Cooperative diversity has been proposed as a powerful means to enhance the performance of high-rate communications over wireless fading channels. It realizes spatial diversity advantages in a distributed manner where two or more nodes share their antennas to mimic a virtual antenna array.

Cooperative diversity has been proposed as a powerful means to enhance the performance of high-rate communications over wireless fading channels. It realizes spatial diversity advantages in a distributed manner where two or more nodes share their antennas to mimic a virtual antenna array.

As the data rates and performance of current telecommunications technologies reach their limits, MIMO offers promising results allowing for higher spectral efficiencies (or capacities) through the use of multiple element antennas (MEAs). Conventional testing methods, however, cannot be used for multi-antenna systems due to the co-dependence of antenna and RF effects, and baseband hardware and software design. This dissertation specifies a novel MIMO-OFDM, BLAST-based testing design using a hybrid FPGA/DSP development platform from Lyrtech. The design allows for rapid implementation and a consistent indication of the channel impulse response. In addition, a multipath environment is further created to mimic a realistic high scattering scenario. A study of MIMO system capacity is performed along with measurements of an actual over-the-air (OTA) channel. Observations about capacity and the effect of MEA antenna separations are then drawn and conclusions made as to the overall ability to effectively test MIMO systems. The platform used is the result of efforts from several individuals within UW's CST group. My contributions and research are documented in this dissertation.

Ultra-Wideband (UWB) wireless communication systems employ large bandwidths and low transmitted power spectral densities, and are suitable for operation as underlay systems which reuse allocated spectrum. The subject of this dissertation is Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) UWB for high data-rate communication. We address four main questions: (1) What are the theoretical performance limits and practical system performance of MB-OFDM? (2) What extensions can be used to increase the system power efficiency and range? (3) Is it possible to estimate the system error rate without resorting to time-consuming simulations? and (4) What is the effect of interference from narrowband systems on MB-OFDM, and can this interference be mitigated? As for questions 1 and 2, we investigate the MB-OFDM performance, and propose system enhancements consisting of advanced error correcting codes and OFDM bit-loading. Our methodology includes the development of information-theoretic performance measures and the comparison of these measures with performance results for MB-OFDM and our proposed extensions, which improve the power efficiency by over 6 dB at a data rate of 480 Mbps. To address question 3, we develop novel analytical methods for bit error rate (BER) estimation for a general class of coded multicarrier systems (of which MB-OFDM is one example) operating over quasi-static fading channels. One method calculates system performance for each channel realization. The other method assumes Rayleigh distributed subcarrier channel gains, and leads directly to the average BER. Both methods are also able to account for sum-of-tones narrowband interference. As for question 4, we first present an exact analysis of the uncoded BER of MB-OFDM in the presence of interference from incumbent systems such as IEEE 802.16 ("WiMAX"). We also present a Gaussian approximation for WiMAX interference, and establish its accuracy through comparison with exact analysis and simulations. We then propose a two-stage interference mitigation technique for coded MB-OFDM, consisting of interference estimation during silent periods, followed by metric weighting during decoding, which provides substantial gains in performance in return for modest increases in complexity, and without requiring any modifications to the MB-OFDM transmitter.

Cognitive Radio (CR) is considered to be a novel approach to improve the underutilization of precious radio resources by exploiting the unused licensed spectrum in dynamically changing environments. Designing efficient resource allocation algorithms for dynamic spectrum sharing and for power allocation in OFDM-CR networks is still a challenging problem. In this thesis, we specifically deal with these two problems. Dynamic spectrum sharing for the unlicensed secondary users (SU)s with device coordination could minimize the wastage of the spectrum. But this is a feasible approach only if the network considers the fairness criterion. We study the dynamic spectrum sharing problem for device coordinated cognitive radio networks with respect to fairness. We propose a simple modified proportional fair algorithm for a dynamic spectrum sharing scenario with two constraints, time and utility. Utility is measured by the amount of data processed and time is measured as the duration of a slot. This algorithm could result in variable or fixed length time slots. We will discuss the several controls possible on the algorithm and the possible extension of this algorithm for multicarrier OFDM based CR systems. Traditional water-filling algorithm is inefficient for OFDM-CR networks due to the interaction with primary users (PU)s. We consider reliability/availability of subcarriers or primary user activity for power allocation. We model this aspect mathematically with a risk-return model by defining a general rate loss function. We then propose optimal and suboptimal algorithms to allocate power under a fixed power budget for such a system with linear rate loss. These algorithms as we will see allocate more power to more reliable subcarriers in a water-filling fashion with different water levels. We compare the performance of these algorithms for our model with respect to water-filling solutions. Simulations show that suboptimal schemes perform closer to optimal scheme although they could be implemented with same complexity as water-filling algorithm. We discuss the linearity of loss function and guidelines to choose its coefficients by obtaining upper bounds on them. Finally we extend this model for interference-limited OFDM-CR systems.

As the data rates and performance of current telecommunications technologies reach their limits, MIMO offers promising results allowing for higher spectral efficiencies (or capacities) through the use of multiple element antennas (MEAs). Conventional testing methods, however, cannot be used for multi-antenna systems due to the co-dependence of antenna and RF effects, and baseband hardware and software design. This dissertation specifies a novel MIMO-OFDM, BLAST-based testing design using a hybrid FPGA/DSP development platform from Lyrtech. The design allows for rapid implementation and a consistent indication of the channel impulse response. In addition, a multipath environment is further created to mimic a realistic high scattering scenario. A study of MIMO system capacity is performed along with measurements of an actual over-the-air (OTA) channel. Observations about capacity and the effect of MEA antenna separations are then drawn and conclusions made as to the overall ability to effectively test MIMO systems. The platform used is the result of efforts from several individuals within UW's CST group. My contributions and research are documented in this dissertation.

