Wireless communication systems, aside from path-loss, also suffer from small scale up-and- down variations in the power of the received signal. These fluctuations in the received signal power, commonly referred to as multi-path fading, result in a significant perfor- mance degradation of the system. One way to combat fading is diversity. The idea behind diversity is to provide the receiver with multiple independent copies of the transmitted signal, either in time, frequency or space dimension. In broadcast networks with underlying slow-faded channels, an appropriate option for exploiting diversity is transmit diversity, which deploys several antennas in the transmitter terminal. Based on the amount of available channel state information on the transmitter side, various transmit diversity schemes have been proposed in the literature. Because of certain limitations of broadcast networks, a practical assumption in these networks is to provide no channel state information for the transmitter. In this dissertation, a new scheme is proposed to exploit transmit diversity for broad- cast networks, assuming no channel state information in the transmitter. The main idea of our proposed method is to virtually impose time variations to the underlying slow-faded channels by multiplying quantized pseudo-random phases to data symbols before trans- mission. Using this method, all necessary signal processing can be transferred to the RF front-end of the transmitter, and therefore, the implementation cost is much less than that of alternative approaches. Under the proposed method, the outage probability of the system is analyzed and the corresponding achievable diversity order is calculated. Simulation results show that the performance of our proposed scheme falls slightly below that of the optimum (Alamouti type) approach in the low outage probability region.

The energy and data rate requirements for the next generation cellular networks urge the need for innovative solutions. Inspired by its massive bandwidth, millimeter wave (mmWave) band is thought-out to be one of the key elements to meet the aspirations. However, mmWave links are known to have short coverage distance due to the propagation losses introduced at high frequencies. The proposed solutions to overcome the transmission challenges include using large arrays with improved directivity, adopting smaller cells, and relying on cooperative networks to extend the mmWave link and avoid shadowing areas. This work aims to improve the connectivity of the mmWave link in the outdoor environments. One of the cost effective methods is to increase the array gain by using Analogue Beamforming (ABF). The performance of the ABF system in the presence of phase quantization error has been analytically investigated. The study also includes comparing three different channel sounding techniques, namely: exhaustive search, side-to-side search, and n-tier search. The time overhead related to each method and their energy consumption are calculated. The numerical results assist in determining the optimum search period to obtain a reasonable spectral efficiency using minimal power consumption. The results also help identify the minimum number of quantization bits required to produce about ninety percent of the optimistic results. In order to extend the coverage further, relay networks are considered an essential component in mmWave communications. The performance of a single hybrid beamforming full-duplex relay system and multi-relay networks were investigated. The design algorithms for the processors in the network are proposed based on the greedy pursuit approach. The performance of the proposed algorithms is analysed under various scenarios. The analysis highlights the influence of the array size, the number of RF chains, and the length of the channel sounding period. The performance of the proposed systems is compared from both the spectral efficiency and power consumption prospects. The results also establish that the number of antennas at the source and the relay receiver arrays have a superior impact on the system performance than the sizes of the array at the destination and the relay transmitter.

Multiple-input multiple-output (MIMO) radar employs orthogonal or partially correlated transmit signals to achieve performance benefits over its phased-array counterpart. It has been shown that MIMO radar can achieve greater spatial resolution, improved signal-to-noise ratio (SNR) and target localization, and greater clutter resolution using space-time adaptive processing (STAP). This thesis explores various methods to improve the signal-to-interference-plus-noise ratio (SINR) via transmit and receive beamforming. In MIMO radar settings, it is often desirable to transmit power only to a given location or set of locations defined by a beampattern. Current methods involve a two- step process of designing the transmit covariance matrix R via iterative solutions and then using R to generate waveforms that fulfill practical constraints such as having a constant-envelope or drawing from a finite alphabet. In this document, a closed- form method to design R is proposed that utilizes the discrete Fourier transform (DFT) coefficients and Toeplitz matrices. The resulting covariance matrix fulfills the practical constraints such as positive semidefiniteness and the uniform elemental power constraint and provides performance similar to that of iterative methods, which require a much greater computation time. Next, a transmit architecture is presented 
that exploits the orthogonality of frequencies at discrete DFT values to transmit a sum of orthogonal signals from each antenna. The resulting waveforms provide a lower mean-square error than current methods at a much lower computational cost, and a simulated detection scenario demonstrates the performance advantages achieved. It is also desirable to receive signal power only from a given set of directions defined by a beampattern. In a later chapter of this document, the problem of receive beampattern matching is formulated and three solutions to this problem are demonstrated. We show that partitioning the received data vector into subvectors and then multiplying each subvector with its corresponding weight vector can improve performance and reduce the length of the data vector. Simulation results show that all methods are capable of matching a desired beampattern. Signal-to-interference- plus-noise ratio (SINR) calculations demonstrate a significant improvement over the unaltered MIMO case.

