Coded modulation with non-standard signal sets for wireless OFDM systems

Abstract

This paper proposes a scheme that trades complexity for increased diversity and a reduction in the peak-to-mean envelope power ratio (PMEPR) in wireless orthogonal frequency division multiplexing (OFDM) systems. The key idea is to employ non-standard signal sets with small dimension matched to the OFDM framework; these signal sets are chosen to maximize the diversity of an uncoded system under a constraint to control the system PMEPR. These signal sets allow coded modulation schemes to achieve diversity equal to the product of the Hamming distance of the scheme and the frequency diversity of the channel, while still allowing optimal combined equalization/decoding of reasonable complexity in symbol-interleaved (as opposed to bit-interleaved) coded modulation schemes. Numerical results are presented both for systems employing uncoded modulation and for systems employing bit-interleaved coded modulation (BICM). We conclude that the proposed BICM system can be viewed as a hybrid of a coded OFDM system and a coded single-carrier system employing a soft-output equalizer, thus providing the system designer a possible implementation for the correct combination of the two systems for a given application.