Enabling "intelligent environments" that are effortlessly automated is a key promise of sensor networks of the future. These networks have a wide range of domains in which they can be effectively deployed, including health-care, emergency response, manufacturing and surveillance. Unlike the majority of existing (and perhaps better-understood) network configurations, wireless-implemented sensor networks suffer from extremely stringent constraints in terms of scalability and end-goal of deployment. Thus, it is imperative that we determine solutions that are tailored to the constraints and goals of these systems, by bringing together ideas in the domains of control, computing and communications to a common analytical platform. In this dissertation, we build a theoretical framework that uses system theory, stochastic control, queuing theory and information theory to determine the following: 1. A characterization of the stability and optimal control policies with sensor querying (i.e. which set of sensors must be queried and when) using system theory and stochastic control; 2. A delay-optimal energy efficient transmission scheme for these networks (i.e. with what power level must they communicate) using heavy traffic limits and stochastic control; and 3. A cooperative transmission strategy for maximizing capacity of these networks (i.e. how they should encode their data to send the most through) using network information theory.

Not available

The shortage of radio spectrum has become the bottleneck of achieving broadband wire-less access. Overcoming this bottleneck in next-generation wireless networks hinges on successful implementation of multiple-input-multiple-output (MIMO) technologies, which use antenna arrays rather than additional bandwidth for multiplying data rates. The most efficient MIMO techniques require channel state information (CSI). In practice, such information is usually inaccurate due to overhead constraints on CSI acquisition as well as mobility and delay. CSI inaccuracy can potentially reduce the performance gains provided by MIMO. This dissertation investigates the impact of CSI inaccuracy on the performance of increasing complex MIMO networks, starting with a point-to-point link, continuing to a multiuser MIMO system, and ending at a mobile ad hoc network. Furthermore, this dissertation contributes algorithms for efficient CSI acquisition, and its integration with beamforming and scheduling in multiuser MIMO, and with interference cancelation in ad hoc networks. First, this dissertation presents a design of a finite-rate CSI feedback link for point-to-point beamforming over a temporally correlated channel. We address various important design issues omitted in prior work, including the feedback delay, protocol, bit rate, and compression in time. System parameters such as the feedback bit rate are derived as functions of channel coherence time based on Markov chain theory. In particular, the capacity gain due to beamforming is proved to decrease with feedback delay at least at an exponential rate, which depends on channel coherence time. This work provides an efficient way of implementing beamforming in practice for increasing transmission range and throughput. Second, several algorithms for multiuser MIMO systems are proposed, including CSI quantization, joint beamforming and scheduling, and distributed feedback scheduling. These algorithms enable spatial multiple access and multiuser diversity in a cellular system under the practical constraint of finite-rate multiuser CSI feedback. Moreover, this dissertation shows analytically that the throughput of the MIMO uplink and downlink using the proposed algorithms scales optimally as the number of users increases. Finally, the transmission capacity of a MIMO ad hoc network is analyzed for the case where spatial interference cancelation is applied at receivers. Most important, this dissertation shows that this MIMO technique contributes significant network capacity gains even if the required CSI is inaccurate. In addition, opportunistic CSI estimation is shown to provide a tradeoff between channel training overhead and CSI accuracy. / text

M. Tech. Electrical Engineering. / Wireless Sensor Networks (WSNs), which contribute to many applications in the military, environmental, medical, and civil domains, consist of small nodes with sensing, data computation, and wireless-communication capabilities. Node routing protocols have been specifically designed for WSNs in which energy conservation is an essential design issue. Rumor Routing (RR) is a hybrid protocol which combines both proactive and reactive routing methods, which balances event and query flooding quite well. This kind of protocol is well adapted to the case of few data and many queries. In this paper, Relative Coordinate Rumor Routing (RCRR), a straight-line routing method of both event and query, is proposed. It improves RR using some topological and abstract localisation method that shortens the source-to-sink route for the data transmission in order to save energy for broadcasting, even comparing to large data amount Routing Protocol. By adapting the Sensor-MAC protocol, the power consumption is much lower than that of the RR. Nodes can change to idle mode when notification of broadcasting does not apply to them. Simulation studies of RCRR with S-MAC can reduce energy by 60% compared to RR, which is a good improvement

