1. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Advantages of Dual Channel MAC for Wireless Sensor Networks Antonio G. Ruzzelli, Gregory O’Hare, Raja Jurdak † and Richard Tynan School of Informatics and Computer Science University College Dublin Dublin, Ireland {ruzzelli,richard.tynan,gregory.ohare}@ucd.ie †Bren School of Information and Computer Sciences University of California Irvine CA 92697 rjurdak@ics.uci.edu

2. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Summary Wireless sensor networks generality Primary Objectives of MAC for WSNs Motivation of DCMA DCMA/AP protocol overview –Transmission mechanism –Adaptive preamble –Opportunistic crossover Simple transmission timing analysis Simulation Preliminary results Imminent work Conclusion

3. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Background Traditional low cost radios for wireless sensors operate with one frequency channel at any given time, e.g Tr1001, CC1000, CC1010 A profusion of MAC protocols focus on energy efficiency over one frequency channels

4. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Unique frequency channel issues MACs like IEEE802.11, SMAC, TRAMA or BMAC suffer from: – High latency (e.g. due to RTS/CTS/ACK in CSMA/CA) –Low flexibility (Difficult to release slots unused in TDMA) –Inefficient usage of the wireless channel (e.g. the ETP problem in CSMA/CA)

5. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Advances in WSNs Novel transceivers can operate with two channels simultaneously with a relative small increase of energy consumption e.g. nRF2401 Supply current one channel in receive 18 mA Supply current two channels in receive23 mA nRF2401 is effectively mounted on the motes developed at the University of Cork (Ireland)

6. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan DCMA/AP: Dual channel multiple access with adaptive preamble Usage of 2 frequency channels –Data channel Cd for data –Control channel Cc for notifications Pros No table of neighbours required No handshake mechanisms like RTS/CTS Reduced idle listening at the receiver Adaptive wake-up node preamble Cons Small increase of current consumption in dual channel reception mode (18ma  23mA) Suitable for: –Nodes working at very low duty cycle –Dual channel transceiver

7. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan The minimum wakeup concept LCCA Nodes alternate long period of inactivity to tiny period of channel assessment; The Least Clear Channel Assessment LCCA is the shortest time period needed for nodes to sense any activity on the channel (~2.5msec in BMAC) LCCA time period is much shorter than the time required for a packet transmission (e.g. 35msec for 5byte transmission with Tr1001) LCCA can reduce node duty cycle to less than 1% Wakeup period : longest period of consecutive node activity when a signal is detected (Sensing time) Wakeup period Ts Sleep period LCCA Time

8. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan DCMA communication mechanism (1) Node are unsynchronized  asynchronous transmission All nodes apply LCCA periodically on the data channel Cd only A node with data to transmit apply LCCA on control channel Cc firstly.

9. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan The transmitter If the channel is clear then the transmitter starts sending the adaptive preamble Pa on Cd At the same time TX keeps on listening to Cc DCMA communication mechanism (2)

10. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan DCMA communication mechanism (3) The receiver During regular CCA, the receiver can sense channel activity on Cd then reply with a TIP packet on Cc TIP =transmission / reception in progress TIP contains (1)the receiver ID, (2) next Rx ID, (3) packet length

11. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan In case of error, the notification is transmitted on Cc The error packet contain the PackID In case of error the packet is rescheduled DCMA communication mechanism (4)

12. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan The exposed terminal problem removal TIP is sent by the receiver  only nodes around the receiver refrain from transmitting The communication mechanism removes the ETP!

13. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Adaptive Preamble mechanism In case of multiple transmission, asynchronous packets help the receiver to obtain the node ID of the later transmitter Tx2. Consequently Tx2 can be enabled by means of a RIP packet The Preamble transmission stops as soon as the RIP packet is received  adaptive! Note: RIP content = TIP content Difference: RIP is used to identify multiple Tx

14. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Opportunistic Crossover mechanism During periodical LCCA, if activity is sensed, nodes switches to Cc to get the TIP/RIP packet TIP/RIP packet contains info about the next scheduled RX node (nextRx) and ongoing packet length The nextRx is in the position to set up a NAV alarm to wake up right after the packet is transmitted. Other nodes set up a double NAV to wake up just before the packet has been forwarded TX RX Next RX Channel Cd Channel Cc Note: Opportunistic crossover needs the next receiver to sense the channel busy (not only the case)

15. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Timing Analysis against BMAC DCMA reduces the latency of packet with respect to BMAC in the quantity of: (1) 2Tsense –Tcca ( receiver wakes up at the end of Pa: Worst scenario) (2) Ts/2+2Tsense –Tcca (receiver wakes up in the middle of Pa: Average scenario) (3) Ts+2Tsense –Tcca (Best scenario  opportunistic crossover apply) Ts= Sleeping time T = Whole Time period Tsense = Time for a RTS or CTS packet in BMAC

16. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Implementation DCMA/AP has been coded within the OmNet++ based on the object oriented C++.

17. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Preliminary results Decrease of transmission packet delay Increase of network flexibility in terms of access to the channel and node scalability. Some increase of partial overlapping transmissions on the control channel Cc following an increase of packet generation rate In general, initial results follow our expectation that an improved performance could compensate for the increase of energy consumption due to two channel utilization

18. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Future works Compare the protocol with WSNs MACs that use one channel (e.g SMAC and BMAC ) and two channels (e.g STEM, DBTMA); Implement DCMA/AP on real motes that support two simultaneous frequencies for transmission of one channeland reception of the other one; Include DCMA/AP with MERLIN as a routing layer for wireless sensor networks;

19. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Conclusion The paper investigated the advantages of using the two channels distinctively for control packets and data packets. A preliminary version of dual frequency channels multiple access with adaptive has been presented The primarily requirement is that the radio transceiver supports transmission on the first channel and simultaneous reception on the second one. DCMA/AP improve the channel utilization and increase the percentage of node sleeping time Few collision are reported on the Cc channel Initial result at the simulator are promising, more sophisticated results and comparison with other architectures are imminent.

20. UNIVERSITY COLLEGE DUBLINDUBLIN CITY UNIVERSITY SMI || NCSR || CDVP Ruzzelli, O’Hare, Jurdak, Tynan Questions and comments are welcome Thank you for your kind attention!