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Failure of a machine can lead to production downtime and significant financial losses. Condition monitoring is implemented to avoid such downtime and devices can be used to collect data used for monitoring machine health. Vibration data is the most common type of data used for predicting machine failure. To reduce the need for hazardous cables, such devices are often battery-operated, but this can decrease monitoring device lifespans to less than 3 years, if non-rechargeable batteries are used. This thesis first proposes a design framework for implementing radio frequency energy harvesting (RFEH) at a network level. All of the necessary inputs and parameters to ensure the successful implementation of RFEH for a wireless sensor network are explored. A second design framework is then proposed for using RFEH as a source of energy to power devices for condition monitoring. This includes a power analysis of all device components, as well as the design details for an implementation of wireless power transfer using a wireless transmitter and receiver. A comparison of different types of energy sources for the device is given, followed by a case study, using commercially-available components. A simulation is used to analyze the trade-offs for different values of RFEH parameters, trading off the total cost of implementation with the system's lifetime, based on total energy consumed.

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Approved for public release; distribution in unlimited. / In spite of the fact that wireless network technology has been available for long period of time, there has been very limited wireless networks deployments around the world before 1997 due to the lack of widely recognized standard for wireless networks. Thanks to the approval of the IEEE 802.11 family of standards in 1997, the world has witnessed tremendous deployment and proliferation of wireless networks in all aspects of life. Although the IEEE 802.11 family of standards has been ratified to design radio transceivers for wireless computer stations capable of interconnecting with other wireless computer stations in close proximity, the technology has been successfully employed to design and implement wireless networks with great number of distant wireless computer stations with reasonable data throughput and flexibility. This thesis explores the wireless network technology and the primary building blocks and components of a wireless network. It also explores the IEEE 802.11 standard and its technical specifications including the Physical layer (PHY), the Media Access Control layer (MAC) and the ongoing task forces. Additionally, the thesis examines the wireless network security including the vulnerabilities, ongoing improvements and recommendations. Next, it investigates the market for available wireless devices compatible with the IEEE 802.11 standard that can be used to build a wireless network with high data throughput and high level of security. Subsequently, the thesis formulates a design plan for civilian wireless network with different scenarios in order to provide a speedy solution to the limited broadband service availability in the Sultanate of Oman. Additionally, the thesis formulates a generic design plan for a military wireless network with different scenarios that can be rapidly deployed in the field of operations. / Computer Engineer, Royal Army of Oman

In multiuser wireless communications, interference not only limits the performance of the system, but also allows users to eavesdrop on other users’ messages. Hence, interference management in multiuser wireless communication has received significant attention in the last decade, both in the academia and industry. The interference channel (IC) is one of the simplest information theoretic models to analyze the effect of interference on the throughput and secrecy of individual messages in a multiuser setup. In this thesis, the IC is studied under different settings with and without the secrecy constraint. The main contributions of the thesis are as follows: • The generalized degrees of freedom (GDOF) has emerged as a useful approximate measure of the potential throughput of a multiuser wireless system. Also, multiple antennas at the transmitter and receiver can provide additional dimension for signaling, which can in turn improve the GDOF performance of the IC. In the initial part of the thesis, a K-user MIMO Gaussian IC (GIC) is studied from an achievable GDOF perspective. An inner bound on GDOF is derived using a combination of techniques such as treating interference as noise, zero-forcing receiving, interference alignment (IA), and extending the Han-Kobayashi (HK) scheme to K users. Also, outer bounds on the sum rate of the K-user MIMO GIC are derived, under different assumptions of cooperation and providing side information to the receivers. The derived outer bounds are simplified to obtain outer bounds on the GDOF. The relative performance of these bounds yields insight into the performance limits of the multiuser MIMO GIC and the relative merits of different schemes for interference management. • Then, the problem of designing the precoding and receive filtering matrices for IA is explored for K-user MIMO (M × N) GIC. Two algorithms for designing the precoding and receive filtering matrices for IA in the block fading or constant MIMO IC with a finite number of symbol extensions are proposed. The first algorithm for IA is based on aligning a subset of the interfering signal streams at each receiver. As the first algorithm requires global channel knowledge at each node, a distributed algorithm is proposed which requires only limited channel knowledge at each node. A new performance metric is proposed, that captures the possible loss in signal dimension while designing the precoders. The performance of the algorithms are evaluated by comparing them with existing algorithms for IA precoder design. • In the later part of the thesis, a 2-user IC with limited-rate transmitter cooperation is studied, to investigate the role of cooperation in managing interference and ensuring secrecy. First, the problem is studied in the deterministic setting, and achievable schemes are proposed, which use a combination of interference cancelation, relaying of the other user’s data bits, time sharing, and transmission of random bits, depending on the rate of the cooperative link and the relative strengths of the signal and the interference. Outer bounds on the secrecy rate are derived, under different assumptions of providing side information to receivers and partitioning the encoded message/output depending on the relative strength of the signal and the interference. The achievable schemes and outer bounds are extended to the Gaussian case. For example, while obtaining outer bounds, for the Gaussian case, it is not possible to partition the encoded message or output as performed in the deterministic case, and the novelty lies in finding the analogous quantities for the Gaussian case. The proposed achievable scheme for the Gaussian case uses a combination of cooperative and stochastic encoding along with dummy message transmission. For both the models, one of the key techniques used in the achievable scheme is interference cancelation, which has two benefits: it cancels interference and ensures secrecy simultaneously. The results show that limited-rate transmitter cooperation can greatly facilitate secure communications over 2-user ICs.

