On performance analysis and implementation issues of iterative decoding for graph based codes

There is no doubt that long random-like code has the potential to achieve good performance because of its excellent distance spectrum. However, these codes remain useless in practical applications due to the lack of decoders rendering good performance at an acceptable complexity. The invention of turbo code marks a milestone progress in channel coding theory in that it achieves near Shannon limit performance by using an elegant iterative decoding algorithm. This great success stimulated intensive research oil long compound codes sharing the same decoding mechanism. Among these long codes are low-density parity-check (LDPC) code and product code, which render brilliant performance. In this work, iterative decoding algorithms for LDPC code and product code are studied in the context of belief propagation. A large part of this work concerns LDPC code. First the concept of iterative decoding capacity is established in the context of density evolution. Two simulation-based methods approximating decoding capacity are applied to LDPC code. Their effectiveness is evaluated. A suboptimal iterative decoder, Max-Log-MAP algorithm, is also investigated. It has been intensively studied in turbo code but seems to be neglected in LDPC code. The specific density evolution procedure for Max-Log-MAP decoding is developed. The performance of LDPC code with infinite block length is well-predicted using density evolution procedure. Two implementation issues on iterative decoding of LDPC code are studied. One is the design of a quantized decoder. The other is the influence of mismatched signal-to-noise ratio (SNR) level on decoding performance. The theoretical capacities of the quantized LDPC decoder, under Log-MAP and Max-Log-MAP algorithms, are derived through discretized density evolution. It is indicated that the key point in designing a quantized decoder is to pick a proper dynamic range. Quantization loss in terms of bit error rate (BER) performance could be kept remarkably low, provided that the dynamic range is chosen wisely. The decoding capacity under fixed SNR offset is obtained. The robustness of LDPC code with practical length is evaluated through simulations. It is found that the amount of SNR offset that can be tolerated depends on the code length. The remaining part of this dissertation deals with iterative decoding of product code. Two issues on iterative decoding of\u27 product code are investigated. One is, \u27improving BER performance by mitigating cycle effects. The other is, parallel decoding structure, which is conceptually better than serial decoding and yields lower decoding latency

Recent morphodynamic evolution of the largest uninhibited island in the Yangtze (Changjiang) estuary during 1998-2014: Influence of the anthropogenic interference

Estuarine geomorphology worldwide has greatly changed in the Anthropocene due to intensive human inferences in river basin and within estuary, which has received increasing global concerns. Here, recent morphodynamic evolution of Jiuduan Shoal (JDS), the largest uninhabited island in the Yangtze (Changjiang) Estuary, and associated controlling factors were analyzed based on unique high-resolution seasonal-surveyed bathymetric data during 1998–2014. It can be indicated that JDS presents novel 12 and 48 months fluctuations though significant accretion was detected on high flats above −2 m. Meanwhile, morphodynamic evolution of JDS during 1998–2014 was divided into three stages: significant siltation on land-ward half of north JDS and expanding of Jiangya Shoal (JYS, part of JDS) tail, but less accretion at high flats from 1998 to 2002; continuous variations of JYS and reshape of seaward JDS with erosion band and heave appearance from 2002 to 2006; retentive alteration of JYS but recovery of erosion band and heave, together with redistribution of sand between high and low flats on seaward JDS after 2007. Moreover, river discharge could be likely the key factor controlling periodic characteristics of recent JDS evolution. Deep waterway project (DWP) dominates area increase of JDS by inducing accretion in north edge and south edge of Lower Shoal between 1998 and 2014

Spatial performance of skewed continuous rigid-frame bridges based on finite element analysis

