KR102602218B1 - Mlat receiver precise time correction method - Google Patents

Abstract

The TOA correction method according to this embodiment includes: receiving a signal from a transponder of an aircraft, storing the time of arrival (TOA) of the signal, and the stored TOA and a predetermined reception time pattern. It includes comparing and replacing the reception time that is outside the detection margin of the reception time.

Description

MLAT receiver TOA correction method {MLAT RECEIVER PRECISE TIME CORRECTION METHOD}

This technology relates to the MLAT receiver TOA correction method.

The multilateration aerial surveillance (MLAT) method uses a hyperbola or hyperboloid position measurement method to output four signals to the aircraft's transponder (if there are three, two-dimensional position can be calculated). The location of the aircraft is obtained by measuring the Time Difference of Arrival (TDOA) between the above receivers.

The receiver of the MLAT system precisely measures signals provided by the aircraft and transmits the received precise time to the central processing unit. The receivers operate in synchronization to calculate precise TDOA. Receivers receive time information from artificial satellites such as GPS and GLONASS and operate in synchronization with each other.

The receiver of the MLAT system receives the signal from the aircraft transponder, calculates the TOA (Time Of Arrival) of the signal, and transmits it to the Central Processing System (CPS). The central processing system uses the precise time received from the receiver to determine the aircraft's location.

Signals output from aircraft may be distorted due to signal overlap, fading, multipath, etc. These unintended factors may cause glitches in precise time and cause errors when determining the location of the aircraft.

One of the challenges to be solved with this technology is to provide a technology that can correct glitches that occur in precise vision due to unintended factors.

The TOA correction method according to this embodiment includes: receiving a signal from a transponder of an aircraft, storing the time of arrival (TOA) of the signal, and the stored TOA and a predetermined reception time pattern. It includes comparing and replacing the reception time that is outside the detection margin of the reception time.

According to one aspect of this embodiment, the signal received from the aircraft's transponder is a Mode S signal (1090ES) with a frequency of 1090 MHz.

According to one aspect of this embodiment, the step of storing the TOA of the signal is the time when the preamble of the signal is detected.

According to one aspect of this embodiment, the step of storing the TOA of the signal is performed with an accuracy of 2^-30 sec.

According to one aspect of this embodiment, the reception visual pattern may include a rising pattern in which TOA increases over time, a falling pattern in which TOA decreases over time, a composite pattern in which TOA increases and decreases over time, and a time lapse. TOA includes patterns that do not change.

According to one aspect of this embodiment, the reception time pattern includes a rising pattern including a pattern in which the reception time increases linearly or non-linearly over time, and a falling pattern includes a pattern in which the reception time increases over time. It includes patterns that decrease linearly or decrease non-linearly, and complex patterns include patterns in which the reception time increases and then decreases over time, and patterns in which the reception time decreases and then increases over time.

According to one aspect of this embodiment, the step of storing the TOA of signals is performed by recording and storing the TOA of at least five signals.

According to one aspect of this embodiment, the step of comparing the reception time patterns is performed by comparing the TOA of the five stored signals with the reception time patterns.

According to one aspect of this embodiment, the reception time outside the detection margin is a value that is 20% or more greater than the value of the predetermined reception time pattern or 20% or more less than the value of the predetermined reception time pattern.

According to one aspect of this embodiment, the step of replacing the predetermined reception time value is performed by replacing it with one of a value extrapolated from a predetermined reception time pattern value, an average value, and a median value of adjacent reception time pattern values. do.

According to this embodiment, the advantage of being able to correct changes in TOA values due to non-ideal characteristics is provided, and the advantage of being able to detect the aircraft's track more precisely is provided.

1 is a schematic block diagram of an MLAT receiver according to this embodiment.
Figure 2 is a flowchart outlining the method of driving an MLAT receiver according to this embodiment.
Figure 3 is a diagram showing an outline of the TOA correction method according to this embodiment.
Figure 4 is a diagram schematically showing the process of synchronizing a time signal provided by an artificial satellite and a local clock.
Figure 5 shows a Mode 3/A signal with an identification code (squawk code) provided by an aircraft transponder or standard surveillance transponder, a Mode C signal with altitude information, and a 56-bit Mode S signal with an ICAO address, which is a unique aircraft identifier. , This is a diagram showing the reformulation of the 112-bit 1090ES signal, which includes monitoring data.
Figure 6 is a diagram schematically showing the process by which the signal processing unit 300 forms TOA information.
Figure 7 is a diagram illustrating a pre-stored TOA pattern.
FIG. 8(a) is a diagram illustrating a case where an abnormal effect occurs on the TOA information of the signal received by the receivers, and FIG. 8(b) is a diagram in which the signal processing unit performs comparison with the reception time pattern according to this embodiment and replaces the TOA information. This is a drawing illustrating the results of performing.

