Covert communication method based on TACAN navigation

Abstract

The invention belongs to the technical field of communication navigation, and particularly relates to a covert communication method based on TACAN navigation. Inserting an immediate pulse pair into an auxiliary reference pulse of the TACAN signal emission pulse sequence; and performing channel coding on the subsequent pulse pair for transmitting communication data. The uplink transmission communication data frame of the ground control tower sequentially comprises packet header data, first channel estimation data SINBAL1, first effective data DATA1, second channel estimation data SINBAL2, second effective data DATA2 and protection data from front to back; and the lengths of the two bytes are respectively 6 bytes, 2 bytes, 4 bytes, 2 bytes, 4 bytes and 2 bytes.

Description

Technical Field

[0001] The invention belongs to the technical field of communication and navigation, and in particular relates to a covert communication method based on TACAN navigation. Background Art

[0002] With the large-scale application of radio equipment, the radio spectrum is becoming increasingly tight, especially in the L-band field, where there are a large number of communication, navigation and identification surveillance signals, and the frequency usage is very crowded. The TACAN system is a mature short-range aviation radio navigation system with polar coordinate positioning capability. Through the signal transmission and reception between the ground beacon and the corresponding airborne equipment, the distance and azimuth relative to the ground beacon can be measured by the aircraft, thereby determining the position of the aircraft relative to the ground beacon.

[0003] According to the TACAN standard, the signal duty cycle is very low, the frequency band utilization is low, the ground beacon is only about 4%, and the airborne equipment is only about 0.1%. According to the Shannon sampling theorem, TACAN works in the L band, the channel spacing is 1MHz, the pulse modulation signal bandwidth B is generally 300kHz, and the voltage signal-to-noise ratio technical requirement of the receiver receiving channel is about 10dB. Therefore, without affecting the TACAN function, it can have a 9Mbps data transmission efficiency.

[0004] Therefore, by making full use of the signals in the TACAN standard, it is possible to achieve efficiency in data transmission in addition to transmitting navigation signals. Summary of the invention

[0005] The purpose of the present invention is to propose a covert communication method based on TACAN navigation, and to realize the function of covert communication by multiplexing part of the signal formats in TACAN navigation.

[0006] The technical solution of the present invention:

[0007] A covert communication method based on TACAN navigation inserts a random pulse pair into an auxiliary reference pulse of a TACAN signal transmission pulse sequence; and performs channel coding on the random pulse pair for transmitting communication data.

[0008] Furthermore, the ground tower sends communication data frames uplink, including the following from front to back:

[0009] Header data, first channel estimation data SINBAL1, first valid data DATA1, second channel estimation data SINBAL2, second valid data DATA2, protection data;

[0010] The lengths are: 6 bytes, 2 bytes, 4 bytes, 2 bytes, 4 bytes, and 2 bytes respectively.

[0011] Furthermore, the valid data 1 and the valid data 2 together constitute the valid data, which includes seven valid data bytes and one check byte.

[0012] Furthermore, in a one-second data transmission cycle for uplink communication data sent by the ground tower, there are 27 sub-cycles for arranging random pulse pairs, and 20 random pulse pairs are arranged in each sub-cycle to form a data frame.

[0013] Furthermore, the process of sending communication data uplink from the ground tower is as follows:

[0014] Step 1: Send auxiliary reference group pulse;

[0015] Step 2: Determine whether it is necessary to transmit an identification signal. If yes, send the identification signal and wait for the next auxiliary reference group pulse to be transmitted; if not, proceed to Step 3;

[0016] Step 3: Determine whether it is necessary to send a ranging response pulse signal. If yes, send a distance response signal and wait for the next auxiliary reference group to be transmitted; if not, go to Step 4;

[0017] Step 4: Determine whether the number of random filling pulses transmitted is greater than 80% of the maximum number that can be transmitted. If the number of random filling pulses transmitted is greater than 80% of the maximum number that can be transmitted, send random filling pulses and wait for the next auxiliary reference group to be transmitted; if the number of random filling pulses transmitted is less than or equal to 80% of the maximum number that can be transmitted, enter Step 5

[0018] Step 5: Channel encode the random pulse pairs to send communication data frames.

