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AN INTEGRATED ROUTING AND DISTRIBUTED SCHEDULING APPROACH FOR HYBRID IEEE 802.16E MESH NETWORKS FOR VEHICULAR BROADBAND COMMUNICATIONS

Rahul Amin

Electrical and Computer EngineeringClemson UniversityM.S Thesis Defense, 11/25/2008Advisor – Dr. Kuang-Ching Wang

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Outline

• Background and Relevant Work

• Objective

• Network Model

• Routing and Scheduling Solution

• Analytical Model and Simulation studies

• Conclusions and Future Work

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Background – WiMAX Operation Modes

• WiMAX – Worldwide Interoperability for Microwave Access– IEEE 802.16-2004– IEEE 802.16e-2005 (Mobile WiMAX) extends mobility (handover) support

• Point-to-Multipoint (PMP)– Subscriber Stations (SS) connect via Base Station (BS)– BS in charge of coming up with a transmission schedule– Five Classes of Service defined to support QoS

• Mesh– SSs and BSs can communicate directly to other SSs and BSs– Scheduling solution can be centralized or distributed– QoS differentiation is on packet-by-packet basis

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Background – PMP Mode Frame Structure

• Each frame divided into uplink and downlink sub-frame• Uplink-to-downlink ratio adjusted according to traffic demand • Sub-frame further divided into mini-slots to send data bursts

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Background – Mesh Mode Frame Structure

• Each frame divided into control and data sub-frame• No uplink or downlink sub-frame distinction• Control sub-frame length depends on length of the mesh

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Background – WiMAX Handover Support

• Standard Handover– Defined only for PMP mode in IEEE 802.16e-2005 – Each Mobile Station (MS) maintains an up-to-date CINR for

target BSs– Either BS or MS can initiate the handover procedure– MS decides the target BS

• Two optional fast handover methods– Macro-Diversity Handover (Soft Handover)– Fast Base Station Switching (Hard Handover)

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Background – Relevant Work

• WiMAX network architecture – Coverage: IEEE 802.16j workgroup (Relay Station Infrastructure)– Link-level performance: [Hartzog 2006]– Last mile Connectivity: [Bennett 2006], [Wongthavarawat 2003]– Mobile Ad Hoc Networks (MANET): [Sherman 2006], [Lebrun 2006]

• Scheduling schemes– PMP Mode: [Zhe 2007], [Jayaparvathy 2005], [Lera 2007], [Lin 2008]– Mesh Mode

• Centralized: [Wei 2005], [Chen 2006], [Qing 2006]• Distributed: [Cao 2007]

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Objective

• Challenge – WiMAX requires routing and scheduling packets for rapidly changing network topology due to fast moving vehicles

• Goals:– Develop Network Architecture– Routing and Scheduling solution– Throughput performance analysis

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MBS MSSMSS

MBS

MSS

MSS

MBS

MSS

MSS

MSS MBSMSS

Core Command Network

Tactical NetworkGateway

Tactical Network

MBS: Mesh BS

MSS: Mesh SS

MS

MBS MSSMSSMBSMBS MSSMSSMSSMSS

MBS

MSS

MSS

MBSMBS

MSSMSS

MSSMSS

MBS

MSS

MSS

MBSMBS

MSSMSS

MSSMSS

MSS MBSMSSMSSMSS MBSMBSMSSMSS

Core Command Network

Tactical NetworkGateway

Tactical Network

MBS: Mesh BS

MSS: Mesh SS

MS

MBS: Mesh BS

MSS: Mesh SS

MS

Network Model

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Network Model Components

• Routing– Mobility-Aware Intra-Gateway Routing (MAIGR)– Ad Hoc Routing Protocols and Mobile IP

• Scheduling– PMP mode: between MS and MBS/MSS– Mesh mode: among MSS and MBS

• Handover– Scheduling options migrate from current BS to target BS

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BS Protocol Architecture

• Base stations (MBS and MSS) support:– Dual radios (PMP mode, Mesh mode)– Routing: MAIGR

