JP2005308610A - Communication signal wave automatic tracking device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the above-mentioned problems, and to divide a case for each correction frequency region, and to correct by changing a correction formula using a power function or a non-linear function. The purpose is to reduce the correction error.
A communication signal wave automatic tracking device according to the present invention includes a directional antenna that receives a communication signal from a communication partner and a local oscillator that controls an output frequency, and receives a signal based on a transmission frequency of the local oscillator. A tracking receiver that converts the received level of the communication signal into a voltage and outputs it, and a calculator that calculates a predicted value of the Doppler shift amount of the transmission frequency of the communication partner, and a computer that outputs the predicted value to the tracking receiver, In the local oscillator, the transmission frequency is determined by the predicted value of the Doppler amount calculated by the computer, and the Doppler predicted value approximates and corrects the nonlinear characteristic of the local oscillator by a power function.
[Selection] Figure 1

Description

  The present invention relates to an automatic tracking device for a communication signal wave when a communication partner is relatively moving, such as inter-satellite communication or mobile satellite communication.

  A directional antenna that receives a communication signal from a communication partner such as a spacecraft or a flying object, a tracking receiver that has a function of converting the reception level of the communication signal into a voltage and outputting the voltage, and the communication input from the outside From the real-time position data of the communication partner calculated based on the position data of the other party and the reception level voltage of the communication signal, a control signal for directing the antenna in the direction of the position of the communication partner is output to the antenna drive mechanism. It consists of an antenna drive electronic circuit having a function and the above antenna drive mechanism that drives a directional antenna by a control signal output from the antenna drive electronic circuit, and predicts and calculates the Doppler shift amount of the transmission frequency of the communication partner. A computer having a function of outputting the Doppler shift forecast value to the tracking receiver is added, and the antenna is driven. Voltage control installed in a satellite when realizing a communication signal wave automatic tracking device characterized in that the tracking receiver has a function of receiving the Doppler shift forecast value from the slave circuit and performing Doppler correction of the communication signal. In a system that performs Doppler correction using a variable frequency oscillator such as a crystal oscillator (VCXO), if the frequency range of Doppler correction is wider than the linear operation region of VCXO, one method is to calculate the nonlinear characteristics of the VCXO as a computer. The method of correcting and using is used (for example, refer patent document 1).

JP 2002-341004 A (FIG. 1)

  The correction formula used in the Doppler correction method using the non-linear region of VCXO used in the communication signal wave automatic tracking device described above is a single equation based on a power function or non-linear function. There was a problem that it could not be corrected.

  The present invention has been made to solve the above-described problems. The correction error is corrected by changing the correction formula using a power function or a non-linear function for each correction frequency region. The purpose is to make it smaller.

  A communication signal wave automatic tracking device according to the present invention includes a directional antenna that receives a communication signal from a communication partner and a local oscillator that controls an output frequency, and the communication signal wave tracking device receives the communication signal received based on the oscillation frequency of the local oscillator. A tracking receiver that converts the reception level into a voltage and outputs the output, and an antenna driving electronic circuit that outputs a control signal for directing the antenna in the direction of the communication partner based on the reception level voltage from the tracking receiver; An antenna driving mechanism for driving the directional antenna by the control signal output from the antenna driving electronic circuit, and a predicted value of a Doppler shift amount of the transmission frequency of the communication partner is calculated and output to the tracking receiver And the local oscillator has an oscillation frequency determined by a predicted value of the Doppler amount calculated by the computer. Predicted value of the doppler quantity calculated by the computer, is to approximate the correction by the nonlinear characteristic to the functions of the local oscillator.

  According to the present invention, the correction error can be reduced by dividing the case for each correction frequency region and changing the correction formula based on the power function or the nonlinear function for correction.

Embodiment 1 FIG.
FIG. 1 is a schematic view showing an embodiment of the present invention.

  The directional antenna 1 receives a communication signal wave transmitted from a flying spacecraft (not shown) as a communication partner, and then outputs it to a tracking receiver 4 via a power feeding unit 2 composed of a waveguide or the like. To do. As a design example, a parabola antenna, a Cassegrain antenna, a Gregorian antenna center feed, an offset antenna, or the like is used.

  The low-noise amplifier 3 provided inside or outside the tracking receiver 4 (shown in the former in FIG. 1) is configured so that the signal input from the power feeding unit is reduced to a level at which the influence of the noise level at the subsequent stage becomes sufficiently small. Amplify. As a design example, it is 50 dB or more. The low noise amplifier may be mounted on a normal flying spacecraft.

