Guojun Han

EXIT chart based LDPC codes design for 2D ISI channels

Optimization of low-density parity-check (LDPC) codes to two dimensional (2D) intersymbol interference (ISI) channels is proposed, which exploits the modified Extrinsic Information Transfer (EXIT) chart. Specifically, a new degree optimization through EXIT chart fitting is proposed, where optimal variable node degree is search by selecting the best regular check node degree to match the check node decoder (CND) curve to the variable node decoder (VND) curve combined with 2d detector. Simulation result shows that the optimized LDPC code of length 13824 bits is 0.35 dB away from the symmetric information rate (SIR) of 2D ISI channels.

A Survey on DCSK-Based Communication Systems and Their Application to UWB Scenarios

In the past two decades, chaotic modulations have drawn a great deal of attention in low-power and low-complexity wireless communication applications due to their excellent anti-fading and anti-intercept capabilities. Of particular interest is the differential chaos shift keying (DCSK), which is considered as a very promising chaotic modulation scheme that achieves not only good error performance, but also low implementation complexity. In this treatise, we provide an insightful survey on the state-of-the-art research in DCSK-based communication systems through an extensive open literature search. In doing so, we firstly review the principles of DCSK modulation and the significant milestones since its inception. Subsequently, we introduce meritorious variants of DCSK, all of which can outperform the original one in certain aspects. We also present the joint design guidelines when combining DCSK with other critical techniques, e.g., error-correction coding and cooperative communication, in wireless communications under both single-user and multiaccess scenarios. Besides, we summarize research progress in the application of DCSK-based communication systems to ultra-wideband scenarios and their corresponding advantages. Specifically, we restrict our attention to the relevant modulation and system designs, as well as their performance-analysis methodologies. This survey aims not only to allow researchers understanding the development and current status of DCSK-based communication systems, but also to inspire further research in this area.

Deterministic Construction of Compressed Sensing Matrices from Protograph LDPC Codes

This letter considers the design of measurement matrices with low complexity, easy hardware implementation and good sensing performance for practical compressed sensing applications. We construct a class of sparse binary measurement matrices from protograph Low-density parity-check (LDPC) codes, which can satisfy these features simultaneously. The optimal performance of proposed matrices is analyzed from the mutual coherence aspect. Moreover, we obtain a sufficient condition for optimal construction of the matrices using proposed algorithm. Simulation experiments also demonstrate that orthogonal matching pursuit (OMP) algorithm performs better using the constructed matrices as compared with several state-of-the-art measurement matrices, such as random Gaussian matrices.

Construction of Irregular QC-LDPC Codes via Masking with ACE Optimization

Quasi-cyclic low-density parity-check (QC-LDPC) codes constructed by using algebraic approaches, such as finite geometry and finite field, generally have good structural properties and very low error-floors, and facilitate hardware implementation. Irregular QC-LDPC codes constructed from such QC-LDPC codes by using the masking technique, when decoded with the sum-product algorithm (SPA), have low decoding complexity, but often show early error-floors. In this paper, the relationship of cycle, girth and approximate cycle EMD (ACE) between the masking matrix and masked matrix is investigated, and the ACE algorithm is modified and used to construct the masking matrix for irregular QC-LDPC codes. Simulations demonstrate that the codes constructed by masking with ACE optimization exhibit much improved waterfall performance and lower error floors.

Check Node Reliability-Based Scheduling for BP Decoding of Non-Binary LDPC Codes

Scheduling strategy is considered an important aspect of belief-propagation (BP) decoding of low-density parity-check (LDPC) codes because it affects the decoders convergence rate, decoding complexity and error-correction performance. In this paper, we propose two new scheduling strategies for the BP decoding of non-binary LDPC (NB-LDPC) codes. Both the strategies are devised based on the concept of check node reliability and employ a heuristically defined threshold which can adapt to the communication channel variations. As the scheduling strategies only update a subset of the check nodes in each iteration, they result in reduced iteration cost. Furthermore, since the BP performs suboptimally for finite-length LDPC codes, especially for short-length LDPC codes, by enhancing the message propagation over the Tanner Graphs of short-length NB-LDPC codes, the new scheduling strategies can even improve the error-correction performances of BP decoding. Simulation results demonstrate that the new scheduling strategies provide good performance/complexity tradeoffs.

