Differential space-time modulation (DSTM) using unitary-matrix signal constellations is an attractive solution for transmission over multiple-input multiple-output (MIMO) fading channels without requiring channel stat...
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Differential space-time modulation (DSTM) using unitary-matrix signal constellations is an attractive solution for transmission over multiple-input multiple-output (MIMO) fading channels without requiring channel state information (CSI) at the receiver. To avoid a high error floor for DSTM in relatively fast MIMO fading channels, multiple-symbol differential detection (MSDD) has to be applied at the receiver. MSDD jointly processes blocks of several received matrix-symbols, and power efficiency improves as the blocksize increases. But since the search space of MSDD grows exponentially with the blocksize and also with the number of transmit antennas and the data rate, the complexity of MSDD quickly becomes prohibitive. In this paper, we investigate the application of tree-search algorithms to overcome the complexity limitation of MSDD. We devise a nested MSDD structure consisting of an outer and a number of inner tree-search decoders, which renders MSDD feasible for wide ranges of system parameters. Decoder designs tailored for diagonal and orthogonal MM codes are given, and a more power-efficient variant of MSDD, so-called subset MSDD, is proposed. Furthermore, we derive a tight symbol-error rate approximation for MSDD, which lends itself to efficient numerical evaluation. Numerical and simulation results for different DSTM constellations and fading channel scenarios show that the new tree-search MSDD achieves a significantly better performance-complexity tradeoff than-benchmark decoders.
We propose a family of list-based soft demodulators for multiple-input-multiple-output (MIMO) communication systems based on a multistack algorithm for traversing the tree structure that is inherent in the MIMO demodu...
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We propose a family of list-based soft demodulators for multiple-input-multiple-output (MIMO) communication systems based on a multistack algorithm for traversing the tree structure that is inherent in the MIMO demodulation problem. The existing stack algorithm for MIMO soft demodulation stores a single stack of visited nodes in the tree and expands the stack using the "best-first" principle. In the proposed multistack algorithm, the single stack is partitioned into a stack for each level of the tree, and the algorithm proceeds by performing one best-first search step in each of these stacks in the natural ordering of the tree. By assigning appropriate priorities to the level at which this "best-first search per level" processing restarts once a leaf node has been obtained, the proposed demodulators can achieve tradeoffs between performance and complexity that dominate those of several existing methods, including the stack algorithm, in the low-complexity region.
The combination of differential space-frequency modulation (DSFM) with orthogonal frequency-division multiplexing (OFDM) is attractive for transmission over time- and frequency-selective multiple-input-multiple-output...
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The combination of differential space-frequency modulation (DSFM) with orthogonal frequency-division multiplexing (OFDM) is attractive for transmission over time- and frequency-selective multiple-input-multiple-output (MIMO) channels and detection without the need for channel-state information (CSI) at the receiver. It is well known that a simple differential detection already results in a high error floor for moderate time and frequency selectivities of the channel. A more sophisticated multiple-symbol differential detection (MSDD), which jointly processes multiple received symbols, overcomes this limitation, usually at the price of higher detection complexity. In this paper, we consider the DSFM for the MIMO-OFDM transmission and MSDD at the receiver. Inspired by previous work presented in literature, we devise a novel DSFM scheme, which makes use of spatial and/or spectral (multipath) diversity and is particularly suited for the MIMO-OFDM and power-efficient low-delay MSDD. We further investigate the application of a 2-D observation window to the MSDD (2-D MSDD) in order to exploit channel correlations in both time and frequency directions. We develop a representation of the detection problem that is amenable to tree-search decoding, whose application leads to a tremendous reduction in the MSDD complexity or a "fast" MSDD. An analytical approximation of the symbol-error rate of the 2-D MSDD for the MIMO-OFDM under spatially correlated fading is derived, which enables quick and accurate performance evaluations. Numerical and simulation results corroborate the efficacy of our approach and show that power efficiency close to that of a coherent detection with a perfect CSI is feasible in all standard fading scenarios at reasonable decoder complexity.
Sparse code multiple access (SCMA) is a promising code-domain non-orthogonal multiple access (NOMA) technique that supports high-level connectivity. Through the combination of SCMA and multiple-input multiple-output (...
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Sparse code multiple access (SCMA) is a promising code-domain non-orthogonal multiple access (NOMA) technique that supports high-level connectivity. Through the combination of SCMA and multiple-input multiple-output (MIMO) techniques, MIMO-SCMA schemes are capable of enhancing the overall spectral efficiency. This paper proposes novel MIMO-SCMA designs for both uplink and downlink Rayleigh fading channels. Rather than directly combining the SCMA and spatial multiplexing techniques presented in the previous literature, the proposed designs consider not only the frequency or time diversity, but also simultaneously include space diversity. Codebook design criteria for different transmission scenarios are respectively investigated, and a low-complexity codebook design algorithm is proposed based on the cross-entropy method. In addition, since the new designs suggest a dense factor graph, conventional message-passing algorithm (MPA)-based detectors are less suitable. Consequently, low-complexity MIMO-SCMA codeword detectors based on depth-first and breadth-first tree-search algorithms are respectively investigated. It is shown that the overall designs are able to simultaneously achieve a higher diversity order, enhanced BER results, and lower levels of detection complexity for both uplink and downlink scenarios, when compared to conventional MIMO-SCMA schemes.
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