46
MDS iNET Series Reference Manual
05-2806A01, Rev. L
Invisible place holder
Figure 2-37. Auto Data Rate Submenu
•
ADR RSSI Threshold—
A specified received signal strength value, which, if exceeded by the
range of the
RSSI Delta
setting, causes a data rate change in the transceiver. [
-50 to -100; -87 dBm
]
•
ADR RSSI Delta—
A user-specified
difference
from the
RSSI Threshold
figure which, if exceeded,
causes a data rate change in the transceiver. [
0-10; 5
]
•
ADR SNR Threshold—
A user-specified signal-to-noise ratio, which, if exceeded by the range of
the
SNR Delta
setting, causes a data rate change in the transceiver. [
10-30; 26
]
•
ADR SNR Delta—
A user-specified
difference
from the
SNR Threshold
figure which, if exceeded,
causes a data rate change in the transceiver. [
0-10; 2
]
NOTE:
In the following description, “high speed” refers to 512 kbps for the iNET radio and 1 Mbps for
the iNET-II radio.
“Standard speed” refers to 256 kbps for the iNET radio and 512 kbps for the iNET-II.
Using the example of Figure 2-37, assume the current RSSI is -87 dBm. An RSSI reduction of more than 5
dBm (more negative RSSI number) would cause a data rate change from high speed to standard speed. Once
the data speed has changed to standard speed, an RSSI
increase
to the level of -82 dBm would be required
for the radio to switch back to high speed. This provides an operational “window” or hysteresis range over
which the data speed stays constant despite minor changes in signal strength.
The SNR (signal-to-noise ratio) threshold and delta operate in the same manner described above, with the
exception that the units are expressed in relative dB instead of dBm. In the example of Figure 2-37, a drop
of 2 dB from a level of 26 dB would result in a data rate change from high speed to standard speed. For the
radio to return to high speed, the SNR would need to increase to 28 dB. (
See Glossary for definition of SNR.)
RSSI or SNR figures alone mean little when determining signal quality. Both parameters must be consid-
ered to get a true understanding of signal quality. For example, a strong, but noisy signal would likely be
less useful than a weak signal with low noise levels. Proper use of the threshold and delta settings will result
in smoother, more reliable performance from your wireless link.
Figure 2-37 shows the default values for RSSI and SNR parameters but these may be changed to optimize
performance in your environment. In properly designed systems, experience has shown that RSSI levels
between -50 dBm and -90 dBm provide reliable operation, provided the signal-to-noise ratio is 17 dB or
above. Tailoring the thresholds with these baseline values in mind, can provide improved performance in
your system.
Summary of Contents for MDS iNET Series
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