WiFi distance measurement using location packets

• US 8,675,561 B2
• Filed: 09/21/2011
• Issued: 03/18/2014
• Est. Priority Date: 09/21/2011
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sun, Qinfang, Zhou, Hao, Cheng, Hao-Jen
• Primary Examiner(s): Ho, Chuong T
• Application Number:
  US13/239,332
• Publication Number:
  US 20130070607A1
• Time in Patent Office: 909 Days
• Field of Search: 370/328, 370/329, 370/331
• US Class Current: 370/328
• 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 a pseudorandom (PRN) code to conform with a predetermined transmit spectral mask, and modulating the filtered 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, wherein the first and second location packets have power spectrums within the predetermined transmit spectral mask;

determining a 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 determined 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 predetermined transmit spectral mask is for a 40 MHz channel.

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

7. 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 wireless packet indicates the data field includes the location symbol.

8. 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.

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

10. The method of claim 1, wherein the second location packet is identical to the first location packet.

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 coupled to receive a pseudorandom (PRN) code, and in response, provide a filtered PRN code that conforms with a predetermined transmit spectral mask, and modulate the filtered 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 received by the antenna from the second wireless device;

a second receiving portion for bandpass filtering the location symbol separated from the second location packet, demodulating the bandpass filtered location symbol, and tracking the PRN code within the demodulated and bandpass filtered location symbol; and

a processor configured to;

determine a 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 roundtrip time.

12. The transceiver of claim 11, wherein the transmitter further includes a PRN code generator that generates the PRN code.

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 that filters the PRN code to provide the filtered PRN code.

16. The transceiver of claim 11, wherein the first transmitting portion includes a modulator for modulating the filtered PRN code onto a 5 GHz carrier to form the location symbol.

17. The transceiver of claim 11, wherein the second receiving portion includes a demodulator for demodulating the bandpass filtered location symbol with a 5 GHz carrier down-converter signal.

18. The transceiver of claim 17, wherein the second receiving portion includes a data bit removal block for extracting the PRN code from an output of the demodulator.

19. The transceiver of claim 18, 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.

20. The transceiver of claim 19, 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 a PRN mixer and a carrier removal block.

21. The transceiver of claim 20, wherein the code and frequency tracking block performs multiple iterations within at least one epoch period of the PRN code.

22. The transceiver of claim 11, wherein the second location packet is identical to the first location packet.

23. The transceiver of claim 11, wherein the first transmitting portion comprises a memory coupled to receive the PRN code, wherein the memory provides a pre-calculated filtered code sequence as the filtered PRN code in response to the PRN code.

24. 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 filtering a pseudorandom (PRN) code to conform with a predetermined transmit spectral mask, and modulating the filtered 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 located wireless device, then transmitting a second location packet from the located wireless device to the wireless device, wherein the first and second location packets have power spectrums within the predetermined transmit spectral mask;

determining a 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 determined 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.

25. The wireless communication system of claim 24, wherein the second location packet is identical to the first location packet.

26. The wireless communication system of claim 24, wherein at least one of the located wireless devices is an access point (AP).