One-way phase-based high-precision ranging device and algorithm

Abstract

A system and method for one-way ranging is disclosed. The system includes a transmitter and a receiver. The transmitter, also referred to as a tag, transmits a first frequency from a first set of frequencies. The receiver, also referred to as a locator, receives the first frequency and measures the phase at a first point in time. Later, the transmitter switches to a second frequency, which is close in frequency to the first frequency, such that the second frequency is also part of the first set of frequencies. The receiver also switches to the second frequency. Then, the receiver measures the phase of the second frequency at a second point in time. The transmitter and receiver then repeat this sequence for a second set of frequencies. The four phase measurements are used to determine the distance from the transmitter to the receiver. In this way, an increase in accuracy can be achieved by having a large separation between the first set of frequencies and the second set of frequencies.

Description

TECHNICAL FIELD

[0001] The present disclosure describes systems and methods for determining distances between network devices, and in particular, systems and methods for determining distances without establishing a connection between the network devices. BACKGROUND

[0002] Currently, there is interest in extending current network protocols to allow network devices to determine distances to another network device. For example, the Bluetooth specification is being modified to include High Accuracy Distance Measurement (HADM). As currently proposed, HADM discloses a basic measurement technique for two-way ranging. Two-way ranging requires a network connection to be established and maintained between the initiator and reflector. Because a network connection is established, security can be provided. However, because of the need for a network connection, HADM is difficult to extend from a single reference device to a large number of tracked network devices.

[0003] Accordingly, it would be beneficial if there were systems and methods that determined distances between two network devices without requiring a network connection to be established between the two network devices. Furthermore, it would be advantageous if these systems and methods were as accurate as the current two-way HADM process. SUMMARY

[0004] A system and method for one-way ranging is disclosed. The system includes a transmitter, also referred to as a tag, that transmits a first frequency in a first set of frequencies. A receiver, also referred to as a locator, receives the first frequency and measures the phase at a first point in time. Later, the transmitter switches to a second frequency, which is close in frequency to the first frequency, for the second frequency to also be part of the first set of frequencies. The receiver also switches to the second frequency. Then, the receiver measures the phase of the second frequency at a second point in time. The transmitter and receiver then repeat this sequence for a second set of frequencies. The four phase measurements are used to determine the distance of the transmitter to the receiver. In this way, an increase in resolution can be achieved by having a large separation between the first set of frequencies and the second set of frequencies.

[0005] According to one embodiment, a method of measuring a distance between two network devices is disclosed. The method includes transmitting a distance detection signal from a first network device, the distance detection signal including a first frequency (fi) and a second frequency (f2), where the phases of the first and second frequencies are constant; receiving the distance detection signal at a second network device; determining the phases of the first and second frequencies at the second network device, referred to as and and utilizing fi, f2, and a value that calculates a distance between the first network device and the second network device, where the distance is an intra-frequency group distance measurement. In some embodiments, a first frequency is created using the common carrier frequency and a first adjustment frequency, and a second frequency is created using the common carrier frequency and a second adjustment frequency, where the phase of the first adjustment frequency and the phase of the second adjustment frequency are equal. In certain embodiments, the first adjustment frequency and the second adjustment frequency are created using a look up table (LUT). In some embodiments, the second network device removes the common carrier frequency and the first adjustment frequency from the first frequency of the distance detection signal to determine the phase of the first frequency, using a common receiver carrier frequency and a first receiver adjustment frequency, respectively, and removes the common carrier frequency and the second adjustment frequency from the second frequency of the distance detection signal to determine the phase of the second frequency, using a common receiver carrier frequency and a second receiver adjustment frequency, respectively.

[0006] In certain embodiments, the method includes transmitting at least one additional frequency from the first network device, where each additional frequency is generated using a common carrier frequency and an adjustment frequency; and determining, at the second network device, a phase of the at least one additional frequency and using the phase of the at least one additional frequency to calculate an intra-frequency group distance.

