Impact of Constellation and Index Mapper Selection in OFDM-IM Systems

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) offers significant flexibility to address the diverse communication scenarios of 5G and beyond. However, the selection of an appropriate index mapper remains an unresolved issue that could pose challenges to the standardization of OFDM-IM. Through the evaluation of a specific example in this paper, it is observed that without optimizing the index mapper, a performance loss of approximately 0.7 dB (SNR gain) may occur. Additionally, we discovered that the optimized index mapper can be universally applied to various constellations, despite OFDM-IM exhibiting sensitivity to subcarrier power variations.

I. Introduction

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) [1] is a promising technology for next-generation wireless communication. It offers high flexibility in transferring spectral and energy efficiency while maintaining compatibility with current popular OFDM specifications [2], [3]. However, most of the existing literature on OFDM-IM did not describe the design details of an index mapper. optimizing the index mapper is crucial as it can improve the bit error rate (BER) performance without increasing computational complexity [4]. Therefore, selecting a specific index mapper for IM bit detection is essential for standardizing OFDM-IM. This paper investigates a typical OFDM-IM system and evaluates the impact of applying different constellations and index mappers on BER performance. We present numerical results and summarize the observations, highlighting the importance of choosing the appropriate mapping scheme. In addition, we provide insights for future research directions to mitigate the observed impact and enhance the overall performance of OFDM-IM systems.