Abstract: For a wide band ground-air communication system with a low elevation antenna, the channel is of severe multi-path fading, whereas its characteristic is quite different from that of a terrestrial mobile communication channel. In this case, the OFDM technique is considered to be unsuitable, so that a channel model is established and a new scheme based on orthogonal code division multiplexing (OCDM)combined with block coding is proposed. Theoretical analysis and simulation results show that the proposed system can suffer so great a multi-path delay up to dozens of symbol periods, and has very good BER performance even when the Rice fading factor reaches6～7dB. The system can obtain as high a band efficiency as a non-spectrum-spreading system since it realizes OCDM based on M-ary spectrum spreading of multi-level PN codes. Compared with a corresponding OFDM system, it has better adapting capability to dynamic variation of the channel because of its shorter symbol period. Besides, it has low implementation complexity since channel estimation or equalization is not necessary. It has a good potential in wide band ground-air communication applications.

Key words: ground-air communication, code division multiplexing, block coding, multi-path fading