深空测控再生伪码测距技术研究

针对深空测控任务中低信噪比情况下的航天器高精度测距问题,对再生伪码测距技术进行论述。介绍再生伪码测距技术原理,再生伪码测距通过再生方式消除信号上行链路噪声,提高了信噪比,但需要复杂的相关器;分析再生伪码测距采用的陶思沃斯码结构,详细论述再生伪码测距信号的地面上行、星上再生、地面下行处理过程,重点介绍各处理过程中的指标条件,并对再生伪码测距进行误差分析;重点对比分析再生伪码测距与传统透明转发测距,指出前者适合于深空低信噪比条件下的高精度测距,后者适用于近地高信噪比条件下的测距。     

Satellite inclination effects on UHF Satcom operation

The cause, magnitude, and time variance of satellite inclination are examined in light of the effects on military UHF SATCOM operation. The effects on required demodulator acquisition range, earth coverage footprint, and user terminal antenna pointing accuracy are considered. It is shown that the allowable satellite inclination to maximize on-orbit lifetime is not based on earth-terminal antenna pointing accuracy, but on allowable loss of high-latitude satellite coverage area. Worst-case Doppler shift for a UHF military satellite is 85-Hz uplink and 67-Hz downlink for a 5° SATCOM user elevation angle and 10° of satellite inclination. This amount of inclination is a reasonable allowance for station-keeping, to minimize thruster fuel and thus maximize satellite life. It is also shown that uplink Doppler frequency shift due to satellite inclination may be corrected based on satellite ephemeris data and rough user terminal location data     

Time delay estimation at high signal-to-noise ratio

The estimation of the delay between two signals is examined in the limit of high signal-to-noise ratio (SNR). It is shown that for the case of white noise, cross correlation with no prefiltering approaches the optimal maximum-likelihood (ML) estimator as the SNR grows to infinity. In simulation experiments with SNRs greater than 1, it outperforms the approximate ML estimator, which is based on estimated spectra. Other algorithms, such as generalized cross correlation or parameter estimation algorithms, are shown to be suboptimal at high SNRs     

Poly-phase codes and optimal filters for multiple user ranging

A technique is introduced to select poly-phase codes and optimal filters of a pulse compression system that have specific temporal and frequency characteristics. In the particular problem under study, multiple vehicles are assigned unique codes and receiver filters that have nearly orthogonal signatures. Narrowband users, that act as interference, are also present within the system. A code selection algorithm is used to select codes which have low autocorrelation sidelobes and low cross correlation peaks. Optimal mismatched filters are designed for these codes which minimize the peak values in the autocorrelation and the cross correlation functions. An adjustment to the filter design technique produces filters with nulls in their frequency response, in addition to having low correlation peaks. The method produces good codes and filters for a four-user system with length 34 four-phase codes. There is considerable improvement in cross and autocorrelation sidelobe levels over the matched filter case with only a slight decrease in the signal-to-noise ratio (SNR) of the system. The mismatched filter design also allows the design of frequency nulls at any frequency with arbitrary null attenuation, null width, and sidelobe level, at the cost of a slight decrease in processing gain     

基于LAS码的星群多目标测控技术研究

针对星群多目标同时测控问题,基于星群轨道根数的时延特性和多普勒频移特性分析可得,星群多目标测控的上行链路遥控与测距信号可实现S CDMA（Synchronous Code Division Multiple Access,同步码分多址）,由于星间距离较小,下行链路遥测与测距信号满足QS CDMA（Quasi synchronous code division multiple access,准同步码分多址）.上行链路遥控和测距信号形式设计为PCM BPSK CDMA（Pulse Code Modulation Binary Phase Shift Keying Code Division Multiple Access,脉冲编码调制二进制相移键控码分多址）,上行链路信号采用Gold序列扩频;下行链路遥测和测距信号形式设计为PCM BPSK CDMA,根据总的时延差,提出下行链路采用基于等长脉冲间隔法构造的LAS（Large Area Synchronous,大区域同步）码扩频.结果表明：比特信噪比Eb/N0为10.5 dB时,遥控误码率为1＆#215;10 6;Eb/N0为9.6 dB时,遥测误码率为1×10^5——与达到相同误码性能的Gold序列相比有1 dB改善,因此,LAS码相比于Gold码能够获得更好的误码性能.     

Optimal Channelization in FDMA Communications

For most efficient performance in frequency-division multiple access (FDMA), a hard-limiting repeater should be operated completely channelized (i.e., each uplink carrier should be individually filtered and power-controlled prior to spacecraft limiting and downlink transmission). When there are a large number of uplink carriers involved, however, complete channelization is no longer feasible, and the uplink carriers must be grouped together (assigned frequencies), which allows joint filtering and amplification. In this correspondence, it is shown that an optimal grouping procedure always exists for minimizing required repeater power, no matter how many carriers and groups are to be used.     

