WO2015039631A1 - 一种用于卫星导航系统的射频信号质量评估方法 - Google Patents

一种用于卫星导航系统的射频信号质量评估方法 Download PDF

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WO2015039631A1
WO2015039631A1 PCT/CN2014/088745 CN2014088745W WO2015039631A1 WO 2015039631 A1 WO2015039631 A1 WO 2015039631A1 CN 2014088745 W CN2014088745 W CN 2014088745W WO 2015039631 A1 WO2015039631 A1 WO 2015039631A1
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baseband signal
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ideal
component
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French (fr)
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唐祖平
魏蛟龙
张小清
刘昌建
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Huazhong University of Science and Technology
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C21/00—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00
    • G01C21/26—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 specially adapted for navigation in a road network
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/02—Details of the space or ground control segments
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
    • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/396—Determining accuracy or reliability of position or pseudorange measurements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
    • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/42—Determining position
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2556/00—Input parameters relating to data
    • B60W2556/45—External transmission of data to or from the vehicle
    • B60W2556/50—External transmission of data to or from the vehicle of positioning data, e.g. GPS [Global Positioning System] data
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related

Definitions

  • the invention belongs to the field of satellite navigation technology, and more particularly to a radio frequency signal quality evaluation method for a satellite navigation system.
  • Satellite navigation signals are used for timing and ranging of navigation systems.
  • the impact on navigation performance is mainly reflected in three aspects: carrier tracking performance, pseudo-code tracking performance, and telegram demodulation performance.
  • the navigation signal system determines the innate performance of the navigation system, and the spatial signal quality determines the difference between the best performance that the actual system can achieve and the performance of the signal system.
  • the correct demodulation of information is the design goal, and its performance is related to the error of the signal vector at the sampling decision time.
  • the accuracy of the ranging is more concerned, which depends on the quality of the signal waveform. Therefore, the navigation system has higher requirements on signal quality than the general communication system, and correspondingly, it puts forward higher requirements on the comprehensiveness and accuracy of the signal quality evaluation method.
  • CN102571652A discloses a method for evaluating GNSS baseband signals from frequency domain power spectrum, time domain waveform, chip edge, modulation error.
  • the relevant characteristics of these aspects analyze the performance of GNSS baseband signals.
  • the above scheme still has the following limitations: 1) The method only considers the evaluation of the baseband signal quality, and can not truly reflect the influence of spatial signal quality on the navigation performance, and does not give the distortion-free frequency conversion from the RF signal.
  • the signal processing method to the baseband and because the baseband sampling method is adopted, the signals of different frequency points need to be configured with different analog channels, and the delay inconsistency between the analog channels is inevitably introduced, resulting in a decrease in the accuracy of the evaluation of the inter-frequency signal consistency; 2)
  • the six evaluation indicators of the eye diagram are idealistic and difficult to apply to the quality assessment of the composite signals of the three-way and above signal components in the current GNSS.
  • the four mainstream navigation systems including Beidou, GPS, Galileo and GLONASS, a composite signal with three or more signal components Mainly; 3)
  • the application of quadrature phase error and amplitude imbalance evaluation method is narrow, generally used for QPSK modulation, and difficult to apply to the quality evaluation of composite signals of three or more signal components in current GNSS; 4) This method does not clearly explain the relationship between these indicators and signal acquisition, tracking, and demodulation, and cannot quantitatively evaluate the impact of signal quality on navigation performance.
  • the present invention provides a radio frequency signal quality evaluation method for a satellite navigation system, wherein a series of navigation signals are directly sampled from the radio frequency, and combined with the characteristics of the satellite navigation signal itself, a series of designs are designed.
  • the evaluation indicators can further clarify the relationship between signal quality indicators and signal acquisition, tracking and demodulation performance, while clearly and quantitatively assessing the impact of signal quality on navigation performance.
  • a radio frequency signal quality evaluation method for a satellite navigation system characterized in that the method comprises the following steps:
  • s rec (t) represents the variable determined by the time variable t of the actual baseband signal s rec
  • s 0 (t) represents the variable determined by the time variable t of the ideal baseband signal s 0
  • t represents the time variable
  • ⁇ represents the correlation Delay
  • Tp represents the duration of the actual baseband signal s rec
  • s 0 * (t- ⁇ ) represents the conjugate operation performed on the variable of the ideal baseband signal s 0 jointly determined by the time variable t and the associated delay ⁇
  • CCF ( ⁇ ) represents a variable determined by the correlation time delay ⁇ of the cross-correlation sequence CCF between the actual baseband signal s rec and the ideal baseband signal s 0 ;
  • step (4) Using the correlation function constructed in step (4), the quality evaluation index related to the in-band spurs and related loss is calculated correspondingly, thereby realizing the quality evaluation process of the radio frequency signal.
