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ADCA: An Asynchronous Duty Cycle Adjustment MAC Protocol for Wireless Sensor Networks GLOBECOM 2008 Yu-Chia Chang, Jehn-Ruey Jiang and Jang-Ping Sheu.

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Presentation on theme: "ADCA: An Asynchronous Duty Cycle Adjustment MAC Protocol for Wireless Sensor Networks GLOBECOM 2008 Yu-Chia Chang, Jehn-Ruey Jiang and Jang-Ping Sheu."— Presentation transcript:

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2 ADCA: An Asynchronous Duty Cycle Adjustment MAC Protocol for Wireless Sensor Networks GLOBECOM 2008 Yu-Chia Chang, Jehn-Ruey Jiang and Jang-Ping Sheu CSIE Department National Central University

3 Outline Introduction Related work ADCA MAC protocol Experiments and simulation results Conclusions

4 Introduction Wireless sensor networks is composed of a large number of battery-operated sensor nodes Energy conservation is one of the most important issues RF transceiver is the biggest power consumer in a sensor node

5 Introduction (Cont.) Four modes of the radio transceiver: transmitting receiving listening sleeping The first three modes are also called active or wake modes The power consumption of the four modes of MICAz mote is 52.5, 59.1, 59.1 and mW

6 Introduction (cont.) What causes energy waste? Collisions Control packet overhead Overhearing unnecessary traffic Long idle time bursty traffic in sensor-net apps Idle listening consumes 50—100% of the power for receiving (Stemm97, Kasten) Dominant in sensor nets

7 Introduction (cont.) Idle listening can be solved by sleep/wake protocols When the duty cycle (i.e., active period) of the radio is reduced to 1 percent, the power consumption of the sensor node can be reduced by a factor of 50.

8 Introduction (cont.) Collision can be solved by RTS/CTS (CSMA/CA ) (up to 36% improvement) Overhearing can be solved by RTS/CTS with NAV (Network Allocation Vector) However, the overhead of RTS/CTS is relatively large when used in in WSNs since WSN packets are usually very small. In MICA Mote, the maximum data packet size is 41 bytes and the size of an RTS/CTS packet is 18 bytes.

9 Contention-based protocols CSMA — Carrier Sense Multiple Access Ethernet (CSMA/CD) is not suitable for wireless (collision at receiver cannot be detected at sender) MACA — Multiple Access w/ Collision Avoidance RTS/CTS for hidden terminal problem RTS/CTS/DATA CSMA/CA AB C Hidden terminal: A is hidden from C’s CS

10 CSMA/CA Contention-based protocols (contd.) MACAW — improved over MACA RTS/CTS/DATA/ACK Fast error recovery at link layer IEEE Distributed Coordination Function (DCF) Largely based on MACAW Called CSMA/CA

11 Hidden Terminal Problem A and C want to send data to B 1. A senses medium idle and sends data 2. C senses medium idle and sends data 3. Collision occurs at B A B C Data

12 Collision Avoidance w/ RTS/CTS A and C want to send to B 1. A sends RTS (Request To Send) to B 2. B sends CTS (Clear To Send) to A C “ overhears ” CTS from B 3. C waits for duration of A ’ s transmission A B C 1.RTS 2.CTS 3.Data

13 Virtual Carrier Sense Timing relationship

14 Introduction (cont.) ADCA MAC protocol for WSNs Asynchronous sleep/wake protocol Duty cycle adjustment Goals Energy efficiency Without degrading performance Without lengthening transmission delay Without lowering throughput

15 Related work

16 preamble-based B-MAC, Wise-MAC, SyncWUF slot-based P-MAC, TRAMA, Z-MAC, H-MAC duty cycle synchronization-based S-MAC, T-MAC, U-MAC

17 B-MAC Drawbacks Overhearing Bad performance at heavy traffic case Long transmission latency

18 Wise-MAC Drawbacks Maintain neighbors’ time offset Transmission latency is increased

19 P-MAC - Pattern MAC P-MAC [12] divides time axis into frames, each of which consists of two parts: the Pattern Repeat part and the Pattern Exchange part. Both parts contain many slots. During the Pattern Exchange part, nodes advertise their intended sleep/wake patterns, which represent one slot by one bit (0 for sleeping mode and 1 for active mode) and can be dynamically adjusted based on traffic conditions. And during the Pattern Repeat part, a node wakes up according to the advertised pattern. A node also wakes up at a time slot t, if one of its neighbors has advertised to be awake at the time slot t and it has data for sending to the node.