[0007] According to another embodiment, a method of measuring a distance between two network devices is disclosed. The method includes transmitting a first distance detection signal from a first network device, the first distance detection signal including a first frequency (f1) and a second frequency (f2), where the phase of the first frequency and the phase of the second frequency are constant; receiving the first distance detection signal at a second network device; determining, at the second network device, the phase of the first frequency and the phase of the second frequency, referred to as and transmitting a second distance detection signal from the first network device, the second distance detection signal including a third frequency (f3) and a fourth frequency (f4), where the phase of the third frequency and the phase of the fourth frequency are constant; receiving the second distance detection signal at the second network device; determining, at the second network device, the phase of the third frequency and the phase of the fourth frequency, referred to as and and utilizing f1, f2, f3, f4, and a value of a distance between the first network device and the second network device, wherein the distance is an intra-frequency group distance measurement. In certain embodiments, the first frequency and the second frequency belong to a first frequency group, wherein a frequency group is defined as a set of frequencies generated using a common carrier frequency, and wherein the third frequency and the fourth frequency belong to a second frequency group, different from the first frequency group and having a second common carrier frequency. In some embodiments, there is no phase relationship between the common carrier frequency and the second common carrier frequency. In some embodiments, the first frequency is created using the common carrier frequency and a first adjustment frequency, and the second frequency is created using the common carrier frequency and a second adjustment frequency, wherein the phase of the first adjustment frequency and the phase of the second adjustment frequency are equal. In some embodiments, the first adjustment frequency and the second adjustment frequency are created using a lookup table. In certain embodiments, the second network device removes the common carrier frequency and the first adjustment frequency from the first frequency of the first distance detection signal to determine the phase of the first frequency, using a common receiver carrier frequency and a first receiver adjustment frequency, respectively, and removes the common carrier frequency and the second adjustment frequency from the second frequency of the first distance detection signal to determine the phase of the second frequency, using the common receiver carrier frequency and a second receiver adjustment frequency, respectively. In some embodiments, an inter-frequency group distance measurement is calculated based on an inter-frequency group phase difference, defined as a total phase difference between the first network device and the second network device when transmitting and receiving the second distance detection signal minus a total phase difference between the first network device and the second network device when transmitting and receiving the first distance detection signal. In certain embodiments, the second network device performs intra-frequency group distance measurements using f1, f2, and an inter-frequency group distance measurement and a difference value between the inter-frequency group distance measurement and the intra-frequency group distance measurement is greater than a predetermined threshold, adjusts the inter-frequency group phase difference by 2π, recalculates the inter-frequency group distance measurement using the adjusted inter-frequency group phase difference, and repeats the adjusting and recalculating until the difference value is less than the predetermined threshold.

[0008] According to another embodiment, a system for measuring a distance between two network devices is disclosed. The system includes a first network device configured to: transmit a first distance detection signal, the first distance detection signal including a first frequency (f1) and a second frequency (f2), wherein the first frequency and the second frequency belong to a first frequency group, wherein a frequency group is defined as a set of frequencies generated using a common carrier frequency, and wherein a phase of the first frequency and a phase of the second frequency are constant; and a second network device configured to: receive the first distance detection signal; determine the phase of the first frequency and the phase of the second frequency, respectively referred to as and f1, f2, and a value of f1, f2, f3, and f4 to calculate a distance between the first network device and the second network device, where the distance is an intra-frequency group distance measurement. In some embodiments, the first network device generates the first frequency using a common carrier frequency and a first adjustment frequency, and generates the second frequency using the common carrier frequency and a second adjustment frequency, where a phase of the first adjustment frequency and a phase of the second adjustment frequency are equal. In certain embodiments, the first adjustment frequency and the second adjustment frequency are created using a lookup table. In some embodiments, the second network device removes the common carrier frequency and the first adjustment frequency from the first frequency of the first distance detection signal using a common receiver carrier frequency and a first receiver adjustment frequency, respectively, to determine a phase of the first frequency, and removes the common carrier frequency and the second adjustment frequency from the second frequency of the first distance detection signal using the common receiver carrier frequency and a second receiver adjustment frequency, respectively, to determine a phase of the second frequency.

[0009] In certain embodiments, the first network device is further configured to transmit a second distance detection signal, the second distance detection signal including a third frequency (f3) and a fourth frequency (f4), where phases of the third frequency and the fourth frequency are constant; where the second network device is further configured to receive the second distance detection signal; determine the phase of the third frequency and the phase of the fourth frequency, respectively referred to as and and utilize f1, f2, f3, f4, and a value of f1, f2, f3, and f4 to calculate a distance between the first network device and the second network device, where the distance is an inter-frequency group distance measurement. In some embodiments, the first network device generates the third frequency and the fourth frequency using a second common carrier frequency that is different from the common carrier frequency. In some embodiments, the second network device calculates the inter-frequency group distance measurement based on an inter-frequency group phase difference, defined as a total phase difference between the first network device and the second network device when transmitting and receiving the second distance detection signal minus a total phase difference between the first network device and the second network device when transmitting and receiving the first distance detection signal. In certain embodiments, the second network device only utilizes f1, f2, and performs an intra-frequency group distance measurement using f1, f2, f3, and f4, and calculates a difference between the inter-frequency group distance measurement and the intra-frequency group distance measurement, adjusts the inter-frequency group phase difference by 2π if the difference is greater than a predetermined threshold, and recalculates the inter-frequency group distance measurement using the adjusted inter-frequency group phase difference, and repeats the adjusting and recalculating until the difference is less than the predetermined threshold. BRIEF DESCRIPTION OF DRAWINGS

[0010] For a better understanding of the present disclosure, reference will be made to the accompanying drawings, in which like reference numerals refer to like elements, in which:

[0011] Figure 1is a block diagram of a network device that can be used to perform the methods described herein;

[0012] Figure 2A a first network device transmitting a distance detection signal to a second network device is shown;

[0013] Figure 2B the operation of a frequency generator is shown;

[0014] Figure 3 a transmitting circuit of one embodiment of a network device according to Figure 1

[0015] Figure 4 is a block diagram of a receiving circuit of a network device according to Figure 1

[0016] Figure 5 a distance calculation using two frequency sets is shown;

[0017] Figure 6 a flowchart describing the operation of two network devices is shown; and

[0018] Figure 7 a flowchart describing how to compensate for phase wrapping is shown. DETAILED DESCRIPTION

[0019] Figure 1 A network device that can be used to perform the distance detection algorithms described herein is shown. The network device 10 has a processing unit 20 and an associated memory device 25. The processing unit 20 can be any suitable component, such as a microprocessor, an embedded processor, a dedicated circuit, a programmable circuit, a microcontroller, or other similar device. The memory device 25 contains instructions that, when executed by the processing unit 20, enable the network device 10 to perform the functions described herein. The memory device 25 can be a non-volatile memory, such as a flash memory, an electrically erasable read-only memory (ROM), or other suitable device. In other embodiments, the memory device 25 can be a volatile memory, such as a random access memory (RAM) or a dynamic random access memory (DRAM). The instructions contained within the memory device 25 can be referred to as a software program, which is arranged on a non-transitory storage medium.

