Doctor of Philosophy, The Ohio State University, 2021, Electrical and Computer Engineering

The surge in mobile broadband data demands is expected to surpass the available spectrum capacity below 6 GHz. This expectation has prompted the exploration of millimeter-wave (mmWave) frequency bands as a candidate technology for next-generation wireless networks, like 5G-NR and WiFi ad/ay. However, numerous challenges to deploying mmWave communication systems, including channel estimation, need to be met before practical deployments are possible. The channel estimation problem is particularly complex due to the large antenna arrays, i.e., large-MIMO, used in mmWave transceivers. Large-MIMO antennas offer significant performance gains in terms of improved spectral efficiency, superior spatial multiplexing capabilities, as well as the ability to deliver high transmit signal power, which is crucial for compensating for the severe attenuation of high-frequency signals. However, large-MIMO channel estimation is complex since it entails the discovery of large-sized channel matrices, which is a daunting task and may necessitate a large number of measurements. Channel estimation is especially challenging for ``initial link establishment'', where limited prior knowledge about the channel is available. Reducing the number of necessary measurements thus holds the key to faster link establishment. For sparse MIMO channels, such reduction is possible due to the prior knowledge that the channel can be represented in a domain in which most of its components are negligibly small. The problem of "Fast Link Establishment" is the focus of this dissertation. In particular, we focus on the development and evaluation of sparse channel estimation algorithms that only require a small number of measurements. We divide this dissertation into three research objectives, as follows: First: We seek to develop a reliable channel estimation framework that: (1) requires a limited number of measurements (compared to the channel dimensions), and (2) operates using energy-efficient transcei (open full item for complete abstract)

Committee: Eylem Ekici (Advisor); C. Emre Koksal (Advisor); Ness Shroff (Committee Member) Subjects: Communication; Computer Science; Electrical Engineering

Master of Science, The Ohio State University, 2020, Computer Science and Engineering

In recent years, WiFi-based human-computer interaction has achieved significant progress in localization, fall detection, activity recognition applications since the innovation of CSI (Channel State Information). But WiFi sensing for fine-grained activity recognition like hand pose estimation is not yet discovered. In this study, we present a WiFi sensing system that only utilizes commercial off-the-shelf WiFi devices to capture human hand pose. To our knowledge, this is the first system that considers the application of hand pose estimation using CSI. We provide configuration details of data collection, data processing for CSI and image that can be reused for any other WiFi-based sensing research. And we propose a deep learning approach that achieves cross-modal learning from CSI to hand pose labels. Our system collects the CSI signals and 2D images in a time-synchronized manner. The 2D images are used to generate hand pose labels. And the CSI signals are collected from 3 x 3 transmitter and receiver antenna pairs and used as the input to our model. Our model includes 3 different learning targets. Experiment results show that CSI measurements have similar structures to digital images and popular network architecture for hand pose estimation in images can be applied to CSI measurements with slight modification.

Committee: Dong Xuan Dr. (Advisor); Wei-Lun Chao Dr. (Committee Member) Subjects: Computer Science

MS, University of Cincinnati, 2006, Engineering : Electrical Engineering

In this thesis, we present a decision-aided channel estimator for multiple-input multiple-output (MIMO) Rayleigh fading channels. The scheme presented does away with the conventional block fading channel model by making continual updates to the channel estimate using previous decisions. We tailor the WLMS algorithm proposed in [1] which takes advantage of knowledge of the nature of channel fading for prediction, to suit MIMO channel needs. We then analyze the symbol error rate, channel prediction error floor achieved and also test the robustness of the proposed algorithm. The results reveal superior performance of our scheme to previous works in MIMO channel prediction, in all of the areas mentioned above and robustness to decision errors as well.

