Energy Efficiency Optimization in Green Wireless Communications

The rising energy concern and the ubiquity of energy-consuming wireless applications have sparked a keen interest in the development and deployment of energy-efficient and eco-friendly wireless communication technology. Green Wireless Communications aims to find innovative solutions to improve energy efficiency, and to relieve/reduce the carbon footprint of wireless industry, while maintaining/improving performance metrics. Looking back at the wireless communications of the past decades, the air-interface design and network deployment had mainly focused on the spectral efficiency, instead of energy efficiency. From the cellular network to the personal area network, no matter what size the wireless network is, the milestones along the evolutions of wireless networks had always been higher-and-higher data rates throughout these years. Most of these throughput-oriented optimizations lead to a full-power operation to support a higher throughput or spectral efficiency, which is typically not energy-efficient. To qualify as green wireless communications, we believe that a candidate technology needs to be of high energy efficiency, reduced electromagnetic pollution, and low-complexity. In this dissertation research, towards the evolution of the green wireless communications, we have extended our efforts in two important aspects of the wireless communications system: air-interface and networking. In the first aspect of this work, we study a promising green communications technology, the time reversal system, as a novel air-interface of the future green wireless communications. We propose a concept of time reversal division multiple access (TRDMA) as a novel wireless media access scheme for wireless broadband networks, and investigate its fundamental theoretical limits. Motivated by the great energy-harvesting potential of the TRDMA, we develop an asymmetric architecture for the TRDMA based multiuser networks. The unique asymmetric architecture shifts the most complexity to the BS in both downlink and uplink schemes, facilitating very low-cost terminal users in the networks. To further enhance the system performance, a 2D parallel interference cancellation scheme is presented to explore the inherent structure of the interference signals, and therefore efficiently improve the resulting SINR and system performance. In the second aspect of this work, we explore the energy-saving potential of the cooperative networking for cellular systems. We propose a dynamic base-station switching strategy and incorporate the cooperative base-station operation to improve the energy-efficiency of the cellular networks without sacrificing the quality of service of the users. It is shown that significant energy saving potential can be achieved by the proposed scheme

MIMO signal processing in offset-QAM based filter bank multicarrier systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft

WAVEFORM DESIGN AND NETWORK SELECTION IN WIDEBAND SMALL CELL NETWORKS

The explosion in demand for wireless data traffic in recent years has triggered rapid development and pervasive deployment of wireless communication networks. To meet the exponentially increasing demand, a promising solution is the concept of wideband small cells, which is based on the idea of using broader frequency bandwidth and employing more efficient radio frequency resource reuse by dense deployment of wideband, short-range, low cost and low power base-stations. Broader bandwidth provides substantial degrees of freedom as well as challenges for system design due to the abundant multipaths and thus interference in high speed systems under large delay spread channels. Reducing the transmission range and increasing the number of cells permit better spatial reuse of spectrum. With the proliferation of wideband small cells, the strategy of selection among multiple networks has significant impacts to the performance of users and to the load balance of the system. In this dissertation, we address these problems with a focus on waveform design and network selection. In time-reversal communication systems, the time-reversal transmit waveform can boost the signal-to-noise ratio at the receiver with simple single-tap detection by utilizing channel reciprocity with very low transmitter complexity. However, the large delay spread gives rise to severe inter-symbol interference when the data rate is high, and the achievable transmission rate is further degraded in the multiuser downlink due to the inter-user interference. We study the weighted sum rate optimization problem by means of waveform design in the time-reversal multiuser downlink. We propose a new power allocation algorithm, which is able to achieve comparable sum rate performance to that of globally optimal power allocation. Further, we study the joint waveform design and interference pre-cancellation by exploiting the symbol information to further improve the performance by utilizing the information of previous symbols. In the proposed joint design, the causal interference is subtracted using interference pre-cancellation and the anti-causal interference can be further suppressed by waveform design with more degrees of freedom. The second part of this dissertation is concerned with the wireless access network selection problem considering the negative network externality, i.e, the influence of subsequent users' decisions on an individual's throughput due to the limited available resources. We formulate the wireless network selection problem as a stochastic game with negative network externality and show that finding the optimal decision rule can be modelled as a multi-dimensional Markov decision process. A modified value iteration algorithm is proposed to efficiently obtain the optimal decision rule with a simple threshold structure, which enables us to reduce the storage space of the strategy profile. We further investigate the mechanism design problem with incentive compatibility constraints, which enforce the networks to reveal the truthful state information. We analyze a data set of wireless LAN traces collected from campus networks, from which we observe that the number of user arrivals is approximately Poisson distributed; the session time and the waiting time to switch network can be approximated by exponential distributions. Based on the analysis, we formulate a wireless access network association game with both arriving strategy and switching strategy and validate the effectiveness of the proposed best response strategy

New Experimental Limit on the Electric Dipole Moment of the Electron in a Paramagnetic Insulator

We report results of an experimental search for the intrinsic Electric Dipole Moment (EDM) of the electron using a solid-state technique. The experiment employs a paramagnetic, insulating gadolinium gallium garnet (GGG) that has a large magnetic response at low temperatures. The presence of the eEDM would lead to a small but non-zero magnetization as the GGG sample is subject to a strong electric field. We search for the resulting Stark-induced magnetization with a sensitive magnetometer. Recent progress on the suppression of several sources of background allows the experiment to run free of spurious signals at the level of the statistical uncertainties. We report our first limit on the eEDM of $(-5.57 \pm 7.98 \pm 0.12)\times$10$^{-25}$e$\cdot$cm with 5 days of data averaging.Comment: 9 pages, 9 figures, Revtex 4.

