A unilateral two-way ranging method

Abstract

The present invention relates to a unilateral two-way ranging method, and the signal for communication between the initiating party and the responding party is a wireless signal containing a preamble sequence, including the following steps: sending a first message to the responding party and recording the local sending time T of the first message A1 ; receiving a second message replied by the responding party and recording the receiving time T of the second message A2 , where the second message includes the receiving time T of the first message B1 and the local sending time T of the second message B2 ; estimating the clock frequency difference between the initiating party and the responding party according to the preamble sequence of the second message; calculating the distance between the initiating party and the responding party based on the local sending time T of the first message A1 , the receiving time T of the second message A2 , the receiving time T of the first message B1 , the local sending time T of the second message B2 and the clock frequency difference. The present invention can reduce the number of system interaction messages and the system complexity while ensuring the ranging accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless ranging, and particularly to a unilateral two-way ranging method. Background Art

[0002] Wireless ranging systems are widely used in electromagnetic systems of various systems, such as a typical ultra-wideband (UWB) ranging system. Since civilian devices generally do not use high-precision atomic clocks, there is no unified high-precision clock between the transmitting and receiving ends before starting ranging. In addition, due to the difference in crystal oscillators, there is also a certain frequency difference between the clocks at the transmitting and receiving ends. In order to accurately estimate the flight time T prop , it is also necessary to consider two other unknowns of the system, namely the initial clock difference Δt and the system frequency difference. Thus, there are three unknowns in the system to be solved.

[0003] Existing ranging methods include single-sided two-way ranging (SS-TWR) and double-sided two-way ranging (DS-TWR).

[0004] SS-TWR realizes ranging by each sending a message at the transmitting and receiving ends. The ranging formula is:

[0005] T prop =(T round -T reply ) / 2

[0006] This ranging method can solve the problem of the initial clock difference, but does not consider the influence of the system frequency difference on ranging. Since the message interaction takes time, the system clock difference will gradually change due to the system frequency difference during the ranging process. Therefore, the ranging error is relatively large. The ranging error of SS-TWR is proportional to both the relative crystal oscillator frequency difference between devices and the duration of the ranging message response.

[0007] DS-TWR can almost eliminate the influence of the initial clock difference and the system frequency difference by interacting three messages between the transmitting and receiving ends. It is a currently widely used ranging method. The ranging formula is:

[0008]

[0009] The ranging error of DS-TWR basically eliminates the influence brought by the system frequency difference and can achieve a relative error better than 1e-5. However, DS-TWR requires interacting three messages back and forth, increasing the complexity of the system. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a unilateral two-way ranging method, which can reduce the number of system interaction messages and the system complexity while ensuring the ranging accuracy.

[0011] The technical solution adopted by the present invention to solve its technical problems is: to provide a unilateral two-way ranging method, where the signal for communication between the initiating party and the responding party is a wireless signal containing a preamble sequence, including the following steps:

[0012] Send a first message to the responding party and record the local transmission time T of the first message A1 ;

[0013] Receive the second message replied by the responding party and record the reception time T of the second message A2 , where the second message includes the reception time T of the first message B1 and the local transmission time T of the second message B2 ;

[0014] Estimate the clock frequency difference between the initiating party and the responding party according to the preamble sequence of the second message;

[0015] Based on the local transmission time T of the first message A1 , the reception time T of the second message A2 , the reception time T of the first message B1 , the local transmission time T of the second message B2 and the clock frequency difference, calculate the distance between the initiating party and the responding party

[0016] The specific method for estimating the clock frequency difference between the initiating party and the responding party according to the preamble sequence of the second message is:

[0017] Statistical radian of local carrier loop rotation during preamble reception phase

[0018] Statistical number N of received preamble symbols;

[0019] According to the duration T of each preamble symbol s , carrier period T c , and the radian and the number N of preamble symbols, estimate the clock frequency difference between the initiating party and the responding party.

[0020] The formula for estimating the clock frequency difference Δf AB between the initiating party and the responding party is:

[0021] The second message also includes the clock frequency difference Δf BA estimated by the responding party between the initiating party and the responding party.

[0022] Based on the local transmission time T of the first message A1 , the reception time T of the second message A2, the first message reception time T B1 , the second message local transmission time T B2 Before calculating the distance between the initiator and the responder based on the clock frequency difference, it further includes:

[0023] Weighted average the clock frequency difference Δf between the initiator and the responder estimated by the responder BA and the clock frequency difference between the initiator and the responder estimated based on the preamble sequence of the second message, and use the weighted average result as the clock frequency difference used when calculating the distance between the initiator and the responder.

[0024] Based on the local transmission time T of the first message A1 , the second message reception time T A2 , the first message reception time T B1 , the second message local transmission time T B2 and the clock frequency difference, the formula for calculating the distance between the initiator and the responder is: where T prop is the estimated flight time between the initiator and the responder; Δf is the clock frequency difference, D is the distance between the initiator and the responder, and c is the speed of light.

