Bit Allocation Law for Multi-Antenna Channel Feedback Quantization: Single-User Case

This paper studies the design and optimization of a limited feedback single-user system with multiple-antenna transmitter and single-antenna receiver. The design problem is cast in form of the minimizing the average transmission power at the base station subject to the user's outage probability constraint. The optimization is over the user's channel quantization codebook and the transmission power control function at the base station. Our approach is based on fixing the outage scenarios in advance and transforming the design problem into a robust system design problem. We start by showing that uniformly quantizing the channel magnitude in dB scale is asymptotically optimal, regardless of the magnitude distribution function. We derive the optimal uniform (in dB) channel magnitude codebook and combine it with a spatially uniform channel direction codebook to arrive at a product channel quantization codebook. We then optimize such a product structure in the asymptotic regime of $B\rightarrow \infty$, where $B$ is the total number of quantization feedback bits. The paper shows that for channels in the real space, the asymptotically optimal number of direction quantization bits should be ${(M{-}1)}/{2}$ times the number of magnitude quantization bits, where $M$ is the number of base station antennas. We also show that the performance of the designed system approaches the performance of the perfect channel state information system as $2^{-\frac{2B}{M+1}}$. For complex channels, the number of magnitude and direction quantization bits are related by a factor of $(M{-}1)$ and the system performance scales as $2^{-\frac{B}{M}}$ as $B\rightarrow\infty$.Comment: Submitted to IEEE Transactions on Signal Processing, March 201

Throughput-based Design for Polar Coded-Modulation

Typically, forward error correction (FEC) codes are designed based on the minimization of the error rate for a given code rate. However, for applications that incorporate hybrid automatic repeat request (HARQ) protocol and adaptive modulation and coding, the throughput is a more important performance metric than the error rate. Polar codes, a new class of FEC codes with simple rate matching, can be optimized efficiently for maximization of the throughput. In this paper, we aim to design HARQ schemes using multilevel polar coded-modulation (MLPCM). Thus, we first develop a method to determine a set-partitioning based bit-to-symbol mapping for high order QAM constellations. We simplify the LLR estimation of set-partitioned QAM constellations for a multistage decoder, and we introduce a set of algorithms to design throughput-maximizing MLPCM for the successive cancellation decoding (SCD). These codes are specifically useful for non-combining (NC) and Chase-combining (CC) HARQ protocols. Furthermore, since optimized codes for SCD are not optimal for SC list decoders (SCLD), we propose a rate matching algorithm to find the best rate for SCLD while using the polar codes optimized for SCD. The resulting codes provide throughput close to the capacity with low decoding complexity when used with NC or CC HARQ

Grassmannian Beamforming for MIMO Amplify-and-Forward Relaying

In this paper, we derive the optimal transmitter/ receiver beamforming vectors and relay weighting matrix for the multiple-input multiple-output amplify-and-forward relay channel. The analysis is accomplished in two steps. In the first step, the direct link between the transmitter (Tx) and receiver (Rx) is ignored and we show that the transmitter and the relay should map their signals to the strongest right singular vectors of the Tx-relay and relay-Rx channels. Based on the distributions of these vectors for independent identically distributed (i.i.d.) Rayleigh channels, the Grassmannian codebooks are used for quantizing and sending back the channel information to the transmitter and the relay. The simulation results show that even a few number of bits can considerably increase the link reliability in terms of bit error rate. For the second step, the direct link is considered in the problem model and we derive the optimization problem that identifies the optimal Tx beamforming vector. For the i.i.d Rayleigh channels, we show that the solution to this problem is uniformly distributed on the unit sphere and we justify the appropriateness of the Grassmannian codebook (for determining the optimal beamforming vector), both analytically and by simulation. Finally, a modified quantizing scheme is presented which introduces a negligible degradation in the system performance but significantly reduces the required number of feedback bits.Comment: Submitted to IEEE Journal of Selected Areas in Communications, Special Issue on Exploiting Limited Feedback in Tomorrows Wireless Communication Network

GAINING SCIENTIFIC AND ENGINEERING INSIGHT INTO GROUND MOTION SIMULATION THROUGH MACHINE LEARNING AND APPROXIMATE MODELING APPROACHES

