GB2567138A - Method of automatic calibration - Google Patents
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- GB2567138A GB2567138A GB1714273.8A GB201714273A GB2567138A GB 2567138 A GB2567138 A GB 2567138A GB 201714273 A GB201714273 A GB 201714273A GB 2567138 A GB2567138 A GB 2567138A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
- H04B17/20—Monitoring; Testing of receivers
- H04B17/21—Monitoring; Testing of receivers for calibration; for correcting measurements
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
- G01R29/08—Measuring electromagnetic field characteristics
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
- H04B17/30—Monitoring; Testing of propagation channels
- H04B17/309—Measuring or estimating channel quality parameters
- H04B17/318—Received signal strength
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- Computer Networks & Wireless Communication (AREA)
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Abstract
A method of automatic calibration, performed for remote control 1 of access system, e.g. for a vehicle 3; the remote control being able to communicate on low frequency. The method comprises applying at least one low-frequency field along at least one axis, sending at least one low-frequency telegram with information about at least that axis; performing measurements of the received signal strength indicator along at least one axis, adding the measured values, subtracting the minimum value and the maximum value, building an average, and checking deviation of the measured values against the average; repeating as long as a threshold for a next field strength is reached a number of times; calculating offset and gain for at least one axis and saving the respective values into a dedicate memory; continuing measurements of the received signal strength indicator for at least one axis at the same field strength, but in the next range and repeating the above steps for each calibration point on at least one axis. The fields may be applied along the axes in serial or parallel modes.
Description
The invention refers to a method of automatic calibration performed for remote control of access systems.
Wireless sensor networks are used more and more for object localization by means of radio waves, such as the localization based on the received signal strength indication. The received signal strength indicator (or RSSI) returns the value of the received radio signal power in a wireless environment, in relative units, as analog level sampled by an internal analog/digital converter. By this way, the received signal strength indicator becomes a distance estimator. The data quality and reliability play an important role, therefore calibration is mandatory.
Such techniques involving localization based on the received signal strength indication are used extensively in keyless entry systems. For example, for vehicles it has been designed a sophisticated remote keyless system, combining the so-called 'Passive Start and Entry' (or PASE) with remote control (or RKE - Remote Keyless Entry), that exchanges code to car via radio waves as to allow opening, closing and protecting the car. To use this keyless entry system, developed by Continental Engineering Services, the driver needs nothing more than an identification device. The car recognizes the driver automatically upon approach and unlocks the doors, allowing access to the vehicle. As soon as the identification device is located within the vehicle, the driver can start the engine by pushing the start/stop button. If the driver gets out of the vehicle, PASE locks the vehicle - either automatically or at the press of a button.
The remote control, also known as key fob or smart fob, actually a hidden touch-activated keypad, usually comprises a transponder and a low-frequency antenna for the passive and entry system, and uses a radio-frequency as well, by which it communicates with a base station, in a range up to 100 m.
In general, radio-frequency remote controls are manually calibrated, using low-frequency/radio-frequency communication. The calibration aims to set the correction factors (namely offset and gain), specific to the calibrated device, factors which are then written into a memory (for example, an electrically-erasable programmable read-only memory - EEPROM), using a diagnosis command (also by low-frequency/radio-frequency communication). The disadvantages of manual calibration are obvious: it requires human intervention and a rather long time to perform such a procedure .
As for the automatic calibration, the Chinese patent document CN101793948B discloses a low-frequency calibration system and method for a passive entry system for vehicles, based on the value of the received signal strength. According to the mentioned document, a measurement module is manufactured by using a low-frequency receiving antenna at the key end of the passive entry system and an integrated circuit provided with a function of received signal strength indication; measurement path planning is realized by using a measurement control module; the automatic continuous positioning of the measurement module is realized and the calibration time is shortened by using a three-dimensional positioning instrument; and storage of the measured point coordinates and the corresponding measured results are triggered by using a positioning confirmation signal fed back by the three-dimensional positioning instrument. The system and the afferent method avoid the need for a standard low-frequency receiving antenna and a standard receiver, but require equivalent components to be introduced into system, meaning additional communication on low and radio frequencies .
