ITR: Design of Novel Receiver Algorithms for OFDM Incorporating Realistic Indoor Channel Modeling

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

The explosive demand for communication services, fueled by the rapid growth in the areas of mobile communications and the Internet, has generated and will continue to generate immense research efforts in the area of wideband wired/wireless communications. To accommodate the demanding future applications, systems must be designed to perform joint equalization, detection, decoding and estimation of the unknown and possibly time varying channel parameters, while maintaining reasonable complexity (and low cost). Motivated by these requirements, and using an OFDM indoor wireless system as a design example, two main directions are investigated in this project. In the first direction, receiver algorithms are designed for iterative, joint equalization, detection and decoding, that address the critical issues mentioned above. The investigation starts by identifying a powerful model that encompasses all the salient features of the OFDM transmission system. Data detection in OFDM is then stated as a problem of two-dimensional (2D) data detection in the presence of localized, 2D intersymbol interference, non-linear distortion, and unknown and time varying parameters. We then identify fast, joint data detection and channel estimation schemes which are utilized as building blocks for powerful adaptive iterative detection receivers. Unlike the entire iterative receiver, these sub-blocks are optimal in a precisely defined sense, and can be implemented with less-than-exponential complexity with respect to the data sequence length. The second direction is the development of a unified framework for the analysis of the transient and steady-state behavior of adaptive iterative algorithms. In the proposed study, the receiver is assumed to have no explicit knowledge about the channel parameters, other than their statistical description. The minimum signal-to-noise ratio required for convergence to error-free transmission, and the optimal allocation of power in pilot and coded symbols, are some of the issues that are investigated for a wide variety of adaptive iterative receiver architectures. Regarding propagation modeling for the indoor environment, the approach followed herein is a direct divergence from the classical approaches that include either measurements, or the well-established ray-tracing techniques. In particular, ultra-fast algorithms for the numerical solution of the electromagnetic problem are developed. These algorithms result in almost exact solutions that can be evaluated with complexity comparable to the less accurate ray-tracing techniques.