JP2016127356A - Radio communication terminal, frequency control method, and control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preferable operation method regarding frequency offset used for mitigating the impact of Doppler shift in air-to-ground communication between an aircraft and the ground.SOLUTION: A radio communication terminal is mounted on an aircraft for performing air-to-ground communication with a ground station. The radio communication terminal comprises: a radio transmission unit for outputting a transmission wave toward the ground station; a radio reception unit for inputting a wave received from the ground station; and an offset setting unit for setting an offset value for the frequency of the transmission wave. The offset setting unit is configured to be able to switch to any one of an offset value predetermined so as to correspond to the travel speed of the radio communication terminal or an offset value obtained by calculating the amount of Doppler shift of the reception wave.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a frequency offset technique for reducing the influence of Doppler shift in air-to-ground communication (hereinafter referred to as ATG communication; ATG: Air to Ground) between an aircraft and the ground.

  As a frequency used for ATG communication, use of a frequency band of 700 MHz to 2 GHz allocated to a mobile phone service used on the ground has been studied. When this frequency band is allocated to ATG communication, ground base station facilities and frequencies can be reused, which is advantageous to a method using a dedicated frequency from the viewpoint of cost reduction of the entire system and effective use of frequencies.

  However, on the other hand, when this frequency band is used, there is a problem that the influence of the Doppler shift generated between the radio communication terminal attached to the aircraft body and the ground base station cannot be ignored. The influence of Doppler shift depends on the frequency band used for the radio communication line and the relative speed between the radio communication terminal and the ground base station. The Doppler shift amount fd is fd = (v / c) · f, where the transmission frequency f of the wireless communication terminal, the moving speed (aircraft flight speed) v, and the radio wave propagation speed (light speed) c of the wireless communication terminal. It can be obtained from the relational expression. For example, the Doppler shift amount is 2.2 kHz when the frequency used for the radio communication line is 2 GHz and the flight speed of the aircraft is 1,200 km / h. In the LTE system used for mobile phone service, the subcarrier frequency interval is 15 kHz, and the Doppler shift amount of 2.2 kHz causes interference between subcarriers and greatly affects the quality of the radio communication line.

  As patent documents disclosing the influence of the Doppler shift in ATG communication and techniques for mitigating the same, for example, JP-A-2014-510437 and JP-A-2001-127695 are known. These patent documents describe a method of measuring a Doppler shift amount and performing a frequency offset of a transmission wave based on the measurement result, and changing a power or a modulation method. However, no mention is made of any effective operation method related to frequency offset in ATG communication.

Special table 2014-510437 gazette JP 2001-127695 A

An object of the present invention is to provide a more effective operation method regarding a frequency offset used for mitigating the influence of Doppler shift in ATG communication.
This is the issue.

In order to solve the above problems, a wireless communication terminal according to the present invention is a wireless communication terminal that is mounted on an aircraft and performs air-to-ground communication with a ground station, and the wireless communication terminal is directed toward the ground station. A radio transmission unit that outputs a transmission wave, a radio reception unit that inputs a reception wave from the ground station, and an offset setting unit that sets an offset value to the frequency of the transmission wave, the offset setting unit, It is set to be switchable to either an offset value determined in advance corresponding to the moving speed of the wireless communication terminal or an offset value obtained by calculating the Doppler shift amount of the received wave.

Further, the offset setting unit switches from the predetermined offset value to the calculated offset value according to the quality or connection state of the wireless communication line between the wireless communication terminal and the ground station.

Further, the wireless communication terminal specifies the ground station corresponding to the received wave having the largest value of the Doppler shift amount and preferentially connects to the specified ground station.

  In addition, the wireless communication terminal specifies a ground station to which the connection of the wireless communication line is switched from the position information of the ground station and the position information of the wireless communication terminal, and gives priority to the specified ground station. Connect.

