CN112485759A - Indoor positioning method and device based on Bluetooth backscattering - Google Patents
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Abstract
The invention belongs to the technical field of indoor positioning, and particularly relates to an indoor positioning method and device based on Bluetooth backscattering. The utility model aims to have higher stability through the mixture of backscatter technique and bluetooth location for the location, the error rate is lower, and the receiver can adopt general receiver simultaneously, and application scope is more general, has effectively reduced equipment cost.
Description
Technical Field
The invention belongs to the technical field of indoor positioning, and particularly relates to an indoor positioning method and device based on Bluetooth backscattering.
Background
Positioning is one of core technologies of position service, everything interconnection and artificial intelligence application. In the outdoor environment, the satellite positioning technology such as the mature GPS and the Beidou is mainly used, and because satellite signals are difficult to penetrate through buildings and the indoor environment is complex and changeable, the satellite positioning technology is difficult to be used for indoor positioning. Indoor positioning technology is currently not mature enough, but is becoming increasingly important. Therefore, the indoor positioning is realized accurately, reliably and in real time, the public requirements are met, and the method has very important scientific significance and social application value. However, the indoor positioning is constrained by the aspects of spatial layout, topology, complex signal environment and the like, and it is still very challenging to realize accurate, reliable and real-time indoor positioning and meet the requirements of various positioning in the prior art.
At present, researchers have proposed many solutions to indoor positioning technologies based on radio frequency identification technology, and realize indoor real-time three-dimensional positioning by using an environment backscattering technology in combination with beam scanning of a multi-antenna tag, for example, in the patent of application No. 201710697495.1, the method is to transmit a signal through a radio frequency source, then the tag performs environment backscattering, a mobile terminal detects the received tag signal, and finally performs three-dimensional positioning of the mobile terminal; however, this method has a great limitation in implementation, and the receiving end needs a specially designed receiver to be used, so that this receiver has a large volume and high cost, and is not easy to popularize. An indoor positioning method based on bluetooth beacons, such as the indoor positioning method based on bluetooth beacons of the patent application with the application number of 201922212095.4, detects broadcast signals of bluetooth tags through the bluetooth beacons, uploads information to a positioning base station through a bus network, and the positioning base station fuses all beacon information to calculate tag positions; this approach, while effective in reducing cost and bulk, still has a higher power consumption for the tag.
Disclosure of Invention
In order to solve the technical problems that a receiver practical by adopting the traditional backscattering needs to be specially manufactured, has larger volume and higher cost, the invention aims to provide an indoor positioning method and device based on the Bluetooth backscattering, the backscattering technology is utilized to integrate the Bluetooth AoA positioning technology, and the more general receiver is adopted, so that the indoor accurate positioning can be realized, and the adopted technical scheme is as follows:
an indoor positioning method based on Bluetooth backscattering, which comprises the following steps:
1) arranging a plurality of receivers at indoor fixed positions, arranging a radio frequency source in an area surrounded by the receivers, and positioning the mobile tag to be tested in the area surrounded by the receivers; a radio frequency source transmits a main carrier signal, the frequency band of the main carrier signal is in the detection frequency band of a receiver, and the frequency of the main carrier signal is far away from the central frequency of a receiving channel of the receiver;
2) the mobile tag to be tested automatically generates a Bluetooth data packet supporting a direction finding function to form a baseband signal, and a main carrier wave and the baseband signal emitted by a radio frequency source fall in an advertisement channel of BLE after being modulated and mixed in the tag to be tested;
3) the receiver is provided with an array of active antennas, samples the backscattering signal of the Bluetooth data packet, switches among each active antenna in the array, calculates the phase difference of the signal, and calculates the phase difference of the signal according to the phase difference
Calculating to obtain the direction of the mobile tag to be detected;
where λ is the wavelength of the signal, d is the distance between the active antennas,
theta is the phase difference and theta is the arrival angle of the signal;
4) and according to the arrival angle of the receiver, determining the position of the mobile tag to be detected by using the intersection point of the rays formed by taking the receiver as a starting point.
