A novel turbo coded modulation scheme, called the turbo-APPM, for deep space optical communications is proposed. The proposed turbo-APPM is a serial concatenation of turbo codes, an accumulator and a pulse position modulation (PPM), where turbo codes act as an outer code while the accumulator and the PPM act together as an inner code. The generator polynomial and the puncturing rule for generating turbo codes are chosen to lower the bit error rate. At the receiver, the joint iterative decoding is performed between the inner decoder and the outer turbo decoder. In the outer decoder, local iterative decoding for turbo codes is conducted. Simulation results are presented showing that the proposed turbo-APPM outperforms all previously proposed schemes such as LDPC-APPM, RS-PPM and SCPPM reported in the literature.

This letter proposes an initial frame synchronization algorithm for orthogonal frequency division multiplexing (OFDM) systems. Since the proposed scheme utilizes only the cyclic prefix and the phase shift of the demodulated data without the aid of any known signals, it can be applied not only at the beginning of data transmission but also at any instant during transmission. The performance of the proposed algorithm is confirmed by computer simulation for QPSK, 8-PSK, and 16-QAM systems.