CN107749883B

CN107749883B - Aircraft ground-air broadband communication link method based on narrowband wave beam directional antenna

Info

Publication number: CN107749883B
Application number: CN201710984683.2A
Authority: CN
Inventors: 谢映海; 胡汉武; 郝秀娟
Original assignee: Guangzhou Haige Communication Group Inc Co
Current assignee: Guangzhou Haige Communication Group Inc Co
Priority date: 2017-10-20
Filing date: 2017-10-20
Publication date: 2020-10-23
Anticipated expiration: 2037-10-20
Also published as: CN107749883A

Abstract

The invention discloses an aircraft ground-air broadband communication link method based on a narrowband wave beam directional antenna, which comprises an initial link establishment stage: after the aircraft is lifted off and the communication equipment starts to work, signaling handshake can be rapidly carried out between the aircraft and the ground station, so that distance measurement, time reference synchronization and mutual alignment of the antenna of the aircraft and the ground station are realized, and initial establishment of a communication link is realized; and a communication stage: the purpose of the communication phase is to ensure a high-speed and reliable transmission of communication data between the aircraft and the ground station, so that the protocol content is divided into two parts: the method comprises the steps of periodically correcting time reference and adjusting antenna alignment in real time between nodes of two parties, and a channel access mechanism during data communication. The invention can realize the rapid establishment of the link between the aerial vehicle and the ground station after the aerial vehicle is lifted off, simultaneously ensure the real-time alignment and correction between the directional antennas in the flight process, and have the rapid automatic recovery capability after the link is interrupted due to the abnormal maneuver of the aerial vehicle.

Description

Aircraft ground-air broadband communication link method based on narrowband wave beam directional antenna

Technical Field

The invention belongs to the technical field of communication, and particularly relates to an aircraft ground-air broadband communication link method based on a narrowband wave beam directional antenna.

Background

The requirement of communication between an aerial vehicle and a ground station on link rate is continuously improved, and the traditional communication system based on the omnidirectional antenna cannot meet the requirement of long-distance broadband high-speed communication due to lower antenna gain; the communication guarantee means based on satellite relay has limited signal bandwidth and expensive rent cost, so that the method for providing the aircraft with a novel and cheap broadband communication guarantee means is very important.

The frequency resources of the lower frequency band are already basically classified by various types of communication systems because of the better transmission fading characteristics of the wireless channel. Microwave frequency bands with millimeter-scale wavelengths still have more idle frequency resources, and are becoming the priority targets of new communication systems. Compared with a ground communication link, the ground-air communication link has no shielding object, belongs to a typical line-of-sight communication scene, and is very suitable for adopting a microwave communication frequency band with smaller wavelength and poorer diffraction capability.

Due to the high maneuverability of the aircraft, the communication distance between the ground and the air is often required to reach the magnitude of hundreds of kilometers, and the traditional omnidirectional antenna has low gain and cannot meet the broadband communication requirement of the magnitude of the distance. With the rapid development of directional antenna technology, various types of high-gain narrowband beam directional antenna technology on a microwave frequency band have become mature, so that the ground station and the aircraft can consider adopting the high-gain narrowband beam directional antenna in order to better meet the requirement of long-distance broadband high-speed communication between the ground station and the aircraft.

The ground station antenna is less limited in size, weight and power, so that a mechanical servo parabolic antenna widely applied to radar and satellite communication systems is considered, the signal beam angle is very narrow and can reach a level of about 4 degrees, and the antenna gain can reach about 35 dB; the airborne antenna of the aircraft is greatly limited, and therefore a hemispherical multi-beam lens antenna is adopted, the antenna adopts a novel design scheme and a novel material 3D printing technology, has the advantages of omnidirectional high gain, wide band, self-adaptive strong interference suppression, scanning in a wide angle range, simple feed network, low manufacturing cost, small size, light weight and the like, can overcome the defects of other traditional airborne antennas, and has higher cost performance than a phased array antenna. The signal beam angle is on the order of about 30 degrees and the antenna gain can be up to about 13 dB.

Under the condition that both communication parties adopt the narrow-band beam directional antenna to receive and transmit signals, although very high antenna gain can be obtained, under the condition of high-speed flight of an aerial vehicle, automatic alignment and real-time correction of the directional antenna are a key technology for guaranteeing normal operation of a communication link.

Disclosure of Invention

The invention mainly aims to overcome the defects of the prior art and provide an aircraft ground-air broadband communication link method based on a narrowband wave beam directional antenna, which can realize the rapid establishment of a link between an aircraft and a ground station after the aircraft is lifted off, simultaneously ensure the real-time alignment and correction between the directional antennas in the flight process and have the rapid automatic recovery capability after the link is interrupted due to the abnormal maneuver of the aircraft. To increase the security and robustness of the aircraft communication link, the above mechanism does not require assistance from a satellite positioning system, i.e., it continues to operate properly without ground station and aircraft positioning data.

The purpose of the invention is realized by the following technical scheme:

a aircraft ground-air broadband communication link method based on narrow-band beam directional antenna, only install a radio frequency power amplifier module in the aircraft apparatus, therefore the circuit switch can only connect one of them half-duplex narrow-beam antenna, namely can only have one antenna to enter the working condition of receiving or sending of signal in all narrow-beam antennas on a time slice; the position of the ground station antenna is fixed;

s1 initial link establishment phase: after the aircraft is lifted off and the communication equipment starts to work, signaling handshake can be rapidly carried out between the aircraft and the ground station, so that distance measurement, time reference synchronization and mutual alignment of the antenna of the aircraft and the ground station are realized, and initial establishment of a communication link is realized;

s2 communication phase: in the communication stage, the time axis is divided into odd time slots and even time slots, wherein the odd time slots comprise 25 small time slots, the time length of each small time slot is consistent with the signaling small time slot in the link establishing stage and is T_S(ii) a The even number time slot comprises N small time slots, and the definition of the parameter N is consistent with the initial link establishment stage;

the purpose of the communication phase is to ensure a high-speed and reliable transmission of communication data between the aircraft and the ground station, so that the protocol content is divided into two parts: firstly, time reference correction and antenna alignment real-time adjustment are periodically carried out between nodes of two parties, and secondly, a channel access mechanism is adopted during data communication;

an improved ALOHA mechanism is adopted for channel access of data service, and the specific contents are as follows:

1. in the idle state of the link, except the time slots occupied by the periodic synchronous signals and the feedback signals, the antennas of the aircraft and the ground station are always in an RTS signal receiving state on other time slots; the signaling form is the same as the former synchronous signal, and the signaling content is different; the receiving antenna or orientation is maintained by the periodic synchronization signal transmission and feedback mechanism introduced above;

2. if the aircraft or the ground station suddenly generates a data service sending requirement in a link idle state, sending RTS signaling + short data signals immediately, and then waiting for receiving effect ACK feedback of a receiving party; if the ACK feedback of the receiver is received at the appointed time slot position of the sender, the RTS signaling and the long data signal are continuously used for sending the subsequent data, and the ACK feedback of the receiver is waited again; repeating the above process until the service data of the sender is completely sent;

3. if the receiver suddenly generates the requirement of sending service data to the other side in the data receiving process, the receiver enters a bidirectional service transmission state; the two parties respectively use the ACK feedback signals to break the data transmission of the other party in turn and transmit own data immediately.

