A Tight Upper Bound for Enhanced DCT-OFDM With Index Modulation

Orthogonal frequency division multiplexing (OFDM) with index modulation (IM) (OFDM-IM), which employs the activated sub-carrier indices to convey information, exhibits higher energy efficiency and lower peak-to-average power ratio (PAPR) than conventional OFDM systems. To further improve the throughput of discrete Fourier transform (DFT) based OFDM-IM (DFT-OFDM-IM), discrete cosine transform (DCT) based OFDM-IM (DCT-OFDM-IM) can be employed with double subcarriers given the same bandwidth. However, one of the main disadvantage of DCT-OFDM-IM is its lack of circular convolutional property over a dispersive channel. To address this issue, an enhanced DCT-OFDM-IM (EDCT-OFDM-IM) system has been proposed by introducing symmetric prefix and suffix at the transmitter and a pre-filter at the receiver leading to better performance than DFT-OFDM-IM in terms of bit error rate (BER). However, due to its special structure, it is difficult to derive the accurate average bit error probability (ABEP) upper bound, which is essential for the performance evaluation. In this paper, a tight ABEP upper bound is derived using the moment-generating-function (MGF). Our theoretical analysis is validated by simulation results and proven to be very accurate. Consequently the advantages of the EDCT-OFDM-IM system over the classic OFDM-IM system are further demonstrated analytically.