CN102638319B - Modulation performance test method for navigational satellite binary offset carrier signal - Google Patents

Abstract

The invention discloses a modulation performance test method for a navigational satellite binary offset carrier signal. The modulation performance test method comprises the following steps of: firstly, carrying out direct A/D sampling on a BOC (binary offset carrier) modulation navigation signal of a navigational satellite downlink transmission microwave frequency band; then, carrying out variable-frequency filtering and hilbert transform on the signal in a numeric field; carrying out quadrature demodulation, channel gain compensation and phase compensation processing in digital communication, and filtering by a measurement filter to obtain measured data; carrying out symbol detection, reference signal generation processing and reference filtering on the measured data to obtain reference data; and calculating the reference data and the measured data to obtain a parameter and a signal graph which reflects the base band modulation performance. The BOC carrier modulation signal is processed in the numeric field by the modulation performance test method. Because a BOC single sideband frequency spectrum is extracted in the numeric field, the problem that the BOC signal can not be subjected to the modulation characteristic test through a vector signal analysis method because of subcarrier can be solved.

Description

A kind of modulating performance method of testing of navigation satellite binary offset carrier (AltBOC) signal

Technical field

The present invention relates to the descending modulating performance method of testing of broadcasting signal of a kind of navigation satellite.

Background technology

At present, China is carrying out worldwide navigation of new generation and is defending the development of system, from last generation region satellite navigation system different be, in order to improve precision and the antijamming capability of satellite navigation signals, in the signal system of navigation satellite, will increase the navigation signal of BOC (binary offset carrier) modulation, the baseband modulation performance of navigation signal is an importance of navigation signal performance, in satellite development process, the baseband modulation performance parameter of the descending navigation performance of navigation satellite is the key parameter in whole star test.

The baseband modulation performance test of existing digital modulation signals is general adopts following two kinds of modes: (1) utilizes VSA, as the FSQ sequence of German R/S company and 89600 series, the E4406VSA series VSA of U.S. Agilient.(2) utilize oscilloscope or frequency spectrograph in conjunction with Vector Signal Analysis software, as the 89600s Vector Signal Analysis software of Agilient.Existing commercial VSA or Vector Signal Analysis software, only to traditional digital modulation signals, as the modulation signals such as PSK, GMSK, MSK are suitable for.Because BOC is a kind of novel digital modulation signals, be mainly used in navigation signal, Modulation Signal Parameters is not only relevant with carrier frequency and bit rate, and relevant with subcarrier frequency, and existing commercial analyzer or Vector Signal Analysis software are only for carrier frequency and bit rate, cannot complete the test of the whole baseband modulation performance parameters of navigation signal to BOC modulation.

Document about Vector Signal Analysis is also a lot, but there is the weak point of following two types in the method for describing in these documents: the first kind is to need training sequence signal to carry out channel estimating to processes such as signal frequency conversion processing, just can complete the parameter setting of channel magnitude compensation and Phase Compensation Algorithm, require to produce high-quality training signal.As document " Key Algorithms for Accurate GSM EDGE EVM Measurement on ATE Platform " (Shu Xia, 8th International Conference on Solid-State and Integrated Circuit Technology, 2006.ICSICT ' 06.) method that provides.For high-quality navigation satellite BOC signal, meaning needs a higher-quality BOC signal source to carry out calibration test system, and this is very difficult in real work.Equations of The Second Kind is to use adaptive equalization technique to carry out channel estimating to receive channel, as document " EVM measurement techniques for MUOS " (McAllister, IEEE Military Communications Conference, 2009.MILCOM 2009.) method that provides.Because the modulation quality of navigation signal is high, therefore, the error of estimation will impact test result, and channel estimation method is realized complicated in this method.

Summary of the invention

Technology of the present invention is dealt with problems and is: overcome the deficiencies in the prior art, a kind of modulating performance method of testing of navigation satellite BOC signal is provided, can realize the test of the navigation signal baseband modulation performance parameter to BOC modulation.

