Transcript Energy Aware Routing for Low Energy Ad Hoc Sensor Networks

Energy Aware Routing for PicoRadio
Rahul C. Shah
Berkeley Wireless Research Center
Wireless Sensor Networks
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Dominant trend in wireless industry:
 More bits/sec/Hz
Wireless sensor networks offer:
 More bits/$/nJ
PicoRadio System Design
Wireless Sensor Nodes – Constraints
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Low Data Rates << 10 kbps
Self-configuring, maintenance-free and robust
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Aggressive networking protocol stack
Redundancy in deployment
Low cost: < 1$
Small size: < 1 cm3
Low power/energy
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Long lifetime of product requires energyscavenging
Plausible scavenging level: < 100 W
Energy Scavenging
Practical Means of Energy Scavenging
Protocol Stack
Issues at the network layer:
 Addressing
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Addressing will be class based:
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Symbolic addressing may be supported
<location, node type, sub type>
Routing
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Should route packets to the destination
Given:
 Destination location
 Position of self
 Position of the neighbors
Application
Network
Data Link
Physical
Distributed Positioning
Average Position Error (% of grid dimensions)
10 nodes, 25 waves, anchor weight=5, 30 iterations, 30% anchors, NO gradients
10
8
6
4
2
0
60
50
40
40
30
20
Range Error (%)
20
0
10
0
Initial Position Error (%)
[Chris Savarese(UCB)]
Data Link Layer Functions
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Transfers data between
network and physical
layers;
Maintains neighborhood
info
Power control, error
control and access control
Computes location
Sensors
Controller
Actuators
Mostly-Sleepy MAC Layer Protocols
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Receiving a bit is computationally more expensive than
transmitting one (receiver has to discriminate and synchronize)
Most MAC protocols assume that the receiver is always on and
listening!
• Activity in sensor networks is low and random
• Careful scheduling of activity pays off big time, but … has to
be performed in distributed fashion
A Reactive PicoMAC
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Truly Reactive Messaging
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Power Down the Whole Data Radio
Reduce Monitoring Energy Consumption by 103 Times
Wakeup Radio will Power Up Data Radio for Data Reception
Multi-Channel Access Scheme
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To Reduce Collision Rate
To Reduce Signaling Overhead (Shrink Address Space)
Multi-Channel Access Scheme
Channel Assignment
Using Distributed Graph
Coloring
(combined with discovery)
Receiver-based Channel
Assignment:
TCA
Channel code used as address
RCA
SCA
[Chunlong Guo(UCB)]
Reactive Radio Issues
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Broadcast and data communication modes must coexist simultaneously
Sleeping nodes
Communicating nodes
• Sleeping nodes have to wake-up to broadcast signals, and
not to any signal leaking from surrounding communicating nodes
• Broadcast signals should not disrupt data transmission
PicoRadio Routing Protocol
PicoNetwork Specifications
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Density of nodes – 1 node every 1 to 20 sq.
m.
Radio range – 3 to 10 m
Average bit rate per node ~ 100-500 bps
Peak bit rate per node ~ 10 kbps
Very low mobility of nodes
Loose QoS requirements:
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Sensor data is redundant, so reliability is not
required
Most data is delay insensitive
Routing Protocol Characteristics
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Ensure network survivability
Low energy (communication and
computation)
Tolerant and robust to topology changes
Scalable with the number of nodes
Light weight
Network Survivability
Critical node as
it is the only one
of its type
Critical node to maintain
network connectivity
(network issue)
Network survivability is application-dependent – coverage may also be an
issue
Proactive vs. Reactive Routing
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Proactive routing
maintains routes to
every other node in the
network
Regular routing updates
impose large overhead
Suitable for high traffic
networks
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Reactive routing
maintains routes to only
those nodes which are
needed
Cost of finding routes is
expensive since flooding
is involved
Good for low/medium
traffic networks
Traditional Reactive Protocols
Dest
Source
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Finds the best route and then always uses
that!
But that is NOT the best solution!
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Energy depletion in certain nodes
Creation of hotspots in the network
Directed Diffusion†
Setting up gradients
Sending data
Source
Source
Destination
Destination
•Destination initiated
•Multiple paths are kept alive
†C.
Intanagonwiwat, R. Govindan and D. Estrin, “Directed Diffusion: A scalable and robust
communication paradigm for sensor networks”, IEEE/ACM Mobicom, 2000
Energy Aware Routing
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Destination initiated routing
Do a directional flooding to determine various
routes (based on location)
Collect energy metrics along the way
Every route has a probability of being chosen
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Probability  1/energy cost
The choice of path is made locally at every
node for every packet
Setup Phase
Directional flooding
Local Rule
Sensor
p1 = 0.75
Controller
p2 = 0.25
(0.75*10)
10 nJ + (0.25*30)
= 15 nJ
30 nJ
Data Communication Phase
Each node makes
a local decision
0.3 Sensor
0.6
Controller
1.0
1.0
0.4
0.7
What’s The Advantage?
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Spread traffic over different paths; keep
paths alive without redundancy
Mitigates the problem of hot-spots in the
network
Has built in tolerance to nodes moving out of
range or dying
Continuously check different paths
Energy Cost


