Synergy/Perforation Control for 16-QAM in Orthogonal Code Hopping Multiplexing

Orthogonal code hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to accommodate a large number of allowable downlink channels in code division multiple access (CDMA) systems. However, OCHM may yield a worse bit error rate (BER) performance than the conventional CDMA systems due to code collisions. Therefore, a synergy/perforation operation, which is a control scheme for mapping code-colliding modulation symbols to specific constellation points on the - plane, is needed to compensate for BER degradation, and this synergy/perforation operation should be defined separately with modulation types. Previously, synergy/perforation control schemes for quadrature phase shift keying (QPSK) and binary phase-shift keying (BPSK) have been proposed, but there has been no study of 16-quadratic-amplitude modulation (16-QAM) in OCHM. We propose two synergy/perforation control schemes for 16-QAM in OCHM and a log-likelihood ratio conversion scheme for 16-QAM in OCHM. The proposed control schemes are evaluated by an analytical approach and simulations and are compared to the previous scheme for QPSK modulation. We show that the proposed control scheme has a performance similar to that of QPSK modulation in terms of the mean synergy ratio for code-colliding modulation symbols and additional required .