How to Deal With MAC Shortcomings for Sensor Networks or: Sensor - - PowerPoint PPT Presentation

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How to Deal With MAC Shortcomings for Sensor Networks or: Sensor - - PowerPoint PPT Presentation

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How to Deal With MAC Shortcomings for Sensor Networks or: Sensor Network Self Organization Rendezvous Clustering Algorithm March 16, 2004 Kathy Sohrabi Sensoria Corporation Internetworking the Physical World Dagstuhl Seminar 2004 About

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Dagstuhl Seminar 2004

How to Deal With MAC Shortcomings for Sensor Networks

  • r:

Sensor Network Self Organization

Rendezvous Clustering Algorithm

March 16, 2004

Kathy Sohrabi

Sensoria Corporation

Internetworking the Physical World

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Dagstuhl Seminar 2004

About Sensoria

  • Founded in 1999

Founder: Bill Kaiser, UCLA Faculty/Chairman EE Department

  • HQ in San Diego, Design Center in Los Angeles
  • Consequence of work on Sensor Nets at UCLA
  • Builds and markets networked embedded systems

Sensor networking platforms and solutions Ad-hoc Mobile communication systems

  • Hardware, software, system design expertise
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Dagstuhl Seminar 2004

  • Introduction
  • Problem of self organization
  • Observations about MAC
  • Why we need to actively manage links (self-organize)
  • Rendezvous Clustering Algorithm (RCA)

Outline

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What does Self Organization Mean?

  • Self formation at various layers

At the highest level, self organizing is expected to provide a distributed computing environment Self forming routes in the face of fast changing and/or ad-hoc topologies. In fact a lot of work has been concentrated on the self organization at layer 3. The clustering mechanism discussed here is concerned with self –organization at layer 2.

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Sensor Network Scenarios

Different Classes of Sensor Networking Applications Exist

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Dagstuhl Seminar 2004

Wireless MAC

  • Medium Access

Control

Share a common channel with others

  • No Coordination:

ALOHA

  • Total Coordination:

fixed access such as TDMA

  • Others in between:

coordinate only when sending (variations of CSMA, reservation schemes)

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Dagstuhl Seminar 2004

MAC for Multihop – Random Schemes

  • Hidden Terminal Problem
  • Exposed Terminal Problem
  • Requires the receiver be turned on

all the time

  • Channel sensing is not always

accurate

  • Example: ad-hoc mode of 802.11

A B C D

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Dagstuhl Seminar 2004

MAC for Multihop – Fixed Access

Need network link connectivity and interference information (local or global) Assignment of optimal transmission schedules is NP- complete Approximate schemes that are good exist They still need global synchronization Mechanism beyond the ability of simple fixed access radios

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Clustering: Neighbor Discovery & Link Formation

Network Self Assembly Process

Adaptive Routing: Formation of Network Layer Routes

Fixed Radio Transmit Power

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Rendezvous Clustering Algorithm

Kathy Sohrabi, William Merrill, Jeremy Elson, Lew Girod

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About RCA

  • Rendezvous Clustering Algorithm (RCA) is

really a mechanism for distributed collaboration

We use it to form clusters in a distributed fashion Does not necessarily need to be used for managing links Can be used to set up coordinated agreement amongst nodes in a distributed fashion Built on top of the radio’ s native MAC Native MAC must be able to

  • Form local wireless networks (typically with one or two

hop diameter)

  • Operate on different channels
  • Switch between these channels
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Dagstuhl Seminar 2004

Channel Switching

  • The ability of the radio to take on various states and

switch between them rapidly and efficiently affects the operation

Multihop, ad-hoc wireless networks, that need low energy States transitions

  • off->idle
  • idle->on
  • one channel to another channel

Order of seconds to switch from channel to channel (RCA native radios) Other radios such as Bluetooth also require on the order of seconds to switch (needed for scatternet formation) Zigbee very good, on the order of milliseconds to switch

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Dagstuhl Seminar 2004

Factors Contributing to Switching Overhead

  • HW

Phase lock loops : carrier phase and frequency acquisition Power regulators

  • PHY

Code Acquisition Symbol Acquisition Frame acquisition

  • MAC

Protocol

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Dagstuhl Seminar 2004

Issues Related to Radios

  • To mitigate switching delays chose a dual radio option

Each node is equipped with two radios, each operating independently of each other Each radio is a TDMA radio that participates in a start topology network. Each TDMA local network slowly frequency hops (controlled by the star controller)

