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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
Radar / 4G Compatibility
Challenges
The Impetus for a New Spectrum Use Standard?
MR. BRUCE NALEY
Naval Surface Warfare Center, Dahlgren Division
E3 Spectrum Supportability Branch (Q51)
DSN: 234-0703
Comm: (540) 284-0703
[email protected]
2010 IEEE EMC Symposium
Fort Lauderdale, FL - Monday, 26 July 2010
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Mr. Bruce Naley is a native of Edison, New Jersey. He graduated from
the United States Naval Academy in 1992 with a B.S. in Systems
Engineering. After a nine-month assignment as a Military Research
Assistant at Los Alamos National Laboratory, he reported in February
1994 to Pensacola, FL to begin the U.S. Navy’s flight school program.
His active duty service includes tours as a Naval Flight Officer at Fleet
Air Reconnaissance Squadron Three (VQ-3) and as an instructor at the
Navy Reserve Officer Training Command (ROTC) unit Purdue
University. On each active duty tour, he earned an advanced degree on
his off duty time – completing an M.B.A. from Oklahoma City University
in May 1998 and a Masters degree in Electrical Engineering from
Purdue University in May 2001.
Mr. Naley left active duty in September 2001 and began his new career
as a practicing engineer at the Naval Surface Warfare Center, Dahlgren
Division. After three years in Chemical and Biological Weapons
Defense, he transferred to Dahlgren’s Spectrum Management group,
where he has been ever since. As a spectrum engineer Bruce has done
Research and Development (R&D) and Test and Evaluation (T&E) to
resolve spectrum issues with the prototype SPY-3 radar, CREW
systems, and the SM2 missile. Additionally, he provides technical
support to the NAVCENT frequency manager and the U.S. delegations
attending bi-annual RF interference resolution meetings with the Gulf
Cooperation Council (GCC) member Arab nations.
Still an officer in the Navy Reserves, Mr. Naley has served in several
Science & Technology units that support the Naval Research
Laboratory. Additionally, he was mobilized to Active duty August 2007
to be the Officer in Charge (OIC) of a Scan Eagle Unmanned Aerial
Vehicle (UAV) unit deployed to Iraq.
Back from Iraq and again in a civilian capacity, Mr. Naley is now
leading three programs at Dahlgren: Installation of a spectrum
monitoring system for the Dahlgren Naval Base, a joint RF propagation
study with the National Radio Astronomy Observatory (NRAO) and
Virginia Tech University, and the T-REX spectrum monitor installation
for the Pacific Missile Range Facility (PMRF).
MR. BRUCE NALEY Naval Surface Warfare Center, Dahlgren Division
E3 Spectrum Supportability Branch (Q51)
DSN: 234-0703
Comm: (540) 284-0703
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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The Situation
• Globally, nations have authorized mobile broadband wireless access (BWA) services in the 3.3-3.7 GHz bands.
• Frequently, incumbent radar users exist in the same or adjacent frequency bands.
• Based on ongoing analysis and testing, there is a potential for electromagnetic interference (EMI) among 4G and radar systems.
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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The Challenge
• Radars typically have very low duty cycles but have very high peak power.
• Out-of-band (OOB) noise, although very low relative to the fundamental, can be high compared to base station received power levels.
• High-power radar emissions may result in degradation of 4G link performance. – increased packet error rates
– Increased frame error rates
– Packet delays
– Overload of receiver front-ends
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Adjacent Band Sharing Problem
Recent Example
• Legal OOB radar emissions caused
degradation to 4G system.
– Effect to 4G system can be severe when there
is strong atmospheric ducting.
– Enough power to saturate 4G front end during
worst atmospheric ducting conditions.