• MBS also supports:– Routing: IP and Mobile IP

Mesh BSMobile IP

Home/foreign agents

IP

MAIGR

PMPLINK + PHY

Mesh SS

MeshLINK + PHY

PMPLINK + PHY

MeshLINK + PHY

MAIGR

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MS Protocol Architecture

• Mobile Station (MS) supports:– Single radio (PMP mode)– Routing: IP– Transport layer protocols– Application specific protocols

MS

Application

IP

PMPLINK + PHY

Transport (TCP, UDP)

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Network OperationI. Base Station Setup

1. All MBSs use existing ad-hoc solutions to reach core network2. All MSSs find closest path to MBS using MAIGR’s mesh topology discovery phase3. All BSs (MSS and MBS) come up with initial mesh schedule using centralized mesh scheduler4. All BSs maintain Mesh Link Capacity for PMP scheduler using the initially derived mesh schedule5. All BSs use PMP scheduler to communicate with MS

II. Mobile Station Setup

6. MS sets up routes to transmit/receive traffic to/from MBS using MAIGR7. MS uses PMP scheduler to communicate with MSS/MBS

III. Operational Phase

8. Depending on PMP traffic load at each BS, Mesh scheduler at each BS adapts its schedule9. PMP scheduling options for a MS migrate to the target BS during the handover procedure10. Mobile IP used by MBSs to assign care-of address to MS that switches routing zones

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Base Station Route SetupI. Base Station Setup

1. All MBSs use existing ad-hoc solutions to reach core network2. All MSSs find closest path to MBS using MAIGR’s mesh topology discovery phase3. All BSs (MSS and MBS) come up with initial mesh schedule using centralized mesh scheduler4. All BSs maintain Mesh Link Capacity for PMP scheduler using the initially derived mesh schedule5. All BSs use PMP scheduler to communicate with MS

II. Mobile Station Setup

6. MS sets up routes to transmit/receive traffic to/from MBS using MAIGR7. MS uses PMP scheduler to communicate with MSS/MBS

III. Operational Phase

8. Depending on PMP traffic load at each BS, Mesh scheduler at each BS adapts its schedule9. PMP scheduling options for a MS migrate to the target BS during the handover procedure10. Mobile IP used by MBSs to assign care-of address to MS that switches routing zones

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Base Station Route Setup

MSSMBS

Zone 1 Zone 2

MSS MBSMSS MSS

Core Network

Core Network

MSSMS S MSS MSS

MSS: Mesh SSMBS: Mesh BS

MS: Mobile Station

Traditional Ad Hoc Routing Solutions

MSH_NCFG: Entry

MSH_NCFG: Entry

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Base Station Scheduler SetupI. Base Station Setup

1. All MBSs use existing ad-hoc solutions to reach core network2. All MSSs find closest path to MBS using MAIGR’s mesh topology discovery phase3. All BSs (MSS and MBS) come up with initial mesh schedule using centralized mesh scheduler4. All BSs maintain Mesh Link Capacity for PMP scheduler using the initially derived mesh schedule5. All BSs use PMP scheduler to communicate with MS

II. Mobile Station Setup

6. MS sets up routes to transmit/receive traffic to/from MBS using MAIGR7. MS uses PMP scheduler to communicate with MSS/MBS

III. Operational Phase

8. Depending on PMP traffic load at each BS, Mesh scheduler at each BS adapts its schedule9. PMP scheduling options for a MS migrate to the target BS during the handover procedure10. Mobile IP used by MBSs to assign care-of address to MS that switches routing zones

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Base Station Scheduler Setup

Core Network

Core Network

MSSMBS MSSMSSMS SMS S MSS

MSH_CSCH: Request

MSH_CSCH: Request

MSS: Mesh SSMBS: Mesh BS

MS: Mobile Station

MSH_CSCH: Grant

x 2x 3x 3x 2x x

x x x x x x

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Centralized Mesh Scheduling Solution

• Interference-aware solution achieving near-optimal throughput [Wei 2005, VTC]– Procedure:

