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Among various massive multiple-input multiple-output (MIMO) signal detection schemes, expectation propagation (EP) achieves superior performance in high-dimensional systems with high-order modulations and flexible antenna configurations. However, the inevitable matrix inversion in each iteration of EP brings unbearable computational burden, which hinders the efficient implementation. Several reduced-complexity variants of EP are proposed recently, which effectively alleviate the computational cost but at the expense of unacceptable performance loss. In this paper, a low-complexity massive MIMO detection is first proposed based on approximate EP, which relieves the computational complexity of the exact EP while maintaining the good performance. Particularly, the EP moment matching equations are reformulated to simplify the sequential updating procedure. In addition, an approximation based on the channel-hardening phenomenon is proposed to eliminate the matrix inversion at each iteration. Numerical results show that, for high-dimensional MIMO the proposed detector approaches the exact EP in term of bit-error-rate (BER) by a small number of iterations. No matter with symmetric or asymmetric antenna configuration, it outperforms other EP variants, Gaussian tree approximation, and channel-hardening exploiting message passing. An analysis of computational complexity reveals the high efficiency of the proposed detection compared to the state-of-the-art with flexible antenna configurations. [ABSTRACT FROM AUTHOR]

This paper presents an efficient combined bit-flipping (BF) and stochastic low-density parity-check decoder, where a BF decoder is used to achieve a reduction in decoding cycles. A node-wise probability tracer is adopted at each variable node (VN) in order to achieve a BER performance comparable to the normalized min-sum algorithm, where check-to-variable (C2V) messages are used as inputs, rather than the variable-to-check (V2C) messages adopted in previous stochastic decoders. The complexity of the VN units is greatly reduced by sharing common units used in the generation of V2C messages together with a probability tracer. The C2V-based probability tracer enables the design of a decoder that provides a short critical path. The proposed methods are demonstrated by designing a (2048, 1723) decoder that is implemented in a 90 nm process. A total of 1460 K logic gates are integrated in a decoder that has an area of 4.12 \mboxmm^2 and achieves a coded throughput of 39.3 Gb/s at a clock frequency of 749 MHz. To the best of the authors’ knowledge, the proposed decoder achieves the best normalized throughput-to-area ratio among the stochastic decoders reported in the open literatures. [ABSTRACT FROM AUTHOR]

This paper presents a maximum mutual information increase (M^2I^2)-based algorithm that can be used to arrange low-density parity-check (LDPC) decoding schedules for faster convergence, where the increase is used to guide the arrangement of the fixed decoding schedule. The predicted mutual information for the messages to be updated is used in the calculation of the increase. By looking ahead for several decoding stages, a high-order prediction can be realized, which can then be used to devise a schedule with an even faster convergence. For a single received frame, different decoding results can be obtained using different schedules, and, hence, schedule diversity, that lowers the error floor resultant from the dominant trapping sets, is proposed. By adopting the M^2I^2-based schedule together with the schedule diversity, both the convergence speed in the waterfall region and the error-rate in the floor region can be improved. [ABSTRACT FROM AUTHOR]

In this paper, we investigate differential amplitude/phase modulation (APM) schemes for correlated Rayleigh fading channels. Considering the noncoherent maximum-likelihood receiver, a theoretical pairwise error probability (PEP) formula for differential signal vectors with arbitrary power values is derived. The design criterion for the signal set of differential vectors is then proposed based on the asymptotic analysis of the PEP. For both uncoded and coded APM schemes, the design criteria and optimization procedures for bit labeling rules are investigated. The designed differential APM schemes are shown to provide significant improvement in bit-error-rate performance, particularly in the error-floor regions. [ABSTRACT FROM PUBLISHER]

This paper presents a high-throughput decoder architecture for non-binary low-density parity-check (LDPC) codes, where the q-ary sum-product algorithm (QSPA) in the log domain is considered. We reformulate the check-node processing such that an efficient trellis-based implementation can be used, where forward and backward recursions are involved. In order to increase the decoding throughput, bidirectional forward-backward recursion is used. In addition, layered decoding is adopted to reduce the number of iterations based on a given performance. Finally, a message compression technique is used to reduce the storage requirements and hence the area. Using a 90-nm CMOS process, a 32-ary (837,726) LDPC decoder was implemented to demonstrate the proposed techniques and architecture. This decoder can achieve a throughput of 233.53 Mb/s at a clock frequency of 250 MHz based on the post-layout results. Compared to the decoders presented in previous literature, the proposed decoder can achieve the highest throughput based on a similar/better error-rate performance. [ABSTRACT FROM PUBLISHER]

