JP2848353B2 - Doppler measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Doppler measurement method, and more particularly, to measuring the rate of change in distance between a flying object such as an artificial satellite and an earth station, the frequency caused by the uplink Doppler shift received by the flying object itself. The present invention relates to a Doppler measurement method for performing Doppler measurement when it is necessary to reduce displacement and when it is necessary to transmit a reference frequency to a flying object.

[0002]

2. Description of the Related Art A carrier signal is transmitted from an earth station, and a flying object such as an artificial satellite obtains a transmission frequency from a reception frequency by a coherent transponder method, and the earth station receives the transmission frequency and measures a Doppler frequency between transmission and reception. Accordingly, a Doppler measurement method for measuring a distance change rate between an earth station and a flying object has been conventionally used.

FIG. 2 is a block diagram showing an example of a conventional Doppler measurement system. In this conventional Doppler measurement method, a reference frequency generator 1 for generating a reference frequency fs on an artificial satellite is used.
The earth station is provided with a reference frequency generator 2 for generating a reference frequency fs0 different from the reference frequency fs, an antenna device 3, a receiving device 4, and a Doppler measuring device 5.

In this Doppler measurement method, the reference frequency fs transmitted from the artificial satellite is received by the antenna device 3 of the earth station under the Doppler effect due to the movement of the artificial satellite. This reception frequency fd is fs ｛1+ (v /
c) Represented by｝. Where v is the moving speed of the satellite,
c is the speed of light. The reception frequency fd is supplied to the Doppler measurement device 5 through the reception device 4.

The Doppler measuring device 5 uses the received frequency fd from the receiving device 4 and the reference frequency fs0 from the reference frequency generator 2 to obtain a Doppler frequency fD (= fs ｛1+).
After measuring (v / c)｝-fs0), the distance change rate v (= one-way) defined using this Doppler frequency fD
c · fD / fs0) is calculated.

FIG. 3 shows a configuration diagram of another example of the conventional Doppler measurement method. In this conventional measurement method, a coherence transponder 11 capable of obtaining a transmission frequency in a relationship of r times the reception frequency is mounted, and the earth station includes an antenna device 12, a reception device 13, and a Doppler measurement device 1.
4. Uplink frequency generator 15, frequency multiplier 16
And a transmission device 17. Uplink frequency generator 15 generates reference signal frequency fu.

In this conventional Doppler measurement method, the uplink frequency (reference signal frequency) fu (t) (= fu0) generated by the uplink frequency generator 15 passes through the transmitting device 17 and the antenna device 12, respectively, and is artificially generated. It is transmitted to the satellite at time t. In the satellite, the orbital motion v of the satellite itself defined by the uplink delay time Tu
An uplink frequency (reference signal frequency) fu subjected to the Doppler effect from (t + Tu) is received. At this time,
The coherent transponder 11 of the satellite transmits the time (t
+ Tu), fs (t + Tu) = fu (t) [1+ ｛v
(T + Tu) / c}], multiply it by r times and transmit it to the earth station.

The transmission frequency is determined by the orbital motion v (t + Tu + T) of the satellite defined by the downlink delay time Td.
d) again causes the Doppler effect, and at the receiving device 13 via the antenna device 12 of the earth station, the time (t + T)
u + Td), fd (t + Tu + Td) = r · fs (t
+ Tu) [1+ {v (t + Tu + Td) / c}].

The Doppler measuring device 14 uses the received frequency and a reference frequency r · fu0 r times the uplink frequency fu0 input from the frequency multiplier 16 to obtain a Doppler frequency fD (t + Tu + Td) (= fd (t + T)
u + Td) −r · fu0), and further using this Doppler frequency, the distance change rate (v = (c / 2) · fD /
r · fu) is calculated. According to this conventional method, since the earth station transmission frequency fu (= fu0) is fixed, a true round-trip Doppler frequency can be observed without depending on processing such as orbit determination.

[0010]

However, in the former conventional Doppler measurement method shown in FIG. 2, the reference frequency fs generated by the reference frequency generator 1 mounted on the artificial satellite takes account of frequency fluctuations and the like. Then, it becomes unknown, and as a result, the measured Doppler frequency fD includes:
Since the offset including the offset from the earth station reference frequency fs0 is included in the observation, the true Doppler frequency is not observed, and it is necessary to perform an orbit determination process separately. Processing such as estimation must be performed.

