cc1101.pdf page 44 

17.4 Carrier Sense (CS) 

17.4@LAZX(CS) 



Carrier sense (CS) is used as a sync word qualifier and for Clear Channel Assessment (see Section 17.5). 


LAZXiCSj͑IĂdg̎gт悢ԂmF̂ƁAVNM𑗂oƂǎɂ邽߂Ɏg܂B









CS can be asserted based on two conditions which can be individually adjusted: 

CŚAXɒ߂邱Ƃł2̏󋵂ɊÂĕ񍐓s܂BF 








programmable absolute threshold, and deasserted when RSSI is below the same threshold (with hysteresis). 



vO\Ȑ΂lARSSI臒liqXeVXŁjȉɂƂAAT[g~܂B



See more in Section 17.4.1. 

ZNV17.4.1ł茩ĂB 









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. 

RSSI1RSSITv玟܂ŃvO\ȐdBőƂACS̓AT[gARSSIdB̓ŌƂAAT[g~܂B 















This setting is not dependent on the absolute signal level and is thus useful to detect signals in environments with time varying noise floor. 

̃ZbeBO͐΂̐MxɈˑĂȂāÂ悤ɁAԂƂƂɊ̐MGςĂ̂邽߂ɖɗ܂B 












See more in Section 17.4.2. 

ZNV17.4.2ł茩ĂB 







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. 




s铯m点̂߂̂lx荂ƂMxɗvāAMDMCFG2ɃL[ZXMۂƂɂĔzu

铯m点\Iʉߎ҂IOCFGx.GDOx_CFG=14Zbg邱ƂɂGDOŝ1{̏Ŋώ@邱ƂłāAXe[^XWX^

PKTSTATUS.CS.񂾂̂ŁAL[ZXg邱Ƃł܂ 











Other uses of Carrier sense include the TX-if- CCA function (see Section 17.5 on page 46) and the optional fast RX termination (see Section 0 on page 52). 

LA[ZX𑼂̎gŔATX-if-CCA@\i46y[W̏ő17.5߂܂jƃIvV̑RXIi52y[W̏ő0߂܂j܂݂܂B 





CS can be used to avoid interference from other RF sources in the ISM bands. 

CŚAISMшőRF犱邱ƂɎg܂B 




















cc1101.pdf page 45 

17.4.1 CS Absolute Threshold 

17.4.1 CSΕs臒l 






The absolute threshold related to the RSSI value depends on the following register fields: 

RSSIlɊ֘A΂ĺAȉ̃WX^[Ɉˑ܂F 





AGCCTRL2.MAX_LNA_GAIN
AGCCTRL2.MAX_DVGA_GAIN
AGCCTRL1.CARRIER_SENSE_ABS_THR
AGCCTRL2.MAGN_TARGET 



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_LNA_GAINAāA 




AGCCTRL2.MAX_DVGA_GAIN settings, the absolute threshold can be adjusted }7 dB in steps of 1 dB using 

AGCCTRL2.MAX_DVGA_GAINZbeBOA΂̓́A1dB̃XebvŁA}7 dB𒲐߂邱Ƃł܂ 

CARRIER_SENSE_ABS_THR 

CARRIER_SENSE_ABS_THRB 




The MAGN_TARGET setting is a compromise between blocker tolerance/selectivity and sensitivity. 

MAGN_TARGETZbeBÓAubJ[e/I𐫂Ɗx̊Ԃ̑ËłB 





The value sets the desired signal level in the channel into the demodulator. 

̒l𑝂₷ƂŃubJ[AāAߋ̑I𐫂̂߂ɓXy[X炵܂B 




It is strongly recommended to use SmartRFR Studio 8 to generate the correct MAGN_TARGET setting. 

́AMAGN_TARGETZbeBO𐶂ݏo߂SmartRF Studiom8ngƋ߂܂B 










Table 32 and Table 33 show the typical RSSI readout values at the CS threshold at 2.4 kBaud and 250 kBaud data rate respectively. 

