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The performance of concrete with a new admixture MX was studied by using the freeze-thaw cycle, permeability and chemical attack test. The experimental results show that MX improves the durability of concrete. Within the optimum proportion ranges from 0.1% to 1%, the compressive strength of concrete after freeze-thaw is increased by 20%–50%, and Young’s modulus can be increased by 3.76–5.64 times. The strength and weight loss of concrete with 0.4% MX are respectively decreased by 28% and 60% after hydrochloric acid attack. The strength and weight loss of concrete with 0.4% MX are decreased by 5%–20% after sulfuric acid and sodium sulfate attack. The permeability of concrete with 1% MX at 28 days can be decreased by more than 30%. The investigation of the negative temperature property of MX and analysis on concrete composition and microstructure by MIP reveal that the heat conduction is resisted and the freezing procedure of solution in concrete pore is retarded due to the adding of MX. Moreover, the pore structure of concrete with MX is improved, thus improving the durability. Based on this study, a resistance model of MX to block the heat and mass transference was proposed, and the mechanism of durability improvement of concrete with MX was explained.

Based on sound absorption mechanism of material, the special sound absorption material CEMCOM for road sound insulation is introduced. This high sound absorption material is mainly composed of expanded perlite. Using multiple sound absorption structure can improve sound absorption property of material. According to the preparation principle and durability design of material, a new kind of material with low cost and high durability is developed.

According to the characteristics of heterogeneous networks and user demand for seamlessly connection, the necessity of handoff to WLAN was researched. First of all, in order to reduce the influence of shadow fading on received signal strength (RSS), a smoothing algorithm based on support functions was proposed. Then, considering the context of mobile terminals and networks, and by using probabilistic knowledge, we propose an adaptive vertical handoff algorithm based on compensating time. The simulation results show that, compared with two algorithms, the proposed algorithm can make more effective and accurate handoff decisions, reduce the ping-pong effect and interruption probability, thereby greatly improving handoff performance. DOI : http://dx.doi.org/10.11591/telkomnika.v12i5.4276

The auto efficiently hydration heat arrangement and the non-contacting electrical resistivity device were used to test the thermology effect and the resistivity variation of Portland cement hydration. The structure forming model of Portland cement initial hydration was established through the systematical experiments with different cements, the amount of mixing water and the chemical admixture. The experimental results show that, the structure forming model of cement could be divided into three stages, i e, solution-solution equilibrium period, structure forming period and structure stabilizing period. Along with the increase of mixing water, the time of inflexion appeared is in advance for thermal process of cement hydration and worsened for the structure forming process. Comparison with the control specimen, adding Na2SO4 makes the minimum critical point lower, the flattening period shorter and the growing slope after stage one steeper. So the hydration and structure forming process of Portland cement could be described more exactly by applying the thermal model and the structure-forming model.

The properties of high performance color hardener (HPCH) and the mechanism were studied. HPCH is a composite system, which is composed of cementitious and auxiliary cementing materials, composite additives, abrasion resistance component (aggregate) and pigment. The porosity and pore structure of the material are obviously improved due to the activation, filling and adsorption of auxiliary cementing materials, thus resulting in a great increase of binding capacity for ions in HPCH and the obstacles of ion migrating. The density of material structure, bonding capacity of cementitious material to the abrasion-resisting component and the corrosion resistance are greatly and effectively improved by adding the auxiliary cementing materials and compound additives. According to the tests of dry shrinkage, sulphate resistance, chloride permeability and Ca(OH)2 content distribution, the property superiority of HPCH is analyzed. The mechanism of materials modification of HPCH is explained from the microscopic point of view by testing the pore structure and pore distribution via the mercury intrusion pressure method.

Combining network code with cyclic redundancy check (CRC), a two-dimension iterative decoder is proposed for network coded cooperation. The decoder organizes the network code as a row decoder, and CRC as a column decoder. The log-likelihood ratios (LLR) of received signal are used as soft information for iterations. The performances are evaluated by the simulations, and its results show that CRC can be used to improve the decoding performance.

