P440 Data Sheet / User Guide
DRAFT
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This underlying capability allows the generation of the following three different types of range
measurements:
Precision Range Measurements (PRM) are taken using the TW-TOF ranging technique. These
readings typically have high accuracy and are provided with estimates of range error as well as flags
that warn of possible errors. The user can use these range error estimates to drive a Kalman Filter.
The flags can be used to disregard inaccurate readings.
Coarse Range Estimates (CRE) are analogous to RSSI (received signal strength indication) range
estimates produced by continuous wave RF ranging systems in that they relate the strength of the
received signal to range. They are different in two important ways. First, the signal strength reported
is based on the strength of the first arriving energy and not on the strongest overall energy. This
ensures that large signals produced by constructive multipath do not introduce false readings.
Second, the signal strength reported is automatically calibrated based on the last successful Precision
Range Measurement.
Echo Last Range (ELR) measurements are Precision Range Measurements which have been taken
between two other radios in the system. In other words, any time a unit takes a PRM it will broadcast
the last range measurement to any other radios in the area. For example, if Unit A measures the
distance between Unit A and Unit B, it will broadcast this range measurement to Units C, D, E, etc.,
whenever it next initiates a range measurement. This is an alternate way of automatically distributing
range information through a system.
Finally, the P440 uses the API to make the range measurements, error flags, range error estimates,
signal strength measurements, measurements of background noise, and waveform measurements
available to the Host processor.
The RangeNet GUI exercises each of the API commands, thereby allowing the user to configure the
unit and take range measurements. But the GUI adds an extra level of system software in that it will
allow the user to:
Capture, display to the screen, and log waveforms to disk.
Figure 3
illustrates a
representative waveform as displayed by the GUI.
Request a single range measurement, a fixed number of measurements, or a continuous series
of range measurements.
Display the signal strength, noise, and SNR of the received signal.
Display quality metrics that provide a warning if the reading is suspect.
Calculate performance statistics. For example, if the user requests a finite number of ranges,
the GUI will compute the range success rate, the average range, the standard deviation of the
range measurements, the average SNR of the readings, and the standard deviation of the
SNR. These statistics are valuable for determining the quality of service the user can expect.
The system will also filter the received readings using the quality metrics and provide the
same statistics.
Determine if there are interference sources in the area.
Recalibrate a given link such that the bias or offset inherent in a range measurement can be
compensated.
Allow the user to easily enter and transmit data.
Allow the user to receive and display data.
Log all messages exchanged between the host and connected P440.
