Progressive receiver design for underwater acoustic OFDM communications.

摘要

Multicarrier modulation in the form of orthogonal-frequency-division-multiplexing (OFDM) has been intensively pursued for underwater acoustic (UWA) communications recently due to its ability to handle long dispersive channels. However, there are still a lot of challenges when it comes to practical receiver design, such as: How to design a robust receiver to deal with the fast variation of UWA channels? How to initialize the channel estimation with small pilot overhead? How to handle the distributed multiple-input and multiple-output (MIMO)-OFDM in which there exist multiple Doppler scales? This dissertation will answer these issues, and consists of the following three parts:;• Progressive receiver design for OFDM transmission over time-varying UWA channels: Fast variation of UWA channels due to environmental variations such as wind speed, wave height, and the motion of the transceiver platforms destroys the orthogonality of the sub-carriers and leads to inter-carrier interference (ICI), which degrades the system performance significantly. The first part of this dissertation proposes a progressive receiver to deal with time-varying UWA channels which can adapt to different channel conditions in an automatic fashion, i.e., enjoying low complexity in good channel conditions while maintaining excellent performance in adverse channel conditions. Furthermore, we extend the progressive receiver to the multiple transmitter settings, in which both the ICI and co-channel interference (CCI) will be considered explicitly in the MIMO-OFDM progressive receiver design.;• Robust channel initialization for progressive receivers: Operating on a block-by-block basis, the progressive receiver is initialized by measurements on pilot subcarriers inserted in each OFDM block. However, a certain number of pilots is needed to get the satisfactory initialization quality, which reduces the spectral efficiency. By analyzing the real experimental data, we find that the channel correlations between adjacent OFDM blocks can be exploited. The second part of this dissertation investigates a robust initialization method to reduce the pilot overhead while still maintaining the robust performance of the progressive receiver. The basic idea is to leverage the block-adaptive approach that exploits channel correlation between adjacent OFDM blocks, and combine it with pilot-based channel estimation to robustly initialize the progressive receiver.;• Iterative receivers for distributed MIMO-OFDM over UWA channels: A distributed multi-user setting is investigated in which different users have different mobilities. In that case, the conventional UWA OFDM receivers have poor performance as they assume one common dominant Doppler scale for all users. The third part of this dissertation will focus on the iterative receiver design for the distributed MIMO-OFDM systems, and report extensive performance results with experimental data.