No description available.

The design of emergent wireless sensor networks operating near the ground requires channel models that account for previously unconsidered propagation phenomena. Most models used for link planning and radio design of the last century were designed for use in situations where the transmitters were at least tens of meters above the earth surface. However, near the earth surface, the specifics of the ground composition and atmospheric effects have been postulated to play a significant role. This dissertation describes the first set of investigations in this emergent environment. A novel computational electromagnetics model is presented that can calculate electromagnetic fields of a dipole embedded in planar-stratified propagation medium that represents the ground and near-surface atmosphere. It is the first available electromagnetic model to efficiently combine a spectral-domain solution in arbitrary multilayers of lossy-dielectric media with high-order quadrature routines to synthesize the fields of an impressed dipole. For the first time, high-order asymptotic quadrature is used to efficiently obtain solutions at arbitrary ranges from the dipole source. A measurements-based model of the near-ground atmosphere is derived, and results of modeling the atmosphere are used to predict the performance of an ultra-high-frequency radio system operating near the ground surface. Finally, a study is conducted to determine the effects of varying key parameters in the near ground channel, including atmospheric conditions, ground conditions, and frequency. The primary result is that ultra-high-frequency near-earth narrowband channels are largely insensitive to large-scale refractive effects that occur naturally on Earth; however, as the transmitter frequency increases into the super-high-frequency and millimeter wave regimes, refractive effects have significant effects on the radio propagation environment.

Cognitive Radio (CR) is considered to be a novel approach to improve the underutilization of precious radio resources by exploiting the unused licensed spectrum in dynamically changing environments. Designing efficient resource allocation algorithms for dynamic spectrum sharing and for power allocation in OFDM-CR networks is still a challenging problem. In this thesis, we specifically deal with these two problems. Dynamic spectrum sharing for the unlicensed secondary users (SU)s with device coordination could minimize the wastage of the spectrum. But this is a feasible approach only if the network considers the fairness criterion. We study the dynamic spectrum sharing problem for device coordinated cognitive radio networks with respect to fairness. We propose a simple modified proportional fair algorithm for a dynamic spectrum sharing scenario with two constraints, time and utility. Utility is measured by the amount of data processed and time is measured as the duration of a slot. This algorithm could result in variable or fixed length time slots. We will discuss the several controls possible on the algorithm and the possible extension of this algorithm for multicarrier OFDM based CR systems. Traditional water-filling algorithm is inefficient for OFDM-CR networks due to the interaction with primary users (PU)s. We consider reliability/availability of subcarriers or primary user activity for power allocation. We model this aspect mathematically with a risk-return model by defining a general rate loss function. We then propose optimal and suboptimal algorithms to allocate power under a fixed power budget for such a system with linear rate loss. These algorithms as we will see allocate more power to more reliable subcarriers in a water-filling fashion with different water levels. We compare the performance of these algorithms for our model with respect to water-filling solutions. Simulations show that suboptimal schemes perform closer to optimal scheme although they could be implemented with same complexity as water-filling algorithm. We discuss the linearity of loss function and guidelines to choose its coefficients by obtaining upper bounds on them. Finally we extend this model for interference-limited OFDM-CR systems.

Ultra-Wideband (UWB) wireless communication systems employ large bandwidths and low transmitted power spectral densities, and are suitable for operation as underlay systems which reuse allocated spectrum. The subject of this dissertation is Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) UWB for high data-rate communication. We address four main questions: (1) What are the theoretical performance limits and practical system performance of MB-OFDM? (2) What extensions can be used to increase the system power efficiency and range? (3) Is it possible to estimate the system error rate without resorting to time-consuming simulations? and (4) What is the effect of interference from narrowband systems on MB-OFDM, and can this interference be mitigated? As for questions 1 and 2, we investigate the MB-OFDM performance, and propose system enhancements consisting of advanced error correcting codes and OFDM bit-loading. Our methodology includes the development of information-theoretic performance measures and the comparison of these measures with performance results for MB-OFDM and our proposed extensions, which improve the power efficiency by over 6 dB at a data rate of 480 Mbps. To address question 3, we develop novel analytical methods for bit error rate (BER) estimation for a general class of coded multicarrier systems (of which MB-OFDM is one example) operating over quasi-static fading channels. One method calculates system performance for each channel realization. The other method assumes Rayleigh distributed subcarrier channel gains, and leads directly to the average BER. Both methods are also able to account for sum-of-tones narrowband interference. As for question 4, we first present an exact analysis of the uncoded BER of MB-OFDM in the presence of interference from incumbent systems such as IEEE 802.16 ("WiMAX"). We also present a Gaussian approximation for WiMAX interference, and establish its accuracy through comparison with exact analysis and simulations. We then propose a two-stage interference mitigation technique for coded MB-OFDM, consisting of interference estimation during silent periods, followed by metric weighting during decoding, which provides substantial gains in performance in return for modest increases in complexity, and without requiring any modifications to the MB-OFDM transmitter. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate