HK1170308A - Method for determining the distance of a vehicle from a radio beacon and radio beacon for this purpose - Google Patents

Description

Method for determining the distance of a vehicle from a radio beacon and radio beacon

Technical Field

The invention relates to a method for determining the distance of a vehicle passing through a radio beacon of a road toll system from the radio beacon, wherein the vehicle is equipped with an on-board unit which emits a signal having a known profile of its frequency over time. The invention further relates to a radio beacon for implementing such a method.

Background

In radio beacon-based road toll systems, for example, in accordance with the DSRC (dedicated short range communication) or WAVE (wireless access in a vehicular environment) standards, on-board units (OBUs) carried by vehicles communicate with radio beacons as soon as they pass through the geographically distributed radio beacons. Radio communication is commonly used to locate vehicles over the radio coverage area of a radio beacon in order to charge a fee for use of the location, or simply to transmit charging data generated by an OBU to the radio beacon on its way.

It is often desirable to determine the distance of a vehicle through a radio beacon, for example, to penalize a toll violation in the case of a multi-lane road: when a plurality of vehicles traveling in proximity to one another on different lanes pass through a radio beacon and one of their radio communications indicates a toll violation, for example a missed toll debit, an insufficient balancing of the toll account, a defective or incorrectly adjusted OBU, etc., or a lane-dependent rate or toll (multi-occupant lane) is to be calculated, then it is not uncommon to know which of the vehicles traveling in proximity to one another is responsible for being able to recognize this, for example visually on site or on a proof photograph of the road section of the beacon.

Various methods of determining distance are currently known. One solution is to use multiple physically offset receive antennas in the radio beacon to determine the location of the OBU in the radio receive field based on phase difference measurements between OBU signals received by the respective antennas. Another solution is known from us patent 5,790,052 and is based on doppler measurements of different relative velocities of the OBU with respect to physically offset receiving antennas of the radio beacon to determine the ratio of the distances from the two receiving antennas from the ratio of the velocity measurements. Finally, it would also be possible to use a separate radio beacon with low radio coverage for each lane. All these known solutions are expensive, not least because they are based on multiple receiving antennas.

Disclosure of Invention

The object set by the invention is to provide a method for determining the distance of an OBU from a radio beacon in a road toll system, which requires lower equipment expenditure than known solutions for the changeover.

This object is achieved in a first aspect of the invention by means of a method of the above-mentioned type, which method is distinguished by the steps of:

receiving the signal in a radio beacon during passage of the vehicle and recording a plot of signal frequency versus time against a known frequency plot;

detecting a change in the recorded frequency curve that exceeds a predetermined threshold;

looking for two remote areas in the frequency curve that are located before and after the detected change in time and that represent frequency changes below a threshold;

scaling the recorded frequency curve in such a way that the remote area exhibits a predetermined value; and

the distance is determined from the slope of the scaled frequency curve in its inflection point.

The present invention makes use of the following: in the direct pass, the doppler-related frequency change of the OBU signal is inversely proportional to the vertical distance from the radio beacon, when the distance is minimal, as long as the frequency curve is normalized to the natural speed of the vehicle. The latter is achieved by estimating the frequency curve in the "remote area": in these remote areas, the distance of the vehicle is very large compared to the vertical distance, and the vertical distance is negligible, and therefore the degree of doppler shift here depends essentially only on the intrinsic speed, and the degree of doppler shift can be determined from the intrinsic speed. Moreover, the dependence on the vertical distance, and therefore the vertical distance itself, can be determined by an analysis of the frequency curve compensated by the intrinsic velocity in the vicinity of the beacon, in which the greatest change in the frequency pattern ("doppler jump") occurs in its inflection point. As a result, from the radio communication between the OBU and the radio beacon and the single receiver and the single antenna, the passing distance can be determined.

The invention is applicable to on-board units of any type having a known profile of their transmission frequency over time, whether they transmit a constant frequency, for example a constant carrier frequency, in which case the known frequency profile is simply "constant", or they transmit a frequency that varies during a frequency hopping process, the frequency variation profile of which is known so that the frequency profile received in the radio beacon can be normalized or referenced to the known transmission frequency profile.

