Method and apparatus for determining the position of an object using radio frequency signals

Abstract

The subject application relates to a method and apparatus for determining the distance of an object using radio frequency signals. The use of phase interferometry using both amplitude and phase allows multipath signals to be determined and estimated. In order to determine the position of an object, a signal (806) containing sufficient information to allow the amplitude and phase to be determined, such as a data packet (604, 616) containing a sine wave portion (614) is provided from a master device (600). The slave device (602) measures the phase and amplitude of the received data packet and returns the information to the master device (810). The slave device returns a data packet containing a similar sine wave portion to the master device to allow the master device to determine the phase and amplitude (812) of the received signal. Based on the two sets of amplitude and phase of the radio frequency (RF) signal, the master device uses a fast Fourier transform or a technique such as multiple signal classification to determine the indicated distance of each path and thereby more accurately determine the position (816) of the slave device.

Description

Technical Field

[0001] The field relates to position determination using radio frequency signals. Background Art

[0002] It is often useful to use radio frequency (RF) signals to determine the location of an item. The RF signals of most interest are Bluetooth Low Energy (BLE) signals, Signals (especially with a bandwidth of 80MHz) and sub-GHz signals (especially with a bandwidth of 20MHz). One problem with using RF signals is the accuracy that can be enhanced. For example, using only the time of flight of an RF signal can produce an accuracy of about 3-5m, which is not enough in many cases.

[0003] For the RF signal mentioned above, there are several different methods for determining the position based on the RF signal. The first method is the radio signal strength indication (RSSI). RSSI is very susceptible to multipath problems, so its error is + / -10dB. The second method is the time of flight method mentioned earlier. In this time of flight method, the clock frequency used to perform the measurement is crucial. If a typical 40MHz clock is used, the resolution that can be obtained by time of flight is only about 15m. Further, time of flight is also susceptible to multipath problems. The third method is the angle of arrival (AoA). In the angle of arrival mode, a series of antennas are used at different locations, and then the position of the object can be obtained based on the receiving angle at each antenna group. The typical accuracy is 5°, but again, multipath is also a problem. The fourth method that has been used is phase interferometry, in which the phase at two frequencies or at two locations is estimated, and the distance can be determined from this. Once again, when using phase interferometry, multipath is still a problem.

[0004] If the desired positioning accuracy is smaller, such as 10 to 15 cm, conventional methods for BLE, WiFi, and sub-GHz systems cannot be used directly, and multipath issues further make them problematic. Summary of the invention

[0005] Using phase interferometry that utilizes both amplitude and phase rather than just phase provides additional information that allows multipath signals to be determined and estimated. In order to determine the position of an object, a signal containing sufficient information to allow both amplitude and phase to be determined, such as a data packet containing a sine wave portion, is provided from a master device to a slave device. The slave device measures the phase and amplitude of the received data packet and returns the information to the master device. The slave device also returns a data packet containing a similar sine wave portion to the master device to allow the master device to determine the phase and amplitude of the received signal. Based on the two sets of amplitude and phase of the RF signal, the master device utilizes a fast Fourier transform (FFT) or other techniques such as multiple signal classification (MUSIC) to determine the indicated distance of each path and thereby more accurately determine the position of the slave device relative to the master device. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] To describe various examples in detail, reference will now be made to the accompanying drawings, in which:

[0007] Figure 1 is a block diagram showing multipathing.

[0008] Figure 2 is a block diagram of a Bluetooth device.

[0009] Figure 3 is a block diagram showing the control modules in a car.

[0010] Figure 4 yes Figure 3 Block diagram of the Bluetooth control module.

[0011] Figure 5 is the block diagram of the Bluetooth microcontroller.

[0012] Figure 5A yes Figure 5 Block diagram of the RF portion of the microcontroller.

[0013] Figure 6 is a diagram showing example packets of communication and exchange when determining location.

[0014] Figure 7 A diagram that shows the timing of signals and the measurements and calculations performed.

[0015] Figures 7A-7D is a graph showing the calculated multipath.

