Efficient distance measurement algorithm for high-accuracy distance measurement

Abstract

A system and method for determining the distance between two wireless network devices are disclosed. The system uses a power ratio-based algorithm. The power ratio can be calculated as the ratio of the test signal power to the total signal power. The test signal power is defined as the signal power related to a given distance. This algorithm calculates the channel frequency response and uses the phase signal at each frequency and distance to calculate the power ratio and the cumulative power ratio. Based on the slope of the cumulative power ratio curve, the line-of-sight distance is determined. This approach does not rely on eigenvectors or a prior estimate of the number of signals and can therefore be computed quickly and efficiently.

Description

[0001] This application claims priority over the preliminary US patent application with serial number 63 / 669,539, filed on July 10, 2024, and the US patent application with serial number 18 / 825,703, filed on September 5, 2024, the disclosures of which are hereby incorporated in their entirety by reference. Area

[0002] This disclosure describes systems and methods for determining the distance between two wireless network devices, and in particular the use of a novel distance measurement algorithm for determining this distance. background

[0003] The Bluetooth protocol has developed several techniques for implementing high-precision distance measurement (HADM). These include a phase-based distance measurement approach and a round-trip time approach. Typically, these approaches involve two devices: an initiator device that initiates the distance measurement and a reflector device that responds to the initiator device. The measured distance is the distance between these two devices.

[0004] In the round-trip time (RTT) approach, each device uses a timestamp. Specifically, when a packet is sent, the sending device records a transmission timestamp. When this packet arrives, the receiving device uses a reception timestamp.

[0005] In the phase-based approach, the initiator device determines the incoming phase for signals transmitted at two different frequencies. The phase (θ) measured at the initiator device init ) can be approximately the phase difference between the two devices (i.e., Δθ). ir ) correspond, added to the product 2π * f * (tp), where f is the frequency of the transmitted signal and tp is the propagation delay. If this phase is measured at two different frequencies and the difference is calculated, (θ) is obtained. init1 ) - (θ init2) = 2π * f1 * (tp) - 2π * f2 * (tp) or 2 * π * (f1 - f2) * (tp). Based on this equation, the propagation delay can be calculated and then converted into a distance. This approach can be improved by using the MUSIC (Multiple Signal Classification) algorithm. The MUSIC algorithm uses this information to generate pseudo-spectra that can be used to determine the distance between the two devices.

[0006] However, these existing algorithms have limitations. For example, the MUSIC algorithm is very computationally and memory-intensive, which can be problematic for certain devices. Furthermore, the algorithm can also be time-consuming, making its use for measuring moving devices difficult.

[0007] Therefore, an improved system and an improved process would be advantageous. Furthermore, it would be beneficial if the improved system did not require significant computing power. Summary

[0008] A system and method for determining the distance between two wireless network devices are disclosed. The system uses a power ratio-based algorithm. The power ratio can be calculated as the ratio of the test signal power to the total signal power. The test signal power is defined as the signal power related to a given distance. This algorithm calculates the channel frequency response and uses the phase signal at each frequency and distance to calculate the power ratio and the cumulative power ratio. Based on the slope of the cumulative power ratio curve, the line-of-sight distance is determined. This approach does not rely on eigenvectors or prior estimates of the number of signals and can therefore be computed quickly and efficiently.

[0009] According to one embodiment, a method for calculating a distance between two wireless network devices is disclosed.The procedure includes performing a channel sounding procedure at a plurality of frequencies to obtain a channel frequency response; autocorrelating the channel frequency response to obtain an autocorrelated channel frequency response; using the autocorrelated channel frequency response to generate a power ratio as a function of distance, where the power ratio is defined as the test signal power divided by the total power of the autocorrelated channel frequency response; calculating a cumulative power ratio as a function of distance using the power ratio; identifying a ramp in the cumulative power ratio; and using a slope of the ramp, the power ratio, and the cumulative power ratio to determine a distance between the two wireless network devices.In some embodiments, the test signal power at a first distance is initially calculated by de-rotating a phase of a signal path at the first distance from the autocorrelated channel frequency response to obtain a de-rotated frequency response. In certain embodiments, the test signal power at the first distance is calculated by squaring an absolute mean of the de-rotated frequency response at the plurality of frequencies. In some embodiments, the overall power of the autocorrelated channel frequency response is calculated as the square of an absolute value of the autocorrelated channel frequency response at each of the plurality of frequencies. In some embodiments, the two wireless network devices include Bluetooth network devices. In some embodiments, if the slope of the ramp is steep, the distance is defined as a first peak value in the power ratio.In certain embodiments, the power ratio is calculated at a plurality of distances, and the first peak value is defined as a peak value that exceeds a limit at a minimum distance. In certain embodiments, if the ramp slope is steep, the distance is determined using a phase-based approach. In certain embodiments, if the ramp slope is not steep, the distance is defined as the minimum distance at which the cumulative power ratio exceeds a predetermined limit.