The road lane of the multi-lane road, on which the vehicle is moving, is then preferably determined by the defined distance. As a result of this, a toll violation in the case of a parallel pass through vehicle can be unambiguously associated with a lane and one or more vehicles located therein.

According to a first advantageous embodiment of the invention, the inflection point is determined by finding in the frequency curve a point at which the frequency has a predetermined value, in particular a nominal or quiescent frequency (frequency) of the OBU. This embodiment is therefore suitable for situations where the nominal frequency of radio communication of the OBU is previously known.

According to an alternative preferred embodiment of the invention, the inflection point is determined by finding the point in the frequency curve where the frequency corresponds to the average of the frequencies of the remote areas. The nominal frequency of the OBU need not be previously known for this embodiment and the process is automatically adjusted.

The doppler shift estimated with the method of the present invention can be measured at any desired frequency of the signal, whether it be the carrier frequency or preferably its modulation frequency. The modulation frequency is understood to be the frequency of any desired modulation of the OBU signal, whether it be one of a simple frequency or amplitude modulation, a modulation frequency of an OFDM modulation, or a pulse or pulse train modulation (as occurs as a result of a periodic transmission of the entire data block); such a block repetition rate may also be considered a modulation frequency, the doppler shift of which may be measured.

The method of the invention is applicable to all types of radio beacon based road toll systems. The method is particularly applicable to DSRC and WAVE road toll systems in which either the DSRC or the WAVE transmitter of the on-board unit is used to transmit signals. Other configurations using RFID technology, or any of the cellular (e.g., GSM, UMTS, LTE) and short-range radio technologies (e.g., bluetooth, WLAN) are also possible.

In a further aspect, the invention also provides a radio beacon for a road toll system, the radio beacon being arranged to determine the distance of a vehicle passing through it, the vehicle being equipped with an on-board unit which transmits a signal having a known profile of signal frequency over time, the radio beacon being characterised by:

a receiver configured to receive a signal through a vehicle;

a memory connected to the receiver, the memory configured to record a frequency versus time profile of the received signal relative to a known frequency profile over time;

a detector connected to the memory and configured to detect a change in the recorded frequency profile;

an estimation device connected to the probe and the memory and configured to look for two remote areas in the frequency curve that are located before and after the detected change in time and that represent frequency changes below a threshold;

a scaling device connected to the memory and the estimating device and configured to scale the recorded frequency profile in such a way that the remote area exhibits a predetermined value; and

a differentiator connected after the scaling means, the differentiator determining the slope of the scaled frequency curve in its inflection point and thereby determining the distance.

The radio beacon is preferably mounted on a multi-lane road and the differentiator is configured to determine the lane over which the vehicle is passing based on the distance.

In a first embodiment, the differentiator determines the inflection point by finding a point in the frequency curve where the frequency has a predetermined value.

Instead, the differentiator determines the inflection point by finding a point in the frequency curve where the frequency corresponds to the average of the frequencies of the remote areas.

In any case, the received signal may be modulated with a modulation frequency, and the frequency may be a modulation frequency obtained by demodulation in the receiver.

The receiver is preferably a DSRC or WAVE transmitter.

With regard to the advantages of the radio beacon according to the invention, reference is made to the above embodiments of the method.

Drawings

The invention will be explained in more detail below on the basis of preferred exemplary embodiments, with reference to the attached drawings, in which:

FIG. 1 is a schematic plan view of a radio beacon on a multi-lane roadway showing the geometric relationship during the passage of two vehicles;

FIG. 2 shows frequency curves of signals of two vehicles when passing through a radio beacon;

FIG. 3 shows the frequency curve of FIG. 2 after scaling;

FIG. 4 shows the derivative of the scaled frequency curve of FIG. 3; and

fig. 5 is a block diagram of a radio beacon of the present invention.

Detailed Description

Fig. 1 shows a road toll system 1, which road toll system 1 comprises a plurality of geographically distributed radio beacons 2 (only one shown for illustration purposes), which radio beacons 2 are connected to a central control unit (not shown) of the road toll system 1 via a data connection 3. The radio beacons 2 are each mounted on a roadway 4, which roadway 4 may include a plurality of roadways or lanes 5, 6.

