Location of wideband OFDM transmitters with limited receiver bandwidth
First Claim
1. 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:
- 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 said fraction of the signal components to derive location related measurements, wherein said fraction of the narrowband frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy, and wherein the first receiving system is configured to use signal components in said pilot channel to aid in signal acquisition and demodulation;
wherein said first receiving system comprises a first frequency conversion circuit configured to convert a first received 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;
a second receiving system configured to receive said fraction of the signal components transmitted by said first wireless transmitter, and to process said fraction of the signal components to derive location related measurements, wherein the second receiving system is configured to use signal components in said pilot channel to aid in signal acquisition and demodulation;
wherein said second receiving system comprises a second reconstruction circuit configured to receive the coded bits produced by the first demodulation circuit of the first receiving system and to produce the first reconstructed digital baseband OFDM signal; and
a second correlation processing system configured to correlate the first reconstructed digital baseband OFDM signal with a second digital baseband OFDM signal derived by the second receiving system, wherein a peak of the correlation function is indicative of a second time of arrival for the RF signal as received at the second receiving system; and
a processing system, operatively coupled to said first and second receiving systems, wherein said processing system is configured to use location related measurements from said first and second receiving systems, including the first and second times of arrival, to compute the location of said first wireless transmitter.
2 Assignments
0 Petitions
Accused Products
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.
24 Citations
98 Claims
-
1. 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:
-
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 said fraction of the signal components to derive location related measurements, wherein said fraction of the narrowband frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy, and wherein the first receiving system is configured to use signal components in said pilot channel to aid in signal acquisition and demodulation;
wherein said first receiving system comprises a first frequency conversion circuit configured to convert a first received 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;a second receiving system configured to receive said fraction of the signal components transmitted by said first wireless transmitter, and to process said fraction of the signal components to derive location related measurements, wherein the second receiving system is configured to use signal components in said pilot channel to aid in signal acquisition and demodulation;
wherein said second receiving system comprises a second reconstruction circuit configured to receive the coded bits produced by the first demodulation circuit of the first receiving system and to produce the first reconstructed digital baseband OFDM signal; and
a second correlation processing system configured to correlate the first reconstructed digital baseband OFDM signal with a second digital baseband OFDM signal derived by the second receiving system, wherein a peak of the correlation function is indicative of a second time of arrival for the RF signal as received at the second receiving system; anda processing system, operatively coupled to said first and second receiving systems, wherein said processing system is configured to use location related measurements from said first and second receiving systems, including the first and second times of arrival, to compute the location of said first wireless transmitter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
-
-
26. A method 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:
-
at a first receiving system, receiving a fraction of the signal components transmitted by a first wireless transmitter to be located in a fraction of the narrowband frequency channels, and processing said fraction of the signal components to derive location related measurements including a first time of arrival for a first received RF signal component; wherein the processing at the first receiving system comprises; converting the first received RF signal component to a first digital baseband OFDM signal; performing a Fast Fourier Transform (FFT) of the first digital baseband OFDM signal provided by the first frequency conversion circuit producing coded bits based on the output of the FFT circuit; reconstructing the first digital baseband OFDM signal based on the coded bits; and correlating the reconstructed first digital baseband OFDM signal with the first digital baseband OFDM signal, wherein a correlation function peak is indicative of the first time of arrival for the first received RF signal component; at a second receiving system which is geographically separated from said first receiving system, receiving said fraction of the signal components transmitted by said first wireless transmitter, and processing said fraction of the signal components to derive location related measurements including a second time of arrival for the RF signal as received at the second receiving system; wherein the processing at the second receiving system comprises; receiving the coded bits produced by the first receiving system and producing the first reconstructed digital baseband OFDM signal; and correlating the first reconstructed digital baseband OFDM signal with a second digital baseband OFDM signal derived by the second receiving system, wherein a peak of the correlation function is indicative of a second time of arrival for the RF signal as received at the second receiving system; and processing said location related measurements from said first and second receiving systems to compute the location of said wireless transmitter; wherein said fraction of the narrowband frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy, and wherein the first and second receiving systems use signal components in the pilot channel for signal acquisition and demodulation. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51)