Preferably, the bluetooth packet in step 2) is embedded with an additional field of constant tone extension after cyclic redundancy check of the packet protocol data unit, and the additional field of constant tone extension is composed of "1" to form an unwhited sequence and is transmitted at the bluetooth carrier frequency plus the frequency of 250kHz for 16 μ s to 160 μ s.
Preferably, the number of times of modulating the main carrier and the baseband signal in the mobile tag to be tested in step 2) is two.
Preferably, the two modulations are respectively primary modulations of the subcarrier on the baseband signal in the mobile tag to be detected, and the upper sideband of the baseband signal modulated by the subcarrier is reserved by using hilbert transform after the modulation, and the subcarrier is generated by an analog circuit or an FPGA in the mobile tag to be detected; and modulating the external main carrier and the baseband signal subjected to primary modulation for the second time at the transmitting position of the mobile tag antenna to be detected.
Preferably, the upper sideband spectrum of the subcarrier signal comprises the following components: M.Fcw+N·(fsc±δfsc) (ii) a Where M is the harmonic number of the carrier, N is the harmonic number of the subcarrier, FcwIs the primary carrier frequency, δ fscIs a single-sided frequency.
Preferably, the arrival angle of the receiver in step 4) is an arrival angle α calculated by two receivers closest to the mobile tag to be detected1And alpha2。
Preferably, the two antennas of the two receivers closest to the mobile tag to be detected are used as the coordinates, and the two angles of arrival α1And alpha2And solving the position coordinates of the label by a least square method.
Preferably, the gain of the array active antenna in step 3) is GrThe distance between the two linear array antennas is d,
the signal-to-noise ratio SNR of the received signal at the receiver is at least 7 dB.
An indoor positioning device based on Bluetooth backscattering comprises a radio frequency source, a mobile tag to be detected and a receiver, wherein the mobile tag to be detected comprises a coding module, a modulation module and a transmitting module, the coding module generates a Bluetooth data packet supporting a direction finding function, the modulation module performs primary modulation on a baseband signal of the mobile tag to be detected, and the transmitting module mixes the primary modulated signal with a main carrier wave by using a backscattering principle; the receiver comprises a radio frequency receiving module, a positioning calculation module and a power supply module, wherein the radio frequency receiving module receives and demodulates a radio frequency wave beam sent by backscattering of the mobile tag to be detected, the positioning calculation module calculates the arrival angle of the demodulated signal and then calculates the position coordinate of the mobile tag to be detected in a room so as to realize positioning, and the power supply module provides a working power supply for the receiver.
Preferably, a plurality of the receivers are respectively arranged at fixed positions in a room, and the radio frequency source is arranged at the center of an area enclosed by the plurality of receivers.
The invention has the following beneficial effects:
1) the method comprises the steps that a radio frequency source is arranged near a mobile tag to be detected, the radio frequency source sends a fixed main carrier signal, the mobile tag to be detected adds self information after receiving the information and sends the information to a receiver through backscattering, and the radio frequency source is close to the mobile tag to be detected, so that loss of a middle path is reduced, and the communication distance between the mobile tag to be detected and the receiver is enlarged;
2) through twice modulation, the modulated mixed signal can fall into an advertisement channel of BLE, and the compatibility of the Bluetooth protocol can enable the receiver to be more universal, so that the equipment cost is effectively reduced;
3) the method has the advantages of high stability, low error rate, small volume and low power of the whole device, and is suitable for being widely applied to indoor environment, especially the positioning of the Internet of things.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a flow chart of a method of the present invention;
FIG. 2 is a schematic AoA positioning according to the method of the present invention;
FIG. 3 is a schematic diagram of the structure of the apparatus of the present invention;
figure 4 is a BLE advertisement packet frame structure;
figure 5 is an FSK signal in a BLE advertising channel;
FIG. 6 is a test scenario of the apparatus of the present invention;
FIG. 7 is a plot of AoA localization error based on backscattering;
FIG. 8 is a graph of AoA localization error distribution;
FIG. 9 is a cumulative profile of position estimation based on both backscatter and no backscatter.
