CN111147167A - Method for measuring adjacent channel leakage power ratio of low-orbit satellite broadband terminal - Google Patents
Method for measuring adjacent channel leakage power ratio of low-orbit satellite broadband terminal Download PDFInfo
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Abstract
The invention discloses a method for measuring adjacent channel leakage power ratio of a low orbit satellite broadband terminal, which mainly comprises the processes of modifying radio frequency local oscillation frequency, I/Q data acquisition, fine synchronization, data windowing, FFT (fast Fourier transform) and RRC (radio resource control) filter processing, calculating power and adjacent channel leakage power ratio ACLR, carrying out average processing on the calculated result data, judging whether the calculated result meets the requirement, reporting the measured result and the like. The radio frequency local oscillator frequency is modified through software configuration, data are collected, the requirement on the performance of an ADC converter is greatly reduced, the ACLR test of broadband signals under low sampling rate is realized, the system is easy to maintain, good in transportability and flexible in configuration, and the system has good expansion and transportability for the future low-orbit satellite broadband terminal upgrading.
Description
Technical Field
The invention belongs to the technical field of air-space-earth-sea integrated communication, and particularly relates to a method for measuring adjacent channel leakage power ratio of a low-orbit satellite broadband terminal.
Background
In the future air-space-ground integrated mobile communication, low-orbit satellites play an increasingly important role. Compared with a ground communication system, the low-orbit satellite has wider coverage area and is more suitable for global communication in unmanned areas such as deserts, deep forests, plateaus and the like; compared with a high-orbit satellite communication system, the low-orbit satellite has the advantages of small path attenuation, short transmission delay, short development period, low emission cost and the like. Therefore, in future satellite communication systems, low-earth orbit satellite communication systems will take an increasingly important position.
In the process of rapid development of the low-earth orbit satellite, the radio frequency test of the mobile communication terminal of the low-earth orbit satellite is a relatively weak link, and along with the increase of the channel bandwidth, the sampling rate and the hardware processing capacity are also called bottlenecks which restrict the radio frequency index test of the terminal. The ACLR (adjacent channel leakage ratio) is one of important indexes of a radio frequency transmitter of a low-orbit satellite mobile communication terminal, and the important points are that on one hand, the ACLR (adjacent channel leakage ratio) can accurately generate useful signals meeting the spectrum emission standard; on the other hand, it is required to control the unwanted signals such as out-of-band spurs and spurious emissions within a certain level, otherwise it will cause serious interference to other users' systems.
However, the hardware structure of the ACLR consistency test system for the low-earth-orbit satellite mobile communication broadband terminal is complex, the high-speed sampling device is expensive, the requirement on the processing speed of the subsequent FPGA is high due to the high conversion rate, and the implementation is difficult at the present stage; the power supply and heat dissipation problems are caused by excessive power consumption, and the method is only suitable for large-scale systems and is not easy to be widely adopted.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a method for measuring the adjacent channel leakage ratio of a low-orbit satellite broadband terminal, which modifies the radio frequency local oscillator frequency through software configuration, acquires data, greatly reduces the requirements on the performance of an ADC (analog to digital converter), realizes the ACLR (analog to digital converter) test of broadband signals under a low sampling rate, is easy to maintain, has better transportability and flexible configuration, and has better expansion and transportability for the future upgrade of the low-orbit satellite broadband terminal of a system.
In order to achieve the purpose, the technical scheme of the invention is as follows: a method for measuring the adjacent channel leakage power ratio of a low earth orbit satellite broadband terminal comprises the following steps:
s1: modifying the radio frequency local oscillation frequency of the current radio frequency signal to obtain sampling data of a subframe;
s2: I/Q data acquisition is carried out on the sampled data, then the data are modulated, whether the specified measurement bandwidth is met or not is judged, if yes, the data are stored, and if not, the step S1 is repeated;
s3: windowing the data, and then performing FFT processing;
s4: calculating the power of the main channel;
s5: modifying the local oscillation frequency, repeating the steps S2-S4, and calculating the power of the adjacent channel;
s6: calculating the adjacent channel leakage ratio;
s7: judging whether the calculation result meets the requirement or not;
s8: and reporting the measurement result.
As a preferred technical method of the present invention, in step S2, the modulation is to obtain a QPSK burst signal with a multiplying factor of 4 from the analog-to-digital converter, and the burst signal length is NbBit, pair 4 x NbAnalyzing the plural sample values, judging whether the measurement bandwidth meets the regulation, if so, finely synchronizing the data to obtain NbStoring 4 data into two arrays; if not, step S1 is repeated.