On the other hand, in the latter conventional Doppler measurement method shown in FIG. 3, as described above, if the earth station transmission frequency fu (= fu0) is fixed, the reference frequency source mounted on the satellite and the earth station reference frequency are set. Although it is possible to observe the true round-trip Doppler frequency without considering the frequency offset existing between the frequency source and the satellite, at the satellite receiving end, since the uplink frequency is received by receiving the Doppler shift, , The coherent transponder 11 must be designed in consideration of this uplink frequency shift.

In the conventional system shown in FIG. 3, the phase locked loop constituting the coherent transponder 11 always operates under the stress of the frequency offset due to the uplink Doppler shift. The more difficult it is to design.

Further, in order to reduce the operation in a state where the stress of the frequency offset is always applied, a method of controlling the uplink transmission frequency at the earth station in accordance with the orbital motion of the satellite has been conventionally performed. However, in this case, there is a control error in the measured Doppler frequency, so operation to disable Doppler measurement during uplink frequency control or operation to stop uplink frequency control during Doppler frequency measurement is performed. I need.

The present invention has been made in view of the above points,
An object of the present invention is to provide a Doppler measurement method capable of measuring a Doppler frequency even while continuously changing an uplink frequency in order to reduce a loop stress of a coherent transponder.

[0015]

According to the present invention, a coherent transponder mounted on a flying object receives a transmission frequency from a ground station to a flying object and transmits a downlink from the reception frequency. The Doppler calculates the distance change rate by obtaining the frequency and transmitting it to the ground station, receiving the downlink transmission frequency and measuring the Doppler frequency between transmission and reception from this received frequency and the reference frequency. In the measurement method, the ground station estimates the next distance change rate for the flying object from the measured Doppler frequency, and variably controls the uplink transmission frequency from the estimated distance change rate, so that the It is characterized in that the uplink frequency shift is set to zero.

Further, according to the present invention, a transmission frequency from the ground station to the flying object is received by a coherent transponder mounted on the flying object, a downlink transmission frequency is obtained from the received frequency, and transmitted to the ground station. Then, the ground station receives the downlink transmission frequency, and measures the Doppler frequency between transmission and reception from the received frequency and the reference frequency to calculate the distance change rate. By doing so, the above object is achieved. That is, the ground station generates an uplink frequency whose frequency is varied by the control signal, a transmission unit that transmits the uplink frequency to the flying object, and receives a downlink frequency from the flying object. A receiving means, a reference frequency generator for generating a reference frequency, a Doppler measuring device for measuring a Doppler frequency from the receiving frequency and the reference frequency from the receiving means and estimating a next rate of change in distance to the flying object, and an estimated distance An uplink frequency control device for generating a control signal based on the rate of change and supplying the control signal to an uplink frequency generating means, thereby generating an uplink frequency that cancels the Doppler frequency at the receiving end of the flying object.

According to the present invention, a feedback loop is configured such that the uplink transmission frequency is variably controlled based on the distance change rate estimated from the measured Doppler frequency, and the uplink frequency shift at the receiving end of the flying object becomes zero. Therefore, the measured Doppler frequency is a downlink Doppler frequency with a known value of the downlink transmission frequency from the flying object, and it is possible to construct a Doppler measurement method that can measure the downlink one-way distance change rate. it can.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration diagram of an embodiment of the Doppler measurement system according to the present invention. 3, the same components as those of FIG. 3 are denoted by the same reference numerals. As shown in FIG. 1, in this embodiment, an antenna device 12, a receiving device 13, a transmitting device 17, a Doppler measuring device 21, a reference frequency generator 22, an uplink frequency control device 23, an uplink frequency A generator 24 is provided, and the coherent transponder 11 is mounted on the artificial satellite.

The reference frequency generator 22 generates a fixed reference frequency r.fu0. The uplink frequency generator 24 variably controls the generated uplink frequency fu based on a control signal from the uplink frequency control device 23. Further, the uplink frequency control device 23 extrapolates the distance change rate of the artificial satellite based on the Doppler frequency measured by the Doppler measurement device 21 and calculates the distance change rate from the uplink frequency generator 24 based on the estimated value. Control the generated uplink frequency.

