Intra-piconet location determination and tomography

• US 20020168943A1
• Filed: 04/30/2001
• Published: 11/14/2002
• Est. Priority Date: 04/30/2001
• Status: Active Grant

• Current Assignee: ARRIS Enterprises LLC (CommScope Holding Company, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Shi, Qicai, Patwari, Neal K., Perkins, Matthew R., Callaway, Edgar H. Jr.
• Granted Patent: US 6,745,038 B2
• Time in Patent Office: Days
• US Class Current: 455/67.11
• CPC Class Codes: G01S 5/0289 of multiple transceivers, e.g. in ad hoc networks
• CPC Class Codes: H04B 17/27 for locating or positioning the transmitter
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04W 52/08 Closed loop power control
• CPC Class Codes: H04W 52/24 using SIR [Signal to Interference Ratio] or other wireless path parameters

Abstract

A technique for intra-piconet location determination and tomography is described. This technique uses received signal strength indicator (RSSI) values in conjunction with transmitted power levels to determine the relative location of each device within a small network employing frequency hopped spread spectrum transmission. In addition to the location determination properties of the invention, the geometry of the devices in the network, as well as the path loss information between pairs of devices, may be used to infer the location of absorbers and reflectors within the piconet. This absorption and reflection information may be used in creating the piconet tomography. The approach described in this specification may be applied in conjunction with the Bluetooth wireless Personal Area Network (PAN) specification to determine device locations, mitigate the effects of multi-path, and perform indoor location and security functions, and other application functions requiring cost-effective location determination.

Claims

1. A method of intra-piconet device location, comprising:

a) a master device periodically polling a plurality of slave devices of a piconet over a period of time to obtain range information for each slave device of the plurality of slave devices corresponding to a plurality of carrier frequencies over a carrier-frequency range, wherein the range information for each slave device comprises received signal strength indicator (RSSI) values;

b) developing a (RSSI) vs. carrier-frequency curve of each slave device of the plurality of slave devices representative of a plurality of RSSI values corresponding to the plurality of carrier frequencies over the period of time contained in the range information;

c) identifying one or more periodicities occurring in the RSSI vs. carrier-frequency curve of each slave device of the plurality of slave devices;

d) for each slave device of the plurality of slave devices identifying a frequency separation Δ

f corresponding to the one or more periodicities; and

e) using the frequency separation Δ

fin determining a path-length difference, d=a+b−

c, between a direct path distance c from a slave device of the plurality of slave devices to the master device and an indirect path distance, a+b, from the slave device to the master device, wherein d is proportional to Δ

f.

2. The method of claim 1, wherein each slave device of the plurality of slave devices is polled at least once during the period of time.

3. The method of claim 1, wherein the one or more periodicities are the minima of the RSSI vs. carrier-frequency curve.

4. The method of claim 1, further comprising:

determining whether the reflecting object is one of a conducting object or a dielectric object;

wherein if the reflecting object is a conducting object, a higher null of the adjacent pair of nulls is given by;

f_k+1=300/λ

_k+1=150(2k+1)/d MHz, for an integer k;

wherein if the reflecting object is a dielectric object, a higher null of the adjacent pair of nulls is given by;

f_k+1=300/λ

_k+1=150(2k)/d MHz, for the integer k.

5. The method of claim 1, wherein the range information for each slave device of the plurality of slave devices comprises power values.

6. The method of claim 5, further comprising:

adjusting the power level of each slave of the plurality of slaves in order to provide the master device with consistent RSSI information.

7. The method of claim 6, wherein adjusting the power level of each slave further comprises:

if a power level of the RSSI value received by the master device from a slave of the plurality of slaves is not within an acceptable power range, determining whether the power level RSSI value is lower than or higher than the acceptable power range;

if the power level of the RSSI value is too high to be within the acceptable power range, the slave device reducing the power of the slave device in response to a power decrease request from the master device; and

if the power level of the RSSI value is too low to be within the acceptable power range, the slave device increasing the power of the slave device in response to a power increase request from the master device.

8. The method of claim 1, further comprising tomography generation that comprises:

using a master-slave switching protocol to ensure that each device of the piconet is the master device at least once and repeating a)-e) for each device in order to determine the location of each device and any reflectors of the piconet;

collecting the range information of each slave device and the master device of the piconet;

using the range information of each slave device and the master device to determine predicted path losses between the plurality of slave devices and the master device of the piconet;

comparing the predicted path losses to measured path losses between the plurality of slave devices and the master device of the piconet, wherein a loss of a measured path loss of the measured path losses below a predicted path loss of the predicted path losses indicates an attenuator in a corresponding path.

