Adaptive Medium Access Control (MAC) for Heterogeneous Mobile Wireless Sensor Networks (WSNs).

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2007

Adaptive Medium Access Control

(MAC) for Heterogeneous Mobile

Wireless Sensor Networks

(WSNs).

Giorgio Corbellini

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2007

Challenges of the Ph.D.

Study of “urgency” in sensed data

Study of mobility in WSNs

Definition of heterogeneity-awareness

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Adaptability in WSN

An adaptive MAC protocol is able to

modify in real time some of its

parameters with the scope of matching

some network requirements.

Several existing MAC protocols for

WSN can adapt themselves, but they

are adaptive to what?

Energy-adaptive,

Mobility-adaptive..

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Adaptability in WSN

Different perspective, the MAC

protocol must be:

Reactive to the evolving heterogeneity state of

the network,

Able to auto-configure the network for the new

state.

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Heterogeneity in WSN

WSNs are heterogeneous by nature.

Some examples:

Heterogeneity of sources of information;

Heterogeneity of applications;

Heterogeneity of mobility of nodes;

Heterogeneity of quantity and frequency of information

provided

Heterogeneity of urgency of the information provided

Energy heterogeneity (battery level of nodes,

line-powered nodes )

Computational heterogeneity of nodes (type of nodes,

density per area)

Link heterogeneity (some nodes have long-distance

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WSN limitations

Most of the times nodes of a WSN have not direct connection with

line-power and take energy from batteries. Provided that recharging

batteries is often not an option, battery life duration is the main

limitation of WSN.

Consume of energy must be optimized while wastages must be

minimized.

Sources of energy consumption are:

Processing part (CPU),

The wireless interface (radio) that consumes energy.

Major sources of Energy wastage are:

Idle listening - waste of energy in keeping the radio on when it is not necessary

Collisions - waste of energy when two packets collide

Overhearing - waste of energy in receiving a packet destined to another node

Protocol overhead - MAC headers and excessive control messages are

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Medium Access Control

The Medium Access Control (MAC) layer sits

directly on top of the physical layer and controls

the radio (when to send a packet and when to

listen for a packet).

Unlike from other wireless technologies in which

QoS constraints are considered in MAC

protocols, MAC protocols for WSNs are mainly

focused on energy efficiency.

Indeed, most of the protocol propositions in the

literature neglect aspects as:

fairness between nodes,

latency of data,

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Medium Access Control

Access to the medium can be:

Centralized: a base-station manages the access.

Distributed: the access is granted by an accessing rule shared by

nodes

Centralized access:

No collisions

Simple to implement

Most of the complexity load is charged by the base-station

Distributed access:

Necessary when network size is great.

Both techniques can be adopted in WSN but most

of the MAC protocols in the literature use

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Medium Access Control

Both centralized and distributed MAC

protocols for WSN can further be

classified according to the wireless

access scheme in:

Schedule-base protocols,

Contention-based protocols,

Hybrid-protocols.

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Schedule-based protocols

In such protocols a schedule exists, regulating

which node may use which resource at which time.

Schedule can be fixed or variable

Advantages:

Collision-free protocols

No idle listening or overhearing

Weaknesses:

Low scalability,

Complex to manage in very populated networks because time

synchronization is needed

Examples:

TDMA, FDMA

TRAMA[2]

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Contention-based protocols

In contention-based protocols nodes that want to transmit

compete each other for accessing the media.

Advantages:

Simple to setup,

No synchronization needed,

Very scalable.

Weaknesses:

Probability of packets collisions is always not null,

Main sources of energy wastage (collisions, idle listening) must be

addressed.

Examples:

MACAW[4]

S-MAC[5], T-MAC[6]

Preamble sampling[7], LPL[8], B-MAC[9]

PAMAS[10]

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Hybrid protocols

Hybrid approaches combine random access

methods with frame-based scheduling.

Advantages:

Flexibility to adapt to traffic fluctuations.

Weaknesses:

The use of slotting concentrate most of the connection

attempts to the beginning of slots.

