Future wireless networks will have to handle varying combinations of multimedia traffic that present the network with numerous quality of service (QoS) requirements. The continuously growing demand for mobile phones has resulted in radio spectrum becoming a precious resource that cannot be wasted. The current second-generation mobile networks are designed for voice communication and, even with the enhancements being implemented to accommodate data, they cannot efficiently handle the multimedia traffic demands that will be introduced in the near future. This thesis begins with a survey of existing wireless ATM (WATM) protocols, followed by an examination of some medium access control (MAC) protocols, supporting multimedia traffic, and based on code division multiple access (CDMA) physical layers. A WATM link layer protocol based on a CDMA physical layer, and incorporating techniques from some of the surveyed protocols, is then proposed. The MAC protocol supports a wide range of service requirements by utilising a flexible scheduling algorithm that takes advantage of the graceful degradation of CDMA with increasing user interference to schedule cells for transmission according to their maximum bit error rate (BER) requirements. The data link control (DLC) accommodates the various traffic types by allowing virtual channels (VCs) to make use of forward error correction (FEc) or retransmission techniques. The proposed link layer protocol has been implemented on a Blue Wave Systems DSP board that forms part of Alcatel Altech Telecoms' software radio platform. The details and practicality of the implementation are presented. A simulation model for the protocol has been developed using MIL3 's Opnet Modeler. Hence, both simulated and measured performance results are presented before the thesis concludes with suggestions for improvements and future work. / Thesis (M.Sc.)-University of Natal, Durban, 2000.

WCDMA promises to achieve high-speed internet, high quality image transmission and high-speed data services with larger system capacity. However, Multiple Access Interference is one of the major causes of transmission impairment, which reduces the link capacity in WCDMA systems. The Adaptive Antenna Array (AAA) technique reduces multiple access interference by directing antenna beam nulls towards the interfering signals by weighting the received signals from all antennas before combining the signals. With the very rapid advancement of wireless personal communications services, a new challenge to the cellular industry is the integration of multiple systems and applications on a single device. A software radio technique offers a possible solution to achieve this goal including international roaming and multiple standard operations within the same geographical area. The main attraction of a software radio is it's flexibility, in that it can be programmed for emerging cellular standards allowing it to be updated with new software without any changes in the hardware infrastructure. A software radio incorporating adaptive array beamforming at the receiver can increase the total carried traffic in a system and transmit power while the probability of call blocking and forced termination can also be decreased. This dissertation examines WCDMA, AAA, power control and software radio techniques in the world of wireless communication systems. Once the theoretical background of CDMA and AAA has been substantiated, the thesis establishes the need for power control in mobile systems by examining simulation results. An AAA receiver with six antenna elements is proposed and evaluated in different environments as a precursor to implementation. It can be inferred that when the link is interference limited, the link capacity can be increased and it has been shown that the AAA receiver with six antenna elements increases the link capacity to about 2.9 times that of the single antenna RAKE receiver. This thesis also examines the basic concepts of VHDL and considers this as the principle means to program reconfigurable core FPGA's in the software radio. A three-layered (PC/DSP/FPGA) software radio test bed is used to implement an AAA receiver. The architecture of the test bed is designed in such a way that it can be used to evaluate the performance of various FPGA based transceivers and coding schemes etc. Many of the desirable features and flexibilities inherent in the software radio concept are available on this test bed and the system has proved to be capable of high speed digital processing and is ideally suited to the development of time critical system components. The bit error rate achieved using the implemented receiver is assessed and compared to simulation results in an environment incorporating Rayleigh fading and AWGN. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.

