Distance measurement method based on two adjacent frequency detection phases

Abstract

In order to solve the problems that a circuit structure is simple, and distance measurement with good accuracy and precision can be achieved, the invention provides a method which does not need to adopt an array antenna, does not need to measure time difference, and only measures phases of two pilot frequency signals to achieve ambiguity-free and high-precision distance measurement. Different from the existing mode of solving the distance by measuring the phase difference, the new method directly uses a distance measurement equation for measuring the phase. In order to eliminate phase ambiguity, the frequency interval of two different-frequency signals is limited to ensure that the same wavelength integer cycle number exists during different-frequency phase detection on the detected distance length. On the basis, the wavelength whole cycle number can be solved through joint solution of a double-frequency phase ranging equation set. And then the detection distance can be obtained by using the phase distance measurement equation again. Simulation analysis shows that in a distance range without phase shift ambiguity, the double-frequency phase distance measurement method is not only good in accuracy, but also capable of obtaining distance measurement precision smaller than 0.2%.

Description

Technical Field

[0001] This invention relates to radio positioning technology, specifically to a method for achieving unambiguous, high-precision ranging by measuring the phase of two different frequency signals. Background Technology

[0002] Many electronic devices desire ranging capabilities that are simple in circuit architecture yet highly accurate. There are many methods for measuring distance using wireless technology. GPS positioning is unsuitable for indoor use or areas where satellite signals are obstructed; ultrasonic ranging has poor accuracy. Bluetooth is continuously improving its ranging accuracy, and the updated Bluetooth protocol will employ a ranging method combining time difference and phase.

[0003] In theory, a distance measurement method combining time difference and phase can effectively improve the accuracy and precision of distance measurement. The general approach is to first use time difference measurement to obtain a coarse distance value, which is then used to eliminate phase ambiguity. Then, phase measurement results are used to correct the coarse value.

[0004] In fact, phase ranging is an independent ranging technique that does not require time difference measurement. Current industrial phase ranging methods detect distance by assessing the phase difference between transmitted and reflected waves propagating in space. Because it utilizes highly accurate clock information and carrier circuitry to eliminate phase ambiguity, phase ranging based on target echo phase detection is not only a highly accurate method but also easily implemented in engineering. However, if highly accurate clock information and carrier circuitry cannot be used to eliminate phase ambiguity, achieving high-precision phase ranging may still be difficult. Summary of the Invention

[0005] To address the challenge of achieving both simple circuit architecture and high accuracy in ranging, this invention presents a method for unambiguous, high-precision ranging that eliminates the need for array antennas and time difference measurements. This method achieves ranging without ambiguity by measuring the phase of two different-frequency signals. Unlike existing methods that calculate distance by measuring phase difference, this new method directly uses the ranging equations that measure phase. To eliminate phase ambiguity, a defined frequency interval between the two different-frequency signals ensures that they have the same integer number of wavelength cycles during phase detection over the detected distance. Based on this, the integer number of wavelength cycles can be obtained by simultaneously solving the dual-frequency phase ranging equations. The detection distance can then be obtained by applying the phase ranging equations again.

[0006] This invention is achieved through the following technical solution:

[0007] To obtain the relative distance between two electronic devices, one electronic device equipped with a transmitting component actively sends two signals of different frequencies to the electronic device equipped with a receiving component. Because they are signals of different frequencies, they can be sent simultaneously or sent twice consecutively under the condition that the detected distance is relatively fixed.

[0008] The difference between two different frequencies will be limited to a suitable range to ensure that the integer number of wavelengths of the signal is the same over the detection distance.

[0009] After receiving two different frequency signals, the receiving unit uses a phase detection circuit to detect the phase of each of the two different frequency signals.

[0010] Based on this, and assuming that the integer number of wavelengths of the signal is the same in both phase detection processes, the phase ranging formula is directly used to construct a set of boundary equations to solve for the integer number of wavelengths of the signal.

[0011] Then, the distance between the two electronic devices can be obtained by using the phase ranging formula again.

[0012] Specifically, the following steps are included:

[0013] Step 1: An electronic device equipped with a transmitting component actively sends two signals of different frequencies to an electronic device equipped with a receiving component. Because they are different frequency signals, they can be sent simultaneously or sent twice consecutively under the condition that the detection distance remains relatively fixed.

[0014] Step 2: Based on the two frequency measurements, the receiving component uses a phase detection circuit to obtain the phase values ​​of the two different frequency signals.

[0015] Step 3: To remove phase ambiguity, the frequency difference between the two different frequency signals is limited to a suitable range to ensure that the integer number of wavelengths of the signals is the same at the detection distance. This is achieved by simultaneously solving the following two phase ranging formulas:

[0016]

[0017]

[0018] The solution is:

[0019]

[0020] In the formula: L is the distance between the two electronic devices; λ1 and λ2 are wavelengths; n is the number of integer cycles of the wavelength; φ1 and φ2 are phases.

