PW-MAC: An Energy-Efficient Predictive-Wakeup MAC Protocol for Wireless 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 substantially 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 retransmitting 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 sleeping state -> choosing when to wakeup and retransmit 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 prediction 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 wakeups 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 listening. A receiver sends out beacons at a fixed time interval 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 prescheduled rendezvous times to communicate with the receiver the receiver wakes up at the scheduled beacon time

relative delivery delay bound 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 delay 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 number 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 delivery delay

Evaluation Line topology Varying flow length & end-to-end relative delay bound When the flow length is large, RI-MAC cannot provide 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