Further, an exception handling mechanism for signaling handshake interruption in a channel access process of data service: except for the first RTS signal and the short data signal of the data communication initiator, the subsequent communication process is to decide the subsequent transmission process based on the ACK feedback signal of the receiver, wherein the signaling content carried by the ACK signal not only contains the CRC result feedback of the previous data reception, but also comprises the transmission arrangement of the subsequent time slot, and the sender continues to send or the receiver starts to send the data; to avoid deadlock situations, the following rules are made for the data sender and the data receiver:

after finishing data transmission for a certain time, if an ACK feedback signal of a receiving party is lost, the data sending party means that a current link is possibly interfered or the antenna alignment of the receiving party and the receiving party deviates, the subsequent signal sending is immediately stopped, the sending party returns to a link idle state again, and tries to send data again after waiting for finishing the periodic time reference correction and the antenna alignment for a new time;

for the data receiving side, after the ACK signal is completed, if the expected RTS signal cannot be correctly received, it is considered that the current link may be interfered or the antenna alignments of both sides are shifted, and the data receiving side will immediately return to the link idle state.

Preferably, the time reference correction and the antenna alignment real-time adjustment specifically include:

(I) when the link is idle, the aircraft occupies an odd time slot and an even time slot by taking 16 odd number plus 16 even time slots as a period, and sends a synchronization signal, wherein Y represents the most recent best antenna number of the aircraft fed back by the ground station, and Y +/-1 and Y +/-2 represent 4 adjacent surrounding antennas overlapped with the coverage area of the antenna Y, namely the aircraft sends 5 times of synchronization signals by using 5 antennas including a current aligned antenna and 4 adjacent antennas thereof in turn on 25 small time slots of the odd time slot, thereby providing reference data for antenna switching and azimuth adjustment of both sides of the link when the aircraft moves linearly; the N antennas are used for sending a synchronous signal once in turn in even time slots, so that one-time ground full coverage is realized, and the ground station can obtain new antenna alignment data again by using the full coverage signal when the antennas are changed violently due to the nonlinear maneuvering of the aircraft;

(II) for the ground station, delaying and receiving the synchronous signals periodically sent by the aircraft based on the latest path transmission time delay; x represents the best azimuth of the aircraft to which the ground station points last, and X +/-1 and X +/-2 also represent 4 adjacent surrounding azimuths with coverage area overlapping with the azimuth X; the ground station will use this reception strategy to measure the reception quality of the synchronization signal between 25 different antenna and azimuth combinations, thereby providing sufficient reference data for adjacent antenna switching or azimuth adjustment due to linear flight of the aircraft.

(III) a mechanism of transmission and reception of feedback signals: considering the maximum link distance between the ground station and the aircraft, the path transmission delay is relatively large, so that the receiving position of the aircraft for the ground station feedback signal and the arrangement of the corresponding receiving antenna are specified as follows:

in the time slot, the N antennas of the aircraft receive in turn, so that the ground station needs to feed back the receiving result of the aircraft regardless of whether the ground station correctly receives the synchronization signal sent by the aircraft in the current period; considering that the cycle time is very small, the accuracy of the time reference between the aircraft and the ground station and the path transmission delay still keeps a higher level, the ground station adopts a feedback signal early sending mode based on the path transmission delay to ensure that N signals sequentially fall into receiving windows of N antennas when arriving at the aircraft, and the duration of 1 window is Ts + 25/NxTs, which is specifically as follows:

when the ground station decides which direction to use to send the feedback signal, if the ground station successfully receives the synchronous signal of the aircraft, the direction with the best signal receiving quality is selected from the synchronous signal, and the feedback signal is sent; if all the receiving fails, the receiving direction of the ground station arranged in the even time slot is X, then the direction which correctly receives signals in the last 5 periods except X and has the best receiving quality is selected from the historical data for sending the feedback signals; if the reception of the next periodic signal is failed completely, the direction with the inferior reception quality is replaced for the attempt. Repeating the above process until the signal is received again correctly or the failure times reach the upper limit, if the process has the condition of insufficient available azimuth, expanding the selection period of the historical data by one time;

after the aircraft receives the feedback signal, the latest antenna alignment information of the two parties can be obtained, meanwhile, the latest link transmission time delay between the two parties is measured again through the arrival time of the signal, and the ground station is informed to carry out time reference correction in the next signaling signal.

Further, the receiving strategy for even timeslot signals is specifically as follows:

a) if the ground station successfully receives signals 1 time or multiple times in 25 signal receiving opportunities on odd time slots, selecting the azimuth with the best signal receiving quality, recording as XX, and receiving by using the azimuth on even time slots;

b) if the ground station fails to receive all the signals in 25 signal receiving opportunities on an odd number of time slots, the aircraft is likely to generate nonlinear maneuvering in the period to cause severe change of the ground-oriented antenna, and therefore link establishment needs to be carried out again; however, considering that the ground station is static and the aerial position of the aircraft does not change drastically in one period, the aircraft is still in the signal coverage area of the current null-pointing azimuth X with a probability of going to 1, and therefore the azimuth will always be used for signal reception in the case of even-slot signal reception, thus determining the new optimal antenna number to ground for the aircraft.