Effects of two-way decorrelation on radar detection inscintillation

A 3 dB gain in average signal-to-noise ratio of a monostatic radar operating in scintillation has recently been established both theoretically and observationally. The statistics of two-way scintillation are derived here for the case where the uplink and downlink both experience Rayleigh fading and where there is arbitrary correlation between the scintillation on the two paths. These statistics are then used to compute radar detection curves. A surprising result is obtained. The probability of detection is only weakly dependent (for P _D in the range 0.1 to 0.9) on the degree of uplink-downlink correlation in the scintillation when the average (nonfading) signal-to-noise ratio is constant and when proper account is taken of the change in mean power between the monostatic and bistatic cases. Much larger differences are seen in the detection curves with scintillation compared with nonfading curves (for P_D equal to 0.7 this scintillation loss is about 7 dB). Thus the difference in detection performance of monostatic and bistatic radars is determined primarily by the difference in the radar cross section (RCS) of the target for the two cases     

基于高级在轨系统的测控数传一体化方案

针对测控与数据传输信道一体化的需求,采用AOS(Advanced Orbiting System,高级在轨系统)空间链路层的等时业务,设计了一种测控数传信道一体化方案,可在上下行信道采用非相干信息帧同时传输测量信息及高速载荷数据.该方案设计了2种工作模式,模式一在上下行信道同时使用AOS传输帧,双向数据传输速率最高3 Mbit/s,测距精度优于2 m;模式二上行信道使用遥控扩频帧,可进行多站测距,抗多址干扰能力不低于15 dB,抗单频干扰能力不低于23 dB,下行信道使用AOS传输帧,最高数据传输速率3 Mbit/s,测距精度优于1 m.     

宽带信号角跟踪和四通道单脉冲方案

分析了宽带信号角跟踪的特殊问题及其实现方案。基于互相关函数的角误差检测方法,推导出了在非相关噪声及相关噪声背景下差路信号的输出信噪比及其角度随机误差的数学表达式,进而给出了带宽增益和最佳带宽的概念,以及提高输出信噪比的方法。为了在低载噪比（C/N）时获得角捕获所需要的和路信号以及差路的归一化信号,提出了四通道单脉冲方案。最后归纳出了低C/N时宽带信号角捕获和角跟踪的几种方法并提出了建议。     

Geolocation of frequency-hopping transmitters via satellite

An analysis of satellite-communications terminal geolocation performed by means of interception of ground terminal uplink transmissions in which a number of spaceborne interceptors transpond the frequency band of interest to terrestrial location for processing is presented. Interception regions for prototypical terminals and satellites are calculated and the results are presented parametrically as a function of uplink signal-to-noise ratio (SNR). The optimum angular separation of the interceptor satellites is found, and the effect of nonoptimal separation is discussed, as are the practical limitations involved in implementing this geolocation system     

Ground-to-satellite laser communication experiments

Ground-to-satellite laser communication experiments between the optical ground station located in Koganei, central Tokyo, and a low earth orbit (LEO) satellite were jointly performed by the Japan Aerospace Exploration Agency and the National Institute of Information and Communications Technology. In 18 trials during three non-consecutive months, the satellite was acquired and tracked 61 % of the time, when clear or partly-clear conditions were predominant. The optical link was maintained for about 6 minutes when the satellite was visible in spite of the high angular velocity of the satellite. In 3 of the 18 trials, the link was not interrupted due to clouds during the six-minute transit. The failures (39% of the time) occurred when cloudy or rainy conditions were predominant. Fluctuation in the uplink received signal power was minimized by using multiple laser beam transmissions. The measured uplink and downlink bit error ratios were 10^-7-10^-4. These results demonstrate the applicability of free-space laser communication for not only geostationary earth orbit-LEO optical links but also ground-to-LEO optical links.     

COTS星载双模测控应答机基带设计与实现

提出了一种星载双模测控应答机基带设计方案,采用COTS（商用现货）器件实现,能较好解决星载功率受限和空间辐射效应引起的相关问题。测控应答机主处理器由反熔丝FPGA（现场可编程门阵列）实现,可在低功耗条件下保证最基本测控需求,解调上行DPSK（差分相移键控）信号,调制下行扩频信号;协处理器受主处理器控制,由SRAM（静态存储器）FPGA来实现,对上行扩频信号进行解扩解调。测控应答机可根据星载电源功率情况和不同测控任务切换模式,具有成本低、可靠性高、使用灵活等优势。     

Cyclic code shift keying: a low probability of intercept communication technique

A low probability of intercept (LPI), or low probability of detection (LPD) communication technique known as cyclic code shift keying (CCSK) is described. We discuss the basic concepts of CCSK and describe a system based on the use of random or pseudorandom codes for biphase modulation. We use simulation to show that the bit error rate (BER) for CCSK can be closely estimated by using existing equations that apply to M-ary orthogonal signaling (MOS). Also, we show that significantly fewer computations are required for CCSK than for MOS when the number of bits per symbol is the same. We show that using biphase modulation results in waveforms that have a large time-bandwidth product and very low input signal-to-noise ratio (SNR) and thus inherently have an LPI by a radiometer. We evaluate detection by a radiometer and show that LPI can be achieved by using codes of lengths greater than about 2/sup 12/ (i.e., by transmitting more than about 12 bits per symbol). Results illustrate the effect that the CCSK symbol length and error probability, and the radiometer integration time and probability of false alarm (PFA), have on detection by a radiometer. We describe a variation of CCSK called truncated CCSK (TCCSK). In this system, the code of length 2/sup k/ is cyclically shifted, then truncated and transmitted. Although shortened, the truncated code still represents k bits of information, thus leading to an increased data rate. We evaluate radiometer detection of TCCSK and it is shown that the probability of detection is increased compared with the detection of CCSK.     

