Exercise: Sensing a channel

The preamble of the transmitted frame is used by the receiver to find the frequency the sender is using. This implies checking the RSSI before the packet can be received. The problem by measuring the RSSI is to determine, if the signal level is caused by the sender or if it only represents the noise level of the channel. In this excessive this distinction has to be made. And of course, do not forget to disable preamble recognition at the receiver (the a look at CC1200 Users Guide).

This task requires

• a ready BeagleBone Black equipped with the CC1200
• one TI Development Kit for the CC1200
• Smart RF Studio.

• the programming is done by extending the source files from the previous lesson Exercise: Changing the frequency.
• Extend your program by a function that measures the RSSI prior to packet reception. A packet should only be received, if a valid RSSI from the sende is detected. What means a valid RSSI ?
• Don't forger to disable preamble recognition at the receiver.
• For testing, start your program.
• Use SmartRF Studio ransmit packets at the RF frequency the receiver is using. Your program should recognize a valid RSSI and start receiving packets.
• now, stop packet transmission set RF of the sender to a frequency the receiver is not using. Restart packet transmission.
• At the receiver, the BeagleBone Black, you should now measure no valid RSSI and therefore no packet will be received.
• Now, stop the transmitter and change the frequency to your selected frequency.
• Now, you should be able to receive the packets.