[0019] Further, in Step 5, the communication data frame sending process is as follows:

[0020] Step 5.1: Send a synchronization pulse. The synchronization pulse is a random pulse signal of a pseudo small M sequence. The pseudo small M sequence generation formula is as follows:

[0021] g(x)=x5+x1+x1

[0022] g(x) is scrambled by a pseudo-random sequence b(x)=b(0),b(1)...b(5), and the scrambling equation is:

[0023]

[0024] in, is an XOR operation;

[0025] Step 5.2: Send SINBAL1 signal, which is a double pulse 0 and 1 signal;

[0026] Step 5.3: Send DATA1 encoded signal;

[0027] Step 5.4: Send SINBAL2 signal, which is a double pulse 1 and 0 signal;

[0028] Step 5.5: Send DATA2 coded signal, including three BIT data information and 1 CRC check information;

[0029] Step 5.6: Send protection pulse pair information.

[0030] Furthermore, the process of receiving communication data by the airborne device is as follows:

[0031] Step A: According to the auxiliary reference group template, determine whether it is an auxiliary reference group. If not, continue to detect;

[0032] Step B: Determine whether it is an identification signal according to the TACAN standard clock time message template. If it is, perform identification signal processing and wait for the next auxiliary reference group; if not, enter Step C;

[0033] Step C: Determine whether it is a ranging response pulse signal. If so, perform ranging processing and wait for the next auxiliary reference group; if not, enter Step D;

[0034] Step D: Perform communication data processing.

[0035] Further, the communication data processing process is as follows:

[0036] Step D.1: Receive the synchronization pulse signal s(x); the synchronization matching template of the synchronization pulse signal is: g(x)=x5+x1+1;

[0037] The scrambled pseudo-random sequence b(x)=b(0),b(1)...b(5) is used to descramble g(x). The descrambling equation is:

[0038]

[0039] in, is an XOR operation;

[0040] The received signal is synchronously identified with s(x) and g'(x), and the calculation method is as follows:

[0041]

[0042] Here, when Σ≥10, the synchronization is considered to be complete, and the communication data transmitted from the ground is carried out to Step D.2;

[0043] Step D.2: Receive SINBAL1 and SINBAL2 signals. SINBAL signals are used to correct the channel. The synchronous correction method is used. The correction process is as follows:

[0044] The signals are counted as SL1 and SL2 respectively. According to the sending template, the sent signals are SINBAL1 = {0, 1} and SINBAL2 = {1, 0} when:

[0045] 1) SL1 = {0, 1}, SL2 = {1, 0}, the signal is not delayed;

[0046] 2) SL1 = {1,0}, SL2 = {0,0}, the signal is delayed by Δt;

[0047] 3) SL1 = {0,0}, SL2 = {0,1}, the signal is delayed by -Δt;

[0048] 4) Others: The signal side lobe is strong and no processing is performed;

[0049] Step D.3: Receive DATA1 coded signal, which contains four BIT data information;

[0050] Step D.5: Receive DATA2 coded signal, including three BIT data information and 1 CRC check information;

[0051] Step D.6: According to the delay Δt information in Step D.2, perform signal delay and merge analysis on DATA1 and DATA2.

[0052] Furthermore, the airborne device sends downlink communication data frames including, from front to back:

[0053] Header data, beat data, protection data;

[0054] The lengths are: 6 bytes, 6 bytes, 2 bytes respectively;

[0055] Each beat data includes 2 bytes of channel estimation data SINBAL and 4 bytes of valid data;

[0056] The number of beats is determined according to the channel capacity.