Preferably, the processing mechanism after the interruption of the signaling handshake in the real-time adjustment process of time reference correction and antenna alignment is as follows:

considering the unreliability of wireless signals and the unpredictability of the flight state of the aircraft, the signaling interaction process between the two parties may be interrupted, and in order to avoid deadlock, the following provisions are made on the aircraft side: if the aircraft does not receive any signaling signals or data signals of the ground station within 3 periods, the aircraft stops sending the original 5 antennas for 5 times in the odd time slot, and uses the N antennas to send signals in turn, and the signal sending modes of the even time slot are consistent and unchanged; if the ground station signal is not received within 10 periods, the aircraft recovers the initial state and uses the frame structure of the initial link establishment stage;

the ground station side regulation is specifically as follows: if the ground station does not receive any signaling signals or data signals of the aircraft within 10 cycles, the ground station will also resume the searching state using the initial link establishment phase, wherein the searching airspace range will be set to be a sector airspace with the azimuth as the center and the horizontal angle and the elevation angle of the last correctly received signal being +/-10 degrees. If the search time in the airspace exceeds the upper limit, further doubling the search airspace; and repeating the process until the aircraft synchronization signal is reacquired or the search range is expanded to the whole airspace.

Preferably, the communication protocol content of the initial link establishment phase is:

(I) the aerial call signal is sent immediately after the aircraft is lifted off, N narrow-beam antennas use a matrix switch control mode, a parameter N represents the total number of the narrow-beam antennas in the lens antenna of the aircraft, and one antenna is used for synchronization in turnSignal transmission, wherein the N antennas transmit signals once in turn to complete one-time ground signal coverage; after each 10 times of coverage, one narrow beam antenna enters a receiving state with a duration of T_G+T_SAttempting to receive a response signal, T, transmitted by a ground station_SIndicating the time length, T, of the synchronization signalling signal_GIndicating the path propagation delay protection time, T_GManual setting can be carried out manually before the aircraft takes off according to the actual application scene of the system, and the ground station is informed of the option in the signaling;

if the receiving fails, continuing the next air call, replacing the next antenna to receive the response signal, and repeating the process until a certain antenna successfully receives the response signal of the ground station;

(II) the ground station enters a searching state of an air calling signal after being started, if the flying place of the aircraft has prior information, an empty searching area is set based on the information, the parabolic antennas circulate in turn in different empty positions in the area in a mechanical adjustment mode to perform parking, and the parking time of each position is T ═ N +1) multiplied by T_S(ii) a The ground station will try to receive the calling signal of the aircraft in the time period, if the calling signal fails, the ground station is adjusted to the next adjacent position to continue searching; if the ground station has no prior information of the takeoff position of the airplane, the air search range is expanded to the whole airspace;

(III) in the process of searching the ground station, if a calling signal of a certain antenna of the aircraft points to the ground station antenna, and meanwhile, the ground station antenna also points to the aerial aircraft, the calling signal is successfully acquired by the ground station.

(IV) setting the optimal combination estimated by the ground station as an air direction XX and a ground antenna YY, and considering the link symmetry during line-of-sight communication, performing signaling response when a receiving window of the antenna YY arrives so as to complete the first signaling handshake between the ground station and the air vehicle;

(V) after the aircraft receives the response signal, calculating the path transmission time delay between the aircraft and the ground station by using the arrival time of the signal;

(VI) the aircraft carries ACK confirmation information and path transmission delay value of the response signal in the signaling of the synchronous signal of Nx 10 times in the next air call, and declares that the initial link establishment stage is finished and the two parties enter a communication stage.

Specifically, the ground station captures a synchronization signal sent by the Y-th antenna of the air node in the X direction, which means that the two antennas are already in a certain mutual alignment state, and in consideration of certain overlap of signal areas of adjacent antennas of the aircraft and adjacent directions of the ground station, in order to obtain the optimal direction, the ground station uses the Y-th antenna receiving window of the aircraft to receive a previous call signal, measures the signal receiving quality of multiple combinations between the X direction and adjacent 4 directions of the ground station and the Y-th antenna of the aircraft and the adjacent 4 antennas of the ground station, and selects the optimal combination from the signal receiving quality, wherein the coverage range of the adjacent directions or adjacent antennas is defined as a certain proportion of overlap area of a corresponding narrow-band signal beam.

Preferably, after the aircraft receives the reply signal, the arrival time of the signal is used to calculate the path transmission delay between the aircraft and the ground station:

T_dindicating path propagation delay, default uplink and downlink path propagation delay being the same, T_s1T2-T1 is T_d+T_s+(N-YY)×T_s+T_d+T_s1Namely:

T_d＝(T2-T1-T_s-(N-YY)×T_s-T_s1)/2 (1)

preferably, the communication phase defaults to take the end of the following response time slot as a starting point, and the ground station eliminates the influence of the path transmission delay on the basis of one-way synchronization after receiving the path transmission delay value, so that convergence with the clock reference of the air station with higher precision is realized.

Compared with the prior art, the invention has the following advantages and beneficial effects:

the invention can realize the rapid establishment of the link between the aerial vehicle and the ground station after the aerial vehicle is lifted off, simultaneously ensure the real-time alignment and correction between the directional antennas in the flight process, and have the rapid automatic recovery capability after the link is interrupted due to the abnormal maneuver of the aerial vehicle. To increase the security and robustness of the aircraft communication link, the above mechanism does not require assistance from a satellite positioning system, i.e., it continues to operate properly without ground station and aircraft positioning data.

Drawings

FIG. 1 is a frame structure diagram of an initial link establishment phase between an airborne aircraft and a ground station.

FIG. 2 is a timing diagram of synchronization signaling interactions between an airborne aircraft and a ground station.

Fig. 3 is a frame structure diagram of the communication phase.

Fig. 4 is a schematic diagram of a transmitting antenna corresponding to a periodic signal of an aircraft.

Fig. 5 is a schematic diagram of a direction receiving strategy of the ground station for odd time slot signals.

Fig. 6 is a schematic diagram of the azimuth reception strategy of the ground station for the even-numbered slot signals after the successful reception of the odd-numbered slot signals.

Fig. 7 is a schematic diagram of the azimuth reception strategy of the ground station for the even-numbered slot signals after all the odd-numbered slots fail to receive.

Fig. 8 is a schematic view of the aircraft-side receiving location and receiving antenna arrangement.

Fig. 9 is a schematic diagram of feedback signal composition and early transmission at a ground station.

Fig. 10 is a timing diagram for transmission of signaling signals and data signals for unidirectional traffic transmission.

Fig. 11 is a timing diagram for transmission of signaling signals and data signals for bi-directional traffic transmission.

FIG. 12 is a schematic view of the alignment of narrowband beams at different angles from the ground station and the aircraft.

Fig. 13 is a schematic diagram of an air beam scan at a ground station.

