660 research outputs found

    On LOS Contribution to Ultra-Dense Network

    Get PDF
    Ultra-dense networks (UDNs) are widely considered as an effective solution to greatly improve coverage by shortening the communication distance between user equipments (UEs) and base stations (BSs). The reality of UDN is that line-of-sight (LOS) communication becomes more likely to occur but this desirable result also complicates the performance analysis of random UDNs and puts an obstacle on the design and optimization of UDNs. The aim of this paper is to derive analytical results that take into account the phenomenon of having mixed LOS and non line-of-sight (NLOS) links in UDNs. In particular, the use of an arbitrary shaped thinning process to model the LOS wireless links allowed us to investigate a wide set of scenarios for what concerns the desired and interfering power levels. Our contribution is an accurate approximation in closed form for the success content delivery probability (SCDP) that decouples the contribution from LOS and NLOS links. Simulation results corroborate the accuracy of the proposed approximation

    Ultra-Dense Mobile Networks: Optimal Design and Communications Strategies

    Get PDF
    This thesis conducts an extensive analysis within the mobile telecommunications sub-field of the ultra-dense mobile networks, in which a massive deployment of network’s pieces of equipment is assumed. Future cache-enabled mobile networks are expected to meet most of the generated content demands directly at the edge, where each node has the availability to proactively store a set of contents in a local memory. This thesis makes several important contributions. The research being presented in this thesis proposes new analytical expressions to modeling the performance associated to the network’s edge. Base-stations’ idling technologies are also investigated to temporarily turn off some network nodes, saving energy and, in some circumstances, improving the overall performance by contributing less interference at the network’s edge. On the other hand, making use of fewer base-stations however reduces the amount of available resources at the network’s edge. A trade-off is investigated, which balances among interference saturation and available resources to increase the average user’s quality of experience. In this work, we treat the edge node density as a variable of the problem. This greatly increases the difficulty of obtaining analytical expressions, but also offers a direct access for optimizing the users’ average performance and network’s energy consumptions. An energy-focused performance metric is subsequently proposed, with the intention to highlight an interesting duality within the same network’s tier, which can transition from a better efficient to a more performing state, according to the energy expenses from the operators. Nonetheless, under an ultra-dense scenario, line-of-sight wireless links between the user and the nodes become more likely. The introduction of a main component of the multi-path propagated copies of a signal involves analytical complications. A feasible approximation is proposed and validated through a set of computer simulations. The scalability of the proposed technique allows to generalise existing results in the literature

    Distributed Resource Allocation and Performance Analysis in 5G Wireless Cellular Networks

    Get PDF
    This thesis focuses on the study of Heterogeneous Networks (HetNets), Device-to-device (D2D) communication networks, and unmanned aerial vehicle (UAV) networks in fifth generation wireless communication (5G) systems. HetNets that consist of macro-cells and small-cells have become increasingly popular in current wireless networks and 5G systems to meet the exponentially growing demand for higher data rates. Compared to conventional homogeneous cellular networks, the disparity of transmission power among different types of base stations (BSs), the relatively random deployment of SBSs, and the densifying networks, bring new challenges, such as the imbalanced load between macro and small cells and severe inter-cell interference. In the other hand, with the skyrocketing number of tablets and smart phones, the notion of caching popular content in the storage of BSs and users' devices is proposed to reduce duplicated wireless transmissions. To fulfill multi-fold communication requirements from humans, machine, and things, the 5G systems which include D2D communications, UAV communications, and so on, can improve the network performance. Among them, the performance analyses of these emerging technologies are attracting much attention and should be investigated first. This thesis focuses on these hot issues and emerging technologies in 5G systems, analyzing the network performance and conducting the allocation of available resources, such as serving BSs, spectrum resources, and storage resources. Specifically, three main research focuses are included in the thesis. The first focus of this thesis is the impact of the BS idle mode capacity (IMC) on the network performance of multi-tier and dense HCNs with both line-of-sight (LoS) and non-line-of-sight (NLoS) transmissions. I consider a more practical set-up with a finite number of UEs in the analysis. Moreover, the SBSs apply a positive power bias in the cell association procedure, so that macrocell UEs are actively encouraged to use the more lightly loaded SBSs. In addition, to address the severe interference that these cell range expanded UEs may suffer, the MBSs apply enhanced inter-cell interference coordination (eICIC), in the form of almost blank subframe (ABS) mechanism. For this model, I derive the coverage probability and the rate of a typical UE in the whole network or a certain tier. The impact of the IMC on the performance of the network is shown to be significant. In particular, it is important to note that there will be a surplus of BSs when the BS density exceeds the UE density, and thus a large number of BSs switch off. As a result, the overall coverage probability, as well as the area spectral efficiency (ASE), will continuously increase with the BS density, addressing the network outage that occurs when all BSs are active and the interference becomes LoS dominated. Finally, the optimal ABS factors are investigated in different BS density regions. One of major findings is that MBSs should give up all resources in favor of the SBSs when the small cell networks go ultra-dense. This reinforces the need for orthogonal deployments, shedding new light on the design and deployment of the future 5G dense HCNs. The second focus of this thesis is the content caching in D2D communication networks. In practical deployment, D2D content caching has its own problem that is not all of the user devices are willing to share the content with others due to numerous concerns such as security, battery life, and social relationship. To solve this problem, I consider the factor of social relationship in the deployment of D2D content caching. First, I apply stochastic geometry theory to derive an analytical expression of downloading performance for the D2D caching network. Specifically, a social relationship model with respect to the physical distance is adopted in the analysis to obtain the average downloading delay performance using random and deterministic caching strategies. Second, to achieve a better performance in more practical and specific scenarios, I develop a socially aware distributed caching strategy based on a decentralized learning automaton, to optimize the cache placement operation in D2D networks. Different from the existing caching schemes, the proposed algorithm not only considers the file request probability and the closeness of devices as measured by their physical distance, but also takes into account the social relationship between D2D users. The simulation results show that the proposed algorithm can converge quickly and outperforms the random and deterministic caching strategies. With these results, the work sheds insights on the design of D2D caching in the practical deployment of 5G networks. The third focus of this thesis is the performance analysis for practical UAV-enabled networks. By considering both LoS and NLoS transmissions between aerial BSs and ground users, the coverage probability and the ASE are derived. Considering that there is no consensus on the path loss model for studying UAVs in the literature, in this focus, three path loss models, i.e., high-altitude model, low-altitude model, and ultra-low-altitude model, are investigated and compared. Moreover, the lower bound of the network performance is obtained assuming that UAVs are hovering randomly according to homogeneous Poisson point process (HPPP), while the upper bound is derived assuming that UAVs can instantaneously move to the positions directly overhead ground users. From the analytical and simulation results for a practical UAV height of 50 meters, I find that the network performance of the high-altitude model and the low-altitude model exhibit similar trends, while that of the ultra-low-altitude model deviates significantly from the above two models. In addition, the optimal density of UAVs to maximize the coverage probability performance has also been investigated