[0010] According to a further embodiment, a Bluetooth network is disclosed. The Bluetooth network comprises a reflector device and an initiator device, comprising: a Bluetooth network interface, a processing unit, and a storage device, wherein the storage device contains instructions which, when executed by the processing unit, cause the initiator device to: perform a channel sounding procedure at a plurality of frequencies to obtain a channel frequency response; autocorrelate the channel frequency response to obtain an autocorrelated channel frequency response; and use the autocorrelated channel frequency response to generate a power ratio as a function of distance.wherein the power ratio is defined as test signal power divided by the total power of the autocorrelated channel frequency response; calculating a cumulative power ratio as a function of distance using the power ratio; identifying a ramp in the cumulative power ratio; and using a slope of the ramp, the power ratio, and the cumulative power ratio to determine a distance between the reflector device and the initiator device. In some embodiments, the test signal power at a first distance is initially calculated by derotating a phase of a signal path at the first distance from the autocorrelated channel frequency response,to obtain a de-rotated frequency response. In certain embodiments, the test signal power at the first distance is calculated by squaring an absolute mean of the de-rotated frequency response at the plurality of frequencies. In some embodiments, the overall power of the autocorrelated channel frequency response is calculated as the square of an absolute value of the autocorrelated channel frequency response at each of the plurality of frequencies. In some embodiments, if the slope of the ramp is steep, the distance is defined as a first peak value in the power ratio. In certain embodiments, the power ratio is calculated at a plurality of distances, and the first peak value is defined as a peak value that has a magnitude greater than a limit value at a minimum distance. In certain embodiments, if the slope of the ramp is steep,The distance is determined using a phase-based approach. In certain embodiments, if the ramp gradient is not steep, the distance is defined as the smallest distance at which the cumulative power ratio exceeds a predetermined limit.

[0011] According to a further embodiment, a method for calculating a distance between two wireless network devices is disclosed. The method comprises performing a channel sounding procedure at a plurality of frequencies to obtain a channel frequency response; using the channel frequency response to generate a power ratio as a function of distance, wherein the power ratio is defined as the test signal power divided by the total power of the channel frequency response; calculating a cumulative power ratio as a function of distance using the power ratio; identifying a ramp in the cumulative power ratio; and using a slope of the ramp, the power ratio, and the cumulative power ratio to determine a distance between the two wireless network devices.In some embodiments, the test signal power at a first distance is initially calculated by derotating a phase of a signal path at the first distance from the channel frequency response to obtain a derotated frequency response. In certain embodiments, the test signal power at the first distance is calculated by squaring an absolute mean of the derotated frequency response at the plurality of frequencies. In some embodiments, the overall power of the channel frequency response is calculated as the square of an absolute value of the channel frequency response at each of the plurality of frequencies. In some embodiments, the two wireless network devices include Bluetooth network devices. In some embodiments, if the slope of the ramp is steep, the distance is defined as a first peak value in the power ratio.In certain embodiments, the power ratio is calculated at a plurality of distances, and the first peak value is defined as a peak value that exceeds a limit at a minimum distance. In certain embodiments, if the ramp slope is steep, the distance is determined using a phase-based approach. In certain embodiments, if the ramp slope is not steep, the distance is defined as the minimum distance at which the cumulative power ratio exceeds a predetermined limit. Brief description of the drawings