[0016] Figure 8 is a flow chart of operations for determining a position. DETAILED DESCRIPTION

[0017] Reference now Figure 1, the phone 100 attempts to determine the location of a first object 102 (which may be a BLE access point) and a second object 104 (which may be another BLE access point). In this example and the examples described in this specification, 106 and 108. The reflected signal path 108 travels from the phone 100 to the reflector 110 and then reaches the first object 102. Similarly, for the second object 104, i.e., another target Bluetooth device, the Bluetooth signal has a direct path 112 and a reflected path 114, which is reflected from the reflector 116. The presence of the reflectors 110 and 116 causes the first object 102 and the second object 104 to receive the transmitted Bluetooth signal at two different times with two different amplitudes. The reflected signal therefore interferes with the direct signal and hinders the development of an accurate position value due to the interference caused to the direct signal.

[0018] Figure 2 is a block diagram of a simple Bluetooth device, which in the illustrated case is a Bluetooth key fob 200. CC2640SimpleLink TM A Bluetooth microcontroller 202, such as a Bluetooth wireless MCU (microcontroller), is a major component in the key fob 200. An antenna 204 is connected to the Bluetooth MCU 202 through an inductor 206 to allow transmission and reception of Bluetooth signals. A first button 208 and a second button 210 provide user input, such as locking and unlocking. A first light emitting diode (LED) 212 and a second LED 214 provide visual feedback to the user of the operation of the key fob 200. A speaker 216 is connected to the Bluetooth MCU 202 to provide auditory feedback to the user. A battery 218 provides power to the key fob 200, especially the Bluetooth MCU 202. This is a very simple block diagram for explanation purposes, and an actual unit will use many different components and will be more sophisticated.

[0019] Reference now Figure 3, shows a block diagram of a control system 300 of an automobile. A controller area network (CAN) bus 302 in mode C connects itself to an engine control module 304, an anti-lock brake system module 306, a power steering control module 308, a headlight control module 310, a second generation on-board diagnostic system (OBD-II) port 312, and a body computer module 314. A CAN bus 316 in mode B connects to the OBD-II port 312 and the body computer module 314 and connects itself to a parking sensor module 318, an airbag control module 320, an instrument touch panel cluster module 322, an audio control module 324, a convergence module 326, a heating, ventilation and air conditioning (HVAC) module 328, and a Bluetooth module 330. These are merely exemplary modules, and additional or fewer modules may be present in a particular automobile, as may more or fewer CAN buses or alternative or additional buses.

[0020] Figure 4 yes Figure 3 4 is a simplified block diagram of a Bluetooth module 330. A Bluetooth MCU 402, such as the CC2640 described above, forms the main component of the Bluetooth module 330. An antenna 404 is connected to the Bluetooth MCU 402 through an inductor 406. A CAN bus interface 408 is connected to the CAN bus 316 and the Bluetooth MCU 402 to allow the Bluetooth module 330 to communicate with the rest of the car. Again, this is a simplified block diagram for explanation purposes, and an actual module will contain many different components and will be more sophisticated.

[0021] Figure 5 is a block diagram of a Bluetooth MCU 500, such as Bluetooth MCU 402 or Bluetooth MCU 202. For example, CC2640SimpleLink TM The main components of the Bluetooth MCU 500, such as the Bluetooth wireless MCU, include a main processor 502 for performing the main processing and control functions of the Bluetooth MCU 500. A random access memory (RAM) 504 is coupled to the main processor 502 to provide operating memory, while a flash memory and / or a read-only memory (ROM) 506 (both flash memory and ROM are non-transitory computer-readable storage media encoded with computer-executable instructions) is connected to the main processor 502 to store programs used and executed by the main processor 502 to perform the functions of the remote control key 200 or the Bluetooth module 330. In the example shown, an RF section 508, preferably programmable at multiple frequencies and protocols, is connected to the inductor 406 and the antenna 404. As shown in Figure 5A As shown in more detail in FIG. 5 , the RF portion 508 is a programmable radio system and has sufficient capabilities to allow the host processor 502 to set the desired frequency and indicate the desired protocol, such as Bluetooth, Etc. The RF section 508 includes a processor 550 that interfaces with the main processor 502 and controls the RF section 508. Static random access memory (SRAM) 552 and ROM 554 are connected to the processor 550 to provide working memory and store programs. A digital signal processor (DSP) modem 556 is connected to the processor 550, SRAM 552 and ROM 544 and handles the task of converting digital data packets into signals for transmission in analog form and converting received analog signals into digital data packets. A digital phase-locked loop (PLL) 558 is connected to the DSP modem 556 to generate the frequency required for the RF signal used. An output buffer 560 is connected to the inductor 406 to provide an analog RF output signal. An input buffer 562 is also connected to the inductor 406 to receive the incoming RF signal and provide it to a mixer 564, which mixes the received RF signal with the output of the digital PLL 558. The mixer 564 provides outputs to analog-to-digital converters (ADCs) 566 and 568, the outputs of which are provided to the DSP modem 556 for receive decoding. As discussed below, the DSP modem 556 determines the phase and amplitude of the received Bluetooth signal. The programs for the processor 550 and the DSP modem 556 are also stored in the flash memory and / or the ROM 506, as necessary.

