May 2005

CH Yeh, Queen's University

Slide 1

doc.: IEEE 802.11-05/0461r1

Submission

Ad Hoc/Sensor Networking and Multihop WLANs

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Date: 2005-05-18

Name Company Address Phone email Chi-Hsiang Yeh Queen’s

University Dept. of Electrical and Computer Eng., Queen’s University, Kingston, ON K7L 3N6, Canada

1-613-542-2353

yeh@ee.queensu.ca

Authors:

May 2005

CH Yeh, Queen's University

Slide 2

doc.: IEEE 802.11-05/0461r1

Submission

Abstract

This talk presents problems that will be introduced when current MAC protocols are applied to multihop networking, including mobile ad hoc networks, sensor networks, and multihop WLANs. We point out the issues to be addressed, current status for research and development, and incentives for investigating multihop networking.

May 2005

CH Yeh, Queen's University

Slide 3

doc.: IEEE 802.11-05/0461r1

Submission

Examples for Multihop Networks

• Ad hoc networks (MANET)

• Sensor networks

• Mesh networks

• Home networks with repeaters

• Multihop WLANs

• Others: Multihop cellular networks

May 2005

CH Yeh, Queen's University

Slide 4

doc.: IEEE 802.11-05/0461r1

Submission

Mobile Ad Hoc Networks

• Mobile stations communicate with each other directly

• Absence of any predefined infrastructure

• High mobility possible

• Every node acts as a router

Wireless Link

Node

May 2005

CH Yeh, Queen's University

Slide 5

doc.: IEEE 802.11-05/0461r1

Submission

Wireless Sensor Networks

• Large number of small devices

• Static stations communicate with each other directly

• Sinks for gathering data

• Every relay node acts as a router

Sink

Sink

May 2005

CH Yeh, Queen's University

Slide 6

doc.: IEEE 802.11-05/0461r1

Submission

Home Networks

• Intelligent appliances (AIs) communicate with access point (AP) directly or through a repeater

• IEEE 802.11 or ultrawideband (UWB) may be used

AP

Repeater

IA

IA

AI

AI

May 2005

CH Yeh, Queen's University

Slide 7

doc.: IEEE 802.11-05/0461r1

Submission

Mesh Networking

• Mesh points (MPs) communicate with each other wirelessly

• Only some of the access points have wired connections to the Internet

• Every node also acts as a router

AP

MP MP

MP

MP MP

MP

May 2005

CH Yeh, Queen's University

Slide 8

doc.: IEEE 802.11-05/0461r1

Submission

Multihop WLANs

• Combining ad hoc networks and wireless LANs

• Mobile stations communicate with each other directly

• Packets are routed to APs to access the Internet

• Each participating node also acts as a router

May 2005

CH Yeh, Queen's University

Slide 9

doc.: IEEE 802.11-05/0461r1

Submission

Ad Hoc Cellular Networks

• Combining ad hoc networks and cellular networks

• Mobile stations communicate with each other directly

• Packets are routed to APs to access the Internet

• Each participating node also acts as a router

May 2005

CH Yeh, Queen's University

Slide 10

doc.: IEEE 802.11-05/0461r1

Submission

Advantages for Multihop Networking

• Ad hoc networks– Infrastructureless

• Sensor networks– Great commercial values

• WLAN Mesh– Range extension with lower infrastructure cost

• Multihop WLAN/cellular networks– Range extension without additional infrastructure– Dead zone elimination/mitigation– Lower power consumption– Higher speed (due to shorter distance)– Lower interference and better spatial reuse– Higher throughput (potentially)

May 2005

CH Yeh, Queen's University

Slide 11

doc.: IEEE 802.11-05/0461r1

Submission

Why Commercial Ad Hoc Networking Has Not Happened

• Routing protocols were not standardized till 2004• The number of laptop computers did not reach a

critical mass• Lack of killer applications

– E.g., ad hoc networking in conference venues is replaced by WLAN coverage

• Poor performance (in ad hoc networking environments) based on current products

• Low throughput due to relaying• Some problems not solved• Difficult configuration

May 2005

CH Yeh, Queen's University

Slide 12

doc.: IEEE 802.11-05/0461r1

Submission

New Driving Forces for Multihop Networking

• VOIP over WLAN– 802.11 becoming available on smart phones

• Reaching critical mass

• Extended range beneficial for WLAN access

• Energy efficiency is critical

• Proliferation of 802.11 hot spots– Range extension = making more money

– Feasible with higher speeds and advanced technology

• Muni/national WiFi to be deployed– Range extension = infrastructure cost reduction