[0021] Step 4: Then you can calculate the distance again using the phase ranging formula:

[0022]

[0023] or:

[0024]

[0025] Several characteristics:

[0026] 1. Only phase measurement is used; time difference measurement is not required.

[0027] 2. The deblurring method is simple, based solely on phase detection at different frequencies, and phase ambiguity is eliminated by limiting the frequency difference.

[0028] 3. Not only is the ranging accuracy high, but the ranging precision is also very good.

[0029] 4. It eliminates the need for array antennas, reducing design and manufacturing costs and facilitating wide-angle detection. Attached Figure Description

[0030] Figure 1 Relative calculation error of detection distance at different frequency intervals

[0031] Figure 2 Relative calculation error of detection distance at different frequencies

[0032] Figure 3 Relative calculation error of unambiguous ranging at a single frequency point

[0033] Figure 4 The difference in integer cycles of wavelength at different frequency differences

[0034] Figure 5 Relative ranging error at different frequency differences Detailed Implementation

[0035] The following is in conjunction with the appendix Figure 1 —Appendix Figure 5 The invention will be further explained in terms of how it is implemented.

[0036] Example

[0037] A ranging method based on heterogeneous frequency phase detection. (Attached) Figure 1 This refers to the relative calculation error of the detection distance at different frequency intervals; Appendix Figure 2 This refers to the relative calculation error of the detection distance at different frequencies; Appendix Figure 3 It is the relative calculation error of unambiguous ranging at a single frequency point; Appendix Figure 4 It is the difference in integer cycles of the wavelength at different frequency differences; Appendix Figure 5 It represents the relative ranging error at different frequency differences.

[0038] Phase measurement suffers from periodic ambiguity, with the number of integer cycles of the wavelength contained in its boundary value equation being an unknown variable. If only geometric conditions are used, the positioning equation based on phase measurement is unsolvable. This invention demonstrates that by using adjacent dual-frequency phase detection and defining the frequency difference between the two frequencies, high-precision, phase-ambiguity-free ranging can be achieved directly based on the phase ranging formula.

[0039] This invention patent provides a new ranging method for various engineering designs, including ranging requirements in the Internet of Things, and also provides a new solution for high-precision Bluetooth ranging.

[0040] I. Basic Principles

[0041] Various electronic devices that require mutual ranging can be equipped with multi-frequency transceiver components, multi-frequency transmitter components, or multi-frequency receiver components, depending on their usage requirements.

[0042] To determine the relative distance between two electronic devices, the electronic device equipped with a transmitting component actively sends two signals of different frequencies to the electronic device equipped with a receiving component. Because these are different frequency signals, they can be sent simultaneously or consecutively. It is important to note that consecutive frequency transmission is only appropriate when the detected distance remains relatively constant.

[0043] After receiving two different frequency signals, the receiving unit uses a phase detection circuit to obtain the phase of the two signals. Therefore, it seems that the distance measurement can be calculated using the phase ranging formula.

[0044]

[0045]

[0046] In the formula: L is the distance between the two electronic devices; λ1 and λ2 are wavelengths; n1 and n2 are integer cycles of the wavelength; φ1 and φ2 are phases.

[0047] However, the integer number of wavelength cycles included in the boundary value equation is an unknown variable to be determined. If only geometric conditions are used, the positioning equation based on phase measurements is unsolvable. If the difference between two different frequencies is limited to a suitable range, ensuring that the integer number of wavelength cycles of the signal is the same across the detection distance, then:

[0048] n = n1 = n2 (3)

[0049] Based on the condition that the integer number of wavelengths of the signal is the same in both frequency measurements, the result can be directly solved using the two phase-shift ranging formulas:

[0050]

[0051] Then the distance can be directly calculated using the phase ranging formula:

[0052]

[0053] or:

[0054]

[0055] II. Simulation Analysis

[0056] Based on the relationship between wavelength and frequency, the wavelengths at different frequency differences are given:

[0057]

[0058]

[0059] In the formula: v c It is the speed of light; f0 is the frequency; Δf is the frequency interval.

[0060] 1. Relative calculation error of detection distance

[0061] First, the wavelength integer number is calculated using the phase shift value obtained from theoretical calculation. Then, the detection distance is calculated using the phase ranging formula (5). Finally, the calculated value is compared with the theoretical value of formula (1).

[0062] Simulation calculations are performed on the existing 2.4GHz frequency band, and the relative calculation error is calculated using the following formula:

[0063]

[0064] In the formula: L0 is the theoretical value obtained by formula (1); L is the calculated value obtained by formula (5) or (6).