[0012] For a better understanding of the present invention, reference is made to the accompanying drawings, in which identical elements are provided with the same reference numerals and in which: Fig. 1 is a block diagram of a representative initiator device which, according to one embodiment, can estimate the distance; Fig. 2 a network comprising an initiator device and at least one reflector device according to an embodiment; Fig. 3A shows an exemplary graph that represents the power ratio as a function of distance; Fig. 3B the graphic from Fig. 3A shows using autocorrelation; Fig. 4 shows a flowchart that is used to calculate the line-of-sight distance; Fig. 5A-5B show the power ratio and the cumulative power ratio for a first configuration; Fig. 6A-6B show the power-to-weight ratio and the cumulative power-to-weight ratio for a second configuration; and Fig. Figure 7 shows a comparison of two cumulative distribution functions that show the error when a plurality of distance measurements are performed using a conventional approach and the disclosed approach. Detailed description

[0013] Fig. Figure 1 shows a block diagram of a representative network device. This network device can serve as an initiator device 10, as described in more detail below. This network device can also be used to determine the distance to a remote device, also known as a reflector device.

[0014] The initiator device 10 comprises 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, an application-specific circuit, a programmable circuit, a microcontroller, or another similar device. This memory device 25 contains the instructions 26 which, when executed by the processing unit 20, cause the initiator device 10 to perform the functions described herein. This memory device 25 can be non-volatile memory, such as a flash ROM, an electrically erasable ROM, or other suitable devices. In other embodiments, the memory device 25 can be volatile memory, such as RAM or DRAM.

[0015] The initiator device 10 also includes a network interface 30, which can be a wireless interface with an antenna element 35.

[0016] The wireless signals first enter the network interface 30 via the antenna element 35. The antenna element 35 is electrically connected to a low-noise amplifier (LNA). The LNA receives a very weak signal from the antenna element 35 and amplifies this signal while maintaining the signal-to-noise ratio (SNR) of the incoming signal. The amplified signal is then passed to a mixer. The mixer is also connected to a local oscillator, which supplies two phases to the mixer. The cosine of the frequency can be expressed as I o are referred to as , while the sine of the frequency is called Q. o can be described as I o The -signal is then multiplied by the incoming signal to obtain the in-phase signal I. m to generate the Qo The signal is then multiplied by a 90° delayed version of the incoming signal to obtain the quadrature signal Q. m to generate the in-phase signal I. m and the quadrature signal Q m The signals from the mixer are then fed into a programmable amplifier (PGA). The PGA amplifies the signals I. m and Q m by a programmable amount. These amplified signals can be used as I g and Q g be designated. The amplified signals I g and Q g The PGA then feeds these signals into an analog-to-digital converter (ADC). The ADC converts these analog signals into digital signals. d and Q d These digital signals can then pass through a channel filter. The filtered signals are designated I and Q. These signals I and Q can be used to restore the amplitude and phase of the original signal.

[0017] Network interface 30 can support any wireless network, such as Bluetooth, Wi-Fi, networks using the IEEE 802.15.4 specification (e.g., Zigbee), networks using the IEEE 802.15.6 specification, and wireless smart home protocols (e.g., Z-Wave). Network interface 30 is used to enable the initiator device to communicate with other devices on the network.

[0018] The initiator device 10 can include a data storage device 40, which stores data received and sent by the network interface 30. This data storage device 40 is typically volatile memory. The processing unit 20 has the capability to write to and read from the data storage device 40 in order to communicate with the other nodes in the network. Although not shown, the initiator device 10 also has a power supply, which can be a battery or a connection to a permanent power source, such as a wall outlet.

[0019] Although a storage device 25 is disclosed, any computer-readable medium can be used to store these instructions. For example, a read-only memory (ROM), random-access memory (RAM), a magnetic storage device such as a hard disk, or an optical storage device such as a CD or DVD can be used. Furthermore, these instructions can be downloaded to the storage device 25, for example, via a network connection (not shown), via a CD-ROM, or by some other mechanism. These instructions 26 can be written in any programming language not limited by this disclosure. Thus, in some embodiments, there can be multiple computer-readable media containing the instructions described herein. The first computer-readable medium can be associated with the processing unit 20, as shown in Fig. Figure 1 shows the second computer-readable medium, which can be a CD-ROM or other storage device located remotely from the initiator device 10. The instructions contained on this second computer-readable medium can be downloaded to the storage device 25 to enable the initiator device 10 to execute the instructions.