For example, the radio beacon 2 includes a local computer 7, a (transceiver /) receiver 8 and a camera 9, the camera 9 being operated by the computer 7 to record images of the road 4 with its lanes 5, 6 for the purpose of penalising toll violations.

The (transceiver) receiver 8 is used for radio communication 10 with an on board unit or OBU 11, which on board unit or OBU 11 is carried by a vehicle 12 passing the radio beacon 2 in the lane 5, 6. The radio communications 10 are typically two-way packet connections. The analysis of the signal transmitted by the OBU 11 to the (transceiver /) receiver 8 of the radio signal station 2 is sufficient for the purposes of the present invention and therefore only the OBU 11 transmitting the signal 10 to the receiver 8 of the radio signal station 2 will be described below. However, it is to be understood that in practice, the signals are also sent in the opposite direction.

The vehicle 12 with the OBU 11 is in the lanes 5, 6 at different speeds v₁、v₂At different passing or perpendicular distances a₁、a₂By the radio beacon 2, more precisely by its receiver 8. In this case, the signals 10 emitted by the OBU 11 are respectively subjected to frequency-dependent doppler shifts according to the following known formula

Wherein

f_SThe transmission frequency of the signal 10 of the OBU 11;

f_Ddoppler shift of the signal 10 in the radio beacon 2 the reception frequency if the OBU 11 is facing motion towards the radio beacon 2;

v-the speed of the OBU 11; and

c-speed of light.

If the OBU 11 travels over a distance 2 at a distance a, equation (1) can be written by means of geometric considerations:

wherein

a-the vertical distance of the OBU 11 from the radio beacon 2 in the coordinate system of fig. 1;

x-the horizontal distance of the OBU 11 from the radio beacon 2 in the coordinate system of fig. 1; suppose an OBUConstant velocity v or v of 11 horizontal distances₁、v₂Also corresponds to time t; and

f_Bthe doppler shift of the signal 10 in the radio beacon 2 receives the frequency when the OBU 11 is moving through the radio beacon 2 at distance a.

FIG. 2 shows the reception frequency f relative to the horizontal distance x or time t_BTwo exemplary curves of (a). The solid line 13 represents the reception frequency curve of the OBU 11 in the lane 5 and the dashed line 14 represents the reception frequency curve of the OBU 11 in the lane 6. As can be seen, at the maximum variation of the frequency curves 13, 1417 in the "remote areas" 15, 16 before and after the pole, the doppler related frequency shift ± Δ f₁、±Δf₂Very small, i.e. in remote areas 15, 16, frequency variations f_B' lies below the significance threshold epsilon.

Thus, in the far zones 15, 16 (and naturally also far outside these zones), the degree of doppler shift ± Δ f is almost no longer dependent on the passing distance a, and instead almost solely on the velocity v. The influence of the vehicle speed v on the frequency curves 13, 14 can thus be eliminated by scaling these curves in such a way that they assume the same value, for example a predetermined value ± Δ F, in the remote regions 15, 16, respectively.

Fig. 3 shows the result of such a scaling, in fig. 3 the indicated frequency curves 13, 14 have been scaled ("normalized") so that they exhibit a predetermined value ± Δ F in the remote areas 15, 16.

The scaled frequency curves 13 ', 14' thus depend more on the ratio a/x, i.e. on the ratio of the transit distance a to the horizontal distance x or to the time t, according to the following formula

As can be seen from fig. 3, the scaled frequency curves 13 ', 14' are at their slopesThe aspects differ particularly clearly at the position x-t-0, where their curves at the same time point represent the inflection point 20: the larger the passing distance a, the "sharper" the scaled frequency curves 13 ', 14', i.e. the slope f at the inflection point 20_BThe lower the' is. Thus, the passing distance a and the slope f_BIs inversely proportional, i.e.

Slope f at inflection point 20_B' may be determined by differentiating the scaled frequency curves 13 ', 14 ' and the result of the differentiation is shown in fig. 4. Knowing the lane width b of the lanes 5, 6₁、b₂In the case of (a) in (b),and then based on the passing distance a determined in this manner₁、a₂The respective lane 5, 6 in which the OBU 11 is located during transmission of its signal 10 can be determined. Passing distance a₁、a₂A simple relative comparison of (a) is often sufficient to determine the local order of the vehicles.