[0057] Furthermore, the process of downlinking communication data sent by the airborne equipment is consistent with the process of uplinking communication data sent by the ground tower;

[0058] The process of the ground tower receiving communication data downlink is the same as the process of the airborne equipment receiving communication data uplink. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 : TACAN pulse schematic diagram;

[0060] Figure 2 :Schematic diagram of each pulse mode of TACAN;

[0061] Figure 3 : Schematic diagram of X-mode pulse;

[0062] Figure 4 : Schematic diagram of Y-mode pulse;

[0063] Figure 5 : Schematic diagram of X-mode pulse coding;

[0064] Figure 6 : Ground transmission signal format;

[0065] Figure 7 : Ground transmission timing pulse;

[0066] Figure 8 :TACAN transmission signal analysis flow chart;

[0067] Fig. 9 :Flowchart of airborne equipment signal analysis;

[0068] Fig.10 : Frame format of signal transmitted by airborne equipment. DETAILED DESCRIPTION

[0069] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0070] The TACAN system is a mature short-range aviation radio navigation system with polar coordinate positioning capability. Through the coordination of signal transmission and reception between ground beacons and corresponding airborne equipment, the aircraft can measure the distance and azimuth relative to the ground beacon, thereby determining the position of the aircraft relative to the ground beacon. When the geographic coordinates of the beacon are known, the onboard equipment can obtain the longitude and latitude of the aircraft through coordinate transformation.

[0071] The TACAN system uses pulse code modulation to transmit signals. The pulse sequence transmitted by the ground beacon includes the main and auxiliary reference pulses, the answer pulse given after the receiver's onboard ranging inquiry and decoding, and the random filling pulse, with a total of 7200 pulses / s. The system uses a pulse pair basic coding method, which is divided into X and Y modes. A single pulse is a Gaussian envelope modulated carrier. The TACAN pulse form is a single pulse duration of 3.5±0.5μs. The interval between the ranging pulse pairs is: X channel 12±0.1us. Y channel 30±0.1us. The schematic diagram of a single pulse is as follows Figure 1 shown.

[0072] TACAN signals include the main reference group, auxiliary reference group, identification pulse, distance response pulse and random filling pulse. The priority is as follows: main reference group > auxiliary reference group > identification pulse > distance response pulse > random filling pulse. Figure 2 Shown

[0073] Main reference group: TACAN ground equipment measures the rough azimuth information with the ground tower through the main reference group. The tower sends 15 main pulse reference groups (15Hz) per second. The main reference signal format is: in X mode, each pulse interval is 30us, a total of 12 single pulses; in Y mode, each pulse interval is 30us, a total of 13 pulses.

[0074] Auxiliary reference group: TACAN ground equipment measures the rough azimuth information with the ground tower through the auxiliary reference group. The tower sends 135 auxiliary reference groups (135Hz) per second. The signal format of the auxiliary reference group is: X mode, pulse interval is 24us, 6 pulses, and Y mode has a pulse interval of 15us and a total of 13 single pulses.

[0075]

[0076] Identify pulse signal: transmit the signal in a unified standard format according to the specified time.

[0077] Distance reply pulse: According to the information sent by the airborne equipment, a reply signal is sent within a specific time range to form a "secondary radar" type ranging model. The identification signal is transmitted by the TACAN ground navigation station. It is a pulse pair signal that meets a certain coding format. There is another pair of balanced pulses 100μs after each pair of identification pulses. The pulse pair frequency of the identification signal is 1350Hz, that is, there is a pair of pulses every 740μs. The balance pulse appears at 100μs±10μs after the pulse pair, and is also composed of pulse pairs. The information of the identification signal is formed by Morse code points, dashes and gaps.

[0078] Random filling pulse: The filling pulse is used to make the pulse sequence envelope smoother and ensure the accuracy of the angle measurement modulation signal.

[0079] It can be seen from the working mode and signal format of the TACAN system that its signal duty cycle is very low, only about 4% for ground beacons and only about 0.1% for airborne equipment; even if the ground beacon has a closed time of about 60us after each pulse transmission, which increases the occupied time by about 17%, there is still about 80% idle time. According to Shannon's sampling theorem, TACAN works in the L band, the channel spacing is 1MHz, the pulse modulation signal bandwidth B is generally 300kHz, and the voltage signal-to-noise ratio technical requirement of the receiver receiving channel is about 10dB. Therefore, under the premise of not affecting the data transmission characteristics, the channel capacity can be calculated according to Shannon's law:

[0080]

[0081] In this way, the theoretical maximum transmission bandwidth is: 300Kbps. That is, under the condition of satisfying Shannon's sampling theorem, the transmission bandwidth meets the index requirements.

