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Sensor Network II

Sensor Network II. 2002. 3. 26 Lee, chunseung Codesign And Parallel processing laboratory, School of Computer Science and Engineering, SNU cslee@iris.snu.ac.kr http://peace.snu.ac.kr Tel. 880-7292. Outline. What is the “ sensor networks ” ? Application of sensor network

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Sensor Network II

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  1. Sensor Network II 2002. 3. 26 Lee, chunseung Codesign And Parallel processing laboratory, School of Computer Science and Engineering, SNU cslee@iris.snu.ac.kr http://peace.snu.ac.kr Tel. 880-7292

  2. Outline • What is the “sensor networks” ? • Application of sensor network • Characteristic of sensor network • Issues for sensor network • Transmission Control Scheme • Listening mechanism • Backoff mechanism • Contention Based mechanism • Rate Control mechanism • CSMA schemes • Simulation and Empirical results

  3. Outline • Biomedical Sensor • Introduction • Biomedical application • Preliminary results • Two dimensional analysis • Three dimensional analysis • Wireless Communication Protocol • Cluster based approach • Tree based approach • Performance Comparison • Conclusion • Side dishes • Low power technology in system level • Referances

  4. What is the “Sensor Networks” • Ad hoc network of sensors • data event traffic • Emerging area of mobile computing • Primary Function • Sensory information • temperature, humidity • Propagate this data block into the infrastructure

  5. Application of SN • Internet Security Systems’s • RealSecure, Solaris, WindowsNT • 보안 침입 탐지 • EUCOM(미유럽사령부, European Command) • 합동 원격 생물학 조기 경보 체계 • JBREWS(Joint Biological Remote Early Warning System) • JBPDS(Joint Biological Point Detection System) • 공군기지, 항구, 배, 해외 주둔군에 배치 • 개인사병, 헬기, 소형 무인 정찰 비행기 • 부대에서 개인의 보호 수준을 결정하기 위한 첩보 및 기상자료를 송출 • 3kg, 100km

  6. Application of SN • Virtual Keyboard • Each fingernail has a sensor for finger-moving • Or using Sensing board

  7. Application of SN • Monitor pollutions

  8. Application of SN

  9. Application of SN Odyssey is a low-cost AUV specifically developed by the MIT AUV – Autonomous Underwater Vehicles

  10. Application of SN

  11. A Transmission Control Scheme for Media Access in Sensor Networks

  12. Characteristics of SN • A. Woo, D. E. Culler, “A Transmission Control Scheme for Media Access in Sensor Networks”, In MOBICOM, July, 2001 • Unusual application requirements • highly constrained resources • Small packet size • typically 10 bytes or below • Deep ad hoc multihop dynamic topology • A correlated operating • Short periods the traffic may be very intense • Periodic rendezvous

  13. Issues for SN in this paper • Motivation • The design space is different from traditional mobile computer networks • SN needs tight constraints • computational power • Storage • Energy resource • Radio technology • Targets • High channel utilization • Communication efficiency on energy • Fair bandwidth allocation • Propose an adaptive rate control(ARC) mechanism

  14. Listening mechanism • Ethernet environment • CSMA/CD • Very effective and simple • Collision detection is not possible in wireless network without additional circuitry • The radio must be on to listen during backoff • More energy consuming • To conserve energy, it have to shorten the length of carrier sensing • IEEE 802.11  radio off

  15. Backoff Mechanism • A widely used in media access control to reduce contention • Binary backoff algorithm • To restrain a node from accessing the channel

  16. Contention Based Mechanism • Widely used in many MAC protocols • RTS-CTS-ACKs • RTS (Request To Send) • CTS (Clear To Send) • For sensor networks where packet size is small, they can constitute a large overhead • RTS-CTS-ACKs handshaking • Up to 40% • A contention control scheme for sensor networks should use a minimum number of control packets

  17. Contention Based Mechanism • RTS – CTS handshaking • First send a RTS packet to it parent and waits for a CTS reply • If no CTS is received for a timeout period (2 CTS packet time), the node will enter backoff with a binary exponential increasing backoff window • If no CTS has been received after five retries, the transmission will be dropped • If a node hears a CTS before any of its own transmission, it will defer transmission for one packet time to avoid corrupting the traffic.