Fig. 14 is a schematic diagram of the coverage-space domain of the ground-to-space antenna.

Fig. 15 is a schematic diagram of the coverage area of the antenna pair.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.

Example 1

Wireless communication systems based on narrow-band beam-directing antennas have in fact been developed for decades, the most typical example being satellite communication systems. Because the ground and the satellite are very far away from each other, directional antennas with high antenna gain are used for both the satellite and the ground antennas.

With the continuous improvement of the informatization degree, the communication speed requirement between the aircraft and the ground station is improved in different ways, the cost for relay communication guarantee by using the satellite is high, and the available bandwidth cannot completely meet the communication speed requirement of the aircraft in hundreds Mbps magnitude. In order to have the basic capability of guaranteeing the long-distance broadband communication between the ground station and the aircraft, the transmitting side and the receiving side both need to deploy directional antennas to obtain certain antenna gain. However, compared with the satellite link, the ground-air link has the following differences:

satellite communication is a point-to-multipoint communication system, namely, an antenna of a satellite needs to provide relay communication service for a large number of ground terminals simultaneously in a multiple access mode; the ground-air communication is a point-to-point communication link, and one antenna of the ground station only needs to provide communication guarantee for one aerial vehicle;

in terms of mobility, although the moving speed of the satellite is very high, the moving orbit of the satellite can be accurately pre-judged, and the orbit height of the communication satellite is generally higher, so that the relative movement of the ground station is slower; although the speed of the aircraft is much lower than that of the satellite, the moving track predictability of the aircraft is poor, and the communication distance is hundreds of kilometers, so that the relative movement is much larger than that of the satellite, and the real-time alignment and correction difficulty of the antenna is higher.

Based on the above analysis, by using the design concept of the satellite system, the mechanical servo parabolic antenna of the half-duplex mechanism, which has been widely used in the satellite ground station system, is continuously used on the ground station, the signal beam angle is very narrow, and is only about 4 degrees, and the antenna gain can reach about 35 dB. The mechanical servo antenna technology is mature, and a sensor installed on the mechanical servo antenna can automatically acquire the azimuth angle and the elevation angle pointed by a high-precision current signal beam without a satellite positioning system, so that auxiliary information is provided for the antenna alignment and real-time correction of an aerial moving target.

In the aspect of an onboard antenna, factors such as cost, size and weight are considered, a hemispherical multi-beam lens antenna is selected, the antenna adopts a novel design scheme and a novel material 3D printing technology, and the antenna has the advantages of omnidirectional high gain, broadband, self-adaptive suppression strong interference, scanning in a wide angle range, simple feed network and the like, is smooth in surface and small in air resistance, is very suitable for being installed in a belly area of an aircraft in an embedding mode, and effectively guarantees air-to-ground half-space-domain signal sending and receiving. In order to obtain better balance in terms of signal transceiving gain, antenna volume and antenna alignment maintenance overhead (the narrower the signal angle, the larger the signal transceiving gain, but the larger the antenna volume, weight and antenna alignment maintenance overhead will be), the narrowband beam signal angle of the multi-wave lens antenna is about 30 degrees, and the antenna gain can reach about 13 dB.

It is explained here that beam synthesis and waveform switching are two most common means for realizing narrowband beam-oriented signals, the former is a phased array type antenna, and narrowband signal synthesis and directional direction change are performed by controlling the feed phase of a radiating element in an array antenna; the latter is a multi-beam type antenna, a plurality of narrow beam antennas with different azimuth directions are controlled by a switch matrix, and the rapid adjustment of the signal receiving and transmitting directions can be realized by using an electric switch switching mode. Although the former has better performance, the working principle of the antenna is complex, the electronic components are numerous, the manufacturing cost is high, and the volume and the power consumption are larger; the latter has simple working principle, fewer devices, low cost and smaller volume and power consumption, and along with the continuous development of new antenna materials and 3D printing technology, the performance of each aspect of the antenna is obviously improved, so that the phased array antenna is more suitable for being installed on small and medium-sized aircrafts.

In order to simplify the design of the airborne antenna, only one radio frequency power amplifier module is installed in the equipment, so that the circuit switch can only be connected with one half-duplex narrow-beam antenna, namely only one antenna in all the narrow-beam antennas enters a signal receiving or transmitting working state on one time slice. However, because the switch adopts an electric switching mode, the switching time between different working antennas is very short and can be ignored.

Considering that the ground station and the aircraft both adopt directional antennas with narrow wave beams, in order to reduce the difficulty of antenna alignment, the default ground station does not need to support communication-in-motion capability, namely after the mechanical servo parabolic antenna of the ground station is deployed, the ground station does not move any more in the whole communication process (the problem does not exist in the fixed ground station, and the vehicle-mounted system adopts a parking and stopping communication mode), and the air directional orientation of the antenna is automatically adjusted only through a mechanical transmission system according to the requirement.

Based on the ground antenna and the airborne antenna, the following provides frame structures of the ground station and the aircraft in an initial link establishment stage and a communication stage, and a related channel access scheme, specifically as follows:

one) initial link establishment phase

The design scheme of the frame structure at the initial link establishment stage is specifically as shown in fig. 1:

the parameter N represents the total number of narrow beam antennas within the aircraft lens antenna, which is typically between 20 and 30 in the case of a signal beam angle of about 30 degrees and taking into account a certain proportion of the signal overlap coverage between adjacent antennas;

parameter T_SThe time length of the synchronous signaling signal is shown, and the structure of the signal is shown in fig. 1, and the main purpose of the signal is to be used for signal synchronization and a small amount of signaling information interaction between ground and air nodes. The embodiment does not relate to a specific design scheme of a physical layer waveform, and therefore, only a design principle of the waveform is briefly introduced here, that is, a system lowest-level data waveform to which a signaling waveform design needs to be matched is embodied that PN sequence synchronization false alarm and missing detection performance in a signaling signal is very good, and a correct demodulation threshold of subsequent signaling data is slightly lower than that of the lowest-level data waveform by 2-3 dB. Since only about a few are required to be carriedTen bits of signalling data, hence T_SWith typical values of about 0.1ms to 0.15 ms.

Parameter T_GThe path propagation delay protection time is represented, and 4 configurable items are provided, and specific values and corresponding protection distances (signal round-trip bi-directional transmission path protection) are shown in the following table:

TABLE 1T_GConfiguration options and corresponding protection scopes

Guard time slot time length T_G	Scope of protection
		2ms	0km to 300km
4ms	0km to 600km
		6ms	0km to 900km
8ms	0km to 1200km

Note: the configuration item can be manually set before the aircraft takes off according to the practical application scene of the system (approximate distance between the aircraft and the ground station during taking off), and the ground station is informed of the selection item in signaling.

