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Transcript of Sensor Network II 2002. 3. 26 Lee, chunseung Codesign And Parallel processing laboratory, School of...
Sensor Network II
2002. 3. 26Lee, chunseung
Codesign And Parallel processing laboratory, School of Computer Science and Engineering, SNU
[email protected]://peace.snu.ac.kr
Tel. 880-7292
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
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
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
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
Application of SN
• Virtual Keyboard– Each fingernail has a sensor for finger-moving– Or using Sensing board
Application of SN
• Monitor pollutions
Application of SN
Application of SN
Odyssey is a low-cost AUV specifically developed by the MIT
AUV – Autonomous Underwater Vehicles
Application of SN
A Transmission Control Scheme for Media Access in
Sensor Networks
Characteristics of SN• A. Woo, D. E. Culler, “A Transmission Control Scheme for Media Access in Senso
r 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
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
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
Backoff Mechanism
• A widely used in media access control to reduce contention– Binary backoff algorithm
• To restrain a node from accessing the channel
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
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 tim
e), 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.
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
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;
}
CSMA schemes
• 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 packet 을 보냄• 채널용량이 20.8packet/s 이므로 traffic load 는 4 번째 노드이상에서
채널용량을 초과할 것이다 .(saturation)
Simulation Setting
Utilization and Bandwidth of Channel
Constraint
- high channel Utilization(bandwidth)
- energy efficiency
- fairness
실험 결과
명시적인 ACK 을 사용하는 802.11 보다 더 좋은 성능을 나타냈다 .
특히 , constant listen period 와 no random delay 를 갖는 3 개의 스킴은 가장 높은 bandwidth 를 나타냄 .
하지만 그들은 모두 robust 하지 않다 .
( 원인 : 2 개의 dip repeated collision)
또 결과들을 살펴보면 , 802.11 을 제외한 모든 스킴들은 채널용량의 75% 정도 (15.6 packet/s 의 bandwidth) 의 이용률을 보였다 .
20.8*0.75 = 15.6 packet/s
결론적으로 , 성능면에서는 no random delay 와 constant listen 이 좋긴 하지만 robust 하지 않기 때문에 매력이 없다 .
Randomness 를 사용하는 backoff 메커니즘은 repeated collision 을 방지하는데 효과가 좋다 .
실험 결과- 모든 노드가 동시 전송 ( 최악의 경우 )
no random delay 와 constant listening window 를 가지는 3 개의 스킴은 zero bandwidth 가 나왔다 . (repeated collision)
802.11 은 초기에 5 packet/s 로 시작하였고 , 그림 4 보다 낮은 throughput을 보였다 .
802.11 이 no random delay 와 constant listening 주기를 가지고 있을지라도 ACK 가 collision 감지와 backoff 메커니즘을 트리거하기 때문이다 .
나머지 커브들은 random delay 를 가지거나 random listening 주기를 가지는 스킴들이다 .결론 ,
1 . Randomness 를 갖는 알고리즘들은 좋은 채널이용률과 high load 를 잘 견뎌낸다 .
2. Performance 는 backoff 메커니즘에 영향을 받지 않는다 .
3. Backoff 메커니즘을 가지지 않는 ND_RAND 조차도 다른 6 개의 스킴들 만큼이나 잘 동작한다 .
4. Pre-collision 단계안에서의 randomness 는 robustness 를 위해 필수적이다 .
Energy Efficiency
Constraint
- high channel Utilization(bandwidth)
- energy efficiency
- fairness
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
대부분 에너지 효율적인 스킴들은 constant listening 주기와 random delay 이고 , robustness 를 제공한다 .
802.11 이 가장 안 좋은 효율을 보임
이유는 , constant listening 주기를 가지고 있을지라도 , backoff 동안 채널을 항상 listening 하고 있어야 되기 때문이다 .
constant listening 주기를 가지는 scheme들이 좋고 , 10 uJ/packet 으로 네트워크의 크기에 관계없다 .
random listening 주기를 가지는 스킴들은 40 uJ/packet 으로 다소 비싸다 .
특이한 점은 ND_RAND 는 네트워크의 크기가 증가할 수록 에너지가 증가한 이유는 , backoff 가 없기 때문이다 .