[0020] ​​The network device 10 further comprises a network interface 30, which can be a wireless network interface comprising an antenna 37. The network interface 30 can support any wireless network protocol supporting distance detection, such as Bluetooth. The network interface 30 is used to enable the network device 10 to communicate with other devices arranged on a network 39.

[0021] The network interface 30 comprises a radio circuit 31. This radio circuit 31 is used to process incoming signals and convert wireless signals into digital signals. The components within the radio circuit 31 are described in more detail below.

[0022] The radio circuit 31 comprises a receiving circuit 36. The receiving circuit 36 is used to receive, synchronize and decode digital signals received from the antenna 37. In particular, the receiving circuit 36 has a preamble detector for identifying the start of an incoming data packet. The receiving circuit 36 also has a synchronization detector for identifying a specific bit sequence, known as a synchronization character. Furthermore, the receiving circuit 36 has a decoder for converting the digital signal into correctly arranged data bytes.

[0023] The radio circuit 31 further comprises a transmitting circuit 38. The transmitting circuit 38 can comprise a power amplifier (PA) for providing a signal to be transmitted to the antenna 37.

[0024] The network device 10 can comprise a second memory device 40. Data received from or to be sent via the network interface 30 can also be stored in the second memory device 40. This second memory device 40 is conventionally a volatile memory.

[0025] Although a memory device 25 is disclosed, any computer readable medium can be used to store the instructions. For example, a read only memory (ROM), random access memory (RAM), magnetic storage device (e.g. a hard disk drive), or an optical storage device (e.g. a Compact Disk (CD) or a Digital Video Disc (DVD)) can be used. Furthermore, the instructions can be downloaded into the memory device 25, e.g. over a network connection (not shown), via a CD ROM, or through another mechanism. The instructions can be written in any programming language, without limitation. Therefore, in some embodiments, there can be multiple computer readable non-transitory media containing the instructions described herein. As Figure 1As shown, the first computer readable non-transitory medium can be in communication with the processing unit 20. The second computer readable non-transitory medium can be a CD ROM or a different memory device located remotely from the network device 10. The instructions contained on this second computer readable non-transitory medium can be downloaded onto the memory device 25 to allow the network device 10 to execute these instructions.

[0026] Although the processing unit 20, the memory device 25, the network interface 30 and the second memory device 40 are shown in Figure 1 as separate components, it can be understood that some or all of these components can be integrated into a single electronic component. Conversely, Figure 1 the network device 10 is used to illustrate the functionality of the network device 10, and not its physical configuration.

[0027] Although not shown, the network device 10 also has a power source, which can be a battery or a connection to a permanent power source, such as a wall outlet.

[0028] Having described the basic architecture of the network device, a description of the one-way ranging process will be provided.

[0029] First, reference will be made to Figure 2A , which assumes that a first network device 100 (also referred to as a tag or a transmitter) transmits a signal to a second network device 110 (also referred to as a locator or a receiver). Figure 2B The working of this system and method is illustrated.

[0030] A phase locked loop (PLL) or voltage controlled oscillator (VCO) 101 is used to generate a first signal having a first frequency (ω LO ) and a first phase The cosine of this first signal is provided to a first multiplier 102, and the sine of this first signal is provided to a second multiplier 103. A second signal, labeled a, is also provided to the first multiplier 102, and a third signal, labeled b, is provided to the second multiplier 103. Thus, as shown in Figure 2B the output from the first multiplier 102 can be written as and the output from the second multiplier can be written as These two outputs are then added using a summing node 104. The result of this can be represented as:

[0031]

[0032] If b / a is defined as tan(ω IF t+ψ), then the above equation can be rewritten as:

[0033]

[0034] Therefore, by appropriately selecting a and b, the output frequency of the summing node 104 can be improved positively or negatively. Furthermore, if a and b are generated using a lookup table, their frequencies can be changed while maintaining the phase.

[0035] For example, suppose a and b are initially set as cos(ω) IF t+ψ) and sin(ω) IF t+ψ), then switch to cos(-ω) respectively IF t+ψ) and sin(-ω) IF t+ψ). Thus, the transmission frequency will be... and The phase is constant. Therefore, it is easy to see that a small frequency (i.e., 2ω) can be generated with a constant phase. IF Two frequencies separated by a )

[0036] use Figure 2B The principle illustrated allows for the generation of multiple frequency groups. A frequency group is defined as a tightly grouped set of frequencies that can be generated using the common output of PLL 101. For example, using a lookup table, a and b can be set to multiple frequencies, such as between -5MHz and +5MHz. In other embodiments, using a lookup table, a and b can be set to multiple frequencies between -3MHz and +3MHz. Therefore, for the first frequency group, PLL 101 can be set to 2.4GHz, and the output frequency can be between 2.397GHz and 2.403GHz. For the second frequency group, PLL 101 can be set to 2.48GHz, and the output frequency can be between 2.477GHz and 2.483GHz.

