Candidate: Hong Zhang
Advisor: Dr. Ali Abdi
Date: March 29, 2006 (Wednesday)
Time: 10:00 am
Location: 202 ECEC, NJIT

Abstract

Doppler spread, or equivalently, the mobile speed, is a measure of the spectral dispersion of mobile fading channel. Accurate estimation of the mobile speed is of importance in wireless mobile applications which require the knowledge of the rate of channel variations. Typically, these applications include handoff, adaptive modulation, equalization, power control, etc. In this proposal, we first investigate the problem of mobile speed estimation using diversity combining. Then we propose a nonparametric estimation technique, which is robust to different channel variations.

Two common diversity schemes, selection combining (SC) and maximal ratio combining (MRC), are considered for Doppler spread estimation. We derive four new estimators, which rely on the inphase zero crossing rate, inphase rate of maxima, phase zero crossing rate, and the instantaneous frequency zero crossing rate of the output of SC. We also propose two estimators which work based on the level crossing rates of the envelopes at the output of SC and MRC. The performances of all these estimators are investigated in realistic noisy environments with different kind of scatterings and different number of diversity branches. Our simulation results have revealed that a two-branch envelope level crossing rate estimator provides a performance gain. In terms of the implementation complexity, the SC-based estimator is superior to MRC, as it does not need channel estimation.

Then a novel speed estimation technique is proposed, applicable to both mobile and base stations, based on the special feature of the power spectrum of mobile fading channels. Our analytic performance analysis, verified by Monte Carlo simulations, shows that our low-complexity estimator is not only robust to both Gaussian and non-Gaussian noises, but also insensitive to nonisotropic scattering observed at the mobile. The estimator performs very well in both two- and three-dimensional propagation environments. The robustness against both nonisotropic scattering and line of sight can be further increased, by taking advantage of resolvable paths in wideband fading channels, due to the differences among the Doppler spectra observed at different paths. We also extend this technique to base stations with antenna arrays. By exploiting the spatial information, the proposed space-time estimator exhibits excellent performance over a wide range of noise power, nonisotropic scattering, and line-of-sight component, verified by simulation. The utility of the new method is further demonstrated by applying it to the measured data.

Committee Members

Dr. Ali Abdi, Advisor, Assistant Professor, NJIT

Dr. Yeheskel Bar-Ness, Distinguished Professor, NJIT

Dr. Alexander Haimovich, Professor, NJIT

Dr. Hongya Ge, Associate Professor, NJIT

Dr. Dmitry Chizhik, Member of Technical Staff, Bell Lab, Lucent Technologies