JP4386996B2 - Mobile terminal and propagation delay time prediction calculation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mobile terminal for wireless communication using an orbiting satellite, and more particularly to an improvement capable of smoothly restarting communication even when communication is temporarily interrupted between the orbiting satellite and a mobile terminal.
[0002]
[Prior art]
Wireless communication using an orbiting satellite is provided by, for example, Iridium or Globalstar, and is configured using an orbiting satellite SV (Space Vehicle), a mobile terminal SU (Subscriber Unit), and a gateway station (Gateway). Has been. Taking Iridium as an example, the orbiting satellite SV is launched into each orbit about six orbits passing through the pole, covering a total of 66 earths.
[0003]
FIG. 6 is an earth hemisphere diagram showing the area in charge of one orbiting satellite SV. The orbiting satellite SV flies about 780 km on the ground in a much lower orbit than the geostationary satellite, and orbits in about 100 minutes. Since 11 orbiting satellites SV cover one orbit, one orbiting satellite SV has a ground area with a diameter of about 4000 km as a responsible area. In this relationship, the distance between the orbiting satellite SV and the mobile terminal SU is about 780 km at the center of the assigned area and about 2250 km at the end of the assigned area. At this time, the propagation delay time t between the orbiting satellite SV and the mobile terminal SU is about 2 ms at the center of the assigned area and about 11 ms at the end of the assigned area.
[0004]
FIG. 7 is an explanatory diagram of the location of the mobile terminal SU and the area in charge of the orbiting satellite SV. The mobile terminal SUa is located at 0 degrees north latitude and 0 degrees east longitude, and the mobile terminal SUb is located at 0 degrees north latitude and 10 degrees east longitude. The orbiting satellite SV moves from the south pole to the north pole on the longitude line at 0 degrees east longitude.
[0005]
FIG. 8 is an explanatory diagram of the travel time of the orbiting satellite SV and the propagation delay time between the mobile terminal SU. The moving time of the orbiting satellite SV is 0 second when the orbiting satellite SV is located on the equator in FIG. 7, and the south pole side is minus and the north pole side is plus with respect to this equator position. Since one orbiting satellite SV has a revolution period of about 100 minutes and 11 orbiting satellites SV have secured a call on the meridian, the propagation delay time is considered when considering one mobile station SU. Consider about ± 5 minutes (300 seconds). The mobile terminal SUa located immediately below the orbit of the orbiting satellite SV has a propagation delay time of about 2 ms when it is 0 seconds, and a propagation delay time of about 8 ms when ± 300 seconds. On the other hand, the mobile terminal SUb located at 10 degrees east longitude has a propagation delay time of about 5 ms at 0 seconds and a propagation delay time of about 9 ms at ± 300 seconds.
[0006]
FIG. 9 shows a TDMA frame of the orbiting satellite SV. One frame of the orbiting satellite SV includes four uplink UL time slots for communication from the mobile terminal SU to the orbiting satellite SV, and downlink DL time slot 4 for communication from the orbiting satellite SV to the mobile terminal SU. Slots are available. Each mobile terminal SU is assigned one of the four uplink / downlink slots of the orbiting satellite SV. Each mobile terminal SU performs transmission to the orbiting satellite SV with a propagation delay time t earlier so that it can be received in the uplink slot to which the orbiting satellite SV is assigned. Since the orbiting satellite SV transmits in the downlink slot for each mobile terminal SU, the reception time of the mobile terminal SU is delayed by the propagation delay time t.
[0007]
[Problems to be solved by the invention]
However, in mobile communication using a wireless communication system, the state of radio waves is not always good. Radio waves may be blocked by a change in the relative positional relationship between the orbiting satellite SV and the mobile terminal SU, such as in the shadow of a building or in a tunnel. At this time, the orbiting satellite SV does not immediately disconnect the link with the mobile terminal SU, but waits for a grace period until the radio wave condition is improved. Within this grace period, for example, when the radio wave condition from the orbiting satellite SV is improved due to reasons such as exiting from a tunnel, the communication system such as TDMA can reliably receive the radio wave from the mobile terminal SU on the orbiting satellite SV side. Thus, when the mobile terminal SU transmits, the link can be continued and convenience is enhanced.