On the other hand, the computer 9 performs orbital propagation based on the communication partner and its initial orbital position data that have been input in the computer 9 or in an external memory, or input from the outside, and at the same time change every moment. The relative position vector (r) between them and the relative velocity vector (dr / dt) of the rate of change are calculated as needed. Further, the nominal transmission frequency (f _r0 ) that does not include the Doppler shift of the communication partner, the relative position vector (dr / dt), and the relative velocity vector (r) input to the memory in the computer 9 or the like. Based on, the Doppler shift forecast value (Δf _c0 ) at the same time is calculated as needed. An example of the calculation formula is shown in Formula (1).

Here, Δf _r : actual Doppler shift amount, Δf _c0 : predicted Doppler shift value, f _r0 : nominal transmission frequency of communication partner (not including Doppler shift), c: speed of light, r: relative position of communication partner and one's own Vector, dr / dt: The relative speed vector between the communication partner and oneself.

  Note that the actual Doppler shift amount and the Doppler shift forecast value are shown as the same value here for ease of discussion. In addition, since this calculation formula assumes a system that does not have a strict requirement accuracy, it is a formula that does not include special relativistic effects, etc. for simplification of calculation, but when the prediction accuracy requirement of the applied system is strict, It may be possible to apply a stricter calculation formula that takes into account special relativistic effects.

  The Doppler shift forecast value calculated based on the formula (1) is converted into an analog signal or a digital signal and output to the local oscillator I / F circuit 12 provided in the tracking receiver 4.

  The local oscillator I / F circuit 12 provided in the tracking receiver 4 corresponds to the predicted value of the Doppler shift amount received from the computer 9 as shown in Equation (2). Control the applied voltage.

Where F (Δf _c0 ): correction function of the applied voltage of the local oscillator (voltage controlled oscillator), V (Δf _c0 ): local oscillator corresponding to the predicted Doppler shift amount (Δf _c0 ) received from the computer 9 ( (Voltage controlled oscillator) 8 applied voltage.

A local oscillator (voltage controlled oscillator) 8 provided in the tracking receiver 4 is converted into a Doppler shift forecast value (Δf _c0 ) shown in Expression (3) by an applied voltage controlled by the local oscillator I / F circuit 12. Based on this, the frequency (f _Lo ) obtained by adding the frequency component (Δf _c ) added to the output frequency of the local oscillator (voltage controlled oscillator) 8 is oscillated.

Where, f _Lo : Output frequency of local oscillator (voltage controlled oscillator) 8, f ₀ : Output frequency of local oscillator (voltage controlled oscillator) 8 when Doppler shift forecast value is 0 Hz, Δf _c : Calculated by calculator 9 This is a frequency component added to the output frequency of the local oscillator (voltage controlled oscillator) 8 based on the predicted Doppler shift forecast value (Δf _{c0 of the} number (1)).

The frequency converter 5 provided in the tracking receiver 4 is a local oscillator (voltage controlled oscillator) 8 provided in the tracking receiver 4 for receiving a signal received from a communication partner amplified by the low noise amplifier 3. using the output frequency based on the equation (4), to reduce the frequency variation due to Doppler shift by reducing the Delta] f _r -.DELTA.f _c, it converted to a stable intermediate frequency. The necessity is that, as will be described later, the reception level is used to determine the spatial misalignment of the directional antenna 1, so that the signal level stable in frequency within the band of the band limiting filter 6 at the subsequent stage. Because it is necessary to send. The intermediate frequency needs to be determined in consideration of the requirements for the bandwidth of the band limiting filter 6. As a design example, a filter bandwidth of 500 kHz is required to realize a prescribed signal-to-noise ratio based on signal quality requirements, and an intermediate frequency of 140 MHz is set in consideration of the feasibility of the filter.

Where, f _IF : intermediate frequency converted by frequency converter 5, f _r : frequency of received signal from communication partner (including Doppler shift), f _Lo : output frequency of local oscillator (voltage controlled oscillator) 8 , F ₀ : output frequency of local oscillator (voltage controlled oscillator) 8 when Doppler shift forecast value is 0 Hz, Δf _r : actual Doppler shift amount included in received signal from communication partner, Δf _c : Frequency component to be added to the output frequency of the local oscillator (voltage controlled oscillator) 8 based on the predicted Doppler shift forecast value (Δf _{c0 in} equation (2)), f _IF0 : Doppler frequency converted by the frequency converter 5 This is the intermediate frequency (= f _r0 −f ₀ ) when there is no shift.

  The band limiting filter 6 provided in the tracking receiver 4 is a ratio of the received signal from the communication partner converted to the intermediate frequency by the frequency converter 5 and the thermal noise of its own receiving system, that is, signal-to-noise. Installed to improve the ratio above the specified value.

