An approximate eigenmode decomposition for doubly-selective wireless channels

We consider block-based transmissions over doubly-selective wireless channels. It is well-known that orthogonal frequency division multiplexing decomposes linear time-invariant channels into a set of parallel (non-interfering) channels via a Fourier basis. In contrast, for time-varying channels, inter-channel interference occurs and may have a dramatic impact on the performance. Following a mean square error criterion, we propose an approximate eigenmode decomposition for linear time-varying channels, defined directly in the discrete-time domain. We show the effectiveness of the proposed waveform design by evaluating the mutual information (with Gaussian inputs) for doubly-selective terrestrial Rayleigh wireless channels.