[0022] A sensor section 510 is included in the Bluetooth MCU 500 to allow the Bluetooth MCU 500 to perform functions other than just Bluetooth communication. A general purpose input / output (I / O) section 512 is provided, such as to drive a speaker or LED or receive button inputs. A serial I / O section 514 is provided to allow communication with a control processor, such as via the CAN bus interface 408.

[0023] Reference now Figure 6 , 7 , 7A-7D and 8, provide the operation of the first example. In this first example, the master device 600 determines the position of the slave device 602 relative to the master device 600. Referring to the automobile example, the master device 600 can be a Bluetooth module 330, and the slave device 602 is a Bluetooth remote control key 200. As is conventional in Bluetooth operation, the determination of the master device 600 and the slave device 602 is performed in a first step 800. In step 802, the master device 600 provides a signal to the slave device 602 indicating the start of the distance measurement. In step 804, the slave device 602 enters a receive mode. In step 806, the master device 600 sends a measurement data packet to the slave device 602. An exemplary measurement data packet format is shown in Figure 6. A conventional Bluetooth data packet is modified to include an extension portion 614 to allow transmission of a pure sine wave. As in conventional Bluetooth, a first example data packet 604 has a preamble 606, followed by an access address 608, a data protocol data unit (PDU) 610, and a cyclic redundancy check (CRC) 612. The extension or tone portion 614 is provided after the CRC portion 612 and is transmitted as all zeros or all ones, so that a pure sine wave is produced on an actual RF transmitter. A second example measurement data packet 616 includes a preamble 606, an access address 608, and a data PDU 610, which is followed by an extension portion 614 and ends with a CRC portion 612. When the master device 600 has indicated that a distance measurement is in progress, the slave device 602 prepares to receive a data packet 604 or 616 and determines the phase and amplitude of the received signal by analyzing the extension portion 614.

[0024] In step 810, the slave device 602 determines the phase and amplitude of the sine wave portion and provides the phase and amplitude information to the master device 600. In step 812, the slave device 602 sends a similar measurement data packet 604 or 616 to the master device 600. In some instances, steps 810 and 812 are combined so that the data packet providing the determined phase and amplitude is also a measurement data packet from the slave device to the master device. The measurement data packet 604 or 616 from the slave device 602 to the master device 600 is provided at a frequency different from the measurement data packet 604 or 616 provided from the master device 600 to the slave device 602. This frequency change occurs naturally in Bluetooth due to the frequency hopping nature of Bluetooth, but must be performed differently in other protocols. In step 814, the master device determines the phase and amplitude of the sine wave portion of the received data packet 604 or 616. Although this explanation uses only a single measurement transmission from the master device 600 to the slave device 602 and a single measurement transmission from the slave device 602 to the master device 600, in other examples, this pair of measurement transmissions is performed multiple times, such as 20 to 40 times, to obtain measurement results at more than just these two different frequencies. These multiple measurements allow the results to be improved by averaging the results and thereby reducing the impact of abnormal measurements. By obtaining the phase and amplitude of these two signals, in step 816, the master device 600 calculates the distance of the slave device 602.