Another more recent patent application, EP 2942760A1, discloses a method of locating a key, based on measuring the value of received signal strength indicator. The key is determined to be located within a predefined area if the difference between the first received signal strength and the second received signal strength is above a preset threshold. The threshold may be determined through the key calibration steps and stored in the base station of the system, but no specific details are given about the calibration steps per se.
The present invention addresses at least one above-mentioned disadvantage .
The technical problem to be solved is to perform automatic calibration and to minimize the communication on low/radio frequencies as much as possible.
The objective of the invention is to design an automatic calibration algorithm able to calculate the correction factors and save them into the memory of remote control.
In this respect, an aspect of the present invention is to provide a method for automatic calibration for a remote control, the remote control being able to communicate on low frequency, the method comprising: sending a telegram for the remote control wake-up; receiving the telegram by the remote control, activating it and performing an auto-zero measurement; applying at least one low freguency field along at least one axis, and sending at least one low-frequency telegram with information about at least that axis; performing measurements of the received signal strength indicator, along at least one axis, for at least one field applied; extracting a minimum value and a maximum value out of the measured values; adding the measured values, subtracting the minimum value and the maximum value, building an average, and checking deviation of the measured values against the average, as to be sure the measured values are not out of range; repeating the measurements as long as a threshold for a next field strength is reached a number of times, as to resynchronize the remote control within the calibration environment; based on the actual average of values of the received signal strength indicator, calculating offset and gain for at least one axis and saving the respective values into a dedicated memory able to store them; continuing measurements of the received signal strength indicator for at least one axis at the same field strength, but in the next range or measuring them as long as the threshold for the next field is reached a certain number of times; repeating the previous steps for each calibration point on at least one axis; in case a failure occurs, a failure code gives that information; as a final step, if the calibration is successful, the remote control send a radio frequency answer to the environment, to indicate the successful completion of calibration.
By using the automatic calibration method according to the invention, efficient, accurate and complex operations are performed in terms of seconds, without human intervention.
A first embodiment of the invention provides a serial automatic calibration, comprising: sending a telegram for the remote control wake-up; receiving the telegram by the remote control, activating it and performing an auto-zero measurement; applying a first low frequency field along a first axis, and sending one low-frequency telegram with information about first axis; performing measurements of the received signal strength along first axis, for the first field applied; extracting a minimum value and a maximum value out of the measured values; adding the measured values, subtracting the minimum value and the maximum value, building an average, and checking deviation of the measured values against the average, as to be sure the measured values are not out of range; repeating the measurements as long as a threshold for a next field strength is reached a number of times; applying a second low freguency field along first axis and repeating the aforesaid steps, as long as a threshold for a next field strength is reached a number of times; based on the actual average values of the received signal strength, calculating offset and gain for first axis and saving the respective values into memory; continuing measurements of received signal strength at the same field strength, but in the next range or measuring them as long as the threshold for the next field is reached a certain number of times; activating a second axis, by applying the first low frequency field along a second axis and sending another low-frequency telegram with information about the second axis; repeating the above mentioned steps for the second axis; activating a third axis, by applying the first low frequency field along the third axis and sending another low-frequency telegram with information about the third axis; repeating the above mentioned steps for the third axis; and repeating the above steps for each calibration point. In case of failure, a failure code gives that information, and in case of success, the remote control sends a radio-frequency answer to the environment, to indicate the successful completion of calibration.
The advantage of a serial automatic calibration, according to invention, is that it saves sequentially the correction factors into memory.
