Planning for Small Cells in a Cellular Network

In this thesis, we analyze the effect of deploying small cells on the performance of a network comprising several macro cells. We identify potential locations for low-power base-stations based on the coverage patterns of the macro cells and propose three schemes for placing the small cells. We show that by judiciously installing just two small cells for every macro base-station at these locations and allocating separate resources to all the small cells on a global level, we can increase the performance of the network significantly (~ 45%). An added benefit of our schemes is that we can switch o the macro base-stations at night (when the number of active users is low) and significantly reduce their operation cost.4 month

Network lifetime extension, power conservation and interference suppression for next generation mobile wireless networks

Two major focus research areas related to the design of the next generation multihop wireless networks are network lifetime extension and interference suppression. In this dissertation, these two issues are addressed. In the area of interference suppression, a new family of projection multiuser detectors, based on a generalized, two-stage design is proposed. Projection multiuser detectors provide efficient protection against undesired interference of unknown power, while preserving simple design, with closed-form solution for error probabilities. It is shown that these detectors are linearly optimal, if the interference power is unknown. In the area of network lifetime extension, a new approach to minimum energy routing for multihop wireless networks in Rayleigh fading channels is proposed. It is based on the concept of power combining, whereby two users transmit same signal to the destination user, emulating transmit diversity with two transmit antennas. Analytical framework for the evaluation of the benefits of power combining, in terms of the total transmit power reduction, is defined. Simulation results, which match closely the analytical results, indicate that significant improvements, in terms of transmit power reduction and network lifetime extension, are achievable. The messaging load, generated by the new scheme, is moderate, and can be further optimized

Queueing Networks for Vertical Handover

PhDIt is widely expected that next-generation wireless communication systems will be heterogeneous, integrating a wide variety of wireless access networks. Of particular interest recently is a mix of cellular networks (GSM/GPRS and WCDMA) and wireless local area networks (WLANs) to provide complementary features in terms of coverage, capacity and mobility support. If cellular/ WLAN interworking is to be the basis for a heterogeneous network then the analysis of complex handover traffic rates in the system (especially vertical handover) is one of the most essential issues to be considered. This thesis describes the application of queueing-network theory to the modelling of this heterogeneous wireless overlay system. A network of queues (or queueing network) is a powerful mathematical tool in the performance evaluation of many large-scale engineering systems. It has been used in the modelling of hierarchically structured cellular wireless networks with much success, including queueing network modelling in the study of cellular/ WLAN interworking systems. In the process of queueing network modelling, obtaining the network topology of a system is usually the first step in the construction of a good model, but this topology analysis has never before been used in the handover traffic study in heterogeneous overlay wireless networks. In this thesis, a new topology scheme to facilitate the analysis of handover traffic is proposed. The structural similarity between hierarchical cellular structure and heterogeneous wireless overlay networks is also compared. By replacing the microcells with WLANs in a hierarchical structure, the interworking system is modelled as an open network of Erlang loss systems and with the new topology, the performance measures of blocking probabilities and dropping probabilities can be determined. Both homogeneous and non-homogeneous traffic have been considered, circuit switched and packet-switched. Example scenarios have been used to validate the models, the numerical results showing clear agreement with the known validation scenarios

Modelling and Analysis of Resource Management Schemes in Wireless Networks. Analytical Models and Performance Evaluation of Handoff Schemes and Resource Re-Allocation in Homogeneous and Heterogeneous Wireless Cellular Networks.

Over recent years, wireless communication systems have been experiencing a dramatic and continuous growth in the number of subscribers, thus placing extra demands on system capacity. At the same time, keeping Quality of Service (QoS) at an acceptable level is a critical concern and a challenge to the wireless network designer. In this sense, performance analysis must be the first step in designing or improving a network. Thus, powerful mathematical tools for analysing most of the performance metrics in the network are required. A good modelling and analysis of the wireless cellular networks will lead to a high level of QoS. In this thesis, different analytical models of various handoff schemes and resource re-allocation in homogeneous and heterogeneous wireless cellular networks are developed and investigated. The sustained increase in users and the request for advanced services are some of the key motivations for considering the designing of Hierarchical Cellular Networks (HCN). In this type of system, calls can be blocked in a microcell flow over to an overlay macrocell. Microcells in the HCN can be replaced by WLANs as this can provide high bandwidth and its users have limited mobility features. Efficient sharing of resources between wireless cellular networks and WLANs will improve the capacity as well as QoS metrics. This thesis first presents an analytical model for priority handoff mechanisms, where new calls and handoff calls are captured by two different traffic arrival processes, respectively. Using this analytical model, the optimised number of channels assigned to II handover calls, with the aim of minimising the drop probability under given network scenarios, has been investigated. Also, an analytical model of a network containing two cells has been developed to measure the different performance parameters for each of the cells in the network, as well as altogether as one network system. Secondly, a new solution is proposed to manage the bandwidth and re-allocate it in a proper way to maintain the QoS for all types of calls. Thirdly, performance models for microcells and macrocells in hierarchical cellular networks have been developed by using a combination of different handoff schemes. Finally, the microcell in HCN is replaced by WLANs and a prioritised vertical handoff scheme in an integrated UMTS/WLAN network has been developed. Simulation experiments have been conducted to validate the accuracy of these analytical models. The models have then been used to investigate the performance of the networks under different scenarios

Association Control Based Load Balancing in Wireless Cellular Networks Using Preamble Sequences

