MERLIN: A Synergetic Integration of
MAC and Routing for Distributed
Sensor Networks
A.G.Ruzzelli, M.J.O’Grady, R.Tynan, G.M.P.O’Hare.
Adaptive Information Cluster project (AIC)
and
Smart Media Institute (SMI)
Department of Computer Science
University College Dublin
Ireland.
http://www.adaptiveinformation.ie
MERLIN: Integrating energy-efficient MAC and Routing
Summary
• Overview of WNSs and protocols
• Motivation
• Phase1: MERLIN design
–
–
–
–
Motivation and objectives
Fundamental concept
MAC details
Routing details
• Phase2: Simulation and results
– Scheduling performance
– Comparison against SMAC+ESR
• Conclusion
MERLIN: Integrating energy-efficient MAC and Routing
Sensor network characteristics
• Energy consumption: primary objective
• The wake-up concept
•
Very low duty cycle (even less than 5%)
• Small packets smaller than in ad-hoc networks (e.g.
temperature data is few bytes)
• Low data traffic per node
MERLIN: Integrating energy-efficient MAC and Routing
Important issues of protocols for WSNs
Communication reliability: Nodes are prone to fail and bad
channel condition might affect the transmission
Scalability: Medium Access control should be able to deal with
large scale networks
Unique global addressing:
Low processing capability
High end-to-end latency of packets
MERLIN: Integrating energy-efficient MAC and Routing
Protocol generality
What does MERLIN address?
Energy-efficiency
• by an adaptive node activity scheduling
End-to-end latency reduction
• Separate MAC and Routing layers in low duty-cycle multi-hop networks cause an
extremely high latency
– (e.g. SMAC +DSR at 5% duty >35s delay for packets of 10 hops away nodes )
Communication reliability
• failure, interference, depletion, mobility  Addressing a single node can result in high
error probability
Node-to-Gateway routing
What MERLIN does NOT address:
•Node-to-node routing located at several hop distance
Initial idea presented at IWWAN04:
A.G. Ruzzelli, Evers, Dulman, Van Hoesel, Havinga.
“ On the design of an energy-efficient low-latency integrated protocol for Wireless Sensor networks"
MERLIN: Integrating energy-efficient MAC and Routing
Design goals
•MAC+Routing integration into a simple architecture;
•No usage of handshake mechanisms;
•No specific node addressing;
•Reduce latency while ensuring a very low energy consumption
•Increasing communication reliability while limiting packet
overhead;
MERLIN: Integrating energy-efficient MAC and Routing
Initial idea: Timezone division
(European EYES project, NL)
Gateway
Node
Every node sets its zone
and forward the sync
packet to more distant
nodes.
A node division both in
time and space is
generated,
i.e. timezone
Nodes with the same
color are in the same
time zone
MERLIN: Integrating energy-efficient MAC and Routing
Division of the network in timezones
Nodes report to the closest gateway
Nodes within the same zone wake up, transmit and go into sleep simultaneously
MERLIN: Integrating energy-efficient MAC and Routing
Timezone data traffic
Zone 3
Zone 2
Zone 1
Downstream multicast:
Packets transmitted to
higher zones
Upstream multicast:
Packets are forwarded
to lower zones
Sleeping
MERLIN: Integrating energy-efficient MAC and Routing
Local broadcast:
Packets reach all
neighbours. No
forwarding performed
Global allocation
Frame
Frame
Zone 1
Zone 2
Zone 3
Zone 4
Frame
Zone 5
Zone 6
Zone 7
Zone 8
The allocation of further zones can be obtained by appending the same table.
The allocation of further frames is obtained by flanking the same table.
MERLIN: Integrating energy-efficient MAC and Routing
Accessing the table
NZONE = 4
NSLOT =9
To access the current slot in the table:
SLOT# = GlobalTime/SLOTTIME
currentSlot = Mod(SLOT#, NSLOT)
Nodes in the same timezone contend the slot for local broadcast only once
each 4 frametimes
If Mod(FRAME#, NZONE) = Mod(myZone,NZONE)
MERLIN: Integrating energy-efficient MAC and Routing
Intra-zone MAC features
Zone N+1
Zone N
Zone N-1
Recall that
• Nodes in the same zone share the same slot for activity
• transmission in MERLIN (multicast) do not address a
specific receiving node
How can simultaneous transmission be handled?
How can correct/incorrect receptions be notified?