Modeling and Performance Evaluation of Nonlinear Satellite Links-A Volterra Series Approach

An analytical solution to the problem of modeling bandpass nonlinear channels and evaluating the performance of digital communication systems operating on them is presented. A method based on a Volterra series representation of the overall channel is first proposed, which allows one to extend to nonlinearities with memory the well-known concepts of complex envelope of bandpass signals and low-pass equivalent of bandpass linear systems. The general results previously mentioned are then applied to digital satellite communication systems operating over nonlinear channels. The effect of a nonlinear amplifier located in the satellite is considered, in combination with that of transmitting and receiving filters located in the Earth stations. In addition, both uplink and downlink noise are taken into account. Basic advantages of this approach are the generality it offers to the analysis and the fact that it allows accurate evaluation of the error probability in a short computer time.     

海洋重力仪采样质量悬挂系统分析

针对轴对称型海洋重力仪采样质量悬挂系统的刚度设计问题,运用材料力学和最小势能原理重点对水平和垂直方向的等效刚度进行理论分析,分析结果表明:系统在水平面内各方向的刚度相等,与拉丝材料的弹性模量和横截面积成正比,与拉丝的初始长度成反比;系统竖直方向等效刚度与绷紧弹簧的张力成正比,与拉丝的初始长度成反比.对仪器工程应用中,因拉丝弯曲而产生的干扰阻力进行了评估分析,结果表明在正确选择拉丝的材料和几何尺寸的条件下,由干扰阻力所引起的误差可以忽略不计.     

MC-CDMA应用于TDRSS多址业务的关键技术研究

传统TDRSS的多址业务采用单载波CDMA扩频方式,数据传输速率和频带利用率低,设备复杂。本文提出采用MC—CDMA方式代替现有的单载波CDMA方式,结合TDRSS的应用环境对MC—CDMA上下行链路的结构进行分析,并对扩频序列设计、信道估计和系统同步三方面的关键技术问题提出解决方法。采用MC—CDMA可以大大提高现有TDRSS多址业务的数据传输速率,频带利用率提高一倍,设备简单,在未来的航天通信中具有重要的现实意义。     

Proportional Tracking with Clipped-input Matched Filters

A proportional boresight-error measurement is described for tracking systems that is applicable to envelope-producing matched filters with hard-limited inputs. The error response is derived as a function of input SNR and the filter output SNR is estimated.     

星锁异常分析方法及处置策略

扩频模式星锁指示是判断上行信号锁定与否的重要参数,它是关系到双捕能否完成的关键.针对地面测控设备跟踪某遥感卫星时星锁异常的问题,采用FTA(故障树分析法)从星地两方面查找原因,找出了造成星锁异常的主要因素是扩频应答机下行测量帧中CRC(交叉冗余码校验)计算错误,诱因归结为扩频应答机FPGA(现场可编程门阵列)存储器中程...     

Galileo radio science investigations

The radio science investigations planned for Galileo's 6-year flight to and 2-year orbit of Jupiter use as their instrument the dual-frequency radio system on the spacecraft operating in conjunction with various US and German tracking stations on Earth. The planned radio propagation experiments are based on measurements of absolute and differential propagation time delay, differential phase delay, Doppler shift, signal strength, and polarization. These measurements will be used to study: the atmospheric and ionospheric structure, constituents, and dynamics of Jupiter; the magnetic field of Jupiter; the diameter of Io, its ionospheric structure, and the distribution of plasma in the Io torus; the diameters of the other Galilean satellites, certain properties of their surfaces, and possibly their atmospheres and ionospheres; and the plasma dynamics and magnetic field of the solar corona. The spacecraft system used for these investigations is based on Voyager heritage but with several important additions and modifications that provide linear rather than circular polarization on the S-band downlink signal, the capability to receive X-band uplink signals, and a differential downlink ranging mode. Collaboration between the investigators and the space-craft communications engineers has resulted in the first highly-stable, dual-frequency, spacecraft radio system suitable for simultaneous measurements of all the parameters normally attributed to radio waves.     

A320系列飞机ACARS常见故障签派放行处置研究

针对飞机通信寻址与报告系统依托的数据链关联复杂，不同数据链失效对系统影响存在较大差异的问题，全面总结各个数据链与系统的关联、失效后对系统的影响与签派放行的处置方案。首先，介绍了飞机通信寻址与报告系统的组成和传输原理，指出系统由空地网络和地地网络组成，并对上行和下行数据链的传输进 行了解析。其次，分析了系统依托的数据链，指出了甚高频、卫星通信和高频失效都可能会对系统产生影响，这三类设备的故障可能导致系统不可用。最后，列举了系统常见的七个故障，对故障进行了解析，并给出了签派放行的处置方案。