A novel handover scheme using torch nodes and adaptive measurement aggregation mechanism to improve QoS in high-speed railway communication

Technological advancement in the field of trans- portation and communication has been happening at a faster pace in the past few decades. As the demand for high-speed transportation increases, the need for an improved seamless communication system to handle higher data traffic in a highly mobile environment becomes imperative. This paper proposes a novel scheme to enhance the quality of service in high-speed railway （HSR） communication environment using the concept of torch nodes （TNs） and adaptive measurement aggregation （AMA）. The system was modeled using an object-oriented discrete event sim- ulator, and the performance was analyzed against the existing single-antenna scheme. The simulation results show that the proposed scheme with its minimal imple- mentation overhead can efficiently perform seamless han- dover with reduced handover failure and communication interruption probability.

A full-section asphalt concrete waterproof sealing structure for the high-speed railway subgrade

Purpose–This study aims to investigate the service performances of a new full-section asphalt concrete waterproof sealing structure(FSACWSS)for the high-speed railway subgrade through on-site tracking,monitoring and post-construction investigation.Design/methodology/approach–Based on the working state of the waterproof sealing structure,the main functional characteristics were analyzed,and a kind of roller-compacted high elastic modulus asphalt concrete(HEMAC)was designed and evaluated by several groups of laboratory tests.It is applied to an engineering test section,and the long-term performance monitoring and subgrade dynamic performance testing system were installed to track and monitor working performances of the test section and the adjacent contrast section with fiber-reinforced concrete.Findings–Results show that both the dynamic performance of the track structure and the subgrade in the test section meet the requirements of the specification limits.The water content in the subgrade of the test section is maintained at 8–18%,which is less affected by the weather.However,the water content in the subgrade bed of the contrast section is 10–35%,which fluctuates significantly with the weather.The heat absorption effect of asphalt concrete in the test section makes the temperature of the subgrade at the shoulder larger than that in the contrastive section.The monitoring value of the subgrade vertical deformation in the test section is slightly larger than that in the contrastive section,but all of them meet the limit requirements.The asphalt concrete in the test section is in good contact with the base,and there are no diseases such as looseness or spalling.Only a number of cracks are found at the joints of the base plates.However,there are more longitudinal and lateral cracks in the contrastive section,which seriously affects the waterproof and sealing effects.Besides,the asphalt concrete is easier to repair,featuring good maintainability.Originality/value–This research can provide a basis for popularization and application of the asphalt concrete waterproof sealing structure in high-speed railways.

Dynamic behavior of new cutting subgrade structure of expensive soil under train loads coupling with service environment

Expansive soil is sensitive to dry and wet environment change. And the volume deformation and inflation pressure of expansive soil may induce to cause the deformation failure of roadbed or many other adverse effects. Aimed at a high-speed railway engineering practice in the newly built Yun-Gui high-speed railway expansive soil section in China, indoor vibration test on a full-scaled new cutting subgrade model is carried out. Based on the established track-subgrade-foundation of expansive soil system dynamic model test platform, dynamic behavior of new cutting subgrade structure under train loads coupling with extreme service environment(dry, raining, and groundwater level rising) is analyzed comparatively. The results show that the subgrade dynamic response is significantly influenced by service conditions and the dynamic response of subgrade gradually becomes stable with the increasing vibration times under various service environment conditions. The vertical dynamic soil stress is related with the depth in an approximate exponential function, and the curves of vertical dynamic soil stress present a "Z" shape distribution along transverse distance. The peak value of dynamic soil stress appears below the rail, and it increases more obviously near the roadbed surface. However, the peak value of dynamic soil stress is little affected outside 5.0 m of center line. The vibration velocity and acceleration are in a quadratic curve with an increase in depth, and the raining and groundwater level rising increase both the vibration velocity and the acceleration. The vertical deformations at different depths are differently affected by service environment in roadbed. The deformation of roadbed increases sharply when the water gets in the foundation of expansive soil, and more than 60% of the total deformation of roadbed occurs in expansive soil foundation. The laid waterproofing and drainage structure layer, which weakens the dynamic stress and improves the track regularity, presents a positive effect on the control deformation of roadbed surface. An improved empirical formula is then proposed to predict the dynamic stress of ballasted tracks subgrade of expansive soil.

Progress in high-speed train technology around the world

This is a review of high-speed train development in the sense of technology advances all over the world. Three generations of high-speed trains are classified according to their technical characteristics and maximum operating speed. Emphasis is given to the newly developed high-speed train in China, CRH380. The theoretical foundations and future development of CRH380 are briefly discussed.

Design theories and maintenance technologies of slab tracks for high-speed railways in China:a review

The durability and reliability of slab track structures are essential for the long-term safety and stable operation of high-speed railways.In order to provide a solid theoretical basis and technical reference for the advancement of high-speed railway quality,this paper comprehensively discusses design theories of slab track structures,service performance evolution and maintenance technologies,and reviews the innovation happening in the industry.On top of that,the damage evolution,fatigue features and durability of slab tracks,which are highly relevant to serviceability,are summarized,and the future research trend of slab track service behaviours is pointed out.In addition,this paper summarizes the rules of establishing standards for damage maintenance,typical solutions for repairing damage and methods of evaluating the maintenance outcomes that combine field tests and numerical simulations.It also envisions a future direction where advanced testing technologies would assist the evaluation of maintenance effects.

Elliptical Cell Based Beamforming Design with an Improved β-Fairness Power Allocation for HSR Communication Systems

In this paper,a beamforming scheme to improve the coverage in high-speed railway communication systems is investigated.A dedicated coverage model,where the coverage cell is an ellipse rather than the traditional circular or linear,is considered.Based on the elliptical coverage cell,an optimization problem for the beamforming design is formulated to maximize the percentage of railway coverage,subject to the constraints on equal expected designed propagation gain(the gain obtained by a combination of designed beam and propagation channel)on the elliptical curve,i.e.,the expectation of designed propagation gain on the elliptical curve are all equal.Considering that the coverage can be improved by increasing the minimum designed propagation gain on the railway,the problem can be recast to maximizing the equal expected designed propagation gain on the elliptical curve.Subsequently,a beamforming design with an improved β-fairness power allocation,where the optimization problem is formulated to maximize the minimum expected received power over time with the constraints on elliptical cell based beamforming and mobile service amount,is proposed to further improve the coverage.An alternating iteration algorithm is developed to find the optimal beamforming vector and the instantaneous transmit power.Through numerical results,it is found that the beamforming designed on the elliptical curve covers longer railway than beamforming designed on the railway directly,and the coverage of elliptical cell based beamforming can be increased with the eccentricity.In addition,beamforming with the improvedβ-fairness power allocation can further improve the railway coverage and mobile service amount simultaneously.Moreover,it is shown that the larger eccentricity of the ellipse with appropriately chosen BS location,the larger coverage distance.