When does opportunistic routing When does opportunistic routing make sense?make sense?

Rahul C. Shah, Jan RabaeyUniversity of California, Berkeley

Sven Wiethölter, Adam WoliszTechnical University, Berlin

Problems of geographic routing• Fading channel• Inter-packet times are longer than the channel coherence time• Duty cycling of nodes

Geographic RoutingGeographic Routing

Advantages of geographic routing:• Tolerant of node failures/movements• Very small routing table sizes

Channel Variations Over TimeChannel Variations Over TimeB

road

cast

Suc

cess

Rat

e (%

)

Networking Protocol StackNetworking Protocol Stack

Application

Network(Routing, Addressing)

Data Link(MAC, Sleep discipline,

power control)

Physical

Next hop node information

Observes network connectivity

Observes neighbor connectivity

Observes channel quality

Enhance information being exchanged between the layers to maximize power efficiency

Exploiting Spatial Diversity: Exploiting Spatial Diversity: Opportunistic RoutingOpportunistic Routing

Current node

destination

Nodes know:• Their own location• The destination location

MAC chooses next hop based on connectivity

Network layer specifies forwarding region

Exploiting Spatial Diversity: Exploiting Spatial Diversity: Opportunistic RoutingOpportunistic Routing

Current node

destination

Nodes know:• Their own location• The destination location

Network layer specifies forwarding region

MAC chooses next hop based on connectivity

Exploiting Spatial Diversity: Exploiting Spatial Diversity: Opportunistic RoutingOpportunistic Routing

Current node

destination

Nodes know:• Their own location• The destination location

Network layer specifies forwarding region

MAC chooses next hop based on connectivity

Exploiting Spatial Diversity: Exploiting Spatial Diversity: Opportunistic RoutingOpportunistic Routing

Current node

destination

Nodes know:• Their own location• The destination location

Network layer specifies forwarding region

MAC chooses next hop based on connectivity

Opportunistic TICER for Medium AccessOpportunistic TICER for Medium Access

• Extension of TICER (Transmitter Initiated Cycled Receiver) • Provides ability to choose among multiple candidate forwarding nodes• Pseudo-asynchronous rendezvous scheme• Pick the first node that responds to the RTS• Assume channel is stationary over the RTS-CTS-Data-ACK exchange

Other Opportunistic ProtocolsOther Opportunistic Protocols• Geographic Random Forwarding (M. Zorzi & R. Rao)

– Uses geographic location of nodes to find best node– Divides forwarding region into priority regions– MAC protocol signaling is fairly complex

• Extremely opportunistic routing (S. Biswas & R. Morris)

– Ranks forwarding nodes by number of hops– Sender specifies priority of receiving nodes in the packet

• MAC layer anycast (R. Choudhary & N. Vaidya)

– Provides framework for choosing forwarding nodes at the MAC layer

Simulation DetailsSimulation Details• Simulation was done in OMNeT++• Random placement of nodes in a square• Poisson traffic was generated at the edges• Circular radio range of 10m, interference range ~1.5

times radio range• Compared with geographic routing• Metrics of comparison:

– Power consumption– End-to-end delay– Goodput

• Precision of mean within 5%, confidence level of 95%

Varying Node DensityVarying Node Density

Average number of neighbors per node Average number of neighbors per node

Pow

er c

onsu

mpt

ion

per

node

(m

W)

Ave

rage

end

-to-

end

dela

y (s

ec)

Channel Quality VariationsChannel Quality Variations

Pow

er p

er n

ode/

Pkt

del

iver

y fr

acit

on

(mW

)

Pareto distribution shape parameter Pareto distribution shape parameterE

nd-t

o-en

d de

lay

(sec

)

Varying Traffic RatesVarying Traffic RatesP

ower

con

sum

ptio

n pe

r no

de

(mW

)

Packet inter-generation time (sec)

Change in Wakeup RateChange in Wakeup Rate

End

-to-

end

dela

y (s

ec)

Pow

er p

er n

ode

(mW

)

Node wakeup rateNode wakeup rate

Optimum Wakeup RatesOptimum Wakeup Rates

Avg. no. of neighbors

Wakeup rate per node

Duty cycle per node

Avg. # of nodes awake in fwd.

region

6.3 3.3 1.6% 0.04

8.8 3.3 1.6% 0.06

11.3 2.8 1.4% 0.06

13.8 2.2 1.1% 0.06

16.3 2.2 1.1% 0.07

18.8 2.0 1.0% 0.08

Less than one node needs to be awake within the forwarding region!

When does opportunistic routing make When does opportunistic routing make sense? (compared to geographic routing)sense? (compared to geographic routing)

• Node densities > 9-10 neighbors/node• Medium to bad channel quality• Low traffic scenarios (<1 packet/second per

node)

• Improvements– 10-20% lower power consumption– 40% lower delay suffered by the packets– Fewer retransmissions required higher goodput (10-15%

higher for max of 3 retransmits)