Detailed Description
The invention relates to an indoor positioning method and device based on Bluetooth backscattering, which is a flow chart of the method as shown in figure 1 and mainly comprises the following steps:
1) arranging a plurality of receivers at indoor fixed positions, arranging a radio frequency source in an area defined by the receivers, and positioning the mobile tag to be tested in the area defined by the receivers; a radio frequency source transmits a main carrier signal, the frequency band of the main carrier signal is in the detection frequency band of a receiver, and the frequency of the main carrier signal is far away from the central frequency of a receiving channel of the receiver; because the power of the signal directly transmitted to the receiver by the main carrier source is much larger than that of the signal directly transmitted to the receiver after backscatter modulation, in order to avoid the signal after backscatter modulation from being submerged in the signal directly transmitted by the main carrier source at the receiver end, the frequency of the main carrier should be kept as far as possible from the center frequency of the receiving channel.
2) The mobile tag that awaits measuring automatically generates the bluetooth data package that supports direction finding function, and this bluetooth data package is the baseband signal that awaits measuring mobile tag automatically generated, and the information that the bluetooth data package includes has: preamble, access address, header, message, cyclic redundancy check and fixed frequency extension signal, the bluetooth data packet embeds an additional field of Constant Tone Extension (CTE) after Cyclic Redundancy Check (CRC) of data packet Protocol Data Unit (PDU); CTE is an unmodulated signal transmitted at the bluetooth carrier frequency plus 250kHz for 16 mus to 160 mus, and the constant tone spread additional field consists of a "1" in an unwhited sequence with a transmission time long enough for the receiver to extract IQ data from the bluetooth packet without interfering effects on modulation. The mobile tag to be detected is powered by the button battery.
The main carrier and the subcarrier are fixed in frequency, the main carrier is generated by a radio frequency source, the subcarrier is generated by an analog circuit or FPGA in the tag, a baseband signal is generated in the tag by a single chip microcomputer, and after the baseband signal is modulated by the subcarrier, a mixed signal of the main carrier and the modulated baseband signal falls into an advertisement channel of BLE and cannot be distinguished from a BLE advertisement packet sent by traditional BLE equipment; they occur in the same channel, with the same modulation scheme and the same packet format.
BLE operates in the 2.4000GHz to 2.483GHz band, where the band is divided into 40 channels, each channel having a 1MHz bandwidth and a 2MHz distance between channels. In the BLE protocol, 37 data channels and 3 advertising channels are specified (CH37 at 2.402GHz, CH38 at 2.426GHz, and CH39 at 2.480GHz), which provide a connectionless beacon mode. The structure of the advertisement packet is shown in fig. 4, in this mode, this communication mode is very suitable for transmitting the backscatter uplink, because all BLE-compatible receivers need to tune to the advertisement channel periodically to receive the content of the beacon packet, which ensures that the backscatter uplink data can be compatible with the general BLE receiver.
Compatible correlation spectrum as shown in fig. 5, the physical layer of BLE is based on Gaussian Frequency Shift Keying (GFSK) modulation at 1.0Mbps, and the BLE receiver expects to receive at the channel center frequency FcCentered binary FSK signal, single-sided frequency δ fscBetween 185kHz and 500 kHz. Below the channel center frequency FcIs expressed as logic "0" (f)sc,0) Above the channel center frequency FcThe frequency deviation of (a) represents a logical "1" (f)sc,1). The gaussian filter is used to limit the spectrum width of the modulated (first modulated) signal, so as to achieve the purpose of limiting the spectrum width and power consumption.
In order to drop the signal obtained by mixing the baseband signal of the mobile tag to be tested with the main carrier in CH38, the baseband signal of the mobile tag to be tested is modulated once, and after subcarrier modulation, the upper sideband of the baseband signal needs to be preserved by hilbert transform, and when the main carrier is backscatter modulated by using the subcarrier, the obtained upper sideband spectrum contains the following components:
M·Fcw+N·(fsc±δfsc)
where M is the harmonic number of the carrier, N is the harmonic number of the subcarrier, FcwIs the primary carrier frequency, δ fscIs a single-sided frequency.