Technical solution of the present invention is: a kind of modulating performance method of testing of navigation satellite binary offset carrier (AltBOC) signal, and step is as follows:

(1) the descending binary offset carrier (boc) modulated signals of broadcasting of navigation satellite is carried out to direct modulus sampling;

(2) direct modulus sampled data is carried out to digital mixing, digital low-pass filtering, obtain intermediate frequency binary offset carrier digital signal;

(3) intermediate frequency binary offset carrier digital signal is evenly extracted;

(4) the binary offset carrier digital signal after even extraction is carried out to digital low-pass filtering again, in frequency domain, extract the lower sideband in two signal spectrums that binary offset carrier digital signal comprises, and upper sideband spectrum is suppressed;

(5) output signal after digital low-pass filtering is again carried out to Hilbert transform and obtain complex data, then utilize Costas loop to carry out carrier track to complex data, and the output signal completing after carrier track is carried out to channel gain compensation and phase compensation, obtain baseband signal;

(6) according to the transfer function of the definite test filter matching of the characteristic of navigation satellite binary offset carrier (AltBOC) signal transmitting terminal formed filter, then utilize test filter to carry out filtering to the baseband signal after channel gain compensation and phase compensation, obtain IQ base band Wave data to be measured;

(7) according to PSK modulation system, IQ base band Wave data to be measured is carried out to sign bit detection, obtain sign bit data, the sign bit synchronous error Information generation IQ ideal baseband signal then obtaining according to PSK baseband modulation mode, sign bit rate and timing Recovery processing;

(8) according to the characteristic of navigation satellite binary offset carrier (AltBOC) signal transmission channel formed filter and test filter, reference filter is set, then utilizes reference filter to carry out filtering to IQ ideal baseband signal, form IQ base band reference waveform data;

(9) ask for the error amount between IQ base band Wave data to be measured and IQ base band reference waveform data, error amount is carried out to vector error processing, obtain reflecting parameter and the signal graph of baseband modulation performance.

In described step (1), the sample rate of A/D sampling is greater than the more than 10 times of pseudorandom code check of binary offset carrier modulation navigation signal, and the chip number of employing is greater than 200.

The present invention's advantage is compared with prior art:

(1) the inventive method is not carried out frequency-conversion processing to the BOC signal of broadcasting under navigation satellite, but directly after A/D sampling, processes at numeric field, has avoided amplitude-phase distortion that frequency-conversion processing the brings impact on BOC signal modulation performance test result;

(2) in numeric field processing procedure, from BOC double-side band frequency spectrum, extract one of them, utilize the Vector Signal Analysis method of conventional digital PSK modulation to carry out the analysis of BOC modulating characteristic parameter, solved owing to existing subcarrier to cause BOC signal cannot carry out by Vector Signal Analysis method the problem of baseband modulation characteristic test;

(3) in digital COSTAS loop, adopt carrier wave circulator, while carrying out carrier synchronization, eliminate the low pass filter of IQ branch road, while having avoided gain and phase compensation, will carry out the compensation of IQ branch road low-pass filtering, reduce to process and realize difficulty;

(4) common if sampling carries out in the vector signal method of modulating performance test, need to have training sequence signal to carry out channel estimating or adaptive blind channel estimating, realizes gain compensation and phase compensation, realizes complexity, and measuring system adapts to energy difference.In this aspect method to BOC carrier (boc) modulated signals Direct Sampling, signal frequency conversion and filtering are processed and are all carried out at numeric field, while carrying out gain compensation and phase compensation, the equalization algorithm of channel is realized simple, and portfolio effect is good, amplitude and phase distortion in BOC signal modulation performance analytic process are perfectly compensated, and the amplitude-phase characteristic of channel affects and can ignore test result.

Accompanying drawing explanation

Fig. 1 is the theory diagram of the inventive method;

Fig. 2 is the frequency spectrum of Galileo navigation satellite E1A signal BOC (15,2.5) navigation signal;

Fig. 3 is the amplitude-frequency phase-frequency characteristic of the low pass filter after digital mixing;

Fig. 4 is the tap coefficient of the low pass filter after digital mixing;

Fig. 5 is the frequency spectrum of the intermediate frequency BOC signal of low pass filter output after digital mixing;

Fig. 6 is the amplitude-frequency phase-frequency characteristic of the low pass filter after extracting;

Fig. 7 is the tap coefficient of the low pass filter after extracting;

Fig. 8 is the frequency spectrum of the intermediate frequency BOC signal of the low pass filter output after extracting.

Embodiment

As shown in Figure 1, be the schematic diagram of the inventive method.The inventive method mainly comprises the direct A/D sampling and the numeric field signal processing two large divisions that under navigation satellite, broadcast microwave frequency band BOC navigation signal.Sample to broadcasting microwave frequency band BOC navigation signal Direct Sampling under navigation satellite with A/D, data after sampling are carried out down-conversion and low-pass filtering, then extract, bandpass filtering, extract in two signal spectrums in BOC signal spectrum structure and carry out quadrature demodulation.Carry out gain and the phase compensation of passage according to receive channel characteristic, then measure filter filtering according to navigation satellite BOC signal transmission channel characteristic, generate IQ Baseband Testing signal waveform, generate IQ base band reference waveform signal data according to modulation system, character rate and transceiver channel characteristic, IQ base band reference waveform signal data and IQ Baseband Testing signal waveform data are asked error, then process the measurement result that obtains BOC modulating performance parameter.

