1. November 2002
Project: IEEE P 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]
Voice:[ ], FAX: [ ],
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 a ALT PHY]
Notice: This document has been prepared to assist the IEEE P 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 P
Matt Welborn, XtremeSpectrum Inc.

2. Overview UWB effects on other systems Other system’s effects on UWB
November 2002
Overview
UWB effects on other systems
Licensed and unlicensed spectrum
Other system’s effects on UWB
Matt Welborn, XtremeSpectrum Inc.

3. UWB Effects on Licensed Systems
November 2002
UWB Effects on Licensed Systems
This is the set of cases that the FCC studied in proceedings
Result: R&O 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
Matt Welborn, XtremeSpectrum Inc.

4. UWB Effects on Unlicensed Systems
November 2002
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)
Matt Welborn, XtremeSpectrum Inc.

5. Interference and Coexistence
November 2002
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
Matt Welborn, XtremeSpectrum Inc.

6. Specific Example: 802.11a WLAN
November 2002
Specific Example: a WLAN
Active coexistence
Coordination at PHY/MAC or higher layer to improve coexistence performance
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
Matt Welborn, XtremeSpectrum Inc.

7. Geometry, Duty Cycle & Power Control
November 2002
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
Matt Welborn, XtremeSpectrum Inc.

8. Interference of UNII System on UWB
November 2002
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 < 10 m requires some rejection of interference energy
Two issues: MF output SIR and front end protection
SIR
1 m
10 m
1 m
-6 dB
-26 dB
10 m
+14 dB
Matt Welborn, XtremeSpectrum Inc.

9. Three Choices for UNII Protection
November 2002
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
Matt Welborn, XtremeSpectrum Inc.

10. Non-UNII, In-band Interference
November 2002
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 (> 5m)
1/R 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
Matt Welborn, XtremeSpectrum Inc.

11. Conclusions UWB effects on other systems Other system’s effects on UWB
November 2002
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 system’s effects on UWB
UWB will require some mechanism for rejecting UNII band interference, or performance will suffer
Protection method is an engineering trade-off
Matt Welborn, XtremeSpectrum Inc.