The purpose of the initial link establishment stage is to ensure that after the aircraft is lifted off and the communication equipment starts to work, signaling handshake can be rapidly carried out between the aircraft and the ground station, so that distance measurement, time reference synchronization and mutual alignment of the antennas of the aircraft and the ground station are realized, and the initial establishment of a communication link is realized. The communication protocol content at this stage is given below:

(I) the aerial call signal is sent immediately after the aircraft is lifted off, one antenna of the hemispherical lens antennas with the N narrow-beam antennas is used for sending the synchronous signal in turn by using a matrix switch control mode, and the N antennas are used for sending once in turn to finish one-time ground signal coverage. After each 10 times of coverage, one narrow beam antenna enters a receiving state with a duration of T_G+T_SAn attempt is made to receive a reply signal transmitted by the ground station. If the receiving fails, continuing the next air calling, replacing the next antenna to receive the response signal, and repeating the process until a certain antenna successfully receives the response signal of the ground station.

(II) the ground station enters a searching state of an air calling signal after being started, if the flying place of the aircraft has prior information, an empty searching area is set based on the information, the parabolic antennas circulate in turn in different empty positions in the area in a mechanical adjustment mode to perform parking, and the parking time of each position is T ═ N +1) multiplied by T_S. The ground station will try to receive the calling signal of the aircraft in the time period, if the calling signal fails, the ground station is adjusted to the next adjacent position to continue searching; and if the ground station has no prior information of the takeoff position of the airplane, expanding the null search range to the whole airspace.

(III) in the process of searching the ground station, if a calling signal of a certain antenna of the aircraft points to the ground station antenna, and meanwhile, the ground station antenna also points to the aerial aircraft, the calling signal is successfully acquired by the ground station. The ground station captures the synchronous signal transmitted by the Y-th antenna of the air node in the X direction, which means that the two antennas are already in a certain degree of mutual alignment state at the moment. Considering that signal areas of adjacent antennas of the aircraft and adjacent directions of the ground station are overlapped to a certain extent, in order to obtain the optimal direction, the ground station utilizes a Y-th antenna receiving window of the aircraft to call signals in the future, measures the signal receiving quality of a plurality of combinations between the X direction and adjacent 4 directions of the ground station and the antenna Y of the aircraft and adjacent 4 antennas of the ground station, and selects the optimal combination from the signal receiving quality. (Note: there is a certain percentage of overlap in the coverage of the corresponding narrowband signal beams defined by the neighboring azimuth or adjacent antenna.)

And (IV) setting the optimal combination estimated by the ground station as an air direction XX and a ground antenna YY, and considering the link symmetry during line-of-sight communication, performing signaling response (carrying the optimal combination information) when a receiving window of the antenna YY arrives so as to complete the first signaling handshake between the ground station and the aerial vehicle.

(V) after the aircraft receives the reply signal, the arrival time of the signal is used to calculate the path transmission delay between the aircraft and the ground station, the specific principle is as shown in FIG. 2, wherein T_dDenotes the path propagation delay (default path propagation delays are the same for uplink and downlink due to line-of-sight communication), T_s1Indicating the length of time of the sync header in the sync signal. Then based on fig. 2 it can be seen that T2-T1 ═ T_d+T_s+(N-YY)×T_s+T_d+T_s1Namely:

T_d＝(T2-T1-T_s-(N-YY)×T_s-T_s1)/2 (1)

(VI) the aircraft carries ACK confirmation information and path transmission delay value of the response signal in the signaling of the synchronous signal of Nx 10 times in the next air call, and declares that the initial link establishment stage is finished and the two parties enter a communication stage. (note: the default of the communication phase is that the end of the following response time slot is used as the starting point, and the influence of the path transmission delay is eliminated on the basis of one-way synchronization after the ground station receives the path transmission delay value, so that the clock reference of the air station is kept to be converged with high precision.)

Two) communication phase

The frame structure of the communication node is specifically shown in fig. 3, in the communication stage, the time axis is divided into odd number time slots and even number time slots, wherein the odd number time slots include 25 small time slots, the time length of each small time slot is consistent with the signaling small time slot in the link establishment stage, and is T_S(ii) a The even number time slot includes N small time slots, and the definition of the parameter N is consistent with the initial chain building stage.

The purpose of the communication phase is to ensure a high-speed and reliable transmission of communication data between the aircraft and the ground station, so that the protocol content is divided into two parts: the method comprises the steps of periodically correcting time reference and adjusting antenna alignment in real time between nodes of two parties, and a channel access mechanism during data communication. The protocol contents are as follows:

time-base correction and antenna alignment real-time adjustment

In the initial chain building stage, both sides have finished time reference synchronization and antenna alignment, but considering factors such as aircraft movement, crystal oscillator drift of both sides and the like, the precision is ensured by periodic correction and adjustment,

the specific scheme is as follows:

(I) when the link is idle (note: the time reference correction and antenna alignment mechanism are already included in the data communication process, so that the time reference correction and antenna alignment mechanism do not need to be repeated), the aircraft occupies one odd time slot and one even time slot to transmit the synchronization signal by taking 16 odd plus 16 even time slots as a period (note: the value of N is generally between 20 and 30, and the value of T is generally between 20 and 30)_SThe value is generally 0.1ms to 0.15ms, so the time lengths of odd and even time slots are not greatly different, both about 3ms, and the correction period is about 0.1 second), the transmitting antenna condition of the signal is as shown in fig. 4, where Y represents the best antenna number of the aircraft newly fed back by the ground station, Y ± 1 and Y ± 2 represent 4 adjacent surrounding antennas with overlapping coverage areas with the antenna Y, that is, the aircraft uses the currently aligned antenna and its adjacent 4 antennas to transmit 5 times of synchronization signals respectively on 25 small time slots of the odd time slot, so as to provide reference data for antenna switching and azimuth adjustment of both sides of the link when the aircraft moves linearly (linear motion means that the adjacent antennas with overlapping coverage areas are switched due to the movement of the aircraft, and the predictability is strong); and N antennas are used in turn to respectively send a synchronous signal once in an even number of time slots, so that one-time ground full coverage is realized, and therefore when the antennas are severely changed due to nonlinear maneuvering of the aircraft (the nonlinear maneuvering means that the non-adjacent antennas of the ground directional antennas are switched due to side flying or rolling actions of the aircraft, and the predictability is very poor), the ground station can use the full coverage signals to obtain a new antenna againThe lines align the data.