As an example method of the present invention is described in detail with Galileo navigation satellite E1A signal below.BOC is BOC (α, β) expression for modulation system, and wherein parameter beta represents the code check after radix normalization take 1.023Mcps, and parameter alpha represents take 1.023Mcps as the normalized subcarrier frequency of radix.E1A signal center frequency is 1575.42MHz, and modulation signal form is BOC (15,2.5), represents that the speed of pseudo noise code is 2.5 × 1.023=2.5625Mcps, and subcarrier frequency is 15 × 1.023=15.345MHz.(1) first use the spread-spectrum signal source of simulation to produce the Galileo navigation satellite E1A signal of a simulation, centre frequency 1575.42MHz, modulation signal form is BOC (15,2.5), the A/D sampler that is 5GHz by sample rate carries out direct high-speed sampling to E1A navigation signal, and the sampling time is 0.5ms here, and adopting chip number is 1281, sampled point number is 2500000, and the frequency spectrum of BOC signal as shown in Figure 2.

(2) at the digital local oscillator signal of a local 1545.42MHz of numeric field generation, sampled data is carried out to digital mixing, digital low-pass filtering.Low pass filter 1 is selected FIR filter, and the mathematic(al) representation of its transfer function is:

$H_1\left(z_1\right)=\underset{i=1}{\overset{M_1}{\mathrm{\Σ}}}{C}_i{z}_1^{-i}---\left(1\right)$

C in formula _ifor the i tap coefficient of low pass filter 1, M ₁for the exponent number of low pass filter 1,

f _sfor sample frequency, be 5Gsa/s here.

In this example, the exponent number of low pass filter 1 is 156, and as shown in Figure 3, each tap coefficient as shown in Figure 4 for its amplitude-frequency and phase-frequency characteristic.After low-pass filtering, obtaining centre frequency is the BOC digital signal of 30MHz, and the frequency spectrum of the intermediate frequency BOC signal that low pass filter 1 is exported as shown in Figure 5;

(3) selecting extraction coefficient 10, evenly extracts intermediate frequency BOC digital signal, and the BOC signal data after extracting is carried out to digital low-pass filtering again, and low pass filter 2 is also FIR filter, and the mathematic(al) representation of its transfer function is:

$H_2\left(z_2\right)=\underset{i=1}{\overset{M_2}{\mathrm{\Σ}}}{F}_i{z}_2^i---\left(2\right)$

F in formula _ifor the i tap coefficient of low pass filter 2, M ₂for the exponent number of low pass filter 2,

m is extraction yield coefficient.

In this example, low pass filter 2 exponent numbers are 78, and as shown in Figure 6, tap coefficient as shown in Figure 7 for its amplitude-frequency and phase-frequency characteristic.Low pass filter 2 extracts the spectrum of the lower sideband signal in two sidebands in BOC signal spectrum, and upper sideband spectrum is suppressed, and the signal spectrum that low pass filter 2 is exported as shown in Figure 8;

(4) individual signals of low pass filter 2 being exported, first carry out Hilbert transform, be converted to complex data, then utilize the Costas loop of phase discriminator, loop filter, carrier wave circulator and digital vco composition to complete the carrier track to input complex data.The individual signals spectrum structure output signal s (k) that low pass filter 2 is exported is expressed as:

$s\left(k\right)=a\left(k\frac{M}{f_s}\right)\cos ({2\mathrm{\πf}}_{i}k\frac{M}{f_s}+{\mathrm{\θ}}_i)---\left(3\right)$

In formula

for the amplitude of k sample point of low pass filter 2 output signals, f _ifor the center carrier frequencies of low pass filter 2 output signals, θ _ifor k sample point initial phase of low pass filter 2 output signal.

The plural S (k) forming after Hilbert transform is expressed as:

$S\left(k\right)=A\left(k\frac{M}{f_s}\right)e^{j({2\mathrm{\πf}}_{i}k\frac{M}{f_s}+{\mathrm{\θ}}_i)}---\left(4\right)$

In formula

for the amplitude of signal s (k).

