Design considerations of a new HF modem and performance analysis

A new 12.8 kbps high frequency (HF) modem is presented in this paper. To gain the low bit error rate (BER) in frequency-selective fading channels, this modem adopts a set of new technologies, including orthogonal frequency division multiplexing (OFDM) and space time block code (STBC). Extensive BER performance comparison between turbo code, low density parity check (LDPC) code, and punctured convolutional code have been made to determine which combination of technologies can achieve better performance while maintaining low complexity. Furthermore, theoretical analysis is presented for the BER performance hi two typical systems: the two transmit antennas and two receivers (2Tx/2Rx), two transmit antennas and a single receiver (2Tx/1Rx) in CCIR defined poor channel. Simulation results show that the performance of our new modem can be significantly improved. Compared to the conventional OFDM system, the 2Tx/1Rx system has achieved 3-10 dB diversity gain, while the 2Tx/2Rx system yields 4-15 dB