IEEE 802.15-SG3a

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
UWB Coexistence Issues Date Submitted 12
November 2002 Source Matthew Welborn Company
XtremeSpectrum, Inc. Address 8133 Leesburg
Pike, Ste 700, Vienna, VA 22182 Voice703-269-30
00, FAX [phone], E-Mailmwelborn_at_xtremes
pectrum.com Re . Abstract Discussion of
interference and coexistence considerations
involved for the 15.3a ALT PHY Purpose Provide
information to help committee evaluate
coexistence criteria for 802.15.3a ALT
PHY 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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Overview

• UWB effects on other systems
• Licensed and unlicensed spectrum
• Other systems effects on UWB

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UWB Effects on Licensed Systems

• This is the set of cases that the FCC studied in
  proceedings 98-153
• Result RO with emissions and usage limitations
• Conclusion is that rules are very conservative,
  no interference to licensed systems
• Analyzed many systems, commercial and federal
• GPS, PCS, DARS, radars, satellites, aviation and
  navigation, etc.
• Emission limits below 3.1 GHz are significantly
  lower than Class B levels to protect GPS,
  aviation and radars

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UWB Effects on Unlicensed Systems

• ISM and U-NII band systems (IEEE, BT, HomeRF,
  cordless phones, etc.)
• Nearly all such systems are out-of-band for UWB
  communications applications
• Low O.O.B. limits provide significant protection
  for such systems
• Additional protection can be provided
• Engineering cost/benefit trade-off (example
  indoor versus handheld limits)

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Interference and Coexistence

• Biggest design issue is to determine desired
  level of co-existence
• Different analysis techniques to determine
  potential for interference/coexistence
• Noise-floor analysis
• Estimate effect of UWB on thermal noise floor
• Relies on assumptions about real-world effects
• Most conservative approach
• Can lead to overly-restrictive/unrealistic
  results
• SNR-based approaches
• Determine when emissions will actually affect
  operation
• Real-world factors (e.g. RFI, noise, CCI) also
  affect system

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Specific Example 802.11a WLAN

• Active coexistence
• Coordination at PHY/MAC or higher layer to
  improve coexistence performance
• 802.15.3 MAC provides several mechanisms
• Child and neighbor piconets capabilities
• Piconet maximum transmit power limits
• Transmit power control
• Passive coexistence no explicit interaction at
  higher layers
• Implicit scanning for best available channel
• Uncoordinated, simultaneous use of the channel

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Geometry, Duty Cycle Power Control
UWB range 10 m
If WLAN range 30/50/100 m then UWB area
10/4/1

• Relative size- few WLAN devices see UWB effects
• Many WLAN devices far from UWB piconet, no
  effects
• Duty cycle effects reduced probability of
  collision
• e.g. 30 duty cycle 10 impact
• Power control UWB Tx power minimized
• ½ range UWB 6 dB lower Tx power ? better WLAN
  SNR

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Interference of UNII System on UWB

• Back-of-the-envelope example
• Assume 11a device has 17 dBm Tx power
• Assume UWB has 4 GHz BW ? -5 dBm Tx power
• (4000/100 MHz) possible processing gain 16 dB
• Direct approach (-6 dB) SIR at output of MF
• Conclusion 100 Mbps operation with WLAN lt 10 m
  requires some rejection of interference energy
• Two issues MF output SIR and front end protection

SIR UWB _at_ 1 m UWB _at_ 10 m
11a _at_ 1 m -6 dB -26 dB
11a _at_ 10 m 14 dB -6 dB
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Three Choices for UNII Protection

• Never (provide no explicit protection)
• If interference occurs, system uses existing
  mechanisms (FEC, processing gain, re-transmit at
  MAC or higher layer)
• Simplest to build, but impact is potentially
  large
• (2) Always (static protection from UNII
  interferer)
• Assume that UNII protection is always needed
• Potential impact on performance
• (3) Sometimes (dynamic protection from UNII
  interferer)
• Determine presence/frequency of interferer
• Provide adaptive interference rejection mechanism
• Trades implementation complexity for potential
  performance gains when interferer is not present

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Non-UNII, In-band Interference

• Most other in-band systems are outdoors, LOS, use
  directional (high-gain) antennas, and are subject
  to site planning
• Unlikely to cause/receive UWB interference under
  normal conditions
• High EIRP required to have same effect as UNII
  WLAN

5GHz Propagation Free-space 1/R3 (gt 5m) 1/R3 20 dB
10 m range 50 mW 100 mW 10 W
100 m range 5 W 100 W 10 kW
1000 m range 500 W 100 kW 10 MW
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Conclusions

• UWB effects on other systems
• Licensed systems analyzed by FCC- no problem
• Unlicensed systems UNII band is primary issue
• Many factors affect likelihood for interference
  in the real world geometry, duty cycle, power
  control, RFI, etc.
• Other systems effects on UWB
• UWB will require some mechanism for rejecting
  UNII band interference, or performance will
  suffer
• Protection method is an engineering trade-off