[0037] By using a frequency group with a narrow frequency range, the settings of the transmitting circuit 38 can be maintained by transmitting signals.

[0038] Figure 3 This illustrates what can be achieved by the first network device 100. Figure 2B The block diagram shown includes the transmitting circuit 38. As described above, the controlled oscillator (PLL / VCO) 101 is used to generate a frequency with a first carrier frequency (ω). LO ) and the first phase of the first signal. The cosine of the first signal is provided to the first multiplier 102 and the sine of the first signal is provided to the second multiplier 103. The counter 106 is used to index into the look-up table 107, which can be a random access memory device or a read only memory. In some embodiments, a plurality of outputs are created by the look-up table 107, where each output has the same phase, such that all outputs have a constant phase. These outputs can be in the form of sin(ω j t + ψ i ) and cos(ω j t + ψ i ). The outputs from the look-up table 107 are used as inputs to the multiplexer 108. These outputs can be referred to as adjusted frequencies. The multiplexer selects a pair of these adjusted frequencies, which are the cosine and sine of the same frequency (ω j ). These pair of inputs are then passed to the first multiplier 102 and the second multiplier 103, respectively. The two outputs are then added using the summing node 104. The output from the summing node 104 is then transmitted using the power amplifier 105. The output frequency and phase of the power amplifier 105 can be represented as:

[0039]

[0040] where ω j is selected by the multiplexer 108 using a selection signal.

[0041] Similarly, a constant phase must also be maintained at the second network device 110. Figure 4 A block diagram of the receive circuit 36 is shown. The wireless signal first enters the receive circuit 36 through an antenna 37. The antenna 37 is in electrical communication with a low noise amplifier (LNA) 51. The LNA 51 receives a very weak signal from the antenna 37 and amplifies the signal while maintaining the signal-to-noise (SNR) of the input signal. The amplified signal is then passed to two mixers 52. The mixers 52 are also in communication with a local oscillator, such as a PLL 53, which provides two phases to the mixers 52. The frequency of the PLL 53 is (ω LO ) and the phase is The frequency of the PLL 53 can be referred to as the receiver carrier frequency. The cosine of this frequency can be referred to as the I o and the sine of this frequency can be referred to as the Q o . The I o signal is then multiplied with the input signal to create an in-phase signal I m . The Q o signal is then multiplied with the input signal to create a quadrature signal Q mThe in-phase signal I m and the quadrature signal Q m from the mixer 52 are then fed into a programmable gain amplifier (PGA) 54. The PGA 54 amplifies the I m and Q m signals by a programmable amount. These amplified signals are referred to as I g and Q g . The PGA 54 can also include a lowpass filter (LPF). The amplified signals I g and Q g are then fed from the PGA 54 into an analog to digital converter (ADC) 55. The ADC 55 converts these analog signals into digital signals I d and Q d . These digital signals can pass through a second mixer 56. The other input to the second mixer 56 is an output from a digital local oscillator (DLO) 57. The digital local oscillator 57 is fed by a look-up table 58, which can be similar to the look-up table shown in Figure 3 . The output from the digital local oscillator 57 can be a signal with a frequency of ω j and a phase of ψ R . This can be referred to as the adjusted frequency. The output from the second mixer 56 then exits the receive circuit 36 as I and Q. In some embodiments, the I and Q values can be considered as a complex number, where the I value is the real component and the Q value is the imaginary component.

[0042] The I and Q signals then enter a Coordination Rotation Digital Computer (CORDIC) 59, which determines the amplitude and phase of the signal. The amplitude is given as the square root of I 2 and Q 2 , and the phase is given as tan -1 (Q / I). The CORDIC 59 can be disposed in the radio circuit 31 or elsewhere within the network interface 30. Referring to Figures 2A-4 , it can be seen that the resulting phase can be where, is the phase of the PLL 101 in the first network device 100, ψ I is the phase of the look-up table 107 in the first network device, θ p is the phase delay due to the signal transmission, and is the phase of the PLL 53 in the second network device 110, ψ R is the phase of the look-up table 58 in the second network device 110.

[0043] Thus, if the signal is transmitted by the first network device 100 having two different frequencies within a single frequency group and received by the second network device 110, there is the following relationship:

[0044] where, is the phase delay measured at the second network device with the first frequency f1; and

[0045] where, is the phase delay measured at the second network device with the second frequency f2.

[0046] Since the PLL 101 maintains the same frequency with both frequencies in the frequency group, is constant for both frequencies. Similarly, since the PLL 53 maintains the same frequency with both frequencies in the frequency group, is constant for both frequencies. Furthermore, since there is a constant phase in the look-up table 107, I is constant for both frequencies. Similarly, since there is a constant phase in the look-up table 58, R is constant for both frequencies. Thus,

[0047] In other words, by creating a constant phase between the frequencies f1 and f2 in the look-up table and maintaining the PLL at a constant frequency, the distance between the two network devices can be determined. The distance equation can be expressed as:

[0048] where c is the speed of light.