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Radar OOB Power on 4G
Frequencies Radar OOB Power on WIMAX Frequencies
Measured Power at WIMAX Tower
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
3.00 3.10 3.20 3.30 3.40 3.50 3.60
dB
m / 7
MH
z
Mode 1
Mode 2
Mode 1: Not radiating toward tower
Radar Fundamental
WIMAX
Frequencies
F0 F0 + 100 MHz F0 + 200 MHz F0 + 300 MHzF0 - 100 MHz
4G Base Station Tower
4G operator
signals
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Level Of 4G Degradation vs. Radar
OOB Power Levels Measures Trendline for WIMAX System Performance in the presence of Radar OOD Emissions
0
1
2
3
4
5
6
-110.00 -100.00 -90.00 -80.00 -70.00 -60.00 -50.00
Radar OOB Peak Power in WIMAX Band (dBm / 7 MHz)
Av
era
ge
of
WIM
AX
Se
cto
r M
od
ula
tio
n V
alu
es
(6 i
s l
ea
st
de
gra
de
d,
0 i
s m
os
t d
eg
rad
ed
)
Day 1Day 2Day 3TrendLinear (Trend)
4 G
Radar OOB Peak Power in 4G Band (dBm/ 7 MHz)
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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The Goal
• Identify methods to effectively reduce EMI
between radars and communications
systems.
• Push for acceptance of these methods in
the form of national / international
standards.
– For Radar/Comms shared or Adjacent Bands.
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Interference Mitigation
Techniques – 4G systems
• Spectrally – Receiver bandpass filters
– Dynamic Spectrum Allocation
• Spatially – Reducing potential antenna coupling
• Separation distance
• Antenna null on horizon
• Beam forming
• Other – MIMO implementation in 4G
– Forward error correction tailored to pulsed interference.
– Site Shielding
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Spectrally
• Receiver bandpass filters – Protect against out-of-band radar interference.
• Dynamic Spectrum Allocation – Avoiding, or vacating, a channel that is identified as
being occupied by a radar based on cognitive detection, or by database methods.
• In areas where not all the frequency resources are fully utilized
– Network frequency plan would need to be self configuring.
– Most effective if operators purchased non-contiguous spectrum.
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Spatially
• Potentially interfering radar emissions at horizon or above. – Ship and ground-based radars search near and above
the horizon.
– Airborne radars look down toward the ground.
• Reduce antenna coupling – Separation distance
– Antenna null on horizon / sharp max elevation cut-off • Increase Antenna Beam Down-Tilt
– Beam-Forming • Steer maxima towards the desired signal
• Steer nulls towards interfering signals – Effective for small numbers of strong interferers
• Downlink sub-sectorization as an alternate method.
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
Spatial “Sideview” Horizon Null
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Local Users Low Elevation Angles
Distant Users Elevation Angle can Approach Horizon
Interference Sources
Notional Tower
Elevation
Pattern
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
Spatial “Overhead View” Beam Forming
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Distant Users
Interference Sources
Beam Forming gives
customer max gain &
places interfering
sources in a null
Azimuth Separation
Allows
Dynamic EMI Nulling
Local Users
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Other
• Multiple Input Multiple Output (MIMO) / Space
Time Block Code (STBC) implementation
– Redundant data transmission on multiple
frequencies/time slots/polarizations/etc.
• Forward error correction tailored to pulsed
interference.
• Site Shielding
– Using physical or natural shielding at the 4G station.
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
MIMO
Radar Mitigating Effects
F
r
e
q
u
e
n
c
y
Time
Each color represents a particular subscriber – Each pattern a different data packet.
Every data packet is sent twice, on a different frequency and/or time slot.
In-Band radar
Interference
Out-of-Band
radar Interference
At least one copy of each data packet is not interfered with
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Interference Mitigation
Techniques – Radars
• Spectrally – Reduced OOB emissions
• Filtering
• Pre-distortion
• Phase canceling
• Cleaner amplification stages
– Frequency agility
• Spatially – Steerable Nulls
– Lower sidelobes • Taper on transmit
– Sectoring • Power sectoring (multiple power levels)
• Other – Variable chirps / pulse widths / PRFs
– Low Duty Factor
– Orthogonal waveforms
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
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Summary
• The spectrum is becoming more and more
crowded.
• Adjacent Band and In-Band operation
between radars and communications systems
will be more common.
• Effort now to create the proper standards will
improve the future compatibility of radar and
4G services.
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ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT
Way Ahead
• Work Together to Draft “Best Practices”
EMC Guidance in Shared or Adjacent
Bands.
• Research Existing EMC, Communications,
and Radar Standards for Appropriate
Committee/Focus Area(s) to Insert This
New IEEE Standard.
– Update an Existing Standard?
• Spread the Word!
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