The signal I (k) of I branch road is expressed as like this:

$I\left(k\right)=A\left(k\frac{M}{f_s}\right)\cos ({2\mathrm{\πf}}_{i}k\frac{M}{f_s}+{\mathrm{\θ}}_i)---\left(5\right)$

The signal Q (k) of Q branch road is expressed as:

$Q\left(k\right)=A\left(k\frac{M}{f_s}\right)\sin ({2\mathrm{\πf}}_{i}k+\frac{M}{f_s}+{\mathrm{\θ}}_i)---\left(6\right)$

The transfer function H of carrier wave circulator _r(k) be:

$H_R\left(k\right)\exp \left(2\mathrm{\π}{f}_{0}k\frac{M}{f_s}\right)---\left(7\right)$

F in formula ₀for the frequency of digital vco generation.

Output signal S after carrier wave circulator _p(k) be:

S _P(k)＝S(k)H _R(k)(8)

Output signal S after carrier wave circulator _p(k) IQ tributary signal I _p(k), Q _p(k) be respectively:

$I_P\left(k\right)=A\left(k\frac{M}{f_s}\right)\cos (2\mathrm{\π}(f_i-f_0)k\frac{M}{f_s}+{\mathrm{\θ}}_i)---\left(9\right)$

$Q_P\left(k\right)=A\left(k\frac{M}{f_s}\right)\sin (2\mathrm{\π}(f_i-f_0)k\frac{M}{f_s}+{\mathrm{\θ}}_i)---\left(10\right)$

The output signal of carrier wave circulator is carried out to phase demodulation, as adopted the phase demodulation method of arctan function, calculate the phase difference φ of each sample point _e(k):

${\mathrm{\φ}}_e\left(k\right)=\arctan \left(\frac{Q_P\left(k\right)}{I_P\left(k\right)}\right)---\left(11\right)$

(5), according to the transfer function of the low pass filter 2 after low pass filter 1 and extraction after digital mixing, calculate the transfer function H of whole receive path _r:

$H_R=H_1\left(z_1\right)\⊗H_2\left(z_2\right)---\left(12\right)$

In formula

represent circular convolution.Then, calculate the transfer function H of channel gain compensation and phase compensation processing _c,

$H_C=\frac{1}{H_R}---\left(13\right)$

(6) Costas has been encircled to the output signal S set after carrier track _pcarry out channel gain compensation and phase compensation processing, output signal S set _pby each S _p(k) composition.

(7) the BOC modulation signal of navigation satellite has often all passed through molding filtration at transmitting terminal, to limit transmission bandwidth and less intersymbol interference, reduces as much as possible loss of signal simultaneously.Therefore in order to eliminate the impact of transmission channel on modulated signal analysis result, according to the characteristic of the generation of navigation satellite BOC modulation signal and transmission channel, generate a measurement filter, measure filter and navigation satellite BOC signal transmitting terminal formed filter and match.Formed filter has various ways, and as forms such as raised cosine filter, root raised cosine filter, Gaussian filters, different filter time-frequency responses is different, must be according to navigation satellite BOC signal transmitting terminal formed filter characteristic selecting properly.Here, suppose that the transfer function of the transmitting/receiving system in order to make whole navigation satellite BOC signal wants the raised cosine characteristic of symbol without intersymbol interference, and consider the transmitting-receiving coupling requirement in sampling time signal to noise ratio maximum, the frequency domain characteristic of transmitting terminal formed filter is approximate root raised cosine characteristic, therefore measures filter and selects root raised cosine filter.Root raised cosine filter is according to rolloff-factor α (0≤α≤1), sign bit speed, by exponent number and the tap coefficient of Matlab software calculative determination root raised cosine filter, here the twice that sign bit speed is subcarrier frequency, be 30.69MHz, root raised cosine filter transfer function H _stmathematic(al) representation be:

$H_{\mathrm{st}}\left(z_2\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{R}_i{z}_2^i---\left(14\right)$

The exponent number that in formula, N is root raised cosine filter, R _ifor the i tap coefficient of root raised cosine filter.

Measure by obtaining IQ base band after molding filtration the Wave data set S needing _t:

$S_T=S_P\⊗[H_c\⊗H_{\mathrm{st}}\left(z_2\right)]---\left(15\right)$

(8) according to PSK modulation system, IQ base band Wave data to be measured is carried out to sign bit detection, obtain sign bit data, then according to PSK baseband modulation mode, sign bit rate and sign bit synchronous error Information generation IQ ideal baseband signal; Sign bit synchronous error information exchange is crossed to meet and is regularly recovered to realize, and the realization that meets timing recovery can be used the conventional method of digital communication system: Miller-Muller algorithm, Gardner algorithm and morning be door algorithm late.

