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DRAFT
P440 Data Sheet / User Guide
RangeNet RET GUI. To convert from cm to picoseconds, use the following equation:
0.2993 mm of delay = 1 picoseconds
In other words, if you add a cable between an antenna and an antenna port which has exactly 1 meter
of delay, then you should increase the value of the antenna delay for that antenna port by 3341ps.
6.5 CRE Range Measurement Precision and Accuracy
There are three key factors that affect the Precision and Accuracy of a CRE measurement: stability of
the RF channel, changes in antenna pattern and signal strength.
If RF channel characteristics are stable, then the accuracy of the CRE measurement should be close to
that of the reference precision range measurement (PRM). However, if the P440 is physically
moving, such that the associated antenna pattern changes, then the RF channel will change with time.
Therefore, the recalibrating PRMs should be taken frequently enough such that the rate of change
(“drift”) of the RF channel will be small. This rate of change will vary with node speed and change
in orientation and must be determined empirically.
Random effects, including sampling variability, can cause a static node’s signal strength measurement
to vary by as much as 10%. The CRE error is also a function of distance between the transmitter and
receiver largely because as a weaker signal contains a higher proportion of noise elements. This
translates into a CRE standard deviation error of approximately 10% at short distances, growing up to
30% at very long distances. CRE should not be used at distances greater than 100 meters. At these
distances, the change in signal strength with distance is very small and can be less than the average
reading-to-reading variation at any given point. In addition, one will normally encounter Fresnel
enhancement beyond about 100 meters. In these cases the SNR will actually increase with distance.
This is illustrated in
Figure 34
.
6.6 Data Communications Rate and Throughput
The P440 has been optimized for operation either as a Radar or as a Ranging Radio. While the P440
can be used to transmit large quantities of data, this capability will come at the expense of ranging
update rate. It is also important to note that data transmissions are limited to a maximum of 1000
bytes per packet. While fewer bytes can be transmitted, the highest throughput is achieved when the
bytes sent per packet are maximized.
Table 6
shows the relationship between PII (Pulse Integration
Index) and data throughput.
Table 6: Throughput for different Pulse Integrations and buffer sizes
It should also be noted that the bit rate will vary by a few percent depending on which Code Channel
is selected.
Bytes sent using Code Channel 2
100
1000
PII
Bit rate (kbps)
Bit rate (kbps)
4
270.46
612.48
5
192.77
308.48
6
138.56
144.64
7
62.14
76.80
8
34.88
39.04
9
17.41
19.20
