Maximizing Data Rate of Discrete Multitone Systems Using Time Domain Equalization Design

Mr. Milos Milosevic

Department of Electrical and Computer Engineering
The University of Texas at Austin, TX, USA

Thursday, April 17th, 8:00 AM, ENS 637

milos@ece.utexas.edu

Abstract

Asymmetric Digital Subscriber Line in its standardized versions G.DMT and G.Lite and Very-high-speed DSL use discrete multitone modulation (DMT) for data transmission. Orthogonal Frequency Division Multiplexing is a similar modulation standard for wireless transmission that has been adopted in IEEE802.11a, Digital Video Broadcasting and HYPERLAN/2. The transmission channel induces inter-symbol (ISI) and inter-carrier interference (ICI) along with other noise sources. The traditional DMT or OFDM equalizer is a cascade of a time domain equalizer (TEQ) as a single finite impulse response filter, a fast Fourier transform (FFT) multicarrier demodulator, and a frequency domain equalizer as a one-tap filter bank. The TEQ shortens the transmission channel impulse response to mitigate ISI/ICI. Previous TEQ design methods optimize objective functions not directly tied to system bit rate. The author presents TEQ filter bank design that maximizes the bit rate of a DMT or OFDM system at the output of the FFT demodulator. To achieve that goal, the author develops a subchannel Signal-to-Noise Ratio (SNR) model based a circularly convolved data symbol and the channel impulse response at the input of the demodulating FFT block and includes the effects of near-end crosstalk, additive white Gaussian noise, analog-to-digital converter quantization noise and the digital noise floor due to finite precision arithmetic. Using the subchannel SNR model, the author derives the nonlinear dependency of the system bit rate on TEQ coefficients. The author arrives at the optimal time domain per-tone TEQ filter bank (TEQFB) and proposes a novel receiver architecture that uses TEQFB and Goertzel filter bank demodulator at the receiver during data transmission. Also developed is an iterative fractional programming algorithm that produces a single TEQ that achieves on average more than 99% of the performance of TEQFB.

A list of Wireless Networking and Communications Seminars is available at from the ECE department Web pages under "Seminars". The Web address for the Wireless Networking and Communications Seminars is http://signal.ece.utexas.edu/seminars