This thesis focuses on one of the key development areas of Beyond IMT-2000 or Beyond 3rd Generation (B3G) systems recommended by ITU-R M.1645, that is, new radio access systems that provide significantly higher performance for different deployment scenarios which may encompass different access technologies while maintaining seamless access and mobility from the user's perspective. Our objective is to develop various Medium Access Control (MAC) solutions for this new B3G access system. We introduce a novel B3G multi-mode access system framework based on heterogeneous physical layer (PL) modes or configurations, anchored by a common layer 2 and layer 3 protocol stack. Such a system can support a wide variety of physical layer multiple access technologies to target different deployment scenarios and performance targets. The anchor or common layer 2/3 protocols enable seamless handoff and dynamic radio resource/load/spectrum management across the different PL modes to achieve optimum spectrum efficiency and Quality of Service (QoS) support. As a basic form of the proposed B3G multi-mode access system and the first evolution step from the existing 3rd Generation (3G) cellular systems, we propose the multi-carrier expansion of Direct Spread Code Division Multiple Access, i.e. MC DS-CDMA. MC DS-CDMA supports concurrent transmissions on multiple DS-CDMA carriers anchored by a common layer 2/3 protocol stack. The common layer 2/3 protocol stack supports fully asymmetrical and dynamic Forward Link (FL) and Reverse Link (RL) carrier(s) allocation based on QoS requirements and Service Level Agreement (SLA). MC DS¬CDMA also provides backward compatibility to existing single carrier DS-CDMA systems, thus allowing for overlay of legacy and new systems while the network deployment migrates towards B3G broadband support. We further investigate load balancing schemes across multiple PL modes sharing the same spectrum resource in Time Division Multiplex (TDM), Frequency Division Multiplex (FDM) or Code Division Multiplex (CDM) fashions. For TDM and FDM cases, we propose a new Integrated Load Balancing and Scheduling (ILBS) scheme that maximizes the system capacity while meeting users' QoS and SLA. For the CDM case, we propose a dynamic Walsh code and Base Station (BS) transmit power sharing scheme between power-controlled dedicated traffic channels and rate-controlled packet data channels across multiple CDMA carriers. An important aspect of MAC for wireless mobile systems is the MAC states management. We develop a universal MAC state machine concept that anchors the heterogeneous PL modes so that when a user switches from one PL mode to another, the MAC state and the associated context information of the MS can be retained. to minimize packet loss and PL mode switching/handoff latency. We further look into the decision criteria used to transition a user from one MAC state to another. It is an important part of MAC for both the existing 3G systems and the B3G systems. The decision criteria should aim to maximize system capacity while meeting users' QoS and SLA requirements, while at the same time achieving power-saving. We propose a novel priority based state transition algorithm that achieves these objectives. Overall, our research provides key solutions to the challenges of next generation wireless systems envisioned to encompass heterogeneous characteristics and performance targets.

Wireless systems that have traditionally been designed using a layered approach have seen a recent paradigm shift to a cross-layered approach where the interactions between two or more layers are considered explicitly in an integrated framework. This dissertation presents new methodologies that aim to improve the performance of wireless systems through consideration of cross-layer based design. The physical (PHY) and the medium access control (MAC) layers are the primary layers responsible for data transmission and user selection/control, respectively, in wireless systems. This dissertation begins with an analysis illustrating the use of multiple antennas and antenna arrays at. the PHY layer. A framework combining space-time block coding and beamforming for uplink in a wireless systems is con¬sidered for studying the trade-offs between antennas and antenna arrays at the receiver. Results indicate that in high noise environments the diversity achieved by using a large number of antennas combats bit error rate (BER) more efficiently than beamforming. On the other hand, in low noise environments beamforming plays an important role in reducing BER by minimizing the effect of interference from other co-channel users. Two approaches of cross-layer design that are currently available are the bottom-up and top-down approaches. The bottom-up approach uses the PHY laver infor¬mation at the MAC and higher layers to make decisions that affect the system performance. Following a bottom-up approach, a new scheduling algorithm is designed that uses the channel state information and direction of arrival information of mobile users to efficiently schedule users for service. Both semi-analytical (based on the probability density and cumulative distribution functions) and numerical frameworks are used to compare the performance of this algorithm with the traditional round-robin and greedy scheduling algorithms. Both the numerical and semi-analytical frameworks which are shown to be consistent with each other yield improved system capacity for the proposed algorithm compared to the traditional algorithms. This is the result of explicitly considering the angular location of mobile users around the base station that results into the reduced interference between simultaneously served users on one other. The effect of channel availability on the scheduling algorithms is also investigated within a queuing framework and the results indicated that the system performance is also dependent on channel availability and traffic conditions. A top-down approach is based on modifying the PHY layer to support the require¬ments or protocols used at the MAC layer to improve system throughput. Following a top-down approach, a new methodology is presented that reduces null depths of a given beam to address the hidden beam problem in IEEE 802.11 systems. The hidden beam problem occurs in carrier sensing multiple access (CSMA) systems when mobile users lying in deep nulls are unable to sense an ongoing downlink transmission and start transmitting data in an uplink. The modified beam with reduced null depths is compared with the original beam in terms of reducing the hidden beam problem when used in non-persistent CSMA systems. The modified beam is shown to improve the throughput of a slotted non-persistent CSMA system significantly when compared to original beam with relatively small changes to directivity and half power beamwidth. The bottom-up and top-down approaches used in this dissertation illustrate that by jointly addressing the PHY and MAC layer issues in an integrated cross-layer framework the performance of wireless systems can be significantly improved.

