Upload
dakota-okeefe
View
228
Download
1
Tags:
Embed Size (px)
Citation preview
Component Model
• Component has:– Frame (storage)
– Tasks (computation)
– Command and Event Interface
Messaging Component
Internal StateInternal Tasks
Commands Events
TinyOS Application Component Graph
RFM
Radio byte
Radio Packet
i2c
Tempphoto
Messaging Layer
clocksbit
byte
packet
Routing Layer
sensing applicationapplication
HW
SW
ADC
messaging
routing
Thru-RouteMessage
Application OriginatesMessage
CSMA
• Listening to the channel before transmission• Pozitive or negative acknowledgments to
signal collusion• Lean toward a fundamental assumption that
packet transmissions occur with a stochastic distribution, that is very different the correlated trafic found in sensor networks
• Aim to support many point-to-point flows
IEEE 802.11
• Aims to provide a wireless Ethernet illusion• Design based on assumption of a single cell
scenario, with mobile stations always in range of at least one base station– Hand off when migrating from one cell to another
– No multihop scenario
• Assumes peer-to-peer communications rather than many-to-one data propogation
Bluetooth
• Model of creation a “wireless cable” illusion
• Primary MAC protocal is a centrialized TDMA protocal within piconet– Relatively static ad-hoc network supporting a
small number of nodes within single cell
• No multihop scenario
• Inappropriate for sensor networks
Applicable Mechanisms
• Listening Mechanism
• Back off Mechanism
• Contention Based Mechanism
• Rate Control Mechanism
Self-Organization
• A self-organized network is an independent collection of nodes in which enough information—or the ability to retrieve such information--is present in order to allow transfer of information between any two nodes in the network.
• Either at initialization or after a topology-modifying event
• Level can vary depending on the network considered.
Protocols for Self-Organization of a Wireless Network
• Protocols must be able to enable network operation during:1. start up : nodes are booted up, and network is formed.2. steady state : energy reservoirs are full, can support all the sensing, signal processing and communication. Multihop network is formed in this mode.3. failure : re-organization, MAC and routing algorithms for the formation of new links and routes to the sink nodes.
Multihop Network
• Can operate in both sensor-to-sink and sink-to-sensor.
• Bulk of the traffic will belong to the former.
• Significant strain on the energy resources of the nodes near the sink, that neighborhood will be more susceptible to energy depletion and failure.
Energy Conserving Techniques
• Sensor nodes will do local processing, as opposed to exchanging raw data over air
• Protocols must reduce messaging overhead.
• These two will lead to the requirement of highly localized and distributed algorithms for data processing and networking.
Protocols for Self-Organization of a Wireless Network(cont.)
• SMACS(Self-organizing Medium Access Control for Sensor Networks): for network start up and link layer organization
• EAR(Eavesdrop-And-Register)Algorithm: enables seamless interconnection of mobile nodes in the field of stationary nodes
• SAR(Sequential Assignment Routing): facilitates multihop routing
• SWE(Single Winner Election)- MWE(Multi-Winner Election): handle the necessary signalling and data transfer tasks in local cooperative information proccessing.
Link Layer Issues
Channel Access Classes:• Contention or explicit organization in time/freq. : not
suitable for sensor networks since it requires monitoring channel at all times
• Organized channel access: - determines network radio connectivity to discover radio neighbors of each node- assign collision free channels to links
* centalized channel assignment* distributed assignment
SMACS= Neighbor Recovery+Channel Assignmet
• Infrastructure building protocol that forms a flat topology
• A distributed protocol which enables nodes to discover their neighbors and establish transmission/reception schedules for communicating them without the need for any local or global master nodes
EAR(Eavesdrop-And-Register)Algorithm
• Offers continuous service to the mobile nodes under both mobile and stationary constraints.
• Primary constraint: battery power; mobile and stationary sensors must be established with as few messages transmitted by stationary sensors as possible.
• Hand off may not be required.• Mobile nodes have the registry of the neighbors.• Acks are avoided by timeouts, thresholds.
Routing
• Multihop Routing- objective: to provide priority service with robustness on a long term basis- more energy will spent on route setup and maintenance
• Cooperative Routing- reducing overhead in setup since data traffic is light
Multihop Routing
• Minimum energy per packet• Minimum cost per packet• Creation of multiple paths• Parameters:
- energy resources estimated by maximum number of packets
- additive QoS metric(higher metric= lower Qos)
(assumed low mobility)
SAR(Sequential Assignment Routing)
• Selection of a path among multipath by the node which generates the packet
• Objective: to minimize the average weighted QoS metric throuhout the lifetime of the network
• Criteria:
- energy resource
- QoS metric
- Priority level of a packet
Cooperative Signal Processing
• Noncoherent- raw sensor data will be preprocessed to be forwarded to central node- central node selection algorithms:
* SWE(Single Winner Election)* ST(Spanning Tree)
• Coherent-Limited number of sensor generating data- Explicit computation of minimum energy paths- MWE() is used to decrease energy cost.-Longer delay, higher overhead, lower scalability.