And (II) for the ground station, delaying to receive the synchronous signal periodically sent by the aircraft based on the latest path transmission delay. Its reception strategy for odd-numbered slot signals is shown in particular in fig. 5, where X denotes the best position in which the ground station is newly directed to the aircraft, and X ± 1 and X ± 2 likewise denote the adjacent surrounding 4 positions in which there is an overlap of the coverage area with position X. Based on fig. 5, it can be seen that the ground station will use this reception strategy to measure the reception quality of the synchronization signal between 25 different antenna and azimuth combinations, thereby providing sufficient reference data for adjacent antenna switching or azimuth adjustment due to linear flight of the aircraft.

The receiving strategy for even slot signals is specifically as follows:

a) if the ground station successfully receives 1 or more times in 25 signal reception opportunities on the odd slots, then the bearing with the best signal reception quality is selected, denoted as XX, and will be used for reception all on the even slots, as shown in fig. 6.

b) If the ground station fails to receive all of the 25 signal receiving opportunities in the odd number of time slots, the aircraft is likely to have nonlinear maneuvering in the period, which causes drastic changes of the ground-oriented antenna, and therefore link establishment needs to be carried out again. However, considering that the ground station is static and the aerial position of the aircraft does not change drastically in one period (the aircraft flies at high speed at mach 2, and the moving distance in one period is only tens of meters in about 0.1 second), the aircraft is still in the signal coverage area of the current air-pointing direction azimuth X with a probability of approaching 1, and therefore the azimuth will be used for signal reception at the time of even-numbered time slot signal reception, so as to determine the new optimal antenna number to ground of the aircraft, as shown in fig. 7.

(III) a mechanism of transmission and reception of feedback signals: considering that the maximum link distance between the ground station and the aircraft may reach 1200km (see table 1), the path transmission delay is large, and therefore the receiving position and the corresponding receiving antenna arrangement of the aircraft for the ground station feedback signal are specified here as follows (fig. 8):

on this time slot, the N antennas of the aircraft will take turns receiving. Therefore, the ground station needs to feed back the receiving result of the aircraft regardless of whether the synchronization signal sent by the aircraft in the current period is correctly received or not. Considering that the cycle time is very small (about 0.1 second), the accuracy of the time reference and the path transmission delay between the aircraft and the ground station still maintains a high level, and therefore, the ground station will use a feedback signal advanced transmission mode based on the path transmission delay to ensure that N signals (1 signal with a time length of Ts) arrive at the aircraft and all fall into the receiving windows of N antennas (the duration of 1 window is Ts + 25/nxts) in sequence, as follows (fig. 9):

when the ground station decides which direction to use to send the feedback signal, if the ground station successfully receives the synchronous signal of the aircraft, the direction with the best signal receiving quality is selected from the synchronous signal, and the feedback signal is sent; if all reception fails and the receiving direction of the ground station arranged in the even time slot is X, selecting the direction which correctly receives signals in the last 5 periods except X from the historical data and has the best receiving quality to send the feedback signals. If the reception of the next periodic signal is failed completely, the direction with the inferior reception quality is replaced for the attempt. The above process is repeated until the number of times of re-correct reception of signals or failure reaches the upper limit (10 times), and if a situation in which the available azimuth is insufficient occurs, the selection period of the history data is doubled.

After the aircraft receives the feedback signal, the latest alignment information of the two antennae can be obtained, the latest link transmission time delay between the two antennae is measured again through the arrival time of the signal, and the ground station is informed to carry out time reference correction in the next signaling signal.

(IV) mechanism of handling after signalling handshake interruption: given the unreliability of wireless signals and the unpredictability of the aircraft flight status, there may be interruptions in the signaling interaction process between the two parties. In order to avoid a deadlock situation, the following provisions are made on the aircraft side: if the aircraft does not receive any signaling signals or data signals of the ground station within 3 periods, the aircraft stops sending the original 5 antennas for 5 times in the odd time slot, and uses the N antennas to send signals in turn, and the signal sending modes of the even time slot are consistent and unchanged; if the ground station signal is not received within 10 periods, the aircraft recovers the initial state and uses the frame structure of the initial link establishment stage;

the ground station side regulation is specifically as follows: if the ground station does not receive any signaling signals or data signals of the aircraft within 10 cycles, the ground station will also resume the searching state using the initial link establishment phase, wherein the searching airspace range will be set to be a sector airspace with the azimuth as the center and the horizontal angle and the elevation angle of the last correctly received signal being +/-10 degrees. If the search time in this spatial domain exceeds an upper limit (e.g., 8 seconds), the search spatial domain is further doubled. And repeating the process until the aircraft synchronization signal is reacquired or the search range is expanded to the whole airspace.

Channel access mechanism for data traffic

Considering that the system is a point-to-point communication link, and therefore the channel collision probability is very low, in order to reduce the channel access delay, and considering that the link transmission delay is much larger than the signaling signal length (the signaling signal length is about 0.1-0.15ms, and the maximum transmission delay value is 4ms) when transmitting over a long distance, and both sides use directional antennas, and other factors, an improved ALOHA mechanism is adopted for the channel access of the data service, and the specific contents are as follows:

1. in the idle state of the link, except the time slots occupied by the periodic synchronization signal and the feedback signal, the antennas of the aircraft and the ground station are always in the RTS signal receiving state (the signaling form is the same as the former synchronization signal, and the signaling content is different) on other time slots, and the receiving antenna or the direction is the information maintained by the above-described periodic synchronization signal sending and feedback mechanism.

2. If the aircraft or the ground station suddenly generates a data service sending demand in a link idle state, an RTS signaling (carrying time length information of subsequent data signals) + a short data signal (not more than 5 milliseconds) is sent immediately, and then the receiving effect ACK feedback of a receiving party is waited; if the sender specifies the time slot position (2 times of path transmission delay after the data signal) and receives the ACK feedback of the receiver (meaning that the data link is successfully established), the RTS signaling (carrying the time length information of the subsequent data signal) + the long data signal (not more than 25 milliseconds) is continuously used for sending the subsequent data, and the sender waits for the ACK feedback of the receiver again. And repeating the process until all the service data of the sender are sent.

