Low-Complexity MAP Decoding for Turbo Codes

Abstract -Two simplified MAP algorithms for iterative decoding of turbo codes are presented. By using a parameter "decoding depth", our algorithms do not require computation of the aposteriori probability of each decoded information bit throughout the entire trellis, thus reduce the computational complexity and decoding delay considerably. One of the algorithms can achieve the performance very close to the conventional MAP algorithm; the other performs better than SOVA, while retaining a comparable process cost. Their advantages over the MAP and SOVA algorithms are demonstrated in both theoretical analyses and computer simulation assuming a Rayleigh fading channel

Evaluation of the Functional Performance of Paving Materials Based on the Driving Wheel Pavement Analyzer

There is still a lack of suitable methods for evaluating pavement functional performance according to the characteristics of real-world environment and traffic. This study developed an acceleration test method based on the Driving Wheel Pavement Analyser (DWPA) to evaluate the anti-sliding properties, anti-stripping properties, and tire–pavement noise of AC-13, SMA-13, and OGFC-13 asphalt mixtures, and MS-1, MS-2, and MS-3 micro-surfacing materials. The results indicate that the OGFC-13 mixture exhibited the largest texture depth, and the SMA-13 mixture exhibited the largest British pendulum number (BPN) at the end of the test. The MS-3 material had the best anti-sliding performance among the micro-surfacing materials. Coarse gradation improved the anti-stripping performance of the micro-surfacing materials. The tire–pavement noise for all materials increased with the increase of wheel repetitions. The OGFC-13 mixture and MS-3 micro-surfacing material exhibited the best and worse noise reduction performance, respectively. The new measurement method for evaluating the pavement surface functional performance was proved to be efficient

Study on Crystallization Mechanism of Asphalt Mixture in Bridge Deck Pavement

This study focuses on unknown crystal precipitates from an asphalt mixture used in bridge deck pavement layers. X-ray fluorescence spectroscopy was used to analyze the composition and source of crystals in the asphalt mixture used in bridge deck pavement, and infiltration tests, porosity tests, splitting tests and multi-wheel rutting tests were carried out to determine the precipitation area and non-precipitation area to explain the influence of crystals on the road performance of an asphalt pavement. A nuclear-free densitometer and 3D ground-penetrating radar (3D GPR) were used to detect the porosity and thickness uniformity of the whole section to study the formation mechanism of crystals. The results showed that the main components of crystals were water molecules, while the rest mainly came from machine-made sand, and there was no significant difference in pavement performance in the areas where crystals precipitated. The crystals were mainly caused by rainwater penetrating into the pavement through coarse segregation areas and collecting in the depression of the lower bearing layer. Under high temperature, the solution precipitated out of the pavement and formed crystals

Study of Internal Drainage Systems for Steel Bridge Deck Pavements

As large span steel bridges develop rapidly, the type of steel deck paving is also diversifying. However, the current steel deck paving layer is a dense-graded mixture of both upper and lower layers. This makes it difficult for water to drain out of the dense deck when it enters the interior of the deck, and the deck is easily damaged by the traffic load. This paper aims to prolong the service life of the pavement and solve the problem that the pavement is prone to water damage under the existing pavement system. In this paper, a new steel bridge deck paving system is formed by developing a new type of waterproofing binder layer material and developing an open-graded paving layer underlayment. Through indoor tests and finite element software analysis, the effect of the environment on the pull-out strength of the waterproofing binder layer material under different permaculture conditions is investigated; a suitable void ratio control range for the paving layer is explored through paving layer seepage analysis and indoor tests. The study revealed that the new epoxy resin waterproofing bonding layer was able to maintain a large pull-out strength value in a 60 °C water bath for 2 weeks. The paving with void ratios of 18, 20, and 22% were all able to drain 50% of the water inside the paving within 2 h, with excellent drainage capacity. Based on the modeling analysis and indoor test results, the target void ratio of the asphalt mix under the pavement is recommended to be controlled at 20–22%, with a void ratio in this range to solve the problem of water entering the steel bridge deck pavement and causing pavement distress

Meso-structural evaluation of asphalt mixture skeleton contact based on Voronoi diagram

The Voronoi diagram is a fundamental data structure for spatial neighborhood relations used in various fields related to geometric information. Taking four asphalt mixtures as the research object, this study established the skeleton contact Voronoi diagram model to characterize the contact meso-structure between coarse aggregates, and extracted the quantitative information of skeleton contact space. The results show that the skeleton contact Voronoi diagram model can represent important spatial information of asphalt mixtures from the meso-structure including the homogeneity of asphalt mixtures, the extrusion relationship between coarse and fine aggregates, and the skeleton contact distribution characteristics, etc. The shape of the connected tree reflects the coarse aggregate contact distribution and load transfer trend, and the order of the connected tree reflects the contact connectivity strength of the skeleton. We used Voronoi diagram area Vs, connected tree area TVs and the total length of contact points L to quantitatively evaluate the skeleton contact of asphalt mixtures. In the design of asphalt mixtures with dense skeletons, the evaluation criteria of skeleton contact characteristics include Vs (30–180 mm2) proportion ≥75 %, Tr-1 and Tr-2 proportion ≤75 % and L ≥70. The results provide new ideas to promote the quality of asphalt mixtures and pavement construction