[0020] Although the processing unit 20, the storage device 25, the network interface 30 and the data storage device 40 in Fig. The fact that components are shown as separate parts in section 1 should be understood to mean that some or all of these components may be integrated into a single electronic component. Rather, it serves the purpose of Fig. 1 to illustrate the functionality of the initiator device 10, not its physical configuration.

[0021] Fig. Figure 2 shows a network 100 with at least one reflector device 110 and one initiator device 10. In certain embodiments, the reflector device 110 can be a network device and incorporate some of the features described above and in Fig. The components shown in section 1 are included. However, the reflector device 110 may have less storage space and computing power.

[0022] In Fig. 2. The initiator device 10 can send a signal containing a sine wave with a first frequency to the reflector device 110. In response, the reflector device 110 can send a signal containing a sine wave with the same first frequency to the initiator device 10.

[0023] In certain embodiments, this signal is transmitted using a network protocol, such as Bluetooth.

[0024] The initiator device 10 can use the signals I and Q described above to determine the amplitude and phase of the signal arriving at the antenna element 35. This information can then be used to calculate the distance between the initiator device 10 and the reflector device 110.

[0025] Specifically, the Bluetooth specification now describes a channel sounding procedure in which the initiator device 10 sends a first signal at a first frequency to the reflector device 110. The reflector device 110 measures the amplitude and phase of the incoming first signal. In response, the reflector device 110 sends a second signal at the first frequency back to the initiator device 10. The initiator device 10 measures the amplitude and phase of the incoming second signal. This can be repeated for a number of different frequencies. Based on the amplitude and phase information collected by the initiator device 10 and the reflector device 110, the channel transfer function (H) can be estimated. It should be noted that the term "channel transfer function" is synonymous with "channel frequency response."

[0026] As a concrete example, the Bluetooth specification defines the following procedure for determining the channel transfer function.

[0027] First, there is θ c (f) for the phase delay of the channel, where f is the channel frequency, and Δθ LO (f) represents the relative phase difference of the RF carrier between the initiator device and the reflector device. Based on this, the relative phases of a carrier, measured at the reflector and at the antenna of the initiator, θ REFL (f) = θ C (f) + Δθ L0 (f) and θ INIT (f) = θ CH (f) - Δθ LO (f). A REFL (f) and A INI(f) represent the amplitude of this measured carrier at the reflector and the antenna of the initiator, respectively. The phase correction term (PCT) is defined as the angle which, when added to the internal angle of the local oscillator, results in a phase identical to that of the incoming signal. The values ​​I and Q, represented by the PCT, measured at the reflector and the initiator, respectively, are given by PCT REFL (f) = A REFL (f)e iθ REFL (f) and PCT INIT (f) = A INIT (f)e iθ INIT(f). If the communication channel between the initiator device 10 and the reflector device 110 is symmetrical, the measured phases depend on both the communication channel and the relative phase difference of the RF carrier frequency between the devices. The communication channel transfer function can then be derived from H 2 (f) = A REFL (f)e iθ REFL (f) × A INIT (f)e iθINIT (f) = A CH 2 (f)e i2θ CH (f) be estimated.

[0028] The channel transfer function (also known as channel frequency response) can then be used to calculate the distance between the initiator device 10 and the reflector device 110.

[0029] First, an autocorrelation of the channel frequency response is calculated to improve the signal-to-noise ratio. In a specific implementation, the autocorrelation of the channel frequency response is performed using the following algorithm: H^k=∑j=K−k+1KHk+j−KHj*, if k≤K H^k=H^2K−k*, if K <k≤2K−1

[0030] In these equations, we denote HK* the complex conjugate of H k In other words, if H k = a + bi, then Hk*=a−bi. In these equations, K represents the number of frequencies used to generate the channel frequency response.

[0031] Next, the power of a signal path at a predetermined distance can be estimated by de-rotating the signal path phase from the autocorrelated channel frequency response and based on the assumption that the average power of all other components is approximately zero.

[0032] This can then be used to calculate the power-to-weight ratio at any distance x. In particular, the power-to-weight ratio can be defined as follows: φ(x)=Ps(x)PH where P s (x) the test signal power and P H The overall performance of the autocorrelated channel frequency response is given.

