Low Complexity OFDM-IM Detector by Encoding All Possible Subcarrier Activation Patterns

In orthogonal frequency division multiplexing with index modulation (OFDM-IM), the use of a maximum likelihood (ML) detector becomes impractical for large number of subcarriers per subblock, due to its exponentially growing detection complexity. Lower complexity detectors determine the received subcarrier activation pattern (SAP) through detecting the state of the subcarriers by thresholding. These detectors suffer from errors due to the possibility of detecting an invalid SAP since not all of the possible SAPs are used in OFDM-IM. In this letter, it is proposed to exploit all of the possible SAPs to convey data to neglect the possibility of detecting invalid SAPs. The proposed scheme together with a low complexity SAP detector results in a low-complexity (LC)-OFDM-IM. An approximate analytical expression is derived for the BER of the proposed LC-OFDM-IM system. Simulation of the LC-OFDM-IM and an OFDM-IM with a ML detector show that they are almost equivalent in terms of BER performance. The results and the features of the LC-OFDM-IM suggest it as a candidate alternative to conventional OFDM-IM.