Ultra Wide Band Wireless Communications

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Ultra Wide Band Wireless Communications
Department of Computer Science
Engineering University of California, Riverside

• Ioannis Broustis
• March 23rd, 2004

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Motivation

• Current wireless solutions (IEEE 802.11,
  Bluetooth) face some of the following problems
• Limited channel capacity
• High power consumption
• Multipath fading

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Why UWB?

• Advantages
• Low-power operation.
• Low cost.
• Low probability of detection and low probability
  of jamming capabilities.
• Low interference levels to existing services.
• Higher immunity to multi-path fading effects.
• Ability to penetrate walls, etc.
• Availability of precise location information.

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What are we trying to do

• There are no sufficient solutions for the MAC
  layer.
• Limited previous work exists for UWB based ad hoc
  networks.
• We will address the problem of a suitable MAC
  protocol for UWB ad hoc wireless networks.

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Roadmap

• UWB definition and applications
• Possible PHY layer implementations
• MAC principles
• Previous Work on MAC layer
• Conclusions

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UWB What is it?

• Any signal that
• Occupies at least 500MHz of BW, or
• More than 25 of a center frequency

• Wireless Personal Area Networks (WPANs)
• FCC allocates 7,500 MHz in the 3.1 to 10.6 GHz
  band.

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UWB Applications

• Stream DVD content to HDTVs simultaneously.
• Wirelessly synchronize appliance clocks.
• Connect high-data rate peripherals.
• Move huge files between digital cameras,
  camcorders, and computers.
• Military applications (radars, penetrate walls,
  etc.)

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What makes UWB so interesting?

• Manufacturers are still jumping on the UWB band
  wagon even with the frequency and power
  restrictions.
• Why? Let an old friend explain
• Shannons theorem

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PHY Single-Band and Multi-Band

• Single-Band Implementation
• One pulse occupies the whole BW.
• Multi-Band Implementation
• The 7.5GHz are divided into multiple bands.
• Information is independently encoded in the
  different bands.
• The lower limit of 500MHz must be maintained.

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Single-Band and Multi-Band
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Single-Band and Multi-Band
Multi-band signals transmitted at different
discrete times. The sequence repeats at each
symbol. Center frequencies are shown in the
vertical axis.
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Why prefer Multi-Band ?

• Adaptive band selection ? Avoids interference.
• Low complexity ? Smaller transceiver cost.
• Low circuit frequency ? Power conservation.

Sacrifice one band for co-existence
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IEEE 802.15.3a Requirements
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MAC Principles

• Two main aspects
• Intra-WPAN interference
• Polling schemes (master/slave)
• CSMA
• CDMA
• TDMA
• A new idea...
• Inter-WPAN interference
• Time Hopping Spread Spectrum techniques.

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UWB ad-hoc MAC - Previous Work

• 1 Jin Ding, Li Zhao, Sirisha Medidi and K. M.
  Sivalingam, "MAC Protocols for Ultra-Wide-Band
  Wireless Networks Impact of Channel Acquisition
  Time", in SPIE ITCOM Conf. 4869, Boston, July
  2002.
• The channel acquisition time is large enough and
  prohibits CSMA or TDMA approaches

TDMA
CSMA-CA
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UWB ad-hoc MAC - Previous Work

• 2 H. Yomo, P. Popovski, C. Wijting, I. Z.
  Kovacs, N. Deblauwe, A. F. Baena, and R. Prasad,
  "Medium Access Techniques in Ultra-wideband Ad
  Hoc Networks", the 6th national conference of
  ETAI, 2003 September, 2003, Ohrid, Skopia.
• They examine the Inter-WPAN interference approach
  of the MAC layer.
• The only way to control this kind of
  interference is to determine appropriate values
  for some Time-Hopping pattern parameters.

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UWB ad-hoc MAC - Previous Work

• 3 Jean-Yves Le Boudec, Ruben Merz, Bozidar
  Radunovic, Joerg Widmer, A MAC protocol for UWB
  very low power mobile ad-hoc networks based on
  dynamic channel coding with interference
  mitigation, EPFL Technical Report ID IC/2004/02
• It is the 1st ad hoc MAC with Dynamic Channel
  Coding.
• Time-Hopping for Inter-WPAN interference.
• Schemes for
• Interference mitigation.
• Synchronization between transmitter and receiver.
• Dynamic channel coding with incremental
  redundancy.
• Private MAC Enforce that several senders
  cannot communicate simultaneously with one
  destination. ??

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UWB ad-hoc MAC - Previous Work

• PRIVATE MAC
• Request ? Response ? Data? Ack.
• The request is sent to the receivers THS
  (Time-Hopping sequence).
• Response, Data and Ack are transmitted using a
  common Sender-Receiver THS.
• If no feedback is received, the sender will
  re-transmit after a random backoff.

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UWB ad-hoc MAC - Previous Work

• PRIVATE MAC (contd.)
• Assume that B is transmitting to A.
• An interfering node C will send a request to A
  and will wait listening to As THS.
• After the end of a successful transmission, A B
  issue a beacon to their THS to inform other nodes
  that they are idle.
• If multiple nodes wait for A, they start counting
  a backoff timer as soon as they hear the beacon.
• With a proper synchronization scheme, collisions
  are avoided.

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Conclusions

• UWB is an excellent solution for high-speed WPANs
• Many times the maximum required data rate
• Power efficiency and no multi-path fading.
• The Multi-Band approach provides with even more
  advantages.
• A lot of work has been done in PHY.
• Upper layers must be examined in detail.
• Above MAC, nothing has been proposed.

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Questions? (References available upon request)
General Atomics Multi-Band Transceiver Prototype