Applied Mechanics and Materials Vols. 738-739

Abstract: The UEs at the edge of the cell in TD-LTE-Advanced system suffer from a poor communication quality invariably. In this paper, a novel relay mechanism, called Device-to-Device mobile relay (D2DMR), is proposed. In the D2DMR mechanism, the UE at the edge of the cell or in a poor coverage area can communicate with eNodeB via another UE’s relay. The link between these two UEs is established in the Device-to-Device (D2D) communication mode. The D2DMR mechanism can expand the cell coverage and improve the system capacity of TD-LTE-Advanced system with little interference. Numerical analysis and simulation results show that the D2DMR mechanism can improve the throughput of the TD-LTE-Advanced system greatly.

Abstract: This paper mainly surveys the state-of-the-art on real-time communicaton in industrial wireless local networks(WLANs), and also identifys the suitable approaches to deal with the real-time requirements in future. Firstly, this paper summarizes the features of industrial WLANs and the challenges it encounters. Then according to the real-time problems of industrial WLAN, the fundamental mechanism of each recent representative resolution is analyzed in detail. Meanwhile, the characteristics and performance of these resolutions are adequately compared. Finally, this paper concludes the current of the research and discusses the future development of industrial WLANs.

Abstract: OFDM usually incorporates pilot tones in the frequency domain (FD) or training symbols in the time-domain (TD) to facilitate channel estimation algorithms. TD channel estimation becomes more attractive in quasi-static channels because channel estimation scheme will optimize the spectral efficiency by re-using the training symbols designated for FD channel estimation. A channel estimation method based on time domain averaging algorithm is proposed. Due to the principle of centralized energy in time domain, the effective channel impulse response length can be detected by setting of threshold for the estimated channel impulse response length. Computer simulation demonstrates the performance of the proposed algorithms in terms of bit error rate performance.

Abstract: Considering the shortcoming of the traditional Greedy Perimeter Stateless Routing Protocol in the Vehicular Ad hoc Networks ,this paper focuses on an improved GPSR protocol based on the density of vehicle flow .This new scheme includes macro-directing algorithm , micro-forwarding strategy and the maintenance of the neighbor list.The simulation result shows that compared with the traditional GPSR protocol, the new GPSR protocol improves data packet delivery ratio, but its average end-to-end delay is slightly larger than before.

Abstract: For sparse overlay network built by static sensor nodes, this paper proposes the introduction of heterogeneous mobile sensor nodes, and designs a mobile coverage strategy to optimize the coverage performance of sensor network. At first, the monitoring area is divided into several sub-regions by iterative quartering and the sub-regions are represented by a quad-tree structure. Secondly, the mobile coverage strategy is planned based on the idea of divide and conquers and combing the overall regional strategy with local regional strategy. The overall regional mobile strategy is planned by go through all sub-regions according to breadth-first traversal of the quad-tree. The local regional mobile strategy in each sub-region is designed based on the distribution of static nodes after the sub-region meshing. The results show that the mobile coverage strategy can achieve good network coverage, and it is very suitable for multiple mobile nodes.

Abstract: In RFID system, when multiple tags transmit information in the same wireless channel simultaneously, data collisions usually occur which will reduce the identifying efficiency of RFID systems. To resolve this problem, several Dynamic Frame-Slotted ALOHA (DFSA) methods have been proposed. However, these methods are generally not capable of achieving expected performance when the number of tags is much larger or smaller than the initial frame size. Aiming to this problem, a Rapid DFSAI (RDFSAI) method was put forward based on the DFSA with interrupt (DFSAI) in this paper. Firstly, whether the frame size is adjusted or not is judged by comparing the system efficiency with the reference system efficiency. Secondly, the multiple factor of the frame size is determined by the ratio between the collision and empty slots, which leads to a seriels of different multiple factors or. As a result, the proposed RDFSAI elevates the adjustment speed of frame size and reduces the unnecessary empty and collision slots effectively. Simulation results indicate that the RDFSAI method appears better performance than the conventional methods even the tag number is increased up to 1600.

Abstract: In poor coverage area of high-speed railway, the frequent handoff will increase the dropped-call rate. An approach to improving the quality of wireless communication is adding a relay between two base stations. Paper is about analyzing the dropped-call caused by handoff in this scene. This paper proposed a model for dropped-call probability through analyzing the handoff probability, same frequency interference and ping-pong handoff. Based on the simulation and comparison of the dropped-call model, we found that putting a relay between the base stations can significantly improve the dropped-call problem, and the peek rate of dropped-call decreased by an order of magnitude.

Abstract: With the popularity of the Internet and the rise of mobile Internet application, the Internet finance is growing rapidly. The Internet finance includes online shopping, mobile payment, online financial management etc. However, there exists security problems in third-party payment, online shopping, online banking, mobile payment, etc. In order to solve the security problems with Internet finance, on the one hand, government should establish and perfect law and regulation systems, standardize network security technology, strengthen the network supervision, and make more effort to crack down Internet crimes; on the other hand, Internet users need to enhance network security awareness, and network security researchers should provide methods and countermeasures to prevent the online frauds.

Abstract: MPTCP data transfer under asymmetric heterogeneous network conditions has known problems related to receiver’s buffer blocking, caused by out of order packet arrival. In order to solve the problem, we propose a novel scheduling algorithm for multipath transport called Delay-Aware and Self-Adaptive Packet Scheduling for MPTCP, which distributes data to different paths over asymmetric heterogeneous network based on their transmission delay, which is a key factor to the whole performance. Meanwhile, the transmission DSN will also be considered. The results show that the scheduling algorithm can reduce the receiver’s buffer occupancy, improve the throughput significantly and adapt the performance differences among the subflows well in MPTCP.

Abstract: Zigbee technology and RFID technology are combined to design the system that can do real-time positioning and tracking on foreign visitors. The system locates and identifies the visitors who wear RFID card via locater and the locater transmits the ID information of RFID card and position information to the coordinator through Zigbee network and then the coordinator will pass the data after redundancy processing to the monitoring center via Ethernet. This system has advantages in low power consumption, wide deployment range, stable signal transmission and good recognization ability and it is applicable to important places such as high-grade residential area, park, warehouse and research institute, etc.