Search

In this letter, we conduct a comprehensive investigation on tail-biting (TB) spatially coupled protograph (SC-P) low-density parity-check (LDPC) codes under shuffled belief-propagation (BP) decoding. We first propose a shuffled extrinsic information transfer (S-EXIT) algorithm tailored for the shuffled decoding. Exploiting the proposed algorithm, we accurately predict the convergence performance (i.e., decoding thresholds) for TB-SC-P codes under such a schedule and demonstrate that their convergence performance can be further improved. Based on the S-EXIT analysis, we develop an optimization method to generate a new type of TB-SC-P codes, called improved TB-SC double-protograph (I-TB-SC-DP) codes , which can inherit the superiorities of two mother protograph codes and possess more desirable decoding thresholds. Theoretical analyses and simulated results illustrate that the proposed I-TB-SC-DP codes exhibit better error performance than the existing counterparts.

In this letter, we derive a closed-form bit error rate (BER) of M-ary differential chaos shift keying (M-DCSK) systems over multipath Rayleigh fading channels via approximating Gaussian Q-function by polynomials. The approximation is made piecewisely using polynomials of different degrees and Remez algorithm is applied to achieve the minimax approximation. Our method can be extended into the existing non-coherent transmit-reference chaos-based modulation systems, e.g., short-reference DCSK and multi-carrier DCSK systems. The derived closed-form BERs are compared with the simulated ones in order to verify the efficiency of proposed approximation scheme. This work was supported in part by the NSF of China (Nos. 61701121, 61801128), the Research Project of the Education Department of Guangdong Province (No. 2018KTSCX057), the Project of Department of Education of Guangdong Province (No. 2018SFJD-01).

Cell-to-Cell interferences (CCIs), which arise from adjacent cells through parasitic coupling-capacitance, severely degrade the performance of threshold voltage detection. Pre-processing and post-processing methods have been proposed to mitigate the effect of CCIs on threshold voltage variation. The performance of the aforementioned methods heavily depends on the accuracy of the threshold voltages adjacent to the victim cells. However, to obtain high accuracy, these methods requires multi-sensing operations, thus significantly resulting in high detection latency. In this letter, a novel non-uniform detection scheme based on the threshold voltage of cell states, which is referred to as the cell-state adaptive detection (CSAD), is proposed to adapt the shifts of the threshold voltages. Then, the neighbor-a-posteriori information is exploited to mitigate the overcompensation phenomenon and further improve the performance of the CSAD under the block read mode scenario. Simulation results show that the proposed CSAD scheme and its improved version not only achieve better bit-error-rate performance but also keep lower detection latency compared with the existing detection schemes.

The process scaling as well as the multi-level cell technology greatly increase the storage density of NAND flash memory. Unfortunately, the high-density flash memory suffers from severe noise such that its performance will be dramatically deteriorated. In this letter, we propose a cell-state-distribution-assisted threshold voltage detection (CSD-TVD) to optimize read reference voltages. Specifically, the proposed detection method exploits the variation of a number of cells within each sub-window of the overlap region to detect the voltage shift and analyze its distribution. Afterward, the mean of the voltage-shift distribution is viewed as the optimal voltage shift, which is used to boost the accuracy of the read reference voltage. Based on the retention characteristics, we also conceive a novel low-latency (LL) CSD-TVD to reduce the detection range of the CSD-TVD. The experimental results demonstrate that the proposed CSD-TVD and LL-CSD-TVD achieve better error performance than the state-of-the-art retention-optimized-reading (ROR) and nonuniform detection methods. In addition, the LL-CSD-TVD significantly reduces the read latency with respect to the CSD-TVD and ROR.

Multiresolution $M$ -ary differential chaos shift keying (MR- $M$ -DCSK) system enables unequal-priority transmission via exploiting non-uniformly spaced phase constellations. In this letter, an adaptive MR- $M$ -DCSK system is proposed by using a new constellation parameter design. Aiming at maximizing the spectral efficiency, the constellation parameter is carefully selected based on signal-to-noise ratio, and then is further optimized by a new search algorithm. Both the analytical and simulation results show that the proposed adaptive MR- $M$ -DCSK system not only can enhance the spectral efficiency as compared with the adaptive $M$ -DCSK system, but can satisfy different bit-error-rate requirements for different bits within a symbol as well.