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Contact modeling and prediction-based routing in sparse mobile networks
GUO Yang, QU Yugui, BAI Ronggang, ZHAO Baohua
Front. Electr. Electron. Eng.. 2007, 2 (3): 260-267.
https://doi.org/10.1007/s11460-007-0048-1
Mobile ad-hoc networks (MANETs) provide highly robust and self-configuring network capacity required in many critical applications, such as battlefields, disaster relief, and wild life tracking. In this paper, we focus on efficient message forwarding in sparse MANETs, which suffers from frequent and long-duration partitions. Asynchronous contacts become the basic way of communication in such kind of network instead of data links in traditional ad-hoc networks. Current approaches are primarily based on estimation with pure probability calculation. Stochastic forwarding decisions from statistic results can lead to disastrous routing performance when wrong choices are made. This paper introduces a new routing protocol, based on contact modeling and contact prediction, to address the problem. Our contact model focuses on the periodic contact pattern of nodes with actual inter-contact time involved, in order to get an accurate realization of network cooperation and connectivity status. The corresponding contact prediction algorithm makes use of both statistic and time sequence information of contacts and allows choosing the relay that has the earliest contact to the destination, which results in low average latency. Simulation is used to compare the routing performance of our algorithm with three other categories of forwarding algorithm proposed already. The results demonstrate that our scheme is more efficient in both data delivery and energy consumption than previously proposed schemes.
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An improved hypothesis-feedback equalization algorithm for multicode direct-sequence spread-spectrum underwater communications
HAN Jing, HUANG Jianguo, SHEN Xiaohong, WANG Yu
Front. Electr. Electron. Eng.. 2007, 2 (3): 312-316.
https://doi.org/10.1007/s11460-007-0058-z
In underwater acoustic communication, because the available bandwidth of the channel is severely limited, the direct-sequence spread-spectrum scheme can only be realized at low bit rates. To improve the transmission speed, a multicode spread-spectrum scheme is considered. However, in this case, due to the rapid time-variability of the underwater channel, and the influence of inter-symbol interference (ISI) and inter-channel interference (ICI), the conventional rake receiver may fail to function. The hypothesis-feedback equalization algorithm has been proposed for the direct-sequence spread-spectrum system [1]. By updating coefficients at chip rate and feeding back hypothesized chips, it can track time-variability and combat ISI effectively. However, for a multicode system, its performance will be degraded by ICI. An improved algorithm is proposed in this paper, which combines parallel interference cancellation (PIC) with hypothesis-feedback equalization (HFE), with the capabilities of tracking the time-varying channel and suppressing the ISI and ICI at the same time. Simulation results prove that the proposed algorithm can significantly improve the performance of a multicode system.
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New mobile Raman lidar for measurement of tropospheric water vapor
XIE Chenbo, ZHOU Jun, YUE Guming, QI Fudi, FAN Aiyuan
Front. Electr. Electron. Eng.. 2007, 2 (3): 338-344.
https://doi.org/10.1007/s11460-007-0064-1
The content of water vapor in atmosphere is very little and the ratio of volume of moisture to air is about 0.1%–3%, but water vapor is the most active molecule in atmosphere. There are many absorption bands in infrared (IR) wavelength for water vapor, and water vapor is also an important factor in cloud formation and precipitation, therefore it takes a significant position in the global radiation budget and climatic changes. Because of the advantages of the high resolution, wide range, and highly automatic operation, the Raman lidar has become a new-style and useful tool to measure water vapor. In this paper, first, the new mobile Raman lidar’s structure and specifications were introduced. Second, the process method of lidar data was described. Finally, the practical and comparative experiments were made over Hefei City in China. The results of measurement show that this lidar has the ability to gain profiles of ratio of water vapor mixing ratio from surface to a height of about 8 km at night. Meanwhile, the measurement of water vapor in daytime has been taken, and the profiles of water vapor mixing ratio at ground level have been detected.
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Droplets actuating chip based on electrowetting-on-dielectric
WU Jiangang, YUE Ruifeng, ZENG Xuefeng, LIU Litian
Front. Electr. Electron. Eng.. 2007, 2 (3): 345-349.
https://doi.org/10.1007/s11460-007-0065-0
A droplet-based actuating chip by using the method of electrowetting-on-dielectric (EWOD) was developed to manipulate the microfluidics. Here, the actuation mechanism of the sandwiched-configuration EWOD chips was carefully studied, and the movement of droplets was numerically analyzed by using the computational fluidic software, CFD-ACE+. The fabrication of the chip, including a heavily phosphorus-doped poly-silicon micro-electrode array and a thermally grown SiO2 dielectric layer, was exploited to improve the chip stability and decrease the actuation voltage. In experiments, the transportation of a deionized droplet of about 0.5 μL is successfully achieved in air by applying the low voltage of 45 V.
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Imitation of the characteristics of the wind turbine based on DC motor
LIU Qihui, HE Yikang, ZHAO Rende
Front. Electr. Electron. Eng.. 2007, 2 (3): 361-367.
https://doi.org/10.1007/s11460-007-0068-x
This paper analyzed the operating principles and power and torque characteristics of the wind turbine and the direct current motor (DC motor), and investigated the operating characteristics of the wind turbine compared to that of the DC motor. The torque imitation scheme, which has good performance and high feasibility, together with the whole wind turbine imitation system, was provided. The wind turbine imitation system includes not only a hardware platform composed of PC, data-collection board and thyristor-based velocity-regulator, but also monitor software of wind turbine imitation. The experimental results of different occasions verify the correctness and feasibility of the wind turbine imitation scheme proposed in this paper, which provided a valid idea for wind turbine imitation and investigation of wind power generation techniques in the laboratory.
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Optimal planning of high voltage distribution substations
YU Yixin, YAN Xuefei, ZHANG Yongwu
Front. Electr. Electron. Eng.. 2007, 2 (3): 368-373.
https://doi.org/10.1007/s11460-007-0069-9
Aimed at solving the problem of optimal planning for high voltage distribution substations, an efficient method is put forward. The method divides the problem into two sub-problems: source locating and combina tional optimization. The algorithm of allocating and locating alternatively (ALA) is widely used to deal with the source lo cating problem, but it is dependent on the initial location to a large degree. Thus, some modifications were made to the ALA algorithm, which could greatly improve the quality of solutions. In addition, considering the non-convex and non-concave nature of the sub-problem of combinational optimization, the branch-and-bound technique was adopted to obtain or approximate a global optimal solution. To improve the efficiency of the branch-and-bound technique, some heuristic principles were proposed to cut those branches that may generate a global optimization solution with low probability. Examples show that the proposed algorithm meets the requirement of engineering and it is an effective approach to rapidly solve the problem of optimal planning for high voltage distribution substations.
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23 articles
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