[0025] Advantageous Effects

[0026] Due to the adoption of the above technical solution, compared with the prior art, the present invention has the following advantages and positive effects: The present invention optimizes and improves the accuracy of SS-TWR ranging. Through two message transmissions, the ranging accuracy that can only be achieved by three messages in the DS-TWR ranging method can be realized. The method proposed by the present invention combines the carrier loop estimation parameters and the ranging process, introduces the transceiver clock frequency difference estimated by the carrier loop into the ranging estimation algorithm, removes the influence of the clock frequency difference in the ranging process, and improves the ranging accuracy of SS-TWR without the need to additionally increase ranging messages. Description of the Drawings

[0027] Figure 1 is a flowchart of an embodiment of the present invention;

[0028] Figure 2 is a schematic diagram of the receiver carrier tracking loop structure. Detailed Embodiment

[0029] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0030] An embodiment of the present invention relates to a one-way two-way ranging method. The signal for communication between the initiator and the responder is a wireless signal containing a preamble sequence, such as Figure 1 shown, and includes the following steps: sending a first message to the responder and recording the local sending time T of the first message A1 ; receiving a second message replied by the responder and recording the receiving time T of the second message A2 , and the first message reception time T is included in the second message B1 and the local sending time T of the second message B2 ; estimating the clock frequency difference between the initiator and the responder according to the preamble sequence of the second message; based on the local sending time T of the first message A1 , the receiving time T of the second message A2 , the first message reception time T B1 , the local sending time T of the second message B2 and the clock frequency difference to calculate the distance between the initiator and the responder. This embodiment can achieve almost the same ranging accuracy as the DS-TWR ranging method only by interacting two messages, reducing the number of system interaction messages and the system complexity.

[0031] The inventor of the present invention noticed that the reason why DS-TWR needs to perform three message interactions is that the flight time T prop , the initial clock difference Δt and the system clock frequency difference Δf are regarded as unknowns. Three message measurements can obtain three equations, so as to realize the solution of all unknowns.

[0032] During the wireless signal reception process, the relative frequency difference between the receiving end and the sending end consists of two parts, namely the relative frequency difference of the signal caused by the crystal oscillator frequencies of the receiving and sending ends themselves, and the Doppler frequency shift caused by the relative motion of the receiving and sending ends. In ordinary civilian environments, the relative speed is low (generally less than 30 m / s), and the maximum relative Doppler frequency shift is less than 1e-7, which can basically be ignored. Therefore, the relative frequency difference between the receiving end and the sending end is mainly determined by the relative frequency difference of the crystal oscillators of both sides. The clock signal and the radio frequency carrier signal of the receiver are both obtained by multiplying the reference frequency of the crystal oscillator by several times. Therefore, the relative frequency difference of the clock and the relative frequency difference of the radio frequency carrier are the same.

[0033] In many communication systems, the header of a wireless signal contains a preamble, which is a pre-determined sequence. The receiving end can achieve carrier and code loop tracking by following the preamble sequence. The carrier loop realizes continuous tracking and phase correction of the signal carrier, and the code loop mainly realizes code synchronization tracking and code offset correction of the signal.

[0034] For a UWB system, the preamble sequence is periodically repeated a certain number of times, and each time is called a preamble symbol.

[0035] Figure 2 The basic carrier digital tracking loop structure of the receiver is shown, which consists of a carrier phase correction module, an accumulator, a carrier phase detector, and a loop filter. The carrier phase correction module performs phase rotation on the input signal according to the output of the loop filter. The accumulator superimposes the results of different preamble symbols, calculates the inner product of the data of the current input symbol and the data of the accumulator, then obtains the phase deflection angle, and sends it to the loop filter for filtering. The carrier loop filter continuously corrects the phase of the input signal to ensure that each symbol can be superimposed in the same phase.

[0036] From the start of receiving the preamble to the end of detecting the preamble at the receiving end, the local carrier loop has rotated radians in total. The total number of preamble symbols received is N, and the duration of each preamble symbol is T s , and the carrier period is T c , then the relative frequency difference between the transmitter and the receiver can be accurately estimated as:

[0037] The relative frequency difference Δf is only estimated using the preamble sequence and can be performed during any packet reception, or can be estimated separately for each packet reception and then weighted and averaged. It must be noted that if the frequency difference of device A estimated relative to device B is Δf, then the expected value of the frequency difference of device B estimated relative to device A should be -Δf. If Δf is greater than zero, it means that the clock of device B runs faster than that of device A, and vice versa. If Δf is less than zero, it means that the clock of device B runs slower than that of device A. The relative frequency difference in this embodiment refers to the frequency difference measured from device A relative to device B. According to the actual experimental results, the relative frequency difference estimated through the preamble sequence is very accurate and generally does not require multiple averaging.