As a preferred technical method of the present invention, the step S3 of windowing the data is to (N)b4) windowing of the data of the points, and then doing
And (4) FFT processing of the points.
As a preferred technical method of the present invention, the step S3 of windowing data is to add a hamming window to the data, and a calculation expression of the hamming window h (n) is as follows:
wherein, N is the number of points of FFT transformation.
As a preferred technical method of the present invention, the input signal x (n) sequence of step S3 is FFT processed to obtain x (k) calculation expression as follows:
where exp (, x) represents an exponential function.
As a preferred technical method of the present invention, the step S4 includes RRC filter processing, the filter unit impulse response is a square root raised cosine response, and the frequency response characteristic of the square root raised cosine response is as follows:
wherein cos (×) is a cosine function, α is a roll-off coefficient, T is a symbol period, a bandwidth B of the filter is (1+ α) T, and a time domain response of a square root raised cosine response is:
sin (×) is a sine function.
As a preferred technical method of the present invention, the method further includes step S9: averaging the data of the calculation result, and if the average times is 1, directly reporting the ACLR value; if the average number of times is not 1, the data is processed using the following algorithm: and finally reporting the result (the calculation result + the last calculation result (average time one 1))/average time.
The invention has the beneficial effects that:
1. the radio frequency local oscillator frequency is modified through software configuration, data are collected, the requirement on the performance of an ADC converter is greatly reduced, the ACLR test of broadband signals under low sampling rate is realized, the system is easy to maintain, good in transportability and flexible in configuration, and the system has good expansion and transportability for the future low-orbit satellite broadband terminal upgrading.
2. Windowing and FFT (fast Fourier transform) is that FFT transform decomposes a time domain signal into representation in a frequency domain, different frequency components in the signal are analyzed, if the signal contains non-integer periods, frequency leakage occurs, and the condition of frequency leakage is improved by data windowing and FFT processing; meanwhile, the invention adopts the Hamming window which is suitable for 95 percent of conditions, and the Hamming window not only has better frequency resolution, but also can reduce frequency spectrum leakage.
3. The invention carries out average processing on the calculation result, so that the obtained adjacent channel leakage ratio is more accurate.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments will be briefly introduced below, it is obvious that the drawings in the following description are only two of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive labor.
Fig. 1 is a flowchart of a method for measuring an adjacent channel leakage power ratio of a low earth orbit satellite broadband terminal according to the present invention.
Detailed Description
The technical solutions in the present invention will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are merely preferred embodiments of the present invention, rather than all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the method for measuring the adjacent channel leakage power ratio of the low-earth satellite broadband terminal of the present invention includes the following steps:
step S1: and modifying the current radio frequency local oscillator to obtain the sampling data of one subframe.
Step S2: acquiring I/Q data of a subframe, and modulating the data, wherein the specific process of modulation is to acquire a QPSK burst signal with the sampling speed of 4 from an analog-to-digital converter, and the burst signal length is NbBit, pair 4 x NbAnalyzing the plural sample values, judging whether the measurement bandwidth meets the regulation, if so, finely synchronizing the data to obtain NbStoring 4 data into two arrays; if not, step S1 is repeated.
Step S3: windowing the data and then performing FFT processing, specifically, processing (N)bWindowing of data of points 4) to make
And performing FFT on the points to obtain a final FFT result. The invention windows data into original (N)b4) dot data plus Hamming window, and symmetrically supplementing zero before and after data to convert into NFFTData of a point, then NFFTFFT of the points.
Step S4: calculating the center frequency to be +/-f after filtering the signal by an RRC filterc(fcAdjacent channel spacing).
Step S5: sequentially modifying the radio frequency local oscillator frequency to +/-2 fc，±3fc、±4fcAnd repeating the steps S2-S4 to respectively calculate the adjacent channel power.
Step S6: and calculating the adjacent channel leakage power ratio, wherein the adjacent channel leakage power ratio is obtained by subtracting the power dB value of the adjacent channel from the power dB value of the main channel.
Step S7: and averaging the calculated result data. If the average times is 1, directly reporting the ACLR value; if the average number of times is not 1, the data is processed using the following algorithm:
the final reported result is [ the calculation result of this time + the calculation result of the last time (average number of times-1) ]/the average number of times
Step S8: and judging whether the calculation result meets the requirement, if the user selects an automatic judgment mode, judging according to a protocol specified value, and otherwise, judging according to a standard set by the user.