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Details of the Frame Structure for TDMA/FH Radios

Remote Time Line Base Time Line Synch+Control Signal Transmitted TDMA Frame Receive Mode Synch+Control And Data Transmitted Receiving Synch Signal From the Base Idle Transmission to the Base TDMA Frame Remote Transmission Slot Base Transmission Slot

TDMA Frame: Frequency 1 TDMA Frame: Frequency 2

Remote Time Line Base Time Line Synch+Control Signal Transmitted TDMA Frame Receive Mode Synch+Control And Data Transmitted Receiving Synch Signal From the Base Idle Transmission to the Base TDMA Frame Remote Transmission Slot Base Transmission Slot

TDMA Frame: Frequency 1 TDMA Frame: Frequency 2

Synch+Control Signal Transmitted TDMA Frame Receive Mode Synch+Control And Data Transmitted Receiving Synch Signal From the Base Idle Transmission to the Base TDMA Frame Remote Transmission Slot Base Transmission Slot

TDMA Frame: Frequency 1 TDMA Frame: Frequency 2

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Details of RCA

  • Three phases of a node in RCA

Search mode Cluster head Cluster member

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Dagstuhl Seminar 2004

Possible RCA Radio State Combinations

Off

Search Mode

Base Active on “R” channel

Cluster Member

Active On data channel Chi Active On data channel Chk Cluster head On data channel Chg Tuned to “R” Channel/ or Off

Cluster Head

For a dual radio architecture, each radio is tuned to a different channel. For single radio architecture, the single radio interface will switch between various channels. Our current radios form a star network with a Base and a number of remote members.

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Search Mode: When it all begins

Pick radio on random / Turn off the other radio on “R” channel Become a remote on “R” channel. Stay here for Time1 Become a base on “R” channel and stay here for Time2

Did we find enough nets? yes Are the found clusters Split-able? Did we find enough searching neighbors? yes yes

Relay Ads Become a Cluster-head Until a Timeout happens Relay Ads

Did both radios join clusters as CM? yes Done With Search Did this radio connect?

Start the other Radio in SEARCH Turn this radio off Sort heard advertisement based on RSSI, and their neighbor list. Determine how many nets were found to join Try for each radio to become a cluster member

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Cluster-Head Time Out

Kick any existing attached neighbors off this network Make the CH’s data radio inactive, then turn it off. Put the other radio into SEARCH mode Become a Cluster-head until a Timeout happens. Involves inviting other searching nodes to join this radio

Does the CH have less than the minimum number

  • f neighbors?

Continue as a cluster head, until a timeout occurs

yes

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Dagstuhl Seminar 2004

How to Become a Cluster Member

Tune the chosen radio to the proper network, connect to the base on that network. Stay in this condition until a timeout occurs. Stay attached to the base, and set the timeout again Choose the appropriate radio to join the suggested network as a cluster member( SEARCHing radio first, then inactive radios)

Are we attached to the base?

Start SEARCHing again, Or make the other radio start SEARCHing if not connected Precondition: Have received over the “R” channel an invitation from a CH to join its cluster

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Results

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RCA Connected Network

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Scalability

20 40 60 80 100 120 140 160 50 100 150 Network size Connection Time (s)

95% Connection Time Full Connection

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Connectedness Over Time

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Percent Nodes Not Connected

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Traffic Overhead

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Hardware Platform History

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Sensoria Platform History

WINS 2.0 - 2001

  • Custom 32-bit processor system using Linux OS
  • DSP co-processor controlling analog interface
  • 4-channel 16-bit analog interface
  • Dual 2.4 GHz radios
  • External interfaces: Ethernet, PCMCIA/CardBus

WINS 3.0 - 2003

  • 32-bit processor module with up to 128 MB SDRAM using Linux OS
  • Low-power DSP co-processor
  • 16-channel 24-bit analog interfaces
  • External interfaces: RS-232, PCMCIA/CardBus, USB, Ethernet
  • Embedded dual 802.11 cards
  • Fully modular design with system bus

Pico WINS - 1999

  • Wireless sensor tags
  • Low power
  • Miniaturization
  • Small Antenna/Flexible PCB

WINS 1.0 - 1999

  • 4-channel 12-bit analog interface
  • Windows CE processing platform
  • Integrated 2.4 GHz radio
  • COTS processor boards
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Further Questions