The multifocal visual evoked cortical potential in visual field mapping: a methodological study.

The application of multifocal techniques to the visual evoked cortical potential permits objective electrophysiological mapping of the visual field. The multifocal visual evoked cortical potential (mfVECP) presents several technical challenges. Signals are small, are influenced by a number of sources of noise and waveforms vary both across the visual field and between subjects due to the complex geometry of the visual cortex. Together these factors hamper the ability to distinguish between a mfVECP response from the healthy visual pathway, and a response that is reduced or absent and is therefore representative of pathology. This thesis presents a series of methodological investigations with the aim of maximising the information available in the recorded electrophysiological response, thereby improving the performance of the mfVECP. A novel method of calculating the signal to noise ratio (SNR) of mfVECP waveform responses is introduced. A noise estimate unrelated to the response of the visual cortex to the visual stimulus is created. This is achieved by cross-correlating m-sequences which are created when the orthogonal set of m-sequences are created but are not used to control a stimulus region, with the physiological record. This metric is compared to the approach of defining noise within a delayed time window and shows good correlation. ROC analysis indicates a small improvement in the ability to distinguish between physiological waveform responses and noise. Defining the signal window as 45-250ms is recommended. Signal quality is improved by post-acquisition bandwidth filtering. A wide range of bandwidths are compared and the greatest gains are seen with a bandpass of 3 to 20Hz applied after cross-correlation. Responses evoked when stimulation is delivered using a cathode ray tube (CRT) and a liquid crystal display (LCD) projector system are compared. The mode of stimulus delivery affects the waveshape of responses. A significantly higher SNR is seen in waveforms is shown in waveforms evoked by an m=16 bit m-sequence delivered by a CRT monitor. Differences for shorter m-sequences were not statistically significant. The area of the visual field which can usefully be tested is investigated by increasing the field of view of stimulation from 20° to 40° of radius in 10° increments. A field of view of 30° of radius is shown to provide stimulation of as much of the visual field as possible without losing signal quality. Stimulation rates of 12.5 to 75Hz are compared. Slowing the stimulation rate produced increases waveform amplitudes, latencies and SNR values. The best performance was achieved with 25Hz stimulation. It is shown that a six-minute recording stimulated at 25Hz is superior to an eight-minute, 75Hz acquisition. An electrophysiology system capable of providing multifocal stimulation, synchronising with the acquisition of data from a large number of electrodes and performing cross-correlation has been created. This is a powerful system which permits the interrogation of the dipoles evoked within the complex geometry of the visual cortex from a very large number of orientations, which will improve detection ability. The system has been used to compare the performance of 16 monopolar recording channels in detecting responses to stimulation throughout the visual field. A selection of four electrodes which maximise the available information throughout the visual field has been made. It is shown that a several combinations of four electrodes provide good responses throughout the visual field, but that it is important to have them distributed on either hemisphere and above and below Oz. A series of investigations have indicated methods of maximising the available information in mfVECP recordings and progress the technique towards becoming a robust clinical tool. A powerful multichannel multifocal electrophysiology system has been created, with the ability to simultaneously acquire data from a very large number of bipolar recording channels and thereby detect many small dipole responses to stimulation of many small areas of the visual field. This will be an invaluable tool in future investigations. Performance has been shown to improve when the presence or absence of a waveform is determined by a novel SNR metric, when data is filtered post-acquisition through a 3-20Hz bandpass after cross-correlation and when a CRT is used to deliver the stimulus. The field of view of stimulation can usefully be extended to a radius of 30° when a 60-region dartboard pattern is employed. Performance can be enhanced at the same time as acquisition time is reduced by 25%, by the use of a 25Hz rate of stimulation instead of the frequently employed rate of 75Hz

Multi-Sensor Methods for Mobile Radar Motion Capture and Compensation.

Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017

Optimization of a new linear FM detector using digital signal processing techniques

This dissertation describes and synthesizes a new member of the family of FM detectors introduced earlier by Klapper and Kratt. A salient property of these detectors is low delay with excellent sensitivity. The emphasis in the new detector is on the ease of digital implementation. In addition, the new detector is also extremely linear. In congruence with the other Klapper-Kratt detectors, it makes use of zero group delay elements, balance at RF, quasi-synchronous detection and carrier cancellation. The Performance of the detector is mathematically analyzed under the conditions of a modulated input wave, sinewave [sic] interference, and noise. The results indicate improved Performance over other members of the family in terms of linearity, threshold, and ease of digital implementation. Realization of the detector using FIR digital signal processing methods is discussed, including linearity optimization. Substantial algorithm simplification was achieved. High center frequencies with low sampling frequencies are obtainable due to the frequency foldover effect. Narrowband predetection filtering can be included in the detector provided a wider predetection filter is Present. Results of a working model are shown