Improved Eigenfilter Design Method for Channel Shortening Equalizers for DMT Systems

In this paper, we propose an improved eigenfilter design method for time domain equalizer (TEQ) design for discrete multitone (DMT) systems. In conventional DMT systems, TEQs used tend to introduce spectral nulls which degrade the achievable signal-to-noise ratio at the corresponding subcarriers. As a result, bandwidth efficiency decreases. Tkacenko and Vaidyanathan recently proposed a low-complexity eigenfilter method which though performs nearly optimally in terms of observed bit rate but suffers performance loss due to spectral attenuation. We present a joint cost function which, along with good channel shortening, avoids spectral nulls in the useful signal band. Simulation results show that our method allows more subcarriers to carry bits and thus outperforms conventional eigenfilter method in terms of achievable bit rate. We also propose a heuristic choice of optimal transmission delay which yields profitable bit rate performance.