The Development of cost-effective and economically viable telecommunications solutions for rural underdeveloped areas has been a key problem to Africa and South Africa. Selecting an appropriate telecommunications technology and an appropriate network topology that could provide both voice and data communication solutions for these areas would be a major advantage for both the community and industries in these areas. Success lies in our ability to adapt selected technologies and implement it with a viable and affordable telecommunication solution. This paper proposes an appropriate telecommunications technology utilization of a cost effective network that can provide wide bandwidth for voice and data telecommunications solutions that are essential for the education, business and private multi-user needs for the Soshanguve and Ga- Rankuwa areas, North-West of Pretoria..

Not available / text

Not available / text

published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The contribution of the work here presented involves three main topics: Wireless Power Transmission (WPT) technology, phased array systems, and microwave components design and modeling. The first topic presents the conceptual design of a WPT system at 2.45GHz with 90% efficiency and 1MW of DC output power. Second, a comparative study between 2.45 and 35GHz WPT operation is provided. Finally, the optimization of a taper distribution with reduced thermal constraints on a sandwich transmitter is realized. For a 250- and 375-m antenna radius, 89.7% of collection efficiency with 29% reduction in maximum power density (compared to the Gaussian), and 93% collection efficiency with 39% reduction of maximum power density, are obtained respectively with two split tapers. The reduction in maximum power density and the use of split taper are important to alleviate the thermal problems in high power transmission. For the phased array project, the conceptual design of a small-scale system and in-depth analysis using two main approaches (statistical and field analysis) is realized. Practical aspects are addressed to determine the phased array main design features. The statistical method provides less accurate results than the field analysis since it is intended for large arrays. Careful theoretical analysis led to good correlation between statistical, field analysis and experimental results. In the components chapter, efficient loop transitions used in a patch antenna array are designed at K- and W-band. Measured insertion loss (IL) K-band loop is under 0.4dB. The K- and W-band antenna array measured broadside gains are 23.6dB at 24.125GHz and 25dB at 76.5GHz with return loss under 9.54dB from 24 to 24.4GHz and 12 dB from 75.1 to 77.3GHz, respectively. Also, a multilayer folded line filter is designed at 5.8GHz and compared to planar ring filters. Improved measured bandwidth from 2GHz to 7.5GHz and IL of 1.2dB are obtained with approximately half the size of a planar ring resonator. Thirdly, a simplified switch model is implemented for use in broadband phased-shifters. The model presents very good fit to the measured results with an overall total error under 3%, magnitude error less than 8%, and phase errors less than ±0.4°.

Wireless ad hoc networks have been emerged to support applications, in which it is required/desired to have wireless ommunications among a variety of devices without relying on any infrastructure or central managements. In ad hoc networks, wireless devices, simply called nodes, have limited transmission range. Therefore, each node can directly communicate with only those within its transmission range and requires other nodes to act as routers in order to communicate with out-of-range estinations. One of the fundamental operations in ad hoc networks is broadcasting, where a node sends a message to all other nodes in the network. This can be achieved through flooding, in which every node transmits the first copy of the received message. However, flooding can impose a large number of redundant transmissions, which can result in significant waste of constrained resources such as bandwidth and battery power. One of the contributions of this work is to propose efficient broadcast algorithms which can significantly reduce the number of redundant transmissions. We also consider some of the security issues of ad hoc networks. In particular, we carefully analyze the effect of the wormhole attack, which is one of the most severe threats against ad hoc networks. We also propose a countermeasure, which is an improvement over the existing timing-based solutions against the wormhole attack. Finally, in the last chapter, we propose novel point compression techniques which can be used in Elliptic Curve Cryptography (ECC). ECC can provide the same level of security as other public key cryptosystems (such as RSA) with substantially smaller key sizes. Smaller keys can result in smaller system parameters, bandwidth savings, faster implementations and lower power consumption. These advantages make ECC interesting for ad hoc networks with restricted devices.