The efficient allocation and use of radio resources is crucial for achieving the maximum possible throughput and capacity in wireless networks. The conventional strongest signal-based user association in cellular networks generally considers only the strength of the signal while selecting a BS, and ignores the level of congestion or load at it. As a consequence, some BSs tend to suffer from heavy load, while their adjacent BSs may carry only light load. This load imbalance severely hampers the network from fully utilizing the network capacity and providing fair services to users. In this thesis, we investigate the applicability of the preamble code sequence, which is mainly used for cell identification, as an implicit information indicator for load balancing in cellular networks. By exploiting the high auto-correlation and low cross-correlation property among preamble sequences, we propose distributed load balancing schemes that implicitly obtain information about the load status of BSs, for intelligent association control. This enables the new users to be attached to BSs with relatively low load in the long term, alleviating the problem of non-uniform user distribution and load imbalance across the network. Extensive simulations are performed with various user densities considering throughput fair and resource fair, as the resource allocation policies in each cell. It is observed that significant improvement in minimum throughput and fair user distribution is achieved by employing our proposed schemes, and preamble sequences can be effectively used as a leverage for better cell-site selection from the viewpoint of fairness provisioning. The load of the entire system is also observed to be balanced, which consequently enhances the capacity of the network, as evidenced by the simulation results

Proceedings of the Fifth International Mobile Satellite Conference 1997

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments

COMPARATIVE ANALYSIS OF USER-CELL ASSOCIATION METHODS FOR MILIMETER WAVE MASSIVE MIMO BY DEVELOPING A SYSTEM LEVEL SIMULATOR FOR HETNETS

Massive multiple-input-multiple-output (MIMO) base station deployments and millimeter wave (mmWave) spectrum utilization have been identified as promising disruptive technologies, along with ultra-dense Heterogeneous Networks (UDHNs) to meet the exponential data requirement of the next generation cellular networks. With the proliferation of UDHNs, optimal user-cell association in cellular networks, which is a well-known open problem, will be exacerbated due to the power differential of macro and small cells. This study investigates the user-cell association problem for ultra-dense two-tier networks with massive MIMO deployment and small cells operating in mmWave spectrum. The association problem is modeled as a convex utility maximization problem, adapted from [11], and is a function of the user throughput. The problem is solved through a centralized subgradient algorithm. Additionally, a game theoretical user-centric distributed load balancing algorithm, inspired from [32], where each user chooses its serving base station to maximize its user throughput selfishly, is also evaluated. Moreover, these adapted algorithms are compared against smallest pathloss and maximum downlink data rate association methods and it is demonstrated via extensive simulations that both the centralized and user-centric approaches almost equally outperform the smallest pathloss and maximum downlink data rate association methodologies in terms of user throughput and cell load distribution. The results exhibit average throughput gains between 20% and 40% for the majority of users if massive MIMO UDHN deployments are operated in the mmWave spectrum as compared to existing sub-6 GHz bands under the optimal user-cell association schemes

Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial cellular communications services. While the first and second International Mobile Satellite Conferences (IMSC) mostly concentrated on technical advances, this Third IMSC also focuses on the increasing worldwide commercial activities in Mobile Satellite Services. Because of the large service areas provided by such systems, it is important to consider political and regulatory issues in addition to technical and user requirements issues. Topics covered include: the direct broadcast of audio programming from satellites; spacecraft technology; regulatory and policy considerations; advanced system concepts and analysis; propagation; and user requirements and applications

GSM and UMTS mobility simulator

Cataloged from PDF version of article.In this thesis, a mobility simulator for GSM and UMTS has been designed and implemented using Visual C#.Net. The objective has been to design and implement such a simulator that can be used to create and study different traffic load scenarios and mobility patterns that can cause congestion situations. The modular approach adopted for the GSM and UMTS simulator allow us to evaluate the performance of new services. The simulator uses propagation simulation results and terrain profile data to produce capacity and performance metrics related to GSM and UMTS networks. The capacity and the service quality of the network are assessed in a long-term system level simulation scheme. Mobility generation is the core of the simulator program. It generates random paths for the mobile users in the simulation. Then the effects of the mobility patterns of the users on the system capacity are investigated. In GSM mobility simulator, mobility, traffic generation, call-admission and handover are implemented. In UMTS, in addition to GSM modules, power control and soft handover generation is implemented.Öner, MehmetM.S

Efficient offloading and load distribution based on D2D relaying and UAVs for emergent wireless networks

The device to device (D2D) and unmanned aerial vehicle (UAV) communications are considered as enabling technologies of the emergent 5th generation of wireless and cellular system (5G). Consequently, it is important to determine their corresponding performance with respect to the 5G requirements. In particular, we focus on enhancing the offloading and load balancing performance in three directions. In the first direction, we study the achievable data rate of user relay assisting other users in two-tier networks. We propose a novel heuristic communication scheme called device-for-device (D4D). The D4D enables moving users to share their resource by taking advantage of cooperative communication. We study the moving user rate sensitivity to the relay selection and blocking probability. In the second direction, we study the offloading from macrocell to small cell and load balancing among small cell. Also, we design a new utility weight function that enables a balanced relay assignment. We propose a novel low complexity algorithm for centralized scheme maximizing the load among small cells as well as users subject to SINR threshold constraints. The simulations show that our proposed schemes achieve performance in load balancing compared to those obtained with the previous or traditional method. In the third direction, we study the 3D deployment of multiple UAVs for emergent on-demand offloading. We propose a novel on-demand deployment scheme based on maximizing both the operator’s profit and the quality of service. The proposed scheme is based on solving a non-convex problem by combining k-means clustering with pattern search to find the suboptimal location of UAVs. The simulation results show that our proposed scheme maximizes the operator’s profit and improves offloading traffic efficiency. Our global contribution was the development of a scheme to improve the quality of service and the performance in emergent networks through the improvement of the load distribution and resource sharing using D2D and UAV