[0049] Furthermore, with these equations, the phase difference between the transmitter and the receiver can be determined as:

[0050] where N2 / N1 is the ratio of the second frequency (f2) to the first frequency (f1).

[0051] If multiple measurements are made, these results can be averaged to produce an average phase difference between the transmitter and receiver for a particular frequency group

[0052] While this equation is useful for finding distance, it is worth noting that the difference between f1 and f2 can only be a few megahertz. This approximation can limit the accuracy of this calculation, especially at smaller distances.

[0053] Accordingly, to improve the accuracy of the distance calculation, it can be beneficial to have a greater difference between the different frequencies. One way to address this issue is to utilize a second set of frequencies.

[0054] Figure 5 An example is shown using two sets of frequencies labeled X and Y. In this example, f1 and f3 are part of frequency set X, while f2 and f4 are part of frequency set Y. In some embodiments, these two sets of frequencies can be separated by 10 MHz or more. In certain embodiments, the sets of frequencies can be separated by 20 MHz or more. Note that in some embodiments, there is no phase relationship between these different sets of frequencies. A first distance can be calculated using frequencies f1 and f2. This distance can be represented as:

[0055]

[0056] where,

[0057] is the phase of the PLL 101 when used in the second set of frequencies,

[0058] ψ IY is the phase of the lookup table 107 when used in the second set of frequencies,

[0059] is the phase of the PLL 53 when used in the second set of frequencies,

[0060] ψ IY is the phase of the lookup table 58 when used in the second set of frequencies,

[0061] is the phase measured by the second network device when receiving f2, and

[0062] is the phase measured by the second network device when receiving f1.

[0063] Further, where these variables are as described above for the first set of frequencies.

[0064] A second distance can be calculated using frequencies f3 and f4. This distance can be represented as:

[0065]

[0066] where, is the phase measured by the second network device when receiving f4, and

[0067] is the phase measured by the second network device when receiving f3.

[0068] Note that d1 and d2 should be equal. Thus, if these equations are set equal to each other, the following can be obtained:

[0069]

[0070] The above relationships can be expressed in different ways. Equation (1) can be rewritten as:

[0071]

[0072] where, can be easily calculated.

[0073] Similarly, equation (2) can be rewritten as:

[0074]

[0075] where, can also be easily calculated.

[0076] Each of the original distances contains two terms. The first term represents the actual distance (the actual distances are equal), but the second term represents an unknown distance due to the unknown phase relationship between the transmitters and receivers in the frequency sets X and Y. By subtracting equation (5) from equation (4), the actual distances can be eliminated and the phase difference between the frequency sets X and Y can be determined.

[0077] Subtracting equation (5) from equation (4) gives:

[0078]

[0079] Since all of the terms on the right side of equations (3) and (6) are known or can be measured, these equations can be solved to obtain This value can be referred to as the inter-frequency set phase difference. The inter-frequency set phase difference can then be substituted into either distance equation (1) or (2) to give the actual distance between the two network devices. Since two different frequency sets are used to calculate this distance, this distance can be referred to as an inter-frequency set range measurement.

[0080] Note that, Figure 5f1 and f2 are shown to have less dispersion, while f3 and f4 are more dispersed. This configuration can be very useful when calculating the phase difference of frequency group X and frequency group Y, as it maximizes the frequency difference, thereby reducing sensitivity. However, other configurations are possible. For example, f1 and f4 and f2 and f3 can be utilized to generate the above equation if desired. In other words, the only requirement is that f1 and f3 belong to the same frequency group, and f2 and f4 belong to the same frequency group. Furthermore, as mentioned above, frequencies within a given frequency group have the same phase, while in some embodiments, there can be no phase relationship between frequency groups.

[0081] Accordingly, in the present embodiment, the following steps are performed, as shown in Figure 6 First, as shown in block 600, the first network device 100 transmits a first distance detection signal having two frequencies contained within a first frequency group. In certain embodiments, the network interface 30 operates on a wireless network utilizing a Bluetooth network protocol. In the present embodiment, the distance detection signal can include a preamble, which is used to synchronize the clock of the receiver with the frequency and phase of the incoming signal. Next, a synchronization character can occur. The synchronization character is a predetermined bit sequence used to indicate the boundary between symbols. The synchronization character can be equivalent to the 32-bit "access address" in a Bluetooth Low Energy (BLE) packet. The synchronization character can be followed by a header. The header can include information such as the identity of the network device transmitting the distance detection signal. The header can be followed by a first constant tone having a first frequency. Finally, a second constant tone having a second frequency is transmitted. Note that a frequency group can include 2 or more frequencies.

