Noncoherent Communication over the Doubly Selective Channel via Successive Decoding and Channel Re-Estimation

For noncoherent communication over fading channels, pilot-aided transmission is a practical scheme which allows the receiver to compute channel estimates for subsequent use in coherent decoding. We propose an improved scheme whereby the transmitter interleaves several pilot substreams with independently-coded data substreams to facilitate successive decoding and channel re-estimation at the receiver. In particular, an initial pilot-aided channel estimate is used to coherently decode the first data substream, which is then used to refine the channel estimate before coherently decoding the next data substream, and so on. Assuming knowledge of the channel statistics, the pilots and the rates of the data substreams can be chosen to ensure reliable decoding. While similar schemes have been proposed for channels that are either time-selective or frequency-selective, ours is focused on doubly selective channels. We derive a lower bound on the achievable rate of our strategy and further characterize the achievable rate at high SNR. When the channel satisfies a complex-exponential basis expansion model, we show that the pre-log factor of the high-SNR achievable rate expression coincides with that of the ergodic capacity expression. For the same channel, we propose a pilot/data power allocation strategy that maximizes a lower bound on the achievable rate.