3. If the receiver suddenly generates the requirement of sending service data to the other party in the data receiving process, the state of bidirectional service transmission is entered. The two parties respectively use the ACK feedback signals to break the data transmission of the other party in turn and transmit own data immediately.

4. Exception handling mechanism for signalling handshake interrupts: it can be seen from the above 3 protocol contents that, except for the first RTS signal + short data signal of the data communication initiator, the subsequent communication process decides the subsequent transmission process based on the ACK feedback signal of the receiving side, where the signaling content carried by the ACK signal includes both the CRC result feedback for the previous data reception and the transmission schedule of the subsequent time slot (the transmitting side continues to transmit or the receiving side will start to transmit data). To avoid deadlock situations, the following rules are made for the data sender and the data receiver:

after completing a certain data transmission as shown in fig. 10 or fig. 11, if the ACK feedback signal of the receiving side is lost, it means that the current link may be interfered or the antenna alignments of both sides are shifted, the subsequent signal transmission will be stopped immediately, the transmitting side will return to the link idle state again, and wait for completing a new periodic time reference correction and antenna alignment before reattempting to perform data transmission again.

For the data receiving side, after the ACK signal of fig. 10 is completed (the signal will require the other side to continue sending RTS + data signal), if the expected RTS signal cannot be correctly received, it is considered that the current link may be interfered or the antenna alignment of the two sides is shifted, and the data receiving side will immediately return to the link idle state.

It is noted that many existing mobile communication systems based on directional antennas require assistance from a satellite positioning system to achieve antenna alignment with respect to each other. In order to further improve the safety and the robustness of a data communication link of an aircraft, the communication scheme provided by the method does not need to be assisted by the satellite positioning system in consideration of the vulnerability of the satellite positioning system in some special situations, such as being destroyed in wartime or giving a signal to malicious interference.

To verify the practical effect of the above mechanism, some theories and results relating to the alignment of the narrowband directional antennas with each other are provided.

1) Basic principle of mutual alignment of narrowband beam antennas

As shown in fig. 12, when the conical beams with different angles in the 3-dimensional space domain can simultaneously irradiate the antennas of the other party, the antenna transmission and reception gains of the two links reach the maximum value at this time.

2) Time consuming analysis of initial link building phase

For an aircraft, the hemispherical lens antenna of the aircraft comprises N narrow-band root antennas, and the beam angle of each antenna is about 30 degrees, so that the value of N ranges from 20 to 30, and is typically 24. On the premise of ensuring the signal communication performance, the sending time of the primary synchronous signal is 0.1-0.15ms, and the typical value is 0.125ms, so that the signal full coverage of 1 wheel to the ground can be completed every 3ms when the typical value is adopted.

For the ground node, because the volume and weight of the antenna are limited to be small, a mechanical servo parabolic antenna with a large volume and a small angle of a signal receiving and transmitting beam is selected to obtain a higher signal receiving and transmitting gain, and the angle is about 4 degrees. Based on the schematic diagram 13, the ground antenna requirement can be calculated to be about 2/(sin (4/2 degrees))²And 1642 times of space scanning can complete the coverage of the whole sky. Considering the seamless nature of the scanning area, the scanning airspace of adjacent directions needs to have a certain overlapping area, and the number of scanning times is about 2200 when calculated by 25%. And the residence time of the ground station in each position is 3+0.125 to 3.125ms, so the initial link building time between the ground station and the aircraft is not more than 7 seconds without any prior information, and if the prior information exists, the search airspace is obviously reduced, because the prior information existsThis link-up time will also be significantly reduced.

3) Time stability analysis after antenna alignment

First, with respect to the time stability of the ground-to-space azimuth, it can be seen from fig. 14 that if the link distance is L, the coverage area of the ground-to-space signal beam (about 4 degrees) is a circle with a diameter of about 0.07R. Calculated as L-30 km, the diameter reached 2100 m. If the aerial node is horizontally mobile at the speed of 300m/s, the residence time in the area is as long as about 7 s;

secondly, with respect to the time stability of the air-to-ground antenna, it can be seen from fig. 15 that if the link distance is L, the ground coverage area of the air-to-ground signal beam (about 30 degrees) is a circle with a diameter of about 0.5R. When calculated as R ═ 30km, the diameter reached 15000 m. If the aerial node is maneuvered horizontally at a speed of 300m/s, the residence time in the area is as long as about 50 s;

and (4) conclusion: the antenna alignment link quality measurement and feedback mechanism with the period of about 0.1 second is adopted by the aircraft and the ground station, and sufficient link reference information is provided for the mutual alignment and real-time adjustment mechanism of the antennas between the aircraft and the ground station, so that the communication link connectivity is guaranteed to be maintained with the probability of approaching 1 (99.5% of normal maneuver and 98% of other special violent maneuvers such as large-angle climbing or rolling) in the air node height maneuvering scene.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. The aircraft ground-air broadband communication link method based on the narrow-band beam directional antenna is characterized in that only one radio frequency power amplifier module is installed in aircraft equipment, a circuit switch is connected with one half-duplex narrow-beam antenna, namely only one antenna in all narrow-beam antennas enters a signal receiving or transmitting working state on a time slice; the position of the ground station antenna is fixed;

s1 initial link establishment phase: after the aircraft is lifted off and the communication equipment starts to work, signaling handshake is carried out between the aircraft and the ground station, distance measurement, time reference synchronization and mutual alignment of antennas of the aircraft and the ground station are realized, and initial establishment of a communication link is realized;

s2 communication phase: the protocol content is divided into two parts: firstly, time reference correction and antenna alignment real-time adjustment are periodically carried out between nodes of two parties, and secondly, a channel access mechanism is adopted during data communication;

1) in the idle state of the link, except the time slots occupied by the periodic synchronous signals and the feedback signals, the antennas of the aircraft and the ground station are always in an RTS signal receiving state on other time slots; the signaling form is the same as the former synchronous signal, and the signaling content is different; the receiving antenna or orientation is maintained by the periodic synchronization signal transmission and feedback mechanism introduced above;

2) if the aircraft or the ground station suddenly generates a data service sending requirement in a link idle state, sending RTS signaling + short data signals immediately, and then waiting for receiving effect ACK feedback of a receiving party; if the ACK feedback of the receiver is received at the appointed time slot position of the sender, the RTS signaling and the long data signal are continuously used for sending the subsequent data, and the ACK feedback of the receiver is waited again; repeating the above process until the service data of the sender is completely sent;

3) if the receiver suddenly generates the requirement of sending service data to the other party in the data receiving process, the receiver enters a bidirectional service transmission state; the two parties respectively use the ACK feedback signals to break the data transmission of the other party in turn and transmit own data immediately.