The frequency control method according to the present invention is a frequency control method in a radio communication terminal mounted on an aircraft and performing air-to-ground communication with a ground station, wherein the offset setting unit of the radio communication terminal includes the radio communication terminal. It is set so that it can be switched to either an offset value determined in advance to correspond to the moving speed of or an offset value obtained by calculating the Doppler shift amount of the received wave from the ground station.

The control program according to the present invention is a frequency control method in a radio communication terminal that is mounted on an aircraft and performs air-to-ground communication with a ground station, wherein the offset setting unit of the radio communication terminal A frequency control method for setting a switchable to either an offset value predetermined to correspond to a moving speed or an offset value obtained by calculating a Doppler shift amount of a received wave from the ground station; Have the communication terminal execute.

  ADVANTAGE OF THE INVENTION According to this invention, in ATG communication, the influence of a Doppler shift is relieve | moderated and favorable communication quality can be acquired between the radio | wireless communication terminal mounted in the aircraft and the ground station. Further, by making the frequency band of the wireless communication line used in ATG communication the same as the frequency band used in the mobile phone system, the equipment resources of the mobile phone system can be effectively utilized.

It is a conceptual diagram of the frequency offset which concerns on this embodiment. It is explanatory drawing of the offset value which concerns on this embodiment. It is a conceptual diagram of the handover according to the present embodiment. It is a flowchart which shows the procedure of the handover which concerns on this embodiment. It is a flowchart which shows switching of the offset value in the handover which concerns on this embodiment. It is a flowchart which shows the other example of switching of the offset value in the handover which concerns on this embodiment. It is a conceptual diagram which shows the internal structure of the radio | wireless communication terminal which concerns on this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram of a frequency offset according to the present embodiment. One or more wireless communication terminals 20 are mounted on the aircraft 10. Ground stations 100 and 110 having a base station function are arranged on the ground, and ATG communication is performed between the radio communication terminal 20 and the ground stations 100 and 110. The frequency band of the radio communication line used for ATG communication between the radio communication terminal 20 and the ground stations 100 and 110 is not particularly limited, but the frequency band of 700 MHz to 2 GHz used for the terrestrial mobile phone service. May be used. The wireless communication terminal 20 may also be used as a wireless LAN terminal in the aircraft 10.

  The aircraft 10 takes a flight route that takes off from an airport near the ground station 100 and passes over the ground station 110. As the aircraft 10 moves in flight, the wireless communication terminal 20 that has been in the service area of the ground station 100 gradually moves away from the ground station 100. The wireless communication terminal 20 gradually approaches the ground station 110 and moves from the service area of the ground station 100 to the service area of the ground station 110.

  Since the wireless communication terminal 20 is less affected by the Doppler shift until the aircraft 10 exceeds a certain speed, the transmission frequency may be set to the reference frequency f. However, when the flight speed of the aircraft 10 exceeds, for example, about 300 km / h, the influence of the Doppler shift cannot be ignored. Therefore, in order to reduce the influence of the Doppler shift, the radio communication terminal 20 performs frequency offset, and sets the transmission frequency to f−fd obtained by subtracting the offset value fd from the reference frequency f.

  Next, the offset value fd will be described with reference to FIG. FIG. 2 is an explanatory diagram of the offset value fd used for the frequency offset of the radio communication terminal 20. FIG. 2A shows offset values corresponding to respective moving speeds of the wireless communication terminal 20 (same as the flight speed of the aircraft 10), and are represented by linear values. FIG. 2B is an offset value corresponding to each range in which the moving speed of the wireless communication terminal 20 is constant, and is indicated by a step value.

The offset value fd may be calculated by performing a simulation in advance using a computer (not shown), or may be calculated by the wireless communication terminal 20 performing arithmetic processing. When the simulation is performed in advance using a computer, the offset value fd is calculated based on the frequency used for the wireless communication line and the moving speed of the wireless communication terminal 20 by using the above-described relational expression of Doppler shift. In this case, a known method may be used for calculating the offset value fd. The wireless communication terminal 20 may acquire the offset value fd calculated by performing such a simulation from a computer in advance and hold it as a preset value in the wireless communication terminal 20.