[0038] After obtaining the estimation of the relative frequency difference, the ranging estimation formula can be improved based on the SS-TWR ranging process:

[0039] T prop =(T round *(1 + Δf)-Treply ) / 2

[0040] The improved estimation formula basically eliminates the error caused by the clock frequency inconsistency between Device A and Device B. Therefore, the ranging result almost the same as that of DS-TWR three-time ranging can be obtained by transmitting the message only twice.

[0041] The overall ranging process is as follows:

[0042] 1. Ranging is performed between Device A and Device B. Device A is the initiator and Device B is the responder. The signal for communication between Device A and Device B is a wireless signal containing a preamble reference sequence.

[0043] 2. Device A sends Message 1 to Device B and records the local transmission time as T A1 , which is the local transmission time of the first message.

[0044] 3. Device B receives Message 1 and records the local reception time as T B1 , which is the reception time of the first message.

[0045] 4. Optionally, Device B estimates the clock frequency difference between Device A and Device B according to the preamble sequence in Message 1. The estimation method is: count the radian of the local carrier loop rotation during the preamble reception stage Count the number of received preamble symbols N. It is known that the duration of each preamble symbol is T s , and the carrier period is T c , and estimate the relative frequency difference between the transmitter and the receiver through .

[0046] 5. Device B sends Message 2 to Device A. Message 2 carries the reception time T B1 of the first message, and the transmission time T B2 of Message 2, that is, the local transmission time of the second message. Optionally, Message 2 can also carry the relative frequency difference Δf BA .

[0047] 6. Device A receives Message 2 and records the local reception time as T A2 , which is the reception time of the second message, and obtains the reception time T B1 of the first message, the local transmission time T B2 of the second message, and the optional relative frequency difference Δf BA .

[0048] 7. Device A estimates the clock frequency difference Δf between Device A and Device B according to the preamble sequence in Message 2 AB , and the estimation method is the same as that in Step 4. Optionally, Device A estimates according to Δf AB and ΔfBA Perform weighted averaging: If weighted averaging is not performed, Δf = Δf AB .

[0049] 8. Device A estimates the distance between Device A and Device B as: where T prop is the estimated time of flight between the initiator and the corresponding party, D is the distance between the initiator and the responder, and c is the speed of light.

[0050] It is not difficult to find that the present invention optimizes and improves the ranging accuracy of SS-TWR. Through two message transmissions, the ranging accuracy that can only be achieved by three messages in the DS-TWR ranging method can be realized. The method proposed by the present invention combines the carrier loop estimation parameters and the ranging process, introduces the transceiver clock frequency difference estimation obtained by the carrier loop estimation into the ranging estimation algorithm, removes the influence brought by the clock frequency difference in the ranging process, and improves the ranging accuracy of SS-TWR without the need to additionally increase ranging messages.

Claims

1. A unilateral two-way ranging method, wherein the signal for communication between the initiating party and the responding party is a wireless signal containing a preamble sequence, characterized in that It includes the following steps: Send a first message to the responder and record the local transmission time T of the first message A1 ; Receive the second message replied by the receiving respondent and record the second message reception time T A2 , wherein the first message reception time T is included in the second message B1 and the second message local transmission time T B2 ; Estimate the clock frequency difference between the initiator and the responder according to the preamble sequence of the second message, specifically: count the radian of the rotation of the local carrier loop in the preamble reception stage Count the number N of received preamble symbols; Based on the duration T of each preamble symbol s , the carrier period T c , and the radian and the number N of preamble symbols, estimate the clock frequency difference between the initiator and the responder; Based on the local sending time T of the first message A1 , the receiving time T of the second message A2 , the receiving time T of the first message B1 , the local sending time T of the second message B2 and the clock frequency difference to calculate the distance between the initiator and the responder.

2. The unilateral two-way ranging method according to claim 1, characterized in that, The clock frequency difference Δf between the estimation initiator and the responder AB is calculated by the following formula:

3. The unilateral two-way ranging method according to claim 1, characterized in that The second message further includes the clock frequency difference Δf between the initiator and the responder estimated by the responder BA .

4. The one-way two-way ranging method according to claim 3, wherein Based on the local sending time T of the first message A1 , the receiving time T of the second message A2 , the receiving time T of the first message B1 , the local sending time T of the second message B2 Before calculating the distance between the initiator and the responder based on the clock frequency difference, it further includes: The clock frequency difference Δf between the initiator and the responder estimated by the responder BA is weighted and averaged with the clock frequency difference between the initiator and the responder estimated according to the preamble sequence of the second message, and the result after weighted averaging is used as the clock frequency difference when calculating the distance between the initiator and the responder.

5. The unilateral two-way ranging method according to claim 1, characterized in that, Based on the local sending time T of the first message A1 , the receiving time T of the second message A2 , the receiving time T of the first message B1 , the local sending time T of the second message B2 and the clock frequency difference, the calculation formula for the distance between the initiator and the responder is: Among them, T prop is the estimated time of flight between the initiator and the corresponding party; Δf is the clock frequency difference, D is the distance between the initiator and the responder, and c is the speed of light.

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