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S. Ganu, L. Raju, B. Anepu, S. Zhao, I. Seskar and D. Raychaudhuri

Rutgers, The State University of New Jersey

Architecture and Prototyping of an 802.11-based Self-Organizing Hierarchical Ad-Hoc Wireless Network (SOHAN)

PIMRC 2004, Barcelona

Sept 5-8, 2004

•Research supported by NSF NRT Grant #ANI0335244and by a grant from Cisco University Programs

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Introduction

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Introduction: Next Generation Wireless Network

Internet (IP-based)

Infostationcache

WLANAccess Point

WLANHot-Spot

VOIP(multi-mode)

Low-tier clusters(e.g. low power 802.11 sensor)

Ad-hocnetwork

extension

Public Switched Network(PSTN)

BTS

High-speed data & VOIP

Broadband Media cluster(e.g. UWB or MIMO)

BTS

BSC

MSC

CustomMobileInfrastructure(e.g. GSM, 3G)

CDMA, GSMor 3G radio access network

Generic mobile infrastructure

Today Future

GGSN,etc.

Voice(legacy)

High-speed data & VOIP

Relay node

Increasing role forad-hoc networks…

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Introduction: Flat vs. Hierarchical Ad-Hoc Nets� Hierarchical structure is essential, and helps to achieve:

� Scalability, i.e. improved max throughput and delay/QoS� Effective integration with 3G/4G, WLAN and Internet� Improved coverage & power consumption at subscriber radios

Wired Internet Infrastructure

Gateway node

Potential bottleneck

“Flat” mesh network with ad-hoc routing

End-user radios(with routing capability)

Wired Internet Infrastructure

BTS

BTS

AP

Forwarding node

End-user radios(no routing capability)

Multi-tieredInterfaces to

wired network

Wide Area Cell

3G cell

Hierarchical architecture with radio forwarding nodes and AP’s/BS’s

Ad-hoc associations

Ad-hoc associations

Microcell

Forwarding NodeExtended Coverage

Power & computinglimitations at low-tier nodes

Throughput per node scales ~ 1/sqrt(n)

Throughput per node can scale ~1 with right ratio of FN’s, AP’s

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Introduction: Hierarchical Ad-Hoc Net Capacity

320 kbps

77 kbps

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Packet rate (pkts/s)T

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HierFlat

0 10 20 300

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2

3

4

Packet rate (pkts/s)

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ay (s

imul

ated

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HierFlat

0 10 20 300

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0.2

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Packet rate (pkts/s)

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Reference: S. Zhao, I. Seskar and D. Raychaudhuri, "Performance and Scalability of Self-Organizing Hierarchical Ad Hoc Wireless Networks", Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC 2004), March 21-24, 2004, Atlanta

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Introduction: 3-tier ad-hoc hierarchy� Self-organizing hierarchical ad-hoc wireless network (SOHAN)

under consideration at WINLAB� Tier 1: low-tier mobile nodes, e.g. low-power PDA’s, sensors, etc. (MN)� Tier 2: forwarding nodes (FN) with multiple radio interfaces (UWB, WLAN,

cellular…)� Tier 3: wired base stations and access points (BS or AP)� Research on new protocols for: ad-hoc discovery, MAC and routing

InternetInternet

Forwarding node

low-tier (e.g. sensor) user nodes (MN)

Access Point

FN

AP

Wide-AreaCell

personal-area pico-cell

WLANmicro-cell

BTS

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Introduction: Application to WLAN Mesh� Hierarchical ad-hoc concept can be applied to extend coverage and QoS of

802.11 WLAN’s…� Useful for WLAN’s with coverage problems, home networks with QoS and/or coverage needs,

outdoor community networks, etc.� Some nodes (either network elements or terminals without power constraints) serve as FN’s� Requires extended discovery protocols (via beacons) and multi-hop routing� Optional upgrade of 802.11 MAC for efficient multihop operation

Wired Network InfrastructureWired Network Infrastructure

AP1 AP2802.11 Access to AP

Ad-hoc radio link(w/multi-hop routing

Mobile Node (MN)(end-user)

Ad-hoc accessTo FN

Self-organizingAd-hoc WLAN

Forwarding Node (FN)

Forwarding Node (FN)

Ad-hocInfrastructure

links

Supported by a grant fromCisco University Programs

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Hierarchical Ad-Hoc Network Protocols

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SOHAN Protocols: Components� Bootstrapping Mechanism

� Involves the configuration of the different devices in terms of channel assignments and initial transmit power level settings – for now, manual configurations using scripts

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� Filters links made available to the routing protocol based on desired objective function – reduces routing overhead

� Allows each node to apply a different objective depending on the role it plays

� Supports multi-channel operation of network

� Routing Mechanism� Uses the “logical” topology information presented by the discovery

mechanism in order to create and maintain local neighbor� Used to route data from the MN’s into the infrastructure network through

FN’s and AP’s

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SOHAN Protocols: Conceptual Overview

BTS A

AP1

FN1

FN2

FN3

FN4

AP2

AP3Wired Radio Access Network Infrastructure AP beacon(ID, frequency, power, ,bit-rate,service capabilities...)

FN beacon

BTS radiobeacon

BTS serviceadvertisement (into wired net)AP service

advertisement (into wired net)

End-user:seek (FN*, AP*)associate (FN1, AP2)routing update (FN1)routing update (AP2)send data

med-tier radio(e.g. 802.11x)

low-tier radio(e.g. 802.15.x)

Forwarding Node:seek (FN*, AP*)associate (FN3, AP3)routing update (FN3)routing update (AP3)forward data

Protocols needed:Ad-hoc discovery (enhanced beacons, etc.)Ad-hoc MACAd-hoc network routing (extended metrics including energy)handoff, QoS control, multicast (..features)

ad-hocwireless networkinfrastructure

may receiveBTS beaconfor wide-areaservice

laptop

sensor node

Access Point:Seek (AP*, BTS*)Associate (AP2, BTS A)handoff update (AP2)handoff update (BTS A)..forward data & handoff

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Low-tier access links(AP/FN Beacons, MN Associations, Data)

Ad-hoc infrastructure links between FNs and APs(AP/FN Beacons, FN Associations, Routing Exchanges, Data)

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SOHAN Protocols: Discovery Concepts� Creates efficient ad-hoc network topology just above MAC layer in

order to reduce burden on routing protocol…

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SOHAN Protocols: Topology DiscoveryDelay Constrained Energy Minimization:

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