Step S9: and reporting the measurement result.
The unit impulse response of the RRC filter is square root raised cosine response, and the frequency response characteristic of the square root raised cosine response is as follows:
wherein cos (×) is a cosine function, α is a roll-off coefficient, T is a symbol period, a bandwidth B of the filter is (1+ α) T, and a time domain response of a square root raised cosine response is:
sin (×) is a sine function.
The windowing FFT means that FFT transforms decompose a time domain signal into representation in a frequency domain, different frequency components in the signal are analyzed, if the signal contains non-integer periods, frequency leakage occurs, and the condition can be improved through windowing. The input signal x (n) sequence is FFT to obtain X (k) calculation expression as follows:
where exp (, x) represents an exponential function.
The hamming window is suitable for 95% of cases, not only has better frequency resolution, but also can reduce spectral leakage. The Hamming window h (n) is calculated as follows:
wherein, N is the number of points of FFT transformation.
As shown in the following table, the method for measuring the adjacent channel leakage power ratio of the low-earth-orbit satellite broadband terminal is applied to practice, the frequency band is selected to be 29.9GHz in Ka band, the bandwidth is 60MHz, the modulation mode is QPSK, the roll-off factor is 0.25, power values of the channels in table 1 are obtained, and the adjacent channel leakage power ratio can be calculated to be 14.38- (-31.43) to 45.81dB and 14.38- (-30.19) to 44.57 respectively.
| Low-orbit satellite broadband terminal | Main channel | Left channel | Right channel |
| Power level (dB) | 14.38 | -31.43 | -30.19 |
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (7)
1. A method for measuring a low-orbit satellite broadband terminal adjacent channel leakage power ratio is characterized by comprising the following steps:
s1: modifying the radio frequency local oscillation frequency of the current radio frequency signal to obtain sampling data of a subframe;
s2: I/Q data acquisition is carried out on the sampled data, then the data are modulated, whether the specified measurement bandwidth is met or not is judged, if yes, the data are stored, and if not, the step S1 is repeated;
s3: windowing the data, and then performing FFT processing;
s4: calculating the power of the main channel;
s5: modifying the local oscillation frequency, repeating the steps S2-S4, and calculating the power of the adjacent channel;
s6: calculating the adjacent channel leakage ratio;
s7: judging whether the calculation result meets the requirement or not;
s8: and reporting the measurement result.
2. The method for measuring the adjacent channel leakage power ratio of the low earth orbit satellite broadband terminal according to claim 1, characterized in that: in step S2, the modulation is to obtain a QPSK burst signal with a multiplying factor of 4 from the analog-to-digital converter, where the burst signal length is NbBit, pair 4 x NbAnalyzing the plural sample values, judging whether the measurement bandwidth meets the regulation, if so, finely synchronizing the data to obtain NbStoring 4 data into two arrays; if not, step S1 is repeated.
3. The method for measuring the adjacent channel leakage power ratio of the low earth orbit satellite broadband terminal according to claim 2, characterized in that: the step S3 is to window the data (N)b4) windowing of the data of the points, and then doing
And (4) FFT processing of the points.
4. The method for measuring the adjacent channel leakage power ratio of the low earth orbit satellite broadband terminal according to claim 1, characterized in that: the step S3 is to add a hamming window to the data, and the calculation expression of the hamming window h (n) is as follows:
wherein, N is the number of points of FFT transformation.
5. The method for measuring the adjacent channel leakage power ratio of the low earth orbit satellite broadband terminal according to claim 1, characterized in that: the FFT of the input signal x (n) sequence of step S3 yields x (k) calculation expression as follows:
where exp (, x) represents an exponential function.
6. The method for measuring the adjacent channel leakage power ratio of the low earth orbit satellite broadband terminal according to claim 1, characterized in that: the step S4 includes RRC filter processing, where the filter unit impulse response is a square root raised cosine response, and the frequency response characteristic of the square root raised cosine response is as follows:
wherein cos (×) is a cosine function, α is a roll-off coefficient, T is a symbol period, a bandwidth B of the filter is (1+ α) T, and a time domain response of a square root raised cosine response is:
sin (×) is a sine function.
7. The method for measuring the adjacent channel leakage power ratio of the low earth orbit satellite broadband terminal according to claim 1, characterized in that: further comprising step S9: averaging the data of the calculation result, and if the average times is 1, directly reporting the ACLR value; if the average number of times is not 1, the data is processed using the following algorithm: and finally reporting the result (the calculation result + the last calculation result (average time one 1))/average time.
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