실험 결과
Fairness
Constraint
- high channel Utilization(bandwidth)
- energy efficiency
- fairness
앞 bandwidth 와 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 uniform 한 부하면에서 보면 , fairness 가 별 중요치 않다 .
그림 8
802.11 은 unfair 하다 . 표준편차가 1 packet/s 이상이다 .
이유는 , 다른 것보다 이른 전송시간을 갖는 노드가 채널을 capturing 하기 때문이다 .(capturing effect)
실험 결과
표 3.
그림 3 에서의 node 0 을 multihop으로 구성했을 때 node 10 에 대한 bandwidth 를 기준으로 표준화시킨 값이다 .
Send rate 를 보면 노드가 10일때 , 2 packet/s 이고 , 노드수가 1일때 10이므로 산술적으로 노드 1,2,3 은 노드 10 에 비해서 500% 정도가 측정되야 하나 802.11 을 제외한 3 scheme 들은 500% 이상이 측정되었다 .
실험 결과
Backoff 메커니즘은 proportional fairness 에 영향을 준다 .
Phase-shift 를 적용한 802.11 스킴은 bandwidth, fairness 모두 많이 향상되었다 .
Phase-shift
The phase of the sensor sampling interval is shifted by a random amount in response to transmission failure.
실험 결과
Empirical Results on singlehopRandom delay 를 가지는 3 개의 스킴 실측하여 시뮬레이션과 비교
실험한 실측치도 채널 용량의 70% 까지 상승했다 . (performance 측면에서 )
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)
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
• The simulation runs with each node sending packets to the base station at rate of 4 packet/s
• Runs at the same time
Simulation Measurements
그림 15.
ARC 스킴이 가장 좋은 성능을 나타냄 .
802.11 과 RTS/CTS 스킴은 레벨이 2 이하 일 때 전혀 packet 을 발생치 않았다 .(hidden node 문제 )
그림 16.
fairness 에 대한 편차를 , 값을 변경하면서 측정
ARC 가 가장 좋다 .
가 편차에 많은 영향을 준다 .(?)
그림 17.
값이 낮을수록 ( 큰 페널티를 부과 ) 낮은 bandwidth 를 나타낸다 .
802.11 과 D_CONST_FIX 가 더 높은 bandwidth 를 제공 ( 단 , base station 과 근접해 있어야 한다 )
그림 18.
값이 낮을수록 에너지 효율성은 증가
Empirical Result on Multihop
그림 20.
비교적 시뮬레이션 결과와 비슷
ARC 도 D_CONST_FIX보다 더 fair 하다 .
Conclusion
결론적으로 , randomness 를 사용하는 backoff 메커니즘은 repeated collision 을 방지하는데 효과가 좋고 ,
에너지 효율적인 면에서는 constant listening 주기와 random delay 이고 , robustness 를 제공한다 .
Phase-shift 방법을 사용하면 bandwidth 와 fairness 를 보다 향상 시킬 수 있다 .
ARC(Adaptive Rate Control) 방법은 명시적인 control packet 없이 fairness 를 효과적으로 동작시킬 수 있다 .
Research Challenge In Wireless Networks of Biomedical Sensors
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’
Biomedical applications
• Artificial Retina
Biomedical applications
Biomedical applications
• Other applications– Glucose Level Monitors– Organ Monitors– Cancer Detectors– General Health Monitors
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
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
Two dimensional analysis
Edge routing dissipates less power than interior routing in all cases except for 3 neighbors
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
Three dimensional analysis
1. 3D 네트워크의 경우 edge routing 이 interior routing 보다 power 를 적게 소비한다 .
2. 3D 네트워크에서 interior, edge routing 둘 모두 2D 네트워크보다 전송수 , 수신수 , 총 power 소비량이 더 작다 .
1. Neighbor 가 적은 네트워크에서 power 를 적게 소비
2. Neighbor 가 많은 토폴로지라도 적은 홉수가 필요하다 .(같은 neighbor수라도 홉수가 적은 것이 power 소비가 적다 .
Wireless Communication Protocol
• Two communication protocols that were designed to reduce energy consumption
• Using a bi-directional transceiver• The placement of node is predetermined and fixed• All communication is wireless• TDMA is used for media access
– Nodes can sleep when they are not sending/receiving data– Less power usage and extended battery life
• All nodes are perfectly synchronized and are aware of the beginning of each slot
• The communications pattern is deterministic and periodic
• Each node has to transmit its data once in 250ms
Cluster-based approach
• Stipulating• Only a small fraction of the nodes are allowed to
communicate with the base station– These nodes are called leaders – Each leader collects data from nodes in its cluster,
compressing data and transits the data to the base station
• Two major advantages– Only relevant data is transmitted to the external processor– Only a small subset of the nodes make a long distance
transmission and hence energy is conserved
Cluster-based approach
• There are several issues– Which nodes should be leaders?
