Analysis of symbol mapping based on BICM-ID for FM IBOC

Hybrid in-band on-channel (IBOC) broadcasting system as a scheme of digital audio radio could transmit analog FM and digital audio simultaneously. In IBOC systems, broadcasters transmit signals within the allocated channel bands, thus the bandwidth assigned for digital audio transmission is very challenging. BICM-ID can improve BER performance over Rayleigh fading channels without bandwidth expansion, thus it is used in FM IBOC and has been verified it can yield a better coding gain. However, conventional IBOC systems apply Gray mapping as symbol mapping scheme, which can not take full advantage of iterative effects compared with larger diversity mappings such as SSP and MSP mappings. In this paper, various symbol mappings based on transfer functions and harmonic mean of the minimum Euclidean distance are compared and analyzed. Simulation results show that advanced mapping scheme can effectively improve the performance of BICM-ID FM IBOC. When BER is below 10^-4, SSP labeling scheme can achieve more than 3dB coding gains over Rayleigh fading channels compared with the conventional mapping scheme.