\32ƕ\33́Aꂼ2.4kBaud250kBaudf[^MxCSœT^IRSSI\l܂B 







The default CARRIER_SENSE_ABS_THR=0 (0 dB) and MAGN_TARGET=3 (33 dB) have been used. 

ftHgCARRIER_SENSE_ABS_THR=0i0dBjMAGN_TARGET=3i33dBjAg܂B 






For other data rates, the user must generate similar tables to find the CS absolute threshold. 

̃f[^Mx̂߂ɁA[U[CSɐ΂l邽߂ɁAގe[u𐶐Ȃ΂܂B 








cc1101.pdf page 45 

If the threshold is set high, i.e. only strong signals are wanted, the threshold should be adjusted upwards by 
first reducing the MAX_LNA_GAIN value and then the MAX_DVGA_GAIN value. 


lݒ肳Ȃ΁AȂ킿AM߂A
Al͍ŏMAX_LNA_GAINlƂꂩMAX_DVGA_GAINl炷Ƃŏ𒲐߂Ȃ΂Ȃ܂B 







This will reduce power consumption in the receiver front end, since the highest gain settings are avoided. 

łZbeBO鎞A̓V[o[tgGhł̏d͒l炵܂B 









17.4.2 CS Relative Threshold 

17.4.2 CSe臒l 





The relative threshold detects sudden changes in the measured signal level. 

ΓIȂĺATdȐMxŋ}]܂B 





This setting does not depend on the absolute signal level and is thus useful to detect signals in environments with a time varying noise floor. 

̃ZbeBO͐΂̐MxɈˑÂ悤ɁAmCYtA[ςĂ鎞ԂŊŐM邽߂ɖɗ܂B 





The register field AGCCTRL1.CARRIER_SENSE_REL_THR is used to enable/disable relative CS, and to select threshold of 6 dB, 10 dB, or 14 dB RSSI change. 

WX^[AGCCTRL1.CARRIER_SENSE_REL_THR͑ΓICSɋ^/Ȃ̂ɗp܂AāA6dBA10dB܂14dB̏o_IԂ߂ɁARSSI͕ς܂B 













cc1101.pdf page 46 

17.5 Clear Channel Assessment (CCA) 

17.5NA`lAssessment(CCA) 





The Clear Channel Assessment (CCA) is used 

NA`lAssessmentiCCAjAg܂ 




to indicate if the current channel is free or busy. 

݂̃`lł邩ł邩ǂƁB





The current CCA state is viewable on any of the GDO pins by setting IOCFGx.GDOx_CFG=0x09. 

݂CCAXe[ǵAIOCFGx.GDOx_CFG=0x09.Zbg邱ƂɂāAGDOŝǂ̏łł܂






MCSM1.CCA_MODE selects the mode to use when determining CCA. 

MCSM1.CCA_MODÉACCA肷ƂAgp郂[hIт܂B 






When the STX or SFSTXON command strobe is given while CC1101 is in the RX state, the TX or FSTXON state is only entered if the clear channel requirements are fulfilled. 

CC1101RXXe[gɂSTX܂SFSTXON߃Xg[u^ƂANA`lȂ΁ATX܂FSTXONXe[g͓邾łB 





Otherwise, the chip will remain in RX. 

Ȃ΁A`bvRX̂܂܂łB 












If the channel then becomes available, the radio will not enter TX or FSTXON state before a new strobe command is sent on the SPI interface. 

`lꂩ痘pł悤ɂȂȂ΁AVXg[u߂SPIC^[tF[XőOɁAWITX܂FSTXONXe[gɓ܂B 






This feature is called TX-if-CCA. 

̓́ATX-if-CCAƌĂ΂Ă܂B 





Four CCA requirements can be programmed: 

4CCA̓vO邱Ƃł܂F 




Always (CCA disabled, always goes to TX) ? If RSSI is below threshold ? Unless currently receiving a packet ? Both the above (RSSI below threshold and not currently receiving a packet) 

Ɂigps\CCÁATXɍs܂jAIf RSSÍAݔBoth󂯂Ăo_UnlessĂ܂L(āAݎ󂯂ĂȂRSSI) 











-------(|ς)---------------------------------------------------------------------------





