CC1101
SWRS061H Page 46 of 98
Figure 23: Typical RSSI Value vs. Input Power Level for Different Data Rates at 868 MHz
17.4 Carrier Sense (CS)
Carrier sense (CS) is used as a sync word
qualifier and for Clear Channel Assessment
(see Section 17.5). CS can be asserted based
on two conditions which can be individually
adjusted:
CS is asserted when the RSSI is above a
programmable absolute threshold, and de-
asserted when RSSI is below the same
threshold (with hysteresis). See more in
Section 17.4.1.
CS is asserted when the RSSI has
increased with a programmable number of
dB from one RSSI sample to the next, and
de-asserted when RSSI has decreased
with the same number of dB. This setting
is not dependent on the absolute signal
level and is thus useful to detect signals in
environments with time varying noise floor.
See more in Section 17.4.2.
Carrier sense can be used as a sync word
qualifier that requires the signal level to be
higher than the threshold for a sync word
search to be performed and is set by setting
MDMCFG2 The carrier sense signal can be
observed on one of the GDO pins by setting
IOCFGx.GDOx_CFG=14 and in the status
register bit PKTSTATUS.CS.
Other uses of Carrier sense include the TX-if-
CCA function (see Section 17.5) and the
optional fast RX termination (see Section
19.7).
CS can be used to avoid interference from
other RF sources in the ISM bands.
17.4.1 CS Absolute Threshold
The absolute threshold related to the RSSI
value depends on the following register fields:
AGCCTRL2.MAX_LNA_GAIN
AGCCTRL2.MAX_DVGA_GAIN
AGCCTRL1.CARRIER_SENSE_ABS_THR
AGCCTRL2.MAGN_TARGET
For given AGCCTRL2.MAX_LNA_GAIN and
AGCCTRL2.MAX_DVGA_GAIN settings, the
absolute threshold can be adjusted ±7 dB in
steps of 1 dB using
CARRIER_SENSE_ABS_THR.
The MAGN_TARGET setting is a compromise
between blocker tolerance/selectivity and
sensitivity. The value sets the desired signal
level in the channel into the demodulator.
Increasing this value reduces the headroom
for blockers, and therefore close-in selectivity.
It is strongly recommended to use SmartRF
Studio [5] to generate the correct
MAGN_TARGET setting. Table 32 and Table
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