[0033] Fig. Figure 3B shows an example spectrum that can be generated using this approach. It should be noted that each peak represents a distance at which measurable signal power is present. It should be noted that Fig. 3A shows the exemplary spectrum when the channel frequency response is not autocorrelated first.

[0034] The disclosed algorithm generates this spectrum and then determines the line-of-sight path based on several parameters. In particular, the algorithm also integrates the spectrum and uses the slope of the resulting integrated spectrum to determine the line-of-sight path, as explained below.

[0035] The test signal power can be calculated by de-rotating the signal path phase with the autocorrelated channel frequency response, as described above. The signal path phase can be defined using a fixed matrix, where the columns of this matrix represent different distances and the rows represent different frequencies. This matrix represents the signal path phase at various distances and frequencies.

[0036] Thus, D(f, d) is the signal path phase at frequency f at distance d. The values ​​of some of the frequencies used to fill this matrix can be chosen to match frequencies present in the channel frequency response. For example, some of these frequencies might match the frequencies of the various Bluetooth channels. The distances can represent the desired granularity of the measurement. For example, the distance can be set to large numbers (e.g., 1 meter) if the device is known to be far away, but can also be set to a smaller value, e.g., 5 cm, if the device is closer.

[0037] The signal path phase at each position in the matrix can be defined as follows: D(f,d)=ei2πfdc

[0038] Furthermore, the test signal power can be calculated by first multiplying the signal path phase by the autocorrelated channel frequency response Ĥ to obtain the de-rotated frequency response. Ĥ is defined as a (2K - 1) x 1 array, where K represents the number of frequencies used to calculate the channel frequency response. Thus, the de-rotated frequency response, represented by V, can be defined as follows: V=D⊗H^,

[0039] Here, ⊗ represents a point-wise multiplication of each element in each column of D by the corresponding element in Ĥ. In other words V(f,d)=D(f,d)∗H^(f)

[0040] Based on this de-rotated frequency response and the autocorrelated channel frequency response, the power ratio can be calculated as follows: φ(x)=|12N−1∑kV(k,x)|212N−1∑k(|H^(k)|2)

[0041] In this equation, we approximate |12N−1∑kV(k,x)|2 the test signal power across all frequencies at distance x, and 12N−1∑k(|H^(k)|2) This represents the total power of the autocorrelated channel frequency response. The power ratio thus represents the ratio of the power at distance x to the total power. The sum of the power ratios for the distances should therefore be 1, as this also represents the total power.

[0042] Fig. Figure 4 shows a flowchart that can be used to determine a distance between two devices.

[0043] First, as shown in block 400, several variables are initialized. These include the cumulative power ratio (C(x)), the starting distance (x), and the distance step size (x_step).

[0044] Next, as shown in Bloch 405, the signal path phase at each of the frequencies is calculated and stored in the array D(f, d). Specifically, for each frequency, the signal path phase is generated using the equation for D shown above.

[0045] As shown in Block 410, the channel sounding procedure is performed, and the channel frequency response (H) is calculated based on this procedure.

[0046] Subsequently, as shown in Block 420, the autocorrelation of the channel frequency response H, denoted as Ĥ, is calculated using the equations described above.

[0047] As shown in Block 430, the power ratio is then calculated at the distance value x. This is done by multiplying the phase values ​​of the array D (f, d) (one for each frequency) by the autocorrelated channel frequency response at that frequency to generate the de-rotated frequency response for the test signal at each frequency.

[0048] After this has been performed for each frequency, the power of the test signal can be calculated as the square of the mean of the de-rotated frequency response for the test signal across all frequencies. The power ratio can then be calculated using the following formula: φ(x)=|12N−1∑kV(k,x)|212N−1∑k(|H^(k)|2)

[0049] Once the power ratio at a given distance has been determined, this value is multiplied by the x_step value and added to the cumulative power ratio, as shown in block 440.

[0050] This process is then repeated until enough values ​​have been calculated to identify the ramp in the cumulative power-to-performance ratio, as shown in Decision Block 445 and Block 450. The result of these operations is a power-to-performance ratio curve and a cumulative power-to-performance ratio curve. Example curves are shown in Fig. 5A-5B shown. Fig. 5A shows the power ratio calculated for each distance. Fig. 5B is the cumulative power ratio for each distance. It should be noted that the cumulative power ratio is an estimate of the integral of the power-ratio curve in Fig. 5A is.

