Wireless Ad Hoc and Sensor Networks

274 

Wireless Ad Hoc and Sensor Networks

Algorithm 16: The DDC Algorithm

input : CDS-based data collection tree T, R

0

-PCR

output: a distributed asynchronous data collection plan

1 counter(s

i

)←0;

2 s

i

(i ∈[1,n]) sets its CR as R

0

-PCR according to the required threshold of data

receiving rate R

0

;

3 while s

i

has some data packets for transmission do

4 counter(s

i

)← counter(s

i

)+1;

5 j ←counter(s

i

);

6 s

i

randomly sets a backoff time t

j

i

for the transmission of the j-th packet in

window (0,

τ

w

];

7 if j > 1 then

8 t

j

i

← (

τ

w

−t

j−1

i

)+t

j

i

;

9 while t

j

i

is not countdown to 0 do

10 s

i

senses the channel with R

0

-PCR;

11 if s

i

senses that the channel is busy then

12 s

i

stops the countdo ...