Examples:

Z-MAC[11],

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Mobility

Different levels of mobility

Static network

Mobile sensors with immobile sink(s)

Mobile sensors with mobile sink(s)

Mobile sink(s) with immobile sensors

Different types fo mobility

Passive mobility

Active mobility

Effective mobility models for WSN are needed

Examples

A doctor that walks inside the hospital

Herding and wildlife monitoring

Mobility models for WSNs will be addressed during an Internship at

CEA/LETI starting in February/March 2009.

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Sensor-MAC (S-MAC)[5]

Advantages:

idle listening is reduced by cycling sleep/wakeup

periods

Use of virtual clusters

Use of in-channel signaling

Weaknesses:

Does not guarantee high throughput

Latency is increased because of Sleep/wakeup

cycles

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Sensor-MAC (S-MAC)

MACA’s idle listening is particularly unsuitable if average data rate is

low

Most of the time, nothing happens

Idea: Switch nodes off, ensure that neighboring nodes turn on

simultaneously to allow packet exchange (rendez-vous)

Only in these active periods,

packet exchanges happen

Need to also exchange wakeup

schedule between neighbors

When awake, essentially perform

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References

[1]“The MAC Alphabet Soup.” URL:

http://www.st.ewi.tudelft.nl/~koen/MACsoup/

[2]V. Rajendran, K. Obraczka, et J.J. Garcia-Luna-Aceves, “Energy-efficient collision-free

medium access control for wireless sensor networks,” Proceedings of the 1st international

conference on Embedded networked sensor systems, Los Angeles, California, USA:

ACM, 2003, pp. 181-192.

[3] W. Heinzelman, A. Chandrakasan, et H. Balakrishnan, “Energy-efficient

communication protocol for wireless microsensor networks,” System Sciences, 2000.

Proceedings of the 33rd Annual Hawaii International Conference on, 2000, p. 10 pp.

vol.2.

[4]V. Bharghavan, A. Demers, S. Shenker, et L. Zhang, “MACAW: a media access

protocol for wireless LAN's,” Proceedings of the conference on Communications

architectures, protocols and applications, London, United Kingdom: ACM, 1994, pp.

212-225.

[5] Wei Ye, J. Heidemann, et D. Estrin, “An energy-efficient MAC protocol for wireless

sensor networks,” INFOCOM 2002. Twenty-First Annual Joint Conference of the IEEE

Computer and Communications Societies. Proceedings. IEEE, 2002, pp. 1567-1576

vol.3.

[6]T.V. Dam et K. Langendoen, “An adaptive energy-efficient MAC protocol for wireless

sensor networks,” Proceedings of the 1st international conference on Embedded

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References

[7]A. El-Hoiydi, “Aloha with preamble sampling for sporadic traffic in ad hoc wireless

sensor networks,” Communications, 2002. ICC 2002. IEEE International Conference on,

2002, pp. 3418-3423 vol.5.

[8]W. Ye, F. Silva, et J. Heidemann, “Ultra-low duty cycle MAC with scheduled channel

polling,” Proceedings of the 4th international conference on Embedded networked sensor

systems, Boulder, Colorado, USA: ACM, 2006, pp. 321-334.

[9]J. Polastre, J. Hill, et D. Culler, “Versatile low power media access for wireless sensor

networks,” Proceedings of the 2nd international conference on Embedded networked

sensor systems, Baltimore, MD, USA: ACM, 2004, pp. 95-107.

[10] S. Singh et C.S. Raghavendra, “PAMAS - power aware multi-access protocol with

signalling for ad hoc networks,” SIGCOMM Comput. Commun. Rev., vol. 28, 1998, pp.

5-26.

[11]Injong Rhee, A. Warrier, M. Aia, Jeongki Min, et M. Sichitiu, “Z-MAC: A Hybrid MAC

for Wireless Sensor Networks,” Networking, IEEE/ACM Transactions on, vol. 16, 2008, p.

511-524.

[12]G. Halkes et K. Langendoen, “Crankshaft: An Energy-. Efficient MAC-Protocol For