merlin: a synergetic integration of mac and routing for distributed sensor networks a.g.ruzzelli,...

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)

Smart Media Institute (SMI)Department of Computer Science

University College DublinIreland.

http://www.adaptiveinformation.ie/home.asp

MERLIN: MAC and Routing Integration for WSNs by A.G.Ruzzelli @ SAND project

Summary

• Overview of WNSs and protocols

• Phase1: MERLIN design– Motivation and objectives– Fundamental concept– MAC details – Routing details

• Phase2: Simulation and results– Scheduling performance – Comparison against SMAC+ESR

Conclusion


Overview of Wireless Sensor Networks

• Large number of tiny sensors (nodes) distributed in an area network;

• Sensor nodes:– have sensing devices attached;– are self-organizing;– are usually battery operated and of low cost

hence power limited • multi-hop communication to save energy;


WSNs issues: •Nodes must be cheap Limited memory capabilities Limited processing capabilities

Limited power capabilities Maybe not very reliable

•Limited energy Power consumption•High node number Scalability issues•High dynamic condition Reactivity and Self-organization•Always on radio node depletion in few days (e.g. Mobile phone)

MAC issues•Simultaneous msg to same device Packet Collision•Channel access delay•Control packet overhead

•Multihop routing issues•Route maintenance Overhead•E-to-E latency•Global addressing issue•Only useful messages to deliver In-network processing


Wireless sensor network architectureAn example:

Antenna

Sensingdevices

Application

Data aggregation

Routing

MAC

Physical

Sensing coverage

Cro

ss layer in

tera

ction

Localization

•The most suitable network architecture for WSNs is still an open issue

•Each layer has its own task

•Any layer try to achieve the task using the smallest amount of energy possible

•Researchers are evaluating how to use the cross layer interaction at best


Mechanisms applied in Wireless Sensor Networks MACs:

The CSMA/CA approach (Carrier sense multiple access with collision avoidance)

•A potential transmitter listen to the channel for a random time in a CW to sense any ongoing transmission in progress•Channel assumed free Transmit the packet with procedeure RTS/CTS/Data/ACK•Channel busy Transmission postponed then node switches off the radio

•Adv Flexible•Dis High latency and idle listening

node1

node2

node3TX

TX

RTS

CTS

Contention

Listen

Listen Preamble+Data

ACK

Sleep

Sleep

The TDMA approach (Time division multiple access)•Time is divided into slots that are (in some way) assigned to neighbouring nodes

•ADV: collision free and energy efficient•DIS: Low flexibility

Random Time

Tx

Rx


• Due to low duty cycle of WSNs, separate MAC and Routing layers cause an extremely high latency – (e.g. SMAC and DSR tens of seconds delay for packets of

nodes in hop 10 or more)

• Layer modularisation requires higher memory capability Layer integration is beneficial

• Nodes are cheap and not reliable – failure, interference, depletion, mobility Addressing a

single node can result in high error probability

Motivation for MERLIN


Objectives of MERLIN

•MAC+Routing integration features into a simple architecture;

•No usage of handshake mechanisms;

•No specific node addressing;

•Reduce latency while ensuring a very low energy consumption

•Controlled packet duplication to address sensor failure and bad channel condition;


What is the main IDEA behind the MERLIN protocol?

Gateway

Node

Why Time Zones?

Nodes with the same color are in the same time zone

Nodes within the same subset belong to the same gateway

---------------------------------

Nodes within the same zone wake up and go into sleep simultaneously

(European EYES project, NL)


Division of the network in timezones

SYNC packets from the gateway are forwarded to further nodes. Every node sets its zone and forward the packet to more distant nodes.


4-Zone V-scheduling table

Nodes in the same timezone contend the slot for local broadcast only once each 4 frametimes


Data traffic

• Downstream multicast: Packets are transmitted to higher zones

• Local broadcast: Packets reach all neighbours. No forwarding is performed

• Upstream multicast: Packets are forwarded to smaller zones


Transmission Mechanism (I)

The minimum wakeup concept through CCA

• Alternation of long period of inactivity to tiny period of channel assessment;

• The Clear Channel Assessment CCA is the shortest time period needed for nodes to sense any activity on the channel (~2.5msec in BMAC)

• Much shorter CCA period than time required for a control packet (e.g. 35msec for 5byte transmission with Tr1001)

• duty cycle reduced to less than 1%

Ts Sleep periodCCA

Time


2 questions:

• How can a Tx know when the Rx is awake?

• If not addressing a specific node (in multicast and broadcast), how can correct/incorrect receptions be notified?


Burst tone can help

• Properties– Are signal impulse Do not contain any coded

information– Are robusts Several simultaneous burst can still be

as one– They are shorter that a normal ACK

• Utilization

Broadcast: Bursts identify reception errorsMulticast: Bursts identify correct receptions


Transmission Mechanism (II)

Tx1

Tx2

Tx2

Tx1


Disadvantages

1)MERLIN does not address a specific receiving node

multiple copy of the same msg sent can be generated

increase overhead!