It has been assumed hitherto that the transmission frequency f of the signal 10 of the OBU 11 is_SIs constant, i.e. its own frequency curve is a constant curve. However, it is also possible for the OBU 11 to transmit a signal 10 having a transmission frequency profile which is not constant over time, for example in the case of frequency hopping radio communication, in which case the transmission frequency f_SConstantly changing according to a predetermined or known pattern. The recorded reception frequency curves 13, 14 are related to the transmission frequency f of the OBU 11_SThe previously known curve over time, whether it is constant or varying, i.e. referenced or normalized against these, is recorded so that the effect of the known variation in the transmit frequency of the OBU 11 can be compensated.

Therefore, in summary, the method for determining the passing distance a of the OBU 11 passing through the radio beacon 2 is configured as follows:

first, the frequency curves 13, 14 of the signal 10 of the OBU 11 are plotted against time t (═ x), possibly relatively based on the transmission frequency f_SPreviously known curves over time. Then, a region 17 is approximately determined in the frequency curves 13, 14, at which region 17 a significant change does occur, i.e. a change of importance does occurExceeding a predetermined detection threshold sigma. This is used to obtain a temporal reference point for finding two remote areas 15, 16, which areas 15, 16 must be located before and after the change 17 and move so far away from this change 17 that there are no further significant frequency changes in these areasThis occurs, i.e. it lies below a predetermined importance threshold epsilon.

Knowing the remote areas 17, 18 and the Doppler shift + - Δ f present therein₁、±Δf₂(they can also be considered quasi-constant in that their variation does not exceed the importance threshold epsilon.) the frequency curves 13, 14 are now scalable so that they exhibit the same predetermined value + -deltaf in their remote areas 15, 16, respectively.

Then an inflection point 20 is found in the scaled frequency curves 13 ', 14'. For this purpose, a position x or a time t is sought in the frequency curve, at which position x or time t the frequency f is received_BOr an average of the frequencies between the "quasi-constant" remote areas 15, 16 ("median") or, if the nominal frequency of the signal 10 of the stationary OBU 11 is known, this nominal frequency. The inflection point 20 may be determined in two ways, namely both before the scaling of the frequency curves 13, 14 and after the scaling of the scaled frequency curves 13 ', 14'.

After the inflection point 20 is determined, the slope f of the scaled frequency curves 13 ', 14' in the inflection point 20 may now be determined_B' (x ═ t ═ 0) (see fig. 4), and from this, the passing distance a or a can be determined₁、a₂As explained above.

Fig. 5 shows an exemplary hardware configuration of the radio beacon 2 used to perform the outlined method. The radio beacon 2 has a memory 21 connected to the receiver 8, in which memory 21 the time-frequency curves 13, 14 of the received signal 10 are recorded. A detector 22 connected to a memory 21 detects the region of change 17And this information 17 is fed to the estimating means 23. The evaluation device 23 thus determines the frequency curves 13, 14 havingAnd by means of such information 15, 16 activates a scaling means 24, which scaling means 24 scales the frequency curves 13, 14To the scaled frequency curves 13 ', 14'. The latter is fed to a differentiator 25, which differentiator 25 calculates the slope at the location x-t-0 of its inflection point 20To thereby determine the passing distance a₁、a₂。

The components 21-25 may be implemented, for example, by the local computer 8 of the radio beacon 2.

The invention is not limited to the embodiments shown but covers all variations and modifications falling within the framework of the appended claims.