A second embodiment of the invention provides a parallel automatic calibration, comprising: sending a telegram for the remote control wake-up; receiving the telegram by the remote control, activating it and performing an auto-zero measurement;
applying a first low frequency field, and sending a single low-frequency telegram with information about all axes; performing measurements of the received signal strength, for the first field applied and for the first axis; deactivating the first axis and activating the second axis; performing measurements of the received signal strength, for the first field applied and for the second axis; deactivating the second axis and activating the third axis; performing measurements of the received signal strength, for the first field applied and for the third axis; extracting a minimum value and a maximum value out of the measured values; adding the measured values, subtracting the minimum value and the maximum value, building an average, and checking deviation of the measured values against the average; deactivating the third axis and activate the first axis; measuring as long as a threshold for the next field strength is reached a number of times; applying a second low freguency field along first axis and repeating the aforesaid steps provided for the first field applied, as long as a threshold for a next field strength is reached a number of times; based on the actual average values of the received signal strength, calculating offset and gain and saving the respective values into memory; and repeating the above steps for each calibration point. In case of failure, a failure code gives that information, and in case of success, the remote control sends a radio-frequency answer to the environment, to indicate the successful completion of calibration.
The second embodiment of invention gives the advantage of requiring less input overall (just one low-frequency telegram for all three axes, one threshold for every three measurements).
Next, there are given few drawings, in order to better illustrate the invention embodiments, namely:
- Fig.l - the calibration environment, comprising a car with a radio-frequency remote control and the correspondent low-frequency field, generated by at least one antenna, the car being able to read a computer-readable medium containing the programming instructions of the automatic calibration method, according to invention;
- Fig.2 - a section cut through the remote control, revealing an analog/digital converter for the received signal strength indication and a memory;
- Fig.3 - the measured values of received signal strength indicator for a non-calibrated device, as analog values, having a reference value as threshold;
- Fig. 4 - a block-diagram of a serial mode of performing the method;
- Fig. 5 - a block-diagram of a parallel mode of performing the method.
According to the invention, a radio-frequency remote control 1 performs a three-dimensional measurement (on X, Y, Z axes) of low-frequency field strength generated by at least one antenna 2 of a vehicle 3 and sends the measured value (actually, the indicators of the received signal strength) to the corresponding vehicle 3. Based upon the received value, a distance d between radio frequency remote control 1 and car 3 is calculated (see Fig.
1) ·
In order to obtain a good precision, it is mandatory to perform calibration of radio frequency remote control 1, as to generate a linear behavior between the applied field's magnetic flux and the measured received signal strength indicator, and also to compensate potential internal errors . The calibration is done in many points (and/or ranges) and on all axes (X, Y, Z).
In order to perform the calibration based on the received signal strength indication, the remote control is provided with a block comprising an analog/digital converter and a memory (for example, an EEPROM, as illustrated by Fig. 2).
The automatic calibration method, according the invention, is to be performed as follows:
a. sending a telegram for the remote control wake-up;
b. receiving the telegram by the remote control, activating the convertor block and performing an auto-zero measurement;
c. applying at least one low frequency field along at least one axis, and sending at least one low-frequency telegram with information about at least that axis;
d. performing measurements of received signal strength indicator along at least one axis, for at least one field applied; adding the measured values, subtracting the minimum value and the maximum value, building an average, and checking deviation of the measured values against the average; repeating as long as a threshold for a next field strength is reached a number of times;
e. based on the actual average received signal strength values, calculating offset and gain for at least one axis and saving the respective values into memory;
f. continuing measurements of the received signal strength indicator for at least one axis at the same field strength, but in the next range or measuring them as long as the threshold for the next field is reached a certain number of times;
g. repeating the steps c-f for each calibration point on at least one axis;
h. in case a failure occurs, the situation is signalized by a failure code;
i. In case of successful calibration, the remote control sends an answer to the environment, to indicate the successful completion of calibration.
| More particularly, the method is | to be | described | in two exemplary | |
| modes : | ||||
| - A first mode, | when axes | are | serially | calibrated. For |
| activating another | axis, a | new | trigger | (the so-called |
'low-frequency telegram') is needed. In total, for all three axes, three low-frequency telegrams are needed;
- A second mode, when axes are calibrated in parallel, just one trigger (low-frequency telegram) is needed.