Committee: Dr. James Caffery (Advisor) Subjects:

Master of Science, University of Toledo, 2011, Electrical Engineering

Orthogonal frequency division multiplexing (OFDM) is a multi-carrier transmission technology in wireless environment, and can also be seen as a multi-carrier digital modulation or multi-carrier digital multiplexing technology. A large number of orthogonal sub-carriers are used to transmit information. OFDM system has high utilization of frequency spectrum and satisfactory capability of reducing multi-path inference. So, OFDM has been considered as one of the core technologies of 4th generation (4G) wireless communication system in the future. Channel estimation plays a very important role in OFDM system. As a research hotpot, many related algorithms have been presented these years, which can be generally separated into two methods, pilot-based channel estimation and blind channel estimation. Pilot-based channel estimation estimates the channel information by obtaining the impulse response from all sub-carriers by pilot. Compared with blind channel estimation, which uses statistical information of the received signals, pilot-based channel estimation is a practical and an effective method. This thesis is on the pilot-based channel estimation of OFDM system. Firstly, it introduces the basic principle and realization of OFDM system, and describes the system construction and model with summary of some key technologies, such as fast Fourier transform (FFT) and cyclic prefix (CP). We also analyze OFDM modulation in the frequency domain, and discusses some advantages and disadvantages of OFDM system. Next, a summary of multi-path and time varying statistical properties of general wireless channel of OFDM system are presented. This thesis also investigates principles and performances of the channel estimation methods, block type pilot and comb type pilot. In the arrangement of block type pilot, the performance of channel estimation is analyzed with estimators based on three different algorithms, least square (LS) algorithm, linear minimum mean square error (LMMSE) algorithm (open full item for complete abstract)

Committee: Junghwan Kim PhD (Committee Chair); Dong-Shik Kim PhD (Committee Member); Mohammed Niamat PhD (Committee Member) Subjects: Electrical Engineering

Master of Science, The Ohio State University, 2009, Electrical and Computer Engineering

Channel Estimation is an essential component in applications such as radar and data communication. In multi path time varying environments, it is necessary to estimate time-shifts, scale-shifts (the wideband equivalent of Doppler-shifts), and the gains/phases of each of the multiple paths. With recent advances in sparse estimation (or “compressive sensing”), new estimation techniques have emerged which yield more accurate estimates of these channel parameters than traditional strategies. These estimation strategies, however, restrict potential estimates of time-shifts and scale-shifts to a finite set of values separated by a choice of grid spacing. A small grid spacing increases the number of potential estimates, thus lowering the quantization error, but also increases complexity and estimation time. Conversely, a large grid spacing lowers the number of potential estimates, thus lowering the complexity and estimation time, but increases the quantization error. In this thesis, we derive an expression which relates the choice of grid spacing to the mean-squared quantization error. Furthermore, we consider the case when scale-shifts are approximated by Doppler-shifts, and derive a similar expression relating the choice of the grid spacing and the quantization error. Using insights gained from these expressions, we further explore the effects of the choice and grid spacing, and examine when a wideband model can be well approximated by a narrowband model.

Committee: Philip Schniter PhD (Advisor); Potter Lee PhD (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2007, Electrical Engineering

Wireless communication systems targeting at broadband and mobile transmissions commonly face the challenge of fading channels that are both time and frequency selective. Therefore, design of effective equalization and estimation algorithms for such channels becomes a fundamental problem. Although multi-carrier transmissions demonstrate prominent potential to combat doubly selective fading, several factors may retard their applications, such as: high peak-to-average power ratio, sensitivity to phase noise, etc. Meanwhile, single-carrier transmission is a conventional approach and has important applications, such as HDTV broadcasting, underwater acoustic communication. In this dissertation, we focus on receiver design for single-carrier transmissions. Our goal is to design and develop a group of channel estimation and equalization algorithms in the frequency-domain, which enable high performance and low complexity reception of single-carrier transmissions through doubly selective channels. For single-carrier transmissions over moderately fast fading channels with long-delay spread, we present an improved iterative frequency-domain equalization (IFDE) algorithm based on soft-interference-cancellation (SIC) and propose a novel adaptive frequency-domain channel estimation (AFDCE) based on soft-input Kalman filter, where soft information feedback from the IFDE can be exploited in the channel estimator. Simulation results show that, compared to other existing schemes, the proposed scheme offers lower MSE in channel prediction, lower BER after decoding, and robustness to non-stationary channels. We extend the IFDE/AFDCE scheme to accommodate the application of digital television (DTV) signal reception. Compared with the traditional joint decision feedback equalization (DFE) /decoding plus frequency-domain least-mean-square (FDLMS) channel estimation approach, the proposed scheme achieves better performance at a fraction of the implementation cost. For very fast fading large (open full item for complete abstract)

