This research addresses the performance degradation in receivers due to poor selectivity. Poor selectivity is expected to be a primary limitation on the performance of Dynamic-Spectrum-Access (DSA) and millimeter wave (mmWave) technologies. Both DSA and mmWave are highly desired technologies because they can address the spectrum-deficit problem that is currently challenging the wireless industry. Accordingly, addressing poor receiver selectivity is necessary to expedite the adoption of these technologies into the main street of wireless. This research develops two receiver design concepts to enhance the performance of poorly-selective receivers. The first concept is called cognitive RF front-end control (CogRF). CogRF operates by cognitively controlling the local-oscillator and sampling frequencies in receivers. This research shows that CogRF can fulfil the objective of pre-selectors by minimizing the effects of weak and moderately-powered neighboring-channel signals on the desired signal. This research shows that CogRF can be an alternative to high-performance pre-selectors, and hence, CogRF is a viable architecture to implement reliable DSA and mmWave receivers. The theoretical design and hardware implementation of a cognitive engine and a spectrum sensor of CogRF are reported in this dissertation. Measurement results show that CogRF significantly reduces the rate of communication outage due to interference from neighboring-channel signals in poorly-selective receivers. The results also indicate that CogRF can enable a poorly-selective receiver to behave like a highly-selective receiver. The second receiver design concept addresses very strong neighboring-channel signals. The performance of poorly selective receivers can easily suffer due to a strong, unfiltered neighboring-channel signal. A strong neighboring-channel signal is likely for a DSA radio that is operating in military radar bands. Traditionally, strong neighboring signals are addressed using an Automatic-Gain-Control (AGC) that attempt to accommodate the strong received signal into the dynamic range of the receiver. However, this technique potentially desensitizes the receiver because it sacrifices the Signal-to-Noise-Ratio (SNR) of the desired signal. This research proposes the use of auxiliary-receive path to address strong neighboring-channel signals with minimal penalty on the SNR of the desired signal. Through simulation based analysis, and hardware-based measurement, this research shows that the proposed technique can provide significant improvement in the neighboring-channel-interference handling capability of the receiver. / Ph. D.

Typescript, etc. / Digitized by Kansas State University Libraries

Typescript, etc. / Digitized by Kansas State University Libraries

LD2668 .T4 1940 W41 / Master of Science

Call number: LD2668 .T4 1944 H81 / Master of Science

Call number: LD2668 .T4 1965 O38 / Master of Science

Since recent times the importance of wireless communications has experienced a phenomenal growth, thus incurring a considerable increase in usage of the frequency spectrum available for communications and hence creating the need for efficient methods for its utilisation. Multiple-access is one efficient method, which enables several users to share a common frequency bandwidth. A multiple-access technique known as Collaborative Coding Multiple Access (CCMA) has been theoretically investigated and has been shown to give an increase in channel capacity and bandwidth efficiency. This technique uses a special type of codes known as collaborative codes to enable multiple users to communicate simultaneously over a common frequency bandwidth, thus eliminating the use of time, frequency and orthogonal code divisions. However to implement this technique practically, requires a multiple access channel (MAC) that coherently combines the signals originating from different users to give a composite signal. The combining of signals to implement a CCMA scheme can be easily achieved in baseband channels, where signals can be represented as voltages or currents which can add, to give uniquely identifiable code combinations. However when extended to bandpass carrier channels, the combining of signals over radio channels involves the addition of signals of differing, and, in the mobile situation particularly, varying relative phases and amplitudes. This can give rise to a major detection problem due to the resulting destructive signal combining and thus making CCMA non- practical over radio channels. This thesis describes a novel multiple-access scheme known as Complex-Valued Collaborative Coding Multiple Access (CV-CCMA), to provide a practical system over radio channels that achieves the theoretical promises of CCMA. CV_CCMA overcomes the problem associated with the non-coherent combining of multiple signals over radio channels by employing a complex-valued collaborative code and a combined detection and channel estimation process to estimate the data of each user as well as their associated amplitude and phase variations induced by the channel. The research is initiated with the principles and the theoretical foundations of the CV_CCMA technique. A combined signal detection and channel estimation process is presented. The choice of a suitable collaborative coding scheme is investigated. The conditions for the selection of valid codesets are established for a given number of users, modulation levels and code length. In addition, the effect of channel fading is also investigated. AT-user M-PSK CV_CCMA system operating in Rayleigh and Rician fading channels, is modelled and simulated to establish the error-performance. The results from this investigation are obtained for different number of users and modulation levels. The effect of varying signal power levels is also investigated. Observing the obtained results an additional code selection condition is established for a Rician channel, with an improved error performance. The channel capacity of the CV_CCMA scheme operating in a flat Rayleigh fading channel is obtained. In a given T-user M-PSK CV_CCMA scheme the channel outputs result in multi-level signals. Therefore the channel capacity of CV_CCMA is compared with equivalent multi-level single access schemes. It is shown that the channel capacity of CV_CCMA is greater than the corresponding multi-level schemes. The theoretical channel capacity limits of CV_CCMA is also compared with the limits of TDMA, FDMA and CDMA operating in a flat Rayleigh fading channel. The enhancement of the error performance of CV_CCMA in fading channels is investigated by using space diversity reception and error-control coding. It is found that by using these techniques the error performance of CV_CCMA can be greatly enhanced. For example with a dual-diversity scheme in a flat Rayleigh fading channel, the achieved gain is in the order of 20 dB. Using error-control coding, a coding gain is achieved depending on the type of code used. It is also found that using both of these techniques contributes towards further performance gains depending on the number of diversity paths and the coding scheme. The thesis is finally concluded with an overview of the contributions of this thesis, the achieved results and their implications and suggestions for future work in this subject.

