Real Time Network : Schedule Adaptation of Low-Power ...lamspeople.epfl.ch/decotignie/Midterm10-Mobile.pdfIntroduction MiX-MAC Node synchronisation along a path Conclusion Real Time

IntroductionMiX-MAC

Node synchronisation along a pathConclusion

Real Time Network :Schedule Adaptation of Low-Power-Listening

Protocols for Wireless Sensor Networks

Florian Barras, Yorick Brunet

EPFL

May 30, 2010

1 / 27 Florian Barras, Yorick Brunet RTN: Schedule adaptation of LPL protocols for WSN

IntroductionMiX-MAC


1 Introduction

2 MiX-MAC

3 Node synchronisation along a path

4 Conclusion


IntroductionMiX-MAC


Goals & Strategy

Goals

Find solutions to reduce energy consumption, transmission timeand packet delivery delays for networks experiencing differentand changing loads of traffic.

Strategy

The solutions they propose :

Construct an efficient MAC protocol able to adapt to suchvariable networks, using the most appropriate protocol foreach configuration;

Synchronize nodes.


IntroductionMiX-MAC


Literature reviewProtocol descriptionExperimentsExample

1 Introduction

2 MiX-MAC


4 Conclusion


IntroductionMiX-MAC



Literature review

LPL and PS MAC protocols

A solution to reduce energy consumption due to idle listening.

LPL: Low-Power Listening

PS: Preamble Sampling

Two branches of random access protocols

Both use the insight behind Aloha with PS (includingB-MAC1, WiseMAC1, SyncWUF and X-MAC)

LPL MAC protocols do not need to know anythingabout their neighbours and wake-up schedules

* Note that B-MAC and WiseMAC (with a variable preamble length) canno longer be used on the new IEEE 802.15.4 (imposing fixed preamble length).


IntroductionMiX-MAC



Their protocol

They propose to switch the MAC schedules from a fixed pool ofMAC protocols at the transmitter.

MiX-MAC

Based on some existing LPL protocols:

X-MAC

SpeckMAC

MX-MAC (an adaptation of CSMA-MPS)


IntroductionMiX-MAC




IntroductionMiX-MAC



Overview of these protocols

X-MAC schedule

Advantages:

Efficient for unicast packets

Drawbacks:

Not well suited for broadcast transmissions (Bettner et al.)

Sensitive to the hidden node problem

High risk of wrong positive ACKs


IntroductionMiX-MAC




MX-MAC schedule

Based on the PS protocol: CSMA-MPS;

Each node wakes up only periodically to probe the medium.

Advantages:

Immunized against wrong positive ACKs

Suited for broadcast transmissions

Drawbacks:

Less efficient in term of transmission time and so of energyconsumption


IntroductionMiX-MAC




SpeckMAC schedule

Advantages:

Better than the others for broadcast

Drawbacks:

Less efficient than the others in term of energy consumption

No check of packet validity (ACKs, ...)


IntroductionMiX-MAC



Experiments

Goal

Compare MAC protocols to optimize the behaviour of all threeMAC protocols.

Procedure

Find the radio switch time (Tx - Rx) for each protocol

Define and optimize the behaviour of all protocolsfollowing:

Time separation between two CCAsFor X-MAC, the length of the ADV packetACK interpetation (for schedule compatibility)

Determine the switching thresholds following:

Reliable throughtput (or goodput)Lifetime for unicast and broadcast packets


IntroductionMiX-MAC



Results

The optimal schedule they found:


IntroductionMiX-MAC



MiX-MAC may increase the lifetime:


IntroductionMiX-MAC



Remarks

They do not take into account possible errors that causeretransmission. This implies additional energy consumption !

Modifications of existing protocols

No explicit formula or code to check the results


IntroductionMiX-MAC


IntroPrinciplesSimulationsImplementation

1 Introduction

2 MiX-MAC


4 Conclusion


IntroductionMiX-MAC



Intro

Drawback of LPL MAC protocols :

significant burden on sending node for medium to low dutycycles;

a programmer may wish to use such cycles.