Because a digital modulation mode is adopted in the tag, a signal subjected to primary modulation of the subcarrier is a square wave, and a sine wave generated by the external main carrier source and the square wave subjected to primary modulation of the subcarrier are subjected to secondary modulation at the transmitting position of the mobile tag antenna to be detected. The fundamental wave of the post-secondary modulated signal waveform is a bandpass signal that is compatible with the BLE specification and can be normally received and demodulated by the advertising channel, through backscatter.
3) An array of active antennas is arranged on the receiver, the receiver samples IQ data of a backscattering signal data packet and switches between each active antenna in the array, and the phase difference of the signals can be calculated because the phase of the signals is linearly changed, and is caused by the distance difference between each antenna in the array and a single signal transmitting antenna (an antenna of a radio frequency source); calculating the phase difference of the signals
Then, again according to
Calculating to obtain the direction of the mobile tag to be detected;
where λ is the wavelength of the signal, d is the distance between the active antennas,
in the embodiment of the invention, the distance between the two active antennas is 0.05m,
theta is the phase difference and theta is the arrival angle of the signal;
4) the intersection point of the rays formed from the receiver as the starting point may be determined according to the angle of arrival of the receiverAnd determining the position of the mobile tag to be detected. The arrival angle of the receiver is the arrival angle alpha calculated by two receivers closest to the mobile tag to be detected1And alpha2. As shown in FIG. 2, A1And A2For the positions of the two receivers, the coordinates are A1(x1,y1) And A2(x2,y2) If the position coordinate of the mobile tag to be detected is T (x, y), then the following are satisfied:
the position coordinates of the mobile tag T to be detected can be obtained by using a least square method, the mobile tag to be detected is a Bluetooth data packet which supports a direction finding function and is sent by one antenna, the data packet is received by a multi-antenna group of a receiver, and positioning is carried out based on an AoA algorithm.
As shown in FIG. 6, in one embodiment of the present invention, the space is a square space of 10mX10m, and 4 receivers A1、A2、A3And A4The main carrier emission source M is positioned at the midpoint of each side of the square space, and the mobile tag to be tested is positioned in a square area surrounded by the 4 receivers as vertexes.
Under line-of-sight propagation paths, the link budget of a backscatter system is similar to that of a bistatic radar apparatus, where the radio frequency source and receiver are physically separated, and the received power of the receiver is calculated as:
wherein D is1The distance from the radio frequency source to the mobile tag to be detected; d2Is the distance from the moving tag to be measured to the receiver; ptIs the transmission power of the radio frequency source; gtAntenna gain for the radio frequency source; grIs the antenna gain of the receiver; and delta sigma is a check radar scattering cross section, and the following formula is calculated:
wherein G isNFor the gain of the antenna of the mobile tag to be measured, the conjugate matching reflection coefficient gamma*Comprises the following steps:
Zais the impedance of the resonant antenna, ZLIs a complex load impedance (load impedance in complex form).
An external radio frequency source transmits a sine main carrier wave with fixed frequency, and the transmission power of the sine main carrier wave is PtThe antenna gain is GtGenerating a CTE signal specified in a Bluetooth protocol in the mobile tag to be tested, modulating the CTE signal by a single side band of a fixed frequency subcarrier, and then performing backscattering with an external main carrier, wherein the gain of the antenna of the mobile tag to be tested is GN。Za、ZL1And ZL2The result is the actual measurement result. Each receiver is provided with two antennas with a distance d and a gain GrThe sensitivity of the receiver of the linear array antenna is a constant value. In addition, in order to receive BFSK signals with low bit error rate (BER ≦ 0.1%), the signal-to-noise ratio (SNR) of the received signal at the receiver is required to be at least 7 dB.
