User's Manual

P412 User’s Manual & Data Sheet 17
constructed of wood frame and drywall (aka sheetrock or gypsum board), then one will experience a
level of performance that is less than but close to LOS conditions. This is because wood and drywall
do not significantly attenuate or disperse RF signals at the P412’s operating frequency. At the
opposite end of the propagation spectrum would be operation inside a metal ship. Because metal
blocks radio frequencies, the operating range would be limited to the size of the room. Operation in
NLOS must be determined empirically. Having said that, we routinely measure range from one side
of our office space to the other (a distance of 30 meters through an environment that is not only
NLOS but is also occluded by large amounts of metal) with an accuracy of better than +/- 1 meter.
PII Max Range
(meters)
Data rate:
(bps)
Precision Range Measurement
(time, rate)
4
35
632
k
6.5 ms, 15
4 Hz
5
60
316k
8.5 ms, 118 Hz
6
88
158k
12.5 ms, 80 Hz
7
125
79k
20 ms, 50 Hz
8
177
39.5k
36 ms, 28 Hz
9
250
19.7k
67 ms, 15 Hz
10
354
9.86k
132 ms, 8 Hz
Table 2: Data and ranging performance characteristics
Note that these are conservative estimates of range performance and have a healthy safety margin
allowing robust performance. For example, with PII set to 9, Time Domain has routinely achieved
650 meters in clear line of sight conditions over open ground.
Note 3: Precision and Accuracy of CRE: There are three main factors that affect the Precision and
Accuracy of a CRE measurement: stability of the RF channel, signal strength, and changes in antenna
pattern. If RF channel characteristics are stable, then the accuracy of the CRE measurement should
be close to that of the reference PRM range measurement. However, if the RCM is physically
moving, with associated antenna pattern changes, then the RF channel will change with time.
Therefore, the recalibrating PRM measurements 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, along with sampling
variability, can cause a static node’s signal strength measurement to vary as much as 10%. The CRE
error is also a function of distance/SNR as a smaller/farther 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.
Note 4: Setting the transmit power level: The maximum transmit power provided by the P412 will
be at the limit allowed by the FCC. The user has the option to reduce the transmit power from this
maximum and operate at levels as much as 19dB below the limit. This adjustment is made through
the API “Set Configuration” command. Alternatively, this adjustment can be made through the
Graphic User Interface (GUI) RCM RET by modifying the “Transmit Gain” setting on the Config
Tab. Figure 12 shows the relationship between the value selected for Transmit Gain and the radiated
power when using a standard P412. This measurement was taken by directly connecting the output of