光学遥感卫星的辐射定标是卫星数据定量化应用的前提条件,针对静止轨道大面阵光学载荷成像特点,提出一种基于分时-分视场成像的在轨相对辐射定标方法.选取合适的亮、暗均匀场地,通过卫星姿态机动完成整个视场的定标,得到所有探元在轨相对辐射定标系数,可有效解决现有场地难以覆盖卫星视场而带来的在轨相对辐射定标难题.
With the development of space technology, the telemetry system has become an important part of the range measurement and control network.At the same time,all communications companies are constructing base stations in order to achieve universal coverage of 3G communication requirements.This paper studies the impact of Unicom 3G signal on for telemetry system meas?urement environment.The results show that in the airspace affected by 3G signal,the noise temperature increases and the operating range reduces with the decreasing of LNA gain of telemetry system.Based on this,some measures are presented to avoid the effect of complex electromagnetic signal on radio measurement equipment.
The phased array antenna uses digital phase shifters to implement phase adjustment in general.Yet,the phase quantiza?tion leads to phase error.Simultaneously,such factors as element fault,process deviation,etc.bring random amplitude and phase errors.It is illustrated that certain parameters of amplitude and phase errors have great influence on sidelobes,phased array antenna pattern,etc. based on modeling array factor error and array pattern error,analyzing quantization error and random error.The simulation and verifica?tion are performed for quantitative phase and array pattern to provide reasonable range of parameter selection.
A new 3?D Markov chain model is proposed for accurately assessing the actual network performance of IEEE 802.11b DCF.The model takes into account DCF protocol backoff counter frozen and limited number of retransmissions.Combined with M/M/1/K queue model,a theoretical model of DCF system performance with finite load is derived.The simulation results show that the model can accurately predict system performance of IEEE 802.11b DCF protocol.
Traditional SUSAN edge detection algorithm uses constant geometry threshold to calculate the edge response. The edge line is thick and missing would happen.The improved SUSAN edge detection algorithm is based on the Otsu?s method.Otsu?s method is used to get three thresholds which divide the whole image into several areas.Then the points are classified and merged in the regions to get the edge points set.Experimental results show that the edge detection algorithm can improve the accuracy of original SUSAN edge detection.The detected edge is narrow,smooth and of better resistance to noise.
The moving single observer passive localization has such characteristics as high flexibility and high mobility,and it has no need of information synchronization and information exchange,so it can meet the needs of regional burst interference monitoring. In this paper,the relative orientation of the source of interference can be received by using a continuous moving single observer. Then the direction finding data received in real time from the moving single observer is analyzed by using the least squares estimation to deter-mine the location of fixed interference source. The simulation results show that this method can implement the localization of fixed inter-ference source when the observer is moving,and guarantee good positioning accuracy.
The QPSK modulation technology has such features as ideal bit error rate (BER),higher spectrum efficiency,etc.The spurious signal may be generated by AD/DA,low-noise amplifiers,frequency synthesizers,and mixers,which affects the QPSK perform-ance.In the application conditions,some of the spurs are expected to be relatively narrowband signals and as such may be modeled as tone interference.Based on analysis the spur magnitude,frequency and phase effect on QPSK constellation diagram,the spur offset in frequency from the center frequency of QPSK signal,false lock of receiver onto the spur,adversely affects bit error rate performance.The simulations results show that the addition of convolutional coding can effectively suppress the spurious signals and improve the BER per-formance.In the simulation,the applicable condition of convolutional coding in the improvement of BER performance is studies.
The algorithm of “snapshot” receiver autonomous integrity monitoring ( RAIM ) based on parity space can detect the deviation fault of system within one step,but can’t detect the cumulative fault by using redundant GPS satellite.The multivariate cumu-lative RAIM ( MC-RAIM) is deduced by using multivariate cumulative sum to check the parity residual error of GPS redundant equa-tion.The average run length (ARL),used as the performance index of this algorithm,is computed by Markov state transfer matrix under the different condition of window coefficient and alarm threshold.The simulation experiment proves that this algorithm can detect medium cumulative fault and made use of redundant GPS to compute parity residual error,which could detect system fault within one step,but lost the capability for cumulative fault.the multivariate cumulative RAIM (MC-RAIM) Arithmetic was deduced,which using,and using average run length(ARL) as the performance index,which was computed by the.Finally,it was proved that this new Arithmetic could detect medium cumulative fault by the way of simulation and cover the shortage of “snapshot” RAIM.
According to the specific requirements in close ground time transfer,a mobile time and frequency transfer system based on laser synchronization technology is designed,and the software and hardware integration is realized.This paper introduces the principle of laser time transfer,and also describes the hardware and software and the working flow of the system.In the test by experiment,the nanosecond time transfer is achieved.This system has the advantages of simple equipment and convenient operation,can provide a useful reference for those high precision laboratories to solve the problems in close ground time transfer such as poor mobility in temporary net-working,low transfer accuracy,inefficiency in detection and repair after line fault.
The VHF air-ground communication is an important part of air-ground communication.First,the flight shielding effect on VHF air-ground communication is analyzed by theoretical method;then the flight shielding model is established and the quantitative calculation of flight shielding effect on air-ground communications effectiveness for a transport airplane is implemented;finally, the model and the analysis is verified by the measured data.The results play a role in avoiding the flight shielding effect on VHF air-ground communication effectiveness.