Example 1: Serial mode
In this example, illustrated by the block-diagram of fig. 4, the low-frequency field generated by antenna (a Helmholtz coil, for example) is serially applied on axes, one axis at a time . The first axis (for example, X-axis) is completely calibrated, which means many ranges adjusted, then the field is applied to the next axis (for example, Y-axis), until that second axis is also completely calibrated, and finally is applied to the third and last axis (for example, Z-axis).
First mode (serial) of the automatic calibration method comprises :
a. sending a telegram for the remote control wake-up;
b. receiving the telegram by the remote control, activating the block and performing an auto-zero measurement;
c. applying the first low frequency field along the first axis, and sending first low-freguency telegram with information about first axis;
d. performing measurements of the received signal strength indicator along first axis, for the first field applied; adding the measured values, subtracting the minimum value and the maximum value, building an average, and checking deviation of the measured values against the average; repeating measurements as long as a threshold for a next field strength is reached a number of times;
e. applying a second low frequency field along first axis and repeating the aforesaid steps, as long as a threshold for a next field strength is reached a number of times;
f. based on the actual average values of the received signal strength indicator, calculating offset and gain for first axis and saving the respective values into memory;
g. continuing measurements of received signal strength indicator at the same field strength, but in the next range or measuring them as long as the threshold for the next field is reached a certain number of times;
h. activating the second axis, by applying the first low frequency field along the second axis and sending the second low-frequency telegram with information about the second axis;
i. repeating the aforesaid steps d-g for the second axis;
j. activating the third axis, by applying the first low frequency field along the third axis and sending the third low-frequency telegram with information about the third axis;
k. repeating the aforesaid steps d-g for the third axis; and
l. repeating the above mentioned steps c-k for each calibration point;
m. in case a failure occurs, the situation is signalized by a failure code;
n. in case of successful calibration, the completion of calibration is indicated by a radio answer sent by the remote control to the environment.
According to the illustration of a remote control not-calibrated (see Fig. 3), either measurements at the same field strength indicator in the next range are performed or the threshold for the next field strength is reached. This threshold provides a kind of resynchronization between the calibration environment and the remote control, respectively the software itself. How this threshold looks like as reference level is shown in Fig. 3.
The measured values have to be included in an already defined range. All this effort is done in order to get a more precise measurement at each specific calibration point and has to be similarly performed at every point.
The sequence for all calibration points of an axis automatically proceeds in the described way. After successfully calibration of the first axis (e.g., X), the next low-frequency telegram with the information about the axis is sent and the remote control automatically starts again the steps of calibration, similar to those performed for the first axis, and the same is done for the third axis .
Example 2: Parallel mode
In this mode, illustrated by the block-diagram of fig. 5, the low-frequency field is applied in parallel on all three axes. The goal is to calibrate them simultaneously, which means measuring the calibration point of the first axis (e.g., X), deactivating the first axis, activating the second axis (e.g., Y, which has the same or similar field strength), measuring the calibration point of the second axis, then deactivate the second axis and activate the third axis (e.g. Z, also the same or similar field strength) and do the same.
Second mode (parallel) of the automatic calibration method comprises :
a. sending a telegram for the remote control wake-up;
b. receiving the telegram by the remote control, activating the block and performing an auto-zero measurement;
c. applying the first low frequency field, and sending a single low-frequency telegram with information about all axes;
d. performing measurements of the received signal strength indicator for the first field applied and for the first axis ;
e. deactivating the first axis and activating the second axis ;
f. performing measurements of the received signal strength, for the first field applied and for the second axis;
g. deactivating the second axis and activating the third axis ;
h. performing measurements of the received signal strength indicator, for the first field applied and for the third axis ;
i. adding the measured values, subtracting the minimum value and the maximum value, building an average, and checking deviation of the measured values against the average;
j . deactivating the third axis and activate the first axis ;
k. measuring as long as a threshold for the next field strength is reached a number of times;
l. applying a second low frequency field along first axis and repeating the aforesaid steps d-k for the first field applied, as long as a threshold for a next field strength is reached a number of times;
m. based on the actual average values of the received signal strength indicator, calculating offset and gain and saving the respective values into memory; and
n. repeating the aforesaid steps c-m for each calibration point;
o. in case a failure occurs, the situation is signalized by a failure code;
p. in case of successful calibration, the completion of calibration is indicated by a radio answer sent by the remote control to the environment.
