PW-MAC: An Energy-Efficient Predic-tive-Wakeup MAC Protocol for Wire-

less Sensor Networks

Lei Tang∗ Yanjun Sun† Omer Gurewitz‡ David B. Johnson∗

∗Department of Computer Science, Rice University, Houston, TX, USA

†Systems and Applications R&D Center, Texas Instruments, Dallas, TX, USA

‡Department of Communication Systems Engineering, Ben Gurion University, Israel

INFOCOM 2011

Motivation ▣ (receiver-initiated) as the beacon is substan-

tially shorter than a preamble, wireless bandwidth usage

▣ Reduce the duty cycle for recieivers and senders, whereas RI-MAC only reduce the duty cycle only at receivers

▣ Energy-efficiently resolving collisions and re-transmitting lost packets

Preamble vs beacon▣ Sender initiated (X-MAC)

▣ Receiver initiated (RI-MAC)

Reduce duty cycle▣ RI-MAC

▣ PW-MAC

Energy-efficiently resolving collisions▣ Pseudo-random wakeup schedule generater

To enable a sender to accurately predict the wakeup times of a receiver(done in wise mac)

To avoid generating same numbers (waking receivers up at the same time)

Energy-efficiently retransmitting lost packets

▣ Detecting wireless collision -> switching to sleep-ing state -> choosing when to wakeup and re-transmit the packet

On-demand prediction error correction

▣ A node S requests an update of the prediction state of another node R when it detects that the predic-tion error is larger than the sender wakeup advance time.

evaluation▣ Sender wakeup advance time

the prediction error caused by hardware and operating system latency leads to the sender missing some wake-ups of the receiver

evaluation▣ Conflicting wakeup schedule

Once two receivers wake up at the same time, they will continue waking up at the same time in the following cycles due to the fixed wakeup interval of WiseMAC.

evaluation▣ Hidden terminal

WiseMAC is unable to detect the packet collisions of the two hidden senders and does not have an efficient mechanism to handle packet retransmissions

evaluation▣ Multihop network

Delay-Bounded MAC with Minimal Idle Listening for Sensor Networks

Yang Peng, Zi Li, Daji Qiao and Wensheng Zhang

Iowa State University, Ames, IA 50011

INFOCOM 2011

Motivation ▣ RI-MAC uses shorter and less frequent beacons

which consume less bandwidth

▣ A sender needs to remain awake after a data packet arrives, till the receiver wakes up to receive the packet, potentially wastes a lot of time on idle lis-tening.

▣ A receiver sends out beacons at a fixed time inter-val on average and does not adapt to changes of traffic pattern.

Reduce idle listening▣ delay bounded data delivery

▣ only requires the sender to wake up at presched-uled rendezvous times to communicate with the re-ceiver

▣ the receiver wakes up at the scheduled beacon time

relative delivery delay bound▣ Delivery delay

Delay between arrival time of packet and when packet is transmitted

▣ The ratio of the data delivery to the average data arrival interval if data packets arrive every 100 seconds and the delivery de-

lay of a data packet is 10 seconds, the relative delay is 10%.

▣ Conserve energy if a 10% relative delay bound is acceptable, when the data

arrival interval increases from 10 to 100 seconds, the num-ber of beacons sent by the receiver and hence the energy consumed by the receiver can be reduced by an order of magnitude.

delay-bounded data delivery services

▣ if a data packet arrives before the next scheduled listen time, the radio won’t be turned on till the scheduled listen time

adjusts to the varying traffic condition

▣ Dynamic duty cycle sensor nodes adjust their duty cycles dynamically to the

varying traffic condition This shows that CyMAC nodes are able to adjust quickly

to the varying traffic condition and operate in ultra low duty cycles when the traffic is light.

Effects of time asynchrony▣ clock drift

Difeerent clocks counting time at slightly different rates

▣ Extra delay has been added to the packet de-livery delay

Evaluation ▣ Line topology

Varying flow length & end-to-end rela-tive delay bound

▣ When the flow length is large, RI-MAC cannot pro-vide the desired delay bound even with a higher duty cycle than CyMAC.

Evaluation ▣ Line topology

Varying end-to-end relative delay bound & the average packet generation interval

Change data intervals

Evaluation ▣ Star topology

the relative delay in RI-MAC is not affected much by the number of source nodes but by average packet generation interval .

Evaluation ▣ Mesh topology

with multiple flows CyMAC has lower duty

cycle than RIMAC Achieve the desired

delay bound