DCT-assisted multicarrier modulation for next-generation wireless communications

Regarded as one of the most promising transmission techniques for future wireless communications, the discrete cosine transform based multicarrier modulation (DCT-MCM) system hold several inherited advantages over the discrete Fourier transform (DFT) based one (DFT-MCM). However, various technical challenges that hinder practical use of DCT-MCM need to be addressed, e.g., enhanced transceiver design and extensions into several important 5th Generation (5G) communication scenarios. The overall objective of the proposed research is to investigate some of the key practical challenges and optimise the receiver implementation of general DCT-MCM systems, by which effective solutions are proposed for different future wireless communication scenarios. First, an optimised transmitter structure for the pre-filtering based DCT-MCM system is established to improve the overall system performance. We therefore analyse the pre-filtering effect and investigate the output signal-to-noise ratio (SNR) gain among all subcarriers. Based on the derived instantaneous output SNR expression, the minimum-mean-square-error (MMSE) and maximum likelihood (ML) detections are re-designed to effectively compensate the coloured noise effect after pre-filtering at the receiver. Second, we give the system model and performance analysis for the pre-filtering based DCT-MCM system in the presence of transceiver imperfections. In particular, an analytical expression in terms of desired signal, ICI and inter-symbol interference (ISI) is presented by considering carrier frequency offset (CFO), timing offset (TO) and insufficient guard sequence between symbols. In order to compensate for these imperfections, an advanced technique called zero forcing based (ZF-based) iterative channel detection algorithms are proposed to provide significant gain compared with conventional detection methods in terms of BER performance. Third, in order to render the DCT-MCM applicable to multiple-input multipleoutput (MIMO) systems, we trace back to the zero-padding based implementation method for DCT-MCM. Based on the double number of de-multiplexed symbols, we reformulated three effective detection algorithms to maximise the performance gain. Among of the three, we found that the equal gain combining (EGC) based algorithm could successfully achieve the signal transmission on DCT-MCM in MIMO scenarios without interference introduced. Finally, an enhanced structure of DCT-MCM with index modulation (IM) technique (which is called the EDCT-OFDM-IM) is proposed to further increase the spectral efficiency as well as its bit-error rate (BER) performance. Based on the approximate pairwise error probability, a theoretical upper bound on the average bit-error probability of EDCT-OFDM-IM is derived in closed form over frequency-selective Rayleigh fading channels. The achievable performance of our proposed EDCT-OFDM-IM scheme is analysed from several aspects including the spectral efficiency, corresponding Euclidean distance (ED), the peak-to-average power ratio (PAPR) value and its robustness against frequency offset. We demonstrate that the DCT-OFDM-IM scheme is comparable with the DFT-OFDM-IM counterpart in terms of PAPR but is more robust to the ICI effect.