  18. Rate Control Mechanism • The tension between originating traffic and route-thru traffic has a direct impact in achieving fairness goal. • This paper propose an mechanism which adapts the rate of transmission without the use of any MAC control packets • Fairness channel allocation • Channel Capacity / N , where N is total number of node in the entire network • The spontaneous ad hoc of sensor networks make impractical • Proposed transmission rate control mechanism • Linear increase • Multiplicative decrease

  19. Rate Control Mechanism • S : application transmission rate • S*p : the actual rate of originating data. p [0, 1] • p : probability of transmission • : a constant • : multiplicative decrease a factor where 0 < < 1 • route = 1.5 * originate • originate = route / (n + 1) controls the penalty given a failure of transmission S : current rate if(S is acceptance) { p = p + ; S = S * p; } else { p = p * ; S = S * p; }

  20. CSMA schemes

  21. Simulation Setting • Packet size • 30 byte • Manchester encoding • Channel capacity • 10 kbps, 20.8 packet/sec • 16bit CRC error detection for corrupted packet • 각 노드는 근소한 시작시간을 가지고 주기적으로 초당 5 packet을 보냄 • 채널용량이 20.8packet/s이므로 traffic load는 4번째 노드이상에서 채널용량을 초과할 것이다.(saturation)

  22. Constraint - high channel Utilization(bandwidth) - energy efficiency - fairness Utilization and Bandwidth of Channel

  23. 실험 결과 명시적인 ACK을 사용하는 802.11 보다 더 좋은 성능을 나타냈다. 특히, constant listen period와 no random delay를 갖는 3개의 스킴은 가장 높은 bandwidth를 나타냄. 하지만 그들은 모두 robust하지 않다. (원인 : 2개의 dip  repeated collision) 또 결과들을 살펴보면, 802.11을 제외한 모든 스킴들은 채널용량의 75%정도(15.6 packet/s의 bandwidth)의 이용률을 보였다. 20.8*0.75 = 15.6 packet/s 결론적으로, 성능면에서는 no random delay와 constant listen이 좋긴 하지만 robust하지 않기 때문에 매력이 없다. Randomness를 사용하는 backoff 메커니즘은 repeated collision을 방지하는데 효과가 좋다.

  24. 실험 결과 • 모든 노드가 동시 전송(최악의 경우) • no random delay와 constant listening window를 가지는 3개의 스킴은 zero bandwidth가 나왔다. (repeated collision) • 802.11은 초기에 5 packet/s로 시작하였고, 그림 4보다 낮은 throughput을 보였다. • 802.11이 no random delay와 constant listening 주기를 가지고 있을지라도 ACK가 collision 감지와 backoff 메커니즘을 트리거하기 때문이다. • 나머지 커브들은 random delay를 가지거나 random listening 주기를 가지는 스킴들이다. • 결론, • 1 . Randomness를 갖는 알고리즘들은 좋은 채널이용률과 high load를 잘 견뎌낸다. • Performance는 backoff 메커니즘에 영향을 받지 않는다. • Backoff 메커니즘을 가지지 않는 ND_RAND 조차도 다른 6개의 스킴들 만큼이나 잘 동작한다. • Pre-collision 단계안에서의 randomness는 robustness를 위해 필수적이다.

  25. Constraint - high channel Utilization(bandwidth) - energy efficiency - fairness Energy Efficiency

  26. Simulation Setting • In examining the energy consumed in communication • Transmitting and receiving packet • During listening period • The former is determined primarily by the traffic load and the latter is primarily determined by the CSMA protocol

  27. 실험 결과 802.11이 가장 안 좋은 효율을 보임 이유는, constant listening 주기를 가지고 있을지라도, backoff동안 채널을 항상 listening하고 있어야 되기 때문이다. constant listening 주기를 가지는 scheme들이 좋고, 10 uJ/packet으로 네트워크의 크기에 관계없다. random listening 주기를 가지는 스킴들은 40 uJ/packet으로 다소 비싸다. 특이한 점은 ND_RAND는 네트워크의 크기가 증가할 수록 에너지가 증가한 이유는, backoff가 없기 때문이다. 대부분 에너지 효율적인 스킴들은 constant listening 주기와 random delay이고, robustness를 제공한다.

