ISI-reduced modulation over a fading multipath channel

The idea of using the channel eigenvectors as the basis for a block based signaling scheme over a fading multipath channel is introduced. This basis minimizes the product of the average fading attenuations along different dimensions. The ISI from the preceding blocks (intra-block ISI) is modeled by an additive Gaussian noise. To reduce the effect of the intra-block ISI, a number of zeros are transmitted between successive blocks. The number of zeros is optimized to minimize the average probability of error. As the transmission of zeros reduces the bandwidth efficiency, this optimization procedure is more useful for lower bit rates. By applying quadrature amplitude modulation (QAM) to each dimension, a set of two-dimensional subchannels with unequal fadings is obtained. A coherent M-PSK constellation is employed over each QAM subchannel. The authors propose two methods to distribute the rate and energy between the subchannels