In fact, in this mode the method starts again with the first axis (X) , waiting for the next higher field strength, then performing threshold measurements like in the first mode. The calibration points are measured at that second field strength on all three axes and the method continues as long as all of them are measured and the correction factors are calculated.
The difference between the two modes is that, for first mode, a low-frequency telegram is necessary for each axis, so that the remote control to know which of the input shall be activated, that means overall three low-frequency telegrams. Second mode needs only one low-frequency telegram for the whole procedure. Furthermore, in first mode, a threshold is mostly needed after every point, as for the remote control to know when the next field is available at that particular axis . In comparison to the second mode, the threshold is only needed after every third measurement.
The gain is calculated using the following formula:
f CALIB POINT H-CALIB POINT L crx = max 1,------=--- ~ ----=-------=- · m, < Mraw-H 1rAW-L
CALIB POINT H is the reference field [nT] for higher calibration point from a range;
- CALIB POINT L is the reference field [nT] for lower calibration point from a range;
- Mraw h is the ADC value for higher measurement point from a range;
- MraW l is the ADC value for lower measurement point from a range;
- mi = 10 0 0 .
The offset for each range is calculated with the following formula:
Γ, CALIB POINT H-m,
Or. = max L------==----V CRx where
- CALIB POINT H is the reference field [nT] for higher cali5 bration point from a range;
- Mraw h is the ADC value for higher measurement point from a range;
- mi = 10 0 0 .
Claims (4)
1. Method of automatic calibration, performed for remote control of access systems, the remote control being able to communicate on low frequency, the method being initiated by sending a telegram for remote control wake-up, then receiving the telegram by the remote control, activating it and performing an auto-zero measurement, characterized by that it comprises the next steps:
a. applying at least one low-frequency field along at least one axis, and sending at least one low-frequency telegram with information about at least that axis; performing measurements of the received signal strength indicator, along at least one axis, for at least one field applied; extracting a minimum value and a maximum value out of the measured values; adding the measured values, subtracting the minimum value and the maximum value, building an average, and checking deviation of the measured values against the average, as to be sure the measured values are not out of range; repeating the measurements as long as a threshold for a next field strength is reached a number of times, as to resynchronize the remote control within the calibration environment ;
b. based on the actual average of values of the received signal strength indicator, calculating offset and gain for at least one axis and saving the respective values into a dedicated memory able to store them;
c. continuing measurements of the received signal strength indicator for at least one axis at the same field strength, but in the next range or measuring them as long as the threshold for the next field is reached a certain number of times;
d. repeating the steps a-c for each calibration point on at least one axis;
e. in case a failure occurs, a failure code gives that information;
f. as a final step, if the calibration is successful, the remote control send a radio freguency answer to the environment, to indicate the successful completion of calibration.
2. Method of automatic calibration, according to claim 1, characterized by that, in a serial mode, the fields are sequentially applied along axes, as follows: applying the first low-frequency field along first axis, and sending first low-frequency telegram with information about first axis; for the first field applied, performing measurements of the received signal strength indicator along first axis; applying a second low-frequency field along first axis and performing measurements of the received signal strength indicator along first axis; activating the second axis, by applying the first low-frequency field along the second axis and sending the second low-frequency telegram with information about the second axis; performing the received signal strength indicator measurements along the second axis; activating the third axis, by applying the first low-frequency field along the third axis and sending the third low-frequency telegram with information about the third axis; performing the received signal strength indicator measurements along the third axis; continuing the rest of steps.
