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CC110117.4 Carrier Sense (CS)Carrier Sense (CS) is used as a sync wordqualifier and for CCA and can be assertedbased on two conditions, which can beindividually adjusted:• CS is asserted when the RSSI is above aprogrammable absolute threshold, and deassertedwhen RSSI is below the samethreshold (with hysteresis).• CS is asserted when the RSSI hasincreased with a programmable number ofdB from one RSSI sample to the next, andde-asserted when RSSI has decreasedwith the same number of dB. This settingis not dependent on the absolute signallevel and is thus useful to detect signals inenvironments with time varying noise floor.Carrier Sense can be used as a sync wordqualifier that requires the signal level to behigher than the threshold for a sync wordsearch to be performed. The signal can alsobe observed on one of the GDO pins bysetting IOCFGx.GDOx_CFG=14 and in thestatus register bit PKTSTATUS.CS.Other uses of Carrier Sense include the TX-if-CCA function (see Section 17.5 on page 40)and the optional fast RX termination (seeSection 19.7 on page 46).CS can be used to avoid interference fromother RF sources in the ISM bands.17.4.1 CS Absolute ThresholdThe absolute threshold related to the RSSIvalue depends on the following register fields:• AGCCTRL2.MAX_LNA_GAIN• AGCCTRL2.MAX_DVGA_GAIN• AGCCTRL1.CARRIER_SENSE_ABS_THR• AGCCTRL2.MAGN_TARGET• For a given AGCCTRL2.MAX_LNA_GAINand AGCCTRL2.MAX_DVGA_GAIN setting theabsolute threshold can be adjusted ±7 dB insteps of 1 dB usingCARRIER_SENSE_ABS_THR.The MAGN_TARGET setting is a compromisebetween blocker tolerance/selectivity andsensitivity. The value sets the desired signallevel in the channel into the demodulator.Increasing this value reduces the headroomfor blockers, and therefore close-in selectivity.It is strongly recommended to use SmartRF ®Studio to generate the correct MAGN_TARGETsetting.Table 26 and Table 27 show the typical RSSIreadout values at the CS threshold at 2.4kBaud and 250 kBaud data rate respectively.The default CARRIER_SENSE_ABS_THR=0 (0dB) and MAGN_TARGET=3 (33 dB) have beenused.For other data rates the user must generatesimilar tables to find the CS absolutethreshold.MAX_LNA_GAIN[2:0]MAX_DVGA_GAIN[1:0]00 01 10 11000 -97.5 -91.5 -85.5 -79.5001 -94 -88 -82.5 -76010 -90.5 -84.5 -78.5 -72.5011 -88 -82.5 -76.5 -70.5100 -85.5 -80 -73.5 -68101 -84 -78 -72 -66110 -82 -76 -70 -64111 -79 -73.5 -67 -61Table 26: Typical RSSI Value in dBm at CSThreshold with Default MAGN_TARGET at 2.4kBaud, 868 MHzMAX_LNA_GAIN[2:0]MAX_DVGA_GAIN[1:0]00 01 10 11000 -90.5 -84.5 -78.5 -72.5001 -88 -82 -76 -70010 -84.5 -78.5 -72 -66011 -82.5 -76.5 -70 -64100 -80.5 -74.5 -68 -62101 -78 -72 -66 -60110 -76.5 -70 -64 -58111 -74.5 -68 -62 -56Table 27: Typical RSSI Value in dBm at CSThreshold with Default MAGN_TARGET at 250kBaud, 868 MHzIf the threshold is set high, i.e. only strongsignals are wanted, the threshold should beadjusted upwards by first reducing theMAX_LNA_GAIN value and then theSWRS061C Page 39 of 94