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An ultrahigh precise clock (space optical clock) will be installed onboard a low-orbit spacecraft (a usual expression for a low-orbit satellite operating on an orbit at an altitude of less than 1000 km) in the future, which will be expected to obtain better time-frequency performance in a microgravity environment, and provide the possible realization of ultrahigh precise long-range time synchronization. The advancement of the microwave two-way time synchronization method can offer an effective solution for developing time-frequency transfer technology. In this study, we focus on a method of precise satellite-ground two-way time synchronization and present their key aspects. For reducing the relativistic effects on two-way precise time synchronization, we propose a high-precision correction method. We show the results of tests using simulated data with fully realistic effects such as atmospheric delays, orbit errors, and earth gravity, and demonstrate the satisfactory performance of the methods. The accuracy of the relativistic error correction method is investigated in terms of the spacecraft attitude error, phase center calibration error (the residual error after calibrating phase center offset), and precise orbit determination (POD) error. The results show that the phase center calibration error and POD error contribute greatly to the residual of relativistic correction, at approximately 0.1~0.3 ps, and time synchronization accuracy better than 0.6 ps can be achieved with our proposed methods. In conclusion, the relativistic error correction method is effective, and the satellite-ground two-way precise time synchronization method yields more accurate results. The results of Beidou two-way time synchronization system can only achieve sub-ns accuracy, while the final accuracy obtained by the methods in this paper can improved to ps-level.

Inter-satellite link technology is one of hot issues in current satellite navigation field and construction of inter-satellite link system cannot be completed without the cooperation and supports of ground anchor stations. In this paper, with respect to time synchronization issue which is of great importance in the construction of anchor stations for inter-satellite link, key technological issues such as time system design for anchor station, method of synchronization with standard time, clock error of anchor station and the determination of its precision have been deeply discussed and studied. On the base of relevant studies, a complete design method and solution of time synchronization system for anchor station has been proposed herein, thereby offering solution ideas and technological supports for resolving key problems encountered during the construction of anchor stations for inter-satellite link in China. The anchor station time system proposed in this paper can better ensure the time difference between ground station and BDT is less than 1us and the time synchronization precision of anchor station is less than 5ns, thereby guaranteeing the reliability of anchor station acting as Pseudolite being connected to inter-satellite link while offering further reference for subsequent testings and development of inter-satellite link.

With the development of GNSS, the design and optimum selection of the ranging code is of significant importance for navigation system design. This paper describes the generation of the Weil code based on the design of ranging code. And then in order to select ranging codes of better performance, the paper describes a new optimum selection method in detail. This method is a combination of code selection method which is based on MFL and performance analysis method which is based on the peaks of correlation. And the performance of the selected Weil codes is analyzed by the methods based on peaks of correlation and Welch bound. The results demonstrate that the optimum selection method is of good rationality and of great importance for the design of navigation signals.

Remote video monitoring is an important way of residential security. Due to some deficiencies of traditional home monitoring system such as high cost, large power consumption and difficult maintenance, this paper designs an economical and practical home real-time remote monitoring system. This system includes hardware design and software design. The hardware analyzes and compares the processor of different architectures to configure the model of microprocessors and the composition of peripheral circuits, and then identifies the S3C2440 chip as the system’s main controller. For the software part, this paper first studies the construction of embedded Linux system containing bootstrapper, kernel compile, files preparation system and transplantation; then it focuses on a detailed analysis of video capture module under Linux to present the main process of video capture under Linux when the USB camera is selected and design the video capture program based on the Video4Linux2 Linux programming interface; finally, it designs the B/S architecture-based video sending program for the video output module and achieves the real-time browse on a PC through a browser, thereby realizing the remote monitoring for residence. This system relies on the mature embedded technology and achieves the embedded Linux-based real-time remote monitoring system on the Mini2440 development board in accordance with the above design. Compared with the traditional monitoring system, this design has a lower cost and higher cost performance, so it is more practical for the home security.