针对带宽较窄广域IP话音业务报头开销占用较多传输带宽问题,提出了一种IP话音复用技术.采用多路共用协议报头的方式,通过可靠传输协议沟通IP话音报头信息,在发送端语音压缩设备提取每路的话音净荷组成复用分组IP包发送到对端语音压缩设备,接收端语音压缩设备还原分组IP包,发送到终端设备.采用话音复用技术,能够保证话音通话质量,显著提高带宽利用率.
The purpose of this design is to use wireless Internet WiFi technology to collect the related data of car sensor,perform appropriate process and control,and ultimately realize remote control and monitoring functions.The study covers the SCM LPC1768 soft-ware programming of Cortex-M3 core,and the temperature,speed,screen capture processing and transmission of SCM,together with the design and implementation of screen processing,analog dial of speed,analog thermometer and TCP/IP communication under Windows environments.The scheme uses a bottom-up modular programming method to implement the simulation and test for temperature and speed testing module,perform much of data analysis of WiFi communication mechanism,and finally use computer software to achieve the control the car′s movement,collect and display relevant information through wireless WiFi.
Turbo code has a very good performance which is close to the Shannon limit.In 1999,CCSDS(Consultative Committee for Space Data systems) has added Turbo code to the recommendation of Telemetry channel coding due to its excellent properties. This paper introduces the coding structure and decoding principle of Turbo codes of CCSDS standard,and studies important parameters which impact its performance,such as block length,iteration number,bit rate,etc.The decoding performances under different parameter condi-tions are simulated by Matlab software.The proposal for parameter selection in deep-space communication system is given based on anal-ysis on simulation results.
The far-field beacon signal is required to set for single-channel monopulse auto-tracking system debugging and test,and the antenna servo and feed system is required to implement in out-field. Based on this situation, this paper designs a single-channel monopulse auto-tracking signal generator,which can simultaneously simulate a variety of signals,including Doppler signal,azimuth error voltage signal,elevation error voltage signal and square wave modulation signal.Moreover,the debugging and testing environment of auto-tracking receiving demodulation system based on analog signal generator is constructed in the laboratory.The test results show that this simulation method can shorten the debugging time and improve the work efficiency.
It is fairly attractive to implement a long period pseudo-random bit generator based on aperiodic chaotic mapping.The finite precision effect may make chaotic sequence generate dynamical degradation property,which results in short-period phenomenon and low security of chaotic sequence.This paper analyzes the impact of Logistic chaotic sequence implemented by integer type on perio-dicity,and the analysis results show that the integer-type Logistic-map hasn’ t long-period characteristics.This paper proposes an imple-ment scheme of extending the cycle length via perturbation of m-sequence.The output sequence characteristics are simulated and ana-lyzed.The simulation results show that this scheme is easily implemented,by which the period of out sequence is significantly extended and the original chaotic properties can be maintained.
针对认知无线电系统本身的时变特性,将核心树算法与最小连通支配集算法应用于认知无线电系统的拓扑生成中.对于最小连通支配集算法,提出了一种适用于认知无线电系统的基于节点连通度的最小连通支配集算法(NC-MCDS),并对核心树算法与NC-MCDS算法进行了Matlab仿真.通过仿真结果中不同情况下核心节点数与最小连通支配集中的元素个数的对比,比较并分析了核心树算法与NC-MCDS算法的性能.
针对在卫星导航空时二维抗干扰(STAP)中SMI算法和LMS算法低仰角处零陷较多、负增益较大且影响卫星信号接收的问题,在空域波束形成的功率倒置迭代算法上,变形出一种适合卫星导航STAP的功率倒置迭代算法,并对SMI算法、LMS算法和功率倒置迭代算法进行了仿真分析.仿真结果表明,功率倒置迭代算法在低仰角处没有多余零陷、低仰角增益低且增益稳定,适合低仰角要求较高的应用.
When the measurement radar tracks the target,the measurement will be affected by troposphere refraction,resulting in measurement error.This paper analyzes the error of troposphere refraction,and expounds the error reason and the error correction model.Finally a correction model of troposphere refraction suitable for maritime environment is proposed.In the practical radar measurement, the availability and feasibility of this model is proved.
In order to reduce the computational complexity and memory space of LDPC codes without performance loss, a novel method for LDPC codes is presented, which is so called Module-Cyclic LDPC codes. A necessary and sufficient condition for check matrix without 4-circle and 6-circle for this method is given. The performance and experiment results analysis show that the proposed method with low computational complexity and memory space has the same BER level as the LDPC codes proposed in IEEE 802.16e. It can be concluded that the novel method is suitable for broadband communication systems.
As one of the new kind of semiconductor material,the high power density and breakthrough field capacity of GaN fea-tures high bandwidth and efficiency. According to these features of GaN,the input and output matching circuits of power tube are simu-lated and designed by using ADS simulation software,and then the efficiency index of the amplifier is tested. The experiment results show that the output power of continuous wave can be up to 100 W and the efficiency can be better than 50% in L band,at the same time the high efficiency of the GaN power tube are validated.
