Channel Estimation and Bit Loading for WPM with Time-Domain MMSE Equalization

Abstract

Wavelet Packet Modulation (WPM) is a Multi-Carrier Modulation (MCM) technique considered as a possible substitute for Orthogonal Frequency Division Multiplexing (OFDM). Unlike OFDM, symbols of WPM overlap in the time domain, preventing the use Cyclic Prefix (CP) for equalization. This paper uses Minimum-Mean Square Error (MMSE) equalization for WPM considering unknown Channel State Information (CSI). A channel estimation method is proposed based on solving an overdetermined system of linear equations. The Channel Impulse Response (CIR) is estimated using a training sequence. The estimated CIR is used for bit loading that considers limitations of MMSE equalization such as noise amplification and signal attenuation. Numerical results based on quasistatic channels with Rayleigh fading demonstrate that the Bit Error Rate (BER) for WPM is lowered with the proposed bit loading. In addition, with unknown CSI, WPM with bit loading outperforms OFDM with bit loading.