CN114710383A - Method for calibrating instrument radio frequency channel frequency response by utilizing OFDM signal - Google Patents
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- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
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- H—ELECTRICITY
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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- H04L27/2601—Multicarrier modulation systems
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- H04L27/0014—Carrier regulation
- H04L2027/0024—Carrier regulation at the receiver end
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Abstract
The invention relates to the field of instruments and meters, and discloses a method for calibrating a frequency response of an instrument channel by utilizing an OFDM (orthogonal frequency division multiplexing) signal, which is characterized by comprising the following steps of: feeding an OFDM signal with known parameters into a channel to be calibrated of the instrument, measuring the OFDM signal passing through the channel at the output end of the channel, demodulating the signal, and comparing the amplitude and the phase of the frequency domain reference signal demodulated at the output end of the channel with the amplitude and the phase of the original reference signal to obtain the amplitude and phase characteristic data of the instrument channel, thereby obtaining the amplitude and phase calibration data of the instrument channel. The method can quickly realize the vector calibration of the amplitude and the phase of the instrument channel by utilizing the broadband signal, and can avoid the defect of slow speed when the traditional single tone is used for frequency sweep calibration. The amplitude and phase responses of the instrument channel on different frequency points are obtained and stored in instrument hardware as calibration data, and the original measurement result is compensated when the instrument works, so that the accurate measurement of external input signals is realized.
Description
Technical Field
The invention relates to the field of instruments and meters, in particular to a method for calibrating a radio frequency channel frequency response of an instrument by utilizing an OFDM signal.
Background
When the instrument measures, the original measurement data obtained by the instrument is actually the total result of external signals superimposed with the frequency response of the instrument, and in order to obtain the accurate measurement result of the instrument on the external signals, the original measurement data must be compensated and processed to remove the influence of the frequency response of the instrument on the measurement result, so that the accurate measurement result of the instrument on the external signals can be obtained. Therefore, when the instrument leaves the factory, the frequency response data of the instrument channel is obtained firstly, and then the frequency response data is stored in the hardware of the instrument so as to be called when the instrument works normally.
The calibration of the instrument is crucial to the accuracy of the measurement result, the channel calibration of the instrument is needed when the instrument leaves a factory, and how to quickly and accurately obtain the frequency response of the instrument channel is very important to the instrument.
Orthogonal Frequency Division Multiplexing (OFDM) communication technology is widely used in the field of wireless communication, such as wireless communication technologies of 4G, 5G, WLAN, and the like.
In the traditional calibration of the frequency response of the instrument channel, a single tone or multiple tones are used for frequency sweeping to obtain the frequency response of the instrument channel, and the method needs to carry out frequency sweeping, so the speed is slow.
Disclosure of Invention
The invention aims to provide a method for calibrating the frequency response of an instrument channel by using a broadband OFDM signal, and aims to solve the problem that the conventional method for calibrating the frequency response of the instrument channel by adopting a frequency sweeping mode is slow in the prior art.
The invention is realized in such a way that a method for calibrating the frequency response of an instrument channel by utilizing OFDM signals feeds the OFDM signals with known parameters into the channel to be calibrated of the instrument, then measures output signals at the output end of the channel and demodulates the signals, and obtains the amplitude and phase characteristic data of the instrument channel by comparing the amplitude and phase of the frequency domain reference signals demodulated at the output end of the channel with the amplitude and phase of the known frequency domain reference signals at the input end, thereby realizing the amplitude and phase vector calibration of the instrument channel.
Further, it comprises the following steps:
step one, inserting a known pilot signal into an OFDM signal, wherein a pilot value of a k-th subcarrier is si (k), where i represents an OFDM symbol, i is 0,1,2 … M-1, M represents the total number of pilot symbols, k represents a carrier, k is 0,1,2 … N-1, and N represents the total number of carriers;
setting the subcarrier spacing as delta f and the carrier central frequency point as fc, and feeding an OFDM signal into a channel;
thirdly, performing frame synchronization, frequency offset compensation and OFDM signal demodulation on the signals at the channel output end to obtain a received pilot frequency value Ri (k);
step four, calculating the frequency response Hi (k) ═ Ri (k)/Si (k) of the channel;
step five, calculating the frequency response of the channel on the discrete frequency point
And sixthly, performing linear interpolation on the H (k) to obtain the frequency response H (f) of the channel at any frequency point.