[0082] The second network device 110 sets the receive circuit 36 to receive the first distance detection signal, as shown in block 610. The second network device 110 then receives the first distance detection signal, as shown in block 620. The second network device 110 then samples the phase during the first constant tone and during the second constant tone, as shown in block 630. In certain embodiments, each constant tone is transmitted for a predetermined duration of time. In certain embodiments, the time between sampling the first constant tone and the second constant tone by the second network device 110 is equal to the predetermined duration of time. These measured phase samples can be referred to as and

[0083] As shown in block 640, the first network device 100 then transmits a second distance detection signal having two frequencies contained within a second frequency group different from the first frequency group. The first network device 100 can change the frequency and phase of the PLL 101 prior to transmitting the second distance detection signal.

[0084] As represented by block 650, the second network device 110 receives the second distance detection signal. Although not shown, the second network device 110 can change the settings in the receive circuitry 36 to accommodate the frequency transmitted in the second distance detection signal. The second network device 110 samples the phase during the first constant tone and during the second constant tone, as represented by block 660. These samples can be referred to as and

[0085] As represented by block 670, the second network device 110 then calculates the distance between the first network device 100 and the second network device 110. As described above, this calculation can require multiple calculations. For example, the second network device can use equation (3) given above to calculate a value for the inter-frequency group phase difference. Once this value is known, the second network device can use this value in one of the distance equations (1) or (2) given above to find the distance between the second network device and the first network device.

[0086] In many embodiments, the sequence described above is sufficient to obtain the distance between the two network devices. However, in certain embodiments, the inter-frequency group phase difference obtained from equation (3) can not be accurate due to the neglect of phase wrapping.

[0087] Therefore, if the result in equation (3) is not accurate, then the distance calculated using equation (1) or equation (2) can also not be accurate. Therefore, in certain embodiments, compensation for phase wrapping is needed.

[0088] Therefore, in certain embodiments, the process described in block 670 can be more complex. For example, Figure 7 One embodiment that can be used to compensate for phase wrapping is shown.

[0089] First, as described above and as represented by block 700, a value for the inter-frequency group phase difference is determined. This value can then be plugged into one of the distance equations (1) or (2) to derive a theoretical distance between the two network devices, as represented by block 710. As a sanity check, the distance calculation can be performed using frequencies within the same frequency group. Note that for frequencies within the same frequency group, there is no problem with phase wrapping because the phase remains constant and the distance is limited to a range consistent with the frequency dispersion. Therefore, in certain embodiments, an approximate distance is calculated using two frequencies from the same frequency group, as represented by block 720. This distance can be referred to as an intra-frequency group distance measurement. This value will represent the actual distance, but can lack accuracy depending on the distance between the two network devices.

[0090] The approximate distance or intra-frequency bin distance is then compared to the calculated distance, as shown in block 730. If the calculated distance and the intra-frequency bin distance are within a predetermined threshold, the calculated value is considered correct, as shown in block 750. The sequence is then completed.

[0091] However, if the difference between the intra-frequency bin distance and the calculated distance is greater than the predetermined threshold, a phase wrap is considered to have occurred. To compensate for this, the calculated value of the inter-frequency bin phase difference is increased or decreased by 2π, as shown in block 740. For example, if the intra-frequency bin distance is greater than the calculated distance, the inter-frequency bin phase difference can be increased by 2π. Also, if the intra-frequency bin distance is less than the calculated distance, 2π can be subtracted from the inter-frequency bin phase difference.

[0092] The sequence is then continued by repeating the steps shown in blocks 710-740 until the difference between the intra-frequency bin distance and the calculated distance is less than the predetermined threshold.

[0093] In certain embodiments, the predetermined threshold can be a small value, such as 1 meter. In other embodiments, a somewhat larger threshold can be utilized.

[0094] Other modifications can be made to improve the accuracy of this distance measurement. For example, if the frequency of the transmitter differs from the frequency of the receiver by a small amount (e.g., less than 80 ppm), the localizer can measure this frequency error and compensate the phase calculations based on the frequency error. One method of compensation is to make two or more phase measurements over a known time interval, the resulting phase measurements will increase (or decrease) with each successive measurement, from which the frequency error can be calculated and removed from the desired phase measurement by back- projecting the phase measurement to a given time. Alternatively, the receiver can measure the frequency error and modify the frequency of the PLL 53 to match the frequency of the PLL 101 and measure the phase after a settling interval. Other techniques known in the art can be applied.

[0095] For example, the above-described systems and methods rely on the phase of two transmitted signals, each having two different frequencies. The phase delay from the antenna through the receive circuitry 38 to the ADC 55 can differ depending on the frequency. For example, the phase delay caused by components in the path, such as capacitors and inductors, is a function of frequency. This set of components can be referred to as the receive group or Rx group. Thus, in certain embodiments, the Rx group is calibrated at each frequency used for the distance detection signal. The Rx group delay can be calibrated in a variety of ways. For example, the calibration can be performed by the chip manufacturer and provided to the user. In another embodiment, the calibration results can be stored in a one-time programmable (OTP) portion of memory. In another embodiment, the user can perform the calibration and save the results.

[0096] In all these embodiments, when calculating the actual phase of the first and second signals, the phase difference caused by the Rx group delay can be calculated and taken into account.