Claims (12)

1. A method for determining the distance (a) of a vehicle (12) passing a radio beacon (2) of a road toll system (1) from the radio beacon (2), wherein the vehicle (12) is equipped with an on-board unit (11), the on-board unit (11) emitting a signal having a signal frequency (f)_S) Signal (10) of a known profile over time, characterized by the steps of:

during the passage of the vehicle (12), a signal (f) is received in the radio beacon (2)_b) And recording the signal frequency (f) relative to a known frequency curve_b) Curves over time (13, 14); detecting in memoryA change (17) in the recorded frequency curve (13, 14) exceeding a predetermined threshold value (σ);

two remote regions (15, 16) which are located in time before and after the detected change (17) are sought in the frequency curve (13, 14) and the two remote regions (15, 16) represent a frequency change (f) below a threshold value (epsilon)_b′)；

Scaling the recorded frequency curves (13, 14) in such a way that the remote areas (15, 16) exhibit a predetermined value (± Δ F); and

according to the slope (f) of the scaled frequency curve (13 ', 14') in its inflection point (20)_b') determining said distance (a).

2. The method according to claim 1, characterized in that the lanes (5, 6) of the multi-lane road (4) on which the vehicle (12) is moving are determined by the distance (a).

3. Method according to claim 1 or 2, characterized in that the frequency (f) is found by finding the frequency (f) in a frequency curve (13, 14, 13 ', 14')_B) A point having a predetermined value determines an inflection point (20).

4. Method according to claim 1 or 2, characterized in that the frequency (f) is found by finding the frequency (f) in a frequency curve (13, 14, 13 ', 14')_B) The inflection point (20) is determined by a point corresponding to the average of the frequencies of the remote areas (15, 16).

5. Method according to one of claims 1 to 4, characterized in that the signal (10) is transmitted by the on-board unit (11) as at least one carrier frequency modulated with a modulation frequency, wherein the frequency (f) is_B) Is the modulation frequency.

6. The method according to one of claims 1 to 4, characterized in that a DSRC or WAVE transmitter of the onboard unit (11) is used to transmit the signal (10).

7. A radio beacon (2) for a road toll system (1), the radio beacon (2) being arranged to determine the distance (a) of a vehicle (12) passing the radio beacon, the vehicle being provided with an on-board unit (11), the on-board unit (11) emitting a signal having a signal frequency (f)_S) Signal (10) of a known profile over time, characterized in that:

a receiver (8) configured to receive a signal (10) through a vehicle (12);

a memory (21) connected to the receiver (8), the memory (21) being configured to record the frequency (f) of the received signal (10) with respect to a known frequency curve over time_B) Curves over time (13, 14);

a detector (22) connected to the memory (21) and configured to detect a change (17) in the recorded frequency curve (13, 14);

an estimation device (23) connected to the detector (22) and to the memory (21) and configured to find in the frequency curve (13, 14) two remote areas (15, 16) located before and after the detected change (17) in time, and the two remote areas (15, 16) representing a frequency change (f) below a threshold (epsilon)_B′)；

-scaling means (24) connected to the memory (21) and to the estimation means (23) and configured to scale the recorded frequency curves (13, 14) in such a way that the remote areas (15, 16) exhibit a predetermined value (± Δ F); and

a differentiator (25) connected after the scaling means (24), the differentiator (25) determining the slope (f) of the scaled frequency curve (13 ', 14') in its inflection point (20)_B') and determining therefrom the distance (a).

8. The radio beacon according to claim 7, characterised in that the radio beacon is installed on a multi-lane road (4) and the differentiator (25) is configured to determine the lane (5, 6) over which the vehicle (12) is passing depending on the distance (a).

9. Radio signal station according to claim 7 or 8, characterized in that the differentiator (25) is arranged to determine the difference between the frequencies (f) by finding the frequency (f) in the frequency curve (13 ', 14')_B) An inflection point (20) is determined at a point in the frequency curve (13, 14) having a predetermined value.

10. Radio signal station according to claim 7 or 8, characterized in that the differentiator (25) is arranged to determine the difference between the frequencies (f) by finding the frequency (f) in the frequency curve (13 ', 14')_B) The inflection point (20) is determined by a point corresponding to the average of the frequencies of the remote areas (15, 16).

11. Radio beacon according to one of claims 7 to 10, characterised in that the received signal (10) has at least one carrier frequency modulated with a modulation frequency and that said frequency (f) is_B) Is a modulation frequency obtained by demodulation in the receiver (8).

12. The radio beacon of one of claims 7 to 11, characterized in that the receiver (8) is a DSRC or WAVE transmitter.