WIFI Distance Measurement Using Location Packets

• US 20130070607A1
• Filed: 09/21/2011
• Published: 03/21/2013
• Est. Priority Date: 09/21/2011
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm Atheros Incorporated (Qualcomm, Inc.)
• Inventors: Sun, Qinfang, Zhou, Hao, Cheng, Hao-Jen
• Granted Patent: US 8,675,561 B2
• Time in Patent Office: Days
• US Class Current: 370/241
• CPC Class Codes: G01S 13/74 Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
• CPC Class Codes: G01S 13/79 Systems using random coded signals or random pulse repetition frequencies , e.g. "Separation and Control of Aircraft using Non synchronous Techniques" [SECANT]
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

A method of determining a distance between a first wireless device and a second wireless device is provided. In this method, a location symbol can be generated by filtering and modulating a pseudorandom (PRN) code. The location symbol can be provided in a data field of a legacy wireless packet to form a first location packet. The first location packet can be transmitted from the first wireless device to the second wireless device. A second location packet can be transmitted from the second wireless device to the first wireless device, wherein the second location packet is substantially identical to the first location packet. An effective roundtrip time between the first and second wireless devices can be determined based on the first and second location packets. The distance between the first and second wireless devices can be computed using this roundtrip time.

Claims

1. A method of determining a distance between a first wireless device and a second wireless device, the method comprising:

generating a location symbol by filtering and modulating a pseudorandom (PRN) code;

providing the location symbol in a data field of a legacy wireless packet to form a first location packet;

transmitting the first location packet from the first wireless device to the second wireless device, then transmitting a second location packet from the second wireless device to the first wireless device, the second location packet being substantially identical to the first location symbol;

determining an effective roundtrip time between the first and second wireless devices based on the first and second location packets; and

computing the distance between the first and second wireless devices using the effective roundtrip time.

2. The method of claim 1, wherein the PRN code is a GPS 1023 chip code.

3. The method of claim 1, wherein the PRN code is an m-sequence 127 chip code.

4. The method of claim 1, wherein the PRN code has a well-defined autocorrelation function.

5. The method of claim 1, wherein the first and second location packets have power spectrums substantially within a predetermined transmit spectral mask.

6. The method of claim 1, wherein the predetermined transmit spectral mask is for a 40 MHz channel.

7. The method of claim 1, wherein the predetermined transmit spectral mask is for an IEEE 802.11n-compliant channel.

8. The method of claim 1, further including specifying a protocol for the first and second wireless devices, the protocol providing that one predetermined bit of a signal field of the legacy packet indicates the data field includes the location symbol.

9. The method of claim 1, further including specifying a protocol for the first and second wireless devices, the protocol providing that one or more predetermined bits of the data field indicate that the data field also includes the location symbol.

10. The method of claim 1, wherein generating the location symbol includes generating chips of the PRN code using a maximum length shift register (MLSR).

11. A transceiver in a first wireless device for determining a distance between the first wireless device and a second wireless device, the transceiver comprising:

a transmitter comprising;

a first transmitting portion for filtering and modulating a pseudorandom (PRN) code to form a location symbol; and

a second transmitting portion for providing the location symbol in a data field of a legacy wireless packet to form a first location packet;

an antenna for transmitting the first location packet to the second wireless device; and

a receiver comprising;

a first receiving portion for separating the location symbol from a second location packet, the second location packet being substantially identical to the first location packet, the antenna for also receiving the second location packet from the second wireless device;

a second receiving portion for filtering and demodulating of the second location symbol, and tracking of the PRN code within the second location symbol; and

a processor configured to;

determine an effective roundtrip time between the first and second wireless devices based on the first and second location packets using outputs of the second receiving portion; and

compute the distance between the first and second wireless devices using the effective roundtrip time.

12. The transceiver of claim 11, wherein the first transmitting portion further includes a PRN code generator.

13. The transceiver of claim 12, wherein the PRN code generator generates a GPS 1023 chip code.

14. The transceiver of claim 12, wherein the PRN code generator generates an m-sequence 127 chip code.

15. The transceiver of claim 11, wherein the first transmitting portion includes a low pass filter for the filtering of the PRN code.

16. The transceiver of claim 15, wherein the first transmitting portion includes a modulator for modulating an output of the low pass filter onto a 5 GHz carrier to form the location symbol.

17. The transceiver of claim 11, wherein the second receiving portion includes a bandpass filter for filtering the location symbol.

18. The transceiver of claim 17, wherein the second receiving portion includes a demodulator for demodulating an output of the bandpass filter with a 5 GHz carrier down-converter signal.

