Energy Aware Routing for PicoRadio

Rahul C. Shah

Berkeley Wireless Research Center

Wireless Sensor Networks Dominant trend in wireless industry:

More bits/sec/Hz Wireless sensor networks offer:

More bits/$/nJ

PicoRadio System Design

Wireless Sensor Nodes – Constraints Low Data Rates << 10 kbps Self-configuring, maintenance-free and robust

Aggressive networking protocol stack Redundancy in deployment

Low cost: < 1$ Small size: < 1 cm3

Low power/energy Long lifetime of product requires energy-

scavenging Plausible scavenging level: < 100 W

Energy Scavenging

Practical Means of Energy Scavenging

Protocol StackIssues at the network layer: Addressing

Addressing will be class based: <location, node type, sub type>

Symbolic addressing may be supported Routing

Should route packets to the destination Given:

Destination location Position of self Position of the neighbors

PhysicalData LinkNetwork

Application

Distributed Positioning

010

2030

4050

0

20

40

600

2

4

6

8

10

Initial Position Error (%)

10 nodes, 25 waves, anchor weight=5, 30 iterations, 30% anchors, NO gradients

Range Error (%)

Ave

rage

Pos

ition

Err

or (

% o

f gr

id d

imen

sion

s)

2

1

3

4

5

6

7

89

10

1112

13

14

15

16

17

18 1920

[Chris Savarese(UCB)]

Data Link Layer Functions Transfers data

between network and physical layers;

Maintains neighborhood info

Power control, error control and access control

Computes location

ControllerSensors

Actuators

Mostly-Sleepy MAC Layer Protocols

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 randomActivity in sensor networks is low and random• Careful scheduling of activity pays off big time, but … has to Careful scheduling of activity pays off big time, but … has to

be performed in distributed fashionbe performed in distributed fashion

A Reactive PicoMAC Truly Reactive Messaging

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

To Reduce Collision Rate To Reduce Signaling Overhead (Shrink Address

Space)

Multi-Channel Access Scheme

SCA

TCARCA

Channel AssignmentUsing Distributed GraphColoring (combined with discovery)

Receiver-based ChannelAssignment: Channel code used as address

[Chunlong Guo(UCB)]

Reactive Radio Issues Broadcast and data communication modes

must co-exist 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 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:

Sensor data is redundant, so reliability is not required

Most data is delay insensitive

Routing Protocol Characteristics 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 to maintain network connectivity (network issue)

Critical node as it is the only one of its type

Network survivability is application-dependent – coverage may also be an issue

Proactive vs. Reactive Routing Proactive routing

maintains routes to every other node in the network

Regular routing updates impose large overhead

Suitable for high traffic networks

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

Finds the best route and then always uses that!

But that is NOT the best solution! Energy depletion in certain nodes Creation of hotspots in the network

SourceDest

Directed Diffusion†

Destination

Source

Setting up gradients

Destination

Source

Sending data

•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 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 Probability 1/energy cost

The choice of path is made locally at every node for every packet

Setup Phase

Controller

Sensor

Directional flooding

10 nJ

30 nJ

(0.75*10) + (0.25*30) = 15 nJp1 = 0.75

p2 = 0.25

Local Rule

Data Communication Phase

1.01.0

0.6

0.4

Controller

Sensor0.3

0.7

Each node makes a local decision

What’s The Advantage? 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

The metric can also include: Information about the data buffered for a

neighbor Regeneration rate of energy at a node Correlation of data

initial

remainingrxtx E

EEEC )(

Simulation Setup Simulations done in Opnet 76 nodes in a typical office setup

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

Office layout

Nodelayout

Networkmodel

Simulation Measurements Energy used is measured:

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 0.87Energy Aware Routing

11.76 9.67 41.11 0.98

Energy Usage ComparisonDiffusion 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 ComparisonDiffusion Routing Energy Aware Routing

Peak bit rate was 250 bits/sec.Average bit rate was 110 bits/sec.

Network Lifetime Nodes have fixed initial energy – 150 mJ Measure the network lifetime until the

first node dies out Diffusion: 150 minutes Energy Aware Routing: 216 minutes

44% increase in network lifetime

Funneling Algorithm

Controller Sensors

Border Nodes

Controller Sensors

Border Node

Interest Flooding Data Communication[w/ Dragan Petrović (UCB)]

PicoRadio Implementations

PicoNode I

sensor digital power radio

Off-the-shelf fully programmable communication/computation node

PN3 Architecture - Rx

• Two Channel• Channel Spacing ~ 50MHz• 10kbps/channel• Issues include noise suppression and isolation between RF filters• Prototype Target: 3mA @ 1V

RF Filter LNA

fclock

RF Filter PeakDet

fclock

RF Filter PeakDet

PN3 Architecture - Tx

• Use simple modulation scheme (OOK)• Allows efficient non-linear PA• Target output power: 0dBm• Prototype Target: 4mA @ 1V

PA MatchingNetwork

MOD1

MOD2

OSC1

OSC2 Preamp

PN3 Cycled Receiver

RX0

TX0

RX1

TX1