MAX

1
MAX

• Maximal Concurrency Scheduling for Wireless
  Networks with Regular Structure
• (Lots of animations. View in Slideshow Mode)
• Rahul Mangharam
• Dept. Electrical Computer Engineering
• Carnegie Mellon University
• rahulm_at_ece.cmu.edu
• 2005

2
Overview

• Why Wireless Mesh Networks?
• Why we need new protocols for multi-hop?
• CSMA does not work
• WisperNet Network Architectures
• Performance of WisperNet-based Networks
• Implementation Experiences

3
What this talk is about

• Wireless Mesh Networks
• Metro Nets - WiMAX 802.16 Backhaul Cost
• Multimedia Home Nets - WiFi UWB 802.11,
  802.15.3a Range
• Industrial Control Nets - ZigBee 802.15.4
  Flexible Topology
• The Multi-hop Link Scheduling Problem
• Uncoordinated Interference
• Network Scalability
• End-to-end QoS
• Deterministic Multi-hop Mesh Routing
• Solution The WisperNet Protocol Suite
• Near-optimal end-to-end throughput with
  deterministic delay

4
Why Multi-hop Wireless Mesh Networks?
Point-to-Multipoint Networks
Multi-hop Mesh Networks
54Mbps 32Mbps 12Mbps 6Mbps

• High Link Throughput
• Shorter hops ? 3dB SNR Gain
• No Line of Sight
• Pay-As-You-Grow No Infrastructure
• Network Heterogeneity

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The Multi-hop Wireless Problem
Packet 1
Packet 2
C
B
D
E
A
Packet 1

• Chain of Nodes Send 10MB file from A?E
• ? Uncoordinated Contention
• ? Per Packet Contention
• ? Unfairness

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Chain of Nodes CSMA End-to-End Performance
B
A
C
D
E

• Low Throughput Line Network
• End-to-End throughput is 10 the 2Mbps link
  data rate!

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CSMA It Gets Worse!

• Low Throughput 2D Grid Network
• End-to-end throughput is 4.2 the link data rate
  

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WisperNet - Maximal Concurrency Tiles
C
B
D
E
A
1
2
3
1
2
A B C D E

• 3-hop Concurrent Transmission Rule
• WisperNet TDMA Tiles for Networks with Regular
  Structure

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WisperNet Maximal Concurrent Transmission Tiles

• Regular Structures Uniform Degree
• Upper Bound of Performance
• WisperNet Tiles
• Symmetric and Periodic structures
• Optimality
• Locally Optimal Coloring are Globally Optimal
• Cardinality of Max. Concurrency Sets are same

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WisperNet Tiles and Tessellations
1 2 3
4 0 4 0
1 2 3 2
3 4 0
1 0 1 2
3 4 3
4 0 1 2

Transmission Time Slots
Time
DATA ACK 1 ACK 2 ACK 3 ACK 4
Format of single transmission
Assumption Interference range Communication
range (I C 1) Node Schedule s xi (2C
1)yi mod M s TDM slot number C
Communication Range (hops) M Tile Size (Node
degree (N) 1 )
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WisperNet Tiles and Tessellations
1 2 3
4 0 4 0
1 2 3 2
3 4 0
1 0 1 2
3 4 3
4 0 1 2

Temporal View
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WisperNet Tiles and Tessellations
Time Slot 0 1 2 3 4 Tile Position
Spatial View
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Generalized WisperNet

• Network Architectures for ANY Comm.
  Interference range
• Extend to various tile shapes and sizes
• Employ multiple channels
• Bandwidth Management Service
• Throttle bandwidth asymmetry
• Energy Management Service
• TDM-based look-ahead to minimize energy
  consumption
• Burst Data Service
• For low delay tolerance e.g. emergency services
• Routing
• Multiple path and with SuperNodes

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Generalized WisperNetCommunication
Range-Dominated Networks
Generalized for communication range C 1 and I
C N is the node degree
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Generalized WisperNetInterference
Range-Dominated Networks
2-Channel Frequencies
0 1 2 3 4
5 6 3 4 5 6
7 8 9 6 7 8
9 0 1 2 9 0
1 2 3 4 5 2
3 4 5 6 7
8 5 6 7 8 9
0 1 7 8 9 0
1 2 3
For C 1 and I gt C
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WisperNet Performance
Average Link Capacity in a Grid with Horizontal
Flows

• WisperNet outperforms CSMA by 5-8x
• WisperNet delivers deterministic end-to-end delay

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WisperNet Bandwidth Management
M5, L5

• Uplink1/5 Downlink4/5
  Uplink4/8 Downlink4/8
• By assigning 3 virtual neighbors, center nodes
  get 31 slots of 8 slots
• WisperNet Bandwidth Asymmetry control increases
  gateways uplink ratio from 20 to 50

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Will TDM work for Bursty Multimedia Traffic?

• WisperNet first resolves the MAC and then the
  Routing
• Each node has static allocations (e.g. 1/5, 4/5)
• We cannot do better for arbitrary routes with
  random birth-death lifetimes and source-sink
  locations
• To optimize routing further
• Flows will need to be spaced apart by 3-hops with
  no overlaps
• Sparse Networks may be optimized further (e.g.
  2-node case)
• WisperNet essentially provides a Deterministic
  Pipeline
• After the 1st packets delay, the flow throughput
  is constant (e.g. 1/5)

TDM lends itself Naturally to Multi-hop Wireless
Mesh Networks
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WisperNet Energy Management















Time

• 2-frame look-ahead energy efficient MAC

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K-Overlap Routing
Flow 1 Flow 2 Flow 4
Flow 3

• Routing of overlapping and non-overlapping flows
• WisperNet - 70 Average Network Utilization
• CSMA - 45 Theoretical Maximum Utilization

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Routing with SuperNodes
Fully-utilized node SuperNode with additional
capacity

• Overlapping flows cause route blocking
• SuperNodes prevent route blocking by 12

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Multiple-Path Routing
Fully-utilized node Partially utilized node

• Overlapping flows cause route blocking
• Multi-path flows prevent route blocking
• Network Utilization gt 94

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iON Intermittent On-demand NetworkFor Burst
Throughput
Gateway

• Multi-packet events (video snapshot) require
  instantaneous service
• iON facilitates instantaneous burst leases from
  leaf-node to gateway

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ImplementationDistributed Tile Replication
5

5 4 3 4
5 4
2 1 2 4
5 3 1 1
1 3 5
4 2 1 2 4
5 4
3 4 5
5

• Diffusion-based WisperNet Tile replication
  algorithm
• Simulator output in a grid with missing nodes
  (holes)

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Deployment 100-node ZigBee Network

• 100 nodes and 5 Gateways with a 1 year AA battery
  lifetime

• WisperNet Team
• Designed Hardware
• NanoRK - embedded sensor OS
• TDM Network Protocol

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Global Time SyncAM Carrier-Current Transmitter

• 5 uS Global Time Synchronization
• Out of Band Low Power AM Pulse
• Free Air Broadcast
• Carrier Current Broadcast for localized coverage
• Ultra Low Power Receiver
• lt 200 uA _at_ 3.3 volts

To electrical wall- socket
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Conclusion

• WisperNet Optimal MAC for Wireless Meshes with
  Regular Structure
• Outperforms CSMA-based protocols by 5-8x
• Network Services
• Bandwidth Management
• Energy Management
• Burst Throughput Service
• Implementation
• Distributed Tile Replication
• 100 node network being deployed

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