In the scene (without boundary line) of the embodiment of the invention, the accuracy of the positioning position is tested, the method sets a test label at an interval of 0.5m, the test label at each position is tested repeatedly for 100 times, the receiver adopts an AoA algorithm, samples IQ samples in 160 CTE signals each time when calculating the angle, and estimates the arrival angle of the reflected signal of the test label according to a linear model of the phase change of the IQ samples. And in each positioning, two receivers with the closest distance to the label are adopted for receiving, two arrival angles are obtained through calculation, the position coordinates of the tested label are solved through a least square method according to the coordinates and the two arrival angles of each antenna of the receivers, and the positioning errors of all label positions are calculated.
FIG. 7 shows the positioning error of different regions measured by the method of the present invention, FIG. 8 shows the positioning error of different regions based on AoA standard without backscattering, and the measured regions are triangular regions of 5mX5m, and it can be found by comparison that the positioning error is smaller in the inner regions of the test triangles and is below 0.1m regardless of whether backscattering is taken into account; backscatter based bluetooth positioning, the positioning error is higher in the hypotenuse region of the test triangle than without backscatter, where the backscatter based positioning error is from 0.2266m to 0.3074 m; however, in the cathetus region of the test triangle, the error for bluetooth positioning based on backscattering is lower than the error without backscattering, where the backscattering error is 0.1865m and the no backscattering error is 0.2175 m.
FIG. 9 is a graph of the cumulative distribution function for position estimation based on both backscatter and no backscatter, from which it can be seen that although the error is greater for the backscatter based case than for the no backscatter case, the frequency of large errors is lower for both cases; in addition, we calculated that the mean error for localization based on backscattering was 0.1425m and the mean error without backscattering was 0.0461 m. By contrast, in the test area, the positioning accuracy is not significantly reduced by using the bluetooth AoA positioning based on the backscattering, and the average error can be the same as that of the bluetooth AoA positioning directly transmitted by the tag. Therefore, the backscattering technology has better positioning performance on the premise of small volume and low power consumption.
The invention also provides an indoor positioning device based on Bluetooth backscattering, which mainly comprises a radio frequency source, a mobile tag to be detected and a receiver, wherein the mobile tag to be detected comprises a coding module, a modulation module and a transmitting module, the coding module generates a Bluetooth data packet supporting a direction finding function, the modulation module performs primary modulation on a baseband signal of the mobile tag to be detected, and the transmitting module mixes the primary modulated signal with a main carrier wave by using a backscattering principle; the receiver comprises a radio frequency receiving module, a positioning calculation module and a power supply module, wherein the radio frequency receiving module receives and demodulates a radio frequency wave beam sent by backscattering of the mobile tag to be detected, the positioning calculation module calculates the arrival angle of the demodulated signal and then calculates the position coordinate of the mobile tag to be detected in a room so as to realize positioning, and the power supply module provides a working power supply for the receiver.
It should be understood by those skilled in the art that the above embodiments are only for illustrating the present invention and are not to be used as a limitation of the present invention, and that suitable changes and modifications of the above embodiments are within the scope of the claimed invention as long as they are within the spirit and scope of the present invention.
Claims (10)
1. An indoor positioning method based on Bluetooth backscattering, which comprises the following steps:
1) arranging a plurality of receivers at indoor fixed positions, arranging a radio frequency source in an area surrounded by the receivers, and positioning the mobile tag to be tested in the area surrounded by the receivers; a radio frequency source transmits a main carrier signal, the frequency band of the main carrier signal is in the detection frequency band of a receiver, and the frequency of the main carrier signal is far away from the central frequency of a receiving channel of the receiver;
2) the mobile tag to be tested automatically generates a Bluetooth data packet supporting a direction finding function to form a baseband signal, and a main carrier wave and the baseband signal emitted by a radio frequency source fall in an advertisement channel of BLE after being modulated and mixed in the tag to be tested;
3) the receiver is provided with an array of active antennas, samples the backscattering signal of the Bluetooth data packet, switches among each active antenna in the array, calculates the phase difference of the signal, and calculates the phase difference of the signal according to the phase difference
Calculating to obtain the direction of the mobile tag to be detected;
where λ is the wavelength of the signal, d is the distance between the active antennas,
theta is the phase difference and theta is the arrival angle of the signal;
4) and according to the arrival angle of the receiver, determining the position of the mobile tag to be detected by using the intersection point of the rays formed by taking the receiver as a starting point.