• Extending 802.11 to sensor networking– Huge market

May 2005

CH Yeh, Queen's University

Slide 13

doc.: IEEE 802.11-05/0461r1

Submission

Problems with Current WLAN MAC in Multihop Networking Environments

• High collision rate• TCP and 802.11 in multihop networking environments• Interference problems

– Interference-range hidden/exposed terminal problem– Additive interference problem

• Problems associated with power control– Heterogeneous hidden/exposed terminal problem– Single-channel MAC difficult

• QoS and fairness problems– Alternate blocking problems

• Fairness problems• Exposed terminal problem

May 2005

CH Yeh, Queen's University

Slide 14

doc.: IEEE 802.11-05/0461r1

Submission

Interference-range Hidden/Exposed Terminal Problem

• The interference range is typically larger than that of transmission range

• A potential transmitter D that cannot be reached by the CTS message of B may send a packet and collide with B’s reception

A BAB

D

A

D

E

B

(a) (b) (c)

RTSCTS Data

DRTS

May 2005

CH Yeh, Queen's University

Slide 15

doc.: IEEE 802.11-05/0461r1

Submission

Additive Interference Problem

• A receiver is outside the interference radius of any other transmitters (except for its own transmitter), but the sum of nearby interference collide the reception anyway

• Relatively difficult to solve

May 2005

CH Yeh, Queen's University

Slide 16

doc.: IEEE 802.11-05/0461r1

Submission

Heterogeneous Terminal Problem

A

B

CTS

C

DE

F

G

H

May 2005

CH Yeh, Queen's University

Slide 17

doc.: IEEE 802.11-05/0461r1

Submission

Alternate Blocking Problem

D E

CTS

BAC

TSC

May 2005

CH Yeh, Queen's University

Slide 18

doc.: IEEE 802.11-05/0461r1

Submission

Exposed Terminal Problem

(b) (a)

BA

Dat

a

C D

CTS

CA

Data

DB

CTS

May 2005

CH Yeh, Queen's University

Slide 19

doc.: IEEE 802.11-05/0461r1

Submission

Issues Needed to Be Addressed

• Resolving/mitigating aforementioned problems

• Routing

• Mobility

• Energy efficiency

• Security, privacy, and reliability

• Incorporating emerging technologies

• Applicability to sensor networks

• Cooperation from users

• Billing and Business model

May 2005

CH Yeh, Queen's University

Slide 20

doc.: IEEE 802.11-05/0461r1

Submission

Distinction from TGs

• TGs focus on the following context:– Residential networks– Office networks– Campus/public networks– Safety/military networks

• Mesh points are different from laptops/smart phones– Infrastructure– Power supply available– Stationary in nature– Single-hop networking from mobile stations (users) to mesh points

• Likely TGs outcome– Up to 32 nodes only– Most likely infrastructure mode– Not changed for mobile stations (general users)– minimum changes to current MAC protocol

May 2005

CH Yeh, Queen's University

Slide 21

doc.: IEEE 802.11-05/0461r1

Submission

Distinction from TG5

• Current TG5 proposals– Synchronized MAC

– Hierarchical architecture

– Lower mobility

– Smaller range

– Relatively lower speed

– Not applicable to 802.11 PHY

May 2005

CH Yeh, Queen's University

Slide 22

doc.: IEEE 802.11-05/0461r1

Submission

Current Status in Research and Development

• Four experimental routing protocol RFCs standardized by IETF in 2004

• Numerous ad hoc network testbeds in universities• Some commercial products based on AODV• Intensively researched in academia and industry

– Military applications for about 3-4 decades– Renewed interests for about 1 decade– Mainly focused on routing– Problems well known– Interesting techniques and solutions

• but some may be complex or even infeasible

May 2005

CH Yeh, Queen's University

Slide 23

doc.: IEEE 802.11-05/0461r1

Submission

Concluding Remarks

• Everything will be ad hoc in the future

• Multihop networking will be a norm, rather than an exception

• Time to look into multihop networking issues

• Emerging technologies should be incorporated

May 2005

CH Yeh, Queen's University

Slide 24

doc.: IEEE 802.11-05/0461r1

Submission

References

• Sadeghi, B., IEEE 802.11-05/0065r0.

• Yeh, C.-H., “The advance access mechanism for differentiated service, power control, and radio efficiency in ad hoc MAC protocols,” Proc. IEEE VTC’03F, 2003.