<p>Millimeter-wave communications use narrow beams to overcome the enormous signal attenuation. Such narrow-beam communication demands precise beam-alignment between transmitter and receiver and may entail huge overhead, especially in high mobility scenarios. Moreover, detection of the optimal beam is challenging in the presence of beam imperfections and system noise. This thesis addresses the challenges in the design of beam-training and data-communication by proposing various schemes that exploit different timescales. On a short timescale, we leverage the feedback from the receiver to efficiently perform beam-training and data-communication. To this end, we have worked in three different areas. In the first research direction, we design an optimal interactive beam-training and data-communication protocol, with the goal of minimizing power consumption under a minimum rate constraint. The optimality of a fixed-length beam-training phase followed by a data-communication phase is proved under the assumption of perfect binary feedback. In the second research direction, we propose a coded energy-efficient beam-training scheme, robust against the feedback/detection errors. In the third research direction, we investigate the design of the beam-training in the presence of uncertainty due to noise and beam imperfections. Based on the bounding of value-function, the second-best preference policy is proposed, which achieves a promising exploration-exploitation tradeoff. On the other hand, on longer timescales, we exploit the mobility and blockage dynamics and beam-training feedback to design throughput-efficient beam-training and data-communication. We propose a point-based value iteration (PBVI) algorithm to determine an approximately optimal policy. However, the design relies on the a-priori knowledge of the state dynamics, which may not be available in practice. To address this, we propose a dual timescale approach, where on the long timescale, a recurrent deep variational autoencoder (R-VAE) uses noisy beam-training observations to learna probabilistic model of system dynamics; on the short timescale, an adaptive beam-training procedure is optimized using PBVI based on beam-training feedback and a probabilistic knowledge of the UE's position provided by the R-VAE. In turn, the observations collected during the beam-training procedure are used to refine the R-VAE via stochastic gradient descent in a continuous process of learning and adaptation.<br></p>

Optical beamforming networks (OBFNs) are a strong contender for phased array operation, especially using microwave photonics (MWP), with advantages in size, weight, power efficiency and cost. Applications for such systems range from satellite to cellphone communication. The use of OBFNs require multiple components to up-convert, down-convert and process radio frequency (RF) signals in the optical domain. In this thesis, these components and a photonic packaging solution were designed and tested. For the OBFN itself, the modulation for up-conversion was performed with a micro-ring modulator, which was able to perform 1.11V forward bias modulation at 500MHz with a modulation depth of 21 dB. A true time delay optical ring resonator (ORR) was designed and characterized, yielding 784 ps delay at 3.33V heater bias, tunable to any value below this. An accessible, low-cost photonic packaging approach was developed, which achieved an optical coupling loss of 2.8 dB per facet. In conjunction with the photonic packaging was an electromagnetic interference (EMI) enclosure, which was able to block unwanted external RF signals. / Thesis / Master of Applied Science (MASc)

No / In this study, a planar 4×4 phased array including modified E-shaped radiation elements is designed and fabricated to be incorporated in a Relay Station (RS) for realizing the communication with the super-ordinate Base Station. The proposed array provides 12.4% bandwidth at the 3.5GHz frequency band and gain of 21.2dB. Moreover a beamforming module is designed and simulated, aimed to be connected to the proposed array and realizing beamforming applications. This module provides 650 MHz bandwidth around 3.5GHz frequency band and is used for proper power division and controlling the amplitude/phase of the excitation currents.

No / Wavelet based multicarrier systems have attracted the attention of the researchers over the past few years to replace the conventional OFDM systems in the next generation communication systems. In this paper we have investigated the performance of such wavelet based systems using forward error correction with covolutional coding and interleaving in a Wavelet-SISO system and then in a Wavelet multicarrier modulation (WMCM) multiple input multiple output (MIMO) system using Convolutional coding and beamforming to reduce the source bit rate and overall system error and increase the data rate. Results show outstanding Bit Error Rate vs. Signal to Noise Ratio Performance. Other than better performance the proposed systems keep the computational burden off the receiver that has more cost and power constraints.

No description available.

No / In this study, a planar 4×4 phased array including modified E-shaped radiation elements is designed and fabricated to be incorporated in a Relay Station (RS) for realizing the communication with the super-ordinate Base Station. The proposed array provides 12.4% bandwidth at the 3.5GHz frequency band and gain of 21.2dB. Moreover a beamforming module is designed and simulated, aimed to be connected to the proposed array and realizing beamforming applications. This module provides 650 MHz bandwidth around 3.5GHz frequency band and is used for proper power division and controlling the amplitude/phase of the excitation currents.

Smart antenna systems are employed to overcome multipath fading, extend range, and increase capacity by using diversity or beamforming techniques in wireless communication systems. Understanding of the smart base antenna performance mechanisms for various environments is important to design cost effective systems and network. This dissertation focuses on the experimental characterization and modeling of the smart base station antenna performance for various propagation environment scenarios. An eight-channel Virginia Tech smart base station antenna testbed was developed to investigate performances of three reverse link diversity methods. The experiment campaign resulted in 245 sets of collected data over 83 measurement sites, which were used to compare the performance of space, polarization, and angle diversity under identical conditions. Measured propagation path loss, envelope correlation coefficients, power imbalances, and mean effective gain (MEG) are characterized as a function of distance between the base station and the mobile terminal to illustrate the diversity performance mechanisms over different propagation environments. The performance of the three base station diversity methods with selection combining (SC), maximal ratio combining (MRC), and equal gain combining (EGC) techniques for both urban and suburban non-line-of-sight (NLOS) environments are presented and summarized using the measured data. Forward-link performance of a twelve-fixed narrow-beam base station antenna system for urban NLOS environments is investigated using the same measured data. A new procedure is introduced to experimentally model the forward-link performance of muitlple-fixed narrow-beam (MFNB) antennas using the measured reverse-link vector channel response. The experimentally calculated lower bound performance result shows that it achieves 2.5 to 2.8 times higher average RF SIR compared to the conventional three-sector base station system for typical urban NLOS multipath fading environment conditions. Also, a new mobile user angle estimation algorithm using the muitlple-fixed narrow-beam antennas for NLOS multipath fading environment conditions is developed and the experiment results are presented. / Ph. D.