References
• Katayoun Sohrabi, Jay Gao, Vishal Ailawadhi, and Gregory J.Pottie, “Protocols for Self organization of a Wireless Sensor network,” IEEE Pers Commun., Oct. 2000, pp. 16-27
• Christopher A. St. Jean, “Self-Organization in Ad Hoc and Multihop Wireless Communication Networks,” Symposium on Multi-hop/Ad-hoc Wireless Networks, June 2002, France.
• J. Jamont and M. Occello, “Using Self-Organization for Functional Integrity Maintenance of Wireless Sensor Networks,” IEEE Proc., France, 2003.
• R.E. Van Dyck, “Detection Performance in Self-Organized Wireless Sensor Networks,” National Institute of Standards and Technology Gaithersburg, Maryland, USA
Flooding & Gossiping
• Flooding:– Diffuse copies of message to all neighbors– Problems:
• Implosion• Overlap• Resource Blindness
• Gossiping:– Diffuse one copy to random neighbors– Solves implosion problem– Problems:
• Overlap
SPIN
• Overcome the problems of flooding
• Negotiation and Resource-adaptation– Negotiation: helps ensure only useful
information will be transferred– Resource manager: keeps track of resource
consumption
• Disseminate information with low latency and conserve energy at the same time.
SPIN
• ADV, REQ, DATA• Spin1: do not consider energy consumption• Spin2: if energy is low level, reduce its
participation• in terms of energy,
– Spin1 uses 25% as much energy than flooding– Spin2: 60% meta-data per unit energy than
flooding.
Directed Diffusion• Data centric• Attribute-naming• interest including timestamp, gradient, data rate,
duration(lifetime)• Reactive routing• Neighbor-to-neighbor• Can be efficient in highly dynamic networks(changes
in topology is not important)• trade off some energy efficiency for increased
robustness and scale.
LEACH
• Clustering based• Min. Energy dissipation• Randomly select nodes as clusterheads• Setup & steady phases• Clusterhead advertise that they are
clusterheads• Based on signal strength(cluster members
determined)
References
• C. Intanagonwiwat, R. Govindan, D. Estrin and J. Heidemann, “Directed Diffusion for Wireless Sensor Networking”, in IEEE/ACM Transactions on Networking, v.11, no. 1, February 2003.
• J. Kulik, W. Rabiner, and H. Balakrishnan, “Adaptive protocols for information dissemination in wireless sensor networks,” in Proc. 5th Annu. ACM/IEEE Int. Conf. Mobile Computing and Networking(MobiCom’99), Seattle, WA, 1999, pp. 174–185.
Dynamic Power Management in Wireless Sensor Networks
A.Sinha and A.Chandrakasan, IEEE Design Test Comp.,Mar./Apr.2001
Massachusetts Institute of Technology
Sensor Network & Node Architecture
Ck
Nodek
Sensor A/D Micro-OS
StrongARM
Memory
Radio
Battery and DC/DC converter
R
Useful Sleep States for the Sensor NodesSleep State StrongARM Memory Sensor,
A-to-D converter
Radio
s0 Active Active On Tx,Rx
s1 Idle Sleep On Rx
s2 Sleep Sleep On Rx
s3 Sleep Sleep On Off
s4 Sleep Sleep Off OffTx: Transmit
Rx:Receive
Event Generation Model• R: Temporal event behavior over the entire sensing region=> Poisson process with an average
event rate lambda-tot
• Spatial distribution of events: independent probability distribution PXY(x,y)
• pek=prob. that an event is detected by nodek, given the fact that it occurred in R.
=……….
Pk(t,n)= prob.that “n” events occur in time “t” at node k.
Pk(Tth,0)= prob. of no events occurring in Ck over threshold interval Tth
=……………
Pth,k(t)= prob.that at least one event occurs in time t at nodek
=1- Pk(Tth,0)
State Transition Latency & Power
Power ti
Active Idle Actives0
P0
Pk sk
Pk+1 sk+1
t1 t2
taud,k tauu,k
taud,k+1 tauu,k+1
Steady State Shutdown Algorithm
If(eventOccurred()=true){
processEvent();
++eventCount;
lambda_k=eventCount/getTimeElapsed();
for (k=4;k>0;k--){
if(computePth(Tth(k)) < pth0)
sleepState(k);
}
}