For opportunistic spectrum access and spectrum sharing in cognitive radio networks, one key problem is how to develop wireless access schemes for secondary users so that harmful interference to primary users can be avoided and quality-of-service (QoS) of secondary users can be guaranteed. In this research, dynamic wireless access protocols for secondary users are designed and optimized for both infrastructure-based and ad-hoc wireless networks. Under the infrastructure-based model, the secondary users are connected through a controller (i.e., an access point). In particular, the problem of wireless access for eHealth applications is considered. In a single service cell, an innovative wireless access scheme, called electromagnetic interference (EMI)-aware prioritized wireless access, is proposed to address the issues of EMI to the medical devices and QoS differentiation for different eHealth applications. Afterwards, the resource management problem for multiple service cells, specifically, in multiple spatial reuse time-division multiple access (STDMA) networks is addressed. The problem is formulated as a dual objective optimization problem that maximizes the spectrum utilization of secondary users and minimizes their power consumption subject to the EMI constraints for active and passive medical devices and minimum throughput guarantee for secondary users. Joint scheduling and power control algorithms based on greedy approaches are proposed to solve the problem with much less computational complexity. In an ad-hoc wireless network, the robust transmission scheduling and power control problem for collision-free spectrum sharing between secondary and primary users in STDMA wireless networks is investigated. Traditionally, the problem only considers the average link gains; therefore, QoS violation can occur due to improper power allocation with respect to instantaneous channel gain realization. To overcome this problem, a robust power control problem is formulated. A column generation based algorithm is proposed to solve the problem by considering only the potential subset of variables when solving the problem. To increase the scalability, a novel distributed two-stage algorithm based on the distributed column generation method is then proposed to obtain the near-optimal solution of the robust transmission schedules for vertical spectrum sharing in an ad-hoc wireless network.

During the past few years, Power Line Communications (PLC) have become a popular connectivity solution to answer the growing need of home networks for bandwidth. As wireless technologies, this solution spares the user from cabling its Local Area Network (LAN), by directly using the home power grid as a transmission medium. While PLC generally offer a larger coverage than Wireless Local Area Networks (WLAN), the capacity offered by current systems is not sufficient to simultaneously support bandwidth intensive streams. In this thesis, we aim at exploring various solutions for future PLC networks. Firstly, we aim at improving the spectral efficiency of the current systems' Physical (PHY) layer, where two modulation schemes are compared. On the one hand, we study the modulation deployed in current PLC networks, called windowed Orthogonal requency Division Multiplexing (OFDM), and we highlight the main limitation of this solution in the particular context of PLC. On the other hand, we show that and alternative solution, called OFDM/Offset Quadrature Amplitude Modulation (OQAM), offers some degrees of freedom which could highly benefit to PLC networks. Secondly, the study is oriented toward the Media Access Control (MAC) layer of PLC systems, considering a multiuser utilization of the network. In this second part, we aim at proposing allocation solutions that will allow a more efficient utilization of the limited and shared transmission resource. We firstly study the opportunity of defining an Orthogonal Frequency-Division Multiple Access (OFDMA) transmission scheme for point-to-multipoint transmissions, in order to increase data rates by taking advantage of the diversity between users' channels. Finally, the last Chapter is dedicated to the study of broadcast and multicast communications in PLC networks, where we show that a smart aggregation of the set of users to reach could greatly improve efficiency of multicast transmissions.

This thesis is concerned with distributed estimation in a wireless sensor network (WSN) with analog transmission. For a scenario in which a large number of sensors are deployed under a limited bandwidth constraint, a semi-orthogonal multiple-access channelization (MAC) approach is proposed to provide transmission of observations from K sensors to a fusion center (FC) via N orthogonal channels, where K≥N. The proposed semi-orthogonal MAC can be implemented with either fixed sensor grouping or adaptive sensor grouping. The mean squared error (MSE) is adopted as the performance criterion and it is first studied under equal power allocation. The MSE can be expressed in terms of two indicators: the channel noise suppression capability and the observation noise suppression capability. The fixed version of the semi-orthogonal MAC is shown to have the same channel noise suppression capability and two times the observation noise suppression capability when compared to the orthogonal MAC under the same bandwidth resource. For the adaptive version, the performance improvement of the semi-orthogonal MAC over the orthogonal MAC is even more significant. In fact, the semi-orthogonal MAC with adaptive sensor grouping is shown to perform very close to that of the hybrid MAC, while requiring a much smaller amount of feedback. Another contribution of this thesis is an analysis of the behavior of the average MSE in terms of the number of sensors, namely the scaling law, under equal power allocation. It is shown that the proposed semi-orthogonal MAC with adaptive sensor grouping can achieve the optimal scaling law of the analog WSN studied in this thesis. Finally, improved power allocations for the proposed semi-orthogonal MAC are investigated. First, the improved power allocations in each sensor group for different scenarios are provided. Then an optimal solution of power allocation among sensor groups is obtained by the convex optimization theory, and shown to outperform equal power allocation. The issue of balancing between the performance improvement and extra feedback required by the improved power allocation is also thoroughly discussed.

