One of the most important problems in helicopter satellite communications is the periodic blockage of the received signal caused by rotor blades. Code division multiplexing (CDM) has an implicit time diversity effect overcoming the periodic blockage. Performance of CDM employing Walsh-Hadamard code (WHCDM) under the periodic blockage environment is investigated in this paper. First, we show that a simple WHCDM scheme has the implicit time diversity effect by computer simulation. Next, a WHCDM scheme combined with explicit time diversity is proposed. The proposed scheme improves the bit error rate performance of the conventional time diversity scheme in high speed data transmission.
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