  The automatic gain control circuit 7 provided in the tracking receiver 4 amplifies the received signal that has passed through the band limiting filter to a certain level value. Since the automatic gain control circuit 7 functions to keep the output level at a constant value with the control voltage (AGC voltage) according to each reception level, the AGC voltage can correspond to the reception signal level. The AGC voltage is output to the antenna drive electronic circuit 11 as received signal level information.

  Based on the AGC voltage sent from the automatic gain control circuit 7 provided in the tracking receiver 4, the antenna drive electronic circuit 11 is connected to the antenna drive mechanism 10 so that the received signal level from the communication partner is maximized. A control signal is transmitted to control the directivity direction of the directional antenna 1.

  The antenna drive mechanism 10 controls the directional antenna 1 based on the control signal sent from the antenna drive electronic circuit 11.

In the communication signal wave automatic tracking device having the above functions, the actual Doppler shift amount included in the received signal from the communication partner shown in the equation (4) and the Doppler shift forecast value ( If the difference (Δf _r −Δf _c ) of the frequency component added to the output frequency of the local oscillator (voltage controlled oscillator) 8 is reduced based on Δf _c0 ) of the equation (2), the reception level fluctuation due to the frequency fluctuation becomes smaller, and the reception The directivity control performance of the directional antenna 1 using the level is improved.

  With respect to the improvement of the Doppler shift correction effect, the conventional method is shown in FIG. 2, and the method of the present invention is shown in FIG. FIG. 2 (a) shows the relationship between the local oscillation overvoltage (predicted Doppler shift value) and the output frequency of the local oscillator, the solid line shows the characteristics of the local oscillator, and the dotted line shows the local oscillator with a conventional correction function. The characteristics are approximated. FIG. 2B shows a state in which the vertical scale is coordinate-transformed so that this approximate expression (correction function) is linear. By this operation, the actual characteristics of the local oscillator are also corrected, and the nonlinear characteristics are improved. As shown in this figure, large correction deviations Δ1 and Δ2 occur particularly in the non-linear region where the output frequency of the local oscillator is high and low. FIG. 2C shows the degradation of the reception level in the conventional correction method due to the correction deviation, and the area within the BPF (band pass filter) band of the received signal (spectrum) corresponds to the reception level. The left side shows a state where Δ1 is shifted due to the received signal, the BPF, and the correction shift in the non-linear region in the low frequency band. Further, the right side shows a state where Δ2 is shifted due to the received signal, the BPF, and the correction shift. The shift of Δ1 is very small and the degradation of the reception level is small. On the other hand, the shift of Δ2 is very large, and the degradation of the reception level also increases accordingly, so that accurate antenna pointing cannot be determined. Thus, with the conventional correction method, it is difficult to correct in the entire frequency range.

  FIG. 3 shows correction according to the method of the present invention. The relationship between FIGS. 3A and 3B and the vertical axis of the horizontal axis are the same as those in FIG. 3A and 3B, the solid lines indicate the characteristics of the local oscillator, and the dotted lines approximate the characteristics of the local oscillator based on the correction function based on the method of the present invention. In FIG. 2, the correction deviations on the high and low output frequencies of the local oscillator are Δ1 and Δ2, but the deviation Δ1 ′ by the correction of the present invention is Δ1′≈Δ1 and Δ2 ′. Δ2 ′ <Δ2, and the local oscillator characteristics are approximated more accurately in the entire frequency region than in the past. Details will be described with reference to FIG. The right side of FIG. 3C shows a state in which the received signal, the BPF, and Δ2 ′ are shifted due to the correction shift. According to this, since the correction shift can be reduced in the entire frequency region, Deterioration of the reception level within the BPF band can always be kept small, and accurate antenna pointing determination can be made.

  When the frequency region of Doppler shift correction extends to the nonlinear region of the local oscillator (voltage controlled oscillator) 8, the local oscillator (voltage controlled oscillator) with respect to the voltage applied to the local oscillator (voltage controlled oscillator) 8 shown in FIG. 1 or FIG. If the nonlinear characteristic of the output frequency of 8) is corrected to a linear characteristic, the correction error in the nonlinear region can be reduced. As a design example, when receiving a 100ksps random modulated wave (such as BPSK) from a low-orbit satellite with an altitude of 1000km or less using a 500kHz BPF on a satellite in geostationary orbit, an improvement of 5dB or more is realized it can.

