Xingcheng Liu

Effective Informed Dynamic Scheduling for Belief Propagation Decoding of LDPC Codes

The simultaneous flooding scheduling is popular for Low-Density Parity-Check (LDPC) Belief Propagation (BP) decoding. Non-simultaneous sequential scheduling is superior to the flooding scheduling, and asynchronous dynamic scheduling has better FER performance than the sequential scheduling. However, all strategies encounter the trouble of locating the error variable node. This paper proposes an informed dynamic scheduling strategy, which utilizes the instability of the variable node and the residual of the variable-to-check message to locate the message to be updated first. The informed dynamic scheduling overcomes the trapping sets effectively. This paper also designs an informed dynamic scheduling strategy with adaptivity to pass more messages in parallel, which effectively postpones the influence of cycles in the Tanner graph. In some sense, the strategy lengthens cycles. Simulation results show that the two informed dynamic scheduling strategies outperform other algorithms.

An efficient dynamic schedule for layered belief-propagation decoding of LDPC codes

An efficient dynamic schedule for layered belief-propagation (LBP) decoding of low-density parity-check (LDPC) codes is presented, in which the check nodes connecting to a variable node with maximum relative message residual are chosen in each dynamic decoding iteration, and then LBP is performed for these check nodes. In this schedule we combined the features of lazy schedule and node-wise residual belief propagation (NWRBP) together while keeping the extra computational complexity very low. Simulation results show that the new schedule speeds up the convergence rate and greatly improves error performance at medium to high signal-to-noise ratio (SNR) when compared to the standard LBP decoding algorithm.

Reliable Cooperative Communications Based on Random Network Coding in Multi-Hop Relay WSNs

Reliability is an important issue when designing wireless sensor networks (WSNs), since the WSNs need to work for a long time without manual interventions. Many techniques, such as multiple input multiple output systems and low density parity check codes, have been devised to improve the reliability of computer networks and wireless networks. However, these techniques are too complicated to apply in the WSNs due to the extremely limited resources of the wireless sensor nodes. Hence, it is a hot research topic to design a reliable scheme with low complexity in the WSNs. In recent years, there are a few schemes proposed to improve transmission reliability in the WSNs, such as multipath routing and cooperative transmission. In this paper, a network coding-based cooperative communications scheme (NCCC) is proposed. Combining the advantages of both cooperative communications and network coding, the NCCC can improve the packet loss-resistant capability through network coding and the communications fail-resistant capability through cooperative communications. In the NCCC, coding vectors in network coding procedure are chosen from a finite field randomly, which makes the NCCC easy to be implemented in the resource-limited sensor nodes. Theoretical analyses and experimental results show that the NCCC can achieve a good reliability performance at the cost of neglectable delay.

Construction of Quasi-Cyclic LDPC Codes and the Performance on the PR4-Equalized MRC Channel

In this paper, we constructed a type of parity-check matrices of QC-LDPC codes based on the progressive edge-growth (PEG) algorithm with suggested unreliable factors incorporated. The proposed algorithm can eliminate short cycles efficiently and gain low error-floors. With this method, we can avoid the unreliable information transferred in decoding as far as possible. The proposed QC-LDPC codes are hardware-friendly due to the benefit from the quasi-cyclic structure of such codes. Simulation results demonstrate that the codes constructed with the proposed algorithm have better performance than those constructed with the PEG algorithm over the additive white Gaussian noise (AWGN) channel and the PR4-equalized magnetic recording channel (MRC).

Variable-Node-Based Dynamic Scheduling Strategy for Belief-Propagation Decoding of LDPC Codes

Among the belief-propagation (BP) decoding algorithms of low-density parity-check (LDPC) codes, the algorithms based on dynamic scheduling strategy show excellent performance. In this letter, we propose a variable-node-based dynamic scheduling decoding algorithm. For the proposed algorithm, the reliability of variable nodes is evaluated based on the log-likelihood ratio (LLR) values and the parity-check equations; then, a more accurate dynamic selection strategy is presented. Simultaneously, the oscillating variable nodes are processed so that the influence of the spread of error messages caused by oscillation are suppressed. In addition, the proposed algorithm updates the same number of messages in one iteration as the original BP decoding algorithm does, which is different from some other dynamic decoding algorithms. Simulation results demonstrate that the proposed algorithm outperforms other algorithms.