  • r ST [dBc] represents the dB value of the in-band spur
  • CCF( ⁇ ) represents the variable determined by the correlation delay ⁇ of the cross-correlation sequence between the actual baseband signal and the ideal baseband signal
  • LCCF[dB] represents the dB value of the correlation loss
  • CCD( ⁇ ) represents the variable determined by the correlation delay ⁇ of the cross-correlation sequence between the actual baseband signal and the ideal baseband signal.
  • step (5) it is preferable to further include an operation of quantitatively evaluating the pseudo code ranging error and the code tracking performance, the operation being specifically as follows:
  • pseudo-code ranging error index For the pseudo-code ranging error index, firstly, according to the correlation main peak of the ideal baseband signal and the actual baseband signal, a corresponding discriminant function is calculated, and then a linear fitting is performed on the zero-crossing offset of the discriminant function, and the obtained data is correspondingly obtained. Can be used to reflect pseudo-code ranging error;
  • the corresponding discrimination function is first calculated according to the correlation main peak of the ideal baseband signal and the actual baseband signal, and then the linear fitting of the zero-crossing slopes of the two discriminant functions is performed respectively, and the obtained slope is obtained.
  • the ratio can be used to reflect the code tracking performance.
  • step (5) it is preferable to further include an operation of calculating two quality evaluation indexes of the signal component phase difference and the signal component amplitude difference, and preferably calculated according to the following formulas:
  • ⁇ i represents the phase difference of the ith signal component of the actual baseband signal
  • ⁇ i t represents the phase angle of the maximum modulus point in the cross-correlation sequence between the actual baseband signal and the ith signal component of the ideal baseband signal
  • ⁇ i represents the carrier phase design value of the ith signal component of the ideal baseband signal
  • ⁇ p i [dB] represents the dB value of the amplitude difference of the ith signal component of the actual baseband signal
  • p i represents the design value of the ith signal component of the actual baseband signal in the total power ratio
  • p i t represents the actual baseband
  • the ith signal component of the signal is the actual value of the total power ratio.
  • step (5) it is preferable to further include an operation of calculating two quality evaluation indexes of the signal component code phase consistency and the frequency point code phase consistency, and is preferably calculated according to the following formulas:
  • ⁇ i, component ⁇ i, component - ⁇ 0
  • the component represents the code phase deviation of the ith signal component of the actual baseband signal
  • ⁇ i the component represents the discrimination function zero crossing offset value of the ith signal component
  • ⁇ 0 the discrimination function of the reference signal component Zero-crossing offset value
  • the frequency point represents the code phase deviation of the i-th frequency point of the actual baseband signal
  • ⁇ i the frequency point represents the zero-point offset value of the discrimination function of the combined signal of the i-th frequency point
  • ⁇ 1 represents The discrimination function of the reference frequency combination signal cross-zero offset value.
  • the signal power spectrum, the spectral distortion, the constellation, the error vector magnitude, the carrier leakage, and the like are included in the operation of the quality evaluation.
  • the signal is directly sampled from the radio frequency, the distortion caused by the hardware analog frequency conversion channel can be avoided, the signal can be sampled at multiple frequencies, and the phase consistency between the channels can be evaluated at the same time;
  • the eye diagram evaluation is not used, but the corresponding discriminant function is constructed according to the relevant main peak, and then the zero-crossing offset and the zero-crossing slope distortion of the discriminant function are fitted, thereby being quantitatively and accurately evaluated.
  • the evaluation indexes of component phase difference and component amplitude difference are proposed and their calculation methods are studied. The test shows that this method is more suitable for the quality evaluation of composite signals with more than 3 signal components in GNSS. Two evaluation indexes of signal component code phase consistency and frequency point code phase consistency are proposed, which can accurately estimate the phase consistency between channels.
  • the quality evaluation method according to the present invention is easy to control, and can further clarify the relationship between signal quality indicators and signal acquisition, tracking, and demodulation performance, and thus is particularly suitable for RF signal quality evaluation purposes of satellite navigation systems.
  • Figure 1 is a schematic illustration of the process flow of a radio frequency signal quality assessment method constructed in accordance with the present invention.
  • FIG. 1 is a schematic illustration of the process flow of a radio frequency signal quality assessment method constructed in accordance with the present invention. As shown in FIG. 1, the RF signal quality assessment method mainly includes the following steps:
  • the radio frequency signal of the satellite payload is sampled to obtain an intermediate frequency signal, and then the filtering process is performed on the intermediate frequency signal.
  • the satellite signal to be evaluated which is subjected to radio frequency sampling on the star, is obtained, for example, a signal of two code periods is intercepted; and the sampling signal is calculated according to the center frequency and the sampling rate of the radio frequency signal.