3. Method of automatic calibration, according to claim 1, characterized by that, in a parallel mode, the fields are applied along axes in parallel, as follows: sending a single low-frequency telegram with information about all three axes;
applying the first field in parallel on all three axes; performing measurements of the received signal strength indicator along the first axis; deactivating the first axis and activating a second axis; performing measurements of the received signal strength 5 indicator along the second axis; deactivating the second axis and activating a third axis; performing the received signal strength indicator measurements along the third axis; continuing with the rest of steps.
10
4. A computer-readable medium, having thereon programming instructions executable in a vehicle to perform the calibration method of claim 1.
Intellectual Property Office
3. Method of automatic calibration, according to claim 1, characterized by that, in a parallel mode, the fields are applied along axes in parallel, as follows: sending a single low-frequency telegram with information about all three axes; applying the first field in parallel on all three axes; performing the measurements received signal strength indicator measurements along the first axis; deactivating the first axis and activating a second axis; performing measurements of the received signal strength indicator along the second axis; deactivating the second 5 axis and activating a third axis; performing the received signal strength indicator measurements along the third axis; continuing with the rest of steps.
4. A computer-readable medium, having thereon programming 10 instructions executable in a vehicle to perform the calibration method of claim 1.
Amendments to the Claims have been filed as follows: Patent claims
1. Method of automatic calibration, performed for remote control of access systems, the remote control being able to communicate on low frequency, the method being initiated by sending a telegram for remote control wake-up, then receiving the telegram by the remote control, activating it and performing an auto-zero measurement, characterized by that it comprises the next steps:
a. applying at least one low-frequency field along at least one axis, and sending at least one low-frequency telegram with information about at least that axis; performing measurements of the received signal strength indicator, along at least one axis, for at least one field applied; extracting a minimum value and a maximum value out of the measured values; adding the measured values, subtracting the minimum value and the maximum value, building an average, and checking deviation of the measured values against the average; repeating the measurements as long as a threshold for a next field strength is reached at least one time, as to resynchronize the remote control within the calibration environment;
b. based on the previously built average of values of the received signal strength indicator, calculating offset and gain for at least one axis and saving the respective values into a dedicated memory able to store them;
c. continuing measurements of the received signal strength indicator for at least one axis at the same field strength, but in the next range or measuring them as long as the threshold for the next field is reached at least one time;
d. repeating the steps a-c for each calibration point on at least one axis;
e. in case a failure occurs, a failure code gives that information;
f. as a final step, if the calibration is successful, the remote control send a radio frequency answer to the environment, to indicate the successful completion of calibration.
2. Method of automatic calibration, according to claim 1, characterized by that, in a serial mode, the fields are sequentially applied along axes, as follows: applying the first low-frequency field along first axis, and sending first low-frequency telegram with information about first axis; for the first field applied, performing measurements of the received signal strength indicator along first axis; applying a second low-frequency field along first axis and performing measurements of the received signal strength indicator along first axis; activating the second axis, by applying the first low-frequency field along the second axis and sending a second low-frequency telegram with information about the second axis; performing the received signal strength indicator measurements along the second axis; activating the third axis, by applying the first low-frequency field along the third axis and sending a third low-frequency telegram with information about the third axis; performing the received signal strength indicator measurements along the third axis; continuing the rest of steps.
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Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101793948A (en) * | 2010-01-29 | 2010-08-04 | 重庆长安汽车股份有限公司 | Low-frequency calibration system and method for passive entry system for vehicles |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101793948A (en) * | 2010-01-29 | 2010-08-04 | 重庆长安汽车股份有限公司 | Low-frequency calibration system and method for passive entry system for vehicles |
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| GB2567138B (en) | 2020-04-01 |
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