A Study on Modified Walsh-Hadamard Code Division Multiplexing with Enhanced Anti-Periodic-Blockage Capability

In helicopter satellite communications, the periodic blockage (PB) of the transmission channel occurs due to rotor blades. Modified Walsh-Hadamard code division multiplexing (MWHCDM) is suitable for helicopter satellite communications because it has the anti-PB capability, corresponding to 2-branch time diversity. This paper proposes MWHCDM with enhanced anti-PB capability. The proposed MWHCDM implicitly performs 4-branch time diversity processing through multiplexing by trading off with spectral efficiency. Computer simulations show that the proposed MWHCDM achieves excellent bit error rate (BER) performance close to the lower bound in the PB channel with zero-forcing (ZF) and minimum mean square error (MMSE) detection. As a result, the proposed MWHCDM outperforms the conventional MWHCDM and the simple (non-multiplexed) 4-branch time diversity.