[0082] Therefore, by making full and effective use of the channel bandwidth characteristics of TACAN, data transmission can be carried out under the premise of satisfying navigation. According to the TACAN standard, among the five signal modes of TACAN, random filling pulses can effectively transmit data information through certain coding.

[0083] S2, random filling pulse coding design

[0084] According to the TACAN standard, the number of random filling pulses is 2700 (according to the standard, it should be 2700+900 pairs, and the design input here is based on the transmission of 2700 pairs). Since every 9 auxiliary reference groups overlap with the main and quasi groups, the present invention mainly considers the auxiliary and quasi groups. Considering that when sending data, there is a standard transmission signal format. In this way, in the interval between each auxiliary reference group, according to the insertion of 135 auxiliary reference pulses in a 1s period, 20 random pulse pairs can be inserted between the auxiliary pulse groups. Therefore, these 20 random pulse pairs can be channel coded to achieve data transmission. Because there is no specific requirement for the pulse interval of the random filling pulse, it can be achieved through pulse position modulation (PPM). According to the TACAN standard, the random distribution of pulses can be calculated as long as the probability of occurrence efficiency is satisfied. Therefore, when we modulate the pulse pair, we can obtain the trigger time of a pair of pulses in the specific PPM modulation. That is, the maximum transmittable rate can reach 2700bit / s.

[0085] According to the table above, the interval between auxiliary reference groups is 7400us, that is, there are 20 random filling pulses in the middle of this 7400us. The interval between random filling pulses is 370us. According to the standard, the duration of a single pulse of TACAN is 3.5±0.5μs. The interval between ranging pulse pairs is: X channel 12±0.1us. Y channel 36±0.1us.

[0086] Therefore, for the modulation between pulses, it only needs to be greater than one of the max. Here, in order to ensure the deambiguation of the pulse signal, the signal format is designed to be.

[0087] Since the random filling pulse is not a standard filling pulse with a fixed time, the occurrence time of the random filling pulse is pulse coded, and the coding is achieved by adjusting the occurrence time of the random filling pulse. In this way, the pulse coding design is achieved according to the interval between the X mode and the Y mode.

[0088] Pulse coding is in the form of 0 and 1 coding, and is coded according to the pulse occurrence time. The coding form is:

[0089]

[0090] Here Δt is the interval between pulse pairs. Taking X mode as an example, when Δt = 0, the transmitted data is 0, and when Δt = 12us, the transmitted data is 1. Figure 5 shown.

[0091] By controlling the occurrence time of random pulses, effective data transmission can be achieved.

[0092] The distribution requirements of random filling pulses also need to be considered, that is, based on the time interval of 1000 pulse pairs of at least 2700 pairs of random filling pulses, the data is recorded at the closest 25us interval with a relative probability of occurrence within 80%. To ensure that the random filling pulses also need to meet the transmission cycle requirements. Therefore, in the data transmission, only 20% of the cycles can be used for retrograde data transmission, that is, 27 intervals in 135 intervals can transmit data. In this way, the maximum transmission data can be obtained as:

[0093] 27*20=540bps.

[0094] S3. Signal format design

[0095] The TACAN system, which transmits data based on random pulse modulation, is affected by the data transmission of multi-path and other complex signals during detector detection. Therefore, a certain message format design is required to achieve efficient data transmission.

[0096] In a one-second data transmission cycle, each cycle can be divided into 135 sub-cycles, 27 of which can transmit data, and 27 sub-cycles are randomly transmitted within a 1-second cycle. Each sub-cycle can transmit 20 bytes of data. The signal frame format can be designed as follows:

[0097] Only 8 bits of valid data are transmitted in one cycle. The rest are header data, channel estimation data, data bits, check bits, and protection bits. Figure 6The ground transmission signal format is shown below.

[0098] Synchronization header: The synchronization header consists of 6 pulse pairs and is used to synchronize and capture communication data. The synchronization header data is a transmission data header based on a pseudo-random sequence and is designed to ensure the interception of the signal within a specific period.

[0099] SINBAL: The signal is divided into two groups. A SINBAL signal consisting of two signal bytes is inserted into every four data bytes. Considering the channel attenuation and inter-code interference, the SINBAL signal is a specific 0 or 1 signal. The SINBAL signal is estimated and the signal crosstalk is resolved during the DATA data receiving stage.