Below, an overview of the MLAT receiver TOA correction method according to this embodiment will be described with reference to the attached drawings. FIG. 1 is a schematic block diagram of an MLAT receiver according to this embodiment, and FIG. 2 is a flowchart showing an outline of a method of driving an MLAT receiver according to this embodiment. Figure 3 is a diagram showing an outline of the TOA correction method according to this embodiment.

Referring to Figures 1 to 3, the MLAT receiver according to this embodiment includes a precision clock forming unit 100 that forms a precision clock in synchronization with the time signal provided by the satellite, and a base signal that receives the signal provided by the transponder. An RF receiving unit 200 that converts to a band, a signal processing unit 300 that forms TOA (Time Of Arrival) information from the signal converted to a baseband, and a packet containing TOA information is provided to a central processing system (CPS). Includes a message processing unit 400.

The MLAT receiver according to this embodiment includes steps of forming a precision clock synchronized with a time signal provided by a satellite, receiving a signal provided by a transponder and converting it to baseband, and generating TOA from the signal converted to baseband. It operates through the steps of forming (Time Of Arrival) information and providing packets containing TOA information to the central processing unit.

The TOA correction method according to this embodiment includes: receiving a signal from a transponder of an aircraft (S100), storing the time of arrival (TOA) of the signal (S200), and storing the stored TOA It includes a step of comparing a predetermined reception time pattern (S300) and a step of replacing a reception time that is outside the detection margin of the reception time (S400).

Referring to Figures 1 and 3, the precision clock forming unit 100 receives a time signal from a satellite and forms a precision clock in synchronization with it. In one embodiment, the artificial satellite is a Global Positioning System (GPS) satellite, and the time signal is a 1 PPS (Pulse Per Second) signal transmitted at a period of 1 second. In another embodiment, the satellite is a GLONASS satellite, and the time signal is a time signal provided by the GLONASS satellite.

In one embodiment, the precision clock forming unit 100 includes a local clock forming unit (not shown) that forms a local clock synchronized to a time signal provided by a satellite, and a local clock having a frequency higher than the frequency of the local clock. It includes a first clock forming unit (not shown) that forms a first clock. The local clock forming unit and the first clock forming unit may each include a phase locked loop (PLL).

Figure 4 is a diagram schematically showing the process of synchronizing a time signal provided by an artificial satellite and a local clock. Referring to FIG. 4, the local clock forming unit tracks the time signal provided by the artificial satellite and synchronizes the phase and frequency with the phase and frequency synchronized with the time signal provided by the artificial satellite. forms a synchronized local clock. When the phase and frequency of the local clock are locked to the time signal provided by the satellite, the state of the state information (time source state) indicating this changes.

When the phase and frequency of the local clock are synchronized with the time signal provided by the satellite, the first clock forming unit included in the precision clock generator 100 forms a first clock with a higher frequency than the local clock and is transmitted to the RF receiving unit 200. ) is provided. In one embodiment, the first clock has a frequency of 10 MHz.

The precision clock generator 100 receives the CA code (Coarse Acquisition code), P code (Precise code), and navigation message provided by the satellite, Coordinated Universal Time (UTC) information, altitude information of the receiver, NMEA (National Marine Electronics Association) information including location information of the receiver is formed and provided to the message processing unit 400.

The message processing unit 400 initializes the signal processing unit 300 when state information (time source state) changes. As an example, the message processing unit 400 updates the time information of the signal processing unit 300 using UTC time information included in the provided NMEA information and initializes a counter (not shown) for calculating TOA. The time information provided to the signal processing unit 300 forms TOD (Time Of Day) information, which is information about the hour, minute, and second at which the signal provided by the aircraft's transponder was received, and the time at which the signal provided by the transponder was received. It is transmitted to the central processing unit (CPS, not shown) along with TOA information, which is information about.

As will be explained below, the counter included in the signal processing unit receives a sampling clock, counts the number of sampling clock pulses, and forms TOA information, which is information about the time when the signal provided by the transponder is received. Additionally, the message processing unit 400 can update its own time information using NMEA information.

