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Original question:

Carrier sense threshold setting for CC1101

CC1101-Q1: Help Needed with Dynamic Setting of Carrier Sense Absolute Threshold

tech15
Prodigy 100 points
Part Number: CC1101-Q1
Other Parts Discussed in Thread: CC1101

Tool/software:

Hello TI Community,

I am currently working on a project involving the CC1101 transceiver, and I need to implement a feature that allows users to set the Carrier Sense Absolute Threshold (CS threshold) dynamically via a command.According to the datasheet and the Design Note DN505, setting this threshold involves the following parameters:

  • MAX_LNA_GAIN
  • MAX_DVGA_GAIN
  • CARRIER_SENSE_ABS_THR
  • MAGN_TARGET

I have encountered several challenges and would greatly appreciate your guidance:

  1. Table Generation for Different Data Rates: The datasheet mentions that similar tables must be generated for different data rates to find the CS absolute threshold. Is the data rate the only factor that affects table generation, or does the carrier frequency also play a role? (both the 434Mhz and 868Mhz are used in my application) How should I approach this given that I don’t know the user’s data rates or other related parameters in advance?

  2. RSSI Value Discrepancy: In Design Note DN505, the calculation shows an RSSI value of -82 dBm for MAX_LNA_GAIN = 4, MAX_DVGA_GAIN = 1, MAGN_TARGET = 3, and CARRIER_SENSE_ABS_THR = 0. Changing MAGN_TARGET to 7 and CARRIER_SENSE_ABS_THR to 4 gives an RSSI value of -69 dBm. So I could assume the  RSSI value would be -82 + (42 - 33) = -73 dBm if only the MAGN_TARGET  is changed to 7 and CARRIER_SENSE_ABS_THR still remains 0. However, using Table 33 in datasheet for the same parameters results in -74.5 dBm. Could you clarify this discrepancy (between -73dBm and -74.5dBm).

  3. Single Table Feasibility: whether the RSSI value at CS threshold for a fixed combination of MAX_LNA_GAIN  and MAX_DVGA_GAIN is linearly related to MAGN_TARGET  and CARRIER_SENSE_ABS_THR? If so, does that mean for a specific data rate, I can rely on a single table  with any MAGN_TARGET and CARRIER_SENSE_ABS_THR to set the threshold for different combinations of MAX_LNA_GAIN and MAX_DVGA_GAIN? If not, what is the best practice to dynamically adjust the threshold based on user input?

  4. User Requirements: Given the complexity of these settings, should I communicate with my client to make some compromises if the current requirements are hard to meet? If so, what would you recommend as reasonable compromises?

Thank you in advance for your assistance.