1. A Glimpse at Three Wireless Networking Problems Bob Kinicki Bob Kinicki Computer Science Department Computer Science Department rek@cs.wpi.edu rek@cs.wpi.edu Colloquium October 5, 2007 Colloquium October 5, 2007

2. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 2 OutlineOutline  Thoughts and Mini-Motivation  Wireless Networking Primer  #1 Dynamic Rate Adaptation –Performance problems with ARF –Rate Adaptation Algorithms RBAR, CARA, RFT and CARAF  Wireless Sensor Networks (WSNs)  #2 Dynamic Cluster Formation  #3 Power-Aware MAC Protocols –SMAC, TMAC, WiseMAC, SCP-MAC and Crankshaft Crankshaft

3. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 3 My Research Space Networking Wireless Networking WirelessSensorNetworks 19832003 2006 2006

4. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 4 The Future of Sensor Networks?

5. Wireless Primer

6. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 6 LAN Terminolgy 802.3:: Ethernet CSMA/CD Ethernet CSMA/CD802.11a/b/g:: WiFi CSMA/CA 802.15.4:: ZigBee802.11-based lower data rates, lower power Bluetooth::TDMA - wireless Personal Area Networks (PANs) that provide secure, globally unlicensed short-range radio communication. - wireless Personal Area Networks (PANs) that provide secure, globally unlicensed short-range radio communication. –Clusters with max of 8: cluster head + 7 nodes WSNs

7. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 7 Wireless LANS  Infrastructure with AP (Access Point)  Mobile Ad Hoc Networks (MANETs)  Wireless Sensor Networks (WSNs)  Interacting AP Topologies

8. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 8 InfrastructureInfrastructure Access Point client Internet

9. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 9 Mobile Ad Hoc Network (MANET) BS Wireless Sensor Network (WSN)

10. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 10 Wireless LAN Protocols (a) A sending an RTS to B. (b) B responding with a CTS to A. Tanenbaum slide node D is possible hidden terminal

11. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 11 Virtual Channel Sensing in CSMA/CA  C (in range of A) receives the RTS and based on information in RTS creates a virtual channel busy NAV(Network Allocation Vector).  D (in range of B) receives the CTS and creates a shorter NAV. Tanenbaum slide

12. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 12 Basic CSMA/CA [N. Kim] possible collision !! collision !!

13. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 13 One-to-One Configuration {Ad Hoc} Access Point client

14. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 14 One-to-One Configuration {Ad Hoc} Access Point client

15. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 15 One-to-One Configuration {Ad Hoc} Access Point client Distance Impacts: attenuation fading interference

16. #1 Dynamic Rate Adaptation

17. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 17 802.11 Physical Layer [N. Kim] ‘Adjust transmission rate on the fly’

18. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 18 BER vs SNR [Pavon]

19. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 19 Throughput vs SNR [Pavon]

20. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 20 Rate Adaptation versus Distance [J. Kim]

21. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 21 Single AP multiple clients (homogeneous) Access Point client Node Contention: Produces collisions

22. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 22 Node Contention [N. Kim] without RTS/CTS

23. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 23 Single AP multiple clients (heterogeneous) Access Point client Multiple Node Effects Collisions AP queue overflow link capture hidden terminal performance anomaly different NIC cards (Rate Adaptation NOT Standardized!!)

24. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 24 UnfairnessUnfairness [Choi]

25. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 25 Multiple APs multiple clients (heterogeneous) Access Point client Access Point client

26. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 26 Hidden Terminals [Wong] Without a hidden terminal, loss ratio ~5.5%. One hidden AP with mild sending rate (0.379 Mbps) yields:

27. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 27 RTS/CTS Summary  RTS/CTS can reduce collisions.  RTS/CTS can guard against and reduce hidden terminals.  RTS/CTS adds overhead that reduces throughput.  Normally, RTS/CTS is turned off!

28. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 28 Rate Adaptation Algorithms AARF ARFAMRR CARACROARDOFRA Fast-LAHRCLA LD-ARFMiSer MultiRateRetry MPDUOARONOE PERRBARRFT RRAASampleRate SwissRA

29. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 29 Rate Adaptation Algorithms 1997 ARF 199819992000 2001 RBAR 2002 MPDU OAR PER 2003 LA MiSer SwissRA 2004 AARF AMRR HRC MultiRateRetry 2005 Fast-LA LD-ARF RFT SampleRate 2006 CARA CROAR DOFRA RRAA 2007

30. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 30 Rate Adaptation Algorithms Uses recent history and probes: ARF, AARF, SampleRate Long interval smoothing: ONOE, SampleRate Multiple rates: MultiRateRetry, AMRR, RRAA Uses RTS/CTS: RBAR, OAR, CROAR, CARA Uses RSSI to approximate SNR, each node maintains 12 dynamic RSS thresholds: LA Puts checksum on header and use NACK to signal link loss error: LD-ARF Table lookup with thresholds: HRC,MPDU(len,rSNR,count) Fragmentation: DOFRA, RFT Miscellaneous: PER, MiSer, SwissRA, Fast-LA

31. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 31 Auto Rate Fallback (ARF)  If two consecutive ACK frames are not received correctly, the second retry and subsequent transmissions are done at a lower rate and a timer is started.  When the number of successfully received ACKs reaches 10 or the timer goes off, a probe frame is sent at the next higher rate. However, if an ACK is NOT received for this frame, the rate is lowered back and the timer is restarted.

32. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 32 ARF and AARF

33. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 33 Receiver Based Auto Rate (RBAR)  Receivers control sender’s transmission rate.  RTS and CTS are modified to contain info on size and rate {not 802.11 compatible}.  Uses analysis of RTS reception (RSSI) to estimate SNR and send choice back to sender in CTS.  Receiver picks rate based on apriori SNR thresholds in a lookup table.

34. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 34 Collision Aware Rate Adaptation (CARA) CARA uses two methods for identifying collisions: –RTS probing –Clear Channel Assessment (CCA) detection RTS Probing {Idea: Assume all RTS/CTS transmission failures after a successful RTS/CTS exchange must be due to channel errors. (Note – this assumes hidden terminals are not possible) }

35. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 35 RTS Probing CARA-1 CARA-1  Data frame transmitted without RTS/CTS.  If the transmission fails, RTS/CTS exchange is activated for the next retransmission. If this retransmission fails {assume channel quality problem}, then the rate is lowered.  If retransmission with RTS/CTS is successful {assume collision occurred}, stay at same rate and send next frame without RTS/CTS.

36. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 36 Clear Channel Assessment (CCA) [J. Kim] ACK

37. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 37 CCA Option  Case 2: It is a collision. –Transmit without increasing failure count and lowering the transmission rate. No RTS/CTS probe is needed.  Case 1 and Case 3: –Initiate RTS/CTS probe scheme.

38. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 38 CARA-1 (with RTS Probing) [J. Kim]

39. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 39 CARA-2 (with CCA) [J. Kim]

40. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 40 802.11 MAC Fragmentation [Zhu]

41. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 41 Rate-based Fragmentation Thresholding (RFT)  Fragmenting a frame can increase the probability of the fragment being received successfully.  Propose a dynamic fragmentation scheme with different fragmentation thresholds based on different channel conditions.  Namely, fragment sizes vary with the chosen adaptation rate.

42. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 42 CARAF (CARA with Fragmentation) Dan Courcey’s MS thesis: Combine CARA with Fragmentation. Top Level Scheme:  Upon CCA determination of collision, use fragmentation.  If CCA shows idle, initiate RTS/CTS probe.  If probe fails lower transmission rate. {Investigate how to vary fragment size to maximize throughput and increase the likelihood of CCA case 2}

43. Wireless Sensor Networks (WSNs)

44. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 44 Wireless Sensor Networks  A distributed connection of nodes that coordinate to perform a common task.  In many applications, the nodes are battery powered and it is often very difficult to recharge or change the batteries.  Prolonging network lifetime is a critical issue.  Sensors often have long period between transmissions (e.g., in seconds).  Thus, a good WSN MAC protocol needs to be energy efficient.

45. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 45 Wireless Sensor Networks  Another attribute is scalability to change in network size, node density and topology. –In general, nodes can die, join later or be mobile.  Often high bandwidth is not important.  Nodes can take advantage of short- range, mulit-hop communication to conserve energy.

46. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 46 Wireless Sensor Networks  Sources of energy waste: –Idle listening, collisions, overhearing and control overhead. –Idle listening dominates (measurements show idle listening consumes between 50- 100% of the energy required for receiving.) Idle listening:: listen to receive possible traffic that is not sent.

47. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 47 Power Measurements

48. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 48 Wireless Sensor Networks  Duty cycle:: ratio between listen time and the full listen-sleep cycle. central approach – lower the duty cycle by turning the radio off part of the time. central approach – lower the duty cycle by turning the radio off part of the time. Three techniques to reduce the duty cycle: Three techniques to reduce the duty cycle: TDMATDMA Schedule contention periodsSchedule contention periods LPL (Low Power Listening)LPL (Low Power Listening)

49. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 49 Techniques to Reduce Idle Listening  TDMA requires cluster-based or centralized control.  Scheduling – ensures short listen period when transmitters and listeners can rendezvous and other periods where nodes sleep (turn off their radios).  LPL – nodes wake up briefly to check for channel activity without receiving data. –If channel is idle, node goes back to sleep. –If channel is busy, node stays awake to receive data. –A long preamble (longer than poll period) is used to assure than preamble intersects with polls.

50. #2 Dynamic Cluster Formation

51. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 51 Choosing Cluster Heads/ Forming Clusters Two-tier scheme:  A fixed number of cluster heads that communicate with BS (base station).  Nodes in cluster communicate with head (normally TDMA).  TDMA allows fixed schedule of slots for sensor to send to cluster head and receive head transmissions. sensor to send to cluster head and receive head transmissions. BS

52. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 52 BS Choosing Cluster Heads/ Forming Clusters  Periodically select new cluster heads to minimize power consumption and maximize WSN lifetime.  More complex problem when size of cluster changes dynamically.  As time goes by, some sensor nodes die!  Not worried about coverage issues! X X X X X

53. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 53 Dynamic Cluster Formation  TDMA cluster algorithms: –LEACH, Bluetooth, …  Rick Skowyra’s MS thesis: ‘Energy Efficient Dynamic Reclustering Strategy for WSNs’ ‘Energy Efficient Dynamic Reclustering Strategy for WSNs’ –‘Leach-like’ with a fitness function and periodic reclustering. –He hopes to design a distributed genetic algorithm to speed the recluster time.