[0100] DATA: DATA data consists of two parts, which are generated by the forward SINBAL signal and are valid data transmission positions. The DATA signal transmits a total of 7 valid data bytes and 1 CRC check byte.

[0101] Protection: It consists of 2 bytes. The protection byte is pseudo-random data transmission data to ensure crosstalk between auxiliary pulse groups. The protection byte can be randomly encoded according to the occurrence time between auxiliary pulse groups.

[0102] The timing diagram of the transmission signal is as follows: Figure 7 shown.

[0103] S4, ground tower uplink communication function processing

[0104] Since there are 135 auxiliary reference group pulses in a time period of s, the pulse occurrence time can be divided into 135 equal parts. In this way, based on time division multiplexing, the time slices can be equally divided in space according to the use form of TDD-TDMA, thereby realizing network data transmission.

[0105] For the single-point uplink design, since the random fill pulse has the lowest priority and in order to perform covert data transmission, it is necessary to identify the main reference pulse group, auxiliary reference pulse group, identification signal, and distance response pulse sending sequence to determine whether data information can be sent at present.

[0106] The uplink message parsing process for sending data is as follows Figure 8 shown.

[0107] The data sending process is:

[0108] Step 1: Send auxiliary reference group;

[0109] Step 2: Determine whether the identification signal needs to be transmitted. If so, send the identification signal and wait for the next auxiliary reference group to be transmitted; if not, go to Step 3;

[0110] Step 3: Determine whether it is necessary to send a ranging response pulse signal. If yes, send a distance response signal and wait for the next auxiliary reference group to be transmitted; if not, go to Step 4;

[0111] Step 4: According to the 80% transmission probability of random filling pulses, if yes, send random filling pulses and wait for the next auxiliary reference group to be transmitted; if not, go to Step 5;

[0112] Step 5: Send communication signal;

[0113] Step 5.1: Send the synchronization pulse. The synchronization pulse is a random pulse signal of a pseudo small M sequence, and the pulse is also modulated by 0 and 1. The sending method is as follows:

[0114] g(x)=x5+x1+1;

[0115] Here, g(x) is scrambled by a pseudo-random sequence b(x)=b(0), b(1)...b(5), and the scrambling equation is:

[0116]

[0117] in, It is an XOR operation.

[0118] Step 5.2: Send SINBAL1 signal, which is a double pulse 0 and 1 signal;

[0119] Step 5.3: Send DATA1 coded signal, including four BIT data information;

[0120] Step 5.4: Send SINBAL2 signal, SINBAL signal is a double pulse 1, 0 signal;

[0121] Step 5.5: Send DATA2 coded signal, including three BIT data information and 1 CRC check information;

[0122] Step 5.6: Send protection pulse pair information;

[0123] S5. Airborne equipment receiving process

[0124] The communication message processing of the airborne equipment corresponds to the data sent by the ground station. The processing flow is as follows: Fig. 9 shown.

[0125] Step 1: According to the auxiliary reference group template, determine whether it is an auxiliary reference group. If not, continue to detect. ;

[0126] Step 2: According to the TACAN standard clock time message template, determine whether the TACAN station identification signal needs to be transmitted. If yes, perform identification signal processing and wait for the next auxiliary reference group to be transmitted; if not, proceed to Step 3;

[0127] Step 3: Determine whether it is necessary to send a ranging response pulse signal. If yes, perform ranging processing and wait for the next auxiliary reference group to be transmitted; if no, proceed to Step 4;

[0128] Step 4: Process the communication signal;

[0129] Step 4.1: Receive the synchronization pulse. The synchronization pulse signal received here is s(x).

[0130] The synchronization pulse is a random pulse signal of a pseudo small M sequence, and the pulse is also modulated by 0 and 1. The synchronization matching template is:

[0131] g(x)=x5+x1+1;

[0132] The scrambled pseudo-random sequence b(x)=b(0),b(1)...b(5) scrambles g(x), and the scrambling equation is:

[0133]

[0134] in, It is an XOR operation.