9. The method of claim 8, wherein the master-slave switching protocol comprises:

a requesting slave device requesting to become the master device of the piconet;

if the master device agrees to the switching request of the requesting slave device, a qualified slave device that meets predetermined criteria becoming a new master device and the master device becoming one of the slave devices of the piconet.

10. The method of claim 9, wherein the criteria of the qualified slave device is that the qualified slave device has a highest address of the plurality of slave devices and after the master device becomes one of the slave devices, the master device having a lowest address of the plurality of slave devices.

11. The method of claim 10, further comprising incrementing the addresses of the plurality of slave devices after the qualified slave device becomes the new master device.

12. The method of claim 8, wherein the range information is collected by a supermaster device of the devices of the piconet.

14. The piconet of claim 13, wherein the range information for each slave device comprises received signal strength indicator (RSSI) values.

15. The piconet of claim 13, wherein the master device polls each slave device of the plurality of slave devices at least once during the period of time.

16. The piconet of claim 13, wherein the one or more periodicities are the minima of the RSSI vs. carrier frequency curve.

17. The piconet of claim 13, wherein the master device is further operable to determine whether the reflecting object is one of a conducting object or a dielectric object;

and

wherein if the reflecting object is a conducting object, a higher null of the adjacent pair of nulls is given by;

f_k+1=300/λ

_k+1=150(2k+1)/d MHz, for an integer k, and if the reflecting object is a dielectric object, a higher null of the adjacent pair of nulls is given by;

f_k+1=300/λ

_k+1=150(2k)/d MHz, for the integer k.

18. The piconet of claim 13, wherein the range information for each slave device of the plurality of slave devices comprises power values.

19. The piconet of claim 18, wherein the master device is further operable to adjust the power level of each slave of the plurality of slaves in order to obtain consistent RSSI information.

20. The piconet of claim 19, wherein if a power level of the RSSI value received by the master device from a slave of the plurality of slaves is not within an acceptable power range, the master device determines whether the power level RSSI value is lower than or higher than the acceptable power range;

if the power level of the RSSI value is too high to be within the acceptable power range, the slave device reduces the power of the slave device in response to a power decrease request from the master device; and

if the power level of the RSSI value is too low to be within the acceptable power range, the slave device increases the power of the slave device in response to a power increase request from the master device.

21. The piconet of claim 13, wherein the master device is further operable to perform tomography generation comprising:

using a master-slave switching protocol to ensure that each device of the piconet is the master device at least once in order to determine the location of each device and any reflectors of the piconet;

collecting the range information of each slave device and the master device of the piconet;

using the range information of each slave device and the master device to determine predicted path losses between the plurality of slave devices and the master device of the piconet; and

comparing the predicted path losses to measured path losses between the plurality of slave devices and the master device of the piconet, wherein a loss of a measured path loss of the measured path losses below a predicted path loss of the predicted path losses indicates an attenuator in a corresponding path.

22. The piconet of claim 21, wherein the master-slave switching protocol comprises:

a requesting slave device requesting to become the master device of the piconet; and

if the master device agrees to the switching request of the requesting slave device, a qualified slave device that meets a criteria becoming a new master device and the master device becoming one of the slave devices of the piconet.

23. The piconet of claim 22, wherein the criteria of the qualified slave device is that the qualified slave device has a highest address of the plurality of slave devices and after the master device become one of the slave devices, the master device having a lowest address of the plurality of slave devices.

24. The piconet of claim 23, further comprising incrementing the addresses of the plurality of slave devices after the qualified slave device becomes the new master device.

25. The piconet of claim 21, wherein the range information is collected by a supermaster device of the devices of the piconet.

27. The device of claim 26, wherein the range information for each slave device comprises received signal strength indicator (RSSI) values.

28. The device of claim 26, wherein while in the master mode the device polls each slave device of the plurality of slave devices at least once during the period of time.

29. The device of claim 26, wherein the one or more periodicities are the minima of the RSSI vs. carrier-frequency curve.

30. The device of claim 26, wherein while in the master mode, the device is further operable to determine whether the reflecting object is one of a conducting object or a dielectric object;

and

wherein if the reflecting object is a conducting object, a higher null of the adjacent pair of nulls is given by;

f_k+1=300/λ

_k+1=150(2k+1)/d MHz, for an integer k and if the reflecting object is a dielectric object, a higher null of the adjacent pair of nulls is given by;

f_k+1=300/λ

_k+1=150(2k)/d MHz, for the integer k.

31. The device of claim 26, wherein the range information for each slave device of the plurality of slave devices comprises power values.

32. The device of claim 31, wherein while in the master mode the device is further operable to adjust the power level of each slave of the plurality of slaves in order to obtain consistent RSSI information.

