50
DRAFT
P440 Data Sheet / User Guide
Ranging Performance
Ranging Techniques:
Pulsed Two-Way Time-of-Flight (TW-TOF) and
Coarse Range Estimation (CRE)
Two-Way Time-of-Flight
Max Range (standard
Broadspec Antennas)
Free Space: 240 m
Level ground: 1000 m (3200 ft)
See Section 6.2 for details
Precision ( 3 Standard Deviations)
2.3 cm (See Section 6.4)
Accuracy (Bias error):
2.1 cm (See Section 6.4)
Range Measurement Rate
14 – 125 Hz (See Section 6.3)
Non-Line of Sight Performance
See Section 6.4
Coarse Range Estimation (LOS only
)
See Section 6.5
Radar Performance
Approximate Detection Range
(high power transmission)
Person Walking: 80 m
Person Crawling: 40 m
Vehicle: 100 m
(See Section 6.7)
Table 3: P440 performance characteristics
From time to time changes will be made to the P440 design.
Section 6.8
describes how the version
number of any given board can be determined and describes the version to version differences.
6.2 Maximum Operating Range of a P440 Radio
Operating range in any given application will be a function of various obstructions, the height of the
antennas above the ground, various interference and Fresnel constructive and destructive cancellation.
For example, when operating over open fields the Fresnel ground bounce provides signal
enhancement which increases overall range. When operating at PII=8 with antennas 2.5 meters above
the ground one can expect to operate out to 600 meters. An example is shown in
Figure 34.
There
are also exceptional cases. For example, where the antennas are ideally placed or the ground
topology is providing significant antenna gain, it is possible to operate out to 1000 meters. One
customer has reported operating in a tunnel (without clear line of sight) to a range of 3000 meters.
There are also cases where Fresnel destructive interference (cancellation) can be the dominating
factor. Consider the deep null at 100m in
Figure 34
. At this point, the Fresnel cancellation is at a
maximum. If the system were operating at a much lower PII, then the received SNR would drop. At
some point, the SNR would be too low for the radio to operate. Note that in
Figure 34
the radio
works well until the SNR drops below about 15 dB. For the sake of argument let us assume that the
radio does not operate when the SNR drops below 24 dB. (In practice this reduction could be
accomplished by reducing the PII by 3 steps from PII=8 to PII=5). This 24 dB limit is represented by
the dashed black line. In this case, the radio would range successfully between 0 and 90 meters and
from 120 to 210 meters. But between 90 and 120 meters it would not operate because the SNR is
below the 22 dB needed for the receiver to operate.