2) Some collision due to the Hidden Terminal Problem (HTP)

Zone 1 Zone 2Zone 3

Zone 4Zone 5

A

B

Zone 3

A

B

?


Routing characteristics (I)

• 3 small buffers of upstram, 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.

Pro : Reduce overhead in transmission!

Con : Small increase of node activity;

Increase complexity.

Channel contention

messagesMsg-index

Discard msgs already forwarded from their queue

P a c k e t

Listen to the packet index

Controlled multipath


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 node/s reply Connection reestablished

• N-1 failed local broadcast TUR– At least one reply change of zoen to N+1

• N failed downstream broadcast TUR

1

23

3

4

2

4

1

3

4

2

TUR

1

3

4

2

TUR

1

3

4

2

6

5


Phase 2: Simulation and Comparison with two

existing protocol architecture:SMAC (mac)+ ESR (routing)


Simulation and result

Nodes with the same colors are in the same zone (same hop Count Number).

Number slot /frame = 4

Contention period = 30ms

DataRate = 115200 bits/sec

DataSize = 16+8 Bytes (data + 3 bytes preamble + starting code)

Parameters Values

Energy Transmitting 21 mW

Energy Receiving 14.4 mW

Energy stand-by 15 µW

Switch time Tx/Rx 518 µs

Switch time Rx/Tx 12 µs

Switch stanby/Rx 518 µs

Switch stand-by/Tx 15 µs

Eyes node


V-scheduling

0

50

100

150

200

250

300

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Frametime (sec)

Network Lifetime (days)

V-Scheduling

1 Gateway 100 Nodes rand. Distributed.800*500 area network Min signal strength(12 m)50 msg/min sent by 5 rand. nodes Static network

V scheduling Network lifetime.

•The network is considered to fail when 30% of nodes are depleted.•Lifetime calculated for a linear depletion of 2 AA batteries.

The network lifetime depends linearly on the frame length;


V scheduling setup time

V-Scheduling Network Setup

0

2

4

6

8

10

0 50 100 150 200 250

Node Density (nodes/100 m^2)

Tim

e (

se

c)

V scheduling can be setup in less than 10 seconds up to 250 nodes/100m^2 of network density.


End-to-end packet delay

Node density = 125 nodes/100m^2

2.312.87

2.52

5.125.52 5.45

4.12

6.315.52

7.51 7.52

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10 11Node hop count

Late

ncy

(s

ec)

Node density = 275 nodes/100m^2

1.61 1.52 1.51

4.013.52

4.52 4.18

6.18 6.386.85 6.52

7.518.02

8.52

0

1

2

3

4

5

6

7

8

9

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Node hop count

Late

ncy (

sec)

V-scheduling

• The controlled multiple path mechanism may cause a lower delay for nodes farther from the gateway;

• An increase of latency at the intersection of data traffic flows due to periodical stop of nodes activity that go into sleep.

•V-scheduling delay obtained for 2sec frametime length

Frametime length should be based upon application requirements.


The SMAC protocol

• SMAC divides time in two periods: active time and sleeping time;

• Active period = SYNC period for node sync update, Request To Send (RTS), Clear to Send (CTS).

• Communication establishing: – neighboring nodes synchronize to the

start of the active period then local broadcast of SYNC packets.

• Data message exchanges follow the RTS/CTS/DATA/ACK; nodes switch between different states

periodically.

RTS

CTS

Data

Transmitter Receiver

time

ACK

SMAC Coordinated Sleeping

sleeplisten listenlisten

t1 t2

Timing relationship of packet Tx/Rx


Scenario and Setup

•Scenario•5 nodes two-hops

•70 nodes Random multihop

•Metrics:•Energy consumption per RX packet •Network lifetime•E-to-E latency•Total packet overhead•% sleeping time

•Parameters:•Duty cycle (acting on CW and frametime size•Low traffic conditions (12 packet/min)•High traffic conditions (60 packet/min)

Sources

Forwarder

Destinations


Low traffic 2-hops scenario


High traffic 2-hops scenario


Multihop scenario: Lifetime

Note: These graphs have little relevance if not related to the EtoE latency


Multihop scenario: Latency/energy


Total packet overhead

The MAC routing integrated nature MERLIN results in a smaller packet overhead than SMAC+ ESR.


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, the absence of handshake mechanisms help reducing the EtoE packet delay

• EtoE delay can be traded-off for an longer network lifetime Results showed lifetime being extended by a factor of 2.5 of MERLIN with respect to SMAC


Thank you for your kind attention

merlin: a synergetic integration of mac and routing for distributed sensor networks a.g.ruzzelli,...

Documents

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sand project wsns issues

synergetic integration

separate mac

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energy slide

sand project mechanisms

network processing slide