The widespread application of wireless services and the requirements of ubiquitous access have recently triggered rapidly booming energy consumption in wireless communications networks. Such escalation of energy consumption in wireless networks causes high operational expenditure from electricity bills for operators, unsatisfactory user experience due to limited battery capacity of wireless devices, and a large amount of greenhouse gas emission. Green radio (GR), which emphasizes both energy efficiency (EE) and spectral efficiency (SE), has been proposed as an effective solution and is becoming the mainstream for future wireless network design. Unfortunately, EE and SE do not always coincide and may even sometimes conflict. In this dissertation, we focus on energy-efficient transmission and resource allocation techniques for orthogonal frequency division multiple access (OFDMA) networks and the joint energy-efficient design of OFDMA and other promising wireless communications techniques, such as cognitive radio (CR) and two-way relay. Firstly, we investigate the principles of energy-efficient design for pure OFDMA networks. As the first step, we study the fundamental interrelationship between EE and SE in downlink OFDMA networks and analyze the impacts of channel gain and circuit power on the EE-SE relationship. We establish a general EE-SE optimization framework, where the overall EE, SE and per-user quality-of-service (QoS) are all considered. Under this framework, we find that EE is quasiconcave in SE and decreases with SE when SE is large enough. These findings are very helpful guidelines for designing energy- and spectral-efficient OFDMA. To facilitate the application of energy-efficient resource allocation, we then investigate the energy-efficient resource allocation in both downlink and uplink OFDMA networks. For the downlink transmission, the generalized EE is maximized while for the uplink case the minimum individual EE is maximized, both under prescribed per-user minimum data rate requirements. For both transmission scenarios, we first provide the optimal solution and then develop an computationally efficient suboptimal approach by exploring the inherent structure and property of the energy-efficient design. Then we study energy-efficient design in downlink OFDMA networks with effective capacity-based delay provisioning for delay-sensitive traffic. By integrating information theory with the concept of effective capacity, we formulate and solve an EE optimization problem with statistical delay provisioning. We also analyze the tradeoff between EE and delay, the relationship between spectral-efficient and energy-efficient designs, and the impact of system parameters, including circuit power and delay exponents, on the overall performance. Secondly, we consider joint energy-efficient design of OFDMA and CR and two-way relay, respectively, to further enhance the EE and SE of wireless networks. We study energy-efficient opportunistic spectrum access strategies for an OFDMA-based CR network with multiple secondary users (SUs). Both worst EE and average EE of the SUs are considered and optimized subject to constraints including maximum transmit power and maximum interference to primary user (PU) system. For both cases, we first find the optimal solution and then propose a low-complexity suboptimal alternative. The results show that the energy-efficient CR strategies significantly boost EE compared with the conventional spectral-efficient CR ones while the low-complexity suboptimal approaches can well balance the performance and complexity. Then we study energy-efficient resource allocation for OFDMA-based two-way relay, which aims at maximizing the aggregated EE utility while provisioning proportional fairness in EE among different terminal pairs. Different from most exist energy-efficient design, we consider a new circuit power model, where the dynamic circuit power is proportional to the number of active subcarrier. For low-complexity solution, we propose an EE-oriented sequential subchannel assignment policy and discover the sufficient condition for early termination of the sequential subchannel assignment without losing the EE optimality. It is found that the energy-efficient transmission does not necessarily make all the subcarriers active, which is another useful principle for practical energy-efficient system design.

In this thesis new techniques are presented to achieve performance enhancement in wireless cooperative networks. In particular, techniques to improve transmission rate and maximise end-to-end signal-to-noise ratio are described. An offset transmission scheme with full interference cancellation for a wireless cooperative network with frequency flat links and four relays is introduced. This method can asymptotically, as the size of the symbol block increases, achieve maximum transmission rate together with full cooperative diversity provided the destination node has multiple antennas. A novel full inter-relay interference cancellation method that also achieves asymptotically maximum rate and full cooperative diversity is then designed for which the destination node only requires a single antenna. Two- and four-relay selection schemes for wireless cooperative amplify and forward type networks are then studied in order to overcome the degradation of end-to-end bit error rate performance in single-relay selection networks when there are feedback errors in the relay to destination node links. Outage probability analysis for a four-relay selection scheme without interference is undertaken. Outage probability analysis of a full rate distributed transmission scheme with inter-relay interference is also studied for best single- and two-relay selection networks. The advantage of multi-relay selection when no interference occurs and when adjacent cell interference is present at the relay nodes is then shown theoretically. Simulation results for outage probability analysis are included which support the theoretical expressions. Finally, outage probability analysis of a cognitive amplify and forward type relay network with cooperation between certain secondary users, chosen by best single-, two- and four-relay selection is presented. The cognitive amplify and forward relays are assumed to exploit an underlay approach, which requires adherence to an interference constraint on the primary user. The relay selection scheme is performed either with a max-min strategy or one based on maximising exact end-to-end signal-to-noise ratio. The outage probability analyses are again confirmed by numerical evaluations.