[0097] In addition, another source of error can be the phase delay introduced by the transmit circuitry 38 of the first network device 100. This phase error can be calculated in a number of ways. For example, the calibration can be performed by the chip manufacturer and the phase delay per frequency can be provided to the user. In another embodiment, the calibration results can be stored in non-volatile memory. In another embodiment, the user can perform the calibration and save the results. For example, a calibration station can be used to receive the frequencies of interest from the first network device. Thereafter, the calibration station can measure the phase difference between these two frequencies. This difference can then be stored in the non-volatile memory (NVM) portion of the memory. In yet another embodiment, a loopback test can be performed where the transmit circuitry 38 of the first network device is in communication with the antenna. The first network device transmits two frequencies of interest and then simultaneously measures the phase of each of these frequencies as received by the receive group to calculate the phase delay associated with the transmission. The result of this calculation can be referred to as the transmitter phase correction.

[0098] The distance from the first network device 100 to the second network device 110 can be used in a number of applications. For example, the distance detection can be used in conjunction with angle of arrival or bearing algorithms. For example, by determining the angle of arrival and the distance to the first network device 100, the second network device 110 can estimate the three-dimensional location of the first network device 100. This location information can be used in a number of ways. For example, if the first network device (or tag) is installed on each of a number of assets in a warehouse, the second network device (or locator) can identify the location of a particular item. In some embodiments, there can be multiple locators (receivers) each measuring its distance to a tag (transmitter). The locators send their measurements to a master locator (or another processing unit) which uses the known locations of the locators and the distance measurements to calculate the tag location as the intersection of multiple ranges, similar to GPS. In addition, there are applications beyond industrial asset tracking. For example, the two network devices can also be used as proximity sensors. For example, when a user (holding a tag) approaches a car (acting as a locator), the car doors can automatically unlock. This concept can be extended to area creation, where events are triggered when a user enters / exists a geographic area. In addition, the network device system can also be used to track pets or locate personal items.

[0099] The present system and method has many advantages. First, the system and method does not require a network connection between the first network device and the second network device. Thus, the second network device is able to track more devices than if the second network device had to establish a network connection with each device. Thus, the present system and method is much more scalable than a two-way distance detection system. Furthermore, the system and method described herein allows for the use of frequencies that differ by many megahertz. This can improve the accuracy of the measurements, especially in short distance situations.

[0100] The scope of the application is not intended to be limited to the particular embodiments described in this document. Indeed, a variety of other embodiments and modifications to the present application can be apparent to those of ordinary skill in the art from the description and drawings herein. Such other embodiments and modifications are therefore intended to fall within the scope of the application. Further, although the present application has been described herein in terms of particular embodiments for particular applications, those of ordinary skill in the art will appreciate that other embodiments and modifications are possible.

[0101] This application claims priority to U.S. Provisional Patent Application 63 / 221,152, filed July 13, 2021, the disclosure of which is incorporated in its entirety herein.

Claims

1. A method for measuring the distance between two network devices, comprising: A distance detection signal is transmitted from a first network device, the distance detection signal comprising a first frequency f1 and a second frequency f2 transmitted sequentially, wherein the phase of the first frequency and the second frequency is constant; The distance detection signal is received at the second network device; The phase of the first frequency and the phase of the second frequency are determined at the second network device, and are respectively referred to as... and ;as well as Using f1, f2, and The value is used to calculate the distance between the first network device and the second network device, wherein the distance is an intra-frequency group distance measurement value; The first frequency is created using a common carrier frequency and a first adjustment frequency, and the second frequency is created using the common carrier frequency and a second adjustment frequency, wherein the phase of the first adjustment frequency and the phase of the second adjustment frequency are equal.

2. The method according to claim 1, wherein, The first adjustment frequency and the second adjustment frequency are created using a lookup table.

3. The method according to claim 1, wherein, The second network device uses a common receiver carrier frequency and a first receiver adjustment frequency to remove the common carrier frequency and the first adjustment frequency from the first frequency of the distance detection signal to determine the phase of the first frequency, and uses the common receiver carrier frequency and the second receiver adjustment frequency to remove the common carrier frequency and the second adjustment frequency from the second frequency of the distance detection signal to determine the phase of the second frequency.

4. The method according to claim 1, further comprising: Following the second frequency, at least one additional frequency is transmitted from the first network device, wherein each additional frequency is generated using the common carrier frequency and the adjustment frequency; and The phase of the at least one additional frequency is determined at the second network device, and the phase of the at least one additional frequency is used to calculate the intra-frequency group interval.

5. A method for measuring the distance between two network devices, comprising: A first distance detection signal is transmitted from a first network device. The first distance detection signal includes a first frequency f1 and a second frequency f2 transmitted sequentially, wherein the phase of the first frequency and the second frequency is constant. The first distance detection signal is received at the second network device; At the second network device, the phase of the first frequency and the phase of the second frequency are determined, and are respectively referred to as... and ; A second distance detection signal is transmitted from a first network device. The second distance detection signal includes a third frequency f3 and a fourth frequency f4 transmitted in sequence, wherein the phase of the third frequency and the fourth frequency is constant. The second distance detection signal is received at the second network device; At the second network device, the phase of the third frequency and the phase of the fourth frequency are determined, respectively referred to as... and ;as well as Using f1, f2, f3, f4, , , and The value is used to calculate the distance between the first network device and the second network device, wherein the distance is an inter-frequency group spacing measurement value; Wherein, the first frequency and the second frequency belong to a first frequency group, wherein the first frequency group is defined as a set of frequencies generated using a common carrier frequency; wherein, the third frequency and the fourth frequency belong to a second frequency group, wherein the second frequency group is different from the first frequency group, and the second frequency group is defined as a set of frequencies generated using a second common carrier frequency; The first frequency is created using the common carrier frequency and the first adjustment frequency, and the second frequency is created using the common carrier frequency and the second adjustment frequency, wherein the phase of the first adjustment frequency and the phase of the second adjustment frequency are equal. The third frequency is created using the second common carrier frequency and the third adjustment frequency, and the fourth frequency is created using the second common carrier frequency and the fourth adjustment frequency, wherein the phase of the third adjustment frequency and the phase of the fourth adjustment frequency are equal.