Ultra-wideband (UWB) wireless systems rely on signals spanning very wide bandwidths, typically several gigahertz, for information transmission. The distinguishing feature of UWB communications technology is the unrivalled data-rates it provides, with other benefits such as fade resistance and spectral reusability. These characteristics render UWB the technology of choice for a gamut of modern wireless communications applications, including multimedia transmission, personal- and body-area networks, imaging devices, and sensor networks. The use of wide bandwidth signals, however, leads to many complications that necessitate specialised design considerations. The propagation channel and system components acquire frequency-selective characteristics, and their nonlinear and dispersive nature, usually innocuous in a conventional setting, causes signal distortion and erroneous detection. This thesis analyses various aspects of the indoor channel and the distortion to a UWB signal propagating through it. The performance of transmitter and receiver sub-systems is evaluated, with an emphasis on the challenges posed by the large operating bandwidth. The significance of incorporating this knowledge into the system design process is demonstrated, and a novel framework for optimising the performance-complexity tradeoff is presented. • The following are the contributions of this thesis to the state of the art in UWB communications. • Experimental characterisation of the indoor UWB channel spanning the FCC band (3.1-10.6 GHz) • Demonstration of the variability of propagation characteristics in the spectral sub-bands • Assessment of frequency-dependent pathless and the consequent signal waveform distortion • Polarimetric analysis of the temporal, spectral and angular channel evolution • Evaluation of rake receiver performance and its dependence on various channel conditions • Investigation of the effect of antenna angular-spectral distortion on signal propagation • A technique for the normalisation of UWB link aberration due to antennas • Performance evaluation of diversity and spatial multiplexing with multiple-antenna systems • Design of gigabit wireless links for high data-rate applications or high user density scenarios • A novel holistic framework for the design of an optimal UWB communications system.

Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references. / vi, 62 leaves, bound ill. 29 cm

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 94-96). / xv, 96 leaves, bound ill. 29 cm

With the unprecedented growth of the communication industry that the world is experiencing, the demand from rural inhabitants for high quality communications at an economically affordable cost is growing. However, rural areas are rather restricted from deploying communication services due to the rough natural environment, and the shortage of rudimentary communication facilities and technical personnel. Appropriate models for building rural wireless networks and a concomitant simulation environment are, therefore, expected to enable the construction of technologically-optimal and economically-efficient networks in specified rural areas.<br /> <br /> The research has set up two independent models, one for the economic need and the other for the technical need of building networks in rural areas. One model was the Impact of Telecommunications Model, which disclosed the importance of building a wireless network in specified rural areas by choosing an economic parameter to forecast the profitability of the network. The other was the Service Model, which collected primitive data from given rural areas and abstracted these data by flowing them through four technical layers to form the predicted technical wireless network. Both of the models had been applied to real-world cases to demonstrate how to use them.<br /> <br /> A simulation environment was finally designed and implemented to realize the above two models for the sake of instantiation. This environment could simulate the specified rural network by constructing a wireless network on the invented areas and evaluating its quality and economic efficiency. It was written in Scilab simulation language, which was an open source.

Thesis (PhD)--University of South Australia, 2008.

Thesis (PhDTelecommunications)--University of South Australia, 2008.

This thesis investigates the ability of dynamic algorithms to adequately share limited satellite channel resources between explicit user demands for bandwidth, anticipated bandwidth demands from users, and signalling traffic transmitted from user terminals. In particular it investigates the design of multiple access control protocols and the way their features affect the performance of higher layer protocols, and the efficiency of using the underlying resources. / Thesis (PhDTelecommunications)--University of South Australia, 2007.

The ever increasing demand for wireless services using mobile cellular communication technology has lead to intensive efforts by researchers to determine the information theoretic limitations of these systems. Toward this end, numerous cellular models have been formulated and analyzed using information theoretic principles to succinctly identify the impact of system constraints and design parameters on performance. One such model that captures the essence of the uplink of a cellular channel is the Gaussian cellular multiple access channel (GCMAC), which is the focus of this dissertation. / Thesis (PhD)--University of South Australia, 2006