In recent years, localization using angle of arrival (AOA) has gathered more attention, due to the use of smart antenna techniques for performance improvement in mobile communications. In this paper, we propose a precise two dimensional (2-D) localization approach by using AOA measurements which considers the error due to multipath propagation as well as angle estimation error. Specifically, we propose to use three antenna arrays to provide a fix, each with a unique combination of another antenna array. Thus, three sets of antenna arrays are formed altogether. For each set, we first transform angle information into location coordinates by standard geometry and linearization method is used for getting the initial location estimates. Then the Final Position is estimated from the three initial location estimates by the Precision-Weighted Aggregation approach which considers the errors from measurement and multipath propagation. Finally, the performance of the proposed method is evaluated.

According to the heterogeneous characteristics of wireless mesh networks and the QoS requirements of multimedia applications, we design a novel QoS adaptive architecture for WMNs that is cross-domain, cross-layer and cross-node. Furthermore, this architecture is mathematically described by using a bi-level programming model. This model uses the optimization results of subnets as the optimization parameters or optimization constraints of backbone networks, and combines the features of different network domains. Based on this bi-level programming model, we propose an ant colony optimization based routing algorithm. Simulation results show that the bi-level programming model, which fully optimizes various QoS parameters of paths, can effectively adapt to the heterogeneous characteristics of WMNs so as to obtain the optimal path; the proposed routing algorithm, which has both advantages of low complexity and fast convergence speed, can converge to the theoretical optimal solution of bi-level programming model.

The Ad Hoc On-Demand Distance Vector (AODV) protocol is an on-demand protocol specialized for mobile ad hoc network. Because of node's mobility and limited transmission range, the routes created by original AODV become invalid frequently leading to larger control overhead. In this paper, we propose a new scheme to improve AODV protocol by the concept of reliable distance. The reliable distance, which is always smaller than transmission range, is depended on the node's velocity and direction information attained from Global Positioning System (GPS). By the new mechanism, the routes are more reliable. Performance comparison of optimized AODV with conventional AODV by NS-2 simulator in various conditions shows the performance improvement.

Ultra-Wideband (UWB) is a potential technology for the future high-speed wireless network. The multi-access performance of UWB system with high data rates is investigated in this paper. In particular, an existing Interference Suppressing Orthogonal Frequency Division Multiplexing (IS-OFDM) approach is modified, an OFDM UWB multi-access scheme based on successive interference cancellation in a two-user case is proposed. The simulation results show that the proposed scheme can be used to improve the symbol error performance for the uncoded OFDM-based UWB systems to a certain extent.

A class of novel pulses based on modified Hermite functions (NMHPs) for UWB communications is presented according to spectral emission constraints of Federal Communications Commission (FCC) mask and the requirement of short pulse for multiple access. The proposed pulses constitute orthogonal sets and have a constant pulse width regardless of the order, moreover, have no DC component and have an adjustable central frequency, which are important properties in the UWB pulse shaping technologies. Theoretical analyses and simulation results show that the higher order of the proposed pulse has a better anti-jitter performance in both single-link and the multi-access UWB systems than that of the other lower orders and Scholtz's pulse when jitter is not very severe. It provides a flexible and systematic method for designing UWB pulses that both conform to FCC mask and offer good anti-jitter performance.

Timing Hopping Ultra Wideband (TH-UWB) system can provide high data rate and resolve individual multi-path components. To obtain several hundred Mbps data rate, the inter-symbol-interference (ISI) is unavoidable. The conventional Rake receiver is an effective structure for collecting multi-path energy in UWB channel environment, but can't suppress ISI. The Rake receiver with recursive least squares (RLS) equalizer for TH-UWB systems is proposed. The simulation results based on IEEE UWB channel model show that the proposed receive scheme can eliminate the ISI effectively, and improved the performance of the TH-UWB system under ISI remarkably.