    Performance Analysis of Indoor Wireless Communications in Dense Cellular Networks

    Get PDF
    The current decades have witnessed the explosive increase of traffic-data demand. It is predicted that indoor wireless communications will be one of the fastest growing markets, since the vast majority (over 80%) of data demand occurs in indoors. Facing such a huge data demand, the dense deployment of small cells (SCs) in indoor environments is boosted, which brings breakthroughs of throughput for in-building communications. However, the densification of indoor small-cell (SC) networks also poses new challenges, such as complex propagating environments, severe blockage effects and short link distances, which significantly influence the evaluation of network performance. This thesis mainly investigates the performance analysis of indoor dense SC networks. Firstly, the probability of Line-of-Sight (LOS) propagation is crucial to model the real signal propagation channels and to evaluate the performance of cellular networks. However, existing LOS probability models are oversimplified to provide the exact LOS probability in indoor scenarios. By considering the realistic layout of building structures, this thesis proposes a novel and analytical LOS probability model for downlink radio propagations in typical indoor scenarios, which have rectangular rooms and corridors. Through the proposed model, the LOS probability can be calculated directly without the measurement and simulation. Next, in terms of the impact of LOS and Non-Line-of-Sight (NLOS) transmissions, the traditional works do not distinguish them, which is not practical for dense cellular networks. Thus, a tractable path loss model considering both LOS and NLOS propagations is proposed for the performance analysis of indoor dense SC networks. Based on the theory of stochastic geometry, the performance metrics, such as coverage probability, spectral efficiency (SE) and area spectral efficiency (ASE), are analytically derived. The analytical results provide insights into the design of indoor dense SC networks in the future. Thirdly, regarding the severe effects of blockages in indoor environments, the traditional approach that simply considers it as a log-normal shadowing is too simple. Therefore, a wall blockage model is developed to characterize the impact of blockages based on the stochastic geometry. Furthermore, the mathematical expression of coverage probability for the case of impenetrable blockages is derived, which employs a path loss model incorporating both the blockage-based and distance-based path loss

    Cooperative Radio Communications for Green Smart Environments

    Get PDF
    The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

    Max-Min Fair Resource Allocation in Millimetre-Wave Backhauls

    Get PDF
    5G mobile networks are expected to provide pervasive high speed wireless connectivity, to support increasingly resource intensive user applications. Network hyper-densification therefore becomes necessary, though connecting to the Internet tens of thousands of base stations is non-trivial, especially in urban scenarios where optical fibre is difficult and costly to deploy. The millimetre wave (mm-wave) spectrum is a promising candidate for inexpensive multi-Gbps wireless backhauling, but exploiting this band for effective multi-hop data communications is challenging. In particular, resource allocation and scheduling of very narrow transmission/ reception beams requires to overcome terminal deafness and link blockage problems, while managing fairness issues that arise when flows encounter dissimilar competition and traverse different numbers of links with heterogeneous quality. In this paper, we propose WiHaul, an airtime allocation and scheduling mechanism that overcomes these challenges specific to multi-hop mm-wave networks, guarantees max-min fairness among traffic flows, and ensures the overall available backhaul resources are fully utilised. We evaluate the proposed WiHaul scheme over a broad range of practical network conditions, and demonstrate up to 5 times individual throughput gains and a fivefold improvement in terms of measurable fairness, over recent mm-wave scheduling solutions

    Dense Small Cell Networks for Next Generation Wireless Systems

    Get PDF
    • …
    corecore