[0051] A ramp is defined as an upward trend in the cumulative power-to-ratio curve. In certain embodiments, the end of the ramp is defined as the distance, denoted as x_endramp, at which the cumulative power-to-ratio exceeds a predetermined high ramp threshold. This predetermined high ramp threshold can be a fixed value, for example, a value between 0.2 and 0.8, particularly between 0.3 and 0.5. Alternatively, it can be dynamically varied. To properly define the ramp's slope, a ramp start is also required. In certain embodiments, the ramp start is defined as the distance, denoted as x_startramp, at which the cumulative power-to-ratio exceeds a predetermined low ramp threshold. In certain embodiments, the low ramp threshold can be a fixed value, for example, a value between 0.001 and 0.1.The difference between the end distance and the start distance, defined as x_endramp - x_startramp, can be used to determine the steepness of the ramp. Specifically, small values ​​of this difference indicate a steep ramp, while larger values ​​indicate a less steep or flatter ramp. In one embodiment, the difference between the end distance and the start distance is compared to a fixed slope threshold. Differences below this fixed slope threshold are classified as steep ramps; differences greater than this fixed slope threshold are classified as gentle ramps. In certain embodiments, the fixed slope threshold may be between 3 meters and 5 meters, although other values ​​may also be used.In some embodiments, the slope limit can be related to the values ​​chosen for the low ramp limit and the high ramp limit. A wider range of limit values ​​can result in a high slope limit.

[0052] The line-of-sight distance is calculated differently depending on the ramp's steepness. As shown in Block 460, if the ramp is steep, the line-of-sight distance is defined as the first peak value in the power-to-weight ratio curve that exceeds a predefined peak value threshold. This can be referred to as a Type 1 scenario.

[0053] In one embodiment, a peak value is identified by starting from 0 meters and searching for a power-to-power ratio that is smaller than the previous power-to-power ratio. If this power-to-power ratio is smaller than the previous power-to-power ratio, the previous distance is stored as the peak value. Otherwise, the current power-to-power ratio is stored as the previous power-to-power ratio, and the distance is incremented. This process is repeated until the peak value is found. This peak value is then compared to a predetermined peak value threshold. If it is greater than this peak value threshold, this peak value is designated as the first peak value. Thus, the first peak value can be defined as the smallest distance that indicates a power-to-power ratio greater than a predetermined peak value threshold. This peak value threshold can be determined empirically or can be a predetermined value.In some embodiments, the peak value limit can be set to a value of 0.1 or greater. If the peak value is not greater than the predetermined peak value limit, the process is repeated until a first peak value is found.

[0054] This methodology is in Fig. 5A-5B is shown. It should be noted that the ramp in Fig. 5B is very steep. In this scenario, the first peak value in the power-to-weight ratio curve, found at 14.97 meters, is therefore used as the line-of-sight distance.

[0055] If the ramp is not determined to be steep, a different calculation is used to determine the line-of-sight distance, as shown in Box 470. This can be referred to as a Type 2 scenario. For example, show Fig. 6A-6B shows the power-to-weight ratio curve or the cumulative power-to-weight ratio curve for a different environment. It should be noted that in Fig. 6A the first peak is wider than in Fig. 5A and has a small bump on the left side. This likely indicates interference between the actual line-of-sight distance and a reflection. Consequently, the actual peak value related to the line of sight is likely shifted to the right. Therefore, the technique of simply using the first peak as the line-of-sight distance may be inaccurate in this situation and result in a distance greater than the actual line-of-sight distance. In this situation, the line-of-sight distance is therefore defined as the distance at which the cumulative power ratio exceeds a cumulative threshold. The value of this cumulative threshold can be chosen at which a significant power increase begins. In some embodiments, the cumulative threshold may be a fixed value, such as between 0.001 and 0.1, although other values ​​may also be used.In other embodiments, the cumulative limit can be set dynamically. For example, the cumulative limit can be varied according to the gradient of the ramp. A larger value for the cumulative limit can be used for steeper ramps, while a smaller value can be used for flatter gradients.