Compared with the prior art, the invention has the advantages that point-by-point scanning is not needed, the speed is high, and the calibration signal is closer to the excitation signal of the instrument in the real working state. The amplitude and phase responses of the instrument channel on different frequency points are obtained by the invention and are stored in instrument hardware as calibration data, and the original measurement result is compensated when the instrument works, thereby realizing the accurate measurement of external input signals.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention.
FIG. 1 is a general flow diagram of the present invention;
FIG. 2 is a spectrum of an original OFDM signal used for channel calibration;
FIG. 3 is a diagram of the frequency spectrum of an OFDM signal after passing through a channel to be calibrated;
FIG. 4 is the amplitude values of different frequency point channel responses obtained after calibration;
fig. 5 shows the phase values of the channel responses at different frequency points obtained after calibration.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary examples do not represent all implementations consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
The invention will be described in further detail below with reference to the drawings and examples.
A method for calibrating the frequency response of an instrument channel by utilizing OFDM signals comprises the steps of feeding OFDM signals with known parameters into a channel to be calibrated of an instrument, measuring output signals at the output end of the channel, demodulating the signals, and comparing the amplitude and the phase of frequency domain reference signals demodulated at the output end of the channel with the amplitude and the phase of original reference signals to obtain the amplitude and phase characteristic data of the instrument channel, so that the amplitude and the phase vector calibration of the instrument channel is realized.
Here, the OFDM signal is used as an excitation signal, and a pilot of the excitation signal is known as a reference signal.
According to the method for calibrating the frequency response of the instrument channel by using the OFDM signal, the vector calibration of the amplitude and the phase of the instrument channel can be quickly realized by using the broadband signal, and the defect that the speed is slow when the traditional single tone is used for frequency sweep calibration can be avoided; the method does not need point-by-point scanning, has high speed, and the calibration signal is closer to the excitation signal of the instrument in the real working state. The amplitude and phase responses of the instrument channel on different frequency points are obtained by the method and are stored in instrument hardware as calibration data, and the original measurement result is compensated when the instrument works, so that the accurate measurement of the external input signal is realized.
In this particular embodiment:
and taking an OFDM signal with a bandwidth of 100MHz as an excitation signal, and carrying out frequency response calibration on a transmitting channel of the instrument.
The specific calibration steps are as follows:
step one, inserting a known pilot signal si (k) into the OFDM signal, in this embodiment, a total of 4 pilot symbols is used, so that i is 0,1,2 … M-1, where M is 4, in this embodiment, a total of 3276 subcarriers is actually used in a 100MHz bandwidth, so that k is 0,1,2 … 3275, and a pilot value of a k-th subcarrier is si (k), and the pilot value is generated based on the following formula:
c(k)＝(x1(k+Nc)+x2(k+Nc))mod2 Nc＝1600
x1(k+31)＝(x1(k+3)+x1(k))mod2
x2(k)＝(x2(k+3)+x2(k+2)+x2(k+1)+x2(k))mod2
the initial value of x1(n) is x1(0)＝1，x1(n)＝0，n＝1，2，...，30；
The initial value sequence of x2(n) is [ 1110110001000000000000000110 ], and the sequence is the value of each element of x2(n) when n is 0,1,2, … and 30;
mod2 in the formula represents the remainder for 2;
