Hi all. I'm a student of Information Engeenering of University of Pisa. I'm working with TmoteSky ( cc2420 radio stack) motes and TinyOs 2.x with cygwin.
I'm tryng to define the average transmission time of a message in a WSN. Im my testing application there is only one mote that sends messages in BROADCAST, so there is no collisions with messages sent by other motes. In Tossim simulation i found an average transmission time of about 6,8 ms for a message of 22 bytes payload In my test with TmoteSky motes i found an average transmission time of about 10 ms for a message of 22 bytes payload. I tryed to increase payload size of message and I found that : 2 bytes payload ----> avg tx time = 8,5 ms 22 bytes payload ----> avg tx time = 10 ms 42 bytes payload ----> avg tx time = 11,56 ms 62 bytes payload ----> avg tx time = 13,12 ms 82 bytes payload ----> avg tx time = 14,6 ms It seems that, to send additional 20 bytes, the radio takes about 1,5 ms ----> so the bit radio should be of 100 Kbit/sec, but in cc2420 datasheet i found that maximum bit rate is 250Kbit/sec. I't is possible that real bit rate of radio in TmoteSky motes is of 100Kbit/sec? Or this difference between simulation and real tests should be caused by the amount of time that MCU takes to writing 1 byte in the Tx Buffer? If time (taken by MCU) to write 1 byte in the Tx buffer is higher than the time (taken by cc2420 Radio Stack) to transmit via radio 1 byte----> ----> so it can be possible to explain this difference between average time to send messages of 2,22,42,62,82 bytes payload... thank for your answers, please write me also if you have an idea of the possible cause of this problem. Best regards Bye, salvatore
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