Nordic Semiconductor Asa · OSL:NOD

Nordic Semiconductor Asa — Technical Presentation

39 slides from Nordic Semiconductor Asa's technical presentation

1. Slide 1: Introduction to Nordic Distance Toolbox

   Introduction to Nordic Distance Toolbox

2. Slide 2: Nordic Distance Toolbox (NDT)

   © Nordic Semiconductor Nordic Distance Toolbox (NDT)  The goal of NDT is to provide an easy to use interface for distance measurement  The distance is computed based on all information available to the device  All the mathematics necessary to compute distance is performed inside the toolbox 2

3. Slide 3: Physics

   © Nordic Semiconductor Physics  RADIO peripheral use invisible light to communicate.  The light has a frequency from 2.4 GHz to 2.5 GHz.  The invisible light is not focused, it usually radiates roughly equally in all directions, like a diffuse lightbulb.

4. Slide 4: Observable parameters of 2.4 GHz light

   © Nordic Semiconductor Observable parameters of 2.4 GHz light  The RADIO peripheral with one antenna is extremely nearsighted (to use a visible light analogy), it cannot focus, and cannot see direction, it can only observe the  Intensity of the light (Real Signal Strength Indicator or RSSI)  The

5. Slide 5: Intensity

   Intensity of light Intensity 5

6. Slide 6: Distance affects intensity of the light

   © Nordic Semiconductor Distance affects intensity of the light  Intensity is the power per unit area  The transmit power is assumed to be constant  The intensity is assumed to be inversly Antenna 2 = -46 proportional to the area of a sphere (4 π r2) dBm  Thus, we expect the recieved power to red

7. Slide 7: Real World Complications

   © Nordic Semiconductor Real World Complications n Link loss = - 56 Link loss = - 46  Loss is usually modelled as ~ 1/rn dBm dBm 1.6 10.0 m 2.4 m  n is called the path loss factor. Most of the time the path loss factor is determined 2 6.3 m 2.0 m based on measurements in a certain environment. 3 3.

8. Slide 8: Distance measurement based on intensity (RSSI)

   © Nordic Semiconductor Distance measurement based on intensity (RSSI) Even if you measure link loss without any error, you’re still not going to know the distance accurately, since the path loss factor depends on environment. 8

9. Slide 9: Phase

   Intensity of light Phase 9

10. Slide 10: What is Phase?

    © Nordic Semiconductor «What is Phase?» https://en.wikipedia.org/wiki/Phase_(waves)#/media/File:Phase_shifter_using_IQ_modulator.gif

11. Slide 11: Phase and wavelength of light

    © Nordic Semiconductor Phase and wavelength of light  Light is described as a photon, where the photon has a certain length (wavelength)  The wavelength (λ) is the distance the photon travels to go through a full 2π phase rotation (360 degrees). This happens in one period, or 1/frequency.  If we

12. Slide 12: Distance affects the phase of the light

    © Nordic Semiconductor Distance affects the phase of the light Send out light Reflected light Mirror 1 meter, 2 meters round trip Frequency Wavelength Number of Remainder Phase of reflected [GHz] [m] rotations rotations signal 2.400 0.125 2/0.125 = 16 0 0 2.440 0.123 2/0.123= 16.26 0.26 2π x 0.26 =

13. Slide 13: Slope of phase vs frequency vs distance

    © Nordic Semiconductor Slope of phase vs frequency vs distance 13

14. Slide 14: Computing distance from phase

    © Nordic Semiconductor Computing distance from phase  Well known, and used for many years in radar (Multi-carrier phase ranging)  Literally uses complex mathematics to go from I and Q measurements to distance  For current generation of devices ranging requires communication to and from both devic

15. Slide 15: Nordic Distance Toolbox

    Intensity of light Nordic Distance Toolbox 15

16. Slide 16: NDT version 0.6.0

    © Nordic Semiconductor NDT version 0.6.0  Quality indicator  TX power and RSSI for both remote and local device  Distance measurement based on  Link Loss (RSSI)  Multi-carrier phase slope estimation (MCPD)  Inverse Fast Fourier Transform (IFFT)  Hi-Precision: Estimation of multipath channel i

17. Slide 17: Distance estimation comparison

    © Nordic Semiconductor Distance estimation comparison 12  Place one 10 development kit on a Estimated distance [m] 8 chair, and sit on it. 6 4  Actual distance 2 between 0 development kits is 0 5 10 15 20 25 -2 approximately 1 m Sample (one per second) Distance estimate from NDT Distance estimate

18. Slide 18: Time

    Intensity of light Time 18

19. Slide 19: Round Trip Timing

    © Nordic Semiconductor Round Trip Timing Send out light Reflected light Mirror 10 meter, 20 meters round trip  Speed of light 299 792 458 meter per second  3.33ns per meter  In NDT the “mirror” will have a delay  Caused by radio changing from RX -> TX 19

