Wireless Communication Systems Based on DCT-OFDM with Index Modulation
Creators: name: CAO, AIJUN
Publisher: name: University of Surrey
Year: 2022

description: "Conventional DFT-based OFDM has been widely used in the industry from wired communications to wireless communications, providing higher and higher data through- put together with other techniques. However, along with emerging of a new territory called vertical market, where low power, low costs, robustness to imperfections and huge amount of connected devices etc., become the new critical focus and challenges, DFT-OFDM may not be the most efficient solution to handle these challenges. Instead, a new variant which is DCT based seems more suitable for the demands while holding inherited advantages of DFT-OFDM as one of multi-carrier modulation forms. The variant needs to be constructed where both prefix and suffix are added at the transmitter in order to keep circular property of the transmit signal, and an optimum receiver can be designed with a prefilter to enable a one-tap equalizer and followed by a maximum-likelihood (ML) receiver, resulting in the so-called EDCT-OFDM. And several benefits of the EDCT-OFDM are justified compared with its conventional counterpart, such as doubled number of the subcarriers in the same bandwidth, better BER performance, lower complexity, and robustness to frequency offset etc.
description: And the variant can be further improved by exploiting the so-called index modulation techniques, i.e., EDCT-OFDM-IM, by creating a new dimension to convey information. In addition to the advantages of EDCT-OFDM over the conventional OFDM systems, EDCT-OFDM-IM reduces its PAPR and achieves a robust performance enhancement. These merits enable its perfect application scenario, i.e., machine-type communications in the vertical market. Due to its special structure, it is difficult to derive the accurate bit error probability upper bound, which is the essential for the performance evaluation. However, we cross the hurdle by using a method called the moment-generating-function (MGF) and a tight upper bound is derived theoretically. The analysis is validated by simulation results and proven to be very accurate.
description: Since the main potential target application scenarios of the DCT-based OFDM variant is for machine-type communication in the vertical market, low cost and low power consumption at the end devices is the main focus and most critical demand. However, at the downlink direction, a bit more complex scheme may be exploited in the BS transmitter because the pressure from a long battery life and a low cost is set to the devices, therefore, employing transmit diversity is desirable at the downlink direction, and this motivates us to study on enhancements such as the transmit diversity applied to EDCT-OFDM-IM. Our studies have identified a harmonised combination of index modulation and transmit diversity, resulting in a novel supplementary index bit aided transmit diversity (SIB-TD) approach. Both theoretical analysis and simulation results demonstrate that the proposed scheme is capable of providing significant performance gains over the conventional EDCT-OFDM-IM, even under the imperfect channel estimation."