  28. Constraint - high channel Utilization(bandwidth) - energy efficiency - fairness Fairness

  29. 실험 결과 앞 bandwidth와 energy 효율성 측면에서 모두 좋은 random delay, constant listening 주기를 갖는 3개의 스킴을 비교해 보자. 그림 7 위의 3 스킴의 표준편차 : 0.25 packet/s 이고, 트래픽이 증가 할수록 감소하는 경향을 보인다. 결국, backoff 메커니즘의 차이는 uniform한 부하면에서 보면, fairness가 별 중요치 않다. 그림 8 802.11은 unfair하다. 표준편차가 1 packet/s이상이다. 이유는, 다른 것보다 이른 전송시간을 갖는 노드가 채널을 capturing하기 때문이다.(capturing effect)

  30. 실험 결과 표 3. 그림 3에서의 node 0을 multihop으로 구성했을 때 node 10에 대한 bandwidth를 기준으로 표준화시킨 값이다. Send rate를 보면 노드가 10일때, 2 packet/s이고, 노드수가 1일때 10이므로 산술적으로 노드 1,2,3은 노드 10에 비해서 500% 정도가 측정되야 하나 802.11을 제외한 3 scheme들은 500%이상이 측정되었다. Backoff 메커니즘은 proportional fairness에 영향을 준다.

  31. Phase-shift The phase of the sensor sampling interval is shifted by a random amount in response to transmission failure. 실험 결과 Phase-shift를 적용한 802.11 스킴은 bandwidth, fairness 모두 많이 향상되었다.

  32. Empirical Results on singlehop Random delay를 가지는 3개의 스킴 실측하여 시뮬레이션과 비교 실험한 실측치도 채널 용량의 70%까지 상승했다. (performance측면에서)

  33. Figure 12. The average energy consumption - the prediction of around 10uJ/packet ( 10 ~ 40 uJ/packet at simulation) Figure 13. The fairness comparison of throughput - the deviation among the three schemes vary from 0.3 ~ 0.5 packet/s (0.25 packet/s at simulation)

  34. Multihop Scenario Under simulation Maximum uniform origination rate  20/24 = 0.83 packet/s In the implementation, limit origination rate  15.7/24 = 0.66 packet/s

  35. Simulation Measurements • The simulation runs with each node sending packets to the base station at rate of 4 packet/s • Runs at the same time

  36. 그림 15. ARC 스킴이 가장 좋은 성능을 나타냄. 802.11과 RTS/CTS 스킴은 레벨이 2 이하 일 때 전혀 packet을 발생치 않았다.(hidden node 문제) 그림 16. fairness에 대한 편차를 , 값을 변경하면서 측정 ARC가 가장 좋다. 가 편차에 많은 영향을 준다.(?)

  37. 그림 17. 값이 낮을수록 (큰 페널티를 부과) 낮은 bandwidth를 나타낸다. 802.11과 D_CONST_FIX가 더 높은 bandwidth를 제공(단, base station과 근접해 있어야 한다) 그림 18. 값이 낮을수록 에너지 효율성은 증가

  38. Empirical Result on Multihop 그림 20. 비교적 시뮬레이션 결과와 비슷 ARC도 D_CONST_FIX보다 더 fair하다.

  39. Conclusion 결론적으로, randomness를 사용하는 backoff 메커니즘은 repeated collision을 방지하는데 효과가 좋고, 에너지 효율적인 면에서는 constant listening 주기와 random delay이고, robustness를 제공한다. Phase-shift방법을 사용하면 bandwidth와 fairness를 보다 향상 시킬 수 있다. ARC(Adaptive Rate Control) 방법은 명시적인 control packet 없이 fairness를 효과적으로 동작시킬 수 있다.

  40. Research Challenge In Wireless Networks of Biomedical Sensors

  41. Introduction • Constraint • Limited power, computational capacities • Issues • Bio-compatibility • Fault tolerant • Energy efficient, • Scalable design • A smart sensor • Physical, chemical, biological sensors combined with integrated circuits • The examples of smart sensors • Combat scenarios to track troop movements • Mine robots, Pollution detection • Biomedical application • ‘A drop in the bucket’

  42. Biomedical applications • Artificial Retina

  43. Biomedical applications

  44. Biomedical applications • Other applications • Glucose Level Monitors • Organ Monitors • Cancer Detectors • General Health Monitors

  45. Preliminary results • Power-efficient Topology • A function of the distance and number of bits transmitted. • Trade off • The number of neighbors and the total power dissipation • Two Dimensional Analysis • Three dimensional Analysis • Wireless Communication Protocols • Cluster-based Approach • Tree-based Approach • Performance Comparison

  46. Two dimensional analysis • As the number of neighbors increases the number of alternative paths increases. • Interior routing • A route across the diameter of the network • Edge routing • The path travels along the edges of the network

  47. Two dimensional analysis Edge routing dissipates less power than interior routing in all cases except for 3 neighbors

  48. Two dimensional analysis The power dissipated between the source and destination for a message spanning the diameter of the network for networks with 3 and 6 neighbors Increasing the number of neighbors decrease the number of transmissions and the total power dissipated in the system

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