  • the RF sampled signal is passed through an ideal brick filter, for example, to obtain an intermediate frequency signal to be evaluated.
  • an ideal baseband combining signal of one code period and each branch signal component are generated.
  • Down conversion is performed on the intermediate frequency signal subjected to the filtering process, thereby obtaining a corresponding actual baseband signal.
  • a correlation function as shown below is constructed between the actual baseband signal to be evaluated and the ideal baseband signal, and is used in the subsequent calculation process of multiple evaluation indicators:
  • s rec (t) represents the variable determined by the time variable t of the actual baseband signal s rec
  • s 0 (t) represents the variable determined by the time variable t of the ideal baseband signal s 0
  • t represents the time variable
  • ⁇ represents the correlation Delay
  • Tp represents the duration of the actual baseband signal s rec
  • s 0 * (t- ⁇ ) represents the conjugate operation performed on the variable of the ideal baseband signal s 0 jointly determined by the time variable t and the associated delay ⁇
  • CCF ( ⁇ ) represents a variable determined by the correlation time delay ⁇ of the cross-correlation sequence CCF between the actual baseband signal s rec and the ideal baseband signal s 0 ;
  • the quality evaluation indicators related to the in-band spurs and related losses are calculated accordingly, thereby realizing the quality evaluation process of the RF signal.
  • r ST [dBc] represents the dB value of the in-band spur
  • CCF( ⁇ ) represents the variable determined by the correlation delay ⁇ of the cross-correlation sequence between the actual baseband signal and the ideal baseband signal
  • L CCF [dB] represents the dB value of the correlation loss
  • CCF( ⁇ ) represents the variable determined by the correlation delay ⁇ of the cross-correlation sequence between the actual baseband signal and the ideal baseband signal.
  • the present invention In order to carry out a more comprehensive and accurate evaluation of the radio frequency signal quality of the satellite navigation system, in addition to the above-mentioned basic indicators such as in-band spurs and related losses, the present invention also focuses on designing other related quality assessment indicators, and the calculation thereof Or the process is specifically described as follows:
  • the evaluation index may first calculate a corresponding discriminant function according to the relevant main peak of the ideal baseband signal, and then approximate the zero-crossing point of the discriminant function by linear fitting.
  • the offset, the pseudo-code ranging error of the navigation signal is:
  • e DB is the ranging deviation due to signal distortion
  • the unit is m
  • ⁇ b ( ⁇ ) is the zero-crossing offset of the discriminator
  • the unit s, c is the electromagnetic wave propagation rate.
  • the evaluation index may first calculate a corresponding discrimination function according to the correlation main peak of the ideal baseband signal and the actual baseband signal, and then, for example, a linear fitting method to obtain two The slope at the zero crossing of the discriminant function, the ratio between the two slopes, can be used to reflect the code tracking performance.
  • the evaluation index can be calculated according to the following formula inferred:
  • ⁇ i represents the phase difference of the ith signal component of the actual baseband signal
  • ⁇ i t represents the phase angle of the maximum modulus point in the cross-correlation sequence between the actual baseband signal and the ith signal component of the ideal baseband signal
  • ⁇ i represents the carrier phase design value of the ith signal component of the ideal baseband signal
  • the evaluation index can be calculated according to the following formula:
  • ⁇ p i [dB] represents the dB value of the amplitude difference of the ith signal component of the actual baseband signal
  • p i represents the design value of the ith signal component of the actual baseband signal in the total power ratio
  • p i t represents the actual baseband
  • the ith signal component of the signal is the actual value of the total power ratio.
  • the evaluation index can be calculated according to the following formula:
  • ⁇ i, component ⁇ i, component - ⁇ 0
  • the component represents the code phase deviation of the ith signal component of the actual baseband signal
  • ⁇ i the component represents the discrimination function zero crossing offset value of the ith signal component
  • ⁇ 0 the discrimination function of the reference signal component Zero crossing offset value
  • the evaluation index can be calculated according to the following formula:
  • the frequency point represents the code phase deviation of the i-th frequency point of the actual baseband signal
  • ⁇ i the frequency point represents the zero-point offset value of the discrimination function of the combined signal of the i-th frequency point
  • ⁇ 1 represents The discrimination function of the reference frequency combination signal cross-zero offset value.
  • a series of indicators such as signal power spectrum, spectral distortion, constellation diagram, error vector magnitude, and carrier leakage are also included in the quality assessment process, and the calculation and processing thereof are also included. The details are as follows:
  • the FFT algorithm can be used to analyze the Fourier transform s rec (f) of the actual baseband signal s rec (t), then the power spectrum of the signal Correspondingly, the power spectrum can be drawn, where T is the sampling signal length, here is the length of one code period, and Fs is the signal sampling rate.
  • the power spectrum envelope can also be extracted.
  • the time domain correlation is calculated, and the time domain correlation is added with time window processing.