The above-mentioned uplink frequency generator 24, transmitting device 17, antenna device 12, coherent transponder 11, antenna device 12, receiving device 13, Doppler measuring device 21, and uplink frequency control device 23 constitute a feedback loop. To cancel the coherent transponder receiver Doppler frequency,
The output uplink frequency of the uplink frequency generator 24 is controlled.

Next, the operation of this embodiment will be described. At the earth station, the uplink frequency fu (t) generated at time t from the uplink frequency generator 24
Is transmitted to the artificial satellite via the transmitting device 17 and the antenna device 12. This uplink frequency fu (t)
Receives the Doppler effect due to the orbital motion v (t + Tu) of the satellite itself defined by the uplink delay time Tu, and at time (t + Tu), fs (t + Tu) = fu (t)
It is received at a frequency of [1+ {v (t + Tu) / c}]. Here, it is assumed that the artificial satellite is orbiting at a moving speed v toward the earth station.

The coherent transponder 11 mounted on the artificial satellite changes this reception frequency fs (t + Tu) to r
The frequency is doubled and transmitted to the earth station. This downlink transmission frequency r · fs (t + Tu) is the orbital motion v of the satellite defined by the downlink delay time Td.
(T + Tu + Td) again causes Doppler effect,
At the receiving device 13 via the antenna device 12 of the earth station, at time (t + Tu + Td), fd (t + Tu + T)
d) = r · fs (t + Tu) [1 + Δv (t + Tu + T)
d) / c}].

The Doppler measuring device 21 uses the fixed reference frequency r.fu0 input from the reference frequency generator 22 to calculate the Doppler frequency fD (t + Tu + Td) (= fd (t + T) from the received frequency fd (t + Tu + Td).
u + Td) -rfu0) is measured. The measured Doppler frequency fD (t + Tu + Td) can be transformed as follows.

FD (t + Tu + Td) = fd (t + Tu + Td) −r · fu0 = r · fs (t + Tu) [1+ {v (t + Tu + Td) / c}] − r · fu0 = r · fu ( t) [1+ {v (t + Tu) / c}] [1+ {v (t + Tu + Td) / c}]-rfu0 ≒ rfu (t) [1+ {v (t + Tu) / c} + {v (t + Tu + Td) / c}]-r · fu0 Here, assuming that the uplink frequency fu (t) is fixed at fu0 during the Doppler measurement period, The measured Doppler frequency fD (t + Tu + Td) is fu in the above equation.
By substituting (t) = fu0, fD (t + Tu + Td) = r · fu0 [｛v (t + T
u) / c｝ + {v (t + Tu + Td) / c}]. Also, the rate of change of the distance of the reciprocation at this time is expressed by the following equation by rearranging the above equation.

V (t + Tu) + v (t + Tu + Td) =
c · fD (t + Tu + Td) / (r · fu0) Therefore, the measured Doppler frequency fD (t + Tu + Td)
Corresponds to the rate of change of the distance of the round trip.

The uplink frequency controller 23 calculates the next time t ′ (> t + T) from the Doppler frequency fD (t + Tu + Td) measured by the Doppler measuring device 21.
u + Td), the rate of change of the satellite's distance v '(t')
Is estimated by extrapolation, and the uplink frequency generator 2
4 variably controls the uplink frequency output from
The uplink frequency fu (t ') after control is fu0 ｛1
− (V ′ (t ′) / c)}.

Uplink frequency fu after this control
(T ') is transmitted again to the artificial satellite via the transmitting device 17 and the antenna device 12, respectively. The Doppler measurement frequency fD '(t + Tu + Td) after the uplink frequency correction, which is measured again by the Doppler measurement device 21 of the earth station in the same manner as described above, is expressed by the following equation.

FD ′ (t + Tu + Td) = r · fu0 [1− {v ′ (t ′) / c}] [1+ {v (t + Tu) / c} + {v (t + Tu + Td) / c}] − r · fu0 {R · fu0 [− {v ′ (t ′) / c} + {v (t + Tu) / c} + {v (t + Tu + Td) / c}] It is estimated when the uplink frequency correction is correctly performed. It is expected that the distance change rate v '(t') and the uplink distance change rate of the artificial satellite are canceled (the Doppler frequency at the receiving end of the coherent transponder 11 is canceled by the corrected uplink frequency). Since −v ′ (t ′) + v (t + Tu) = 0 holds, the Doppler measurement frequency fD ′ (t
+ Tu + Td) is expressed by the following equation by rearranging the above equation.