20. Slide 20: Round Trip Timing

    © Nordic Semiconductor Round Trip Timing Send out light Reflected light Reflector 10 meter, 20 meters round trip  Speed of light 299 792 458 meter per second  3.33ns per meter  Predictable reflector delay  Measure Round Trip Timing over multiple frequencies and average 20

21. Slide 21: NDT performance

    Intensity of light NDT performance 21

22. Slide 22: Background

    © Nordic Semiconductor Background The measurements have been performed in an office The ceiling and floor is metal rich The measurement of and calculation of the distance has been done with the Nordic Distance Library version 0.6.0 22

23. Slide 23: Measurement setup

    © Nordic Semiconductor Measurement setup Wiral • A Wiral cable cam setup is used to Cable move the reflector cam Mark Car • Continuous ranging's are performed Left side • Reference distance determined by Color sensor LIDAR Reflector 23

24. Slide 24: Nordic Distance Library

    © Nordic Semiconductor Nordic Distance Library nrf_dm_calc() computes 3 distances • Distance from Friis path loss (rssi_openspace) • Distance based on phase slope over frequency (phase_slope) • Distance based on inverse fast fourier transform of the channel spectrum (ifft) nrf_dm_high_precision_calc

25. Slide 25: Friis path loss

    © Nordic Semiconductor Friis path loss 25 20 15 Distance [m] 10 5 0 0 50 100 150 200 250 25 Black is LIDAR reference Seconds [s]

26. Slide 26: Phase slope

    © Nordic Semiconductor Phase slope No attempt has been made to compensate for slope as a function of distance 25 20 15 Distance [m] 10 5 0 0 50 100 150 200 250 26 Black is LIDAR reference Seconds [s]

27. Slide 27: Inverse fast fourier transform

    © Nordic Semiconductor Inverse fast fourier transform 25 20 15 Distance [m] 10 5 0 0 50 100 150 200 250 27 Black is LIDAR reference Seconds [s]

28. Slide 28: Inverse fast fourier transform with median filter

    © Nordic Semiconductor Inverse fast fourier transform with median 3 filter 25 20 15 Distance [m] 10 Standard deviation is 80 cm 5 0 0 50 100 150 200 250 28 Black is LIDAR reference Seconds [s]

29. Slide 29: High Precision

    © Nordic Semiconductor High Precision 25 20 15 Distance [m] 10 5 0 0 50 100 150 200 250 29 Black is LIDAR reference Seconds [s]

30. Slide 30: High Precision with median filter

    © Nordic Semiconductor High Precision with median 3 filter 25 20 15 Distance [m] 10 Standard deviation is 37 cm 5 0 0 50 100 150 200 250 30 Black is LIDAR reference Seconds [s]

31. Slide 31: Probability distribution, and Cumulative Distribution Function

    © Nordic Semiconductor Probability distribution, and Cumulative Distribution Function 31

32. Slide 32: RTT

    © Nordic Semiconductor RTT 25 20 15 10 Distance [m] 5 0 0 50 100 150 200 250 300 -5 Standard deviation is 3.8 m -10 Seconds [s] 32 Black is LIDAR reference

33. Slide 33: Measurement summary

    © Nordic Semiconductor Measurement summary  Phase based ranging gives best accuracy, but is range limited  Maximum range depends on environment  In office space, reliable results up to 8-10 meters with filter  RTT gives lower accuracy but is only range limited to max Bluetooth connectivity range

34. Slide 34: Measurement summary distance <10 meters

    © Nordic Semiconductor Measurement summary distance <10 meters Technique Comment Friis open space Bad estimate of distance in real environment Phase slope Imprecise, few outliers, always larger than real distance IFFT More precise, but outliers High precision Even more precise, but outliers High pre

35. Slide 35: nRF Connect SDK NDT sample

    Intensity of light nRF Connect SDK NDT sample 35

36. Slide 36: nRF Connect SDK sample

    © Nordic Semiconductor nRF Connect SDK sample  One simple demo sample to showcase NDT  Each device is scanning and advertising  Advertising over Bluetooth  Scanning when not advertising  No filtering of devices  Will try to range to all devices in the vicinity  Will range to multiple devices

37. Slide 37: nRF Connect SDK sample

    © Nordic Semiconductor nRF Connect SDK sample  Adding a lot of devices in a small area will impact performance of sample  Will require more advanced application to avoid flooding the system  Bluetooth is only used for synchronization of the ranging  Can be replaced by proprietary radio if wanted

38. Slide 38: nRF Connect SDK sample

    © Nordic Semiconductor nRF Connect SDK sample  Currently supported  nRF52833 DK  nRF52840 DK  Next device  nRF5340-DK  Code is tuned for the device and the board so changes will require to trim offset and gain

39. Slide 39: Thanks!

    © Nordic Semiconductor Thanks! 39

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