electromagnetic & sensor systems … & sensor systems department 9 interference mitigation...

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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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Page 1: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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

Page 2: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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

Page 3: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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.

Page 4: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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

Page 5: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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.

Page 6: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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

Page 7: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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)

Page 8: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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.

Page 9: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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

Page 10: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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.

Page 11: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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.

Page 12: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT

Spatial “Sideview” Horizon Null

12

Local Users Low Elevation Angles

Distant Users Elevation Angle can Approach Horizon

Interference Sources

Notional Tower

Elevation

Pattern

Page 13: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

ELECTROMAGNETIC & SENSOR SYSTEMS DEPARTMENT

Spatial “Overhead View” Beam Forming

13

Distant Users

Interference Sources

Beam Forming gives

customer max gain &

places interfering

sources in a null

Azimuth Separation

Allows

Dynamic EMI Nulling

Local Users

Page 14: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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.

Page 15: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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

Page 16: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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

Page 17: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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.

Page 18: ELECTROMAGNETIC & SENSOR SYSTEMS … & SENSOR SYSTEMS DEPARTMENT 9 Interference Mitigation Techniques – 4G systems • Spectrally – Receiver bandpass filters – Dynamic Spectrum

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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