The RF receiver 200 receives an RF signal provided by an aircraft transponder or a standard surveillance transponder (S100) and converts it to baseband. Referring to Figure 5, the signals provided by the aircraft transponder or standard surveillance transponder are a Mode 3/A signal with an identification code (squawk code), a Mode C signal with altitude information, and 56 with an ICAO address, which is a unique aircraft identifier. It is a 112-bit 1090ES signal that includes bit Mode S signal and monitoring data. As shown, the Mode 3/A signal and the Mode C signal have the same form, and the Mode S signal and the 1090ES signal have the same preamble form.

The RF receiver 200 receives the Mode 3/A signal, Mode C signal, Mode S signal, and 1090ES signal provided by the aircraft transponder or standard monitoring transponder (RMT), converts them to baseband, and transmits them to the signal processor 300. ) is provided. In one embodiment, the RF receiver 200 includes a down conversion unit (not shown) that converts the received signal to baseband and an envelope unit that performs envelope detection on the signal converted to baseband. It may include a detector (not shown). As an example, the envelope detector provides the formed envelope to the signal processing unit 300.

The RF receiving unit 200 receives the first clock formed by the precision clock forming unit 100, forms a sampling clock (SCK, see FIG. 5) with a frequency higher than the frequency of the first clock, and generates a sampling clock (SCK, see FIG. 5) that is connected to the signal processing unit 300. provided to. In one embodiment, the RF receiver 200 may further include a sampling clock forming unit that receives the first clock and forms a sampling clock. For example, the sampling clock may be 100 MHz.

Figure 6 is a diagram schematically showing the process by which the signal processing unit 300 forms TOA information. Referring to FIG. 6, the signal processor 300 receives a sampling clock (SCK) and a baseband-converted signal from the RF receiver 200, samples the TOA information and the baseband-converted signal, and generates data (D). It includes a sampler 310 that forms. The sampler 310 samples the signal converted to baseband using a sampling clock (SCK). When the preamble of a signal is provided as one input of the sampler, the preamble is received using the number of sampling clock cycles counted from the time when the counter (not shown) of the signal processing unit 300 is reset. Find the time of arrival (TOA) (S200). In one embodiment, TOA data is It can have a resolution of .

In one embodiment, the signal processing unit 300 may store the formed TOA information in a buffer (not shown). The signal processing unit 300 can store four or more consecutive pieces of TOA information, and preferably can store five or more pieces of TOA information.

The signal processor 300 has UTC time information obtained from the NMEA signal received while the precision clock generator 400 is synchronized with the time signal provided by the satellite, and continuously calculates the time by a counter (not shown) that counts the sampling clock. Information is updated. Accordingly, the signal processing unit 300 forms TOD (Time Of Day) information containing information on the hour, minute, and second at which the data preamble is received. As an example, TOD information is It can have a resolution of .

However, as described above, the received TOA information may have errors due to unintended, non-ideal effects such as signal overlap, fading, and multipath.

The signal processing unit 300 compares the pre-stored TOA pattern with the continuous TOA pattern recorded in the buffer (S300). Figure 7 is a diagram illustrating a pre-stored TOA pattern. In FIGS. 7(a) to 7(d), the horizontal axis represents time, and the vertical axis represents TOA expressed in precise time. TOA patterns refer to the trajectory of TOAs received by the receiver over time according to the movement of the aircraft transmitting the signal. Figure 7(a) shows rising patterns. The left diagram of FIG. 7(a) shows that TOA increases linearly with time, and is a case where the aircraft accelerates over time. The diagram on the right shows that TOA increases non-linearly with time, and it can be seen that the acceleration of the aircraft increases with time.

Figure 7(b) shows the falling patterns. The left diagram of FIG. 7(b) shows that TOA decreases linearly with time, and is a case where the aircraft decelerates with time. The diagram on the right shows that TOA decreases non-linearly with time, and it can be seen that the acceleration of the aircraft decreases with time.

Figure 7(c) shows complex patterns. The left diagram of FIG. 7(c) shows that TOA increases and then decreases with time, and is a case where the aircraft accelerates and then decelerates with time. The diagram on the right shows that TOA decreases and then increases over time, and is when the aircraft accelerates after decelerating. The composite patterns in FIG. 7(c) are mainly TOA patterns formed during takeoff and/or landing of an aircraft. Figure 7(d) shows a parallel pattern when the aircraft's motion is at the same speed.