33. The device of claim 32, wherein if a power level of the RSSI value received by the device from a slave of the plurality of slaves is not within an acceptable power range, the device determines whether the power level RSSI value is lower than or higher than the acceptable power range;

if the power level of the RSSI value is too high to be within the acceptable power range, the slave device reduces the power of the slave device in response to a power decrease request from the device; and

if the power level of the RSSI value is too low to be within the acceptable power range, the slave device increases the power of the slave device in response to a power increase request from the device.

34. The device of claim 26, wherein while in the master mode the device is further operable to perform tomography generation comprising:

using a master-slave switching protocol to ensure that each slave device of the plurality of slave devices of the piconet is a master device at least once in order to determine the location of each device of the piconet and any reflectors of the piconet;

collecting the range information of each slave device and the device of the piconet;

using the range information of each slave device and the device to determine predicted path losses between the plurality of slave devices and the device of the piconet; and

comparing the predicted path losses to measured path losses between the plurality of slave devices and the device of the piconet, wherein a loss of a measured path loss of the measured path losses below a predicted path loss of the predicted path losses indicates an attenuator in a corresponding path.

35. The device of claim 34, wherein the master-slave switching protocol comprises:

a requesting slave device requesting to become the master device of the piconet; and

if the requesting slave device meets a criteria and the device agrees to the switching request of the requesting slave device, the requesting slave device becoming a new master device and the device becoming one of the slave devices of the piconet.

36. The device of claim 35, wherein the criteria is that the requesting slave device has a highest address of the plurality of slave devices and after the device become one of the slave devices, the device having a lowest address of the plurality of slave devices.

37. The device of claim 36, further comprising incrementing the addresses of the plurality of slave devices after the requesting slave device becomes the new master device.

38. The device of claim 26, wherein the timing element provides a reference clock of the device for generation of a random channel hopping sequence of the device.

13. A piconet of a wireless communication network capable of intra-piconet device location, comprising:

a plurality of slave devices of the piconet;

a master device of the piconet coupled to the plurality of slave devices that is operable to periodically poll the plurality of slave devices over a period of time to obtain range information for each slave device of the plurality of slave devices corresponding to a plurality of carrier frequencies over the carrier-frequency range, identify for each slave device of the plurality of slave devices a frequency separation Δ

f corresponding to one or more periodicities occurring in a RSSI vs. carrier-frequency curve of each slave device of the plurality of slave devices, and determine from the frequency separation Δ

f a path-length difference, d=a+b−

c, between a direct path distance c from a slave device of the plurality of slave devices to the master device and an indirect path distance, a+b, from the slave device to the master device,

wherein the (RSSI) vs. carrier-frequency curve is developed for each slave device of the plurality of slave devices representative of a plurality of RSSI values corresponding to the plurality of carrier frequencies over the period of time contained in the range information, and wherein d is proportional to Δ

f.

26. A device operable in a piconet of a wireless communication network, comprising:

a controller element having a link management element that controls a power level of the device and controls switching of the device between a master mode and a slave mode, wherein while in the slave mode the device switches to the master mode only upon receiving permission from a master device of the piconet;

a receiver element operable to receive incoming messages to the device;

a processor element, coupled to the receiver element and having a master processor operational in the master mode and a slave processor operational in the slave mode, that is controlled by the controller element to process the incoming messages, generate outgoing messages of the device, and select channel assignments of the device;

a transmitter element coupled to the processor element and operable to transmit the outgoing messages of the device;

a timing element coupled to the receiver element, the transmitter element, the controller element, and the processor element that provides timing for the channel assignments of the device;

a storage element coupled to processor element and the timing element;

wherein in the master mode the device is operable to periodically poll a plurality of slave devices of the piconet to obtain range information for each slave device of the plurality of slave devices corresponding to a plurality of carrier frequencies over the carrier-frequency range, identify for each slave device of the plurality of slave devices a frequency separation Δ

f corresponding to one or more periodicities occurring in a RSSI vs. carrier-frequency curve of each slave device of the plurality of slave devices, and determine from the frequency separation Δ

f a path-length difference, d=a+b−

c, between a direct-path distance c from a slave device of the plurality of slave devices to the master device and an indirect-path distance, a+b, from the slave device to the master device,

wherein in the master mode the device develops the (RSSI) vs. carrier-frequency curve of each slave device of the plurality of slave devices representative of a plurality of RSSI values corresponding to the plurality of carrier frequencies over the period of time contained in the range information, and wherein d is proportional to Δ

f, and

wherein in the slave mode the device is operable to provide range information of the device corresponding to the plurality of carrier frequencies over the carrier-frequency range.