• Base station– Which cluster to join?
• The best signal-to-noise ratio• Using a TDMA scheme for collision
Tree-based approach
• To make a spanning tree– The base station selects one or more nodes to be its children
based on proximity and node density– These selected nodes then make a low intensity transmission,
each at a different frequency– If nodes that receive this transmission at a predefined minimum
signal-to-noise ratio can then request the transmitting node to be its parents using the subscribing protocols
– This continues until all nodes in the system the covered
• Data transmission– When a node wants to send data, it will send it to its parent node
by a low-energy transmission– The parent will collect data from all its children, compress the data
if required, and it turn transmit to the base station
Performance Comparison
- Two dimensional array of nodes with the base station
- The distance of the base station from the center of the arraywas assumed to be twice tat of the inter-node distance
- The variation of power consumption with respect to distance between nodes as well as the number of nodes in the network
Performance Comparison
Cluster based approach shows better results
Conclusion
• Smart sensor offer the promise of significant advances in medical– Artificial Retina– Glucose Level Monitors, Organ Monitors, Cancer Detectors
• Total power consumption is reduced for topologies with fewer neighbors
• Cluster based approach shows better energy-efficiency on distance between nodes and number of nodes than tree based one’s
Conclusion on SNII
• Existing communication protocols are not necessarily sufficient for the sensor network– Due to many different constraints and requirements– New network topology or application requires a new
regime
• Especially, power management will be more significantly
Side dishes
• Low power technology in system level– DPM(Dynamic Power Management)
• idle 상태에서 device 의 전압을 낮춘다 .• 최근 device 의 사용 history 에 근거하여 다음 idle 주기를 예측하는 것이 중요
• DLPM(Device level power management) : old approach• TBMP(Task Based Power Management) : new approach
– DVS(Dynamic Voltage Scaling)• 전압 스케쥴러 (voltage scheduler) 가 시간 제약 조건을
만족하는 범위에서 프로세서의 동작 전압을 조절하여 최소한의 에너지를 소모하도록 하는 방식 (voltage scalable processor)
• PDA 부류의 디바이스에 장착
• MAC Schemes– A. Woo, D. E. Culler, “A Transmission Control Scheme for Media Access in Sensor Netw
orks”, In MOBICOM, July, 2001
• Biomedical Sensors– L. schwiebert, S. K. S. Gupta, J. Weinmann, “Research Challenges in Wireless Networks
of Biomedical Sensors", In MOBICOM,
• Cooperative Sensing Networks– J. Agre, L. Clare, “An Integrated Architecture for Cooperative Sensing Network”, Rockwell
Science Center, May, 2000, COMPUTER, IEEE/ACM p106~p108
• Distributed Surveillance Sensor Network– http://www.spawar.navy.mil/robots/undersea/dssn/dssn.html
References
References
• Low power– DPM
• M. B. Srivastava, A. P. Chandrakasan, R. W. Brodersen, “Predictive System Shutdown and Other Architectural Techniques for Energy Efficient Programmable Computation”, IEEE Transaction on VLSI System, Vol. 4, No1, Mar. 1996
• Y. H. Lu, E. Y. Chung, T. Simunic, L. Benini, G. De Micheli, “Quantitative Comparison of Power Management Algorithms”, Proc. Of Design Automation and Test in Europe, pp. 20~26, 2000
– DVS• T. Pering, T. Burd, R. Brodersen, “The Simulation and Evaluation of Dynamic Voltag
e Scaling Algorithms”, Proc. Of International Symposium on Low Power Electronics and Design, Aug. 1998
• T. Burd, R. Brodersen, “Design Issues for Dynamic Voltage Scaling”, Proc. Of International Symposium on Low Power Electronics and Design, Jul, 2000