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Inter-Code Interference Reduction in Walsh-Hadamard Code Division Multiplexing for Helicopter Satellite Communications

In helicopter satellite communications, where rotor blades periodically block the transmission channel, Walsh-Hadamard code division multiplexing (WHCDM) is attractive because of its implicit time diversity effect overcoming the periodic blockage. However, inter-code interference (ICI) due to various factors decreases the implicit time diversity effect. This paper addresses reducing of ICI caused by the periodic blockage in WHCDM. As ICI reduction methods, the explicit time diversity with maximal ratio combining (MRC), zero-forcing (ZF), and minimum mean square error (MMSE) are investigated. The computer simulation shows that the three methods are effective for reducing the ICI. We also confirm that MMSE is superior to MRC and ZF in terms of BER performance.