20 S-MAC or Sensor-MAC Medium Access Control with Coordinated, Adaptive Sleeping for Wireless Sensor Networks [YHE03]

21 S-MAC: Periodic Listen & Sleep Frame Frame schedule Nodes are free to choose their listen/sleep schedule Requirement: neighboring nodes synchronize together Exchange schedules periodically (SYNC packet) Synchronization period (SP) Nodes communicate in receivers scheduled listen times Listen Sleep CABD

22 Periodic Listen and Sleep Schedules can differ Prefer neighboring nodes have same schedule — easy broadcast & low control overhead Border nodes: two schedules broadcast twice Node 1 Node 2 sleep listen sleep listen sleep Schedule 2 Schedule 1

23 S-MAC: Coordinated Sleeping (1) Frame Schedule Maintenance 1. Choosing a schedule Listen to the medium for at least SP Nothing heard, choose a schedule Broadcast a SYNC packet (should contend for medium) 2. Following a schedule Receives a schedule before choosing/announcing Follows the schedule Re-broadcast a SYNC packet 3. Adopting multiple schedules Receives a schedule after choosing/announcing Follow both the schedules – suffer more energy loss A node only re-broadcast SYNC for the first schedule heard

24 S-MAC: Coordinated Sleeping (2) Neighbor Discovery chance of failing to discover an existing neighbor corrupted SYNC packet, collisions, interference New sensor in the border of two schedules discover only the first schedule, if schedules do not overlap Periodically, listen for the complete SP frequency?  - if a sensor has no neighbors S-MAC experimental values: SP = 10 seconds Neighbor discovery period = 2 minutes, if at least 1 nbr

25 S-MAC: Coordinated Sleeping (3) Maintaining Synchronization Clock drifts – not a major concern (listen time = 0.5s, which is 10 5 times longer than typical drift rates) Need to mitigate long term drifts – schedule updating using SYNC packet (sender ID, its next scheduled sleep time – relative); Listen is split into 2 parts – for SYNC and RTS/CTS Once RTS/CTS is established, data sent in sleep interval Receiver Listen Sleep for SYNCfor RTSfor CTS

26 S-MAC: Coordinated Sleeping (4) Adaptive Listening – Low-duty cycle to active mode * Overhearing nodes – wakeup at the end of the current transmission (duration field in RTS/CTS) Listen R Listen ON RTS Sender Receiver CTS Overhearing nodes (ON) DATA ACK Sleep (based on RTS) Sleep (based on CTS) Wakes up even though it is not the correct listen- interval

27 S-MAC Summary Latency and throughput are problems, but adaptive listening improves it significantly Energy saving is significant compared to “ non- sleeping ” protocols

28 S-MAC Information URL: Released S-MAC source code (for TinyOS 0.6.1) Currently porting to nesC environment (TinyOS 1.0)

29 T-MAC or Timeout-MAC An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks [vL03]

30 Drawbacks of S-MAC Active (Listen) interval – long enough to handle the highest expected load If message rate is lower – energy is still wasted in idle-listening S-MAC fixed duty cycle – is NOT OPTIMAL

31 T-MAC: Preliminaries Adaptive duty cycle: A node is in sleep mode if no activation event occurs for time TA Active Sleep TA

32 T-MAC: Choosing TA Requirement: a node should not sleep while its neighbors are communicating, potential next receiver TA > C+R+T C – contention interval length R – RTS packet length T – turn-around time (a short time between the end of the RTS packet and the beginning of the CTS packet) TA = 1.5 * (C+R+T);

33 T-MAC: Asymmetric Communication (1) Early-Sleeping Problem – in convergecast (A to D) C – may lose medium to B (RTS) or A (B ’ s CTS) C loses to B; D will hear CTS from C; C loses to A; D will hear nothing, since C is silent; A B C D contend RTSCTSDATAACK RTS? activesleep TA