  • the time window width is generally taken as 5 chip widths (the size of the time window determines the fineness of the power spectrum envelope). The wider the time window, the finer the power spectrum envelope curve is, and the fast Fourier transform is performed on the time domain correlation of the time window to obtain the power spectrum envelope.
  • the ideal baseband signal and the actual baseband signal are subjected to amplitude normalization processing, and the actual baseband signal is divided by its average amplitude to obtain a normalized actual signal, and the same method can obtain a normalized ideal signal;
  • the I branch of the normalized actual signal is the abscissa
  • the Q branch is the ordinate
  • the scatter plot of the actual signal is drawn, and the range of the horizontal and vertical axis is set to [X min , X max , Y min , Y max ], X min is the abscissa with the smallest signal point, X max is the largest abscissa of the signal point, Y min is the ordinate with the smallest signal point, and Y max is the ordinate of the largest signal point. ;
  • the coordinate axis plane is divided into square lattices of areas such as N*N, for example, N is taken as 100. Count the number of signal points in each square, and set the color depth of the square according to the number of points; use the same method to draw the ideal signal points in the same coordinate map for comparison.
  • the actual baseband signal to be evaluated and the ideal baseband signal are normalized, and the average amplitude of the normalized signal is 1;
  • the carrier leakage is calculated as follows, where G(f) is the signal power spectrum calculated in step 6), f c is the carrier frequency (in Hz), and [f l , f h ] is the frequency range of the specified frequency band:

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
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Abstract

本发明公开了一种用于卫星导航系统的射频信号质量评估方法，包括：对卫星有效载荷的射频信号执行采样以获得中频信号，并对其执行滤波处理；对执行滤波处理后的中频信号执行下变频以获得对应的实际基带信号；基于所获得的实际基带信号及其信号体制，生成理想基带信号各支路的信号分量；将用于评估实际基带信号的理想基带信号予以复现；以及为待评估的实际基带信号与理想基带信号之间构建相关函数，然后相应计算得出带内杂散、相关损耗等一系列的质量评估指标，由此实现射频信号的质量评估过程。通过本发明，能够明确信号质量指标与信号捕获、跟踪以及解调性能之间的关系，同时得以清晰、定量地评估信号质量对导航性能的影响。