[0135] The received signal is synchronously identified with s(x) and g'(x). The calculation method is as follows:

[0136]

[0137] Here, when Σ≥10, the synchronization is considered complete. is the communication signal transmitted from the ground, and Step 4.2 is performed.

[0138] Step 4.2: Receive SINBAL1 and SINBAL2 signals. SINBAL signals are used to correct the channel. The present invention adopts a synchronous correction method. The correction process is as follows:

[0139] The signals are counted as SL1 and SL2 respectively. According to the template sent, the sent signals are SINBAL1 = {0,1} and SINBAL2 = {1,0} when:

[0140] 5) SL1 = {0,1}, SL2 = {1,0}, the signal is not delayed;

[0141] 6) SL1 = {1,0}, SL2 = {0,0}, the signal is delayed by Δt;

[0142] 7) SL1 = {0,0}, SL2 = {0,1}, the signal is delayed by -Δt;

[0143] 8) Others: The signal side lobe is strong and no processing is performed.

[0144] The delayed signal shows that DATA data can be matched with high precision. In addition, SINBAL signal can also be used as a covert transmission signal.

[0145] Step 4.3: Receive DATA1 coded signal, which contains four BIT data information;

[0146] Step 4.5: Receive DATA2 coded signal, which contains three BIT data information and 1 CRC check information;

[0147] Step 4.6: According to the delay Δt information obtained in Step 4.2, perform signal delay and merge analysis on DATA1 and DATA2.

[0148] S6. Design of downlink signal for airborne equipment

[0149] The signal sent by the airborne equipment to the ground station is mainly a distance inquiry pulse signal. The signal format standard is: the inquiry pulse is encoded according to the pulse pair. The difference from the distance response pulse is that the duration of a single pulse is 3.5±0.5μs. The interval between the ranging pulse pairs is: X channel 12±0.1us. Y channel 36±0.1us. In the air-to-ground mode, the inquiry signal sent by the airborne equipment should not exceed 150 pulse pairs / s in the search phase. It should not exceed 30 pulse pairs / s in the tracking state. In this way, through effective pulse pair coding, the downlink design of the airborne equipment can be realized in the case of distance measurement.

[0150] Compared with the resource limitation of uplink data, pulse coding can be performed as long as there is no conflict with the ranging pulses during the search and tracking cycle.

[0151] Downlink transmission can be designed in the same way as the terrestrial uplink data signal, which is divided into synchronization pulses, SINBAL, data bits and protection bit pulses. Downlink signals can be completed using a variety of modulation methods.

[0152] Different from the uplink data of the ground tower, the SINBAL and DATA data transmission amount can be determined according to the channel capacity. Each beat transmits 2 bits of SINBAL and 4 bits of DATA signals respectively. The signal frame format is as follows: Fig.10 shown.

[0153] The signal processing method is the same as that in steps S4 and S5.

[0154] The above is only a specific embodiment of the present invention, and the present invention is described in detail. The unexplained part is a conventional technology. However, the protection scope of the present invention is not limited to this. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A covert communication method based on TACAN navigation, characterized in that: A random pulse pair is inserted into the auxiliary reference pulse of the TACAN signal transmission pulse sequence; and the random pulse pair is channel-coded for transmitting communication data.

2. The method according to claim 1, characterized in that: The communication data frames sent by the ground tower uplink include: Header data, first channel estimation data SINBAL1, first valid data DATA1, second channel estimation data SINBAL2, second valid data DATA2, protection data; The lengths are: 6 bytes, 2 bytes, 4 bytes, 2 bytes, 4 bytes, and 2 bytes respectively.

3. The method according to claim 2, characterized in that: The valid data 1 and the valid data 2 together constitute the valid data, which includes seven valid data bytes and one check byte.

4. The method according to claim 3, characterized in that: In a one-second data transmission cycle for uplink communication data sent by the ground tower, there are 27 sub-cycles for arranging random pulse pairs, and 20 random pulse pairs are arranged in each sub-cycle to form a data frame.

