Robot Communication over Wireless Ad Hoc Network

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Robot Communication over Wireless Ad Hoc Network

• M.Sc. Feng Xu
• 03.02.2005

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Agenda

• Why communication among robots is necessary
• 3 examples
• Two categories network centralized network and
  ad hoc network
• Properties of ad hoc network, and examples
• Current Main Stream Techniques
• Hardware structure for the communication node
• Constrains for portable devices energy, space,
  computing ability
• MAC protocol, CSMA/CA
• Current two hot research directions on MAC layer
• Directional communication
• Dynamic multi-channel allocation
• 3 means to close the gap between theory and
  realization
• Summary

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Why communication among Robots

• Goal of RoBoCup To fully develop autonomous
  humanoids that can win against human world
  champion soccer team by 2050
• Each robot player should have more powerful
  individual ability over human player
• Communication among robots is necessary for the
  high level coordination (deliberation-based high
  level behavior control!)
• In special robot application scenarios like war
  field and emergency field, communication among
  robots can significantly enhance their ability
• Contrariwise, robots with wireless communication
  module can help simulate or experiment the
  wireless network

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Example 1, AIBO
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Example 2, BiM-2
Receiver on a PCB
Receiver unit on a robot
Seattle University RoboCup Team, USA
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Example 3, Khepera
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Two Categories of Network
Centralized Network
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Properties of Ad Hoc Network, examples
Properties

• MANET is a decentralized wireless network without
  pre-built infrastructure
• Each node acts as host and router simultaneously,
  and signals may be transmitted via multi hop to
  the destination
• The network topology may change rapidly and
  unpredictably due to movements, joining and
  leaving of nodes at any moment
• MANET may operate in a standalone fashion, or may
  be connected to other existent network as its
  extension

Examples

• Conferencing and home networking
• Wireless sensor network
• Multi-hop extensions for cellular
  telecommunication systems
• And networks of vehicles, robots

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Current Main Stream Techniques

• Bluetooth
• WLAN IEEE 802.11 b,g,a
• HiperLAN/II
• ZIgBee
• WiMax (near future)

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Hardware Structure, different network layers
Baseband Processor
MAC controller
RF transceiver
physical
MAC
Host
Hardware structure for each node
other high layers
OSI/ISO Reference Model
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Constrains for Portable Devices

• Physical space
• Limited energy (battery powered devices)
• Limited computing power

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CSMA/CA

• MAC protocol carrier sense multiple access
  with collision avoidance
• Prerequisites Omnidirectional communication on
  single frequency channel

RTS, CTS, data and NAV setting
Resulted space allocation condition
Basic media access process
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Current hot research topics

• Goals
• Increase resource efficiency, the resource mainly
  means frequency band
• Make the communication link more robust
• Means
• Directional communication to increase the space
  reuse factor
• Multi-channel dynamic allocation scheme

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Smart Antenna, directional antenna

• Smart Antenna
• Realized by antenna array and additional array
  signal processing unit
• Enable various advantages on network, but also
  consume much additional resource like space,
  energy and computing power
• Directional Antenna
• The directivity is attributed to the directional
  property of the antenna element itself
• With the mechanical turning assistance, or
  multiple directional antennas equipped on each
  node with proper orientation, each node can
  communicate on the direction it wishes
• Less additional resource is needed comparing to
  SM, however, less improvement is anticipated

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Multi-channel scheme CDMA, OFDM
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Theoretical Research, Practical application, 3
means close the gap

• Theoretical research
• New schemes are firstly put forward on the
  physical layer
• Higher layers (MAC, network layers) need adapting
  to the modifications
• Cross-layer optimization
• Close the gap between theoretical research and
  practical application
• In practice, many constrains are imposed
• Rely on the chip layer improvement
• Use the simplified scheme to make it more
  practical
• The combination of aforementioned 2 means

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Summary

• To reach the goal of RoBoCup, the communication
  ability among robots is necessary
• To communicate efficiently and effectively, a
  network called mobile ad hoc network is
  meaningful for the robot team
• Contrariwise, robot team with communication
  ability can help contribute to the network system
  improvement
• Many constrains are imposed on the portable
  devices due to its limited resource
• Numerous new schemes are put through on the
  physical layer to increase transmission data rate
  and communication link robustness
• Cross-layer optimization is important for the
  whole system performance
• 3 means to close the gap between theoretical
  research and practical application

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Thank you for your attention!
Heinz Nixdorf Institut Universität
Paderborn Schaltungstechnik Prof. Dr.-Ing. Ulrich
Rückert Fürstenallee 11 33102 Paderborn Feng
Xu Tel. [phone] Fax. [phone]
6351 Email xu_at_hni.upb.de http//wwwhni.upb.de/sct