[Tinyos-help] initial backoff in CC2420

[renjie huang]

Hi

I have some question related to CC2420.

My environment: Tinyos-1.x  + Imote2

For CC2420, there is a initial backoff period before sending packets. The
default value is (random()&0xF +1)*320us= [320us, 3.84ms]. When I use the
default value, the packet loss rate is low, which is near 2%.  If I decrease
the value to  (random()&0x7 +1) or a smaller value, the packet loss rate
increases significantly to 20~50%. The RF power is 31. Only one node is
sending packets, thus there are should not have intense transmission
collision. Inside a node, there is continuing data stream from upper layer
to radio. So after a packet is sent, another one will continue immediately.

Can someone tell me why the initialbackoff has such a big impact on packet
loss rate. Before I thought the purpose for intialbackoff is to reduce
collision. Now It seems not. Is such a long period(more than 2ms) used for
the transistion from RX->TX? But it should not take such a long time


-- 
Renjie Huang
Sensorweb Research Laboratory
http://sensorweb.vancouver.wsu.edu/
Washington State University
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