in this embodiment, the first 70 values of the pilot sequence on each carrier on the pilot symbol with i being 0 are:
0.7071-0.7071i-0.7071-0.7071i-0.7071-0.7071i-0.7071-0.7071i -0.7071-0.7071i-0.7071+0.7071i 0.7071+0.7071i 0.7071+0.7071i -0.7071-0.7071i-0.7071-0.7071i-0.7071-0.7071i-0.7071+0.7071i -0.7071+0.7071i 0.7071-0.7071i 0.7071+0.7071i 0.7071-0.7071i 0.7071+0.7071i 0.7071-0.7071i-0.7071+0.7071i 0.7071-0.7071i -0.7071-0.7071i-0.7071-0.7071i 0.7071+0.7071i-0.7071+0.7071i -0.7071-0.7071i 0.7071+0.7071i 0.7071+0.7071i 0.7071+0.7071i -0.7071-0.7071i 0.7071+0.7071i 0.7071-0.7071i-0.7071+0.7071i -0.7071+0.7071i-0.7071-0.7071i-0.7071-0.7071i-0.7071+0.7071i 0.7071 -0.7071i-0.7071+0.7071i-0.7071+0.7071i 0.7071+0.7071i-0.7071+ 0.7071i 0.7071-0.7071i-0.7071-0.7071i-0.7071-0.7071i 0.7071+ 0.7071i-0.7071+0.7071i 0.7071+0.7071i 0.7071-0.7071i 0.7071-0.7071i 0.7071+0.7071i-0.7071+0.7071i-0.7071+0.7071i-0.7071+0.7071i 0.7071+0.7071i 0.7071-0.7071i-0.7071-0.7071i 0.7071+0.7071i 0.7071-0.7071i-0.7071+0.7071i 0.7071+0.7071i-0.7071+0.7071i 0.7071+0.7071i 0.7071-0.7071i 0.7071-0.7071i 0.7071-0.7071i 0.7071-0.7071i 0.7071-0.7071i 0.7071+0.7071i-0.7071+0.7071i -0.7071-0.7071i
step two, setting the subcarrier spacing as Δ f, the carrier center frequency point as fc, and feeding an OFDM signal into a channel, in this embodiment, the subcarrier spacing is 30kHz, the spectrum of the original excitation signal is shown in fig. 2, an x axis in the diagram represents a relative frequency, a frequency point where x is 0 represents the carrier center frequency point fc, in this embodiment, fc is set to 500MHz, and a y axis in the diagram represents power of different frequency points, and a unit is dBm;
sampling an output signal at a channel output end, then carrying out frame synchronization, frequency offset compensation and OFDM signal demodulation on the signal, and obtaining a received pilot frequency value Ri (k);
the spectrum of the output end signal is shown in fig. 3, wherein the x axis in the graph represents the relative frequency, the frequency point with x being 0 represents the central frequency point fc of the carrier wave, in this embodiment, fc is set to be 500MHz, and the y axis in the graph represents the power of different frequency points, and the unit is dBm;
step four, calculating the frequency response Hi (k) ═ Ri (k)/Si (k) of the channel;
step five, calculating the frequency response of the channel on the discrete frequency point
The results of hi (k) calculations in this example are as follows, only the top 70 values being listed:
0.0923+0.4324i-0.0881+0.4280i-0.1820+0.3927i-0.3075+0.3251i -0.4075+0.2086i-0.4151+0.0779i-0.4380-0.0699i-0.4018-0.1703i -0.3301-0.2703i-0.2309-0.3779i-0.0780-0.4274i 0.0352-0.4403i 0.1659- 0.3668i 0.3135-0.3182i 0.3724-0.2162i 0.4338-0.1123i 0.4287+ 0.0384i 0.4030+0.2021i 0.3217+0.2633i 0.2019+0.3625i 0.1232+ 0.4719i-0.0387+0.4228i-0.1893+0.4018i-0.3124+0.3226i-0.3709+ 0.2088i-0.4419+0.0967i-0.4314-0.0432i-0.3954-0.1570i-0.3600- 0.3094i-0.2297-0.3760i-0.1024-0.4453i 0.0428-0.4263i 0.1775- 0.4123i 0.2892-0.3485i 0.3589-0.2270i 0.4362-0.0839i 0.4393+ 0.0150i 0.3914+0.1524i 0.3283+0.2876i 0.2332+0.3881i 0.1035+ 0.4163i-0.0662+0.4887i-0.1694+0.4058i-0.2700+0.3331i-0.3579+ 0.2459i-0.4047+0.0978i-0.4171-0.0241i-0.3979-0.1458i-0.3350- 0.2852i-0.2405-0.3571i-0.1205-0.4133i 0.0254-0.4855i 0.1778- 0.4157i 0.2875-0.3556i 0.3478-0.2270i 0.4110-0.1131i 0.4363+0.0134i 0.4199+0.1395i 0.3297+0.2596i 0.2446+0.3644i 0.1144+0.4379i -0.0034+0.4537i-0.1482+0.4055i-0.2795+0.3197i-0.3404+0.2540i -0.3932+0.1151i-0.4187-0.0177i-0.4393-0.1559i-0.3473-0.2761i -0.2596-0.3598i。
the amplitude value of the frequency response h (k) is shown in fig. 4, the y-axis of fig. 4 represents the amplitude in dB, the phase value of the frequency response is shown in fig. 5, the y-axis of fig. 5 represents the phase, the x-axis of fig. 4 and 5 represents the relative frequency, the frequency point where x is 0 represents the center frequency point fc of the carrier, and fc is set to 500MHz in this embodiment.