• Transmission occurs in order of highest transmission demand • Non-interfering links transmit simultaneously

– Proposed changes:• QoS considered

– Constraints: • Unidirectional traffic considered

MSSMBS MSSMSSMS SMS S MSSx 2x 3x 3x 2x x

Carrier Sense Range: 1

Tx RxTxRx

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Mobile Station SetupI. Base Station Setup

1. All MBSs use existing ad-hoc solutions to reach core network2. All MSSs find closest path to MBS using MAIGR’s mesh topology discovery phase3. All BSs (MSS and MBS) come up with initial mesh schedule using centralized mesh scheduler4. All BSs maintain Mesh Link Capacity for PMP scheduler using the initially derived mesh schedule5. All BSs use PMP scheduler to communicate with MS

II. Mobile Station Setup

6. MS sets up routes to transmit/receive traffic to/from MBS using MAIGR7. MS uses PMP scheduler to communicate with MSS/MBS

III. Operational Phase

8. Depending on PMP traffic load at each BS, Mesh scheduler at each BS adapts its schedule9. PMP scheduling options for a MS migrate to the target BS during the handover procedure10. Mobile IP used by MBSs to assign care-of address to MS that switches routing zones

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Mobile Station Setup

Core Network

Core Network

MSSMBS MSSMSSMS SMS S MSS

MSS: Mesh SSMBS: Mesh BS

MS: Mobile Station

x 2x 3x 3x 2x x

x x x x x x

DHCP REQ

DHCP REP

Service Flow: REQService Flow: REP

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Operational Phase Scheduler InteractionI. Base Station Setup

1. All MBSs use existing ad-hoc solutions to reach core network2. All MSSs find closest path to MBS using MAIGR’s mesh topology discovery phase3. All BSs (MSS and MBS) come up with initial mesh schedule using centralized mesh scheduler4. All BSs maintain Mesh Link Capacity for PMP scheduler using the initially derived mesh schedule5. All BSs use PMP scheduler to communicate with MS

II. Mobile Station Setup

6. MS sets up routes to transmit/receive traffic to/from MBS using MAIGR7. MS uses PMP scheduler to communicate with MSS/MBS

III. Operational Phase

8. Depending on PMP traffic load at each BS, Mesh scheduler at each BS adapts its schedule9. PMP scheduling options for a MS migrate to the target BS during the handover procedure10. Mobile IP used by MBSs to assign care-of address to MS that switches routing zones

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PMP Mode Scheduler

UGS ertPS rtPS nrtPS BE

Enough Free SlotsAvailable?

New Flow Requests

Active Connection Queue

Mesh link limitation?

Reject Flow

Yes

Yes

No

No

Pending Connection Queue

Pending Connection Queue Empty?

Yes

No Queue Size >

Threshold?

Yes

PMP Scheduler

Distributed Adaptation

CentralizedScheduling

Mesh Scheduler

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Mesh Scheduler Distributed Adaptation (General Case)

MS S MSSMBS MSSMSSMS S MSSx 2x 3x 3x 2x x

MS S MSSMBS MSSMSSMS S MSS 0 2x 3x 3x 2x x

x x x x x x

2x 0 x x x x

– Up to x slots can be borrowed in general

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Mesh Scheduler Distributed Adaptation(Upper Bound)

• Case I:– Borrowing occurs from MSS away from MBS– 2x slots can be borrowed as an upper bound

MS S MSSMBS MSSMSSMS S MSSx 2x 3x 3x 2x x

MS S MSSMBS MSSMSSMS S MSS0 3x 3x 3x 2x x

x x x x x x

3x0 0 x x x

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Mesh Scheduler Distributed Adaptation(Upper Bound)

• Case II:– Borrowing occurs from MSS closer to MBS– x/2 slots can be borrowed as upper bound

MS S MSSMBS MSSMSSMS S MSSx 2x 3x 3x 2x x

MS S MSSMBS MSSMSSMS S MSS1.5x 1.5x 3x 3x 2x x

x x x x x x

1.5x 0 x x x x

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Operational Phase Handover ScenarioI. Base Station Setup

