Adaptive bit and power allocation for dual mode index modulation based OFDM system

Abstract

Orthogonal frequency division multiplexing (OFDM) along with index modulation (IM) is a promising technique for wide applications that can enhance the spectral efficiency (SE) and simultaneously able to mitigate the harmful effects of dispersive wireless channels. The IM technique utilizes an additional dimension to transmit information in terms of determining whether the OFDM subcarrier is active or inactive. In OFDM-IM system, only active subcarriers carry the modulated data symbol while inactive subcarriers remain empty. The concept of dual-mode (DM) OFDM-IM has been proposed to increase the SE with data transmission through inactive subcarriers employing different constellation alphabets with the same modulation order. In DM-OFDM-IM, all the symbols are modulated with a fixed modulation scheme which provides a constant SE over all the channel conditions. In adaptive DM-OFDM-IM, the modulation order for each subblock of OFDM subcarriers is decided according to the instantaneous received signal to noise ratio (SNR) to improve the bit error rate (BER) performance for enhanced SE. In this work, an idea of simultaneous adaptive bit and power loading (BPL) in DM-OFDM-IM system has been provided in which the information bits and power are allocated for each subblock satisfying both target BER of the system and the total transmission power constraints. The numerical results illustrate that adaptive BPL based DM-OFDM-IM system provides a significant gain in SE for the same BER performance as compared to the conventional DM-OFDM-IM system.