Asymmetric Iterative Multi-Track Detection for 2-D Non-Binary LDPC-Coded Magnetic Recording

Inter-track interference (ITI) is a major source of signal impairment in the next-generation magnetic recording systems. The single-track read channel model, combined with anti-ITI signal detection schemes, is a popular way to recover single-track data from a readback signal corrupted by the ITI. On the other hand, the multi-track read channel model can be used to simultaneously recover multi-track data from a readback signal. However, the performance of multi-track detection is severely degraded by the weak signals from the sidetracks and the indistinguishable symbols. To improve this performance, in this paper we propose a two-dimensional coding in conjunction with an asymmetric iterative multi-track detection (A-IMD) scheme, which uses joint channel detection and decoding of two parallel six-symbol-based detectors concatenated with two parallel non-binary low-density parity-check (NB-LDPC) decoder over GF(4), to iteratively recover four-track data from two readback signals. Simulation results demonstrate that the performance of the multi-track detection can indeed be greatly improved by using the proposed A-IMD scheme.

A Square-Constellation-Based

In this paper, a square-constellation-based M-ary differential chaos-shift-keying (M-DCSK) communication system framework is proposed. The symbol-error-rate expression of the proposed system is derived over additive white Gaussian noise as well as multipath Rayleigh fading channels. Moreover, the peak-to-average-power-ratio (PAPR) performance is carefully analyzed for the newly proposed system. Based on the square-constellation-based M-DCSK framework, a simple least-square estimator is designed to demodulate the information exploiting pilot-assistant symbols. Analytical and simulated results show that the proposed system benefits from a lower energy consumption, but suffers from a higher PAPR compared with the circle-constellation-based M-DCSK system.

M

A novel informed fixed scheduling (IFS) scheme for shuffled belief-propagation (BP) decoding of binary low-density parity-check (LDPC) code is introduced to improve the BP decoding convergence. The IFS finds an appropriate order of variable nodes in accordance with the number of updated neighbors in the code graph, ensuring that the maximum number of latest message updates is utilized within a single iteration. This allows the utilization of most reliable message updates in a timely manner, leading to faster error-rate convergence. Simulation results show that the proposed IFS scheme improves the convergence speed of BP decoder by up to 20% for regular LDPC codes and 45% for irregular LDPC codes, without affecting the error-rate performance, at medium-to-high signal-to-noise ratio over binary-input additive white Gaussian noise channel.

-Ary DCSK Communication System

Written-in errors (WIEs), which include written-in substitutions, insertions, and deletions, as well as 2-D inter-symbol interference (2-D-ISI), form one of the major challenges for the new emerging bit-patterned media recording technology. Coding and detection scheme with performance/complexity tradeoffs is expected to address such a challenge. In this paper, a new channel model with WIEs and ISI (WIE-ISI) is presented, and the embedded marker code scheme (EMCS) with Bahl-Cocke-Jelinek-Raviv (BCJR) detector is employed to perform channel detection. By investigating the effect of ISI on the WIE-ISI channel considering BCJR detector, a virtual written-in substitution probability is introduced and a new synchronization algorithm with written-in substitution detection (SA-WSD) is developed. The EMCS employing the proposed SA-WSD demonstrates better error correction performance than that of the original SA. Furthermore, the SA-WSD is found to be robust to small estimation errors in the written-in substitution probability.

Informed Fixed Scheduling for Faster Convergence of Shuffled Belief-Propagation Decoding

New magnetic recording technologies such as bit-patterned media recording (BPMR), heat (or microwave) assisted magnetic recording (HAMR) and shingled writing (SW)/two-dimensional magnetic recording (TDMR) have been proposed to push the storage density of future hard disks beyond 1Tb/in2. However, at such high recording density, many new challenges from the magnetic recording medium, read/write head as well as writing and reading channels arise. These challenges hinder the realization of Tb/in2 hard disks and should be addressed. In this paper, we review these major challenges from a communication theory perspective, and propose ways to mitigate the channel impairments by using low-complexity two-dimensional (2D) channel detection, new low-density parity-check (LDPC) code design paradigm, as well as re-synchronizable coding schemes.