International Telemetering Conference Proceedings / October 13-16, 1986 / Riviera Hotel, Las Vegas, Nevada / The Airborne Platform Telemetry Relay System (AP/TM) is currently being built for the Gulf Range Instrumentation System. The AP/TM will allow air-to-air missile test and training missions to be conducted beyond the line-of-sight of land-based instrumentation. The AP/TM is comprised of the following subsystems: C a Telemetry Data Relay C a Sea Surveillance Radar and Radar Data Link C a Drone Control Relay C a UHF Radio Relay The Telemetry Data Relay Subsystem will receive telemetry signals from five independent sources and will retransmit them to land based receiving sites. This subsystem contains a 75 square foot, electronically steerable, five beam phased array antenna and uses polarization diversity to eliminate polarization mismatch loss and to improve reception in the presence of multipath propagation. The AP/TM will also have the capability of relaying four channels of voice communications and drone tracking data and to perform sea surveillance of the mission area. The coordinates of targets detected by the radar will be relayed to the range control center over a high frequency (HF) data link. In addition to the airborne equipment, the system also includes a ground support instrumentation van which is used for pre- and post-flight checkout and maintenance.

Relay techniques have the potential to enhance capacity and coverage of a wireless network. Due to rapidly increasing number of smart phone subscribers and high demand for data intensive multimedia applications, the useful radio spectrum is becoming a scarce resource. For this reason, two way relay network and cognitive radio technologies are required for better utilization of radio spectrum. Compared to the conventional one way relay network, both the uplink and the downlink can be served simultaneously using a two way relay network. Hence the effective bandwidth efficiency is considered to be one time slot per transmission. Cognitive networks are wireless networks that consist of different types of users, a primary user (PU, the primary license holder of a spectrum band) and secondary users (SU, cognitive radios that opportunistically access the PU spectrum). The secondary users can access the spectrum of the licensed user provided they do not harmfully affect to the primary user. In this thesis, various resource allocation and optimization techniques have been investigated for wireless relay and cognitive radio networks.

High voltage transmission system availability and system security are key performance criteria for electricity utilities worldwide. System disturbances need to be cleared quickly and accurately in order to minimise the impact of faults and to facilitate speedy system restoration. In this context, the South African utility, Eskom has maintained a process of refreshing protective relaying technology as older equipment becomes obsolete and is no longer capable of meeting the utility’s requirements. The difficulties which a process of equipment renewal presents the organisation with include the risk of incorrectly applying the newer technologies within the complex electrical network. The application of new technology is affected by the complexities of the newer technology with respect to the older, more familiar technologies. Some of the difficulties can be addressed with revised commissioning procedures or the use of modern test equipment. Enhanced relay algorithms and settings calculation methodologies can however not be simplified. Protective relay maloperations cannot always be completely avoided and when they do occur, these must be investigated and addressed to prevent future recurrences. The research covered by this dissertation focuses on a number of protective relay maloperations on transmission lines using impedance protection algorithms. The research undertaken identifies the previously unidentified causes of the maloperations and describes a relay settings solution for improving the accuracy of the protective relays. The methodology that was followed in the research covers the following aspects: • Identification and highlighting of some of the protection relay maloperations that occurred during system faults, • Review of the fundamental principles involved in system fault analysis, • Comprehensive study of the theory involved in the calculation of an overhead line conductor self and mutual-inductance, as well as the calculation of the positive, negative and zero sequence impedances of an overhead line, • Brief evaluation of the effect of load impedance on relay measurements and the impact on fault clearing operation, • Analysis of the theoretical operation of various numerical relays during singlephase- to-earth faults in radial and meshed (complex) network conditions, • Mathematical calculations using typical Newton-Raphson methods to study the impact of resistive single-phase-to-earth faults on the voltage and current measurements at the relaying position with the exclusion of the capacitive components between conductors and conductors and earth, • Comparison and evaluation of mathematical calculations and system studies using network simulation software which included all steady state network parameters, • Review and analysis of actual system faults that had been previously analysed without definitive conclusion. The faults were re-analysed in an attempt to correlate findings with the hypothesis of the research, • Comparison of the performance of protective relay impedance charactersitics using positive sequence domain versus loop domain analysis techniques. This study concluded that significant benefits can be achieved by analysing system faults and relay operation using loop quantities in primary impedance values as opposed to positive sequence or apparent impedance quantities in secondary values. The inherent differences between the positive or apparent impedance characteristics of the relays are nullified when considered in the loop impedance domain, provided that the relays reach settings were calculated correctly. The study also showed that load current cannot be ignored when calculating settings as it has significant impact on the actual impedance measured during fault conditions. It is therefore crucial that when relays from different manufacturers are being used to protect the same circuit that the differences between the relays and the subsequent measurements are clearly understood and compensated for. Finally relay setting changes have been proposed for implementation based on the findings of this research. The combination of the theory, network simulations and secondary injections performed on the relays all correlate and therefore validate the research. It is left for the utility and or users of these relays to evaluate the results of this research and implement the necessary changes as applicable. / Thesis (MSc (Electrical Engineering))--North-West University, Potchefstroom Campus, 2012

