In recent year, wireless communications systems require transmission of higher and higher data rates to foster various multimedia services. The multiple-input multiple-output (MIMO) antennas system has been studied to increase wireless channel capacity and reliability. The mutual coupling of MIMO antennas affects the capacity of the wireless channel. Traditionally, the minimal mutual coupling distance between antenna elements needs to be at least one half wavelength. When MIMO antenna system is used in miniature mobile device, the problem of mutual coupling becomes even more serious. In the first part of this thesis we propose a WLAN/WiMAX antenna that can be operated in 2.4 GHz (2.4¡V2.48 GHz) WLAN band; 2.5 GHz (2.5¡V2.7 GHz) and 3.5 GHz (3.4¡V3.7 GHz) WiMAX band. We use the inverted U slot band notch and omega slot band notch to reduce the mutual coupling in MIMO antennas. Our design is able to reduce the mutual coupling to be less than ¡V20 dB in all interested bands. In the second part, we propose a planar WLAN/WiMAX antenna that can be operated in 2.4 GHz (2.4¡V2.48 GHz), 5.2/5.8GHz (5.15-5.35GHz/5.725-5.825GHz) WLAN band; 2.5 GHz (2.5¡V2.7 GHz), 3.5 GHz (3.4¡V3.7 GHz) and 5.5 GHz (5.25-5.85 GHz) WiMAX band and mutual coupling of MIMO antenna is less than ¡V20 dB in all interested bands.

Multiple-input multiple-output (MIMO) is a well-known technique for efficiently increasing bandwidth utilization. However, the implementation of the MIMO receiver with a reasonable hardware cost is a big challenge. Most MIMO receivers exploit minimum mean-square error (MMSE), zero-forcing (ZF) and maximum-likelihood (ML) to detect MIMO signals. Among the detectors, the ZF detector is simple detector with low computational complexity, but lower performance compared to ML decoder, which has huge computational complexity. If the K-Best sphere decoding algorithm (SDA) is adopted, the system complexity can be substantially reduced and the performance can approach that of the ML scheme when the value K is sufficiently large. In this paper, a hard-output MIMO detector is implemented using the K-Best SDA for 4¡Ñ4 64-quadrature amplitude modulation (QAM) MIMO detection. The implementation is realized by using a 0.18-£gm CMOS technology. The implementation chip core area is 3.35mm2 with 229K gates, and the decoding throughput is up to 3.12Mb/s with a 25MHz clock rate.

This dissertation systematically explores multiple-input converters (MICs) configuration and topologies, and then proposes improvements on certain beneficial MICs—time-sharing MICs and soft-switching MICs for distributed generation (DG) applications with high voltage transfer ratio. Compared with other MIC families which are derived from same input and output cells, time-sharing MICs have the fewest circuit components. However, time-sharing MICs lack for bi-directional power flow capability due to their special input switches requirement. In addition, their hard-switching characteristic leads to a low efficiency problem when isolation is necessary. The dissertation investigates into time-sharing MIC input switch selection, which leads to a new driving strategy and new input switch combinations. With the new input switch combinations, bi-directional and high efficiency time-sharing MICs are made possible. Besides isolated time-sharing MIC, Soft-switching MICs might also be a common choice for high voltage transfer ratio DG applications. However, the enormous amount of circuit components makes the soft-switching MICs become less attractive. An input cell reduction method is introduced in this dissertation to greatly reduce the component count of isolated MICs, including soft-switching MICs. In addition to the improvement on existing MIC families, a new push-pull connected MIC family is proposed in this dissertation as another choice of high voltage transfer ratio DG applications. Moreover, a comparison among MIC families is made to provide a sense of topologies selection in certain applications. Prototypes of time-sharing dual-input (DI) SEPICs, a push-pull connected DI-Boost converter, and a DI full-bridge (FB) converter are built to verify aspects discussed in this dissertation. Bi-directional power flow capability of time-sharing MIC is confirmed with a time-sharing DI-SEPIC and a soft-switching time-sharing MIC is realized by an isolated time-sharing DI-SEPIC with an active clamping leg. Maximum power point tracking control feasibility in these converters is evaluated with real photovoltaic modules that are connected to the push-pull connected DI-Boost converter that uses a perturb-and-observe method. Finally, an efficiency comparison is made between time-sharing MIC and push-pull connected MIC. / text

ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / This paper investigates the performance of a multiple-input multiple-output (MIMO) digital communication system, when the transmitter is located on a spinning vehicle. In particular, a 2x2 MIMO system is used, with Alamouti coding at the transmitter. Both Rayleigh and Rayleigh plus line-of-sight, or Rician, models combined with a deterministic model to simulate the channel. The spinning of the transmitting vehicle, relative to the stationary receive antennas, modulates the signal, and complicates the decoding and channel parameter estimation processes. The simulated system bit error rate is the primary performance metric used. The Alamouti channel code is shown to perform better than the maximal ratio receiver combining (MRRC) and single receiver (2x1) system in some circumstances and performs similarly to the MRRC in the broadside case.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / Wireless communication systems may use training signals for the receiver to learn the fading coefficients of the channel. Obtaining channel state information (CSI) at the receiver is often times necessary for the receiver to correctly detect and demodulate transmitted symbols. The type of training signal, the length of time to spend training, and the frequency of training are all important parameters in these types of systems. In this work, we derive an analytic expression for calculating the optimal training parameters for continuously fading channels. We also provide simulation results showing why this training scheme is considered optimal.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / This paper describes the design of an inexpensive and scalable transmitter for a Multiple-Input Multiple-Output (MIMO) communication system. The transmitter is intended to be used in aerospace applications, especially in spin stabilized vehicles. A field programmable gate array (FPGA) in the modulator will implement a modified Alamouti space time block code which will take advantage of the cyclostationary nature of the channel to increase the system data rate.