5. The method according to claim 4, characterized in that: The process of sending communication data uplink from the ground tower is as follows: Step 1: Send auxiliary reference group pulse; Step 2: Determine whether it is necessary to transmit an identification signal. If so, send the identification signal and wait for the next auxiliary reference group pulse to be transmitted; If not, go to Step 3; Step 3: Determine whether it is necessary to send a ranging response pulse signal. If yes, send a distance response signal and wait for the next auxiliary reference group to be transmitted; if not, go to Step 4; Step 4: Determine whether the number of random filling pulses transmitted is greater than 80% of the maximum number of transmittable pulses. If the number of random filling pulses transmitted is greater than 80% of the maximum number of transmittable pulses, send random filling pulses and wait for the next auxiliary reference group to transmit. If the number of random filling pulses transmitted is less than or equal to 80% of the maximum number of transmittable pulses, enter Step 5. Step 5: Channel encode the random pulse pairs to send communication data frames.

6. The method according to claim 5, characterized in that: In Step 5, the communication data frame sending process is as follows: Step 5.1: Send a synchronization pulse. The synchronization pulse is a random pulse signal of a pseudo small M sequence. The pseudo small M sequence generation formula is as follows: g(x)=x5+x1+1 g(x) is scrambled by a pseudo-random sequence b(x)=b(0),b(1)...b(5), and the scrambling equation is: in, is an XOR operation; Step 5.2: Send SINBAL1 signal, which is a double pulse 0 and 1 signal; Step 5.3: Send DATA1 encoded signal; Step 5.4: Send SINBAL2 signal, which is a double pulse 1 and 0 signal; Step 5.5: Send DATA2 coded signal, including three BIT data information and 1 CRC check information; Step 5.6: Send protection pulse pair information.

7. The method according to claim 6, characterized in that: The process of receiving communication data by the airborne equipment is as follows: Step A: According to the auxiliary reference group template, determine whether it is an auxiliary reference group. If not, continue to detect; Step B: According to the TACAN standard clock time message template, determine whether it is a TACAN station identification signal. If so, perform identification signal processing and wait for the next auxiliary reference group; if not, enter Step C; Step C: Determine whether it is a ranging response pulse signal. If so, perform ranging processing and wait for the next auxiliary reference group; if not, enter Step D; Step D: Perform communication data processing.

8. The method according to claim 7, characterized in that: The communication data processing process is as follows: Step D.1: Receive the synchronization pulse signal s(x); the synchronization matching template of the synchronization pulse signal is: g(x)=x5+x1+1; The scrambled pseudo-random sequence b(x)=b(0),b(1)...b(5) is used to descramble g(x). The descrambling equation is: in, is an XOR operation; The received signal is synchronously identified with s(x) and g'(x), and the calculation method is as follows: Here, when Σ≥10, the synchronization is considered to be complete, and the communication data transmitted from the ground is carried out to Step D.2; Step D.2: Receive SINBAL1 and SINBAL2 signals. SINBAL signals are used to correct the channel. The synchronous correction method is used. The correction process is as follows: The signals are counted as SL1 and SL2 respectively, and the transmitted signals are SINBAL1 = {0,1} and SINBAL2 = {1,0} when: 1) SL1 = {0, 1}, SL2 = {1, 0}, the signal is not delayed; 2) SL1 = {1,0}, SL2 = {0,0}, the signal is delayed by Δt; 3) SL1 = {0,0}, SL2 = {0,1}, the signal is delayed by -Δt; 4) Others: The signal side lobe is strong and no processing is performed; Step D.3: Receive DATA1 coded signal, which contains four BIT data information; Step D.5: Receive DATA2 coded signal, including three BIT data information and 1 CRC check information; Step D.6: According to the delay Δt information in Step D.2, perform signal delay and merge analysis on DATA1 and DATA2.

9. The method according to claim 8, characterized in that: The downlink communication data frames sent by the airborne equipment include: Header data, beat data, protection data; The lengths are: 6 bytes, 6 bytes, 2 bytes respectively; Each beat data includes 2 bytes of channel estimation data SINBAL and 4 bytes of valid data; The number of beats is determined according to the channel capacity.

10. The method according to claim 9, characterized in that: The process of downlink communication data sent by airborne equipment is the same as the process of uplink communication data sent by the ground tower; The process of the ground tower receiving communication data downlink is the same as the process of the airborne equipment receiving communication data uplink.

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