For opportunistic spectrum access and spectrum sharing in cognitive radio networks, one key problem is how to develop wireless access schemes for secondary users so that harmful interference to primary users can be avoided and quality-of-service (QoS) of secondary users can be guaranteed. In this research, dynamic wireless access protocols for secondary users are designed and optimized for both infrastructure-based and ad-hoc wireless networks. Under the infrastructure-based model, the secondary users are connected through a controller (i.e., an access point). In particular, the problem of wireless access for eHealth applications is considered. In a single service cell, an innovative wireless access scheme, called electromagnetic interference (EMI)-aware prioritized wireless access, is proposed to address the issues of EMI to the medical devices and QoS differentiation for different eHealth applications. Afterwards, the resource management problem for multiple service cells, specifically, in multiple spatial reuse time-division multiple access (STDMA) networks is addressed. The problem is formulated as a dual objective optimization problem that maximizes the spectrum utilization of secondary users and minimizes their power consumption subject to the EMI constraints for active and passive medical devices and minimum throughput guarantee for secondary users. Joint scheduling and power control algorithms based on greedy approaches are proposed to solve the problem with much less computational complexity. In an ad-hoc wireless network, the robust transmission scheduling and power control problem for collision-free spectrum sharing between secondary and primary users in STDMA wireless networks is investigated. Traditionally, the problem only considers the average link gains; therefore, QoS violation can occur due to improper power allocation with respect to instantaneous channel gain realization. To overcome this problem, a robust power control problem is formulated. A column generation based algorithm is proposed to solve the problem by considering only the potential subset of variables when solving the problem. To increase the scalability, a novel distributed two-stage algorithm based on the distributed column generation method is then proposed to obtain the near-optimal solution of the robust transmission schedules for vertical spectrum sharing in an ad-hoc wireless network.

Aquesta tesi suggereix usar un compte enrere determinista després de les transmissions exitoses en les xarxes d'àrea local sense fils. Com que les estacions que han transmès amb èxit en el seu darrer intent no poden col·lisionar entre elles en el seu proper intent, el nombre de col·lisions es redueix. Per tant, anomenem el protocol accés múltiple per detecció de portadora amb evitament de col·lisions millorat. El protocol es modela i es simula en diversos escenaris per a la seva avaluació. S'arriba a la conclusió de que el protocol proposat ofereix un rendiment igual o major que l'existent. / This thesis suggests the use of a deterministic backoff after successful transmissions in the MAC protocol of WLANs. Since those stations that successfully transmitted in their last collision attempt cannot collide among them in their next transmission attempt, the number of collisions is reduced. Hence, the protocol is called Carrier Sense Multiple Access with Enhanced Collision Avoidance. The protocol is modelled and simulations are used to assess its performance in a variety of scenarios. It is concluded that the proposed protocol performs always equal or better than the legacy one.

Thesis (Ph.D.)--University of Melbourne, Dept. of Electrical and Electronic Engineering, 2007. / Typescript. Includes bibliographical references (leaves 143-154).

Thesis (M. App. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 80-83). Also available in electronic format on the Internet.

Thesis (M.App.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 131-134). Also available in electronic format on the Internet.