Multiple-Input Multiple-Output (MIMO) communication uses multiple transmit and receive antennas to improve the throughput in wireless channels. In cellular networks, self-interference greatly degrades MIMO's potential gain, especially in multiuser MIMO systems where multiple users in each cell share the spatial channel in order to maximize the total throughput. In a multiuser MIMO downlink, the two main causes of this self-interference are residual inter-user interference due to imperfect spatial separation between the users and other-cell interference due to cochannel transmissions in other cells. This dissertation develops adaptive transmission strategies to deal with both residual inter-user interference and other-cell interference in cellular MIMO networks. For the residual inter-user interference caused by imperfect channel state information at the transmitter, we explicitly characterize the impact of channel quantization and feedback delay. Achievable ergodic rates for both single-user and multiuser MIMO systems with different channel state information are derived. Adaptive switching between single-user and multiuser MIMO modes is proposed to improve the throughput, based on the accuracy of the available channel information. It is then extended to a multi-mode transmission strategy which adaptively adjusts the number of active users to control residual interference and provide additional array gain. To adaptively minimize the other-cell interference, two practical base station coordination strategies are proposed. The first is a cluster based coordination algorithm with different coordination strategies for cluster interior and cluster edge users. It performs full intra-cluster coordination for enhancing the sum throughput and limited inter-cluster coordination for reducing the interference for cluster edge users. A multi-cell linear precoder is designed to perform the coordination. The second is an adaptive intercell interference cancellation strategy, where multiple base stations jointly select transmission techniques based on user locations to maximize the sum throughput. Spatial interference cancellation is applied to suppress other-cell interference. Closed-form expressions are derived for the achievable throughput, and the proposed adaptive strategy is shown to provide significant average and edge throughput gain. The feedback design to assist the interference cancellation is also discussed. / text

This thesis examines the use of ripple correlation control as a maximum power point tracking algorithm with an interleaved SEPIC converter for use with a solar array. The suitability of existing topologies for use with photovoltaic applications and the tradeoffs involved are discussed. The advantages of interleaving in converters are examined and the benefits it provides to photovoltaic applications are discussed. An interleaved SEPIC converter operated in interleaved mode with a photovoltaic array is studied. The operation of ripple correlation control as a maximum power point tracking technique applied to the interleaved SEPIC converter is examined and simulations with results are presented. / text

This document explores the isolated multiple-input single ended primary inductor converter (IMISEPIC) and discusses its application. This thesis proposes the following control methods such as current feed-forward control, voltage feedback control and maximum power point control to analyze the IMISEPIC. Zero-ripple technique is also applied to IMISEPIC in order to increase the converter’s life-time. Design strategy and concerns about the IMISEPIC are also presented, and simulations and circuit experiments are conducted to verify the analysis. Finally, the discussion about control limitation is used for future design consideration. / text

Multiple-input multiple-output (MIMO) radar has been receiving increasing attention in recent years due to the dramatic advantages offered by MIMO systems in communications. The amount of energy reflected from a common radar target varies considerably with the observation angle, and these scintillations may cause signal fading which severely degrades the performance of conventional radars. MIMO radar with widely spaced antennas is able to view several aspects of a target simultaneously, which realizes a spatial diversity gain to overcome the target scintillation problem, leading to significantly enhanced system performance. Building on the initial studies presented in the literature, MIMO radar is investigated in detail in this thesis. First of all, a finite scatterers model is proposed, based on which the target detection performance of a MIMO radar system with arbitrary array-target configurations is evaluated and analyzed. A MIMO radar involving a realistic target is also set up, whose simulation results corroborate the conclusions drawn based on theoretical target models, validating in a practical setting the improvements in detection performance brought in by the MIMO radar configuration. Next, a hybrid bistatic radar is introduced, which combines the phased-array and MIMO radar configurations to take advantage of both coherent processing gain and spatial diversity gain simultaneously. The target detection performance is first assessed, followed by the evaluation of the direction finding performance, i.e., performance of estimating angle of arrival as well as angel of departure. The presented theoretical expressions can be used to select the best architecture for a radar system, particularly when the total number of antennas is fixed. Finally, a novel two phase radar scheme involving signal retransmission is studied. It is based on the time-reversal (TR) detection and is investigated to improve the detection performance of a wideband MIMO radar or sonar system. Three detectors demanding various amounts of a priori information are developed, whose performance is evaluated and compared. Three schemes are proposed to design the retransmitted waveform with constraints on the transmitted signal power, further enhancing the detection performance with respect to the TR approach.