34 T-MAC: Asymmetric Communication (2) Future RTS (FRTS) Let others know that it cannot access the medium; C – sends FRTS – has duration field; receiver of FRTS – schedule timer; FRTS might affect data; so, DATA postponed until FRTS is over; Prevent others from taking medium, send dummy DS packet; A B C D contend RTSCTSDATAACK RTS active TA DS FRTS active TA = C+R+T+CTS_length

35 T-MAC: Asymmetric Communication (3) Full-Buffer Priority – suitable for unidirectional flows Buffer – almost full – prefer sending than receiving Receive RTS, send its own RTS back instead of CTS Higher chance of transmitting its own message, lesser probability of early- sleeping, limited form of flow control A B C D contend RTS CTSDATAACK active TA RTS contend

36 S-MAC and T-MAC

37 U-MAC Similar to S-MAC Calculate utilization (U) U = (T tx + T rx ) / (T tx + T rx +T idle ) Duty cycle adjustment If U> high traffic threshold  duty cycle increase If U> low traffic threshold  duty cycle decrease Drawbacks High contention Preliminary parameter setting (un-adaptable) Rule of thumb The experience or knowledge of the experiments

38 ADCA- Initial phase Decide its start time of its sleep/wake schedule Broadcast its schedule to the neighbors The initial period last for a certain time to collect neighbors’ schedules

39 ADCA- Adjusting phase The cycle length of all the nodes is the same The schedule of ADCA is adjustable Contention period SYN period Extended period Sleeping period

40 The schedule of ADCA

41 ADCA Listen to the channel for the incoming packets at the contention period Broadcast the SYN packet at the SYN period The extended period prolongs the active time immediately Tune into sleeping period to save energy

42 The adjustment of ADCA The extended period adjustment The next contention period adjustment

43 The radio status Bad situation Success reception but destining to other nodes Failed reception Channel unstable

44 The adjustment of ADCA The extended period compensates for the bad receiving situations The next contention period accommodates to the variable traffics Time records T i : idle listen T b : channel busy N oh : number of overheard packets

45 The length of the extended period T bad = time of collision + channel unstable

46 The length of the next contention period CCP is the length of the current contention period  : negative value (idle time) Decrease the length  : positive value (busy time) Increase the length

47 Simulation environments NS-2 simulator Two scenarios All-to-one and end-to-end (n-to-n) Packet size Data packet: 50 bytes Control packet: 10 bytes Deploy 20, 30 and 40 nodes in 100 x 100 m 2 area (average node degree is 4, 6 and 8) Traffic (CBR) 1, 10, 20, 30, 40, 50 and 60 packets per second Energy consumption Tx:Rx:Idle:Sleep = 52.5: 59.1: 59.1: (mW) =17.4: 19.7: 19.7: (mA)

48 Energy consumption (all-to- one)

49 Energy consumption (n-to-n)

50 Transmission delay (all-to-one)

51 Transmission delay (n-to-n)

52 Goodput (all-to-one)

53 Goodput (n-to-n)

54 Implementation an indoor wireless sensor network testbed which consists of a number of Octopus II sensor nodes Each Octopus II sensor node is equipped with a MSP430 microcontroller and a CC2420 radio module, which operates at 2.4 GHz and transmits at 250 Kbps.

55 Implementation And each node is also attached to a USB interface that provides both power supply and a backchannel for programming and data collection.

56 Implementation

57

58 The average energy consumption for the all-to-one scenario

59 The average energy consumption for the end-to-end scenario

60 The average transmission delay for the all-to-one scenario

61 The average transmission delay for the end-to-end scenario

62 The average packet transmission success rate for the all-to-one scenario

63 The average packet transmission success rate for the end-to-end scenario

64 Conclusion Asynchronous Duty Cycle Adjustment MAC protocol Two adjustments are presented to compensate for bad situation and to adapt to the current traffic The asynchronous scheme separates the competitors into different transmission period which reduce the affection of collision and overhearing Improve utilization, lower energy consumption, lower transmission delay and increase success rate


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