[0025] Figure 7 The timing of these events and the specific parameters measured are shown. At time t = 0, Figure 7 The master device represented by A in Figure 7 The slave device represented as B in FIG transmits a measurement data packet. The phase of the transmitted signal at A at frequency f at t = 0 is φ A (f), and at the same time the phase at B is φ B (f). The transmitted signal at time t dArrives at B. The received signal is processed by device B, which takes processing time t proc At slave device B, the measured phase of the signal of the single-path channel is φ A (f 1 )-φ B (f 1 )-2*π*f 1 *t d Then, slave device B transmits a measurement data packet to master device A. Note that, while the measurement is being performed, both master device A and slave device B are each at the specific frequency f 1 In this way, the initial phase φ is maintained while receiving and transmitting data packets at both the master device A and the slave device B. A (f 1 ) and φ B (f 1 ). During the transmission period, the phase of the transmitted signal at B is now φ B (f 1 )+2*π*f 1 *(t d +t proc ). Note that the term φ B (f 1 ), because the phase of the PLL at slave B is maintained. The transmitted signal at time 2t d +t proc Arrives at A. The master device A processes the received signal, which takes processing time t proc At the master device A, the measured phase of the signal of the single-path channel is φ B (f 1 )+2*π*f 1 *(t d +t proc )-φ A (f 1 )-2*π*f 1 *(2*t d +t proc )=φ B (f 1 )-φ A (f 1 )-2*π*f 1 *(t d ). Note again that the phase φ in the above terminology A (f 1 ), because the phase of the PLL at the master device A is maintained.

[0026] For a multipath channel, at frequency f 1 The signal measured at slave device B is:

[0027]

[0028] The signal measured at the master device A is:

[0029]

[0030] where a p are the attenuation coefficients of the different multipath reflections and the total number of multipaths is given by P. Since the channels between master A and slave B are reciprocal, these attenuation coefficients and the total number of multipaths are the same in both directions. Distance d p is the distance travelled by the multipath p between the slave and the master, and vice versa. As in the above equation for frequency f 1 Similarly, similar equations can be written for other Bluetooth frequencies. Note that Bluetooth uses 1 MHz bandwidth per channel in the 2400-2480 MHz band, which means that Bluetooth can make up to 80 such measurements.

[0031] Each of these measurements includes both the phase and amplitude of the received signal. After the master completes its measurements of the signal, the master then calculates the multipath content as given below. Depending on whether the signal is phase coherent at the frequency being measured, there are two alternatives.

[0032] If coherent, the master performs a Fast Fourier Transform (FFT) on the measured signal to obtain the channel impulse response in the time domain. This result is then used to estimate the distance to the transmitter, i.e., the master, by utilizing the first multipath that appears in the FFT (assuming the first multipath is the shortest distance between the master and the slave). Fig. 7A is a graph showing the multipath detected when the reflector, i.e. the target or slave device and the reflector causing the multipath, is 20m and 25m away from the master device. Two distinct peaks can be seen, one for each path. Figure 7B This is for the case where the reflector is 22.5m and 25m from the transmitter. In this case, there is only one obvious peak because the reflector is so close relative to the 80MHz Bluetooth bandwidth. Since the bandwidth of the signal is 80MHz, which means the wavelength is about 3.75 meters, this means that the accuracy of the FFT will be limited to this range. Therefore, the two paths at 22.5m and 25m do not produce obvious peaks for the FFT algorithm.

[0033] For a system employing a B Hz bandwidth and a signal-to-noise ratio (SNR) snr, the limits to the accuracy with which the time of flight can be determined are given by the Cramer Rao bound and the Barankin bound, as given in Equation 7 below: A. Zeira, PM Schultheiss, "Realizable Lower Bounds for Time Delay Estimation: Part 2—Threshold Phenomena," IEEE Transactions on Signal Processing, Vol. 42, Issue Date: May 5, 1994, pp. 1001-1007, which is incorporated herein by reference to the [Zeira paper] provided herein.