6. The method according to claim 5, wherein, There is no phase relationship between the common carrier frequency and the second common carrier frequency.

7. The method according to claim 5, wherein, The first adjustment frequency and the second adjustment frequency are created using a lookup table.

8. The method according to claim 5, wherein, The second network device uses a common receiver carrier frequency and a first receiver adjustment frequency to remove the common carrier frequency and the first adjustment frequency from the first frequency of the first distance detection signal to determine the phase of the first frequency, and uses the common receiver carrier frequency and the second receiver adjustment frequency to remove the common carrier frequency and the second adjustment frequency from the second frequency of the first distance detection signal to determine the phase of the second frequency.

9. The method according to claim 5, wherein, The inter-frequency group distance measurement value is calculated based on the inter-frequency group phase difference, which is defined as the total phase difference between the first network device and the second network device when transmitting and receiving the second distance detection signal minus the total phase difference between the first network device and the second network device when transmitting and receiving the first distance detection signal.

10. The method according to claim 9, wherein, The second network device only utilizes f1, f2, and Perform intra-frequency group spacing measurement and calculate the difference between the inter-frequency group spacing measurement value and the intra-frequency group spacing measurement value. If the difference is greater than a predetermined threshold, adjust the inter-frequency group phase difference by 2π, recalculate the inter-frequency group spacing measurement value using the adjusted inter-frequency group phase difference, and repeat the adjustment and recalculation until the difference is less than the predetermined threshold.

11. A system for measuring the distance between two network devices, comprising: The first network device is configured as follows: A first distance detection signal is transmitted, comprising a first frequency f1 and a second frequency f2 transmitted sequentially, wherein the first frequency and the second frequency belong to a first frequency group, wherein the frequency group is defined as a set of frequencies generated using a common carrier frequency, and wherein the phases of the first frequency and the second frequency are constant; and The second network device is configured as follows: Receive the first distance detection signal; The phase of the first frequency and the phase of the second frequency are determined, respectively referred to as... and ;as well as Using f1, f2, and The value is used to calculate the distance between the first network device and the second network device, wherein the distance is an intra-frequency group distance measurement value; The first network device generates the first frequency using the common carrier frequency and the first adjustment frequency, and generates the second frequency using the common carrier frequency and the second adjustment frequency, wherein the phase of the first adjustment frequency and the phase of the second adjustment frequency are equal.

12. The system according to claim 11, wherein, The first adjustment frequency and the second adjustment frequency are created using a lookup table.

13. The system according to claim 11, wherein, The second network device uses a common receiver carrier frequency and a first receiver adjustment frequency to remove the common carrier frequency and the first adjustment frequency from the first frequency of the first distance detection signal to determine the phase of the first frequency, and uses the common receiver carrier frequency and the second receiver adjustment frequency to remove the common carrier frequency and the second adjustment frequency from the second frequency of the first distance detection signal to determine the phase of the second frequency.

14. The system according to claim 11, wherein, The first network device is further configured as follows: A second distance detection signal is transmitted, comprising a third frequency f3 and a fourth frequency f4 transmitted sequentially, wherein the phases of the third and fourth frequencies are constant; and The second network device is further configured as follows: Receive the second distance detection signal; The phase of the third frequency and the phase of the fourth frequency are determined, respectively referred to as... and ;as well as Using f1, f2, f3, f4, , , and The value is used to calculate the distance between the first network device and the second network device, wherein the distance is an inter-frequency group distance measurement value.

15. The system according to claim 14, wherein, The first network device uses a second common carrier frequency, which is different from the common carrier frequency, to generate the third frequency and the fourth frequency.

16. The system according to claim 14, wherein, The second network device calculates the inter-frequency group distance measurement value based on the inter-frequency group phase difference. The inter-frequency group phase difference is defined as the total phase difference between the first network device and the second network device when transmitting and receiving the second distance detection signal minus the total phase difference between the first network device and the second network device when transmitting and receiving the first distance detection signal.

17. The system according to claim 16, wherein, The second network device only utilizes f1, f2, and Perform intra-frequency group spacing measurement and calculate the difference between the inter-frequency group spacing measurement value and the intra-frequency group spacing measurement value. If the difference is greater than a predetermined threshold, adjust the inter-frequency group phase difference by 2π and recalculate the inter-frequency group spacing measurement value using the adjusted inter-frequency group phase difference. Repeat the adjustment and recalculation until the difference is less than the predetermined threshold.

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