Novel hybrid modulation scheme for pilot-assisted block transmission technology

When PABT (Pilot-Assisted Block Transmission) signal is transmitted over severe multipath channels, consecutive pilot block and data block may partially overlap each other. If no guard interval is inserted between them, a process to cancel the mutual interference is usually adopted in the receiver. But this process, as well as channel equalization, may suffer severe performance degradation when channel estimation is not so reliable. A hybrid modulation scheme is proposed in this paper, in which the overlapped part in data block is modulated using lower order constellation, while the other part keeps using higher order constellation. Its advantage in BER performance and robustness over conventional PABT schemes is demonstrated with simulation in some multipath channels with large delay spread.