(9) according to the characteristic of BOC signal transmission channel formed filter and measurement filter, reference filter parameter is set; Reference filter is for the combined effect of balanced BOC signal transmission channel formed filter and measurement filter, and here, BOC signal transmission channel formed filter and measurement filter are root raised cosine filter, and transfer function is H _stso, the mathematic(al) representation H of reference filter transfer function _srcan be defined as:

$H_{\mathrm{sr}}=H_{\mathrm{st}}\⊗H_{\mathrm{st}}---\left(16\right)$

After the processing of signal by reference to filter, form IQ base band reference waveform signal data acquisition system S _r:

$S_R=S_T\⊗H_{\mathrm{sr}}---\left(17\right)$

(9) ask for the error amount between IQ base band measuring-signal Wave data and IQ base band reference waveform signal data, error amount is carried out to vector error processing, thereby the parameter and the signal graph that obtain reflecting baseband modulation performance, comprising: spectrogram, the error vector time domain waveform etc. of vector amplitude error EVM, vector phase error E VP, error vector.

Vector error EV calculates:

EV(k)＝S _T(k)-S _R(k)(18)

S in formula _t(k) for IQ base band is measured the Wave data set S needing _tin k data, S _r(k) be IQ base band reference waveform signal data acquisition system S _rin k data.

Vector amplitude error EVM calculates:

${\mathrm{EVM}}_{\mathrm{RMS}}=\sqrt{\frac{\underset{i+}{\overset{N}{\mathrm{\Σ}}}{\left|\mathrm{EV}\left(k\right)\right|}^2}{\underset{i+1}{\overset{N}{\mathrm{\Σ}}}{\left|S_T\left(k\right)\right|}^2}}---\left(19\right)$

In formula, N is the total number of data of participating in calculating.

Vector phase error E VP calculates:

$\mathrm{EVP}\left(k\right)=\arctan \left(\frac{\mathrm{Re}\left(\mathrm{EV}\left(k\right)\right)}{\mathrm{Im}\left(\mathrm{EV}\left(k\right)\right)}\right)---\left(20\right)$

Re in formula (EV (k)) represents the real part of EV (k), and Im (EV (k)) represents the imaginary part of EV (k);

The frequency spectrum of error vector is processed and can be obtained by vector error EV being carried out to FFT.

The content not being described in detail in specification of the present invention belongs to those skilled in the art's known technology.

Claims (2)

1. a modulating performance method of testing for navigation satellite binary offset carrier (AltBOC) signal, is characterized in that step is as follows:

(1) the descending binary offset carrier (boc) modulated signals of broadcasting of navigation satellite is carried out to direct modulus sampling;

(2) direct modulus sampled data is carried out to digital mixing, digital low-pass filtering, obtain intermediate frequency binary offset carrier digital signal;

(3) intermediate frequency binary offset carrier digital signal is evenly extracted;

(4) the intermediate frequency binary offset carrier digital signal after step (3) evenly extracts is carried out to digital low-pass filtering again, in frequency domain, extract the lower sideband in two signal spectrums that the binary offset carrier digital signal after digital low-pass filtering comprises, and upper sideband spectrum is suppressed;

(5) output signal after digital low-pass filtering is again carried out to Hilbert transform and obtain complex data, then utilize Costas loop to carry out carrier track to complex data, and the output signal completing after carrier track is carried out to channel gain compensation and phase compensation, obtain baseband signal;

(6) according to the transfer function of the definite test filter matching of the characteristic of navigation satellite binary offset carrier (AltBOC) signal transmitting terminal formed filter, then utilize test filter to carry out filtering to the baseband signal after channel gain compensation and phase compensation, obtain IQ base band Wave data to be measured;

(7) according to PSK modulation system, IQ base band Wave data to be measured is carried out to sign bit detection, obtain sign bit data, the sign bit synchronous error Information generation IQ ideal baseband signal then obtaining according to PSK baseband modulation mode, sign bit rate and timing Recovery processing;

(8) according to the characteristic of navigation satellite binary offset carrier (AltBOC) signal transmission channel formed filter and test filter, reference filter is set, then utilizes reference filter to carry out filtering to IQ ideal baseband signal, form IQ base band reference waveform data;

(9) ask for the error amount between IQ base band Wave data to be measured and IQ base band reference waveform data, error amount is carried out to vector error processing, obtain reflecting parameter and the signal graph of baseband modulation performance.

2. the modulating performance method of testing of a kind of navigation satellite binary offset carrier (AltBOC) signal according to claim 1, it is characterized in that: in described step (1), the sample rate of modulus sampling is greater than the more than 10 times of pseudorandom code check of binary offset carrier modulation navigation signal, and the chip number of employing is greater than 200.

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