2. The bluetooth backscatter based indoor positioning method of claim 1, wherein: the Bluetooth data packet in the step 2) is embedded with an additional field of constant tone expansion after the cyclic redundancy check of a data packet protocol data unit, the additional field of the constant tone expansion consists of '1' to form an unbleached sequence, and the unbleached sequence is transmitted at the frequency of a Bluetooth carrier frequency plus 250kHz and lasts for 16 mu s to 160 mu s.
3. The bluetooth backscatter based indoor positioning method of claim 1, wherein: the modulation times of the main carrier wave and the baseband signal in the step 2) in the mobile tag to be detected are twice.
4. The bluetooth backscattering based indoor positioning method of claim 3, wherein: the two times of modulation are respectively the primary modulation of the subcarrier on the baseband signal in the mobile tag to be detected, and the Hilbert transform is adopted to reserve the upper sideband of the baseband signal modulated by the subcarrier after modulation, and the subcarrier is generated by an analog circuit or FPGA (field programmable gate array) in the mobile tag to be detected; and modulating the external main carrier and the baseband signal subjected to primary modulation for the second time at the transmitting position of the mobile tag antenna to be detected.
5. The indoor positioning method based on Bluetooth backscattering of claim 4, wherein: the upper sideband spectrum of the subcarrier signal comprises the following components: M.Fcw+N·(fsc±δfsc)；
Where M is the harmonic number of the carrier, N is the harmonic number of the subcarrier, FcwIs a main loadWave frequency, δ fscIs a single-sided frequency.
6. The bluetooth backscatter based indoor positioning method of any one of claims 1-5, wherein: the arrival angle of the receiver in the step 4) is the arrival angle alpha calculated by two receivers closest to the mobile tag to be detected1And alpha2。
7. The bluetooth backscatter based indoor positioning method of claim 6, wherein: according to the coordinates of each antenna of two receivers nearest to the mobile tag to be detected and two arrival angles alpha1And alpha2And solving the position coordinates of the label by a least square method.
8. The bluetooth backscatter based indoor positioning method of claim 1, wherein: the gain of the array active antenna in the step 3) is GrThe distance between the two linear array antennas is d,
the signal-to-noise ratio SNR of the received signal at the receiver is at least 7 dB.
9. The utility model provides an indoor positioner based on bluetooth backscatter which characterized in that: the mobile tag to be detected comprises a radio frequency source, a mobile tag to be detected and a receiver, wherein the mobile tag to be detected comprises a coding module, a modulation module and a transmitting module, the coding module generates a Bluetooth data packet supporting a direction finding function, the modulation module performs primary modulation on a baseband signal of the mobile tag to be detected, and the transmitting module mixes the primary modulated signal with a main carrier wave by using a backscattering principle; the receiver comprises a radio frequency receiving module, a positioning calculation module and a power supply module, wherein the radio frequency receiving module receives and demodulates a radio frequency wave beam sent by backscattering of the mobile tag to be detected, the positioning calculation module calculates the arrival angle of the demodulated signal and then calculates the position coordinate of the mobile tag to be detected in a room so as to realize positioning, and the power supply module provides a working power supply for the receiver.
10. The bluetooth backscatter based indoor positioning device of claim 9, wherein: the receivers are respectively arranged at fixed positions in a room, and the radio frequency source is arranged in the center of an area enclosed by the receivers.
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| CN113285768A (en) * | 2021-04-21 | 2021-08-20 | 思澈科技(上海)有限公司 | Bluetooth development platform and testing method thereof |
| CN114966542A (en) * | 2022-07-29 | 2022-08-30 | 合肥有感科技有限责任公司 | Digital key positioning system and positioning method |
| WO2023070260A1 (en) * | 2021-10-25 | 2023-05-04 | Oppo广东移动通信有限公司 | Wireless communication method and device |
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