FD ′ (t + Tu + Td) ≒ r · fu0
{V (t + Tu + Td) / c} Therefore, in this case, the Doppler measurement frequency fD ′ (t +
Tu + Td), one-way distance change rate v in downlink
(T + Tu + Td) is obtained from the following equation obtained by rearranging the above equation.

V (t + Tu + Td) = c.fD '(t +
Tu + Td) / (r · fu0) Also, by performing feedback control in which this one-way distance change rate is used as an observation value for extrapolating the next uplink frequency control amount, while controlling the uplink frequency, The rate of one-way distance change of the downlink can be measured.

When the uplink Doppler correction is normally performed, the reception frequency of the coherent transponder 11 is fs (t + Tu) = fu0 ｛1- (v ′).
(T ′) / c) + (v (t + Tu) / c)｝ = fu0, and the reference frequency fu0 without the Doppler effect can be transmitted to the orbiting artificial satellite, and the coherent transponder 11 Loop stress can be reduced.

The present invention is not limited to the above embodiment, but is applicable to all Doppler measurement systems for measuring the rate of change in distance between an aircraft other than an artificial satellite or other flying object and a ground station. It is.

[0034]

As described above, according to the present invention,
The transmission frequency of the uplink is variably controlled based on the distance change rate estimated from the measured Doppler frequency, and the measurement is performed by forming a feedback loop so that the uplink frequency shift at the receiving end of the flying object is zero. The Doppler frequency is a downlink Doppler frequency with the downlink transmission frequency from the flying object as a known value, and it is possible to measure the downlink one-way distance change rate, and to reduce the loop stress of the flying object Even while the uplink frequency is continuously changing, it can transmit the reference frequency without Doppler effect to the orbiting projectile, measure the Doppler frequency, and easily design the transponder. it can. Further, according to the present invention, it is possible to transmit a reference frequency from a ground station to a flying object such as an artificial satellite without being aware of the Doppler effect, thereby reducing the risk of developing a high stability frequency source mounted on a flying object. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional example.

FIG. 3 is a configuration diagram of another example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Coherent transponder 12 Antenna device 13 Receiving device 17 Transmitting device 21 Doppler measuring device 22 Reference frequency generator 23 Uplink frequency control device 24 Uplink frequency generator

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01S 13/74-13/84 H04B 1/59 H04B 7/185

Claims (3)

(57) [Claims] A coherent transponder mounted on the flying object receives a transmission frequency from the ground station to the flying object, obtains a downlink transmission frequency from the received frequency, and transmits the downlink transmission frequency to the ground station. The ground station receives the downlink transmission frequency, and measures a Doppler frequency between transmission and reception from the reception frequency and the reference frequency, thereby calculating a distance change rate. By estimating the next distance change rate with respect to the flying object from the calculated Doppler frequency, and variably controlling the uplink transmission frequency from the estimated distance change rate, the uplink frequency shift at the receiving end of the flying object is calculated. Doppler measurement method characterized by zero. 2. A transmission frequency from the ground station to the flying object is received by a coherent transponder mounted on the flying object, a downlink transmission frequency is obtained from the received frequency, and the downlink transmission frequency is transmitted to the ground station. A ground station receives the downlink transmission frequency, and measures a Doppler frequency between transmission and reception from the reception frequency and the reference frequency to calculate a distance change rate. In the Doppler measurement method, the ground station includes a control signal An uplink frequency generating unit that generates an uplink frequency whose frequency is varied by: a transmitting unit that transmits the uplink frequency to a flying object; a receiving unit that receives a downlink frequency from the flying object; A reference frequency generator for generating a frequency; A Doppler measuring device for measuring a frequency and estimating a next distance change rate with respect to the flying object; and generating the control signal from the estimated distance change rate and supplying the control signal to the uplink frequency generating means, thereby performing the flying. An uplink frequency control device for generating the uplink frequency that cancels the Doppler frequency at the body receiving end. 3. The Doppler measuring device measures a Doppler frequency between the transmission and reception and calculates a downlink one-way distance change rate, and the uplink frequency control device calculates a downlink one-way distance change rate. The Doppler measurement method according to claim 2, wherein the Doppler measurement method is input as an observation value for extrapolating a next uplink frequency control amount.