TB8100 Installation and Operation Manual Functional Description 65
© Tait Electronics Limited June 2005
4.8.5 Configuring Receiver Gating for Base Stations with Power Save
Settings for receiver gating can adversely affect Power Save.
In low-noise situations, Tait recommends that you use the default settings
(RSSI disabled, SINAD enabled at 12dB).
In high-noise situations, follow these guidelines:
■ Use RSSI and SINAD gating.
■ Set the RSSI level to be above the ambient noise level, for example
–113dBm (0.5µV).
■ Set the SINAD level as desired.
■ Set the gating logic to OR.
■ Have no receiver cycling in Normal mode.
■ Set short idle times (for example 1 minute for Sleep mode and 10
minutes for Deep Sleep mode).
The background to these recommendations is as follows:
Receiver gating operates differently when the receiver is cycling. Whenever
the receiver cycles on, it first measures the RSSI, even if its configuration
disabled RSSI gating (this is because detecting the RSSI is very quick). If the
RSSI exceeds the threshold, power stays on. (If the configuration doesn’t
specify a threshold, –117dBm is used.)
If gating is configured for RSSI alone, the receiver unmutes straight away. If
SINAD gating is enabled, the base station must first determine whether the
SINAD is above the threshold. If it is, the base station stays on, otherwise it
returns to cycling in its existing mode.
To ensure the full benefits of power saving, it is important to use an RSSI
level that prevents the base station unnecessarily turning the receiver on
while it checks the SINAD. For example, if the RSSI gate is turned off, the
SINAD gate is set to 20dB, and the receiver cycling time is 100ms, the
following can happen in the presence of channel noise:
1. The receiver cycles on.
2. It detects a signal that is above the RSSI threshold.
3. It stays on for 100ms to check whether the SINAD is good enough.
4. The SINAD is too low, so the receiver cycles off.
5. 100ms later, it’s time for the receiver to cycle on again and repeat the
procedure.
The result is that the receiver is on for about 120ms out of every 220ms,
instead of for about 20ms out of every 120ms.
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