Multiresolution acquisition scheme for the physical layer design of a direct sequence spread spectrum transequatorial HF ionospheric data link

This study presents the final implementation of a multiresolution acquisition structure, designed and tested for a long-distance ionospheric High Frequency link from Antarctica to Spain. It completes the receiver's physical layer design for this link of 12,760 km, improving the performance of the communications system. The goals of this proposal are to achieve a faster convergence, as well as a more robust and stable acquisition and demodulation. The multiresolution structure is based on least mean square adaptive filters. Acquisition is achieved when a filter converges to a decimated version of the Pseudo-Noise sequence. Convergence parameters have been adjusted for best performance in the long-haul time variant ionospheric channel. The information about channel's multipath dispersion is used to improve the direct sequence spread spectrum demodulation at the receiver. The results presented in this study are obtained from real data transmitted through the ionospheric Antarctic channel in the austral summer of 2008 and show the improvements in terms of stability, robustness and Bit Error Rate in the receiver. These improvements led us to choose this multiresolution acquisition structure for the receiver of the Antarctic HF system.