Department Publications

This paper presents a comprehensive framework to analyze the impact of aggregate interference from an underlay clustered Device-to-Device (D2D) network on the performance of its primary cellular network, when different power control schemes are used at the D2D network. A single base station, located at the center, operates with a cellular network and a D2D network, modeled using a homogeneous spatial Poisson Point Process and a Poisson Cluster Process, respectively. Using this system, the cellular network performance is examined under three power control schemes used by the D2D network namely, no power control, path loss inversion and channel inversion. For each scheme, the coverage probability of the cellular network is analyzed. Numerical results indicate that the cellular network performance is greatly dependent on the D2D system parameters such as density, size of a cell, number of …

Power control schemes are proposed for a full-duplex (FD) device-to-device (D2D) network operating as an underlay of a primary FD network. As networks with different quality of service (QoS) requirements may coexist in future heterogeneous networks, it is assumed that the underlay D2D network is operating with best effort QoS provisioning, while the primary FD network requires guaranteed QoS. A centralized power control (CPC) solution is proposed by casting the power control problem as a convex optimization problem. Furthermore, a heuristic distributed power control (DPC) solution is proposed to reduce information feedback overhead. It is found that the heuristic DPC achieves D2D user data rate that is within 87% and 80% of that provided by the CPC scheme in 3-node and 2-node FD primary network, respectively.

This paper introduces a model to study both single tier and multitier wireless communication systems consisting of a multitude of wireless access points (AP), and operating according to the classical opportunistic beamforming framework. The AP locations in the proposed network model are determined by using planar Poisson point processes. The extreme value distribution of signal-to-interference-plus-noise-ratio (SINR) on a beam is of fundamental importance for obtaining performance bounds for such an opportunistic communication system. Two tight distribution approximation results are provided for the distribution of maximum SINR on a beam, which is hard to obtain due to correlation structure of the underlying inter-AP interference field, using key tools from stochastic geometry. These approximations hold for general path loss models that satisfy some mild conditions. Simulations and numerical evaluations …

We present the development and testing of a cellular network built on open source technologies. This network supports voice calls and text messages within the network or between networks. The main objective of this work is to develop a stand-alone mobile network consisting of one base station and a switch, the access to which can be controlled as required. The mobile network is also connected to public networks. The designed network is based on Global System for Mobile Communications (GSM). Our work includes the configuration of the embedded hardware components, selection and integration of the proper software combination, testing of compatible versions of the software, hardware-software integration within the embedded system, and interconnecting the systems via the Internet. The key contribution and novelty of the project is the development of a stand-alone mobile network base station/ switch …

The outage probability of a two-hop coordinated decode-and-forward relay network is investigated. The case of two interfering cells is considered. This is analogous to the case when network coordination is performed with the dominant cochannel interfering cell. Different levels of network coordination are studied and their performances are compared. Exact expressions are derived for of the system for each coordination method. The impact of user location randomness on the outage probability is investigated.

The outage probability of a two-hop coordinated decode-and-forward relay network is investigated. Relay coordination is performed only with the dominant interferer. Different levels of network coordination are studied and their performances are compared. Exact expressions are derived for the outage probability of a particular mobile user for each coordination scheme. Asymptotic outage probability is derived to identify the diversity and coding gains for each coordination scheme.

An ergodic rate analysis is presented for relay coordination schemes of two-hop decode-and forward relay networks. A simplified two-cell network model is used in the analysis. This model is related to a practically significant case, where the relay coordination is implemented with the cell which causes the most dominant cochannel interference level. Closed-form expressions are derived for the ergodic rate of the system. Simplified approximations are derived to approximate the ergodic rate behaviour in the asymptotically high signal-to-noise ratio regime.

