Topology Formation and Public Policy

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Topology Formation andPublic Policy

• Jeff Pang
• 15-848E

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Topology Formation Overview

• Principles and Protocols for Power Control in Ad
  Hoc Networks, V. Kawadia and P. R. Kumar, IEEE
  Journal on Selected Areas in Communications.
• Vikas Kawadia and P. R. Kumar, A Cautionary
  Perspective on Cross Layer Design.'' To appear in
  IEEE Wireless Communication Magazine.
• Roger Wattenhofer, Li Erran Li, Victor Bahl and
  Yi-Min Wang, Distributed Topology Control for
  Power Efficient Operation in Multihop Wireless Ad
  Hoc Networks. Proc. of IEEE INFOCOM, pages
  1388-1397, April 2001
• Ning Li and Jennifer C. Hou, Topology control in
  heterogeneous wireless networks problems and
  solutions, in Proc. of IEEE INFOCOM 2004, March,
  2004.

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Power Control
1mW
4 mW
1 mW
4mW
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Power Control Cross-Layer Design Issues

• Physical Layer
• Power control affects quality of signal
• Link Layer
• Power control affects number of clients sharing
  channel
• Network Layer
• Power control affects topology/routing
• Transport Layer
• Power control changes interference, which causes
  congestion
• Application/OS Layer
• Power control affects energy consumption

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Cross Layer Design ExampleRate Adaptive MAC

• 802.11 MAC adapts rate to minimize errors
• DSDV routes using shortest hop-count paths
• Uses lowest rate to determine links
• short paths can have less bandwidth than longer
  paths!

4Mbps
1Mbps
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Cross Layer Design ExampleRate Adaptive MAC
Plain
Adaptive
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Cross Layer Design ExampleTopology Control

• Goal choose node degree to maximize end-to-end
  throughput
• Set transmit power to achieve target-degree
• Short time-scale
• Modify target-degree to increase end-to-end
  throughput
• i.e., try to follow gradient to a maxima
• Long time-scale
• Problem can cause oscillations
• Topology can oscillate between connected and
  disconnected states

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Cross Layer Design ExampleTopology Control
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Topology Control Protocols

• Kawadia and Kumar
• COMPOW
• CLUSTERPOW
• Tunneled CLUSTERPOW
• MINPOW
• Wattenhofer, et al.
• Angle-based
• Li and Hou
• Directed Relative Neighbor Graph (DRNG)
• Directed Local Minimum Spanning Tree (DLMST)

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COMPOW

• Everyone transmits at same power
• Find minimum power s.t. topology remains
  connected
• Pros
• Ensures all links bidirectional
• Allows higher layers to work properly
• Cons
• Single outlying node causes high-power

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CLUSTERPOW

• Run a separate routing protocol at each power
  level pi
• Route packets using routing table at minimum pi
  where destination is present
• Pros
• Clustering is distributed
• Any base routing protocol works
• Routing is loop-free (power levels monotonically
  decrease)
• Cons
• Routing overhead (one per power-level)
• Cant use initial lower-power hops

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CLUSTERPOW
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Tunneled CLUSTERPOW

• Recursively lookup path to next hop
• e.g., if D is reachable through N1, search for
  min-power route to N1, etc.

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Tunneled CLUSTERPOW

• Simple recursion is not loop-free

• Solution Tunnel packet to intermediate hop

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MINPOW

• Goal Route using min-energy route
• Energy cost of using a link at power level p
• PTotal(p) PTx PTxRad(p) PRx
• Topology
• Graph is union of topology at all power levels
• Link-cost minreachable-p(PTotal(p))
• Run DSDV (Bellman-Ford) on resulting graph
• Pros
• Globally optimal in terms of energy consumption
• Loop-free (just DSDV)
• Cons
• Not optimal for capacity (but close if PTxRad(p)
  dominates)
• Does not take into account interference! (i.e.,
  retransmits)

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COMPOW/CLUSTERPOWThroughput vs. Delay
(clustered topology -- mostly 1 hop paths)
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COMPOW/CLUSTERPOWRouting Overhead
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Cone-based

• Goal topology with power efficient routes
• Assumptions
• Transmit power dominates energy cost
• Nodes can determine angle of reception
• Trasmit power p(d) ?(dx) for x gt 2
• Basic Idea
• Use min power needed to reach at least 1 node in
  each cone of 2p/3 around node (p/2 for optimal
  efficiency)
• Refine by removing unneeded neighbors

X
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Cone-based Properties

• Topology is connected
• Pf. Intuition consider disconnected u,v with min
  d(u,v). For any neighbor w, ? gt p/3

