28 research outputs found
Architecture of a cognitive non-line-of-sight backhaul for 5G outdoor urban small cells
Densely deployed small cell networks will address the growing demand for broadband mobile connectivity, by increasing access network capacity and coverage. However, most potential small cell base station (SCBS) locations do not have existing telecommunication infrastructure. Providing backhaul connectivity to core networks is therefore a challenge. Millimeter wave (mmW) technologies operated at 30-90GHz are currently being considered to provide low-cost, flexible, high-capacity and reliable backhaul solutions using existing roof-mounted backhaul aggregation sites. Using intelligent mmW radio devices and massive multiple-input multiple-output (MIMO), for enabling point-to-multipoint (PtMP) operation, is considered in this research. The core aim of this research is to develop an architecture of an intelligent non-line-sight (NLOS) small cell backhaul (SCB) system based on mmW and massive MIMO technologies, and supporting intelligent algorithms to facilitate reliable NLOS street-to-rooftop NLOS SCB connectivity. In the proposed architecture, diffraction points are used as signal anchor points between backhaul radio devices. In the new architecture the integration of these technologies is considered. This involves the design of efficient artificial intelligence algorithms to enable backhaul radio devices to autonomously select suitable NLOS propagation paths, find an optimal number of links that meet the backhaul performance requirements and determine an optimal number of diffractions points capable of covering predetermined SCB locations. Throughout the thesis, a number of algorithms are developed and simulated using the MATLAB application. This thesis mainly investigates three key issues: First, a novel intelligent NLOS SCB architecture, termed the cognitive NLOS SCB (CNSCB) system is proposed to enable street-to-rooftop NLOS connectivity using predetermined diffraction points located on roof edges. Second, an algorithm to enable the autonomous creation of multiple-paths, evaluate the performance of each link and determine an optimal number of possible paths per backhaul link is developed. Third, an algorithm to determine the optimal number of diffraction points that can cover an identified SCBS location is also developed. Also, another investigated issue related to the operation of the proposed architecture is its energy efficiency, and its performance is compared to that of a point-to-point (PtP) architecture. The proposed solutions were examined using analytical models, simulations and experimental work to determine the strength of the street-to-rooftop backhaul links and their ability to meet current and future SCB requirements. The results obtained showed that reliable multiple NLOS links can be achieved using device intelligence to guide radio signals along the propagation path. Furthermore, the PtMP architecture is found to be more energy efficient than the PtP architecture. The proposed architecture and algorithms offer a novel backhaul solution for outdoor urban small cells. Finally, this research shows that traditional techniques of addressing the demand for connectivity, which consisted of improving or evolving existing solutions, may nolonger be applicable in emerging communication technologies. There is therefore need to consider new ways of solving the emerging challenges
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Millimeter wave picocellular networks: capacity analysis and system design
The explosive growth in demand for wireless mobile data, driven by the proliferationof ever more sophisticated handhelds creating and consuming rich multimedia, calls fororders of magnitude increase in the capacity of cellular data networks. Millimeter wavecommunication from picocellular base stations to mobile devices is a particularly promisingapproach for meeting this challenge because of two reasons. First, there is a largeamount of available spectrum, enabling channel bandwidths of the order of Gigahertz(GHz) which are 1-2 orders of magnitude higher than those in existing WiFi and cellularsystems at lower carrier frequencies. Second, the small carrier wavelength enables therealization of highly directive steerable arrays with a large number of antenna elements,in compact form factors, thus significantly enhancing spatial reuse. Hence, we propose toemploy the 60 GHz unlicensed band for basestation to mobile communication in outdoorpicocells.We first investigate the basic feasibility of such networks, showing that 60GHz linksare indeed viable for outdoor applications. For this purpose, we provided link budgetcalculations along with preliminary simulations which show that despite the commonconcerns about higher oxygen absorption and sensitivity to movement and blockage,picocloud architecture provides availability rate of more than 99%.Next, we explore the idea of increasing spatial reuse by shrinking picocells hopingthat interference is no longer the bottleneck given the highly directive antenna arrays atthis band. Our goal is to estimate the achievable capacity for small picocells along an urban canyon. We consider basestations