GE MDS iNET 900, Справочное руководство

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58 iNET Series Reference Manual 05-2806A01, Rev. J
Using the example of Figure 2-29, 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 2-29, 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 considered 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 perfor-
mance from your wireless link.
Figure 2-29 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.
NOTE: The RSSI is an average of the last 20 RSSI samples. The RSSI
value is reset every time the radio returns to scanning mode.
2.5.5 Mobility Configuration Menu
A mobile environment requires special considerations that are not a
factor in fixed installations. Use the following menu to set Remote
radios for mobile operation.