5.2 5.3. rssi vs. distance

You will modify the code for the mote taken from 5.2. Creating a Spectrum Analyzer to Measure Noise in order to read 200 times the RSSI value from the same channel . A python script will then average those read values. To this end:

• Use the code from 5.2. Creating a Spectrum Analyzer to Measure Noise , but comment out line mrfiSpiWriteReg(CHANNR,channel); . The mote will now read the RSSI 200 times on channel 0.
• Reprogram the receiver board and visualize the values outputted on the COMx port using PuTTY (see 1.3. Read directly from COM Port ). We are interested in calculating the average value of each 200 point line.
• Copy-paste the code presented below to a new file called txrx_rssi_dist.py Alternatively, this file is already present in the downloadable source code , in the directory source_code/c_files/ . ;
• in Cygwin, run the python script cat /dev/comx | ./txrx_rssi_dist.py In Cygwin, you should first go to the folder containing txrx_rssi_dist.py , see 5.2. Creating a Spectrum Analyzer to Measure Noise . . This script outputs the average value of the RSSI 200 readings.
• Reprogram a second board using the code described in 4.3. Continuous Tx/Rx , so that it continuously sends data, on channel 0 and with a transmission power of 0dBm.
• Start the continuous sending and see how the RSSI decreases as the transmitter is moved away from the receiver.

The figure below plots the evolution of RSSI as transmitter and receiver boards are parted away in three different directions. Because these measurements are not done in aninfinite open space, shadowing and fading effects introduce randomness into the relationship between RSSI and distance.