The demand for high data rate wireless services has grown tremendously. The demand is expected to grow further at an increased pace. The scarcity of the usable radio frequency spectrum is a major bottleneck to cater to the growing demand for high data rate wireless services. Current cellular wireless networks rely on deploying small cells as a possible solution to cater to the growing demand. However, this practice has resulted in severe co-channel interference (CCI) levels in cellular networks. The first phase of this thesis investigates the impact of CCI on relay networks and distributed antenna systems, which are included in recent wireless standards such as long-term evolution advanced (LTE-A). The analytical results derived for system performance metrics, such as the outage probability and the ergodic rate, are used to obtain valuable insights for system design. The second stage of this thesis research …

A theoretical framework is presented for the evaluation of sum ergodic rate of a full-duplex underlay device-to-device network, when it shares the uplink resources of a conventional cellular user. The sum-rate of the full-duplex network is compared with a half-duplex network with equivalent radio frequency hardware complexity. Closed-form approximations are derived for the sum ergodic rate of the systems. Furthermore, the sum-rate performances are investigated for the case when a transmit power constraint is imposed on the underlay network to minimize the interference on the cellular network. The analytical results presented can be used as a tool to identify when full-duplex transmissions are viable in underlay device-to-device networks.

This paper studies downlink coverage maximization for cellular networks in which base station (BS) locations are modeled using a spatial Poisson point process, considering three different coverage models, and under constraints on transmit power, BS density and transmit power density. Firstly, the coverage optimization problem is solved analytically for the first coverage model that focuses on noise-limited communication by ignoring interference and random fading effects. This model provides useful insights into the significance of bounded path loss models to obtain meaningful solutions for this problem. The other two coverage models are based on the users' received signal-to-interference-plus-noise-ratio (\sinr) from their associated BSs. For these models, it is shown that the coverage optimization problem can be reduced to a constrained single dimensional optimization problem without any loss of optimality …

This paper studies the coverage maximization for wireless networks in which base station (BS) locations are drawn from a homogenous spatial Poisson point process, and user locations are arbitrary. A user is covered for communication if its received signal-to-noise-ratio (SNR) is above a given threshold value, and the objective is to maximize the coverage probability under per unit area power density constraints. The resulting optimization problem is solved analytically by making use of the underlying concavity in the objective function when transmissions are impaired only by a power-law bounded path loss. Our results show that the optimal transmit power per BS is independent of the power density constraint, and the solution to the optimization problem represents the Pareto optimal boundary between the power density constraint and the coverage probability. Then, these results are extended to a system in which …

The downlink performance of a two-cell relay enhanced wireless network is investigated. A single relay is shared by the two base stations in the system. The relay is assumed to be placed in a geographic region covered by both base stations. The relay station is operating in the decode-and-forward mode. Closed-form approximations which estimate the exact results extremely closely are derived for the outage probability and the ergodic rate of the system. The impact of finite rate channel state information feedback on the user ergodic rate is examined.

In this paper, we consider a multi-cell multi-user MISO broadcast channel. The system operates according to the opportunistic beamforming framework in a multi-cell environment with variable number of transmit beams (may alternatively be referred as the transmission rank) at each base station. The maximum number of co-scheduled users in a cell is equal to its transmission rank, thus increasing it will have the effect of increasing the multiplexing gain. However, this will simultaneously increase the amount of interference in the network, which will decrease the rate of communication. This paper focuses on optimally setting the transmission rank at each base station such that a set of Quality of Service (QoS) constraints, that will ensure a guaranteed minimum rate per beam at each base station, is not violated. Expressions representing the achievable region of transmission ranks are obtained considering different …

The downlink performance of a dual-cell relay enhanced wireless network is investigated. A single relay is shared by the two base stations in the system. The relay is assumed to be placed in a region covered by both base stations. The relay station is operating in the decode-and-forward mode. Closed-form approximations which follow the exact results extremely closely are derived for the outage probability and the ergodic rate of the system.

This paper studies a cellular network in which base station (BS) locations are modeled using a homogenous spatial Poisson point process, and user locations are modeled using an arbitrary stationary homogenous point process. The objective is to maximize the Coverage-Intensity Product (CIP), which represents the average number of users covered per unit area, under constraints on transmit power, BS intensity and transmit power density (per unit area). Expressions for the CIP are obtained considering two user coverage models that differ from each other depending on the BS-user association. Using these expressions, solutions for the optimization problem are provided. All these results are presented for general bounded path loss models that satisfy some mild conditions. The results are also illustrated using a specific bounded path loss model to provide further insights.