And sixthly, performing linear interpolation on the H (k) to obtain the frequency response H (f) of the channel at any frequency point. H (k) is a discrete frequency point, in this example, fc is 500MHz, the total number of subcarriers is 3276, and the subcarrier spacing is 30kHz, so that h (k) corresponds to a discrete frequency point Fk ═ fc + (k-3276/2-0.5) × 30kHz, that is: fk ═
[450.845 450.875 450.905 450.935 450.965 450.995 451.025 451.055 451.085 451.115 451.145 451.175 451.205.....]MHz
For example, for a frequency response with F being 450.92MHz, F2 being 450.905MHz when the discrete frequency point adjacent to the frequency response is k 2 and F3 being 450.935MHz when k is 3, the frequency response calculation procedure with F being 450.92MHz according to the linear interpolation formula is:
(1) finding a discrete frequency point F (k) which is closest to the arbitrary frequency point f, wherein the discrete frequency point is not more than the arbitrary frequency point;
(2) calculating the mean square error of the adjacent discrete frequency points closest to any frequency point f:
(3) and obtaining the frequency response of the arbitrary frequency point f through linear interpolation:
H(f)＝H(k)+β*(H(k+1)-H(k))。
for example, in the present embodiment, the mean difference:
frequency response: h (f) ═ H (2) + β (H (3) -H (2)) ═ 0.2447+0.3589 i.
The amplitude and phase responses of the instrument channel obtained by the method on different frequency points are stored in instrument hardware as calibration data, and the original measurement result is compensated when the instrument works, so that the accurate measurement of the external input signal is realized.
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 and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (2)
1. A method for calibrating instrument channel frequency response by using OFDM signals is characterized in that: feeding an OFDM signal with known parameters into a channel to be calibrated of the instrument, measuring an output signal at the output end of the channel, demodulating the signal, and comparing the amplitude and the phase of the frequency domain reference signal demodulated at the output end of the channel with the amplitude and the phase of an original reference signal to obtain the amplitude and phase characteristic data of the instrument channel, thereby realizing the amplitude and phase vector calibration of the instrument channel.
2. A method of calibrating a meter channel frequency response using OFDM signals as claimed in claim 1, the method comprising the steps of:
step one, inserting a known pilot signal into an OFDM signal, wherein a pilot value of a k-th subcarrier is si (k), where i represents an OFDM symbol, i is 0,1,2 … M-1, M represents the total number of pilot symbols, k represents a carrier, k is 0,1,2 … N-1, and N represents the total number of carriers;
setting the subcarrier spacing as delta f and the carrier central frequency point as fc, and feeding an OFDM signal into a channel;
thirdly, performing frame synchronization, frequency offset compensation and OFDM signal demodulation on the signals at the channel output end to obtain a received pilot frequency value Ri (k);
step four, calculating the frequency response Hi (k) ═ Ri (k)/Si (k) of the channel;
step five, calculating the frequency response of the channel on the discrete frequency point
And sixthly, performing linear interpolation on the H (k) to obtain the frequency response H (f) of the channel at any frequency point.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116868079A (en) * | 2022-11-10 | 2023-10-10 | 长沙天恒测控技术有限公司 | Zero phase calibration method, computer device and storage medium |
| CN116868079B (en) * | 2022-11-10 | 2024-02-27 | 长沙天恒测控技术有限公司 | Zero phase calibration method, computer device and storage medium |
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