Location of wideband OFDM transmitters with limited receiver bandwidth

• US 8,145,238 B2
• Filed: 10/21/2010
• Issued: 03/27/2012
• Est. Priority Date: 12/01/2006
• Status: Active Grant

• Current Assignee: Skyhook Holding, Inc. (Liberty Broadband Corp.)
• Original Assignee: TruePosition Incorporated
• Inventors: Anderson, Robert J., Mia, Rashidus S.
• Primary Examiner(s): Corsaro, Nick
• Assistant Examiner(s): Choo, Munsoon
• Application Number:
  US12/909,732
• Publication Number:
  US 20110033002A1
• Time in Patent Office: 523 Days
• Field of Search: 455/456.1, 455/456.2, 370/319, 370/344
• US Class Current: 455/456.1
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/0226 Transmitters
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

One illustrative embodiment takes the form of a system for locating wireless transmitters employing an Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme. The OFDM scheme comprises transmitting signal components over narrowband frequency channels spanning a wideband channel. The system includes a first receiving system configured to receive a fraction of the signal components transmitted by a first wireless transmitter to be located in a fraction of the narrowband frequency channels, and to process the fraction of the signal components to derive location related measurements. The system further includes at least a second receiving system configured to receive the fraction of the signal components transmitted by the first wireless transmitter, and to process this fraction of the signal components to derive location related measurements. The system also includes a processing system configured to use location related measurements from the first and second receiving systems to compute the location of the wireless transmitter.

Claims

1. A receiving system for use in a system for locating wireless transmitters employing an Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme, wherein said OFDM scheme comprises transmitting signal components over a plurality of narrowband frequency channels spanning a wideband channel, comprising:

means for receiving a fraction of the signal components transmitted by a first wireless transmitter to be located in a fraction of the narrowband frequency channels;

means for processing said fraction of the signal components to derive location related measurements;

means for communicating said location related measurements to a processing system for use in computing the location of said first wireless transmitter;

a first frequency conversion circuit configured to convert a first received radio frequency (RF) signal component to a first digital baseband OFDM signal;

a Fast Fourier Transform (FFT) circuit configured to perform an FFT of the first digital baseband OFDM signal provided by the first frequency conversion circuit;

a demodulation circuit configured to produce coded bits based on the output of the FFT circuit;

a first reconstruction circuit configured to reconstruct the first digital baseband OFDM signal based on the coded bits produced by the demodulation circuit; and

a first correlation processing system configured to correlate the first reconstructed digital baseband OFDM signal with the first digital baseband OFDM signal, wherein a correlation function peak is indicative of a first time of arrival for the first received RF signal component.

2. A receiving system as recited in claim 1, wherein said fraction of the narrowband frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy.

3. A receiving system as recited in claim 2, wherein the receiving system is configured to use signal components in said pilot channel to aid in signal acquisition and demodulation.

4. A receiving system as recited in claim 1, wherein said location related measurements comprise at least one of the following:

time difference of arrival (TDOA) measurements, time of arrival (TOA) measurements, angle of arrival (AOA) measurements, round trip time measurements, and received power measurements.

5. A receiving system as recited in claim 1, wherein said fraction of the narrowband frequency channels excludes guard channels in which said first wireless transmitter transmits minimal energy.

6. A receiving system as recited in claim 1, further comprising an (RF) filter and an intermediate frequency (IF) filter, wherein the receiving system is configured to receive signal components within a bandwidth compatible with said RF and IF filters.

7. A receiving system as recited in claim 1, further comprising an analog to digital converter (ADC) characterized by a sample rate, wherein the receiving system is configured to receive signal components within a bandwidth compatible with said sample rate.

8. A receiving system as recited in claim 7, wherein said ADC is further characterized by a sample rate after decimation, wherein the receiving system is configured to receive signal components within a bandwidth compatible with said sample rate after decimation.

9. A receiving system as recited in claim 1, further comprising memory for storing data representing received signal components, wherein said receiving system is configured to receive signal components within a bandwidth compatible with said available memory.

10. A receiving system as recited in claim 1, further comprising a digital signal processor (DSP) characterized by DSP processing throughput, wherein said receiving system is configured to receive signal components within a bandwidth compatible with said DSP processing throughput.

11. A method for use in a system for locating wireless transmitters employing an Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme, wherein said OFDM scheme comprises transmitting signal components over a plurality of narrowband frequency channels spanning a wideband channel, comprising:

receiving a fraction of the signal components transmitted by a first wireless transmitter to be located in a fraction of the narrowband frequency channels;

processing said fraction of the signal components to derive location related measurements;

communicating said location related measurements to a processing system for use in computing the location of said first wireless transmitter;

converting a received RF signal component to a digital baseband OFDM signal;

performing a Fast Fourier Transform (FFT) of the digital baseband OFDM signal;

producing coded bits based on the output of the FFT;

reconstructing the digital baseband OFDM signal based on the coded bits; and

correlating the reconstructed digital baseband OFDM signal with the digital baseband OFDM signal, wherein a correlation function peak is indicative of a first time of arrival for the received RF signal component.

12. A method as recited in claim 11, wherein said fraction of the narrowband frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy.

13. A method as recited in claim 12, further comprising using signal components in said pilot channel to aid in signal acquisition and demodulation.

14. A method as recited in claim 11, wherein said location related measurements comprise at least one of the following:

time difference of arrival (TDOA) measurements, time of arrival (TOA) measurements, angle of arrival (AOA) measurements, round trip time measurements, and received power measurements.

15. A method as recited in claim 11, wherein said fraction of the narrowband frequency channels excludes guard channels in which said first wireless transmitter transmits minimal energy.