With the rapid development of wireless networks, mesh networks are evolving as a new important technology, presenting a high research and commercial interest. Additionally, wireless mesh networks have a wide variety of applications, offering the ability to provide network access in both rural and urban areas with low cost of maintenance. One of the main functionalities of a wireless mesh network is load balancing routing, which is the procedure of finding the best, according to some criteria, routes that data need to follow to transfer from one node to another. Routing is one of the state-of-the-art areas of research because the current algorithms and protocols are not efficient and effective due to the diversity of the characteristics of these networks. In this thesis, two new routing algorithms have been developed for No Intra-Cell Interference (NICI) and Limited Intra-Cell Interference (LICI) networks based on WiMAX, the most advanced wireless technology ready for deployment. The algorithms created are based on the classical Dijkstra and Ford-Fulkerson algorithms and can be implemented in the cases of unicast and multicast transmission respectively.

Multiple-input multiple-output (MIMO) systems have recently emerged as one of the most significant wireless techniques, as they can greatly improve the channel capacity and link reliability of wireless communications. These benefits have encouraged extensive research on a virtual MIMO system where the transmitter has multiple antennas and each of the receivers has a single antenna. Single-antenna receivers can work together to form a virtual antenna array and reap some performance benefits of MIMO systems. The idea of receiver-side local cooperation is attractive for wireless networks since a wireless receiver may not have multiple antennas due to size and cost limitations. In this thesis we investigate a virtual-MIMO wireless system using the receiver-side cooperation with the compress-and-forward (CF) protocol. Firstly, to perform CF at the relay, we propose to use standard source coding techniques, based on the analysis of its expected rate bound and the tightness of the bound. We state upper bounds on the system error probabilities over block fading channels. With sufficient source coding rates, the cooperation of the receivers enables the virtual-MIMO system to achieve almost ideal MIMO performance. A comparison of ideal and non-ideal conference links within the receiver group is also investigated. Considering the short-range communication and using a channel-aware adaptive CF scheme, the impact of the non-ideal cooperation link is too slight to impair the system performance significantly. It is also evident that the practicality of CF cooperation will be greatly enhanced if a efficient source coding technique can be used at the relay. It is even more desirable that CF cooperation should not be unduly sensitive to carrier frequency offsets (CFOs). Thus this thesis then presents a practical study of these two issues. Codebook designs of the Voronoi VQ and the tree-structure vector quantization (TSVQ) to enable CF cooperation at the relay are firstly described. A comparison in terms of the codebook design complexity and encoding complexity is presented. It is shown that the TSVQ is much simpler to design and operate, and can achieve a favourable performance-complexity tradeoff. We then demonstrate that CFO can lead to significant performance degradation for the virtual MIMO system. To overcome it, it is proposed to maintain clock synchronization and jointly estimate the CFO between the relay and the destination. This approach is shown to provide a significant performance improvement. Finally, we extend the study to the minimum mean square error (MMSE) detection, as it has a lower complexity compared to maximum likelihood (ML) detection. A closed-form upper bound for the system error probability is derived, based on which we prove that the smallest singular value of the cooperative channel matrix determines the system error performance. Accordingly, an adaptive modulation and cooperation scheme is proposed, which uses the smallest singular value as the threshold strategy. Depending on the instantaneous channel conditions, the system could therefore adapt to choose a suitable modulation type for transmission and an appropriate quantization rate to perform CF cooperation. The adaptive modulation and cooperation scheme not only enables the system to achieve comparable performance to the case with fixed quantization rates, but also eliminates unnecessary complexity for quantization operations and conference link communication.