Query Processing in Multi-User Scenario for Wireless Sensor Networks

In wireless sensor networks (WSNs) how to judiciously utilize the limited energy capacity of sensor nodes is very important, especially in multi-user application scenarios. In this paper data query processing strategies are discussed and the multi-user scenario is defined. In this scenario, there is a large-scale monitored region with a large number of original queries requested from thousands of users. Such a huge number of query requests to sensornets are a heavy load for traditional query processing methods. To mitigate this problem, a novel query processing strategy, NER-MQ (Network Event Report based Multi-user Query), is proposed for these applications. In NER, queries from users can be processed at a Base Station (BS), and then sent to the exact event regions based on the information reported by the event reporting mechanism which is employed in NER. In order to restrict the distribution of queries within the event regions, a special subnet, termed as the embedded network (EN), is employed. Simulation results show that a significant performance improvement is gained with the proposed NER-MQ algorithm in the multi-user scenario of WSNs.

A Unified Early Stopping Criterion for Binary and Nonbinary LDPC Codes Based on Check-Sum Variation Patterns

In order to detect uncorrectable error frames and early terminate their iterative belief-propagation (BP) decoding for binary or nonbinary LDPC codes, a unified early stopping criterion using check-sum variation patterns is proposed. In addition to low computational overhead and easy choice of threshold parameters, it can be adapted to different channels. Simulation results show that the proposed criterion greatly reduces the average number of iterations (ANI) at low to medium signal-to-noise ratio (SNR) while keeping the error performance degradation negligible over a wide SNR region.

Improved Decoding Algorithm of Serial Belief Propagation With a Stop Updating Criterion for LDPC Codes and Applications in Patterned Media Storage

In high density patterned media storage system, the “multiple islands per read head” model is taken into account for inter-track interference (ITI) in bit-patterned media (BPM). It has been proposed that low-density parity-check (LDPC) codes could improve the symbol error rate (SER) performance significantly when only considering AWGN noise alone over the storage channel. LDPC decoding algorithm could be applied in LDPC joint decoder of patterned media storage system. In this paper, we proposed a decoding algorithm of serial belief propagation (SBP) with a stop updating criterion for LDPC decoder. Simulation results show that the proposed decoding algorithm could reduce the times of generating and propagating the message in decoding with negligible error rate performance loss over AWGN channels when appropriately choosing the parameter that determines which variable node has been converged. By taking advantage of extrinsic information transfer (EXIT) charts, it is demonstrated that the proposed decoding algorithm could maintain superior SER performance and convergence rate compared with the traditional SBP decoding algorithm. To further explore the performance of the proposed decoding algorithm in “multiple islands per read head” model, we performed a large number of simulations over this channel model with different distribution percentages between the AWGN and the island position jitter noise. Simulation results show that the LDPC codes could improve the SER performance when considering jitter noise while the proposed decoding algorithm behaves excellently over the patterned media storage channel and over the AWGN channel.

Informed Decoding Algorithms of LDPC Codes Based on Dynamic Selection Strategy

Among most of the message scheduling strategies for low-density parity-check (LDPC) codes, the dynamic scheduling strategy behaves best in error correction performance. Dynamic selection is an integral part of dynamic scheduling decoding, which plays a decisive role throughout the decoding process. Usually, the dynamic selection strategy based on the message residuals only is employed in dynamic decoding algorithms, while other potentials of the dynamic selection strategy are rarely cared about. In this paper, we propose the triple judgment dynamic selection strategy combined with a Stability Criterion. Interestingly, the new strategy can be well applied to two different dynamic algorithms, namely, the V-VCRBP and the V-CVRBP algorithms. The proposed strategy has a great advantage: locating the message to be preferentially updated is extremely quick and accurate. Simulation results demonstrate that the V-VCRBP algorithm outperforms existing decoding algorithms in terms of BER performance and convergence speed, while the V-CVRBP algorithm has good error correction performance with a lower computational complexity.

Error Correction Coding With LDPC Codes for Patterned Media Storage

Recently, the ldquomultiple islands per read headrdquo model has been proposed for patterned media storage systems. In this paper, we investigated the applications of nonbinary low-density parity-check (LDPC) codes to such channels. Different nonbinary LDPC codes are designed for different read head models. We have also investigated the iterative decoding/detection algorithms for such coded systems. Simulation results show that significant performance improvements in terms of the symbol error rate (SER) can be achieved, especially when iterative decoding/detection algorithms are implemented, whereby soft extrinsic messages are exchanged between the belief-propagation-based decoder for the nonbinary LDPC code and the Bahl-Cocke-Jelinek-Raviv (BCJR)-based detector for the patterned media storage channel.