[0065] Appendix Figure 1 The relative calculation errors are presented for different frequency intervals and detection distances. For clarity, the latter two curves have been artificially reduced and increased by a value; otherwise, the three curves would overlap and become indistinguishable in the near-zero region. It can be seen that the larger the frequency difference, the smaller the unambiguous ranging distance. Simulation calculations show that if the frequency difference is only tens of hertz, the unambiguous phase ranging distance can reach hundreds of kilometers.

[0066] Appendix Figure 2The relative calculation errors at different frequencies and detection distances are presented when the frequency difference is 0.5MHz. Similarly, the method of artificially increasing and decreasing a fixed value is used to improve the visualization of the graphs. It can be seen that within the frequency range around 2.4GHz, 2.4GHz seems to be a better choice, yielding a larger ranging distance. In reality, the 2.4GHz band is arbitrarily chosen. The characteristics of each band may differ, requiring recalculation.

[0067] Appendix Figure 3 The relative calculation error of the detection range at a single frequency of 2.4 GHz is presented within the unambiguous range. It can be seen that the relative calculation error of the ranging formula is very small within the unambiguous range.

[0068] 2. Difference in integer cycles of wavelength

[0069] The present invention achieves phase ambiguity removal based on the condition that the number of integer cycles of the wavelength obtained when measuring two different frequencies over the same probed distance is the same.

[0070] Let the difference between the integer cycles of the two wavelengths be:

[0071] Δn=n2-n1 (10)

[0072] in:

[0073]

[0074]

[0075] Based on the preceding analysis, we assume the detection distance varies linearly within a 500-meter range, while simultaneously taking different frequency differences. (Appendix) Figure 4 Curves showing that the difference between two wavelengths with integer cycles is not zero are presented. It can be seen that the larger the frequency difference between the two frequencies, the smaller the unambiguous phase ranging distance. Furthermore, the simulation calculations here further demonstrate that if the frequency difference is only tens of hertz, the unambiguous phase ranging distance can reach hundreds of kilometers.

[0076] III. Error Analysis

[0077] 1. Partial differential

[0078] Using the ranging equation (5), calculate the partial derivative of the distance with respect to the two different frequency phase shifts:

[0079]

[0080]

[0081] The partial differential of the wavelength integer number with respect to the phase shift is solved by equation (4):

[0082]

[0083]

[0084] In the formula: Δλ=λ1-λ2.

[0085] 2. Relative ranging error

[0086] According to error analysis theory, the ranging error caused by phase measurement error is:

[0087]

[0088] In the formula: σ φ The root mean square value of the phase measurement error is taken during analysis and calculation.

[0089] Appendix Figure 5 The relative ranging error curves at different detection distances with different frequency differences are presented. Since the relative ranging error is inversely proportional to the detection distance, the longer the detection distance, the smaller the relative ranging error. Simultaneously, the relative ranging error is inversely proportional to the wavelength difference, which, after conversion, becomes inversely proportional to the frequency difference. Therefore, the smaller the frequency difference, the larger the relative ranging error.

[0090] Based on the simulation results of the relative calculation error and relative ranging error above, it can be seen that the frequency difference should not be too large or too small. If it is too large, the relative calculation error will increase. If it is too small, the relative ranging accuracy will deteriorate.

[0091] Simulation results show that phase-shift ranging based on heterodyne measurement can achieve a ranging accuracy of less than 0.2%. That is, at a distance of 100 meters, the deviation is only 0.2 meters. The simulation also indicates that the ranging error diverges at very close distances. However, from the perspective of practical engineering applications, measurement accuracy may not be crucial at very close distances.

Claims

1. A method for achieving unambiguous, high-precision phase ranging without requiring an array antenna or time difference measurement, but solely by measuring the phase of two different frequency signals. Its main feature is the use of dual-frequency phase detection to remove phase ambiguity. Firstly, by limiting the frequency difference between the two frequencies, it ensures that the same integer number of wavelength cycles exists within the same distance range being detected during phase detection at different frequencies. Secondly, a phase ranging equation system is constructed based on the two measurements to solve for the integer number of wavelength cycles, and then the distance is obtained again using the phase ranging equation system. The method specifically includes the following steps: Step 1: An electronic device equipped with a transmitting component actively sends two signals of different frequencies to an electronic device equipped with a receiving component. Because they are different frequency signals, they can be sent simultaneously or sent twice consecutively under the condition that the detection distance remains relatively fixed. Step 2: Based on the two frequency measurements, the receiving component uses a phase detection circuit to obtain the phase values ​​of the two different frequency signals. Step 3: To remove phase ambiguity, the frequency difference between the two different frequency signals is limited to a suitable range to ensure that the integer number of wavelengths of the signals is the same at the detection distance. This is achieved by simultaneously solving the following two phase ranging formulas: The solution is: In the formula: L is the distance between the two electronic devices; λ1 and λ2 are wavelengths; n is the number of integer cycles of the wavelength; φ1 and φ2 are phases. Step 4: Then you can calculate the distance again using the phase ranging formula: or:

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