Study on Mechanics-Based Cracking Resistance of Semiflexible Pavement Materials

Semiflexible mixture is a composite paving material combining the advantages of both asphalt and cement concrete materials. It consists of matrix asphalt skeleton and cement mortar. Due to the different volume characters between asphalt structure and cement mortar, stress concentration always happens in this semiflexible mixture, leading to internal cracking. The objective of this study is to alleviate the internal cracking concern of the semiflexible mixture by adjusting the material components. To this end, optimal material design and numerical simulation have been conducted. Matrix asphalt structures with four different air voids were incorporated with different dosages of cement mortar. The contraction strain and expansion strain of cement mortar as well as the indirect tensile strength of matrix asphalt structure were measured. The results were input into ABAQUS for numerical simulation. The results indicated that (1) the internal stress in this semiflexible mixture is mainly determined by the contraction of cement mortar, rather than expansion; (2) larger air void of matrix asphalt structure and less volumetric variation of cement mortar reduce the internal stress; (3) once the air void of matrix asphalt structure is decided, both maximum contraction and expansion deformations of cement mortar should meet specific requirement to ensure less internal cracking. This is a practical-ready paper that provides reference for the anticracking design of semiflexible pavement

Laboratory Investigation of Lignocellulosic Biomass as Performance Improver for Bituminous Materials

Lignocellulosic biomass has gained increasing attention as a performance modifier for bituminous material due to the vast amount available, its low cost and its potential to improve the durability of pavement. However, a comprehensive study concerning both the binder and mixture performance of modified bituminous material with lignocellulose is still limited. This research aims to evaluate the feasibility of applying lignocellulose as bitumen modifier by rheological, chemical and mechanical tests. To this end, two lignocellulosic biomass modified bituminous binders and corresponding mixtures were prepared and tested. The chemical characterization revealed the interaction between lignocellulosic biomass and bitumen fractions. Rheological test results have shown that lignocellulosic modifiers improve the overall performance of bituminous binder at high, intermediate and low temperatures. The findings obtained by mixture mechanical tests were identical to the binder test results, proving the positive effect of lignocellulosic biomass on overall paving performance of bituminous materials. Although lignocellulosic modifier slightly deteriorates the bitumen workability, the modified bitumen still meets the viscosity requirements mentioned in Superpave specification. This paper suggests that lignocellulosic biomass is a promising modifier for bituminous materials with both engineering and economic merits. Future study will focus on field validation and life cycle assessment of bituminous pavement with lignocellulosic biomass

Recycled asphalt mixture's discrete element model-based composite structure and mesoscale-mechanical properties

To investigate the composite structure and mesoscale-mechanical properties of recycled asphalt mixture, this paper has established discrete element models of recycled asphalt mixture with distinct characteristics of new aggregates, recycled asphalt pavement, new asphalt, and old asphalt according to the coarse aggregate contour characteristic parameters obtained by three-dimensional scanning. The composite skeleton and micro-crack development characteristics of recycled asphalt mixture were also studied. Finally, a method for determining the recycled asphalt pavement content was proposed considering the balance between rutting and crack resistance. The results show that the recycled asphalt pavement content has a negligible impact on the number of contact points of the composite skeleton, and this component primarily impacts the interfacial mechanical properties and contact of asphalt mortar. When the recycled asphalt pavement contents were 0 %, 15 %, 30 %, 45 %, and 60 %, the bottom stresses of the rutting specimens were approximately 0.6, 0.55, 0.5, 0.48, and 0.44 times of the bearing plate stress, respectively. In the composite skeleton, there were compressive, tensile, and tensile–compressive stresses at the contact point of coarse aggregates, the proportions of which were generally 70–80 %, 15–20 %, and 5–10 %, respectively. Shear cracks mainly occurred in the recycled asphalt pavement contact interface area, while tensile cracks occurred at the aggregate–aggregate contact interface, as well as in the asphalt mortar. The number of shear cracks was 50–80 % that of the tensile cracks. The maximum micro-crack length is 8–12 mm, and its minimum length is approximately 0.3 mm with micro-crack generally in the asphalt mortar. The results can provide a reference for the recycled asphalt mixture design to improve road performance