Opportunistic Beamforming is a promising scheme with potential usage in a variety of applications ranging from cellular audio/video communications to wireless mesh-networks. However, some aspects in this scheme are open to further improvements, such as effective quality of service (QoS) provisioning, and efficient handling of sparse/realistic networks. We focus on the downlink channel of a multi-rate time-division multiplexing MISO (multiple input single output) point-to-multi-point wireless communication system, and design a cross-layer scheme. We employ a two-stage opportunistic scheduler. The scheduler receives channel state information in the form of SNR (signal to noise ratio) measurements from each terminal, and schedules one terminal in each time-slot. At the first stage in a time-slot a terminal is chosen, and our gradient descent channel estimator finds an estimation of its channel vector. Then the beamformer produces a beamforming vector in an adjacent pilot channel, or in the first part of the time-slot in the data channel. Our beamforming is based on the estimation of the channel, as opposed to the random beamformer used in the opportunistic beamforming. Each terminal measures its perceived SNR even when the channel is assigned to another terminal, and sends this information back to the basestation subject to a feedback-reduction policy. The scheduler uses the new channel state information for its second stage and assigns a terminal for the succeeding time-slot. The channel estimation procedure uses the reported SNRs for each terminal, which is a significantly lower feedback rate than the amount required for coherent beamforming. Our approach efficiently handles sparse/realistic networks, and also provides a better QoS than the opportunistic beamforming scheme. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2007-06-30 07:00:20.468

This thesis introduces the substantive grounded theory of personal legitimising. It has emerged from a study of small consulting firms. Personal legitimising is about how individuals in organisations influence their work to take account of personal priorities and agendas. Colloquially, it can be described as consultants 'getting away with it' The theory introduces six behavioural categories. These are called 'opportunistic accommodating', 'sequential impressioning', 'voluntary championing', 'support mustering', 'pseudo endorsing' and 'retrospective justifying'. The first four are concerned with how individuals align personal and work agendas. The latter two report strategies that individuals use to defend their territory. Personal legitimising makes the distinction between those strategies which contain 'implicit' legitimacy and those which are 'explicit' in nature. With implicit strategies, people are able to chose the direction of their endeavours without recourse to management. This freedom is afforded by them operating within the bounds of 'organisational tolerance'. A comparison with literature in the substantive area of management consulting notes the presence of many of the ingredients of personal legitimising, but no theoretical explanation that links them together. The theory has implications for practitioners regarding the consequences on organisational strategy of individual actions, creating an appealing working environment for people (consultants) who are readily employable elsewhere, and the management of marketing. This is set in a context where knowledge based working is likely to account for an even greater proportion of enterprise in the future. The study also suggests further research in the area of impression management, and helps illuminate the practicalities of grounded theory study.

Routing in highly dynamic wireless networks such as Vehicular Ad-hoc Networks (VANETs) is a challenging task due to frequent topology changes. Sustaining a transmission path between peers in such network environment is difficult. In this thesis, Previous Hop Routing (PHR) is poposed; an opportunistic forwarding protocol exploiting previous hop information and distance to destination to make the forwarding decision on a packet-by-packet basis. It is intended for use in highly dynamic network where the life time of a hop-by-hop path between source and destination nodes is short. Exploiting the broadcast nature of wireless communication avoids the need to copy packets, and enables redundant paths to be formed. To save network resources, especially under high network loads, PHR employs probabilistic forwarding. The forwarding probability is calculated based on the perceived network load as measured by the arrival rate at the network interface. We evaluate PHR in an urban VANET environment using NS2 (for network traffic) and SUMO (for vehicular movement) simulators, with scenarios configured to re ect real-world conditions. The simulation scenarios are configured to use two velocity profiles i.e. Low and high velocity. The results show that the PHR networks able to achieve best performance as measured by Packet Delivery Ratio (PDR) and Drop Burst Length (DBL) compared to conventional routing protocols in high velocity scenarios.

Wireless and pervasive computing research continues to study ways the Internet of Things (IoT)<br />can make lives easier and more productive. Areas of interest include advances in new<br />architectures and frameworks that support large-scale IoT deployments beyond research<br />prototypes, simple and inexpensive human-to-device and device-to-device interfaces, and user<br />decision making support with opportunistic information services.<br /><br />This dissertation investigates the design and implementation of a general-purpose framework<br />upon which IoT and opportunistic computing (OC) systems can be built.<br /><br />The result of this work is Pebbles and Urns (P&U), a casually accessible system designed to<br />deliver information to a person that is pertinent and beneficial to them with respect to their<br />current activity, location and other contexts. P&U is a proximity-based information delivery<br />framework that leverages a simple, inexpensive tangible interface and context-rich, physicallysituated,<br />distributed information repositories. By its proposed use of enforced proximity, local<br />context, and location-specific services, P&U can support the situated interaction between user<br />and place.<br /><br />The P&U framework is based on a layered architecture consisting of an isolated physical<br />communication layer, a data repository supporting opportunistic service composition and<br />delivery, and a controller/interface providing user feedback. Serving as a potential IoT design<br />pattern, P&U application developers can use the framework API\'s and software tools to build<br />and deploy P&U systems.<br /><br />As validation of this work, P&U prototypes are constructed using the framework, API\'s and<br />software tools. The prototypes are based on use cases depicting a person engaged in the day-today<br />activities of attending class, going to the gym and grocery shopping. Performance<br />measurements are performed on the prototypes profiling core components of the framework.<br />Results indicate proper functioning of P&U tangible interfaces, communication connections,<br />service request and delivery, and internal framework operations.<br /><br />Contributions of this research include a general-purpose framework, a simple IoT interface and<br />an opportunistic engine. / Ph. D.