MERLIN: Integrating energy-efficient MAC and Routing
Burst tones can help
• Properties
– Are signal impulse Do not contain any coded information
– Are robust  Several simultaneous burst can still be
identified as one burst
– They are shorter that a normal ACK
• Utilization
In transmission to the gateway
Multicast: Bursts identify correct receptions
BACK
MERLIN: Integrating energy-efficient MAC and Routing
In local broadcast
Broadcast: Bursts identify reception errors
BNACK
Asynchronous transmission Mechanism
Tc
Tc
CCA
Tx1
Preamble
CCA
Packet
Sleep
Tc
Rando
m
CCA
Preamble
CCA
Packet
Sleep
Tx2
Rando
m
Sleep
Listen
Sleep
Transmit
CCA
Rx1
Burst*
Listen
Sleep
Sleep
Burst*
CCA
Rx2
Listen
Sleep
Sleep
Slot length
Rx1
* burstACK if local broadcast, burst NACK if multicast
Rx1
Tx1
Tx1
Tx2
Rx2
Rx2
MERLIN: Integrating energy-efficient MAC and Routing
Tx2
Disadvantages
1)MERLIN does not address a
specific receiving node 
Zone 1
Zone 2
Zone 3
A
multiple copy of the same msg
sent can be generated
B
increase overhead!
2) Some collisions due to the
Hidden Terminal Problem (HTP)
Zone 3
A
?
B
MERLIN: Integrating energy-efficient MAC and Routing
Zone 4
Zone 5
Routing characteristics (I)
Controlled multipath
•
3 small buffers of upstream, downstream and local broadcast are provided
•
Packets organised in multiple msgs of the same data traffic type;
•
Packets contain a msg-ID index of included msgs;
•
Nodes, which lose the contention, keep on listening to the beginning of the transmitted
packet then go into sleep;
•
Nodes discard from their buffer the msgs already fowarded.
P
Msg-index
a
c
k
e
Channel contention
t
messages
Pro : Reduce overhead in transmission!
Con : Small increase of node activity;
Increase complexity.
MERLIN: Integrating energy-efficient MAC and Routing
Discard msgs
already
forwarded from
their queue
Listen
to the
packet
index
Routing characteristics (II)
Timezone maintenance
•
Timezone update are sent periodically;
•
Failed reception of timezone update from zone N-1 node to zone N node triggers
a upstream multicast of Timezone Update request (TUR)
–
•
N-1 failed  local broadcast TUR
–
•
N-1 node/s reply  Connection reestablished
At least one reply  change of zoen to N+1
N failed  downstream broadcast TUR
2
1
2
1
1
3
3
2
1
3
4
2
2
3
4
4
4
6
TUR
4
3
MERLIN: Integrating energy-efficient MAC and Routing
TUR
5
Assessment
Simulation tool: OmNet++
Framework: EU EYES project
Evaluation against SMAC+ESR
In Progress:
Philips Sand node implementation
MERLIN: Integrating energy-efficient MAC and Routing
Scenario and Setup
•Scenarios
•Metrics:
•Energy consumption per RX packet
•Network lifetime
•E-to-E latency
•Total packet overhead
•% sleeping time
•5 nodes two-hops
Forwarder
Sources
Destinations
•Parameters:
•70 nodes Random
multihop
MERLIN: Integrating energy-efficient MAC and Routing
•Duty cycle (acting on CW and frametime size)
•Low traffic conditions (12 packet/min)
•High traffic conditions (60 packet/min)
Low traffic 2-hops scenario
MERLIN: Integrating energy-efficient MAC and Routing
High traffic 2-hops scenario
MERLIN: Integrating energy-efficient MAC and Routing
Multihop scenario: Lifetime
Note: These graphs have little relevance if not related to the EtoE latency
MERLIN: Integrating energy-efficient MAC and Routing
Multihop scenario: Latency/energy
Given a certain sustainable latency, MERLIN consumes between 2 and 2.5 times
less energy than SMAC+ESR
MERLIN: Integrating energy-efficient MAC and Routing
Total packet overhead
The MAC routing integrated nature MERLIN results in a smaller
packet overhead than SMAC+ ESR.
MERLIN: Integrating energy-efficient MAC and Routing
Conclusion
• Description and simulated results of MERLIN have been presented;
• MERLIN is suitable for large scale sensor networks with energy
consumption as main goal;
• MERLIN is suitable for communication to a from the gateway
• The multicast mechanism with burst ACK showed large improvement
on the communication reliability
• The integrated nature and the absence of handshake mechanisms
help reducing the EtoE packet delay
• EtoE delay can be traded-off for a longer network lifetime Results
showed lifetime being extended by a factor of 2.5 of MERLIN with
respect to SMAC
MERLIN: Integrating energy-efficient MAC and Routing
Thank you for your kind attention
MERLIN: Integrating energy-efficient MAC and Routing