Energy consumption has recently become a key issue from both environmental and economic considerations. A typical mobile phone network in the UK may consume approximately 40-50 MW, contributing a significant proportion of the total energy consumed by the information technology industry. With the worldwide growth in the number of mobile subscribers, the associated carbon emissions and growing energy costs are becoming a significant operational expense, leading to the need for energy reduction. The Mobile VCE Green Radio Project has been launched, which targets to achieve 100x energy reduction of the current wireless networks by 2020. In this thesis, energy-efficient resource allocation strategies have been investigated taking the LTE system as an example. Firstly, theoretical analysis of energy-efficient design in cellular environments is provided according to the Shannon Theory. Based on a two-link scenario the performance of simultaneous transmission and orthogonal transmission for network power minimization under the specified rate constraints is investigated. It is found that simultaneous transmission consumes less power than orthogonal transmission close to the base station, but much more power in the cell-edge area. Also, simulation results suggest that the energy-efficient switching margins between these two schemes are dominated by the sum total of their required data rates. New definitions of power-utility and fairness metrics are further proposed, following by the design of weighted resource allocation approaches based on efficiency-fairness trade-offs. Apart from energy-efficient multiple access between different links, the energy used by individual base stations can also be reduced. For example, deploying sleep modes is an effective approach to reduce radio base station operational energy consumption. By periodically switching off the base station transmission, or using fewer transmit antennas, the energy consumption of base station hardware may decrease. By delivering less control signalling overhead, the radio frequency energy consumption can also be reduced. Simulation results suggest that up to 90% energy reduction can be obtained in low traffic conditions by employing time-domain optimization in each radio frame. The optimum on/off duty cycle is derived, enabling the energy consumption of the base station to scale with traffic loads. In the spatial-domain, an antenna selection criterion is proposed, indicating the most energy-efficient antenna configuration with the knowledge of users’ locations and quality of service requirements. Without time-domain sleep modes, using fewer transmit antennas could outperform full antenna transmission. However, with time-domain sleep modes, using all available antennas is generally the most energy-efficient choice.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / The National Radio Astronomy Observatory (NRAO) operates the Very Large Array (VLA) Radio Observatory in New Mexico, and the Very Long Baseline Array (VLBA) with 10 radio antenna in locations from Hawaii to St. Croix, as well as other radio telescopes at Green Bank, West Virginia, and the 12 meter radio antenna near Tucson, AZ. Although radio frequency (RF) bands have been set aside for passive use by these radio telescopes, harmful interference from increased demands on the radio spectrum is a growing problem for earth-based radio astronomy. For example, locating a radio observatory in a remote area is little defense from satellite downlink telemetry. This paper describes why the operation of the radio telescopes is susceptible to RF telemetry interference, what bands are particularly vulnerable and at what power levels, and how data collection and centralized control of the arrays are accomplished without RF telemetry.

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / Using a network-based telemetry system places additional requirements on the Radio Frequency (RF) link. Limitations imposed by this link must be considered in advance when designing a network-based telemetry system.