Applied Mechanics and Materials Vols. 336-338

Abstract: For the using of multi-modulation, the precondition of receiving and demodulating signal is to decide the type of the modulation. So automatic recognition of modulation signal has significant influences on the analysis of communication signals. In this paper, nine types of M-nary digital modulations are recognized by using four effective key features and utilizing the decision-theoretic approachThe simulation results shows that overall success rate is over 99% at SNR4dBThis algorithm is verified its good performance. It has simple structure, less calculation and good performance of real time. It can realize automatic modulation recognition.

Abstract: orthogonal frequency division multiple access (OFDMA) and single carrier frequency division multiple access (SC - FDMA) are the two kinds of 4 g wireless multiple access scheme. In the long term evolution (LTE) downlink link access scheme based on OFDMA, at the same time, the uplink access scheme based on SC - FDMA. In this article, we deduced the OFDMA and SC - FDMA basic performance difference, and then demonstrates the comprehensive performance comparisons between them. Theoretical derivation results show that the system capacity is better than that of SC - FDMA OFDMA. Then, we use the numerical simulation results confirm the conclusion. Keywords: OFDMA SC - FDMA basic capacity of the uplink transmission

Abstract: Based on oblique sounding system, a short-term forecasting method of maximum usable frequency for HF communication was presented. The method include four steps: firstly, maximum usable frequency of oblique sounding circuit was forecasted based on its sounding data; secondly, the critical frequency of sounding path midpoint was determined from the oblique sounding data and its forecast data by using ray-path theory; thirdly, the critical frequency was reconstructed for forecast circuit; in the end, maximum usable frequency for HF communication circuit was given. Using the oblique sounding data during March 2012, the accuracy and practicability of the method was validated. The root-mean-square error of the short-term forecast is 1.56 MHz, and is reduced 0.40MHz contrast to that of the long-term prediction. The research provides the important reference for frequency selection and frequency management of HF communication.

Abstract: The Hill differential equation is used to describe the change characteristic of the ephemeris prediction error in order to calculate the satellite broadcast ephemeris error and the error change rate. After the ECEF coordinate system converses the satellite inertial coordinate system, both the satellite ephemeris correction and the correction accuracy can be calculated by the Kalman filter. When the GEO, IGSO and MEO satellites move over the China, the calculation algorithms based on the weighted least square, the velocity model of the Kalman filter and the Hill differential equation are compared in the computing performance of the ephemeris corrections by using the reference date of IGS website. The simulation results show that: the ephemeris correction solver value based on the Hill differential equation can accurately reflect the ephemeris error characteristics at the current time. And it is able to correctly reflect the perturbation impact for the satellite ephemeris error. The Hill differential equation method is more suitable at the master station for engineering application about the MEO, IGSO and GEO satellites.

Abstract: The L-band Digital Aeronautical Communication System Type-1 (L-DACS1) has been considered as the potential standard for future aeronautical communications. As an important parameter for L-DACS1, the noise variance can be estimated via the well known Second-Moment-Fourth-Moment (M2M4) blind algorithm. However, due to influence from aeronautical fading channels, performance degradation is encountered by conventional M2M4 algorithm in L-DACS1. In this paper, channel responses obtained from L-DACS1 pilot symbols were carried out to compensate the estimation degradation brought by channel fading, which lead to an improved M2M4 algorithm for L-DACS1. It is shown through simulations that the proposed approach outperforms conventional M2M4 estimator in terms of estimation error for L-DACS1 in aeronautical fading channels.

Abstract: Wireless communication devices are often battery-powered. Reducing energy consumption during transmission has become a major challenge. We propose an optimal adaptation scheme and a suboptimal scheme based on the continuous-power discrete-rate adaptation (CPDR) for energy efficient transmission over fading channels. In our proposed schemes, we optimize the average transmit power according to data rate of the source node and buffer level, and then we adapt the transmit rate and power according to the CPDR scheme. Simulation results show that our proposed schemes have outstanding performance on energy-saving.

Abstract: Conical conformal microstrip patch antenna is very important in wireless communication and microwave instrument. In this paper, a Ka-band rectangular inset-fed microstrip patch antenna which conforms to a conical surface has been designed, the specific designed method and parameters were given. Then a conical conformal microstrip antenna is simulated by CST, the difference between planar antenna and conical conformal antenna has been discussed, and the effect of surface curvature on conical conformal antenna resonant frequency of has been analyzed.

Abstract: Recently, the environment problem has been more serious, especially the water-quality problem. In this paper, we develop the portable water-quality monitoring terminal, which can collect and real-time transmit water-quality parameters. The monitoring center received the data based on Modbus protocol by using wireless radio station. System structure and transmitting data frame are discussed here. The paper also introduced the monitoring software function in the monitoring center. The result of system test proved that the water-quality terminal can transfer the data to the remote monitoring center for a long time successfully, the system can achieve real-time and on-line water-quality monitoring functions.

Abstract: Exact and closed form expressions for the average level crossing rate (LCR) and average fade duration (AFD) of the output signal envelope of selection diversity system are derived, assuming each branch is subject to independent but nonidentical composite fading in distributed antenna systems (DAS). Numerical results validate the derived expressions. It shows that DAS promise significant diversity gains over collocated multiple antenna system.

Abstract: PEP device can be used to improve the performance of TCP in satellite networks. An implementation of PEP device was discussed in this paper. Its software architecture and experiment in satellite networks were presented. The experiment results show that this PEP device can greatly improve the performance of user applications. And the other advantage is that the software and protocol stack in user applications need not be modified.