[0056] It should be noted that one advantage of this approach is that it does not encompass the entire spectrum that is in Fig. Figure 3 shows that calculations are necessary to determine the actual distance. Instead, the only calculations performed are those required to identify and classify the ramp in the cumulative power-to-weight ratio curve.

[0057] It should also be noted that the flowchart in Fig. Section 4 represents only one approach to determining the line-of-sight distance. For example, a different algorithm can be used to detect peak values. In another embodiment, the peak value can be detected by monitoring the gradient and searching for a change in the gradient's polarity. Additionally, instead of looping over distances, a statistical method or the Monte Carlo method can be used to select the distances to be checked. Of course, other known computational optimization techniques can also be used. Furthermore, in some embodiments, autocorrelation can be omitted, for example, by not executing block 420. In this embodiment, the power ratio, cumulative power ratio, and other metrics are calculated using the channel frequency response instead of the autocorrelated channel frequency response.If the scenario is of type 1, a different distance measurement algorithm can be used. For example, a phase-based approach, such as the one described above, can be used to determine the line-of-sight distance. Additionally, the MUSIC algorithm with a phase-based approach can be used to determine the line-of-sight distance.

[0058] It should be noted that this calculation can be performed by the initiator device 10. The initiator device 10 can contain the necessary computing power and memory to perform these calculations. Alternatively, the initiator device 10 can offload the calculations to a computer device (not shown).

[0059] The present system has many advantages. First, this method requires very little memory, as only a few values ​​need to be stored. Second, this algorithm is very fast to compute and does not require the calculation of eigenvectors, as is the case with some other approaches. This approach is also very accurate. Fig. Figure 7 shows the cumulative distribution function for the measurement error when a plurality of measurements are taken using a conventional approach and the procedure from Fig. 4. The distance to be measured varied between 0.5 meters and 70 meters. In this test, the actual distance was known and was compared with that measured using a conventional method as well as with the method shown in the flowchart. Fig.Figure 4 shows the calculation used to generate measurement error values. These measurement error values ​​were then used to create this graph. Line 700 shows the cumulative distribution function when a conventional approach is used. Note that the 90th percentile of the distance measurement error for the conventional approach is approximately 3 meters. The 95th percentile is only reached at a distance of 6 meters. In contrast, as shown in line 710, the 95th percentile of the distance measurement error for the entire dataset is approximately 3 meters with this new approach. Furthermore, note that with the conventional approach, approximately 7% of all measurements had a distance measurement error greater than 4 meters, whereas with the new method, almost no distance measurement errors of this magnitude occurred.

[0060] The scope of the present invention is not to be limited by the specific embodiments described herein. Indeed, it will be apparent to those skilled in the art from the foregoing description and the accompanying drawings that various other embodiments and modifications of the present invention exist in addition to those described herein. Therefore, such other embodiments and modifications are to be included within the scope of the present invention. Although the present invention has been described here in connection with a particular implementation in a particular environment for a particular purpose, it will be clear to those skilled in the art that its usefulness is not limited thereto and that the present invention can be advantageously implemented in any number of environments for any number of purposes.Consequently, the claims listed below are to be interpreted in light of the full scope and basic concept of the present invention as described herein.

