Flexible Multi-Group Single-Carrier Modulation: Optimal Subcarrier Grouping and Rate Maximization

Orthogonal frequency division multiplexing (OFDM) and single-carrier frequency domain equalization (SC-FDE) are two commonly adopted modulation schemes for frequency-selective channels. Compared to SC-FDE, OFDM generally achieves higher data rate, but at the cost of higher transmit signal peak-to-average power ratio (PAPR) that leads to lower power amplifier efficiency. This paper proposes a new modulation scheme, called flexible multi-group single-carrier (FMG-SC), which encapsulates both OFDM and SC-FDE as special cases, thus achieving more flexible rate-PAPR trade-offs between them. Specifically, a set of frequency subcarriers are flexibly divided into orthogonal groups based on their channel gains, and SC-FDE is applied over each of the groups to send different data streams in parallel. We aim to maximize the achievable sum-rate of all groups by optimizing the subcarrier-group mapping. We propose two low-complexity subcarrier grouping methods and show via simulation that they perform very close to the optimal grouping by exhaustive search. Simulation results also show the effectiveness of the proposed FMG-SC modulation scheme with optimized subcarrier grouping in improving the rate-PAPR trade-off over conventional OFDM and SC-FDE.Comment: Submitted for possible conference publicatio

Reduced complexity impulse radio ultra wide band direction finding systems

The research works presented in this thesis are motivated by the low complexity and high accuracy capabilities of UWB Impulse Radio (IR) systems. In particular, this thesis addresses UWB IR direction finding (DF) system designs using a reduced complexity receiver structure. The first contribution of the thesis is the DF receiver using digital channelization receiver architecture, where the use of Nyquist rate sampling is no longer required. In a multipath environment, this approach requires a multipath suppression technique. Due to the low complexity constraint, we propose a simple analog level threshold detector (LTD). Performance analysis reveals that the error in detection due to the LTD will give rise to the estimation errors. An alternative means for DF is using a simple analog differentiator with a peak-and-hold detector. This approach is motivated by the observation of a staircase-shape waveform whose slope indicates the direction of arrival (DOA). In view of the error from the LTD’s operation, we propose a time-delay-based DF system. The DF is calculated from the time delay estimates from each channel of the array. Lastly, we extend the DF problem from single source to multiple sources transmission, using Time Hopping Multiple Access scheme.DOCTOR OF PHILOSOPHY (EEE

A robust approach to optimum widely linear MVDR beamformer

In many array processing, the received signals are nonstationary, or in particular, noncircular. Widely linear minimum variance distortionless response (WL MVDR) beamformers can exploit the noncircularity of received signals and improve the performance of the conventional MVDR beamformer. However, in the optimum WL MVDR beamformer, the array steering vector (ASV) and the signal noncircularity coefficient should be known a priori for the signal of interest. This requirement puts strict limitation to the implementation of this beamformer. We therefore in this paper propose a robust approach to the optimal WL MVDR beamformer that can deal with the uncertainties in the ASV and noncircularity coefficient. Two variants of the proposed approach are developed based on the treatment of the uncertainties. By doing so, the requirement on the exact information is relaxed while the performance improvement can still be obtained. Simulation studies are also provided to illustrate the performance of the proposed approach

Single antenna power measurements based direction finding

In this paper, the problem of estimating direction-ofarrival (DOA) of multiple uncorrelated sources from single antenna power measurements is addressed. Utilizing the fact that the antenna pattern is bandlimited and can be modeled as a finite sum of complex exponentials, we first show that the problem can be transformed into a frequency estimation problem. Then, we explain how the annihilating filter method can be used to solve for the DOA in the noiseless case. In the presence of noise, we propose to use Cadzow denoising that is formulated as an iterative algorithm derived fromexploiting the matrix rank and linear structure properties. Furthermore, we have also derived the Cramér–Rao Bound (CRB) and reviewed several alternative approaches that can be used as a comparison to the proposed approach. From the simulation and experimental results, we demonstrate that the proposed approach significantly outperforms other approaches. It is also evident from the Monte Carlo analysis that the proposed approach converges to the CRB.Accepted versio

Joint Gain/Phase and Mutual Coupling Array Calibration Technique with Single Calibrating Source

An iterative-based method for joint gain/phase and mutual coupling array calibration is proposed in this paper. It estimates the array gain/phase and mutual coupling coefficients with a set of simultaneous equations formed by using the beam pattern property of the array. Only one calibrating source with known direction is requiblue to obtain the unique estimate. The effectiveness of this approach is illustrated by simulation results and by experimental data collected with an antenna array operating in high-frequency radio band