When residual belief-propagation (RBP), which is a kind of informed dynamic scheduling (IDS), is applied to low-density parity-check (LDPC) codes, the convergence speed in error-rate performance can be significantly improved. However, the RBP decoders presented in previous literature suffer from poor convergence error-rate performance due to the two phenomena explored in this paper. The first is the greedy-group phenomenon, which results in a small part of the decoding graph occupying most of the decoding resources. By limiting the number of updates for each edge message in the decoding graph, the proposed Quota-based RBP (Q-RBP) schedule can reduce the probability of greedy groups forming. The other phenomenon is the silent-variable-nodes issue, which is a condition where some variable nodes have no chance of contributing their intrinsic messages to the decoding process. As a result, we propose the Silent-Variable-Node-Free RBP (SVNF-RBP) schedule, which can force all variable nodes to contribute their intrinsic messages to the decoding process equally. Both the Q-RBP and the SVNF-RBP provide appealing convergence speed and convergence error-rate performance compared to previous IDS decoders for both dedicated and punctured LDPC codes. [ABSTRACT FROM AUTHOR]

In this paper, we investigate noncoherent transmission schemes using amplitude/phase modulation. For uncoded transmission schemes, we derive the pairwise error probability (PEP) and its high-SNR approximation for signal vectors with unequal power values using a noncoherent maximum-likelihood detector under Rayleigh block fading channels. For coded transmission schemes, we consider differential amplitude/phase modulated signals and introduce a codeword-interleaving strategy to improve the error performance. The design criteria for the signal labelling and bit interleaving are also derived via the high-SNR approximation of the PEP. At the receiver, we devise an iterative channel amplitude estimator to enhance the detection reliability. With the help of a specially-designed iterative receiving algorithm, the designed noncoherent coded scheme can provide a significant improvement, either in the error-floor or the waterfall region. [ABSTRACT FROM PUBLISHER]

In this paper, a low-density parity-check (LDPC) coded recording system is investigated, for which the run-length-limited (RLL) constraint is satisfied by deliberate flipping at the write side and by estimating the flipped bits at the read side. Two approaches are proposed for enhancing the error performance of such a system. The first approach is to alleviate the negative effect of incorrect estimation of the flipped bits by adjusting the soft information. The second approach is to increase the likelihood of the correct detection of flipped bits by designing a flipped-bit detection algorithm that utilizes both the RLL constraint and the parity-check constraint of the LDPC code. These two approaches can be combined to obtain significant improvement in performance over previously proposed methods. [ABSTRACT FROM AUTHOR]

Presents information on a study which proposed two trellis coding schemes with large free distances. Review of the proposed trellis coding schemes using delay processor and signal mapper; Performance evaluation; Conclusions.

In this paper, a joint design of sparse code multiple access (SCMA) codebook and peak-to-average power ratio (PAPR) reduction based on the partial transmit sequence (PTS) technique is proposed for the downlink orthogonal frequency division multiplexing (OFDM) scheme. A benchmark scheme is firstly devised based on a direct extension of the conventional PTS-based OFDM scheme. Based on the characteristics of the near-optimal SCMA codebook designs reported in our previous work, a PTS-based SCMA-OFDM design is proposed by carefully determining the rotation angles of the SCMA codebooks, according to the adopted signal sub-constellations. A receiver which does not need the side information is further devised. Considering the phase ambiguity issue of the receiver, the PTS angles have been carefully refined. When compared to both the original scheme that does not consider PAPR reduction techniques and the benchmark scheme, the proposed scheme achieves a significantly enhanced PAPR performance with approximately the same error performance. In addition, a comparable PAPR performance, an improved error performance, and a lower computational complexity can be achieved when compared to the clipping-based SCMA-OFDM scheme reported in the previous literature. [ABSTRACT FROM AUTHOR]

In this paper, we present a turbo coded space-time modulation scheme for noncoherent block fading channels, where neither the transmitter nor the receiver knows the channel state information. The turbo coded bits are divided into two parts which are respectively transmitted through information-bearing pilots and spatial multiplexing (SM). Since this approach effectively increases the cardinality of the set of possible transmit (space-time) signal matrices, a large rate gain can be obtained without increasing the modulation order, as shown through achievable-rate analysis. At the receiver, an iterative detection-decoding algorithm is performed cooperatively among the turbo decoder, the coherent demapper for the SM, and the noncoherent demapper for the information-bearing pilots through the help of the proposed signal matrix detector, which enables these two demappers to utilize the channel information inherent in all the received symbols within the same fading block. Compared to the previous work in the literature, the proposed scheme can provide advantages in both error performance and complexity. [ABSTRACT FROM AUTHOR]

In this paper, we investigate Raptor-coded distributed unitary space–time modulation (USTM) schemes, where both the amplify-and-forward (AF) and decode-and-forward (DF) relaying scenarios are considered, under a wireless relay network with arbitrary path gains for the channel fading coefficients. First, the AF and DF relaying procedures are investigated based on the use of an inner USTM signal and an outer Raptor code, and the related noncoherent detectors are also derived. The constellation search for the USTM signal, as well as the optimization for the Raptor code, is then investigated in order to enhance the system performance. It is shown that the designed systems effectively approach the predicted limit in throughput performances and outperform the noncoherent distributed MIMO scheme reported in the previous literature. [ABSTRACT FROM PUBLISHER]