Time
Difference of Arrival (TDOA) Technology
The system uses a Time Difference of
Arrival (TDOA) technique applied
to the transmission from a radio signal source, in this case a stroke
of lightning. This TDOA technique is based on the time
differences between the receptions of a radio signal at three remote
receivers at known points from a single source at an unknown
point. Each signal, traveling at the speed of light, or
approximately 186,000 miles per second, is time-stamped by the
receivers at the three known points. The time-stamp differences
are then used in highly complex hyperbolic curve generation
calculations to locate the source of the unknown radio signal. In
general, this method defines hyperbolic curves by their arrival time
differences at the known receivers, (R1, R2, R3 below). The point
of intersection of two hyperbolic curves defines the location of the
source of the radio transmission (the location of the lightning
stroke).
Time
Difference of Arrival Technique
Only three receivers are needed for
the hyperbolic calculations, but
more than three receivers may intercept the same signal. With
more than three receivers reporting we have redundant information
available to improve accuracy calculations and verify the
performance. Furthermore, our Network Monitoring Program can also
use the redundant reception to automatically monitor receiver
performance. The system monitoring function can also determine
whether or not a redundant receiver that should have received,
processed, and transmitted a signal’s data to the Central Analyzer did
receive the data.
If a sensor is seen to have problems
and needs diagnostic
interrogation, it is a simple matter to access and operate a remote
diagnostic program on the network. All TOA Systems, Inc.
receivers can be accessed remotely. This allows an operator at
the Central Analyzer (ASP) or a technician with communication links to
the ASP or receiver to perform periodic diagnostic tests for over a
dozen receiver and sensor functions. This very powerful design
feature means that maintenance adjustments can then be made or upgraded
software can be downloaded without visiting the receiver site.
Furthermore because much of the hardware has been designed to be under
remote software control through special devices known as Field
Programmable Gate Arrays (FPGAs), the receivers’ hardware design can
also be reconfigured from a remote location, typically over the
Internet.
