System Model Considerations for mmWave PHY

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Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Adapting the IEEE 802.15.3 MAC to WPAN systems
employing directional antennas Date
Submitted 7 May 07 Source Khusro Saleem,
Bryan Beresford-Smith (NICTA Ltd) Address
Building 193, University of Melbourne Melbourn
e, VIC, 3010, Australia Voice 61 3 8344 8407
FAX none, E-Mail khusro.saleem_at_nicta.com.au Re
Adapting the IEEE 802.15.3 MAC to WPAN systems
employing directional antennas Purpose This is
a discussion only document. No action is
recommended. Notice This document has been
prepared to assist the IEEE P802.15. It is
offered as a basis for discussion and is not
binding on the contributing individual(s) or
organization(s). The material in this document is
subject to change in form and content after
further study. The contributor(s) reserve(s) the
right to add, amend or withdraw material
contained herein. Release The contributor
acknowledges and accepts that this contribution
becomes the property of IEEE and may be made
publicly available by P802.15.
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Adapting the IEEE 802.15.3 MAC to WPAN systems
employing directional antennas

• Khusro Saleem, Bryan Beresford-Smith
• NICTA Ltd

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Outline

• Overview
• Benefits of directional antennas
• Challenges at the MAC layer
• Proposed amendments to the IEEE 802.15.3 MAC
  layer
• Conclusions and further work

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Overview

• IEEE 802.15.3 TG3c is developing a mm-wave-based
  alternative PHY for the existing WPAN standard
  IEEE 802.15.3-2003
• Signal propagation at mm-wave frequencies has
  high path loss
• Signals also experience greater attenuation
  through most materials
• High TX power not expected to overcome
  attenuation
• Directional antennas are a cost-effective
  solution to this problem
• How do we adapt IEEE 802.15.3-2003 to work
  effectively with directional antennas?

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Directional antennas - benefits

• Antenna elements are small in the mm-wave
  spectrum and can be integrated into the package
• This in-turn allows for beam-forming thereby
  increased antenna gain and spatial re-use
• A side benefit is increased resilience to
  multi-path fading and interference

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Challenges at the MAC layer

• Neighbor discovery
• PNC-DEV communication
• DEV-DEV communication
• Hidden node problems
• Exposed node problems
• Spatial reuse

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Adapting IEEE 802.15.3

• The following proposals enhance the current
  standard whilst ensuring
• Interoperability with DEVs that only employ
  omni-directional antennas.

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Adapting IEEE 802.15.3 Main change

• MAC beacons are transmitted by the PNC
  omni-directionally
• To overcome the resulting antenna gain asymmetry
  in the PNC-DEV links, the MAC beacons are
  transmitted at a lower rate
• The lower rate transmission rate results in a
  lower SNR requirement
• Select the lower rate, such that the lower SNR
  requirement overcomes for the antenna gain
  asymmetry in the PNC-DEV links
• We should end up with the same probability of
  correct frame reception
• We can readily adapt this to any PHY
  specification with the addition of a few PHY-SAP
  primitives
• This represents a form of cross-layer optimization

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Adapting IEEE 802.15.3 Main change

• For example, consider the current 2.4GHz PHY
  specification in IEEE 802.15.3-2003
• For 64-QAM-TCM, to achieve FER8, we need
  SNR20dB
• Assume we transmit MAC beacon as per the MAC
  header at 22Mb/s using DQPSK
• To achieve FER8, SNR13dB
• ?SNR7dB
• Loosely speaking, we can lose about 7dB in
  antenna gain
• Yes, there will be a reduction in throughput but
  the beacon is a small fraction of the superframe
  anyway

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Adapting IEEE 802.15.3 Main change

• How do we address Neighbor Discovery?
• The PNC MAC beacon is transmitted
  omni-directionally and DEVs scan using
  directional beams
• By transmitting the PNC MAC beacon
  omni-directionally, neighbor discovery is a
  trivial process
• And by lowering the data rate we overcome the
  asymmetric antenna gain
• This approach is interoperable with
  omni-directional DEVs as well
• The beacon must be lengthened to facilitate
  Angle-Of-Arrival (AOA) estimation

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Adapting IEEE 802.15.3 PNC-DEV communication

• So what does the PNC-DEV link look like?
• The PNC is omni and the DEV is directional or
  omni (depending on capability)
• So when the directional-capable DEVs are
  expecting the beacon they point their beams at
  the PNC
• The beam pointing direction (AOA) is learned each
  time a PNC beacon is received

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Adapting IEEE 802.15.3 DEV-DEV communication

• So what does the DEV-DEV link look like?
• The DEV-DEV link could be omni-omni,
  omni-directional, or directional-directional
  depending on device capability
• The main question is how to two DEVs employ a
  directional-directional link?
• This requires a training sequence for AOA
  estimation, so lets reuse our PNC-DEV link
  communication model again

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Adapting IEEE 802.15.3 DEV-DEV communication

• How do two DEVs establish a directional-directiona
  l link?
• After successful stream creation, the two DEVs
  undergo an AOA estimation sequence during the
  first allocated CTAP
• Assume DEV1 initiated the stream request
• DEV1 transmits an DEV-beacon omni-directionally,
  just like the PNC beacon, at a lower rate
• DEV2 scans directionally and receives this and
  estimates the AOA
• DEV2 then acknowledges this DEV-beacon
  directionally which is then received by DEV1 and
  used to estimate its AOA
• The training sequence is complete
• DEVs use this training phase to ascertain if
  there is sufficient gain in the link to meet the
  stream throughput and latency requirements.

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Adapting IEEE 802.15.3 DEV-DEV communication
PNC
DEV2
DEV1
Create stream procedure
Omni beacon
AOA estimation
Directional special-ACK
AOA estimation
Directional-directional link
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Adapting IEEE 802.15.3 Communicating in the CAP

• How do we communicate during the CAP?
• This is where we should exploit spatial reuse
• Borrow ideas from 1, employ
• Directional RTS/CTS
• Directional NAV (DNAV)
• AOA caching
• Beam lock and unlocking
• Combat hidden node problem

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Conclusions and further work

• A simple set of amendments to the existing IEEE
  802.15.3-2003 standard are proposed
• Ensuring compatibility with omni-directional DEVs
• Many outstanding issues
• Impact on throughput
• Modulation format (PHY dependent)
• Details training sequence for DEV-DEV AOA
  training phase
• Need simulation results for overall MAC behaviour
  with these modifications