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Table of Contents
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).
Requirements
This task requires
- a ready BeagleBone Black equipped with the CC1200
- one TI Development Kit for the CC1200
- Smart RF Studio.
Tasks
- 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 compare your computed values of the FREQ registers with SmartRF Studio.
- now, set RF to an arbitrary value within the supported frequency band of CC1200
- Bring SmartRF Studio in “Packet TX” mode using the default frequency.
- start the transmitter. At the receiver, the BeagleBone Black, you should now receive NO packet.
- Now, stop the transmitter and change the frequency to your selected frequency.
- Now, you should be able to receive the packets.