Claims

[1] Method for calculating a distance between two wireless network devices, comprising: Performing a channel sounding procedure at a plurality of frequencies to obtain a channel frequency response; Autocorrelate the channel frequency response to obtain an autocorrelated channel frequency response; Using the autocorrelated channel frequency response to generate a power ratio as a function of distance, where the power ratio is defined as test signal power divided by the total power of the autocorrelated channel frequency response; Calculating a cumulative power ratio as a function of distance using the power ratio; Identifying a ramp in the cumulative performance ratio; and Using a ramp slope, power ratio, and cumulative power ratio to determine a distance between the two wireless network devices. [2] Method according to claim 1, wherein the test signal power at a first distance is first calculated by dero-rotating a phase of a signal path at the first distance from the autocorrelated channel frequency response to obtain a dero-rotated frequency response. [3] Method according to claim 2, wherein the test signal power at the first distance is calculated by squaring an absolute mean of the de-rotated frequency response at the plurality of frequencies. [4] Method according to claim 2, wherein the total performance of the autocorrelated channel frequency response is calculated as the mean of an absolute value of the autocorrelated channel frequency response at each of the plurality of frequencies, squared. [5] Method according to claim 1, wherein the two wireless network devices comprise Bluetooth network devices. [6] Method according to claim 1, wherein, if the slope of the ramp is steep, the distance is defined as a first peak value in the power ratio. [7] Method according to claim 6, wherein the performance ratio is calculated at a plurality of distances and the first peak value is defined as a peak value with a magnitude greater than a limit value at a smallest distance. [8] Method according to claim 1, wherein, if the slope of the ramp is steep, the distance is determined using a phase-based approach. [9] Method according to claim 1, wherein, if the slope of the ramp is not steep, the distance is defined as the smallest distance at which the cumulative power ratio exceeds a predetermined limit. [10] Bluetooth network, comprehensive: a reflector device; and an initiator device, comprising: a Bluetooth network interface; a processing unit; and a storage device, wherein the storage device contains instructions which, when executed by the processing unit, cause the initiator device to: Performing a channel sounding procedure at a plurality of frequencies to obtain a channel frequency response; Autocorrelate the channel frequency response to obtain an autocorrelated channel frequency response; Using the autocorrelated channel frequency response to generate a power ratio as a function of distance, where the power ratio is defined as a test signal power divided by the total power of the autocorrelated channel frequency response; Calculating a cumulative performance ratio as a function of distance using the performance ratio; Identifying a ramp in the cumulative performance ratio; and Using a ramp slope, power ratio, and cumulative power ratio to determine a distance between the reflector device and the initiator device. [11] Bluetooth network according to claim 10, wherein the test signal power at a first distance is first calculated by dero-rotating a phase of a signal path at the first distance from the autocorrelated channel frequency response to obtain a dero-rotated frequency response, wherein the test signal power at the first distance is calculated by squaring an absolute mean of the dero-rotated frequency response at the plurality of frequencies, and the overall power of the autocorrelated channel frequency response is calculated as the square of an absolute value of the autocorrelated channel frequency response at each of the plurality of frequencies. [12] Bluetooth network according to claim 10, wherein, if the slope of the ramp is steep, the distance is defined as a first peak value in the power ratio. [13] Bluetooth network according to claim 12, wherein the performance ratio is calculated at a plurality of distances and the first peak value is defined as a peak value with a magnitude greater than a limit value at a smallest distance. [14] Bluetooth network according to claim 10, wherein, if the slope of the ramp is steep, the distance is determined using a phase-based approach. [15] Bluetooth network according to claim 10, wherein, if the slope of the ramp is not steep, the distance is defined as the smallest distance at which the cumulative power ratio exceeds a predetermined limit. [16] Method for calculating a distance between two wireless network devices, comprising: Performing a channel sounding procedure at a plurality of frequencies to obtain a channel frequency response; Using the channel frequency response to generate a power ratio as a function of distance, where the power ratio is defined as a test signal power divided by the total power of the channel frequency response; Calculating a cumulative power ratio as a function of distance using the power ratio; Identifying a ramp in the cumulative performance ratio; and Using a ramp slope, power ratio, and cumulative power ratio to determine a distance between the two wireless network devices. [17] Method according to claim 16, wherein the test signal power at a first distance is first calculated by dero-rotating a phase of a signal path at the first distance from the channel frequency response to obtain a dero-rotated frequency response, wherein the test signal power at the first distance is calculated by squaring an absolute mean of the dero-rotated frequency response at the plurality of frequencies, and the total power of the channel frequency response is calculated as an average of an absolute value of the channel frequency response at each of the plurality of frequencies, squared. [18] Method according to claim 16, wherein, if the slope of the ramp is steep, the distance is defined as a first peak value in the power ratio, wherein the power ratio is calculated at a plurality of distances and the first peak value is defined as a peak value with a magnitude greater than a limit value at a smallest distance. [19] Method according to claim 16, wherein, if the slope of the ramp is steep, the distance is determined using a phase-based approach. [20] Method according to claim 16, wherein, if the slope of the ramp is not steep, the distance is defined as the smallest distance at which the cumulative power ratio exceeds a predetermined limit.

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