Odd choices :

study MiX-MAC with only MX-MAC;

packets are delivered in a best effort manner.


IntroductionMiX-MAC



Principles

a node learns the active schedule of its destination whenreceiving an ACK;

if receiver wakes up each ti [s], the sender will wake up ti − ts[s] later.


IntroductionMiX-MAC



Unicast process

the number of unicast packets required to synchronisedepends on the number of hops;

to synchronise n nodes, n-1 packets are required;

on pipelined path, a packet must be sent every 2 ∗ ti [s].


IntroductionMiX-MAC



Urgent packets

regular packets are forwarded in the next duty cycle;

urgent packets are retransmitted immediatly, radio is kept on;

the retransmission must start before the next hop probes thechannel : trx + tp < ts .


IntroductionMiX-MAC



Several unidirectional paths

When two nodes want to send a packet to the same node at thesame time, there is collision.Several techniques may be used to avoid collisions :

information exchange between neighbours;packet rate reduction;back off;using the synchronisation of this paper.


IntroductionMiX-MAC



Intro

use Matlab;

10 nodes placed to form a multihop network;

source sends 40 B packets;

duty cycle is low since ti is expected to be allowed to increase.


IntroductionMiX-MAC



Example


IntroductionMiX-MAC



Packet delay

time between the first attempt to send and the successfulreception;

simulation with 5 nodes, thus 4 hops (n = 4);

delay of regular packets is 9.7 [s] when not synchronised;

delay of regular packets is 4.74 [s] when synchronised, approx.equal to ts + (n − 1) ∗ (ti + ts) + trx ;

delay of urgent packets is 220 [ms], approx. equal ton ∗ ts + trx .


IntroductionMiX-MAC



Energy consumption

MX-MAC WiseMACSync Non-Sync

Parameter E [J] D [s] E [J] D [s] E [J] D [s]

h (ti = 1.5[s])

1 1.59 0.065 12.73 0.76 2.53 0.132 1.50 1.63 9.76 2.91 2.57 0.873 1.49 3.21 9.37 6.10 2.60 1.524 1.54 4.91 9.00 10.63 2.61 2.285 1.45 6.34 8.80 13.54 2.61 5.15

ti (h = 4)

0.5 1.77 1.74 5.73 3.08 2.72 1.121.0 1.67 3.26 8.99 6.62 2.62 2.111.5 1.54 4.91 9.00 10.63 2.61 2.282.0 1.31 6.26 9.10 13.98 2.59 2.92


IntroductionMiX-MAC



Intro

use Tmote Sky board;

use 5 boards to have 4 hops (h = 4) in linear topology;

Matlab collects info about packets due to delicatetime-stamping ops;

nodes can hear each other;

due to synchro, nodes don’t compete for the medium at thesame time (if only one line !);


IntroductionMiX-MAC



Intro

results obtained from another mote in RX mode;

time-stamping op is a delicate task in time-sensitive MX-MAC;

– not able to display individual channel probe;

– tests are not done with other tasks running;

cannot show the energy consumption of the implementationusing the motes only;

ADC is noisy so is deactivated;

– in real ops, there are noisy components working.


IntroductionMiX-MAC



Result for regular packets

motes synchronise after the predicted number of packets;

regular packet delay is 4.5 [s] (approx. predicted);


IntroductionMiX-MAC



Result for urgent packets

urgent packets delay is between 172 [ms] and 766 [ms];

hard to measure due to slow link between RX mote and PC;

simulation was less accurate than for regular packets.


IntroductionMiX-MAC


1 Introduction

2 MiX-MAC


4 Conclusion


IntroductionMiX-MAC


Synchro + MiX-MAC

MiX-MAC : up to 30% of increased lifetime;

Synchro : reduce packet delivery by up to 50%;

Synchro : decrease energy consumption by 18%.


IntroductionMiX-MAC


Questions

Thank you for listening !

Questions ?


Documents

Real Time Network : Schedule Adaptation of Low-Power ...lamspeople.epfl.ch/decotignie/Midterm10-Mobile.pdfIntroduction MiX-MAC Node synchronisation along a path Conclusion Real Time