[0008]
On the other hand, since the reception window of the orbiting satellite SV is narrower than the fluctuation of the propagation delay time of 2 to 11 ms as described in FIG. 9, it is transmitted accurately at a timing suitable for the uplink allocated slot, It is necessary to prevent interference with adjacent slots. For prediction of propagation delay time, it is conceivable to use a general-purpose prediction filter such as a Kalman filter or a low-pass filter. However, the conventional prediction filter requires a certain number of samples because of the prediction based on the trend so far, and the prediction accuracy is high until the sample collection is sufficiently performed or when the initial value of timing deviation is large. There has been a problem of lowering.
[0009]
The present invention solves the above-described problem, and predicts a propagation delay time that can be reliably transmitted in a time slot assigned at the time of restoration of communication even if communication between the orbiting satellite SV and the mobile terminal SU is temporarily interrupted. An object is to provide an apparatus.
[0010]
[Means for Solving the Problems]
The mobile terminal according to claim 1, which solves the above-mentioned problem, is assigned uplink and downlink time slots with an orbiting satellite, and considers a propagation delay time with reference to the arrival time of radio waves from the orbiting satellite. In the mobile terminal that performs uplink transmission so as to enter the time slot of the orbiting satellite, the means for obtaining the Doppler frequency of the radio frequency at the time of the downlink of the orbiting satellite and the start of blockage of communication with the orbiting satellite A cutoff time measuring means for measuring the elapsed time from the time until the restart of downlink reception, a Doppler frequency at the start of the cutoff of communication with the orbiting satellite, a frequency used for wireless communication, and a measurement of the cutoff time measuring means Prediction calculation means for calculating a propagation delay time with the orbiting satellite from the elapsed time, and downlink reception re-transmission of the orbiting satellite. And performing transmission for the uplink in consideration of the sometimes propagation delay time calculated by said prediction calculating means.
[0011]
If the communication between the mobile terminal SU and the orbiting satellite SV is ensured in the apparatus configured in this way, the orbiting satellite SV notifies the transmission timing shift of the mobile terminal SU, so that the accurate orbiting The delay time to the satellite SV can be easily known. If the radio wave from the orbiting satellite SV can be received, the Doppler frequency can be easily measured. The interruption time measuring means 34 measures the elapsed time from the start of interruption of communication with the orbiting satellite SV to the time when downlink reception is resumed. The prediction calculation means 36 is the Doppler frequency at the start of communication interruption with the orbiting satellite SV, the frequency used for wireless communication, the elapsed time measured by the interruption time measuring means 34, and the orbiting satellite SV at the start of communication interruption. From the delay time, the propagation delay time with the orbiting satellite SV is calculated. The mobile terminal SU performs uplink transmission using the propagation delay time calculated by the prediction calculation means 36 when the downlink reception of the orbiting satellite SV is resumed. The orbiting satellite SV is moving at such a high speed that it can ignore the moving speed of the mobile terminal SU, and it can be predicted when the downlink reception is resumed from the Doppler frequency and the elapsed time at the start of the communication interruption. If it is a temporary phenomenon, communication can be resumed smoothly by maintaining the link.
[0012]
Preferably, as described in claim 2, when the prediction calculation unit 36 is configured to further calculate the propagation delay time with the orbiting satellite SV using the Doppler frequency when the downlink reception of the orbiting satellite SV is resumed, Even if the disconnection becomes longer and the difference from the start of the communication disconnection becomes large, the transmission for the uplink when the downlink reception is resumed can be performed successfully. Further, as described in claim 3, when the Doppler frequency at the start of communication cut-off and the Doppler frequency at the time of restarting downlink reception are separated by a predetermined value or more, the prediction calculation means 36 When the propagation delay time calculated with the Doppler frequency at the start of communication cut-off and when the downlink reception is resumed, and the elapsed time measured by the cut-off time measuring means, the propagation delay time with the orbiting satellite is calculated. When the interruption is short, the prediction calculation means 36 can perform the uplink transmission when the downlink reception is resumed by a simple calculation using the Doppler frequency at the start of the communication interruption.
[0013]
Preferably, as described in claim 4, the prediction calculation means 36 calculates the propagation delay time with the orbiting satellite using the average of the Doppler frequency at the start of communication interruption and the Doppler frequency at the time of restarting downlink reception. With the configuration to calculate, even if the communication cut-off becomes longer and the deviation from the start of the communication cut-off becomes large, the uplink transmission when the downlink reception is resumed can be performed successfully. Further, as described in claim 5, when the prediction calculation means 36 is configured to calculate the propagation delay time with the orbiting satellite SV using the relationship between the Doppler frequency and the change in the propagation delay time, the prediction calculation is performed. Easy to do.
[0014]
According to a sixth aspect of the present invention, in the propagation delay time predicting / calculating apparatus, uplink and downlink time slots are assigned to orbiting satellites, and the propagation delay time is taken into account based on the arrival time of radio waves from the orbiting satellites. A prediction computation device of a mobile terminal that performs uplink transmission so as to enter a time slot of the orbiting satellite, and obtains a Doppler frequency of a radio frequency emitted by the orbiting satellite toward a ground station or a mobile terminal And an elapsed time measuring means for measuring an elapsed time from the start of communication cut-off with the orbiting satellite to the time when downlink reception resumes, and a Doppler frequency and radio communication at the start of communication cut-off with the orbiting satellite. after being frequency and the elapsed time measured in said elapsed time measuring means, by comprising, a prediction calculating means for calculating a propagation delay time between the orbiting satellites And butterflies.
If comprised in this way, future propagation delay time can be estimated from the present information of an orbiting satellite, and it can apply to observation of an orbiting satellite and propagation delay time prediction at the time of handoff from one orbiting satellite to the next orbiting satellite.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating an embodiment of the present invention. In the figure, the mobile station SU is assigned uplink UL and downlink DL time slots with the orbiting satellite SV, and enters the time slot of the orbiting satellite SV with reference to the arrival time of radio waves from the orbiting satellite SV. It performs transmission for the uplink. The antenna 20 transmits and receives radio between the orbiting satellite SV and the mobile terminal SU. The receiving device 22 receives a downlink DL signal from the orbiting satellite SV, extracts a voice signal, and sends it to the audio device 26. The transmission device 24 transmits an uplink UL signal to the orbiting satellite SV, converts the audio signal transmitted from the audio device 26 so as to conform to the wireless specifications, and transmits the converted signal to the orbiting satellite SV. The audio device 26 is a microphone or a speaker that interfaces with an operator. The uplink transmission slot time adjustment unit 28 adjusts the timing of transmission from the mobile terminal SU to the orbiting satellite SV.
[0016]
The uplink transmission slot time adjustment unit 28 determines the transmission timing using the error signal of the orbiting satellite SV while the communication between the orbiting satellite SV and the mobile terminal SU is ensured. On the other hand, when the delay time from the orbiting satellite SV is zero, the mobile terminal SU receives radio waves from the orbiting satellite SV and uses the TDMA (Time Division Multiple Access) determined by the system on the basis of the received radio wave. What is necessary is just to transmit according to timing. However, when the propagation delay time from the orbiting satellite SV is t1, the mobile terminal SU receives the radio wave from the orbiting satellite SV with a delay of t1. At this time, ignoring the delay of t1 and transmitting the mobile terminal SU in accordance with the TDMA timing as it is, when the radio wave of the mobile terminal SU reaches the orbiting satellite SV, it is only twice t1. It will be late. Therefore, when the delay time is t1, the mobile station SU must receive the radio wave of the orbiting satellite SV and transmit the transmission timing at an earlier timing by 2 × t1 from the original TDMA timing. Don't be. That is, since the accurate transmission timing of the mobile terminal SU can be determined from the transmission timing error notified from the orbiting satellite SV, half of the time becomes the propagation delay time of the orbiting satellite SV and the mobile terminal SU.
[0017]
The link maintenance function unit 30 corrects the deviation using the error signal notified from the orbiting satellite SV to maintain the link during normal communication and further temporarily interrupts the communication between the orbiting satellite SV and the mobile terminal SU. In this case, communication is resumed smoothly using a link that is continued when downlink reception is resumed. Then, each part which comprises the link maintenance function part 30 is demonstrated. The Doppler frequency acquisition unit 32 acquires the Doppler frequency of the radio frequency when the orbiting satellite SV is in the downlink. When the orbiting satellite SV and the mobile terminal SU are communicating, maintenance is exchanged for maintaining the link at a rate of one frame per four frames, for example. In the maintenance frame, a burst is transmitted from the mobile terminal SU. Then, the orbiting satellite SV measures timing and frequency, and transmits the difference in propagation delay time to the mobile terminal SU as DTOA (Differential Time of Arrival).
[0018]
The blocking time measuring unit 34 measures the elapsed time from the start of blocking communication with the orbiting satellite SV to the time when downlink reception is resumed. The elapsed time measured by the cut-off time measuring unit 34 is supplied to the propagation delay time prediction calculation unit 36 together with the Doppler frequency at the start of communication cut-off with the orbiting satellite SV, and the propagation delay time with the orbiting satellite SV is calculated. . The details of the prediction calculation will be described later in detail. The orbiting satellite data storage unit 38 stores parameters used in the propagation delay time prediction calculation unit 36, for example, the delay time to the orbiting satellite SV at the start of communication interruption, the radio frequency, and the like. The propagation delay time calculated by the propagation delay time prediction calculation unit 36 is sent to the uplink transmission slot time adjustment unit 28 when the downlink reception of the orbiting satellite SV is resumed, and the mobile terminal SU performs transmission for the uplink. .
[0019]
Next, the operation of the apparatus configured as described above will be described. FIG. 2 is an explanatory diagram of the Doppler frequency and the travel time of the orbiting satellite SV. 2 and 3, a corresponds to the mobile terminal SUa in FIG. 7, and b corresponds to the mobile terminal SUb. The Doppler frequency is obtained by dividing the distance D (t) between the mobile terminal SU and the orbiting satellite SV by time and dividing it by the wavelength λ (= c / f: c is the speed of light) of the operating frequency f. The formula holds.
D (t) ′ / λ = −D (t) ′ f / c (1)
The mobile terminal SUa located immediately below the orbit of the orbiting satellite SV has a Doppler frequency of 0 kHz at 0 seconds and a Doppler frequency of about 35 kHz at ± 300 seconds. On the other hand, the mobile terminal SUb located at 10 degrees east longitude has a Doppler frequency of about −2 kHz at 0 seconds and a Doppler frequency of about 30 kHz at ± 300 seconds.
[0020]
FIG. 3 is an explanatory diagram of the DTOA and the travel time of the orbiting satellite SV. Since DTOA is obtained by time-differentiating the distance D (t) and dividing by the speed of light c, the following equation is established.
DTOA = D (t) '/ c (2)
The mobile terminal SUa located immediately below the orbit of the orbiting satellite SV has a DTOA of 0 (μsec / sec) at 0 seconds and a DTOA of −22 (μsec / sec) at ± 300 seconds. On the other hand, the mobile terminal SUb located at 10 degrees east longitude has a DTOA of about 2 (μsec / sec) at 0 seconds and a DTOA of about ± 20 (μsec / sec) at ± 300 seconds. The explanatory diagram of the Doppler frequency and the traveling time of the orbiting satellite SV in FIG. 2 has the same shape as that obtained by reversing the sign of the vertical axis of the DTOA in FIG.
FIG. 4 is an explanatory diagram of the Doppler frequency and DTOA. The Doppler frequency and DTOA are in a proportional relationship. If the Doppler frequency from the orbiting satellite is known, the change DTOA of the propagation delay time per unit time can be obtained by dividing the Doppler frequency by the frequency used for wireless communication. it can.
DTOA (μsec / sec) = − Doppler (kHz) / radio frequency (GHz) (3) The radio frequency used for communication between the orbiting satellite SV and the mobile terminal SU is, for example, 1.6 GHz band in the case of Iridium. Since it is used, the equation (3) is as follows.
DTOA (μsec / sec) = − 0.625 * Doppler (kHz) (4)
[0022]
DTOA changes as shown in FIG. 3, and in the range where linear approximation is possible, approximation with excellent delay time can be performed by using this DTOA. For example, when the Doppler frequency immediately before entering the tunnel is Df1, the Doppler frequency when exiting the tunnel is Df2, and the time T required to pass through the tunnel is T, the average DTOA during the time T is expressed by the following equation: be able to.
Average DTOA = − (Df1 + Df2) / 2f (5)
[0023]
On the other hand, during the time T, the change Δt in the delay time is an average DTOA × T, so Δt = − (Df1 + Df2) × T / 2f (6)
It becomes. The correct delay time can be obtained by adding the delay time change Δt in the equation (6) to the delay time t before entering the tunnel. If the time in the tunnel is very short,
Δt = −Df1 × T / f (7)
Gives a very good approximation.
[0024]
Next, the reason why the error is small even when approximated by the approximate expression “−Df1 × T / f” of Expression (7) will be described. As can be seen from the comparison between FIG. 2 and FIG. 3, when the relationship between DTOA and Doppler frequency is seen, the larger the Doppler frequency, the larger the DTOA absolute value, but the smaller the change in DTOA per unit time. Further, since the absolute value of DTOA is small where DTOA changes greatly, the error is small even if approximated by “−Df1 × T / f”. Preferably, when entering the tunnel, the delay time is corrected by approximating with “−Df1 × T / f”, and when exiting the tunnel and receiving the radio wave from the satellite and determining the Doppler Df2, Df2 and Df1 In the case where the difference is equal to or greater than a certain value, the correction may be made using equation (6).
[0025]
FIG. 5 is an explanatory diagram of the amount of change per time of DTOA and the moving time of the orbiting satellite SV. Even where the amount of change in DTOA is the largest, such as when the satellite passes directly above, it is about 0.22 μsec / sec / sec, and the change in DTOA for 10 seconds is 2.2 μsec / sec. It can be seen that DTOA hardly changes even when compared with the satellite reception window ± 65 μsec. Therefore, it can be seen that if the communication cut-off time is about a few tens of seconds, sufficient prediction can be made by using equation (6).
[0026]
In the above embodiment, the case where the mobile terminal SU side measures the Doppler frequency of the radio frequency and transmits it to the orbiting satellite SV side is shown, but the present invention is not limited to this, and the orbiting satellite SV. The Doppler frequency of the radio frequency may be measured on the side.
[0027]
【The invention's effect】
As described above, according to the present invention, the propagation delay time with the orbiting satellite SV is calculated from the Doppler frequency at the start of communication interruption with the orbiting satellite SV by the prediction calculation means and the elapsed time measured by the interruption time measuring means. Since the mobile terminal SU is configured to perform transmission for the uplink using the propagation delay time calculated by the prediction calculation means when the downlink reception of the orbiting satellite SV is resumed, the communication interruption is a temporary phenomenon. If there is, there is an effect that the communication can be smoothly resumed by maintaining the link.