This thesis attempts to explore the discursive construction of Olympic ideology in the 2008 Torch Relay news coverage by the British and the Chinese media. It applies a corpus-based Discourse-Historical Approach in Critical Discourse Analysis (DHA-CDA) to analyse how and why the complexity, contradiction and conflicts in linguistic interpretations of Olympism are demonstrated by the media discourse between East and West. This study first focuses on the underpinning ideology and the study of the media, considering the historical development of Olympic ideology (Olympism) along with the respective mainstream ideologies in Britain (Liberalism) and China (Harmony), as well as the philosophical foundations and prominence of CDA. It then draws on the elaborated analytical approach-corpus-based CDA-in detail to analyse four specially constructed corpora drawn from the China Daily, BBC News and The Guardian. Thereafter corpus techniques including frequency and concordance analysis are applied and results obtained that reveal comparative differences and diachronic shifts across the corpora. Having first described the data, they are then interpreted in their linguistic contexts, and subsequently explained in the broader historical and socio-political contexts surrounding the dynamic life of the Olympic Torch Relay. This study demonstrates that there are contrasting expressions of Olympic ideology in the media discourse of the two countries. At a deeper level, this social practice is revealed to be dominated by the mainstream ideologies of the hosting and participating nations, which have been entrenched throughout their respective histories. The involvement of Britain and China in Olympic history and the relevant socio-political events surrounding the 2008 Torch Relay are explored in order to inform our analysis. The conclusion to this thesis reinforces its significant contribution to the study of Olympism. The Olympic philosophy of integrating diversified ideologies was certainly not manifest in the confrontation between the eastern and western media in 2008. Liberalism and harmony had never confronted each other face to face on the world stage before or attempted to find a common ground on which to coexist as revealed in this study. Based on this, respect for and tolerance of diverse ideology, history and culture will hopefully promote the solidarity and prosperity represented by Olympism in the new era.

Wireless sensor networks are widely applied to many fields such as animal habitat monitoring, air traffic control, and health monitoring. One of the current problems with wireless sensor networks is the ability to overcome communication failures due to hardware failure, distributing sensors in an uneven geographic area, or unexpected obstacles between sensors. One common solution to overcome this problem is to place a minimum number of relay nodes among sensors so that the communication among sensors is guaranteed. This is called Relay Node Placement Problem (RNP). This problem has been proved as NP-hard for a simple connected graph. Therefore, many algorithms have been developed based on Steiner graphs. Since RNP for a connected graph is NP-hard, the RNP for a survivable network has been conjectured as NP-hard and the algorithms for a survivable network have also been developed based on Steiner graphs. In this study, we show the new approximation bound for the survivable wireless sensor networks using the Steiner graphs based algorithm. We prove that the approximation bound is guaranteed in an environment where some obstacles are laid, and also propose the newly developed algorithm which places fewer relay nodes than the existing algorithms. Consequently, the main purpose of this study is to find the minimum number of relay nodes in order to meet the survivability requirements of wireless sensor networks.

In this thesis, the relay communication between landed assets on the surface of Mars via a relay orbiter to Earth is studied for its latencies and the times which can be provided for the landed asset to work and for the ground to plan depending on the operational margins, the available ground station network and the available relay orbiters. In this context, an automated solver is developed to evaluate a locally optimal strategy of relay pass assignment respecting the different constraints and is proven to provide a solution close to the globally optimal one. The solver is determining the link opportunities and reasons on them, by minimising a cost function for each relay pass and choosing the cheapest ones in an iterative process. With this solver, it is shown that the best operational approach is to await commands confirmation and to provide the possibility of resending corrupted files. Moreover, it is shown that a 24/7 ground station coverage should be ideally provided, on which priority for booking should be given to relay missions since they depend on the actual timing of the orbiter overflights over the lander. Further- more, it is shown that adding additional relay orbiters increases the solution space drastically, making it desirable to use them. The possibility to restrict cross-agency support is assessed, showing that cross-support is still eligible. Finally, the data volume is shown to be sufficient to fulfil the ExoMars Rover and Surface Platform mission requirements, when using multiple orbiters, even though the solver itself would need extra capabilities to cope with allocating appropriate relay passes.