[0034]

[0035] Where β=2*π*BWδ=2π / ω 0 and In the case of Bluetooth, the bandwidth (BW) is about 80 MHz, and the center frequency ω 0 = 2440MHz. Under high SNR conditions, the first term tends to zero because the bandwidth is much smaller than the center frequency and the boundaries converge to We call this the carrier frequency limited accuracy. On the other hand, at low SNR, the first term passes through the limit we call the inverse of the signal bandwidth To dominate the border.

[0036] The above bounds indicate that, under sufficiently high SNR conditions, the performance of the positioning algorithm is limited by the inverse of the carrier frequency, which is approximately 12.5 cm in the case of Bluetooth. Therefore, under sufficiently high SNR, it is possible to exceed the apparent limit of the FFT (which is the inverse of the signal bandwidth - approximately 3.75 m in the case of Bluetooth) to a carrier wavelength of 12.5 cm. Super-resolution algorithms attempt to achieve this higher carrier frequency limited accuracy compared to bandwidth limited accuracy to resolve multipath issues.

[0037] An example super-resolution algorithm is MUSIC (Multiple Signal Classification). Applying the MUSIC algorithm allows a resolution of 10 to 20 cm to be obtained by understanding the multipath. The super-resolution algorithm works on the net channel estimate between the master and slave devices across different frequencies. Before describing this algorithm, we first explain how the channel estimate is obtained.

[0038] Before the FFT and subsequent super-resolution algorithms can be applied to obtain the master-slave channel response across frequency, further processing is required. As a first step, s A (f l ) and s B (f l ). This yields the net channel estimation equation:

[0039]

[0040] The equation is of the form (H(w)) 2 , i.e. h(t)*h(t), and h(t) needs to be solved for then. Since there may be a phase ambiguity of + / - pi over the entire frequency range, a direct square root cannot be taken.

[0041] As a first option, the phase change at consecutive frequencies is checked to determine if the phase change is less than a certain threshold, such as pi / 2. If the phase change is greater than the threshold, then the pi phase is additionally added or subtracted. When this is completed at all frequencies analyzed, the FFT is applied and the results are produced as shown above for the coherent case.

[0042] As a second option, note that |(H(w)) 2 |=|H(w)| 2 . Solve for |H(w)| 2The minimum phase root of is equivalent to determining h(t)*h(-t). This is because for a minimum phase system, the frequency response can be uniquely recovered from the amplitude alone, as discussed in "Discrete-Time Signal Processing, OpenCourseWare 2006, Lecture 3, Minimum-Phase and All-Pass Systems", Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science, ocw.mit.edu / courses / electrical-engineering-and-computer-science / 6-341-discrete-time-signal-processing-fall-2005 / lecture-notes / lec03.pdf, especially in the spectral decomposition of Section 2, which is incorporated herein by reference. The resulting h(t) is the solution, and the phase-corrected net channel estimate as given in the above equation is FFT-ed. Figure 7C , the root determination is shown for a case where there are two reflectors, one at 7m and one at 9m, and the actual object or target is at 3m. Fig.7D The FFT results for the 7m case are shown in , with the peaks at 2.8m and 7.4m representing the target object and the reflector. For the object, the error of 20cm is within the expected accuracy.

[0043] After the FFT, the main multipath components (the top 1-2 multipath components) can be sorted, and the remaining terms of the FFT in the time domain can be set to zero. An inverse FFT (IFFT) can now be performed to return to the frequency domain. At this point, the channel is windowed in the time domain to retain the main multipath components. The super-resolution algorithm can now be applied to this frequency domain channel (or the super-resolution algorithm can also be applied to the entire channel as given in the channel estimation equation above). The basic MUSIC algorithm that can be used for super-resolution is given in GIRD Systems, Inc., "An Introduction to MUSIC and ESPRIT", which is incorporated herein by reference. The MUSIC algorithm is typically applied to multi-antenna systems to solve the problem of multiple targets impacting the array manifold. However, in the current problem, we can treat different frequency measurements in Bluetooth like a multi-antenna system. As given in "Introduction to MUSIC and ESPRIT", one of the problems in applying the MUSIC algorithm is the correlation between the various sources that can occur in the case of a multipath channel (since the sources are the same for different multipaths). In order to address this problem of correlated sources, modifications to the basic MUSIC algorithm have been proposed, as given in Chongying Qi, Yongliang Wang, Yongshun Zhang and Ying Han, "Spatial Difference Smoothing for DOA Estimation of Coherent Signals", IEEE Signal Processing Letters, Vol. 12, Issue Date: November 11, 2005, pp. 800-802, which is incorporated herein by reference. Likewise, the received signal X(t) in "Spatial Difference Smoothing for DOA Estimation of Coherent Signals" is equivalent to the net channel estimation equation given above.