Continuous rigid-frame bridges are usually symmetrically designed along the bridge center line for simplicity and clarity purposes. However, the skewed bridges are necessary in case of complex intersections with space constraint in highways. Previous research mainly focuses on the discussion of skewed angle and the interaction between girders and cross frames on I shape section. Box sections are also used for skewed bridge due to large torsion stiffness, which have many problems during service time. This paper analyzed coupled skew and bending effect for the bridge which combines the continuous rigid-frame system and skewed system. For skewed bridges, significant out-of-lane effect occurs in bridges, which is hard to be predicted through linear analysis. For continuous bridges, at the interior supports, negative bending moments exist. In addition, a part of each diaphragm of the bridge is connected to the main girder, and the rest part only carries its self-weight, which makes the girder behavior more complex in the transverse direction. Therefore, the spatial performance of the bridge is very complex. The design cannot only use simple two dimension analysis. In the paper the three dimensional finite element analysis was conducted to find the effect due to dead load, live load, temperature, and brake force to find critical position for monitoring and maintainance. Primary bending normal stress, warping normal stress, coefficient of shearing force lag and stress distribution of consolidation pier were analyzed and output. The behavior of both superstructure and sub structure were investigated. The effect of coupled bending and torsion is significant to the behavior of the bridge. Finally the design recommendations about the skew bridge are given. The critical positions for the further test and monitoring are found

A Clinical Report of Two Cases of Cryptogenic Brain Abscess and a Relevant Literature Review

Brain abscess, a severe intracranial infectious disease, refers to the parenchyma abscess caused by local infection or remote spread. Recently, advancements in modern medicine, especially the wide application of antimicrobial drugs, have contributed to the gradual decrease in the prevalence of this disease. However, cases of cryptogenic brain abscess that feature an unknown origin and atypical symptoms are rising. In this retrospective study, we report and analyze two cases of cryptogenic brain abscess. The first patient was a 30-year-old healthy man who was admitted to our hospital due to 1 week of headache and 3 days of headache aggravation, accompanied by nausea and vomiting. Head MRI shows a circular space-occupying as well as apparently enhanced DWI signals were observed in the right parietal lobe, and the ring wall manifested an apparent increase in signal intensity after enhancement. The patient was diagnosed as a brain abscess before operation and given craniotomy. The postoperative pathology confirmed brain abscess and recovered well after surgery. The second patient was a 45-year-old healthy woman who was hospitalized in a local hospital due to symptoms of headache and right limb weakness for 1 week. Head MRI shows a circular space-occupying lesion in the left basal ganglia, and the ring wall manifested an apparent increase in signal intensity after enhancement. The patient was suspected of glioma at the local hospital and was transferred to our hospital. Twelve hours after hospitalization, the patient was suspected of developing cerebral palsy and thus underwent emergency surgery including lesion resection in the left basal ganglia, resection of the polus temporalis, and a decompressive craniotomy. Postoperative pathology confirmed brain abscess. The patient was eventually conscious, but left the right limb hemiplegia. Hence, when a patient develops the classical triad of fever, headache, and focal neurologic deficits, the possibility of brain abscess should be investigated. Early diagnosis and treatment are crucial to minimize various complications and the number of deaths

Research on dynamic behaviors of wheel loaders with different layout of hydropneumatic suspension

The traditional wheel loader is built without any axle suspension and experiences severe vibration. Three different layouts of hydropneumatic suspension, namely, unconnected strut (UCS), interconnected in roll plane (IC-R) and interconnected in roll and pitch plane (IC-RP), are installed on the wheel loader to improve ride comfort. This study mainly focuses on the damping effect of different layouts of suspensions and investigates whether the suspensions will affect the driving and operation stability of the wheel loader. The multibody model of the wheel loader with hydropneumatic suspension is developed by RecurDyn in co-simulation with MATLAB/Simulink. Detailed analysis was performed as the wheel loader was traveling on a C-class road, turning on a flat road, and scooping and unloading crushed rocks. Results showed that (1) the three layouts of suspensions can greatly reduce the vector sum of weighted acceleration; (2) the UCS suspension affects both the driving and operation stability of the wheel loader, and the IC-R suspension affects the operation stability when the wheel loader scoops and unloads crushed rocks, (3) the IC-RP suspension with anti-roll and anti-pitch functions has little effect on the driving and operation stability of the wheel loader