This dissertation presents a series of methods for gaining scientific and engineering insight into earthquake ground motion simulation in three areas: synthetic validation, attenuation modeling, and nonlinear effects estimation. First, I present guidelines to reduce the number of metrics used to evaluate the goodness-of-fit (GOF) between ground motion synthetics and recorded data in an application independent framework. Validation of ground motion simulations is mostly done using metrics that are user- or application-biased. Comparisons between synthetics from regional scale ground motion simulations and recorded data from past earthquakes provide opportunities to approach the problems using data-driven methods. I used a combination of semi-supervised and supervised learning methods to prioritize GOF metrics based on a large dataset and was able to identify the response spectra- and energy integral-based metrics as the most dominant ones for estimating the accuracy of simulations. Second, in two related studies, I present an application of customized solutions used to characterize attenuation (quality factor Q) with respect to shear wave velocity (Vs) for individual stations within a simulation. I used an artificial neural network as a supervised learning method to develop pseudo-simulators to be used in an optimization process to estimate the dominant Vs range for each station, and thus estimate Q. Using parameters such as peak ground acceleration, response spectra, the area under the velocity signal\u27s envelope and the peak ground velocity, I show it is possible to improve the optimization process to locate the most accurate Q parameters. Last, I present an approximate model to estimate nonlinear soil effects in ground motion simulations by implementing an approach inspired in the equivalent linear method. This implementation is done for three-dimensional simulations, from source to site, without any pre- or post-processing of data. Fully nonlinear ground motion simulation methods need comprehensive input data and are computationally challenging. The approach implemented can be used to estimate first-order nonlinear soil effects (e.g., deamplificaiton and resonant frequency shift) effectively. I calibrate the approach using idealized models

Characterization of tissue response to localized cooling and design of a safer cryotherapy device

Localized cooling is often used to manage both acute and chronic phases of soft tissue injuries by reducing pain, swelling, and inflammation. Cold application would result in a decline in skin temperature and reduction of blood perfusion at the treatment site. In some instances, the use of cryotherapy has been associated with tissue necrosis and nerve damage. Tissue damage was shown to be due to both the direct effect of cooling as well as tissue ischemia resulting from the reduced blood perfusion. The purpose of this research was to examine the effect of localized cooling on skin temperature and blood perfusion and to develop a method to stimulate blood perfusion in tissue following development of cold-induced vasoconstriction. Out of various methods used, thermal stimulation was shown to successfully increase tissue perfusion during cryotherapy experiments. As a part of this research, tissue response to localized cooling was quantified for each of a variety of cryotherapy units (CTU). Moreover, diverse methods were implemented to investigate and quantify the non-uniformity of surface temperature for multiple cooling pads in combinations with their brand-specific CTUs. It was demonstrated through further studies and tissue blood perfusion comparisons (caused by using different CTUs) that there were no significant differences between studied units. Additionally, no significant difference was observed between knee and ankle/foot in their vasocosnstrictive response to cooling. Using multiple statistical methods, it was illustrated that a significant degree of vasoconstriciton occurred that lasted well beyond the active cooling period while skin temperature had increased significantly. Furthermore, a hysteresis effect was observed between skin perfusion and temperature during cooling and rewarming periods. In addition, a dose-dependent response in skin perfusion in relation to applied temperature was reported. A hysteresis effect between the skin temperature and perfusion was observed for both cooling and warming experiments and the area of the hysteresis plot was shown to be linearly dependent on applied temperature. Moreover, non-uniformity of skin temperature during cryotherapy was noted, which was independent of pad temperature distribution.Biomedical Engineerin

Space-Time Signal Design for Multilevel Polar Coding in Slow Fading Broadcast Channels

Slow fading broadcast channels can model a wide range of applications in wireless networks. Due to delay requirements and the unavailability of the channel state information at the transmitter (CSIT), these channels for many applications are non-ergodic. The appropriate measure for designing signals in non-ergodic channels is the outage probability. In this paper, we provide a method to optimize STBCs based on the outage probability at moderate SNRs. Multilevel polar coded-modulation is a new class of coded-modulation techniques that benefits from low complexity decoders and simple rate matching. In this paper, we derive the outage optimality condition for multistage decoding and propose a rule for determining component code rates. We also derive an upper bound on the outage probability of STBCs for designing the set-partitioning-based labelling. Finally, due to the optimality of the outage-minimized STBCs for long codes, we introduce a novel method for the joint optimization of short-to-moderate length polar codes and STBCs

Compliant, low profile, independently releasing, non-protruding and genderless docking system for robotic modules

An apparatus for coupling with a mating coupling module to facilitate the joining of two disjoined structures without requiring precise alignment between the disjoined structures during the coupling of them may include a rotating drive mechanism, a hollow cylindrical body operatively connected to the rotating drive mechanism, wherein the hollow cylindrical body has at least one internal spiral channel, and at least one connector claw positioned within the hollow cylindrical body and guided by the internal spiral channel, wherein the at least one connector claw is configured to extend outwardly from the coupling module to engage the mating coupling module when brought in close proximity but not necessarily in precise alignment with the mating coupling module