This paper suggests a decision support system for vehicle drivers, accessible via mobile phone. Concept behind the system is to help drivers to schedule their activities, best utilizing their time along the way, minimizing the impacts of traffic. This is in contrast to existing approaches focused on controlling traffic in highways. Vehicle is continuously tracked along the journey and information presented to user is adapted according his location and time dimensions. System is based on a decision tree based classification model to predict the future traffic and use those results for decision making. System mines spatio-temporal data to build the decision tree, therefore developed in a distributed architecture to avoid load for a single server. System is exposed to community via existing social networks, bringing social networks into vehicular context. Decision trees to predict traffic are periodically rebuilt using most recent data …

The Disaster and Emergency Warning Network (DEWN) is a last-mile disaster early warning system based on a suite of mobile technologies. It alerts citizens of impending disasters through SMS/Cell Broadcast activated remote-alarm devices, cell broadcasting to handsets and multi-lingual SMS.

The rapid growth of mobile broadband penetration across the world indicates that these markets will approach maturity more quickly than previously thought. However in Asian market like Sri Lanka, the mobile broadband market is in its early stages. The operators do not have a clear approach in promoting mobile broadband to consumers; in the other hand consumers do not have previous experience in this method of internet access. Hence there is a definite requirement to identify the key factors & formulate a strategy to increase the adoption of mobile broadband, which in terms increase the penetration & competition in the market. The aim of this study is to examine the penetration; competition & what are the key factors affecting the penetration of mobile broadband in Sri Lankan market. Thus this study includes examining the various attitudinal, normative and control factors affecting the adoption of mobile …

A framework to support creation of location based services (LBS) applications using map services is designed and implemented. It provides a means to develop interoperable LBS applications which are independent of service provider, device or data providers. Application developers can use the framework to utilize multiple map servers following Web Map Service (WMS) and Web Feature Service (WFS) standards in creating the LBS applications. Mobile phone users can access the applications created by the framework through mobile Internet. A cascading map server and a application database is used at the application server. The LBS applications developed by the framework can provide directory assistance services on wide spectrum of mobile phones ranging from mid-range to smart phones. Thus many LBSs which have hitherto been denied to mid-range phones are made possible, exploiting their available …

We present an effective solution for both digital map generation and real time user tracking for teams operating in hazardous environments or unfamiliar territory. The system is based on the client server model, where the client is a GPS enabled mobile phone which is capable of capturing coordinates and serving dynamic maps to the user. The maps plot the team's navigational routes and enables real time tracking of each other. The server builds a GIS at the back end based on the data sent by the users, and also develops maps on demand. The system is implemented with simple hardware and uses the available GPRS network for data gathering. This enables the system to be used both in hazardous environments and by the general public.

Estimation of the location of a Mobile Station accurately is a key requirement to effectively provide a wide range of Location Based Services over mobile networks. Hence developing cellular positioning techniques has been a key research problem, with numerous localization solutions been proposed. These include technologies such as Cell ID, angle and time of arrival methods, statistical methods and fingerprinting methods. This paper presents fingerprinting based positioning techniques suitable for outdoor and indoor positioning. Multiple positioning techniques were proposed, implemented and evaluated with outdoor and indoor trials. The ultimate solution proposed in this paper is not a single positioning technique; rather it presents several positioning techniques that achieve optimum performance in each test environment. The results reports 67% positioning error as 112 m, 299 m and 221 m for urban …

The paper presents the combined application of Geographical Information Systems (GIS), the Global Positioning System (GPS), the General Packet Radio Service (GPRS) and the Internet for tracking of vehicle fleets. It is one component of an enterprise solution that is designed to manage and track a large fleet. The key features of the system are an open-source GIS platform, real-time location information update, and a web-based user interface. The system consists of GPS-based vehicle tracking devices, a communications server, a web-server, a database server, and a map server. The tracking devices mounted in the vehicles collect location information in real-time via the GPS. This information is transferred continuously through GPRS to a central database. The users are able to view the current location of each of the vehicles in the fleet via a web-based application, and thereby manage the fleet. The vehicle positions and other related information are displayed on a digital map, which is made available by a map server.