A Modified Power Saving Mode in
IEEE 802.11
Distributed Coordinator Function
Mr. Ye Minghua
Supervisor: Dr. Lau Chiew Tong
CeMNET
School of Computer Engineering
Outline
Vision and challenge
Background and Review of Power
saving mode in IEEE 802.11
Our proposed algorithm
Simulation result
Conclusion and future work
Vision
“Computing and communication anytime,
anywhere and to anybody else”
Challenge
1. Mobility and Flexibility
2. Standardized communication
protocol (IEEE802.11, Blue Tooth,
etc.)
3. Finite battery power of mobile
device
Energy Consumption Inverstigation
4%
18% 25%
Wireless NIC
Display
CPU&Memory
18% Harddisk
Other
35%
Energy Consumption model
Active mode 2
1.8 1.65 W
Transmit state
1.6 1.4 W
Receiving state 1.4
1.15 W
Idle state
1.2
1 Energy
Power Saving mode 0.8
0.6
0.4
0.2 0.045 W
0 Tranmit Receiving Idle state Power
state state saving state
Power Saving
Mechanism for IEEE
802.11
Idle receiving state is dominating power
waste;
The cost of power state transition.
800 micro-second for a doze to awake
transition;
During this transition, a node will consume
twice the power than idle mode.
Note: Conservative estimation,
depend on hardware implementation.
Example of the operation
Our proposed algorithm
The time synchronization beacon is
moved to the end of the ATIM window;
The beacon sender will operate in the
promiscuously listening mode within
the ATIM window;
Scheduling information will be
computed and sent along with the
beacon.
The Beacon transmission
In each of the ATIM window, the station
that send the ATIM announcement first
will send the timing beacon;
Parameter Beacon_tran_time
IF (clock mod aBeacon_interval ==
Beacon_tran_time)
THEN { all STAs defer any of their ongoing
transmission };
Specific STA will transmit beacon at
Beacon_tran_time + SIFS
Implementation details –
inside ATIM window
each node will piggyback the
number_of_pending_packets for current
destination in each ATIM announcement
packet transmitted;
Only one specific node have to operate
in the promiscuously listening mode
within the ATIM window;
Beacon is transmitted by this node
along with the scheduling information
which explicitly gives out the order of
transmission.
Implementation details –
outside ATIM window
All STAs transmit their announced data
packets according to the scheduling;
STAs can switch to doze if the following
criteria satisfied:
Finished sending the announced packets
of its own;
No packets destined for it as stated in the
schedule;
Remaining time of current beacon interval
is larger than 1600 microseconds.
(conservatively consider 800
microseconds for both state transitions)
Example of the operation
Beacon Interval Beacon Interval
Beacon ATIM ATIM
Window Window
Xmit ATIM
Rcv ACK Xmit Beacon Rcv Beacon
Station A
RCV ATIM
Send ACK Rcv Beacon Xmit Beacon
Station B
Rcv Beacon Rcv Beacon
Station C
Power-saving state
Simulation
we developed the simulation programs
using C++;
The simulator closely follows the
protocol details of Power Saving Mode
in 802.11 (802.11PSM) and our proposed
algorithm (S-PSM);
beacon generation, ATIM window,
contention based DCF access
procedure and 2Mbps physical layer.
Parameters used in Simulation
Parameters Value
Packet Length Slot time
Minimum Contention window 31
Maximum Contention window 1024 Data 1024 bytes 392
ATIM window size 5ms ACK 39 bytes 15
Beacon Period 100ms
DIFS 50 s ATIM 39 bytes 15
SIFS 10 s Beacon 300 bytes 115
Slot time 10 s
mode Energy
Idle 1.15W
Receiving 1.4W
Transmitting 1.65W
Doze 0.005W
Simulation result Average sending attempt 802.11PSM
per received packet 802.11PSM
Delivery Ratio
S-PSM
S-PSM
1.5 1.1
total packets sent / total packets
1.45
1
1.4
0.9
1.35
Delivery Ratio
0.8
1.3
0.7
received
1.25
0.6
1.2
1.15
0.5
1.1
0.4
1.05 0.3
1 0.2
0.95 0.1
0.9 0
0 64 128 192 256 0 64 128 192 256
Number of Nodes Number of Nodes
Average Delay 802.11PSM
S-PSM Energy per packet
1350 802.11PSM
1300 S-PSM
1250
1200 0.06
1150
1100
Average energy per packet
1050 0.055
1000 0.05
950
900
Average delay
850 0.045
800
750 0.04
(ms)
700
650 0.035
600
550 0.03
500
450 0.025
400
350 0.02
300
250 0.015
200
150 0.01
100
50 0.005
0
0 64 128 192 256 0 64 128 192 256
Number of Nodes Number of Nodes
Conclusion
Up to 70% of the total energy saving;
Only a little bit longer delay than
traditional IEEE802.11 PSM in some
cases;
Probability of collision is greatly
reduced by schedule which ensure the
data transmission to be contention free;
Maintain the network performance
comparing with PSM of 802.11,
throughput, delivery ratio, average
packet delay, etc.
Future work
Investigate the possibility of applying
this mechanism to the multi-hop
scenario;
Achieve more efficiency by dynamically
adjusting the ATIM window size;
Research the integration and interaction
of MAC layer protocol and the routing
layer.
Investigate the time synchronization
issue.
Thank you!