The patterns illustrated in FIGS. 7(a) to 7(d) show TOA information of signals received by receivers over time, and most navigation trajectories are included in one of the above patterns.

Accordingly, the consecutive TOA patterns stored in the buffer form any one of the patterns in FIGS. 7(a) to 7(d) and/or a part thereof, and if they deviate from this, the receiver misdetects the TOA due to non-ideal characteristics. It can be understood that this has been done.

In one embodiment, the signal processing unit 300 compares the reception time pattern by comparing the five stored TOA data with a pre-stored reception time pattern. Comparing a large number of TOA data with the received time pattern can result in more precise comparison results, but the latency of providing TOA data to the central processing system (CPS) increases, and signal distortion stored in the buffer increases. This increases the probability of errors occurring during pattern analysis.

In one embodiment, the signal processor 300 may discard TOA data that is outside the detection margin. The detection margin may be 20% or more larger than the TOA value of the detection pattern, or 20% or more smaller than the value of the predetermined reception time pattern. Additionally, the signal processor 300 may replace TOA data outside the detection margin with any one of a value extrapolated from a reception time pattern, an average value, or a median value of TOA values stored in a buffer.

FIG. 8(a) is a diagram illustrating a case where an abnormal effect occurs on TOA information of signals received by receivers. It can be seen that the TOA information received by the receiver forms a falling pattern as illustrated in FIG. 8(a), but it can be confirmed that noise is generated due to non-ideal effects. However, referring to FIG. 8(b), it can be seen that the non-ideal influence has been removed according to the result of the signal processing unit comparing and replacing the received time pattern with the received time pattern according to this embodiment. In this way, TOA data with non-ideal effects removed is transmitted to a central processing system (CPS). The central processing system determines the location of the aircraft from TOA data transmitted by multiple systems.

In one embodiment, the signal processing unit 300 compares the five TOA data stored in the buffer with a predetermined pattern. For example, if all five TOA data are outside the detection margin, the TOA data stored in the buffer is transmitted to the central processing system without performing any correction work on them, and the central processing system performs processing using higher computing resources. Let it be done.

Although the present invention has been described with reference to the embodiments shown in the drawings to aid understanding, these are embodiments for implementation and are merely illustrative, and those skilled in the art will be able to make various modifications and equivalents therefrom. It will be appreciated that other embodiments are possible. Therefore, the true technical protection scope of the present invention should be determined by the attached patent claims.

1: Receiver 100: Precision clock forming unit
200: Receiving unit 300: Signal processing unit
400: Message processing unit
S100~S400: Exemplary steps of the TOA correction method

Claims (10)

Receiving a signal from a transponder of the aircraft;
storing the time of arrival (TOA) of the signal;
Comparing the pattern formed by the stored reception time with a predetermined reception time pattern; and
A step of replacing a reception time that is outside the detection margin of the reception time with any one of an extrapolated value, an average value, and a median value of the stored reception time,
The reception time pattern is,
A rising pattern in which the reception time increases over time,
A falling pattern in which the reception time decreases over time,
A complex pattern in which the reception time increases and decreases over time, and
A TOA correction method including a pattern in which the reception time does not change over time. According to paragraph 1,
The signal received from the aircraft's transponder is:
TOA correction method for Mode S signal (1090ES) with 1090MHz frequency. According to paragraph 1,
The step of storing the TOA of the signal is,
TOA correction method, which is the time at which the preamble of the signal is detected. According to paragraph 1,
The step of storing the TOA of the signal is,
TOA correction method performed with a precision of 2 ^-30 sec. delete According to paragraph 1,
The reception time pattern is,
The rising pattern includes a pattern in which the reception time increases linearly or non-linearly over time,
The falling pattern includes a pattern in which the reception time decreases linearly or non-linearly over time,
The composite pattern includes a pattern in which the reception time increases and then decreases over time, and a pattern in which the reception time decreases and then increases. According to paragraph 1,
The step of storing the TOA of the signal is,
A TOA correction method performed by recording and storing the TOA of at least five signals. In clause 7,
The step of comparing the reception time patterns is,
A TOA correction method performed by comparing the TOA of the five stored signals with the received time pattern. According to paragraph 1,
The TOA correction method wherein the reception time outside the detection margin is a value that is 20% or more greater than the value of the predetermined reception time pattern or a value that is 20% or more less than the value of the predetermined reception time pattern.

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