• Routes are minimum power
• Pf. Intuition multiple short hops cheaper than
  one long hop

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Cone-based Topology
Max Power
After Phase 1
Final
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Cone-based Results
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DLMST Motivation

• Goal Topology formation for nodes with
  heterogeneous max power levels
• Problem with Cone-based topology (any MRNG based
  method)

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DLMST Protocol

• Each node broadcasts HELLO at its max power
• With knowledge of directed graph in its
  neighborhood, construct minimum spanning tree
• Pros
• Connectivity guaranteed
• Node degree bounded by constant (limits
  interference)
• Cons
• Links not necessarily bidirectional (can fix, but
  may sacrifice global connectivity)

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DLMST Results
Average Radius
Average Degree
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Topology Control Discussion

• What else besides transmit power affects
  topology?
• Is power control a problem in infrastructure AP
  networks?
• How can power control affect fairness?

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Public Policy Spectrum Management

• Spectrum Management Policy Options, Jon Peha,
  IEEE Communications Surveys, Fourth Quarter 1998,
  Vol. 1, No. 1.
• Approaches to Spectrum Sharing, Jon M. Peha, Feb.
  2005.
• Dynamic Spectrum Policies Promises and
  Challenges, Paul J Kolodzy, Jan 2004.

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The Bigger Picture
Staggering Market Statistics

• 9 million hotspot users in 2003 (30 million in
  2004)
• Approx 4.5 million WiFi access points sold in
  3Q04
• Sales will triple by 2009
• Many more non-802.11 devices

Technology
Economy
Society
Government
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US Spectrum Allocation
802.11 Bluetooth
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The Status Quo

• Government licenses spectrum
• By frequency e.g., for a television channel
• By location e.g., for the Pittsburgh area
• Only licensees allowed to transmit
• Licenses are temporary
• Allows change in spectrum policy
• New spectrum usually auctioned
• But 99.9 always renewed
• A small number of unlicensed bands
• Industry, Science, and Medicine (prev. slide)
• PCS, NII
• Anyone can transmit (with limitations)

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Governing Spectrum Blocks

• Open access Flexible use doctrine
• Let market forces decide applications
• gt most value, innovation, competition
• Exclusive access
• Government chooses application/transmission
  standard
• gt international interoperability, positive
  externalities (e.g., for police, fire
  fighters), standardization

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Distributing Licenses

• Lotteries
• Avoids political favoritism
• Does not necessarily maximize value
• Auctions
• Tries to maximize value of application
• Can be synchronized to allow buyers to get larger
  chunks

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Alternatives to Licensing

• Property Rights
• Treat spectrum same as land
• Allows resale, renting, etc. gt opens up
  secondary markets for spectrum
• But interference (trespassing) on region
  boundaries unavoidable
• Commons
• WiFi model cooperative sharing
• Maximize spectrum use if transmission is bursty
• Requires some common protocol for cooperation
• Requires some altruism

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Dynamic Spectrum Management

• Goal Allocate spectrum more dynamically
• For example, without humans in the loop
• Why? Lots of spectrum is wasted!
• Time of day (some radio stations turn off at
  night)
• Location (rural areas dont use all TV
  frequencies)
• Workload (data applications are bursty)
• Enabling Technology
• Software Defined Radios
• Adaptive Cognitive Radios
• Example Cordless phones vs. Baby monitors --
  manual to automatic freq. adjustment

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Enabling Technologies

• Flexibility
• Can change waveform on the fly (i.e., modulation
  protocol)
• Agility
• Can change the freq. on the fly (i.e., channel)
• Sensing
• Aware of environmental conditions (i.e.,
  interference)
• Networking
• Can interact with other radios (i.e., ad hoc
  nets)

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Dynamic Policy Options

• Can policy be varied by
• Transmission duration? (e.g., TDM)
• RF condition? (e.g., interference sensing)
• Short time scales?
• Via negotiation between radios?
• Impact on environment? (e.g., interference)
• Implementation Options
• High power beacon to all devices?
• P2P networked radio enforcement?

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Implementation Challenges

• Quantifying interference
• FCC definition unwanted energy
• Measurement infrastructure
• Analog to pollution monitors
• Dedicated or networked P2P based?
• Liability policies
• How to punish policy non-compliance
• Do devices need to be certified? What about
  software?
• Identity management
• How to identify violators

Example
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Public Policy Discussion

• How could more dynamic spectrum allocation
  impact
• WiFi Testbeds?
• Community Mesh Networks?
• Mixed Networks?
• Other topics?