54. #3 Power-Aware MAC Protocols

55. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 55 Tiered WSN Architectures [ Stathopoulos]

56. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 56 Power Aware MAC Protocols 1997 1998 PAMAS 19992000 2001 SMAC 2002 LPL NPSM 2003 TMAC TRAMA TinyOS-MAC EMACs 2004 BMAC DMAC LMAC WiseMAC 2005 PMAC ZMAC SP 2006 SCP-MAC 2007 Crankshaft

57. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 57 Power Aware MAC Protocols Three approaches to saving power: 1. TDMA: TRAMA, EMACs, LMAC Crankshaft Crankshaft 2. Schedule: PAMAS, SMAC, TMAC, DMAC, PMAC, SCP-MAC 3. Low Power Listening: LPL, BMAC, WiseMAC Cross-Layering: SP, BSD

58. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 58 SMACSMAC  All nodes periodically listen, sleep and wakeup. Nodes listen and send during the active period and turn off their radios during the sleep period.  The beginning of the active period is a SYNC period used to accomplish periodic synchronization and remedy clock drift.  Following the SYNC period, data may be transferred for the remainder of the active period using RTS/CTS for unicast transmissions.  Long frames are fragmented and transmitted as a burst.  SMAC controls the duty cycle to tradeoff energy for delay.  However, as density of WSN grows, SMAC incurs additional overhead in maintaining neighbors’ schedules.

59. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 59 SMACSMAC

60. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 60 TMACTMAC  TMAC employs an adaptive duty cycle by using a very short listening window at the beginning of each active period.  After the SYNC portion of the active period, RTS/CTS is used in listening window. If no activity occurs, the node goes to sleep.  TMAC saves power at the cost of reduced throughput and additional delay.

61. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 61 TMACTMAC

62. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 62 WiseMACWiseMAC  Algorithm focused on downlink protocol for infrastructure WSNs: –Access Point (AP) is assumed to have wired link to Internet and not battery-powered.  Based on preamble sampling.  WiseMac regularly samples (via listening) for a short duration during preamble. –All sensor nodes sample with same constant period T W.

63. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 63 WiseMACWiseMAC  Normally, wake-up preamble needs to be of size T W. –This implies low power use when WSN is idle. –But this yields large power consumption overhead for reception.  WiseMAC AP learns and keeps the sampling schedule of all sensors in a up-to-date table.  Sensors’ ACKs provide info for the table.  WiseMAC then minimizes the preamble duration, T P.  Needs to deal with clock drift to get this right.

64. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 64 WiseMACWiseMAC

65. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 65 Zigbee MAC  802.11 MAC PSM (Power Save Mode) uses beacon frames to coordinate and periodic wake-up by sensor nodes.  Mike Putnam’s thesis: ‘A Beaconless Protocol for Improving Energy Efficiency in Wireless Sensor Networks’

66. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 66 WiseMACWiseMAC

67. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 67 Scheduled Channel Polling (SCP-MAC)  With channel polling (LPL scheme), receiver efficiency is gained through cost to sender.  LPLs are very sensitive to tuning for neighborhood size and traffic rate.  By synchronizing channel polling times of all neighbors, long preambles are eliminated and ultra-low duty cycles (below the LPL 1-2% limits) are possible.

68. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 68 Scheduled Channel Polling (SCP-MAC)  The issue is knowing my neighbors’ schedule information.  SCP piggybacks schedule info on data packets when possible or a node broadcasts its schedule in a SYNC packet in synch period (as in SMAC)  Knowing schedules  short wakeup tone.  Optimal synchronization reduces overhearing.

69. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 69 SCP-MACSCP-MAC

70. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 70 CrankshaftCrankshaft  Designed specifically for dense WSNs.  Employs channel polling mechanism similar to SCP- MAC.  Employs synchronization, framing and slotting mechanisms similar to TDMA-based LMAC.  Unlike LMAC, Crankshaft schedules receivers rather than senders.  Basic principle: nodes are only awake to receive messages at fixed offsets from the start of a frame.  The hope is to develop modified version of Crankshaft.  I need students interested in exploring this idea!!

71. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 71 CrankshaftCrankshaft

72. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 72 Crankshaft Simulations  Focused on two traffic types that are common in WSNs:  Convergecast – monitoring traffic –All sensor nodes periodically send data to a sink node (either AP or sensor cluster head)  Broadcast floods – packets sent in the other direction to either send routing update or to distribute queries over the WSN.

73. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 73 Energy Conservation Results

74. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 74 LatencyLatency

75. Three Wireless Networking Problems October 5, 2007 Three Wireless Networking Problems 75 Questions?Questions? Thank You! Go Tribe!!!