Description

一种用于卫星导航系统的射频信号质量评估方法 【技术领域】
本发明属于卫星导航技术领域，更具体地，涉及一种用于卫星导航系统的射频信号质量评估方法。
【背景技术】
卫星导航信号用于导航系统的授时和测距，对导航性能的影响主要体现在载波跟踪性能、伪码跟踪性能、电文解调性能三个方面。导航信号体制决定导航系统的先天性能，空间信号质量则决定了实际系统所能达到的最佳性能与信号体制性能之间的差距。在通信系统中，信息的正确解调是设计目标，其性能与采样判决时刻信号矢量的误差相关；而在导航系统中，更加关注测距精度，它取决于信号波形的质量。因此，导航系统对信号质量的要求高于一般通信系统，相应地，对其信号质量评估方式的全面性和准确性方面提出了更高的要求。
现有技术中已经提出了一些用于卫星导航系统的质量评估方案，例如，CN102571652A中公开了一种GNSS基带信号的评估方法，并从频域功率谱、时域波形、码片边缘、调制误差、相关特性这几个方面分析GNSS基带信号的性能。然而，进一步的研究表明，上述方案仍然存在以下的局限：：1)该方法仅考虑对基带信号质量的评估，不能真实反映空间信号质量对导航性能的影响，没有给出从射频信号无失真变频到基带的信号处理方法，而且由于采用基带采样方式，不同频点的信号需配置不同的模拟通道，不可避免地引入模拟通道间的时延不一致性，导致频间信号一致性的评估精度降低；2)眼图的六项评估指标偏理想化，且难以应用到目前GNSS中三路及以上信号分量的复合信号的质量评估，而现阶段主流的四大导航系统，包括北斗、GPS、伽利略和GLONASS，都以三路及以上信号分量的复合信号 为主；3)正交相位误差和幅度不平衡性评估方法的适用范围较窄，一般用于QPSK调制，也难以应用到目前GNSS中三路及以上信号分量的复合信号的质量评估；4)该方法没有明确说明这些指标与信号捕获、跟踪、解调之间的关系，无法定量评估信号质量对导航性能的影响。
【发明内容】
针对现有技术的以上缺陷或改进需求，本发明提供了一种用于卫星导航系统的射频信号质量评估方法，其中通过直接从射频采样导航信号，并结合卫星导航信号自身的特点来设计一系列的评估指标，相应能够进一步明确信号质量指标与信号捕获、跟踪以及解调性能之间的关系，同时得以清晰、定量地评估信号质量对导航性能的影响。
为实现上述目的，按照本发明，提供了一种用于卫星导航系统的射频信号质量评估方法，其特征在于，该方法包括下列步骤：
(1)对卫星有效载荷的射频信号执行采样以获得中频信号，然后对该中频信号执行滤波处理；
(2)对执行滤波处理后的中频信号执行下变频，由此获得对应的实际基带信号；
(3)基于步骤(2)所获得的实际基带信号及其信号体制，生成相同采样率、一个码周期长度的理想基带信号各支路的信号分量；接着，利用所述实际基带信号和所述理想基带信号各支路的信号分量，将用于评估实际基带信号的理想基带信号予以复现；
(4)为待评估的实际基带信号与理想基带信号之间构建如下所示的相关函数：
Figure PCTCN2014088745-appb-000001
其中,srec(t)表示实际基带信号srec由时间变量t而确定的变量，s0(t)表示 理想基带信号s0由时间变量t而确定的变量，t表示时间变量，τ表示相关时延，Tp表示实际基带信号srec的时长，s0 *(t-τ)表示对理想基带信号s0由时间变量t和相关时延τ共同确定的变量所执行的共轭运算，CCF(τ)表示实际基带信号srec与理想基带信号s0之间的互相关序列CCF由相关时延τ而确定的变量；
(5)利用步骤(4)所构建的相关函数，相应计算得出与带内杂散、相关损耗相关的质量评估指标，由此实现射频信号的质量评估过程。
作为进一步优选地，对于所述计算带内杂散和相关损耗的操作，优选分别按照以下公式计算得出：
rST[dBc]＝10×log10(1-max(|CCF(τ)|2))
其中，rST[dBc]表示带内杂散的dB值，CCF(τ)表示实际基带信号与理想基带信号之间的互相关序列由相关时延τ而确定的变量；
LCCF[dB]＝20×log10(max(|CCF(τ)|2))
其中，LCCF[dB]表示相关损耗的dB值，CCD(τ)表示实际基带信号与理想基带信号之间的互相关序列由相关时延τ而确定的变量。
作为进一步优选地，在步骤(5)中，优选还包括定量评估伪码测距误差和码跟踪性能的操作，该操作具体如下：
对于伪码测距误差指标，首先根据所述理想基带信号与实际基带信号的相关主峰，计算出相应的鉴别函数，然后对该鉴别函数的过零点偏移执行线性拟合，相应所获得的数据即可用来反映伪码测距误差；
对于码跟踪性能指标，首先根据所述理想基带信号和实际基带信号的相关主峰，分别计算出相应的鉴别函数，然后分别对两个鉴别函数的过零点斜率执行线性拟合，相应所获得的斜率比值即可用来反映码跟踪性能。
作为进一步优选地，在步骤(5)中，优选还包括计算信号分量相位差和信号分量幅度差两项质量评估指标的操作，并且优选分别按照以下公式计算得出：
Δθi＝θi t-θi
其中，Δθi表示实际基带信号的第i个信号分量的相位差，θi t表示实际基带信号与理想基带信号第i个信号分量之间的互相关序列中，其最大模值点的相角，θi表示理想基带信号第i个信号分量的载波相位设计值；
Figure PCTCN2014088745-appb-000002
其中，Δpi[dB]表示实际基带信号的第i个信号分量的幅度差的dB值，pi表示实际基带信号的第i个信号分量占总功率比例的设计值，pi t表示实际基带信号的第i个信号分量占总功率比例的实际值。
作为进一步优选地，在步骤(5)中，优选还包括计算信号分量码相位一致性和频点码相位一致性两项质量评估指标的操作，并且优选分别按照以下公式计算得出：
Δεi，分量＝εi，分量-ε0
其中，Δεi，分量表示实际基带信号的第i个信号分量的码相位偏差，εi，分量表示该第i个信号分量的鉴别函数过零点偏移值，ε0表示基准信号分量的鉴别函数过零点偏移值；
Δεi，频点＝εi，频点-ε1
其中，Δεi，频点表示实际基带信号的第i个频点的码相位偏差，εi，频点表示该第i个频点的合路信号的鉴别函数过零点偏移值，ε1表示基准频点合路信号的鉴别函数过零点偏移值。
作为进一步优选地，在步骤(5)中，优选还包括将信号功率谱、频谱失真、星座图、误差矢量幅度、载波泄漏等一系列指标纳入质量评估的操作。
总体而言，通过本发明所构思的以上技术方案与现有技术相比，主要具备以下方面的技术优点：
1、由于直接从射频采样信号，可避免硬件模拟变频通道给信号带来的失真，能够多频点采样信号，同时评估通道间相位一致性；
2、在本发明中没有使用眼图评估，而是根据相关主峰来构建相应的鉴别函数，进而拟合出该鉴别函数的过零点偏移和过零点斜率失真，以此方式能够定量、精确评估得出伪码测距误差和码跟踪性能指标；
3、提出了分量相位差和分量幅度差两项评估指标并对其计算方式进行了研究，测试表明，此方式更加适用于目前GNSS中含3路以上信号分量的复合信号的质量评估；此外，提出了信号分量码相位一致性和频点码相位一致性两项评估指标，相应得以准确评估通道间相位一致性；
4、按照本发明的质量评估方式便于操控，并且能够进一步明确信号质量指标与信号捕获、跟踪以及解调性能之间的关系，因而尤其适用于卫星导航系统的射频信号质量评估用途。
【附图说明】
图1是按照本发明优选所构建的射频信号质量评估方法的工艺流程示意图。
【具体实施方式】
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。此外，下面所描述的本发明各个实施方式中所涉及到的技术特征只要彼此之间未构成冲突就可以相互组合。
图1是按照本发明优选所构建的射频信号质量评估方法的工艺流程示意图。如图1中所示，该射频信号质量评估方法主要包括下列步骤：
步骤一
对卫星有效载荷的射频信号执行采样以获得中频信号，然后对该中频信号执行滤波处理。
具体而言，首先获取星上载荷射频采样的待评估卫星信号，例如截取两个码周期的信号；根据射频信号的中心频率和采样率计算出采样信号的 中频频率，将射频采样的信号例如通过理想砖状滤波器，得到待评估的中频信号。然后，根据待评估信号的信号体制，生成一个码周期的理想基带合路信号和各支路信号分量。
步骤二
对执行滤波处理后的中频信号执行下变频，由此获得对应的实际基带信号。
步骤三
基于步骤二所获得的实际待评估基带信号及其信号体制，生成相同采样率、一个码周期长度的理想基带信号各支路的信号分量；接着，利用所述实际基带信号和所述理想基带信号各支路的信号分量，将用于评估实际基带信号的理想基带信号予以复现。
步骤四
为待评估的实际基带信号与理想基带信号之间构建如下所示的相关函数，并将其用于后续的多个评估指标的计算过程：
Figure PCTCN2014088745-appb-000003
其中,srec(t)表示实际基带信号srec由时间变量t而确定的变量，s0(t)表示理想基带信号s0由时间变量t而确定的变量，t表示时间变量，τ表示相关时延，Tp表示实际基带信号srec的时长，s0 *(t-τ)表示对理想基带信号s0由时间变量t和相关时延τ共同确定的变量所执行的共轭运算，CCF(τ)表示实际基带信号srec与理想基带信号s0之间的互相关序列CCF由相关时延τ而确定的变量；
步骤五
利用以上所构建的相关函数，相应计算得出与带内杂散、相关损耗相关的质量评估指标，由此实现射频信号的质量评估过程。
按照本发明的一个优选实施方式，对于所述计算带内杂散的操作，优 选按照以下公式计算得出：
rST[dBc]＝10×log10(1-max(|CCF(τ)|2))
其中，rST[dBc]表示带内杂散的dB值，CCF(τ)表示实际基带信号与理想基带信号之间的互相关序列由相关时延τ而确定的变量；
对于所述计算相关损耗的操作，同样优选按照以下公式计算得出：
LCCF[dB]＝20×log10(max(|CCF(τ)|2))
其中，LCCF[dB]表示相关损耗的dB值，CCF(τ)表示实际基带信号与理想基带信号之间的互相关序列由相关时延τ而确定的变量
为了对卫星导航系统的射频信号质量执行更为全面、准确的评估，除了上述的带内杂散、相关损耗等基本指标之外，本发明还重点设计了其他一些相关的质量评估指标，其计算或处理过程分别具体说明如下:
·伪码测距误差
按照本发明的一个优选实施方式，该评估指标优选可以先根据所述理想基带信号的相关主峰，计算出相应的鉴别函数，然后譬如采用线性拟合的方式拟合得出该鉴别函数的过零点偏移量，则导航信号的伪码测距误差为：
eDB＝εb(σ)×c
式中，eDB为由于信号失真带来的测距偏差，单位为m，εb(σ)为鉴别器过零点偏移量，单位s，c为电磁波传播速率。
·码跟踪性能
按照本发明的一个优选实施方式，该评估指标可以先根据所述理想基带信号和实际基带信号的相关主峰，分别计算出相应的鉴别函数，然后譬如采用线性拟合的方式拟合得出两个鉴别函数的过零点处的斜率，两个斜率之间的比值即可用来反映码跟踪性能。
·信号分量相位差
按照本发明的一个优选实施方式，该评估指标可以按照以下公式计算 得出：
Δθi＝θi t-θi
其中，Δθi表示实际基带信号的第i个信号分量的相位差，θi t表示实际基带信号与理想基带信号第i个信号分量之间的互相关序列中，其最大模值点的相角，θi表示理想基带信号第i个信号分量的载波相位设计值；
·信号分量幅度差
按照本发明的一个优选实施方式，该评估指标可以按照以下公式计算得出：
Figure PCTCN2014088745-appb-000004
其中，Δpi[dB]表示实际基带信号的第i个信号分量的幅度差的dB值，pi表示实际基带信号的第i个信号分量占总功率比例的设计值，pi t表示实际基带信号的第i个信号分量占总功率比例的实际值。
·信号分量码相位一致性
按照本发明的一个优选实施方式，该评估指标可以按照以下公式计算得出：
Δεi，分量＝εi，分量-ε0
其中，Δεi，分量表示实际基带信号的第i个信号分量的码相位偏差，εi，分量表示该第i个信号分量的鉴别函数过零点偏移值，ε0表示基准信号分量的鉴别函数过零点偏移值。
·频点码相位一致性
按照本发明的一个优选实施方式，该评估指标可以按照以下公式计算得出：
Δεi，频点＝εi，频点-ε1
其中，Δεi，频点表示实际基带信号的第i个频点的码相位偏差，εi，频点表示该第i个频点的合路信号的鉴别函数过零点偏移值，ε1表示基准频点合路信号 的鉴别函数过零点偏移值。
此外，对于按照本发明的射频信号质量评估方式，还包括将信号功率谱、频谱失真、星座图、误差矢量幅度、载波泄漏等一系列指标也纳入到质量评估过程之中，其计算及处理过程分别具体说明如下：
·画出信号功率谱
首先，譬如可以用FFT算法分析实际基带信号srec(t)的傅里叶变换srec(f)，则信号的功率谱
Figure PCTCN2014088745-appb-000005
相应可画出功率谱，其中，T为采样信号时间长度，在这里为一个码周期长度，Fs为信号采样率。
此外，还可以提取功率谱包络。根据频域信号乘积的反傅里叶变换计算时域相关，对时域相关作加时间窗处理，时间窗宽度一般取为5个码片宽度(时间窗的大小决定功率谱包络的精细程度，时间窗越宽，功率谱包络曲线越细)，对通过时间窗的时域相关作快速傅里叶变换，得到功率谱包络。
·信号频谱失真
首先，分别计算出实际基带信号和理想基带信号的频谱srec(f)和ss(f)，然后可按照下列公式计算出频谱失真，相应画出失真图：
Figure PCTCN2014088745-appb-000006
·画出星座图
首先，对理想基带信号和实际基带信号均作幅度归一化处理，将实际基带信号除以它的平均幅度，得到归一化的实际信号，同样的方法可以得到归一化的理想信号；
然后，在坐标图中，以归一化的实际信号的I支路为横坐标，Q支路为纵坐标，画出实际信号的散点图，设定横纵坐标轴的范围为[Xmin，Xmax，Ymin，Ymax]，Xmin为信号点最小的横坐标，Xmax为信号点最大的横坐标，Ymin为信号点最小的纵坐标，Ymax为信号点最大的纵坐标；将坐标轴 平面分成N*N等面积的方格子，譬如N取100。统计每个方格子内的信号点数，根据点数设定方格子的颜色深度；用同样的方法在同一个坐标图中，画出理想信号点，作对比。
·误差矢量幅度
首先，可以对待评估的实际基带信号和理想基带信号都作归一化处理，并使得归一化处理后信号的平均幅度为1；
接着，将理想基带信号按照其信号点在坐标图上的分布位置予以编号，，记为Vk＝Ik+jQk，然后根据实际基带信号点与这K个理想基带信号点之间的距离，将所有实际基带信号点与理想基带点均属于最接近距离划分为一类，记作：
{(Irec(m)，Qrec(m))|(Iideal(m)，Qideal(m))＝Vk，m＝1，2，...，Mk}
其中，Mk为样本中与信号矢量Vk对应的采样点个数，(Irec(m)，Qrec(m))为实际信号点(Iideal(m)，Qideal(m))为理想信号点；
最后，按照以下公式来计算待评估信号与信号矢量Vk对应的矢量误差幅度：
Figure PCTCN2014088745-appb-000007
其中，(Irec k，Qrec k)为分为第k类的实际信号点，即理想信号矢量Vk对应的实际信号点。
·载波泄漏