Specifically, as shown in FIG. 2 or FIG. 3, the characteristics of the output frequency (f _Lo ) of the local oscillator (voltage controlled oscillator) 8 corresponding to the applied voltage based on the predicted Doppler shift value (Δf _c0 ) are Doppler shifted. Within the range, coordinate conversion is performed by correcting with the correction function shown in Expression (5). As a result, the difference (Δf _r −) between the actual Doppler shift amount (Δf _r ) in the nonlinear region and the output frequency of the local oscillator (voltage controlled oscillator) 8 based on the predicted Doppler shift value (Δf _c0 ). Δf _c ) is reduced.

Where, f _Lo : Output frequency of local oscillator (voltage controlled oscillator) 8, f ₀ : Output frequency of local oscillator (voltage controlled oscillator) 8 when Doppler shift forecast value is 0 Hz, Δf _c : Calculated by calculator 9 Frequency component to be added to the output frequency of the local oscillator (voltage controlled oscillator) 8 based on the predicted Doppler shift forecast value (Δf _{c0 in the} equation (1)), F (Δf _c0 ): Doppler shift amount received from the computer 9 A correction function of the applied voltage of the local oscillator (voltage controlled oscillator) 8 corresponding to the predicted value (Δf _c0 ), Δf _r : an actual Doppler shift amount included in the received signal from the communication partner.

  In the conventional method shown in FIG. 4, since the above correction uses a single expression based on a nonlinear function or a power function as shown in Expression (6) or Expression (7), as shown in FIG. It was difficult to accurately correct the area.

Here, Δf _{c0 is} the Doppler shift forecast value calculated by the computer 9, and a _i is the coefficient of the correction function.

Here, Δf _{c0 is} a Doppler shift forecast value calculated by the computer 9, and a _ij is a coefficient of the correction function.

  By defining the correction function of the local oscillator (voltage controlled oscillator) 8 in equation (1) for each frequency as shown in equation (8), the conventional correction capability is improved as shown in FIG. It becomes possible to make it.

Where V (Δf _c0 ): local oscillator (voltage controlled oscillator) control voltage based on the Doppler shift forecast value calculated by the computer 9, F _i (Δf _c0 , a _i1 , a _i2 ,..., A _in ): local oscillator (Voltage controlled oscillator) input / output nonlinear characteristic correction function, Δf _c0 : Doppler shift forecast value calculated by calculator 9, f _i : Frequency indicating the application range of each correction function, a _ij : Correction function coefficient.

It is explanatory drawing which shows an example of the communication signal automatic tracking apparatus which has a Doppler correction function including a local oscillator nonlinear compensation function. It is explanatory drawing which shows the shift | offset | difference of the Doppler shift amount in the case of a conventional compensation system, and a Doppler correction value. FIG. 4 is an explanatory diagram showing that when the proposed correction method is implemented, the difference between the Doppler shift amount and the Doppler compensation value is smaller than that in the case where the nonlinear correction of FIG. 2 is not performed. It is explanatory drawing which shows an example of the communication signal automatic tracking apparatus which has the conventional Doppler correction function.

Explanation of symbols

1 .. Directional antenna, 2 .. Feeding unit, .. Antenna drive mechanism, 11 .. Antenna drive electronic circuit, 12 .. Local oscillator I / F circuit.

Claims (1)

A directional antenna for receiving communication signals from a communication partner;
A tracking receiver that includes a local oscillator that controls an output frequency, converts a reception level of the communication signal received based on an oscillation frequency of the local oscillator into a voltage, and outputs the voltage;
An antenna driving electronic circuit that outputs a control signal for directing the antenna in the position direction of the communication partner based on the reception level voltage from the tracking receiver;
An antenna driving mechanism for driving the directional antenna by the control signal output from the antenna driving electronic circuit;
A computer that calculates a predicted value of the Doppler shift amount of the transmission frequency of the communication partner, and outputs the predicted value to the tracking receiver, and
The local oscillator, the oscillation frequency is determined by the predicted value of the Doppler amount calculated by the computer,
The predicted value of the Doppler amount calculated by the computer is a communication signal wave automatic tracking device in which the nonlinear characteristic of the local oscillator is approximately corrected by a power function of the following equation.

V (Δf _c0 ): the local oscillator (voltage controlled oscillator) control voltage based on the Doppler shift forecast value calculated by the computer
F _i (Δf _c0 , a _i1 , a _i2 ,..., A _in ): correction function of input / output nonlinear characteristics of the local oscillator (voltage controlled oscillator) Δf _c0 : Doppler shift forecast value calculated by the computer
f _i : Frequency indicating the application range of each correction function
a _ij is a coefficient of the correction function.

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