Maximum likelihood decoding for wavelet packet modulation

The multi-carrier modulation (MCM) technique is an attractive approach for high-speed digital radio communication systems in order to achieve a high spectral efficiency and to combat the frequency selectivity of the channel. Orthogonal frequency division multiplexing (OFDM) is a kind of MCM technique. Wavelet packet modulation (WPM) is another kind of MCM technique using the wavelet transformation instead of the Fourier transformation to multiplex information symbol sequences. In this paper we propose a maximum likelihood decoding method for WPM without coding before transmitting the signal. The proposed method performs maximum likelihood sequence estimation by utilizing a signal obtained in an intermediate stage of the demultiplexing process. Then, bit error performance under a flat fading channel and frequency-selective fading channel is evaluated by computer simulation. According to the results, the proposed method can improve the bit error performance in the region of high Doppler frequency