In this thesis, we consider the more broad-based spectrum sharing where primary and secondary users transmit simultaneously in the same band. In the first part of thesis, we consider an overlay cognitive radio downlink network with non-causal primary message knowledge at cognitive base station. While conventional linear precoding techniques in cognitive radio networks aim to limit or completely cancel the interference to the primary users, we investigate new interference driven linear precoding techniques to improve the performances of primary and cognitive links by exploiting the use of interference energy when interference is constructive. In the second part of thesis, we investigate cooperative relaying in overlay cognitive radio network and analyze the outage performance of overlay cognitive radio network when cognitive nodes relay the causal primary message to the primary destination to improve the performance of the primary system. Further, assuming causal knowledge of the primary user's message at the cognitive transmitter, we investigate the problem of transmit power allocation and linear beamforming design in an overlay cognitive radio network in single-input-multiple-output (SI MO) and the rnultiple-input-sinqle- output (MISO) configurations. The third part of the thesis deals with the underlay spectrum sharing cognitive radio. We investigate the multiuser diversity introduced by opportunistic user selection in underlay cognitive radio network, Based on a simple cognitive user selection strategy aiming at maximizing the received signal-to- interference-plus-noise ratio (SINR) under interference constraints to the primary receiver, we study the statistics of the SINR at the cognitive receiver, and derive exact analytical expressions of its probability density function (PDF). We use it to analytically calculate the multiuser diversity gains introduced in the system due to the selection of one cognitive user amongst multiple cognitive users. We also analyze the asymptotic behaviour of multiuser diversity gains for different parameters.

The objective of this research is to design passive UHF RFID tags that are insensitive to the platform they are applied to. The tag antennas developed in this work will exhibit good read range in harsh electromagnetic environments, such as metallic objects, liquid containers and human skin, while balancing the tag unit cost and form factor with perfonnance. In the early part of this thesis a brief introduction to RFID, the essential antenna parameters, the physics of RFID and the environmental effects on tag antennas sets the background necessary for understanding the procedure used when designing and measuring tag performance. As part of this fundamental research process, a tag design methodology is developed and evaluated by designing a global tag, before proceeding to design passive tags specific for unfriendly electromagnetic environments. In later part of the thesis, passive platform tolerant tags will be designed to identify electromagnetically unfriendly objects in different real working environments. The first design will identify large EM unfriendly objects. The requirement for this tag is ruggedness and long read range on any object, while keeping the tag profile as low as possible. The second tag will be designed to identify curved metallic objects such as gas cylinder. This tag will be designed on a tou-gh flexible substrate to conformal on curved objects. This main objective of this design is to identify metallic cylinder from all direction in the plane of the tag antenna. The third tag will be an ultra-thin design for identification of objects where low profile and low cost platform tolerant tagging is required. Ultra low profile platform tolerant tag design is also one of the main objectives of this work, which will be achieved in this design. The last tag in this work will ~ designed to identify humans in secure environments, where temporary access to facilities or sites is paramount. This non-transferable tag will be designed to be mountable directly onto the skin surface in the form of a transfer patch in much the same way that a temporary tattoo could be applied. - Since passive tags have ·to be designed for massive production at low cost and high reliability, all the designs in this work will aim at uncomplicated planar structures with high efficiency and high manufacturing tolerance on low cost commonly available substrates .

Traditional perspectives derived from wired networks treat each user as an individual and are subject to a layered architecture which is unnecessarily restrictive as it ignores two key characteristics of wireless medium: broadcast nature and spatial diversity. Inspired by the recent idea of cooperative communication, it is realised that intelligent cooperation among nodes may significantly improve network performance by exploiting the above physical characteristics. The popular IEEE 802.11 protocol has been widely deployed in public due to its simple but effective distributed contention-based access mechanism. It is essential to incorporate cooperation into contention-based networks to exploit the benefits of cooperation while keeping the effectiveness of the contention-based access mechanism.