In addition, when the wireless communication terminal 20 performs arithmetic processing, the wireless communication terminal 20 measures the frequency deviation of the actual received wave with respect to the reference frequency of the radio wave (received wave for the wireless communication terminal) transmitted from the ground station. Thus, the Doppler shift amount is estimated, and the offset value fd is calculated based on the estimation. A known method may be used to calculate the offset value fd from the measurement of the frequency shift of the received wave. For example, the propagation variation of the received wave that varies in proportion to the moving speed of the radio communication terminal 20 is measured, and the Doppler spectrum is calculated by performing Fourier transform on the measured variation. It may be estimated.

  Next, an overview of handover in ATG communication will be described with reference to FIG. FIG. 3 is a plan view showing the structure of the service area of the ground station and the concept of handover in ATG communication. The ground station 100 constitutes three sectors of sec1, sec2, and sec3 by radiating a beam whose center is 120 degrees apart toward the sky. Similarly, the ground station 110 has a three-sector configuration of sec21, sec22, and sec23, and the ground station 120 has a three-sector configuration of sec31, sec32, and sec33.

  The aircraft 10 takes a flight route that takes off from the airport belonging to the service area of the ground station 100 and passes over the ground station 110. As the aircraft 10 flies and moves, the wireless communication terminal 20 located in the service area of the ground station 100 moves away from the ground station 100 and gradually approaches the ground station 110. The wireless communication terminal 20 will eventually move from the service area of the ground station 100 to the service area of the ground station 110. With this movement, handover is performed in the order of sec1 to sec2 of the ground station 100 to sec13 to sec12 of the ground station 110.

  Now, if the flight speed when the aircraft 10 is flying at sec A point A of the ground station 100 is less than 300 km / h, for example, the wireless communication terminal 20 is less affected by the Doppler shift. At this time, the radio communication terminal 20 sets the transmission frequency to the reference frequency f. Thereafter, if the aircraft 10 continues to fly while increasing its speed and the flight speed when moving to the B point of sec2 of the ground station 100 exceeds, for example, 300 km / h, the radio communication terminal 20 is affected by the Doppler shift. It becomes easy to receive. Therefore, the radio communication terminal 20 sets an offset value for the transmission frequency in order to reduce the influence of the Doppler shift. The radio communication terminal 20 performs transmission by setting the transmission frequency to f−fd obtained by subtracting the offset value fd from the reference frequency f. The offset value fd may be a preset value calculated by performing a simulation in advance, or a value obtained by analyzing the received wave by the wireless communication terminal 20.

  The wireless communication terminal 20 analyzes radio waves (received waves) transmitted from a plurality of ground stations such as the ground stations 110 and 120 in addition to the ground station 100, and shows the largest vibration amount (Doppler shift amount). Identify radio waves. A value corresponding to the observed maximum vibration amount (Doppler shift amount) may be used as the offset value fd.

  In the example of FIG. 3, since the ground station 110 is in front of the flight direction of the aircraft 10, the vibration amount (Doppler shift amount) of the radio wave (received wave) transmitted from the ground station 110 is the largest. The wireless communication terminal 20 preferentially connects to the ground station 110 that transmits a radio wave indicating the largest vibration amount (Doppler shift amount) from a plurality of ground stations such as the ground stations 110 and 120. It may be.

  Next, with reference to FIG. 4, a procedure for handover of the radio communication terminal 20 will be described. FIG. 4 is a flowchart showing an example of handover when the radio communication terminal 20 moves from the service area of the ground station 100 to the service area of the ground station 110. First, the wireless communication terminal 20 is located in the service area of the ground station 100 and communicates with the ground station 100 (S401). If the moving speed of the wireless communication terminal 20 at this time (the flight speed of the aircraft 10) is less than 300 km / h, the wireless communication terminal 20 sets the reference frequency f as the transmission frequency for communication with the ground station 100.

  The radio communication terminal 20 observes radio waves (received waves) transmitted from the surrounding ground stations 110, 120,. The reference frequencies of the radio waves transmitted by the peripheral ground stations 110, 120,... Are defined by standards, and are known information for the wireless terminal 20. The radio communication terminal 20 identifies the ground station 110 that exhibits the largest Doppler shift amount by analyzing the difference between the reference frequency, which is known information, and the actually observed frequency of the received wave (S402).

The radio communication terminal 20 acquires the flight speed of the aircraft 10 and sets an offset value for the transmission frequency when the speed exceeds, for example, 300 km / h. As this offset value, an offset value fd1 corresponding to the moving speed may be set from preset values calculated in advance held in the radio communication terminal 20. Then, the wireless communication terminal 20 sets the transmission frequency to f−fd1 obtained by subtracting the offset value fd1 from the reference frequency f (S403).

Here, the radio communication terminal 20 may set the offset value fd2 calculated from the Doppler shift amount estimated by analyzing the received wave, instead of fd1. In this case, the offset value fd2 calculated from the largest Doppler shift amount may be set. Then, the radio terminal 20 may set the transmission frequency to f−fd2 obtained by subtracting the offset value fd2 from the reference frequency f (S403). In setting the offset value fd2, the noise power of the received wave from the ground station 110 showing the largest Doppler shift amount is measured, and the offset value fd2 is weighted according to the level value of the noise power. You may do.

Next, the wireless communication terminal 20 calculates the difference between the reception level of the radio wave (reception wave) transmitted from the ground station 100 and the reception level of the radio wave (reception wave) transmitted from the ground station 110, It is determined whether or not the difference between the two reception levels satisfies a predetermined condition (S404).

If the reception level difference between the two satisfies the predetermined condition, the wireless communication terminal 20 switches the communication with the ground station 100 to the communication with the ground station 110. Thereby, the handover from the service area of the ground station 100 to the service area of the ground station 110 is executed (S405). If the handover is successful, the radio communication terminal 20 is disconnected from the ground station 100 and switched to communication with the ground station 110 (S406, S407). If the handover fails, the procedure returns to the procedure of S404 and the handover is performed again.

,
Here, the detailed processing related to the handover procedure may take a known method. Further, this handover may be a hard handover in which the connection between the radio communication terminal 20 and the ground station is temporarily disconnected when switching from the ground station 100 to the ground station 110, or a soft handover in which the connection is not disconnected. It may be.

Next, switching of the offset value will be described with reference to FIG. FIG. 5 is a flowchart showing another procedure for handover when moving from the service area of the ground station 100 to the service area of the ground station 110. In the handover procedure shown in FIG. 4, the offset value to be set is set to either the offset value fd1 calculated in advance or the offset value fd2 obtained by analyzing the received wave. The procedure differs in that an offset value fd1 calculated in advance is set as the offset value to be set first, and when handover fails, the offset value is reset to fd2 and the handover is retried.

5, the radio communication terminal 20 communicates with the ground station 100 (S501) and analyzes received waves from the surrounding ground stations 110, 120... In the same manner as in S401 and S402 of FIG. The ground station 110 having the largest Doppler shift amount is specified (S502).

Next, the radio communication terminal 20 acquires the flight speed of the aircraft 10 and sets an offset value for the transmission frequency when the speed exceeds, for example, 300 km / h. As this offset value, an offset value fd1 corresponding to the moving speed may be set from preset values calculated in advance held in the radio communication terminal 20. Then, the radio communication terminal 20 sets the transmission frequency to f−fd1 obtained by subtracting the offset value fd1 from the reference frequency f and transmits (S503).

The wireless communication terminal 20 calculates the difference between the reception level of the radio wave (reception wave) transmitted from the ground station 100 and the reception level of the radio wave (reception wave) transmitted from the ground station 110, and receives both of them. It is determined whether the level difference satisfies a predetermined condition (S504).