1. All MBSs use existing ad-hoc solutions to reach core network2. All MSSs find closest path to MBS using MAIGR’s mesh topology discovery phase3. All BSs (MSS and MBS) come up with initial mesh schedule using centralized mesh scheduler4. All BSs maintain Mesh Link Capacity for PMP scheduler using the initially derived mesh schedule5. All BSs use PMP scheduler to communicate with MS

II. Mobile Station Setup

6. MS sets up routes to transmit/receive traffic to/from MBS using MAIGR7. MS uses PMP scheduler to communicate with MSS/MBS

III. Operational Phase

8. Depending on PMP traffic load at each BS, Mesh scheduler at each BS adapts its schedule9. PMP scheduling options for a MS migrate to the target BS during the handover procedure10. Mobile IP used by MBSs to assign care-of address to MS that switches routing zones

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Operation Phase Handover Scenario

MSSMBS

Zone 1 Zone 2

MSS MBSMSS

MS

MSS

TacticalNetwork Gateway

TacticalNetwork Gateway

MSSMS S MSS MSS

MSS: Mesh SSMBS: Mesh BS

MS: Mobile Station

HO_IND Msg

Care-of Address

Mobile IP Msg

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Analytical Model

• Throughput Comparisona) centralized only mesh scheduling algorithmb) centralized with distributed adaptation algorithm

• Topology considered– Symmetric Chain Topology – Single Intersection Topology

• Throughput bounds derived for– Dense Network– Sparse Network

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Percentage Increase in Network Throughput per Routing Zone (Dense Network)

MBSMSS1’

MSS1

MSS2’

MSS2

MSS3

MSS3’

Link 1 Link 2 Link 3Link 1’Link 2’Link 3’

x 2x 3x 3x 2x x

Case I:

Case II:

x – q3’

Parameter Description

qi Number of unused PMP data slots at base station i

z Total number of data slots per Mesh Frame

n+n’ Total number of MSS in routing zone

k Borrowing MSS’s # of hops from MBS

x – q2’ x – q1’ x – q2x – q1 x – q3

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Percentage Increase in Network Throughput per Routing Zone (Sparse Network)

MBSMSS1’

MSS1

MSS2’

MSS2

MSS3

MSS3’

Link 1 Link 2 Link 3Link 1’Link 2’Link 3’

x 2x 3x 3x 2x x

0

Case I:

Case II:

Parameter Description

qi Number of unused PMP data slots at base station i

x PMP data slots per frame at Lender

k Borrowing MSS’s # of hops from MBS

x-q2’ 0 0 0 0

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Simulation Studies

• Network Simulator ns-2 used– Based on NIST IEEE 802.16 module (version pre-release2)

• Supports PMP mode, standard handover• Scheduler functionality added• Extension made to support:

– TDD mesh links between base stations (emulated with wired links)– Dual radios at each base station

– Chain topology presented

– Carrier sensing range equal to communication range assumed

– Analytical Model verified using simulation results

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Mesh Mode Simulation ParametersParameter Value

Channel Bandwidth 10 MHzModulation Scheme OFDM_64QAM_3_4

Bits/Symbol 856Symbol/Slot 1

Frame Duration 10 msSlots/Frame 221

Control Sub-Frame 7 * MSH_CTRL_LEN = 49Data Sub-Frame 221 – (7 * MSH_CTRL_LEN) = 172

Pending Queue Threshold 0Communication Range 1Carrier Sensing Range 1

Maximum Routing Zone Rate 18.91 Mbps (14.72 Mbps for Data)

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Simulation Model – Dense NetworkInternet Sink

Tactical Network Gateway

MBSMSS2

MSS3

MSS1

MSS4

MSS5

MSS0

28 56 84 84 56 28

MS

MS

MS MS MS MS MS MSMS

.

.

