Performance Evaluation of Scheduling Algorithms with Different MIMO Techniques in LTE Systems

MIMO techniques are used in Wireless Broadband Access (BWA) networks to maximize spectrum efficiency and minimize the bit error rate. LTE is one such BWA network which has adopted MIMO techniques in both the uplink and downlink along with Radio Resource Management (RRM) aspects like scheduling to improve the data rate. Scheduling is mainly concerned with allocating the available radio resources among the users depending upon the metrics such as Quality of Service (QoS) requirements of users, channel conditions etc. Hence in this paper, an attempt is made to study and compare the performance of scheduling algorithms (RR, PF, MT and BET) with MIMO techniques such as SISO, SIMO, SFBC and OLSM for Constant Bit Rate (CBR) traffic scenario. The performance metrics used are average throughput and average delay

Maximising spectral efficiency in LTE cells

The efficiency with which spectrum is used in wireless communications systems is becoming increasingly important as a result of the expected growth in traffic demand and the finite nature of usable spectrum. Spectral efficiency, defined as throughput divided by bandwidth, is a useful metric for evaluating the use of spectrum in wireless systems. In any given area the achievable spectrum efficiency is impacted by the underlying user population. This paper presents the methodology for finding the transmit power which maximises the spectral efficiency of a LTE cell for a given user density and traffic type. The impact of different user densities and traffic profiles on the choice of transmit power is evaluated. Results show that the transmit power which maximise spectral efficiency decreases as the user density and average data rate of the traffic profile increases. Two non ideal real world scenarios which require an increase in cell spectral efficiency are also considered and a modified user admission scheme which can increase the cell spectral efficiency is presented and evaluated. Results showed that the spectral efficiency was improved but the maximum improvement depended on the traffic profile and practical constraints of the LTE standard

HetHetNets: Heterogeneous Traffic Distribution in Heterogeneous Wireless Cellular Networks

A recent approach in modeling and analysis of the supply and demand in heterogeneous wireless cellular networks has been the use of two independent Poisson point processes (PPPs) for the locations of base stations (BSs) and user equipments (UEs). This popular approach has two major shortcomings. First, although the PPP model may be a fitting one for the BS locations, it is less adequate for the UE locations mainly due to the fact that the model is not adjustable (tunable) to represent the severity of the heterogeneity (non-uniformity) in the UE locations. Besides, the independence assumption between the two PPPs does not capture the often-observed correlation between the UE and BS locations. This paper presents a novel heterogeneous spatial traffic modeling which allows statistical adjustment. Simple and non-parameterized, yet sufficiently accurate, measures for capturing the traffic characteristics in space are introduced. Only two statistical parameters related to the UE distribution, namely, the coefficient of variation (the normalized second-moment), of an appropriately defined inter-UE distance measure, and correlation coefficient (the normalized cross-moment) between UE and BS locations, are adjusted to control the degree of heterogeneity and the bias towards the BS locations, respectively. This model is used in heterogeneous wireless cellular networks (HetNets) to demonstrate the impact of heterogeneous and BS-correlated traffic on the network performance. This network is called HetHetNet since it has two types of heterogeneity: heterogeneity in the infrastructure (supply), and heterogeneity in the spatial traffic distribution (demand).Comment: JSA

Spectrum Sharing: Quantifying the Benefits of Different Enforcement Scenarios

Recent studies have forecasted major growth in mobile broadband traffic. Due to the predicted high growth rate of mobile broadband traffic over the coming years (demand), there is a need for more wireless network capacity (supply). One of the major approaches to expand mobile wireless capacity is to add more spectrum to the market by enabling “spectrum sharing”. The FCC has issued many reports indicating that the US is dangerously close to running out of capacity for mobile data, which is why the FCC and the NTIA have been working continually to enable spectrum sharing. The spectrum usage rights granted by the Federal government to spectrum users/licensees come with the expectation of protection from harmful interference. As a consequence of the growth of wireless demand and services of all types, technical progress enabling smart agile radio networks, and on-going spectrum management reform, there is both a need and opportunity to use and share spectrum more intensively. This dissertation is written on the premise that spectrum sharing will be a major factor in increasing the capacity supply in the near future. The focus of this dissertation is to examine and quantify the benefits of spectrum sharing through different enforcement scenarios. Enabling spectrum sharing regimes on a non-opportunistic basis means that sharing agreements must be implemented. To have meaning, those agreements must be enforceable. This dissertation will examine the spectrum sharing between government and commercial users and try to generalize some finding, which can be implemented, in different spectrum sharing cases. This analysis is valuable because it will help regulators/governments prepare for possible future scenarios in addressing the potential capacity crunch. In addition, it can give the incumbents more insight into expected future sharing as well as into how to optimize mitigation of possible harmful interference that may result. It is also of value to commercial users and operators in that they can use the results of this work to make more informed decisions about the economic benefits of different spectrum sharing market and opportunities

Heterogeneous Cellular Networks: From Resource Allocation To User Association

Heterogeneous networking paradigm addresses the ever growing need for capacity and coverage in wireless networks by deploying numerous low power base stations overlaying the existing macro cellular coverage. Heterogeneous cellular networks encompass many deployment scenarios, with different backhauling techniques (wired versus wireless backhauling), different transmission coordination mechanisms and resource allocation schemes, different types of links operating at different bands and air-interface technologies, and different user association schemes. Studying these deployment scenarios and configurations, and understanding the interplay between different processes is challenging. In the first part of the thesis, we present a flow-based optimization framework that allows us to obtain the throughput performance of a heterogeneous network when the network processes are optimized jointly. This is done under a given system ``snapshot'', where the system parameters like the channel gains and the number of users are fixed and assumed known. Our framework allows us to configure the network parameters to allocate optimal throughputs to these flows in a fair manner. This is an offline-static model and thus is intended to be used at the engineering and planning phase to compare many potential configurations and decide which ones to study further. Using the above-mentioned formulation, we have been able to study a large set of deployment scenarios and different choices of resource allocation, transmission coordination, and user association schemes. This has allowed us to provide a number of important engineering insights on the throughput performance of different scenarios and their configurations. The second part of our thesis focuses on understanding the impact of backhaul infrastructure's capacity limitation on the radio resource management algorithms like user scheduling and user association. Most existing studies assume an ideal backhaul. This assumption, however, needs to be revisited as backhaul considerations are critical in heterogeneous networks due to the economic considerations. In this study, we formulate a global $\alpha$-fair user scheduling problem under backhaul limitations, and show how this limitation has a fundamental impact on user scheduling. Using results from convex optimization, we characterize the solution of optimal backhaul-aware user scheduling and show that simple heuristics can be used to obtain good throughput performance with relatively low complexity/overhead. We also study the related problem of user association under backhaul-limitations. This study is a departure from our ``snapshot'' approach. We discuss several important design considerations for an online user association scheme. We present a relatively simple backhaul-unaware user association scheme and show that it is very efficient as long as the network has fine-tuned the resource allocation