-
-
52. A non-transitory computer readable medium comprising executable instructions for use by a receiving system deployed 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 predefined narrowband frequency channels spanning a predefined wideband channel, the computer readable medium comprising executable instructions for causing a receiving system to carry out a method comprising the steps of:
-
at a first receiving system, receiving a fraction of the signal components transmitted by a first wireless transmitter to be located in a fraction of the narrowband frequency channels, and processing said fraction of the signal components to derive location related measurements including a first time of arrival for a first received RF signal component; wherein the processing at the first receiving system comprises; converting the first received RF signal component to a first digital baseband OFDM signal; performing a Fast Fourier Transform (FFT) of the first digital baseband OFDM signal provided by the first frequency conversion circuit; producing coded bits based on the output of the FFT circuit reconstructing the first digital baseband OFDM signal based on the coded bits; and correlating the reconstructed first digital baseband OFDM signal with the first digital baseband OFDM signal, wherein a correlation function peak is indicative of the first time of arrival for the first received RF signal component; at a second receiving system which is geographically separated from said first receiving system, receiving said fraction of the signal components transmitted by said first wireless transmitter, and processing said fraction of the signal components to derive location related measurements including a second time of arrival for the RF signal as received at the second receiving system; wherein the processing at the second receiving system comprises; receiving the coded bits produced by the first receiving system and producing the first reconstructed digital baseband OFDM signal; and correlating the first reconstructed digital baseband OFDM signal with a second digital baseband OFDM signal derived by the second receiving system, wherein a peak of the correlation function is indicative of a second time of arrival for the RF signal as received at the second receiving system; and processing said location related measurements from said first and second receiving systems to compute the location of said wireless transmitter; wherein said fraction of the narrowband MHz frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy, and wherein the first and second receiving systems use signal components in the pilot channel for signal acquisition and demodulation. - View Dependent Claims (53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77)
-
-
78. A network-based 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, wherein the narrowband frequency channels have a bandwidth on the order of 3-5 MHz and the wideband channel has a bandwidth on the order of 20 MHz, comprising:
-
(a) 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 3-5MHz frequency channels, wherein said fraction of the narrowband 3-5 MHz frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy; wherein said first receiving system comprises; (a1) a first frequency conversion circuit configured to convert a first received RF signal component to a first digital baseband OFDM signal having a sample rate which is substantially lower than the 48 MHz required to properly sample a 20 MHz signal, wherein the first frequency conversion circuit includes a filter bandwidth which is substantially less than 20 MHz; (a2) 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; (a3) a demodulation circuit configured to produce coded bits based on the output of the FFT circuit; (a4) a first reconstruction circuit configured to reconstruct the first digital baseband OFDM signal based on the coded bits produced by the demodulation circuit, wherein the first reconstruction circuit is configured to modulate the coded bits into one of PSK or QAM symbols, and to perform an inverse FFT (IFFT) of the symbols to produce a first reconstructed digital baseband OFDM signal; and (a5) 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 (TOA) for the first received RF signal component; (b) a second receiving system configured to receive said fraction of the signal components transmitted by said first wireless transmitter, wherein said second receiving system comprises; (b1) a second reconstruction circuit configured to receive the coded bits produced by the first demodulation circuit of the first receiving system and to produce the first reconstructed digital baseband OFDM signal; and (b2) a second correlation processing system configured to correlate the first reconstructed digital baseband OFDM signal with a second digital baseband OFDM signal derived by the second receiving system, wherein a peak of the correlation function is indicative of a second time of arrival (TOA) for the RF signal as received at the second receiving system; and (c) a processing system, operatively coupled to said first and second receiving systems, wherein said processing system is configured to use the first and second TOA values from said first and second receiving systems to compute the location of said wireless transmitter. - View Dependent Claims (79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98)
-
Specification