[0044] A series of experiments were performed using the above method for different reflector distances. In the experiments, the main path or target was at 0.5m and the reflector position was varied from 1m to 4.5m in steps of 0.5m. Table 1 presents only the estimated values ​​and errors of the phase interferometry method, the additional amplitude measurement and FFT processing and the final MUSIC processing.

[0045] Table 1

[0046]

[0047] It can be seen that after MUSIC processing, the error is generally within the range of 10cm-20cm. This allows for more accurate determination of objects than other techniques. In the automotive example, this allows for determination of when the remote key is inside the car (as required for unlocking and starting) or outside the car (as required for locking and unlocking).

[0048] Although the above description uses Bluetooth as an exemplary RF protocol, other protocols, such as Wi-Fi, may also be used. Further, frequencies other than 2.4 GHz Bluetooth may be used, such as the 900 MHz spectrum.

[0049] While cars and key fobs are used as examples where accurate distance measurement is required, many other environments are also suitable. For example, in a warehouse, the target objects are boxes and packages. In a construction environment, power tools are target objects. In a retail environment, various items are target objects. In a farm environment, livestock are target objects. The specific protocol used depends on the desired distance, but in all cases, the protocol allows for the transmission of specific information about the object to help identify the object. In the automotive example, a security code for the key fob is exchanged with the car to identify the key fob's association with a specific car. The above examples can be used in combination with each other. The described embodiments may be modified within the scope of the claims, and other embodiments are also possible.

Claims

1. A method for determining a distance between a first and a second device, the method comprising: The first device transmits a first measurement data packet to the second device at a first frequency; receiving, by the first device, from the second device, a first phase and a first amplitude determined by the second device for the first measurement data packet; receiving, by the first device, a second measurement data packet from the second device at a second frequency different from the first frequency; determining, by the first device, a second phase and a second amplitude for the second measurement data packet; as well as The distance between the first and second devices is determined by the first device based on the first phase and the first amplitude determined by the second device for the first measurement data packet and the second phase and the second amplitude determined by the first device for the second measurement data packet.

2. The method of claim 1 , wherein determining the distance comprises: determining a net channel estimate by multiplying a first multipath signal determined based on the first phase and the first amplitude and a second multipath signal determined based on the second phase and the second amplitude; Performing a fast Fourier transform (FFT) on the net channel estimate to obtain a channel impulse response; determining multipath components at peaks in the channel impulse response; as well as The distance is determined based on the multipath components.

3. The method of claim 2, wherein the FFT is performed directly on the net channel estimate when the first and second phases are coherent.

4. The method of claim 2, wherein determining the distance further comprises correcting the first and second phases for phase changes before performing the FFT when the first and second phases are incoherent.

5. The method of claim 2, wherein determining the distance further comprises determining a minimum phase root of the first and second phases before performing the FFT when the first and second phases are incoherent.

6. The method of claim 2, wherein determining the distance further comprises: Performing inverse Fourier transform IFFT on the first 1-2 multipath components in the channel impulse response to obtain an IFFT result; and A super-resolution algorithm is applied to the IFFT results.

7. The method according to claim 1, wherein the first measurement data packet includes a first portion having all ones or all zeros, the first portion being used to generate a first sine wave for determining the first phase and the first amplitude of the first measurement data packet, and the second measurement data packet includes a second portion having all ones or all zeros, the second portion being used to generate a second sine wave for determining the second phase and the second amplitude of the second measurement data packet.