19. The transceiver of claim 18, wherein the second receiving portion includes a data bit removal block for extracting the PRN code from an output of the demodulator.

20. The transceiver of claim 19, wherein the second receiving portion includes a correlator dump block for receiving the PRN code and generating N (noise), E (early), P (prompt), and L (late) correlation results for use in code and frequency tracking.

21. The transceiver of claim 20, wherein the second receiving portion includes a code and frequency tracking block for receiving an output of the correlator dump block and providing outputs to the PRN mixer and a carrier removal block.

22. The transceiver of claim 21, wherein the code and frequency tracking block performs multiple iterations within at least one epoch period of the PRN code.

23. A transceiver in a first wireless device for determining a distance between the first wireless device and a second wireless device, the transceiver comprising:

a transmitter comprising;

a first transmitting portion for accessing a pre-calculated filtered code sequence based on a pseudorandom (PRN) code and modulating the pre-calculated filtered code sequence to form a location symbol; and

a second transmitting portion for providing the location symbol in a data field of a legacy wireless packet to form a first location packet;

an antenna for transmitting the first location packet to the second wireless device; and

a receiver comprising;

a first receiving portion for separating the location symbol from a second location packet, the second location packet being substantially identical to the first location packet, the antenna for also receiving the second location packet from the second wireless device;

a second receiving portion for filtering and demodulating of the second location symbol, and tracking of the PRN code within the second location symbol; and

a processor configured to;

determine an effective roundtrip time between the first and second wireless devices based on the first and second location packets using outputs of the second receiving portion; and

compute the distance between the first and second wireless devices using the effective roundtrip time.

24. The transceiver of claim 23, wherein the first transmitting portion further includes a PRN code generator.

25. The transceiver of claim 24, wherein the PRN code generator generates a GPS 1023 chip code.

26. The transceiver of claim 24, wherein the PRN code generator generates an m-sequence 127 chip code.

27. The transceiver of claim 23, wherein the first transmitting portion includes a modulator for modulating an output of the low pass filter onto a 5 GHz carrier to form the location symbol.

28. The transceiver of claim 23, wherein the second receiving portion includes a bandpass filter for filtering the location symbol.

29. The transceiver of claim 28, wherein the second receiving portion includes a demodulator for demodulating an output of the bandpass filter with a 5 GHz carrier down-converter signal.

30. The transceiver of claim 29, wherein the second receiving portion includes a data bit removal block for extracting the PRN code from an output of the demodulator.

31. The transceiver of claim 30, wherein the second receiving portion includes a correlator dump block for receiving the PRN code and generating N (noise), E (early), P (prompt), and L (late) correlation results for use in code and frequency tracking.

32. The transceiver of claim 31, wherein the second receiving portion includes a code and frequency tracking block for receiving an output of the correlator dump block and providing outputs to the PRN mixer and a carrier removal block.

33. The transceiver of claim 32, wherein the code and frequency tracking block performs multiple iterations within at least one epoch period of the PRN code.

34. A wireless communication system comprising:

a wireless device; and

a plurality of access points, each access point (AP) having a known location,

wherein the wireless device is configured to determine a distance between itself and each AP using a method comprising;

generating a location symbol by modulating a pseudorandom (PRN) code;

providing the location symbol in a data field of a legacy wireless packet to form a first location packet;

transmitting the first location packet from the wireless device to the AP, then transmitting a second location packet from the AP to the wireless device, the second location packet being substantially identical to the first location symbol;

determining an effective roundtrip time between the wireless device and the AP based on the first and second location packets; and

computing the distance between the wireless device and the AP using the effective roundtrip time, and

wherein the wireless device is further configured to determine its location based on computed distances from the wireless device to the plurality of APs.

35. A wireless communication system comprising:

a wireless device; and

a plurality of located wireless devices, each located wireless device having a known location,

wherein the wireless device is configured to determine a distance between itself and each located wireless device using a method comprising;

generating a location symbol by modulating a pseudorandom (PRN) code;

providing the location symbol in a data field of a legacy wireless packet to form a first location packet;

transmitting the first location packet from the first wireless device to the located wireless device, then transmitting a second location packet from the located wireless device to the wireless device, the second location packet being substantially identical to the first location symbol;

determining an effective roundtrip time between the wireless device and the located wireless device based on the first and second location packets; and

computing the distance between the wireless device and the located wireless device using the effective roundtrip time, and

wherein the wireless device is further configured to determine its location based on computed distances from the wireless device to the plurality of located wireless devices.