with multiple faces or sectors, each with one or more antenna arrays. Each such array, termed subarray can employ Radio Frequency(RF) beamforming to communicate with one mobile user at a time. We first focus oncharacterization and modeling the inter-cell interference for one subarray on each face.Our analysis provides a strong indication of very large capacity (in the order of Tbps/km)with a few GHz of bandwidth.Following this, we explore the impact of adding multiple subarrays per face. This leadsto intra-cell interference as well as additional inter-cell interference. While the effect ofadditional inter-cell interference can be quantified within our previous framework, intracellinterference has inherently different features that call for new approaches for analysisand design. We propose a cross-layer approach to suppress the intra-cell interference intwo stages: (a) Physical layer (PHY-layer) method which mitigates interference by jointprecoding and power adaptation and (b) Medium Access Control layer (MAC-layer)method which manages the residual interference by optimizing resource allocation. Wethen estimate the capacity gain over conventional LTE cellular networks and establishthat 1000-fold capacity increase is indeed feasible via mm-wave picocellular networks.Lastly, we examine fundamental signal processing challenges associated with channelestimation and tracking for large arrays, placed within the context of system designfor a mm-wave picocellular network. Maintainance of highly directive links in the faceof blockage and mobility requires accurate estimation of the spatial channels betweenbasestation and mobile users. Here we develop the analytical framework for compressivechannel estimation and tracking. We also address the system level design discussinglink budget, overhead, and inter-cell beacon interference. Simulation results demonstratethat our compressive scheme is able to resolve mm-wave spatial channels with a relativelysmall number of compressive measurements
Enhancement in Network Architectures for Future Wireless Systems
This thesis investigates innovative wireless deployment strategies for dense ultra-small cells networks. In particular, this thesis focuses on improving the resource utilisation, reliability and energy efficiency of future wireless networks by exploiting the existing flexibility in the network architecture. The wireless backhaul configurations and topology management schemes proposed in this thesis consider a dense urban area scenario with static outdoor users.
In the first part of this thesis, a novel mm-wave dual-hop backhaul network architecture is investigated for future cellular networks to achieve better resource utilization and user experience at the expense of path diversity available in dense deployment of base stations. The system-level performance is analysed and compared for the backhaul section using mm-wave band. Followed by the performance of the network model which is validated using a Markov Model.
The second part of the thesis illustrates a topology management strategy for the same dual-hop backhaul network architecture. The same path diversity is also utilized by the topology management technique to achieve high energy savings and improvement in performance. The results show that the proposed architecture facilitates the topology management process to turn-off some portion of the network in order to minimize the power consumption and can deliver Quality-of-Service guarantee.
Finally, the methodology to admit new users into the system, to best control the capacity resource, is investigated for radio resource management in a multi hop, multi-tier heterogeneous network. A novel analytical Markov Model based on a two-dimensional state-transition rate diagram is developed to describe system behaviour of a coexistence scenarios containing two different sets of users, which have full and limited access to the network resources. Different levels of restriction to access the network by specific groups of users are compared and conclusions are drawn
Determination of Single Knife Edge Equivalent Parameters for Double Knife Edge Diffraction Loss by Deygout Method
In this paper, the computation of dual knife edge diffraction loss by Deygout multiple knife edge diffraction loss method is presented for  a 6 GHz  C-band microwave link. Also,  the computation of equivalent  single knife edge obstruction that will replace the dual obstruction by giving the same diffraction loss as the dual obstructions is presented. The results shows that for the dual obstructions M1 and M2  the total diffraction loss is 54.57746 dB as computed by the Deygout method. The individual diffraction loss from obstructions M1 and M2 are  32.85901 dB and 21.71845 dB respectively. Furthermore, a single knife edge obstruction located at the middle of the link (a distance of 1275m from the transmitter and receiver) and with line of sight clearance height of 483.5089m will be give the same diffraction loss as the dual knife edge obstructions M1 and M2. Essentially, the line of sight clearance height of the equivalent single knife edge obstruction are much more than the sum of the line of sight clearance height of the two initial obstructions