8. The method according to claim 1, wherein the first phase and the first amplitude determined for the first measurement data packet are contained in the second measurement data packet.

9. The method according to claim 1, wherein: Initial phases of respective phase locked loops in the first device and the second device are maintained when transmitting the first measurement data packet and the second measurement data packet, when determining the first phase and the first amplitude, and when determining the second phase and the second amplitude.

10. An apparatus for determining distance, comprising: a radio frequency circuit configured to: transmit a first measurement data packet to a second device at a first frequency and receive a second measurement data packet from the second device at a second frequency different from the first frequency; as well as a processor coupled to the radio frequency circuit and configured to: receiving from the second device a first phase and a first amplitude determined for the first measurement data packet; determining a second phase and a second amplitude for the second measurement data packet; determining a multipath component based on the first phase and the first amplitude determined by the second device for the first measurement data packet and the second phase and the second amplitude determined for the second measurement data packet; as well as A distance to the second device is determined based on the multipath components.

11. The device of claim 10, wherein the processor being configured to determine the multipath component comprises the processor being configured to: determining a net channel estimate by multiplying a first multipath signal determined based on the first phase and the first amplitude and a second multipath signal determined based on the second phase and the second amplitude; Performing a fast Fourier transform (FFT) on the net channel estimate to obtain a channel impulse response; and The multipath components are determined at peaks in the channel impulse response.

12. The apparatus of claim 11, wherein the FFT is performed directly on the net channel estimate when the first and second phases are coherent.

13. The apparatus of claim 11, wherein the processor being configured to determine the multipath component comprises the processor being configured to perform phase change correction on the first and second phases prior to performing the FFT when the first and second phases are incoherent.

14. The device of claim 11, wherein the processor being configured to determine the multipath component comprises the processor being configured to determine a minimum phase root of the first and second phases prior to performing the FFT when the first and second phases are incoherent.

15. The device of claim 11, wherein the processor being configured to determine the distance comprises the processor being configured to: Performing inverse fast Fourier transform (IFFT) on the first 1-2 multipath components in the channel impulse response to obtain an IFFT result; and A super-resolution algorithm is applied to the IFFT results.

16. The device of claim 10, wherein the first measurement data packet comprises a first portion having all ones or all zeros, the first portion being used to generate a first sine wave for determining the first phase and the first amplitude of the first measurement data packet, and the second measurement data packet comprises a second portion having all ones or all zeros, the second portion being used to generate a second sine wave for determining the second phase and the second amplitude of the second measurement data packet.

17. The apparatus of claim 10, wherein the first phase and the first amplitude determined for the first measurement data packet are included in the second measurement data packet.

18. The apparatus of claim 10, wherein: The radio frequency circuit comprises a first phase-locked loop; and The processor is further configured to: An initial phase of the first phase locked loop is maintained when transmitting the first measurement data packet, when receiving the second measurement data packet, and when determining the second phase and the second amplitude for the second measurement data packet.

19. An apparatus for use in determining distance, comprising: a radio frequency circuit configured to receive a first measurement data packet from a distance determining device at a first frequency and to transmit a second measurement data packet to the distance determining device at a second frequency different from the first frequency, the radio frequency circuit comprising a first phase locked loop; as well as a processor coupled to the radio frequency circuit and configured to: determining a phase and an amplitude for the first measurement data packet; sending the determined phase and amplitude for the first measurement data packet to the distance determination device; as well as When determining the phase and the amplitude for the first measurement data packet and when transmitting the second measurement data packet to the distance determination device, an initial phase of the first phase locked loop is maintained.

20. The device of claim 19, wherein the first measurement data packet comprises a first portion having all ones or all zeros, the first portion being used to generate a first sine wave for determining the phase and the amplitude of the first measurement data packet, and the second measurement data packet comprises a second portion having all ones or all zeros, the second portion being used to generate a second sine wave for determining the phase and the amplitude of the second measurement data packet.

21. The device of claim 19, wherein the processor is further configured to: Enters receive mode after receiving an indication to start distance measurement.

22. The apparatus according to claim 19, wherein the first measurement data packet and the second measurement data packet are sent as Bluetooth signals.

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