Multi-carrier faster-than-Nyquist (MC-FTN) signalling, which is a non-orthogonal data transmission scheme, is broadly viewed as one of the potential candidates for the future high spectral-efficient communications. In...
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Multi-carrier faster-than-Nyquist (MC-FTN) signalling, which is a non-orthogonal data transmission scheme, is broadly viewed as one of the potential candidates for the future high spectral-efficient communications. In this study, a discrete time-frequency packing scheme based on the discrete Fourier transform (DFT) block transmission for MC-FTN signalling (DBT-MC-FTN) is proposed. Firstly, by transforming the blockwise MC-FTN signalling into the frequency domain, an efficient implementation transceiver structure incorporating a bank of DFTs, circular expanding operation, and cyclic shift summation operation is obtained. Thus, flexible packing in both time and frequency domains can be achieved efficiently within a DBT-MC-FTN block. Secondly, to deal with the inter-symbol interference (ISI) introduced by time packing and inter-carrier interference (ICI) introduced by frequency packing in the proposed DBT-MC-FTN scheme, a subcarrier-level equalisation combined with a soft interference cancellation scheme operated in the frequency domain is further proposed to detect the DBT-MC-FTN signals at the receiver. Simulation results show that the proposed DBT-MC-FTN scheme performs close to the corresponding orthogonal system with negligible bit error rate performance loss in the case of moderate ISI and ICI. Additionally, the post-processing signal-to-interference-plus-noise ratio of the proposed scheme is also given in detail.
An uplink direct sequence spread spectrum communications systems employing a multi-sequence model over a quasi-static frequency-selective fading channel is considered. In analogy with bit-interleaved coded modulation ...
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An uplink direct sequence spread spectrum communications systems employing a multi-sequence model over a quasi-static frequency-selective fading channel is considered. In analogy with bit-interleaved coded modulation (BICM) technique, a group of bits at the output of a bit-wise interleaver is mapped uniquely to a complex signalling vector belonging to an orthogonal plane sequence modulation signal space, which is constructed over a set of expanded signature sequences. This transmission system provides not only bandwidth efficiency offered by additional signal planes but also time diversity resulting from the BICM technique. It is observed that at high system traffic load error performance could degrade substantially due to user cross-correlations, multi-access asynchronism as well as channel frequency selectivity. The authors employ a 'turbo principle' receiver, consisting of a soft interference cancellation scheme, soft demappers and maximum a posteriori decoders, to avert this capacity loss by exploiting the serially concatenating structure at the transmitter. After simple mathematical manipulation, a soft space-time linear minimum mean-square error multi-user detector could even be explored on the basis of per signal plane per user. Both analytical performance-bound and computer simulation of the proposed framework in terms of bit-error rate (BER) are revealed. Further, performance comparisons with convolutionally coded and conventional bandwidth-efficient coded direct sequence code division multiple access systems under the same system conditions are illustrated. The authors have also investigated the impact of labelling maps on the BER performance.
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