If the reception level difference between the two satisfies the predetermined condition, the wireless communication terminal 20 switches the communication with the ground station 100 to the communication with the ground station 110. Thereby, the handover from the service area of the ground station 100 to the service area of the ground station 110 is executed (S505). If the handover is successful, the wireless communication terminal 20 is disconnected from the ground station 100 and switched to communication with the ground station 110 (S506, S507).

Here, when the handover fails, the radio communication terminal 20 recalculates the offset value fd2 calculated from the Doppler shift amount estimated by analyzing the received wave. Then, the wireless terminal 20 sets the transmission frequency to f−fd2 obtained by subtracting the offset value fd2 from the reference frequency f (S508). Even if the offset value is set to fd2 based on the analysis of the received wave, if the handover fails again, the received wave may be analyzed once again to set the offset value fd2. Thus, the possibility of a successful handover to the ground station 110 is increased by attempting the handover again after switching the offset value.

Next, another example of switching the offset value will be described with reference to FIG. In FIG. 5, the received waves from the surrounding ground stations 110, 120... Are analyzed to identify the ground station 110 having the largest Doppler shift amount (S502). However, in FIG. The difference is that the ground station to which the connection of the wireless communication line is switched is specified by the information and the current position information of the wireless communication terminal 20, and the ground station to be connected next is specified (S602).

  In FIG. 6, the radio communication terminal 20 holds the position information of the ground station in advance. Further, the current position information of the aircraft 10 is acquired as its own position information. Alternatively, the current position information obtained by the GPS function provided in the wireless communication terminal 20 is acquired. The wireless communication terminal 20 specifies a ground station that is expected to perform communication after the currently communicating ground station from the position information of the ground station and its own position information. In other words, the ground stations that are candidates for handover may be narrowed down to connect preferentially.

In the example of FIGS. 5 and 6, the setting of the offset value is switched when the handover from the ground station 100 to the ground station 110 fails, but the switching of the offset value depends on the connection state of such a wireless communication line. Switching may be performed, or switching may be performed when the quality of the wireless communication line does not satisfy a certain value. For example, the setting of the offset value may be switched based on quality information such as error rate and delay of the wireless communication line.

  Next, the internal configuration of the wireless communication terminal 20 will be described with reference to FIG. FIG. 7 is an example schematically showing the internal configuration of the wireless communication terminal 20. In FIG. 7, the wireless communication terminal 20 includes a wireless reception unit 21, a wireless transmission unit 22, a Doppler calculation unit 23, an offset setting unit 24, and a control unit 25.

  The radio receiving unit 21 receives radio waves (received waves) transmitted from the ground stations 100, 110, 120. The wireless transmission unit 22 transmits radio waves to the ground stations 100, 110, 120. The transmission frequency of the radio wave transmitted from the wireless transmission unit 22 is the reference frequency f when the offset value is not set, but is f-fd obtained by subtracting the offset value fd from the reference frequency when the offset value fd is set. .

The Doppler calculator 23 calculates the Doppler shift amount from the received wave received by the wireless receiver 21. The frequency of the received wave from the ground stations 100, 110, 120... Is predetermined by a standard or the like. The wireless communication terminal 20 holds this known reference frequency in the control unit 25. The Doppler calculating unit 23 calculates the Doppler shift amount fdp by analyzing the difference between the reference frequency of each ground station held in the control unit 25 and the frequency of the received wave received by the wireless receiving unit 21. The calculation of the Doppler shift amount fdp is performed with reference to the moving speed (flight speed of the aircraft 10) information of the wireless communication terminal 20.

  The Doppler calculation unit 23 identifies the ground station that performs the handover. For example, the ground station corresponding to the received wave having the largest Doppler shift amount can be identified and handed over. Specifically, when calculating the Doppler shift amount fdp by analyzing the frequency shift of the received wave received by the radio reception unit 21, the ground station with the largest frequency shift is close to the traveling direction of the radio communication terminal 20. For this reason, the connection with the ground station may be preferentially performed.

Further, the Doppler calculation unit 23 can specify the ground station to which the connection of the wireless communication line is switched from the position information of the ground station and the position information of the wireless communication terminal 20, and this specification is performed at the time of handover or the like. You may make it connect preferentially to the ground station. More specifically, the current position information of the wireless communication terminal 20 (current position information of the aircraft 10) and the position information of each ground station are used to narrow down the number of ground stations that are subject to calculation of the Doppler shift amount fdp. It may be. For example, from the positional relationship between the wireless communication terminal 20 and each ground station, the received wave may be analyzed by focusing on the ground station located in the traveling direction of the wireless communication terminal 20 (the traveling direction of the aircraft 10). Thereby, the scale of the arithmetic processing is reduced, and the Doppler shift amount can be calculated in a shorter time.

  The offset setting unit 24 may set the offset value fd based on the Doppler shift amount calculated by the Doppler calculation unit 23. The calculated Doppler shift amount fdp may be set as the offset value fd2, or a value obtained by weighting the calculated Doppler shift amount fdp according to the noise power level value of the received wave is set as the offset value fd2. Also good. The offset value fd may be set as an offset value fd1 that is calculated in advance by computer simulation. The offset setting unit can set the offset value fd1 calculated in advance and the offset value fd2 obtained by analyzing the received wave to be switchable.

  The control unit 25 controls and manages execution of processing for the wireless reception unit 21, the wireless transmission unit 22, the Doppler calculation unit 23, and the offset setting unit 24. The control unit 25 includes hardware such as a CPU and a storage device, and various application programs and software including a control program for executing processing related to setting of an offset value. In addition, the offset value calculated in advance is held, and the flight speed information, position information, and information related to the flight route of the aircraft 10 are held. Information regarding these aircraft 10 may be acquired from the aircraft 10. Regarding the position information, the GPS function may be provided inside the aircraft 10 or the wireless communication terminal 20, and information measured by the GPS function may be acquired. In addition, the control unit 25 holds various types of information such as ground station position information.

DESCRIPTION OF SYMBOLS 10 ... Aircraft 20 ... Wireless communication terminal 21 ... Wireless reception part 22 ... Wireless transmission part 23 ... Doppler calculation part 24 ... Offset setting part 25 ... Control part 100,110, 120 ... Ground station

Claims (6)

A wireless communication terminal that is mounted on an aircraft and performs air-to-ground communication with a ground station,
The wireless communication terminal is
A wireless transmission unit that outputs a transmission wave toward the ground station;
A radio reception unit for inputting a reception wave from the ground station;
An offset setting unit that sets an offset value to the frequency of the transmission wave, and
The offset setting unit is set to be switchable to either an offset value determined in advance to correspond to a moving speed of the wireless communication terminal or an offset value obtained by calculating a Doppler shift amount of the received wave. A wireless communication terminal. The wireless communication terminal according to claim 1,
The offset setting unit switches from the predetermined offset value to the calculated offset value according to the quality or connection state of the radio communication line between the radio communication terminal and the ground station, Wireless communication terminal. The wireless communication terminal according to claim 1 or 2,
A radio communication terminal characterized by identifying the ground station corresponding to the received wave showing the largest value of the Doppler shift amount and preferentially connecting to the identified ground station. The wireless communication terminal according to claim 1 or 2,
From the position information of the ground station and the position information of the wireless communication terminal, identify the ground station to which the connection of the wireless communication line is switched, and preferentially connect to the identified ground station, Wireless communication terminal. A frequency control method in a wireless communication terminal that is mounted on an aircraft and performs air-to-ground communication with a ground station,
Either an offset value predetermined by the offset setting unit of the radio communication terminal to correspond to the moving speed of the radio communication terminal or an offset value obtained by calculating the Doppler shift amount of the received wave from the ground station A frequency control method, characterized in that it is set to be switchable to either one of them.   A control program for causing a radio communication terminal to execute the frequency control method according to claim 5.

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