Methods and apparatus for identifying asset location in communication networks
The location of unmodified wireless assets in a wireless communication network may be identified using time differences of arrivals of a communication sequence at different network receivers. Time-stamping devices may include correlator circuits in parallel with signal decoders to time-stamp communication sequences. Cellular wireless networks may be frequency-multiplexed to increase spatial time-stamping density. Tags may be attached to passive assets to provide location identification information to network devices. Locations of assets broadcasting standard 802.11 radio frequency structures may be identified. Noise inherent in correlating a communication sequence may be reduced by using a selected correlation function.
1. A method for identifying a location of an asset in a communication network, said network having a first receiver device and a second receiver device, each receiver device having a known position, said method comprising:
estimating more than one first time-of-arrival estimates using a correlation function, said first time-of-arrival estimates corresponding to arrival at said first station of a communication signal from said asset;
estimating more than one second time-of-arrival estimates using said correlation function, said second time-of-arrival estimates corresponding to arrival of said communication signal at said second station;
calculating more than one time-difference-of arrival corresponding to the difference in arrival of said communication signal at said first and second stations from said asset using said first and second time-of-arrival estimates; and
determining the location of the asset using said more than one time-difference-of arrival.
2. The method of claim 1 wherein said calculating comprises:
for each second time-of-arrival estimate that corresponds to one first time-of-arrival estimate, quantifying a difference between said second time-of-arrival estimate and said first time-of-arrival estimate; and
if at least two differences are quantified, averaging said differences.
3. The method of claim 2 wherein said averaging comprises setting said time-difference-of arrivals equal to an average of said first and second time-of-arrival estimates.
4. The method of claim 1 further comprising:
receiving said communication signal using said first receiver; and
receiving said communication signal using said second receiver.
5. The method of claim 1 further comprising selecting said correlation function.
6. An apparatus for identifying a location of an asset in a communication network, said network having a first receiver device and a second receiver device, each receiver device having a known position, said apparatus comprising:
an estimator of more than one first time-of-arrival estimates using a correlation function, said first time-of-arrival estimates corresponding to arrival at said first station of a communication signal from said asset;
an estimator of more than one second time-of-arrival estimates using said correlation function, said second time-of-arrival estimates corresponding to arrival of said communication signal at said second station;
a calculator of more than one time-difference-of arrival corresponding to the difference in arrival of said communication signal at said first and second stations from said asset using said first and second time-of-arrival estimates; and
means for determining the location of the asset using said more than one time-difference-of arrival.
7. The apparatus of claim 6 wherein said calculator comprises:
means for quantifying, for each second time-of-arrival estimate that corresponds to one first time-of-arrival estimate, a difference between said second time-of-arrival estimate and said first time-of-arrival estimate; and
means for averaging said differences.
8. The apparatus of claim 7 wherein said means for averaging said differences sets said time-difference-of arrivals equal to an average of said first and second time-of-arrival estimates.
9. The apparatus of claim 8 further comprising:
means for receiving said communication signal using said first receiver; and
means for receiving said communication signal using said second receiver.
10. The apparatus of claim 6 wherein said correlation function is selectable.