Indoor and outdoor geolocation and time of arrival estimation using wireless signals
A method for estimating a time of arrival of a signal transmitted over a wireless channel, includes receiving the signal by a receiving device to produce a received signal; filtering by a filter either the received signal or a code sequence, wherein the filter is designed to produce a correlation output that is near causal; correlating the received signal with the code sequence to create the correlation output that is near causal; wherein near causal means that early side lobes and an early part of a main lobe of the correlation output are sufficiently suppressed in order to substantially reduce an impact of delayed multipath onto a first path component in the received signal, wherein the first path is in an operating region; identifying in the correlation output, an observation window associated with a main lobe in the correlation output; processing the observation window to determine a time of arrival of the first path component in the received signal.
1 . A method for estimating a time of arrival of a signal transmitted over a wireless channel, the method comprising:
receiving the signal by a receiving device to produce a received signal;
filtering by a filter either the received signal or a code sequence, wherein the filter is designed to produce a correlation output that is near causal;
correlating the received signal with the code sequence to create the correlation output that is near causal; wherein near causal means that early side lobes and an early part of a main lobe of the correlation output are sufficiently suppressed in order to substantially reduce an impact of delayed multipath onto a first path component in the received signal, wherein the first path is in an operating region;
identifying in the correlation output, an observation window associated with a main lobe in the correlation output;
processing the observation window to determine a time of arrival of the first path component in the received signal.
2 . The method of claim 1 wherein the early part of the main lobe is a part of the main lobe before a peak of the main lobe.
3 . The method of claim 1 wherein the side lobes and the early part of the main lobe are suppressed by predetermined amounts selected to reduce TOA error in predetermined operational conditions.
4 . The method of claim 1 wherein the side lobes and the early part of the main lobe are sufficiently suppressed to decrease the impacting early side lobes and the first 50% or less of the main lobe by at least 20 dB below the peak of the main lobe.
5 . The method of claim 1 wherein the filter is designed to produce a correlation output that is near causal by iteratively reweighting a cost function until the early side lobes and a part of the main lobe of the output correlation are suppressed.
6 . The method of claim 1 wherein the filtered code sequence is precomputed and stored by the receiving device.
7 . The method of claim 1 wherein the filtered code sequence is computed by the receiver.
8 . The method of claim 1 wherein the shaping sequence is a square wave or binary offset carrier (BOC) waveform.
9 . The method of claim 1 wherein the power delay profile is an expected power delay profile of the wireless channel.
10 . The method of claim 1 wherein the power delay profile is a measured power delay profile of the wireless channel.
11 . The method of claim 1 wherein the code sequence is a PRN code sequence, CDMA code sequence, GNSS code sequence, or GPS L1 code sequence.
12 . The method of claim 1 wherein identifying an observation window associated with a main lobe comprises identifying a rising edge in the correlation output.
13 . The method of claim 1 wherein identifying an observation window associated with a main lobe comprises identifying a falling edge in the correlation output.
14 . The method of claim 1 further comprising correlating the observation window with correlator sequences that reduce the effect of colored noise after a hypothetical first path component.
15 . The method of claim 14 wherein the correlator sequences correspond to different time shifts of the hypothetical first path component.