Eremaining 

C  ( Etx  E rx ) 

E
 initial 
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The metric can also include:
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Information about the data buffered for a
neighbor
Regeneration rate of energy at a node
Correlation of data
Simulation Setup
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Simulations done in Opnet
76 nodes in a typical office setup
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47 light sensors
18 temperature sensors
7 controllers
4 mobile nodes
Light sensors send data every 10 seconds,
while the temperature data is sent every 30
seconds
Comparison with directed diffusion routing
Simulation Model
Network
model
Office layout
Node
layout
Simulation Measurements
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Energy used is measured:
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For reception: 30 nJ/bit
For transmission: 20 nJ/bit + 1 pJ/bit/m3
Packet sizes are ~ 256 bits
1 hour simulation time
Energy (mJ)
Avg.
Std. Dev.
Max
Min
Diffusion
14.99
12.28
57.44
0.87
Energy Aware
Routing
11.76
9.67
41.11
0.98
Energy Usage Comparison
Diffusion Routing
Energy Aware Routing
Peak energy usage was ~50 mJ for 1 hour
simulation
Normalized Energy Comparison
Diffusion Routing
Energy Aware Routing
Energy of each node is normalized with respect to
the average energy
Bit Rate Comparison
Diffusion Routing
Peak bit rate was 250 bits/sec.
Average bit rate was 110 bits/sec.
Energy Aware Routing
Network Lifetime
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Nodes have fixed initial energy – 150 mJ
Measure the network lifetime until the first
node dies out
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Diffusion: 150 minutes
Energy Aware Routing: 216 minutes
44% increase in network lifetime
Funneling Algorithm
Controller
Sensors
Border
Nodes
Interest Flooding
Controller
Sensors
Border
Node
Data Communication
[w/ Dragan Petrović (UCB)]
PicoRadio Implementations
PicoNode I
Off-the-shelf fully programmable
communication/computation node
sensor
digital
power
radio
PN3 Architecture - Rx
fclock
RF Filter
RF Filter

fclock
LNA
RF Filter
•
•
•
•
•
Peak
Det
Peak
Det

Two Channel
Channel Spacing ~ 50MHz
10kbps/channel
Issues include noise suppression and isolation between RF filters
Prototype Target: 3mA @ 1V
PN3 Architecture - Tx
OSC1
MOD1
OSC2
Preamp
PA
MOD2
•
•
•
•
Use simple modulation scheme (OOK)
Allows efficient non-linear PA
Target output power: 0dBm
Prototype Target: 4mA @ 1V
Matching
Network
PN3 Cycled Receiver
TX0
TX1
RX0
RX1