of the licensed spectrum. A macrocell underlaid with femtocells constitutes a typical two-tier network for improving spectral efficiency and indoor coverage in a spectrum sharing environment. Considering the end-user access control over the small cell base station (SBS), with shared usage of the macrocell’s spectrum, this dissertation contribution is an investigation of mitigation techniques of crosstier interference. Such cross-tier interference mitigation leads to possible implementation of multi-tier and heterogeneous networks. The above arguments underpin our work which is presented in the hereby dissertation. The contributions in this thesis are three-fold. Our first contribution is an interference cancellation scheme based on the transmitter symbols fed back to the femtocell base station (FBS) undergoing harmful cross-tier interference. We propose a cross-tier interference management between the FBS and the macrocell base station (MBS) in uplink communications. Our proposal uses the network infrastructure for interference cancellation at the FBS. Besides, we profit from terminal discovery to derive the interference level from the femtocell to the macrocell. Thus, additionally, we propose an interference avoidance method based on power control without cooperation from the MBS. In our second contribution, we dismiss the use of the MBS for symbol feedback due to delay issues. In a multi-tier cellular communication system, the interference from one tier to another, denoted as cross-tier interference, is a limiting factor for the system performance. In spectrum-sharing usage, we consider the uplink cross-tier interference management of heterogeneous networks using femtocells overlaid onto the macrocell. We propose a variation of the cellular architecture and introduce a novel femtocell clustering based on interference cancellation to enhance the sum rate capacity. Our proposal is to use a DAS as an interface to mitigate the cross-tier interference between the macrocell and femtocell tiers. In addition, the DAS can forward the recovered data to the macrocell base station (MBS); thus, the macrocell user can reduce its transmit power to reach a remote antenna unit (RAU) located closer than the MBS. By distributing the RAUs within the macrocell coverage, the proposed scheme can mitigate the cross-tier interference at different locations for several femtocell clusters. Finally, we address the issue of cross-tier interference mitigation in heterogeneous cognitive small cell networks comparing equal and unequal signal-to-noise ratio (SNR) branches in multi-input multi-output (MIMO) Alamouti scheme. Small cell networks enhance spectrum efficiency by handling the indoor traffic of mobile networks on a frequency-reuse operation. Because most of the current mobile traffic happens indoor, we introduce a prioritization shift by imposing a threshold on the outage generated by the outdoor mobile system to the indoor small cells. New closed-form expressions are derived to validate the proposed bit error rate (BER) function used in our optimization algorithm. We propose a joint transmit antenna selection and power allocation which minimizes the proposed BER function of the outdoor mobile terminal. The optimization is constrained by the outage at the small cell located near the cooperating transmit relays. Such constraint improves the initialization of the iterative algorithm compared to randomly choosing initial points. The proposed optimization yields a dynamic selection of the relays with power control pertaining to the outdoor mobile terminal performance.電気通信大学201

Recent Advances in Cellular D2D Communications

Device-to-device (D2D) communications have attracted a great deal of attention from researchers in recent years. It is a promising technique for offloading local traffic from cellular base stations by allowing local devices, in physical proximity, to communicate directly with each other. Furthermore, through relaying, D2D is also a promising approach to enhancing service coverage at cell edges or in black spots. However, there are many challenges to realizing the full benefits of D2D. For one, minimizing the interference between legacy cellular and D2D users operating in underlay mode is still an active research issue. With the 5th generation (5G) communication systems expected to be the main data carrier for the Internet-of-Things (IoT) paradigm, the potential role of D2D and its scalability to support massive IoT devices and their machine-centric (as opposed to human-centric) communications need to be investigated. New challenges have also arisen from new enabling technologies for D2D communications, such as non-orthogonal multiple access (NOMA) and blockchain technologies, which call for new solutions to be proposed. This edited book presents a collection of ten chapters, including one review and nine original research works on addressing many of the aforementioned challenges and beyond