This research aims at exploring novel approaches that can enable information and communications technologies to play significant roles in aiding the development agenda in challenged rural and poor environments, focusing on ad-hoc and sensor networks. This is addressed through two stages: first the needs and particularities of a typical, rural farming community in Sub-Saharan Africa are identified and analyzed through work carried out within the Engineering and Physical Sciences project VESEL (village e-science for life). Based on this higher level treatment the thesis employs an integrated approach to Information and Communication Technologies for Development (lCTD) and proposes an informed top-bottom generic technical framework for utilizing WSNs as a development enabling tool in challenged communications contexts. Second the thesis extracts specific low level technical challenges and focuses on how joint distributed storage management, rate-adaptive data generation and topology control can enable ad-hoc and sensor j networks operate efficiently and reliably in extreme conditions where network disconnections and interruptions are the norm. This results in developing new distributed algorithms for managing the network's storage and data generation in a way that adaptively responds to the network state and application requirements. These show considerable improvement over conventional 'local' storage approaches while keeping their advantage under different deployment conditions. The thesis also studies the spatio-temporal network devolution and connectivity- related effects of radio-wave shadowing and fading and quantifies their impacts on the performance of distributed storage and data management. By utilizing network optimization tools the thesis further shows how the problem of distributed storage in challenged sensor networks can be treated as a distributed storage allocation problem where effective strategies can be established to jointly optimize storage selection, storage routing and storage energy consumption. The design of optimum storage topologies is also possible through this approach. This part results in designing practical decentralized heuristics that achieve close-to-optimum dynamic allocation of distributed storage and hence enable storage-aided efficient data dissemination in challenged sensor networks lacking a continuous data upload capability.

In this thesis the problem of distributed detection, localization, and estimation (DDLE) of a stationary target in a fusion center (FC) based wireless sensor network (WSN) is considered. The communication process is subject to time-critical operation, restricted power and bandwidth (BW) resources operating over a shared communication channel Buffering from Rayleigh fading and phase noise. A novel algorithm is proposed to solve the DDLE problem consisting of two dependent stages: distributed detection and distributed estimation. The WSN performs distributed detection first and based on the global detection decision the distributed estimation stage is performed. The communication between the SNs and the FC occurs over a shared channel via a slotted Aloha MAC protocol to conserve BW. In distributed detection, hard decision fusion is adopted, using the counting rule (CR), and sensor censoring in order to save power and BW. The effect of Rayleigh fading on distributed detection is also considered and accounted for by using distributed diversity combining techniques where the diversity combining is among the sensor nodes (SNs) in lieu of having the processing done at the FC. Two distributed techniques are proposed: the distributed maximum ratio combining (dMRC) and the distributed Equal Gain Combining (dEGC). Both techniques show superior detection performance when compared to conventional diversity combining procedures that take place at the FC. In distributed estimation, the segmented distributed localization and estimation (SDLE) framework is proposed. The SDLE enables efficient power and BW processing. The SOLE hinges on the idea of introducing intermediate parameters that are estimated locally by the SNs and transmitted to the FC instead of the actual measurements. This concept decouples the main problem into a simpler set of local estimation problems solved at the SNs and a global estimation problem solved at the FC. Two algorithms are proposed for solving the local problem: a nonlinear least squares (NLS) algorithm using the variable projection (VP) method and a simpler gird search (GS) method. Also, Four algorithms are proposed to solve the global problem: NLS, GS, hyperspherical intersection method (HSI), and robust hyperspherical intersection (RHSI) method. Thus, the SDLE can be solved through local and global algorithm combinations. Five combinations are tied: NLS2 (NLS-NLS), NLS-HSI, NLS-RHSI, GS2, and GS-N LS. It turns out that the last algorithm combination delivers the best localization and estimation performance. In fact , the target can be localized with less than one meter error. The SNs send their local estimates to the FC over a shared channel using the slotted-Aloha MAC protocol, which suits WSNs since it requires only one channel. However, Aloha is known for its relatively high medium access or contention delay given the medium access probability is poorly chosen. This fact significantly hinders the time-critical operation of the system. Hence, multi-packet reception (MPR) is used with slotted Aloha protocol, in which several channels are used for contention. The contention delay is analyzed for slotted Aloha with and without MPR. More specifically, the mean and variance have been analytically computed and the contention delay distribution is approximated. Having theoretical expressions for the contention delay statistics enables optimizing both the medium access probability and the number of MPR channels in order to strike a trade-off between delay performance and complexity.

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