[Brief description of the drawings]
FIG. 1 is a configuration block diagram illustrating an embodiment of the present invention.
FIG. 2 is an explanatory diagram of the Doppler frequency and the travel time of the orbiting satellite SV.
FIG. 3 is an explanatory diagram of DTOA and the travel time of the orbiting satellite SV.
FIG. 4 is an explanatory diagram of Doppler frequency and DTOA.
FIG. 5 is an explanatory diagram of a change amount of DTOA per time and a moving time of the orbiting satellite SV.
FIG. 6 is a diagram of the earth hemisphere showing the area in charge of one orbiting satellite SV.
FIG. 7 is an explanatory diagram of the location of the mobile terminal SU and the area in charge of the orbiting satellite SV.
FIG. 8 is an explanatory diagram of the travel time of the orbiting satellite SV and the propagation delay time between the mobile terminal SU and FIG.
FIG. 9 shows a TDMA frame of the orbiting satellite SV.
[Explanation of symbols]
SV orbiting satellite SU mobile terminal 20 antenna 22 reception device 24 transmission device 26 audio device 28 uplink transmission slot time adjustment unit 30 link maintenance function unit 32 Doppler frequency acquisition unit 34 cutoff time measurement unit 36 prediction calculation unit 38 orbit satellite data Memory

Claims (6)

Uplink and downlink time slots are assigned to orbiting satellites, and uplink transmission is performed so that propagation delay times are taken into account with reference to the arrival time of radio waves from the orbiting satellites and the time slot of the orbiting satellite is entered. In the mobile terminal that performs
Means for acquiring a Doppler frequency of a radio frequency at the time of downlink of the orbiting satellite;
An interruption time measuring means for measuring an elapsed time from the start of interruption of communication with the orbiting satellite to the time when downlink reception is resumed;
Prediction calculation means for calculating the propagation delay time with the orbiting satellite from the Doppler frequency at the start of communication interruption with the orbiting satellite, the frequency used for wireless communication and the elapsed time measured by the interruption time measuring means,
A mobile terminal that performs uplink transmission in consideration of the propagation delay time calculated by the prediction calculation means when downlink reception of the orbiting satellite is resumed.   The mobile terminal according to claim 1, wherein the prediction calculation means further calculates a propagation delay time with the orbiting satellite by using a Doppler frequency when downlink reception of the orbiting satellite is resumed.   When the Doppler frequency at the start of communication cut-off and the Doppler frequency at the time of restarting downlink reception are separated by a predetermined value or more, the prediction calculation means The mobile terminal according to claim 1 or 2, wherein a propagation delay time with the orbiting satellite is calculated from a Doppler frequency and an elapsed time measured by the cutoff time measuring means.   The prediction calculation means calculates a propagation delay time with the orbiting satellite using an average of a Doppler frequency at the start of communication cut-off and a Doppler frequency at the time of restarting downlink reception. Item 4. The mobile terminal according to Item 3.   5. The prediction operation unit according to claim 1, wherein the prediction calculation unit calculates a propagation delay time with the orbiting satellite using a relationship between a Doppler frequency and a change in the propagation delay time. Mobile device terminal. Uplink and downlink time slots are assigned to orbiting satellites, and uplink transmission is performed so that propagation delay times are taken into account with reference to the arrival time of radio waves from the orbiting satellites and the time slot of the orbiting satellite is entered. A predictive computation device for a mobile terminal that performs
It means for obtaining a Doppler frequency of the radio frequency which the orbiting satellite is propelled toward the ground station or mobile terminal,
Elapsed time measuring means for measuring the elapsed time from the start of blocking communication with the orbiting satellite until the time when downlink reception is resumed ;
Prediction calculation means for calculating the propagation delay time with the orbiting satellite from the Doppler frequency at the start of communication interruption with the orbiting satellite , the frequency used for wireless communication and the elapsed time measured by the elapsed time measuring means,
An apparatus for predicting propagation delay time, comprising:

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