In this paper, a control method for making automated distributed management decisions is studied. And the consequences of externalized management on services and the system architecture is studied also. A simulation is performed to evaluate the suggested control method. The simulation results show that the automated manager needs 1) a system view classifying the current system state based on local knowledge, 2) a learner providing an optimal decision policy, and 3) an adaptive service architecture with abilities to compensate disturbance.

Ultra wideband (UWB) wireless communication technology has been regarded as a very important way of indoor short distance, high speed transition at present. In this paper the system structures and working principles of indoor positioning using UWB are introduced. The basic location principles and realization ways based on TDOA (Time-Difference-Of Arrival) are discussed and a new method to estimate the value of TDOA is proposed. In the indoor positioning system, the content being transmitted are simple, the system complexity is low, and it is prone to link with other outdoor positioning system such as GPS to realize accurate positioning.

Precise indoor positioning is becoming increasingly important in commercial, military and public service applications for tracking people and asset. Ultra Wide Band (UWB) can provide high accuracy position with strong anti-jamming and low power consumption. It is very suitable for indoor positioning application. This paper will put emphasis on indoor positioning system based on UWB.Analysis and implementation of indoor positioning systems based on UWB require an accurate channel model to determine that can be achieved, to design efficient modulation and coding schemes, and to develop associated signal-processing algorithms and effective method of hardware implementation. The structure of indoor positioning system based on UWB is introduced and some system parameters and modulation are determined in this paper. After description the structure of receiver and transmitter of system, a detailed analysis of UWB indoor channel characteristics is given and some algorithms of channel estimation and equalization are discussed in this paper. Some channel estimation techniques based on preamble training sequences and pilot sub-carriers are researched in depth. Further more, the linear estimations of least square (LS) and minimum mean square error (MMSE) are analyzed and compared under different UWB channel conditions and then suitable algorithm for this system is selected. Based on this selection, a scheme for FPGA implementation is proposed, and then some most significant modules for channel estimation and equalization has validated with Xilinx Virtex IV FPGA. It has been shown by some modelsim simulations that this channel estimation and equalization approach has some merits, such as simple implementation and less consumption of resource. It can meet the requirement of system design and some good performances can be achieved.

Multi-band orthogonal frequency division multiplexing (MB-OFDM) is a suitable solution to implementation of high speed data transmission in ultra wideband (UWB) spectrum by dividing the spectrum available into multiple bands. MB-OFDM system structure and transmitted signal is introduced in this paper. Channel models are fundamental to the study and design of communication systems. A survey on indoor wireless channels for UWB radio is given and the IEEE 802.15.3a model for UWB channel models is introduced in detail in this paper. The least square (LS ) channel estimation based on comb type pilot and linearity insertion are described and some simulation results is given in this paper. The simulation results have shown that this method has good performance, can meet the demand of MB-OFDM system with high estimation precision, strong resistance to ICI and easy realization.

The convolutional code cell is an essential part in a transmitter of multi-band orthogonal frequency division multiplexing ultra wide band (MB-OFDM-UWB) system introduced in this paper as a kind of useful channel coding to offer more protection against all kinds of channel noise under indoor channel environments. In this paper, some kinds of convolutional codes for MB-OFDM-UWB system are designed. And then, two different structures for the implementations of convolutional codes are presented respectively. The two different structures of convolutional codes are implemented based on field programmable gate array (FPGA) chip with the software tools of ISE foundation and modelsim. The simulation results show that the performance of parallel structure is better than that of pipe line structure and that it's convenient to implement based on a mother code rate of 1/3 the punctured convolutional code with different code rates that are needed by different modules of the OFDM-UWB system. The implementation of convolutional code technique with FPGA chip can be fit to all kinds of applications of OFDM-UWB system with no transformations.

Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) is a suitable solution to implementation of high speed data transmission in ultra wideband spectrum by dividing the spectrum available into multiple bands. The baseband of transmitter is one of the most important parts in MB-OFDM system. The structure of MB-OFDM system transmitter is introduced in this paper and the design of transmitter baseband based on FPGA is described in detail. The design has been validated with Xilinx Virtex II FPGA. The results show that all modules designed has achieved the expected purpose both in precision and resource, with simplicity and high efficiency, and can meet the demand of MB-OFDM systems.