In this thesis, we investigate the impact of channels that have a bursty nature in a cognitive radio network scenario. Our goal is to design a general channel usage model that can handle bursty primary user channel usage. The proposed model describes idle periods with a discrete platoon arrival process and describes busy periods with a discrete phase type distribution. The performance of the proposed model is compared with two more traditionally encountered channel usage models in three different secondary user access schemes. First, we design a reactive access scheme to show the poor performance results an in- vestigator can potentially obtain when ignoring bursty data traffic. We have also analyzed two proactive secondary network access schemes. Numerical results show that the achiev- able utilization and interference probability of the network are affected when traditional channel models are used in a bursty PU channel.

In this thesis, we investigate the impact of channels that have a bursty nature in a cognitive radio network scenario. Our goal is to design a general channel usage model that can handle bursty primary user channel usage. The proposed model describes idle periods with a discrete platoon arrival process and describes busy periods with a discrete phase type distribution. The performance of the proposed model is compared with two more traditionally encountered channel usage models in three different secondary user access schemes. First, we design a reactive access scheme to show the poor performance results an in- vestigator can potentially obtain when ignoring bursty data traffic. We have also analyzed two proactive secondary network access schemes. Numerical results show that the achiev- able utilization and interference probability of the network are affected when traditional channel models are used in a bursty PU channel.

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In the expanding spectrum marketplace, there has been a long term evolution towards more market€“oriented mechanisms, such as Opportunistic Spectrum Access (OSA), enabled through Cognitive Radio (CR) technology. However, the potential of CR technologies to revolutionize wireless communications, also introduces challenges based upon the potentially non€“deterministic CR behaviour in the Electrospace. While establishing and enforcing compliance to spectrum etiquette rules are essential to realization of successful OSA networks in the future, there has only been recent increased research activity into enforcement. This dissertation presents novel work on the spectrum monitoring aspect, which is crucial to effective enforcement of OSA. An overview of the challenges faced by current compliance monitoring methods is first presented. A framework is then proposed for the use of random spectral sampling techniques to reduce data collection complexity in wideband sensing scenarios. This approach is recommended as an alternative to Compressed Sensing (CS) techniques for wideband spectral occupancy estimation, which may be difficult to utilize in many practical congested scenarios where compliance monitoring is required. Next, a low€“cost computational approach to online randomized temporal sensing deployment is presented for characterization of temporal spectrum occupancy in cognitive radio scenarios. The random sensing approach is demonstrated and its performance is compared to CS€“based approach for occupancy estimation. A novel frame€“based sampling inversion technique is then presented for cases when it is necessary to track the temporal behaviour of individual CRs or CR networks. Parameters from randomly sampled Physical Layer Convergence Protocol (PLCP) data frames are used to reconstruct occupancy statistics, taking account of missed frames due to sampling design, sensor limitations and frame errors. Finally, investigations into the use of distributed and mobile spectrum sensing to collect spatial diversity to improve the above techniques are presented, for several common monitoring tasks in spectrum enforcement. Specifically, focus is upon techniques for achieving consensus in dynamic topologies such as in mobile sensing scenarios.

The goal of this thesis work is to analyze how design elements and wireless attributes affect opportunistic routing, and in this context develop a new protocol. The algorithm developed aims to improve opportunistic elements in comparison to a well-known opportunistic protocol Simple Opportunistic Adaptive Routing (SOAR).

Scheduling in wireless networks plays an important role. The undeterministic nature of the wireless channel is usually considered as an undesirable property. Recently, the idea of opportunistic scheduling is introduced and it takes advantage of the time-varying channel for performance improvement such as throughput and delay. Since the introduction of opportunistic scheduling, there are two main bodies of works. The first body of works assume that each user is greedy and has infinite backlog for transfer. With this assumption, fairness objective becomes an important factor in designing a scheduling algorithm to avoid severe starvation of certain users. Typical fairness involve processor sharing time fairness, proportional fairness, and minimum performance guarantee. On the other hand, delay performance is not a appropriate factor to evaluate the effectiveness of a scheduling algorithm because of the infinite backlog assumption. In reality, this assumption is not true as data arrives and leaves the network randomly in practice. The second body of works deal with the relaxation of the infinite backlog assumption. Thus, the notion of stability region arises. The definition of stability is that the queue at each source node remains finite. Stability region can be defined as the set of traffic intensities which can all be stabilized by the network. The well known throughput optimal algorithm is proven capable of achieving the largest stability region. In this thesis, two innovative opportunistic scheduling algorithms which aim to minimize the amount of resources used to stabilize the current traffics are proposed. The key feature of our algorithm is that the incoming traffic rates are available to the scheduler, whereas the throughput optimal algorithm has no such prior traffic knowledge. Performance comparisons are made by means of simulation to demonstrate that the proposed algorithms can achieve the same stability region as the throughput optimal algorithm. Moreover, the delay performance is better than that of the throughput optimal algorithm, especially under heavy traffic conditions.