Applied Mechanics and Materials Vols. 303-306

Abstract: The application of navigation, such as guidance of pedestrians, requires a certain accuracy of continuous outdoor and indoor positioning. In outdoor environments GPS system has proved to be effective. However in indoor it is challenging to control the accuracy within 2 to 3 meters. At present several approaches have been developed for indoor positioning, such as RFID. But they are mainly been implemented in professional areas, for general user such as tourists and visual incapable users it is difficult to take advantage of these technologies because of the high price of terminal and the navigation service covered area is extremely limited. In this paper, a new approach of indoor navigation method is proposed to solve the problems of traditional methods. It is based on INS and wifi positioning technology. As hardware, wifi receiver, smart phone built-in accelerometer and digital compass are selected and investigated. User’s indoor position is first estimated by dead reckoning method with INS navigation system and then be recalibrated by wifi position information. Several experiments performed in the test verified the effectiveness of this indoor continuous positioning method described in this paper.

Abstract: A delay-locked loop is proposed for accurate code tracking over frequency-selective fading channels in this paper. Taking advantage of the shift-and-add property of maximum length pseudorandom spread-spectrum sequences, the differential multiplier is employed to separate each multipath component and reduce the effects of other multipath signals. The contribution of all the multipath signals is combined to enhance the error characteristic. Simulation results verify the performance improvement of the proposed loop.

Abstract: This paper system based on GPRS and a single chip microcomputer. System is applied to facility agriculture. Work aims to realize the wireless data transmission. Using digital temperature sensors, humidity sensors and carbon dioxide concentration sensors, they could collect greenhouse related parameters data. After that, GPRS wireless module send these data to farmers' mobile phones and remote expert system. After system set up, practice has proved that farmers mobile phone can receive temperature data from ds18b20 temperature sensor and with no delay. Stored in SD card crop picture can transmit through GPRS model. In the picture size below 20 KB situation, delay is not obvious. Transmission effect is good.

Abstract: To meet the demands of different high bandwidth services, we demonstrated a hybrid access network simultaneously transmitting wired and wireless signals. In the downstream, wireless signals are modulated and transmitted in phase modulation format at the optical carrier and wired signals are re-modulated in intensity modulation format, different de-modulation schemes are used at optical network unit (ONU) side; In the upstream, carrier reuse technology are adopted to re-modulate and transmit uplink signals to the optical line terminal (OLT). Simulation results show user ends could get acceptable performance of the wirless and wired signals.

Abstract: Abstract：With the complexity of network structure and the network expanded rapidly, AS-level network macroscopic topology measurements will be more and more important in the network studies. If we can catch a network macroscopic topology which is more close to the actual world, it will help researchers explore the inherent laws of network structure and the relationships between network structure and political, and economic in the real world, it also useful for network providers to prediction of network problems and improve the network environment more accurate and timely. Our paper puts forward method that combined BGP routing table with traceroute measurement and use the given BGP data to predict the result of traceroute measure, and change the sequence of measurement target, so as to improve the accuracy and efficiency of the traceroute measurements result.

Abstract: Most of traditional modulation and coding techniques do not adapt to fading or nonlinear conditions. These non-adaptive methods require a fix-link margin to maintain acceptable performance when the channel quality is poor. Thus, these systems are effectively designed for the worst-case channel conditions, resulting in insufficient utilization of the full channel capacity. Adapting to signal fading allows the channel to be used more efficiently since the power rate can be adjusted to take advantage of favorable channel conditions. In this paper, we present a simplified mathematical model to calculate the probability of SER for any given constellation of M-QAM. This model plays an important role in designing spectrally efficient adaptive modulation over nonlinear mobile channels. Instantaneous spectral efficiency and its histogram distribution are found for linear and nonlinear channel cases.

Abstract: This paper proposed an echo canceller to reduce the computational complexity of the long delay echo cancellation. Two adaptive filters were used for constructing this echo canceller. One was designed as a delay estimator, which used down-sampled sub-band signals to estimate the echo delay time. The other was designed as a short-tap filter to subtract the echo from the recorded signal with delay compensation. Experimental results showed that the output signal-to-noise ratio from the proposed canceller with low complexity is similar to that from the conventional canceller based on a long-tap filter.

Abstract: Centralized 2PC protocol is inefficiency when there is an unilateral cancel. The coordinator must wait for the messages of all participators, although there is a unilateral enable. In this case, Centralized 2PC wastes a lot of resource, such as time and network. The improved centralized 2PC protocol will make a decision of cancel and send to other participators as soon as there is an unilateral enable.

Abstract: In the ad hoc network, the unfairness of the system will affect the quality of service seriously. This paper proposed a new algorithm---FBGT, the algorithm use successfully send rate as measurement parameter, and use the Nash equilibrium of game theory as each flow transmission probability. The algorithm calculate every flow’s successfully send rate, and then exchange with the neighbor nodes, combing with the node's own information and neighbor node information to determine the backoff time to improve the system fairness. Due to FBGT algorithm taking into account the system’s local and global fairness and throughput, experimental analysis and data simulation showed the system's fairness index has been increased by 10% - 15%, the throughput of the system has also been improved to a certain degree.

Abstract: For UHDTV systems specified by ITU, the paper calculated gamut coverage of UHDTV systems. The paper also constructed a three-dimensional gamut model for UHDTV and computed the color solid volume in the L*a*b* color space. Then it was compared with HDTV systems and Pointer gamut. The result shows that UHDTV gamut completely contains HDTV gamut and Pointer gamut.