2 * 0.64 Mbps UGS Flows per MS (16 Data Slots)

28-12 28-12 28-12 28-12 28-12 28-1228-4

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Simulation Results – Dense Network (Stationary)

Centralized Scheduling Only

Distributed Adaptation Scheduling

Centralized Distributed

Throughput (Mbps) 8.27 (13 flows) 8.95 (14 flows)

Pending Flows 0/1/3/5/7 0/0/2/4/6

1 2 3 4 50

1

2

3

4

5

6

7

8

9

Throughput (Mbps)

Pending Flows

Group Size (Number of MS)

1 2 3 4 50

1

2

3

4

5

6

7

8

9

Throughput(Mbps)

Pending Flows

Group Size (Number of MS)

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Simulation Model – Sparse Network

Internet Sink

Tactical Network Gateway

MBSMSS2

MSS3

MSS1

MSS4

MSS5

MSS0

MS

MS

MS

MS

MS

28 56 84 84 56 28

1 * 0.64 Mbps UGS Flow per MS (8 Data Slots)

28-4 0 0 0 0 0

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Simulation Model – Sparse Network

Internet Sink

Tactical Network Gateway

MBSMSS2

MSS3

MSS1

MSS4

MSS5

MSS0

MS

MS

MS

28 56 84 84 56 28

1 * 0.64 Mbps UGS Flow per MS (8 Data Slots)

.

.

.

28-40 0 0 0 0

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Simulation Results – Sparse Network (Stationary)

Centralized Throughput

(Mbps)

Distributed Throughput

(Mbps)

% Increase

5 MSs 1.92 (3 flows) 3.19 (5 flows) 66

10 MSs 1.92 (3 flows) 6.38 (10 flows) 232

5 MSs 10 MSs0

1

2

3

4

5

6

7

Centralized OnlyDistributed Adaptation

Th

rou

gh

pu

t (M

bp

s)

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Conclusions

• The network architecture simplifies scheduling re-computation by only involving base-stations as opposed to a complete ad-hoc solution

• Distributed adaptation does not increase the throughput

significantly under dense network conditions (~8.2 %) due to the inability of neighboring BSs to lend slots

• Distributed adaptation increases throughput significantly under sparse network conditions (~ 232 %)

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Future Work

• Different topologies such as grid topology need to be studied

• Borrowing from 1-hop neighbor only is not optimal and studies needs to be expanded to determine the performance improvement if borrowing from multi-hop neighbors is allowed

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Thank You

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Backup - Routing Partitions

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Mobility-Aware Intra-Gateway Routing

• Mesh Topology discovery– Each Mesh BS sends a flooding message at periodic intervals– Each Mesh SS records the next hop towards the closest Mesh BS

• Packet Forwarding from Mesh BS to MS– At serving BS, the next hop is the connection identifier (CID) of MS’s data

connection established during network entry or handover– At non-serving BS, the next hop is a mesh link CID which is obtained in one

of two ways• When receiving a packet from neighboring BS forwarded by an unknown MS,

record the neighboring BS as next hop to the unknown MS • When notified of a handover of currently associated MS, record target BS as

next hop to MS• Packet Forwarding from MS to Mesh BS

– At MS, the next hop is always the CID of currently serving BS’s data connection– At subsequent Mesh SS’s, the next hop is the mesh link CID towards the closest

Mesh BS obtained during Mesh Topology discovery phase

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Scheduling Solution• PMP Mode Scheduling

– Order determined according to service classes (UGS, ertPS, rtPS, nrtPS, BE)– Same service classes are serviced in FIFO order

• Mesh Mode Scheduling– Centralized interference-aware solution

• Transmission occurs in order of highest transmission demand [Wei]– Distributed Adaptation

• Need-based borrowing

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Mesh Mode Scheduler• Initial schedule using centralized algorithm

– Upon network deployment– Every time BS is added to the mesh– Uses average traffic load information if available, else

assumes uniform traffic distribution

• Distributed adaptation copes with changes in traffic loads– Whenever pending queue length exceeds predefined

threshold– Slots borrowed from immediate (1-hop) neighbors– Three-way handshake technique used

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Distributed Adaptation

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Centralized Algorithm