D. ZHANG ET AL.
Copyright © 2013 SciRes. CN
performance of S-PSM. First, let’s observe the perfor-
mance of S-PSM without Idle Timer. From the simula-
tion result, we can see the station will spend some time in
idleness when M < 8. And the corresponding energy
consumption is very large. When AP has no buffered
data, AP will check the buffer frequently, and stations
will receive empty GAS frame and have nothing to do.
When the number of stations is little or network load is
low, this issue will appear frequently and cause the most
energy wasting, which is consistent with the performance
analysis of Equation (9). We introduce the Idle Timer
whose value is set as 50 slots to solve this problem.
When there are no packets buffered in AP, AP sends
GAS frame to tell all the stations turn to sleep state and
opens the idle timer. After the timer expires, all stations
switch to active state and AP checks buffer information
to begin the next transmission. We can see the energy
consumption remaining about 3Joule, which is a huge
energy saving improvement.
We have verified the two mechanism’s validity and
analyze their performances from three aspects (resident
time, system throughput, and energy consumption). We
observed that our proposed scheme has a better perfor-
mance in energy saving. By introducing the Idle Timer
and using message-driven scheme to let stations know
the transmission schedule, S-PSM overcomes the short-
age of the PSM and obtains a significant improvement in
terms of energy saving.
6. Conclusions
We have proposed the S-PSM that increases energy effi-
ciency of all wireless clients in an infrastructure network.
The AP in S-PSM determines the transmission sequence
and stations change their own states by the information
attached in GAS frames. AP plays a centralized role that
controls the transmission process. The stations convert
the state according to the transmission sequence which
can reduce unnecessary wake ups and maximize energy
saving. The Respond Contention Window (RCW) could
reduce collision probability effectively, which is helpful
to improve the system throughput, and the transmission
cycle assures fairness among stations. However, how the
AP communicates with sleep stations through broadcast
needs to be paid more attentions. We utilize the Idle Ti-
mer to solve this problem in our model, but cause unne-
cessary packets delay. Our needs to switch the interface
frequently, and that does harm to the interfaces. So, in
future work, we can improve S-PSM performance via
these aspects.
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