2. The aircraft ground-air broadband communication link method based on the narrowband beam-oriented antenna, according to claim 1, wherein the exception handling mechanism for signaling handshake interruption during channel access of data traffic comprises: except for the first RTS signal and the short data signal of the data communication initiator, the subsequent communication process is to decide the subsequent transmission process based on the ACK feedback signal of the receiver, wherein the signaling content carried by the ACK signal not only contains the CRC result feedback of the previous data reception, but also comprises the transmission arrangement of the subsequent time slot, and the sender continues to send or the receiver starts to send the data;

the following rules are made for the data sender and the data receiver:

3. The aircraft ground-air broadband communication link method based on the narrowband beam directional antenna according to claim 1, wherein the time reference correction and the antenna alignment real-time adjustment are specifically:

(II) for the ground station, delaying and receiving the synchronous signals periodically sent by the aircraft based on the latest path transmission time delay; x represents the best azimuth of the aircraft to which the ground station points last, and X +/-1 and X +/-2 also represent 4 adjacent surrounding azimuths with coverage area overlapping with the azimuth X; the ground station measures the receiving quality of the synchronous signals among 25 different antenna and azimuth combinations by using the receiving strategy, thereby providing sufficient reference data for adjacent antenna switching or azimuth adjustment caused by linear flight of the aircraft;

(III) a mechanism of transmission and reception of feedback signals: the receiving position of the aircraft for the ground station feedback signal and the arrangement of the corresponding receiving antenna are specified as follows:

in the time slot, N antennas of the aircraft receive in turn, and the ground station feeds back the receiving result of the aircraft regardless of whether the synchronization signal sent by the aircraft in the current period is correctly received; the ground station adopts a feedback signal early sending mode based on path transmission time delay to ensure that N signals sequentially fall into receiving windows of N antennas when arriving at the aircraft, the duration of 1 window is Ts + 25/NxTs, and T_SThe time length of the synchronization signaling signal is represented as follows:

when the ground station decides which direction to use to send the feedback signal, if the ground station successfully receives the synchronous signal of the aircraft, the direction with the best signal receiving quality is selected from the synchronous signal, and the feedback signal is sent; if all the receiving fails, the receiving direction of the ground station arranged in the even time slot is X, then the direction which correctly receives signals in the last 5 periods except X and has the best receiving quality is selected from the historical data for sending the feedback signals; if the reception of the next periodic signal is still failed, the direction with the inferior receiving quality is replaced for trial; repeating the above process until the signal is received again correctly or the failure times reach the upper limit, if the process has the condition of insufficient available azimuth, expanding the selection period of the historical data by one time;

4. The aircraft ground-air broadband communication link method based on the narrowband beam-directing antenna of claim 3, wherein the reception strategy for even timeslot signals is specifically as follows:

5. The aircraft ground-air broadband communication link method based on the narrowband beam-directing antenna of claim 3, wherein the processing mechanism after the signaling handshake is interrupted during the time reference correction and the antenna alignment real-time adjustment is:

the ground station side regulation is specifically as follows: if the ground station does not receive any signaling signal or data signal of the aircraft within 10 periods, the ground station also restores the searching state of the initial chain building stage, wherein the searching airspace range is set to be a sector airspace with the azimuth as the center and the horizontal angle and the elevation angle of plus or minus 10 degrees respectively, wherein the azimuth of the last correctly received signal is the center; if the search time in the airspace exceeds the upper limit, further doubling the search airspace; and repeating the process until the aircraft synchronization signal is reacquired or the search range is expanded to the whole airspace.

6. The aircraft ground-air broadband communication link method based on the narrowband beam-directing antenna of claim 1, wherein the communication protocol content of the initial link setup phase is:

(I) the aerial call method comprises the steps that an aerial call signal is sent immediately after an aerial vehicle is lifted off, N narrow-beam antennas use a matrix switch control mode, a parameter N represents the total number of the narrow-beam antennas in aerial vehicle lens antennas, one of the N narrow-beam antennas is used for sending a synchronous signal in turn, and the N narrow-beam antennas can finish one-time ground signal coverage after being sent once in turn; after each 10 times of coverage, one narrow beam antenna enters a receiving state with a duration of T_G+T_SAttempting to receive a response signal, T, transmitted by a ground station_SIndicating the time length, T, of the synchronization signalling signal_GIndicating the path propagation delay protection time, T_GManual setting can be carried out manually before the aircraft takes off according to the actual application scene of the system, and the ground station is informed of the option in the signaling;

(III) in the process of searching the ground station, if a calling signal of a certain antenna of the aircraft points to a ground station antenna, and meanwhile, the ground station antenna also points to an aerial aircraft, the calling signal is successfully captured by the ground station;

7. The aircraft ground-to-air broadband communication link method based on narrowband beam-directing antennas of claim 6, it is characterized in that in the step (III), the ground station captures the synchronous signal sent by the Y-th antenna of the air node in the X direction, this means that at this time, the two antennas are already in a certain degree of mutual alignment, and considering that the signal areas of the adjacent antennas of the aircraft and the adjacent directions of the ground station all have certain overlap, in order to obtain the best direction, the ground station will utilize the Y-th antenna receiving window of the aircraft to call signals in the future, measure the signal receiving quality of a plurality of combinations between the X-direction of itself and its adjacent 4 directions and the antenna Y of the aircraft and its adjacent 4 antennas, and selecting the best combination from the combination, wherein the coverage area of the corresponding narrow-band signal beam defined by the adjacent azimuth or the adjacent antenna has a certain proportion of overlapping area.

8. The aircraft ground-air broadband communication link method based on the narrowband beam directional antenna of claim 6, wherein after the aircraft receives the reply signal, the arrival time of the signal is used to calculate the path transmission delay between the aircraft and the ground station:

T_d＝(T2-T1-T_s-(N-YY)×T_s-T_s1)/2；

t1 is the time when the aircraft's own antenna transmits the synchronization signal, and T2 is the correlation peak detection time when the ground station should signal.

9. The aircraft ground-air broadband communication link method based on the narrowband beam directional antenna according to claim 1, wherein a communication phase defaults to a starting point at the end of a following response time slot, and the influence of path transmission delay is eliminated on the basis of one-way synchronization after the ground station receives the path transmission delay value, so as to realize convergence with a clock reference of the aerial station with a certain range of precision.