Committee: Philip Schniter (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2007, Electrical Engineering

Wireless communication systems transferring broadband data in high mobility situations encounter fading channels which are both time and frequency selective. In the noncoherent scenario, the time varying impulse response of the doubly selective channel (DSC) is not available at both the transmitter and the receiver. In this dissertation, we consider the problem of communications over such noncoherent doubly selective channels. Our work has two main themes: to find the fundamental limits on the information rates for reliable communication across noncoherent DSC and to develop simple and efficient encoding/decoding techniques to achieve the promised information rates. Towards this end, we consider block transmissions over DSC and utilize complex-exponential (CE) basis expansion model (BEM) to characterize the channel variation within a block. For noncoherent CE-BEM DSC, we characterize the prelog factor of the constrained ergodic channel capacity in the high SNR regime, when the channel inputs are continuously distributed. Next, we consider the design of pilot aided transmissions (PAT) for CE-BEM DSC, which embeds known pilot signals that the receiver uses to estimate the channel. For a given fixed pilot energy, we derive the necessary and sufficient conditions on the pilot/data pattern to attain minimum mean squared error (MMSE), uncover time-frequency duality of MMSE-PAT structures and obtain novel MMSE-PAT patterns. We obtain bounds on the ergodic achievable rates of MMSE-PAT schemes and perform high signal to noise ratio (SNR) asymptotic analysis which suggests that, a multi-carrier MMSE-PAT achieves higher rates than a single-carrier MMSE-PAT when the channel's delay spread dominates its Doppler spread, and vice versa. We also establish that the pre-log factor of the ergodic rates of all the MMSE-PAT patterns are strictly less than that of the constrained channel capacity, for strictly doubly selective channels. We also design spectrally efficient PAT schemes who (open full item for complete abstract)

Committee: Philip Schniter (Advisor) Subjects:

Master of Science in Engineering, University of Akron, 2011, Electrical Engineering

Modern wireless transceivers use multiple transmit and/or receive antennas, higher order modulation and large bandwidth to satisfy the high data rate requirements of voice, data and multimedia applications. As wireless systems become more complex, the need to make wireless transceivers more efficient, compact and cost effective becomes challenging. It is partly due to the impairments resulting from imperfections in analog radio frequency (RF) components that reduce the efficiency of wireless transceivers. Two of the most common impairments that significantly limit the performance of wireless transceivers are in phase and quadrature (IQ) imbalance and phase noise. These are caused by the mismatch in oscillator output and random frequency fluctuations at the I and Q branches of IQ transceivers, respectively. Low-complexity estimation and compensation techniques that can jointly remove the effect of these impairments are highly desirable. The degrading effect of RF impairments is more pronounced in multi-input-multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. As many of the modern and future wireless systems employ MIMO-OFDM, studying the effect of and addressing the techniques to mitigate RF impairments in these systems are essential to meet the stringent requirements of modern wireless applications. In this thesis, a simple joint estimation and compensation technique to estimate multi-path channel, phase noise and IQ-Imbalance parameters in MIMO-OFDM systems under slow fading is proposed. A subcarrier multiplexed (SM) preamble structure to estimate the channel and impairment parameters with minimum overhead is introduced and used in the estimation of IQ-Imbalance parameters as well as the initial estimation of effective channel matrix including common phase error (CPE). We then use a novel tracking method based on the second order statistics of the inter-carrier interference (ICI) and noise to update the effective channel matrix throughout (open full item for complete abstract)

Committee: Hamid Reza Bahrami Dr. (Advisor); Nathan Ida Dr. (Committee Member); Alexis De Abreu Garcia Dr. (Committee Member) Subjects: Electrical Engineering