We consider optimal power allocation policies for a single server, multiuser wireless communication system. The transmission channel may experience multipath fading. We obtain very efficient, low computational complexity algorithms which minimize power and ensure stability of the data queues. We also obtain policies when the users may have mean delay constraints. If the power required is a linear function of rate then we exploit linearity and obtain linear programs with low complexity. We also provide closed-form optimal power policies when there is a hard deadline delay constraint. Later on, we also extend single hop results to multihop networks. First we consider the case, when the transmission rate is a linear function of power. We provide low complexity algorithms for joint routing, scheduling and power control which ensure stability of the queues, certain minimum rates, end-to-end hard deadlines, and/or upper bounds on the end-to-end mean delays. Further we extend these results to the multihop networks where the power is a general monotonically increasing function of rate. For our algorithms, we also provide rates of convergence to the stationary distributions for the queue length process and also approximate end-to-end mean delays. Finally, we provide computationally efficient algorithms that minimize the total power when there is a end-to-end hard deadline delay constraint.

Wireless Sensor Networks(WSNs) have gained a lot of attention because of their potential to immerse deeper into people' lives. The applications of WSNs range from small home environment networks to large habitat monitoring. These highly diverse scenarios impose different requirements on WSNs and lead to distinct design and implementation decisions. This thesis presents an optimization framework for WSN design which selects a proper set of protocols and number of nodes before a practical network deployment. A Genetic Algorithm(GA)-based Sensor Network Design Tool(SNDT) is proposed in this work for wireless sensor network design in terms of performance, considering application-specific requirements, deployment constrains and energy characteristics. SNDT relies on offine simulation analysis to help resolve design decisions. A GA is used as the optimization tool of the proposed system and an appropriate fitness function is derived to incorporate many aspects of network performance. The configuration attributes optimized by SNDT comprise the communication protocol selection and the number of nodes deployed in a fixed area. Three specific cases : a periodic-measuring application, an event detection type of application and a tracking-based application are considered to demonstrate and assess how the proposed framework performs. Considering the initial requirements of each case, the solutions provided by SNDT were proven to be favourable in terms of energy consumption, end-to-end delay and loss. The user-defined application requirements were successfully achieved.

The rapid growth of the Internet of Things (IoT) introduces an additional challenge to the existing spectrum under-utilisation problem as large scale deployments of thousands devices are expected to require wireless connectivity. Dynamic Spectrum Access (DSA) has been proposed as a means of improving the spectrum utilisation of wireless systems. Based on the Cognitive Radio (CR) paradigm, DSA enables unlicensed spectrum users to sense their spectral environment and adapt their operational parameters to opportunistically access any temporally unoccupied bands without causing interference to the primary spectrum users. In the same context, CR inspired Machine-to-Machine (M2M) communications have recently been proposed as a potential solution to the spectrum utilisation problem, which has been driven by the ever increasing number of interconnected devices. M2M communications introduce new challenges for CR in terms of operational environments and design requirements. With spectrum sensing being the key function for CR, this thesis investigates the performance of spectrum sensing and proposes novel sensing approaches and models to address the sensing problem for cognitive M2M deployments. In this thesis, the behaviour of Energy Detection (ED) spectrum sensing for cognitive M2M nodes is modelled using the two-wave with dffi use power fading model. This channel model can describe a variety of realistic fading conditions including worse than Rayleigh scenarios that are expected to occur within the operational environments of cognitive M2M communication systems. The results suggest that ED based spectrum sensing fails to meet the sensing requirements over worse than Rayleigh conditions and consequently requires the signal-to-noise ratio (SNR) to be increased by up to 137%. However, by employing appropriate diversity and node cooperation techniques, the sensing performance can be improved by up to 11.5dB in terms of the required SNR. These results are particularly useful in analysing the eff ects of severe fading in cognitive M2M systems and thus they can be used to design effi cient CR transceivers and to quantify the trade-o s between detection performance and energy e fficiency. A novel predictive spectrum sensing scheme that exploits historical data of past sensing events to predict channel occupancy is proposed and analysed. This approach allows CR terminals to sense only the channels that are predicted to be unoccupied rather than the whole band of interest. Based on this approach, a spectrum occupancy predictor is developed and experimentally validated. The proposed scheme achieves a prediction accuracy of up to 93% which in turn can lead to up to 84% reduction of the spectrum sensing cost. Furthermore, a novel probabilistic model for describing the channel availability in both the vertical and horizontal polarisations is developed. The proposed model is validated based on a measurement campaign for operational scenarios where CR terminals may change their polarisation during their operation. A Gaussian approximation is used to model the empirical channel availability data with more than 95% confi dence bounds. The proposed model can be used as a means of improving spectrum sensing performance by using statistical knowledge on the primary users occupancy pattern.