载波泄漏的计算公式如下，其中G(f)为步骤6)中计算的信号功率谱，fc为载波频率(单位Hz)，[fl，fh]为规定频带的频率范围：
Figure PCTCN2014088745-appb-000008
上述信号功率谱、频谱失真、星座图、误差矢量幅度、载波泄漏等一系列指标的基本计算及处理公式属于本领域的公知常识且为本领域的技术人员所熟知，因此在此不再赘述。
本领域的技术人员容易理解，以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (6)

  1. 一种用于卫星导航系统的射频信号质量评估方法，其特征在于，该方法包括下列步骤：
    (1)对卫星有效载荷的射频信号执行采样以获得中频信号，然后对该中频信号执行滤波处理；
    (2)对执行滤波处理后的中频信号执行下变频，由此获得对应的实际基带信号；
    (3)基于步骤(2)所获得的实际基带信号及其信号体制，生成相同采样率、一个码周期长度的理想基带信号各支路的信号分量；接着，利用所述实际基带信号和所述理想基带信号各支路的信号分量，将用于评估实际基带信号的理想基带信号予以复现；
    (4)为待评估的实际基带信号与理想基带信号之间构建如下所示的相关函数：
    Figure PCTCN2014088745-appb-100001
    其中,srec(t)表示实际基带信号srec由时间变量t而确定的变量，s0(t)表示理想基带信号s0由时间变量t而确定的变量，t表示时间变量，τ表示相关时延，Tp表示实际基带信号srec的时长，s0 *(t-τ)表示对理想基带信号s0由时间变量t和相关时延τ共同确定的变量所执行的共轭运算，CCF(τ)表示实际基带信号srec与理想基带信号s0之间的互相关序列CCF由相关时延τ而确定的变量；
    (5)利用步骤(4)所构建的相关函数，相应计算得出与带内杂散、相关损耗相关的质量评估指标，由此实现射频信号的质量评估过程。
  2. 如权利要求1所述的射频信号质量评估方法，其特征在于，对于所述计算带内杂散和相关损耗的操作，优选分别按照以下公式计算得出：
    TST[dBc]＝10×log10(1-max(|CCF(τ)|2))
    其中，TST[dBc]表示带内杂散的dB值，CCF(τ)表示实际基带信号与理想基带信号之间的互相关序列由相关时延τ而确定的变量；
    LCCF[dB]＝20×log10(max(|CCF(τ)|2))
    其中，LCCF[dB]表示相关损耗的dB值，CCF(τ)表示实际基带信号与理想基带信号之间的互相关序列由相关时延τ而确定的变量。
  3. 如权利要求1或2所述的射频信号质量评估方法，其特征在于，在步骤(5)中，优选还包括定量评估伪码测距误差和码跟踪性能的操作，该操作具体如下：
    对于伪码测距误差指标，首先根据所述理想基带信号与实际基带信号的相关主峰，计算出相应的鉴别函数，然后对该鉴别函数的过零点偏移执行线性拟合，相应所获得的数据即可用来反映伪码测距误差；
    对于码跟踪性能指标，首先根据所述理想基带信号和实际基带信号的相关主峰，分别计算出相应的鉴别函数，然后分别对两个鉴别函数的过零点斜率执行线性拟合，相应所获得的斜率比值即可用来反映码跟踪性能。
  4. 如权利要求1-3任意一项所述的射频信号质量评估方法，其特征在于，在步骤(5)中，优选还包括计算信号分量相位差和信号分量幅度差两项质量评估指标的操作，并且优选分别按照以下公式计算得出：
    Δθt＝θt t-θt
    其中，Δθt表示实际基带信号的第i个信号分量的相位差，θt t表示实际基带信号与理想基带信号第i个信号分量之间的互相关序列中，其最大模值点的相角，θt表示理想基带信号第i个信号分量的载波相位设计值；
    Figure PCTCN2014088745-appb-100002
    其中，Δpt[dB]表示实际基带信号的第i个信号分量的幅度差的dB值，pt表示实际基带信号的第i个信号分量占总功率比例的设计值，pt t表示实际基带信号的第i个信号分量占总功率比例的实际值。
  5. 如权利要求1-4任意一项所述的射频信号质量评估方法，其特征在于，在步骤(5)中，优选还包括计算信号分量码相位一致性和频点码相位一致性两项质量评估指标的操作，并且优选分别按照以下公式计算得出：
    Δεt，分量＝εt，分量-ε0
    其中，Δεt，分量表示实际基带信号的第i个信号分量的码相位偏差，εt，分量表示该第i个信号分量的鉴别函数过零点偏移值，ε0表示基准信号分量的鉴别函数过零点偏移值；
    Δεt，频点＝εt，频点-ε1
    其中，Δεt，频点表示实际基带信号的第i个频点的码相位偏差，εt，频点表示该第i个频点的合路信号的鉴别函数过零点偏移值，ε1表示基准频点合路信号的鉴别函数过零点偏移值。
  6. 如权利要求5所述的射频信号质量评估方法，其特征在于，在步骤(5)中，优选还包括将信号功率谱、频谱失真、星座图、误差矢量幅度、载波泄漏等一系列指标纳入质量评估的操作。
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