Assuming the numbers you give are packet sequence numbers, and that
you have somehow considered the two different numbers from both
transmitters, it sounds like about 20% loss. Which, in the scheme
of things is not all that bad...
Generally loss can be attributed to bad signal (distance, antenna,
multi-path issues) or undetected collisions. My (limited) experience
with 2240 on micaz indicates that the bad signal stuff is handled
pretty well, but I have not tested the CSMA behavior. You do need
to make sure that there are no "hidden node" problems, where the
two transmitters can't "hear" each other and thus transmit at the
same time and garbage up each other's messages.
The only way I know to improve reliability is to implement
ACKnowlegments of some kind. The 2240 does something at the
hardware level, but there is a software level ACK (on the mica2's
at least...I think it's carried over to other platforms) that
sort of works. I have an old report and code from my testing here:
http://www.etantdonnes.com/Motes/
and of course, google should be your friend.
MS
liangjing wrote:
Hi, everyone!
I am using T1 to implement the CSMA-CA in CC2420. I initiate two motes
to send packets periodically to cause packet congestion and initiate one
mote to receive the packets. I counted and calculated the sum of numbers
of packets of sending and receiving on both ends. But they are not
equal, and actually there is a big packet loss between the two sides.The
packet number of sending mote is 0x039F and 0x03A6 separately and
the packet number of receiveing mote is 0x0477. I am confused about the
result, since the CC2420 can use the CCA to detect and avoid the
congestion and interference of packets, how could the packet loss
happened dramatically ?
Any advice is appreciated.
Best Regards
Jing
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