fundamentals of microwave radio communication for ip and tdm

1

BASIC INTRODUCTION INTO MICROWAVE THEORY AND IP

APPLICATIONS

FUNDAMENTALS OF MICROWAVE RADIO

COMMUNICATION FOR IP AND TDM

Presented by: Richard Laine / Ivan Zambrano

Silicon Valley, CA.

Agenda

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Introduction……………………………………..………….…….A

What is Microwave……….…………………….………….…….B

• Spectrum……………………………………………………………….…..B.1

• A Terrestrial Microwave Link and Applications...……………………....B.2

• How Far can Microwave Go………………………………………..........B.3

• How Microwave Radios Communicate……………………………….....B.4

• How Repeaters Extend the Range……………………………………....B.5

• Microwave Tower Issues………………………………………………….B.6

• Causes of Microwave Disconnect Periods……………………………...B.7

L2 Radio Technology………..………………………………......C

Why Propagation…………………......…………..…………......D

Antennas and Feeder Systems.…………………….………….E

RF Protection……………………………………………………..F

A. INTRODUCTION

• The field of terrestrial microwave communications is constantly experiencing a steady

technological innovation to accommodate the ever-demanding techniques telecom

providers and private microwave users employ when deploying microwave radios in their

cloud networks.

• In the beginning of this wireless evolution, the ubiquitous DS1s/E1s and DS3s/E3s

crisscrossed networks transporting mainly voice communications, data, and video.

• With the advent of Carrier Ethernet and IP, new techniques had to be developed to

ensure the new Layer 2 radios were up to par with the new wave of traffic requirements

including wideband online-streamed media. These new techniques come in the form of

Quality of Service (QoS), Traffic Prioritization, RF Protection and Design, Spectrum

Utilization, and Capacity Enhancement.

• With Carrier Ethernet and IP, network design becomes more demanding and complex in

terms of RF, Traffic Engineering, and QoS. However, the propagation concepts remain

unchanged from TDM link engineering while the link’s throughput of L2 radios doubles,

triples, or quadruples employing enhanced DSP techniques.

Introduction

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B. WHAT IS TERRESTRIAL MICROWAVE?

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Terrestrial Microwave?………..What is it?

A line-of-sight point-to-point wireless technology

for the transmission of Internet, voice, data, and

online-streamed media.

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Refracted Beam

Direct Beam

Reflected Beam

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Terrestrial Microwave?………..What is it? (cont'd)

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Terrestrial Microwave?………..What is it? (cont'd)

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60% F1

60% F1

B.1 SPECTRUM

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Frequency Spectrum

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Some Standard Frequency Bands for Terrestrial Microwave

Band Radio Frequency Recommendations (MHz) FCC, NTIA, and ITU-R)

4 GHz 3,600 – 4,200 FCC Part 101 and Rec F.635-6 (2006)

U4 GHz 3,803.5 – 4,203.5 ITU-R Rec F.382-8 (2006)

5 GHz 4,400 – 5,000 ITU-R Rec F.1099-3 Annex-1 (2007)

5 GHz 4,400 – 4,990 U.S. Federal (NTIA)

L6 GHz 5,925 – 6,175 FCC Part 101, Rec F.383-7 (2007)

U6 GHz 6,525 – 6,875 FCC Part 101

U6 GHz 6,430 – 7,110 ITU-R Rec F.384-9 (2007)

7/8 GHz 7,125 – 8,500 U.S. Federal (NTIA)

L7 GHz 7,125 – 7,425 ITU-R Rec F.385-8 Annex-1 (2007)

U7 GHz 7,425 – 7,725 ITU-R Rec F.385-8 (2007)

7W GHz 7,110 – 7,750 ITU-R Rec F.385-8 (2007)

L8 GHz 7,725 – 8,275 ITU-R Rec F.386-7 Annex-6 (2007)

10 GHz 10,550 – 11,680 FCC Part 101, Rec F.747 (1992)

11 GHz 10,700 – 11,700 FCC Part 101, Rec F.387-10 (2010)

13 GHz 12,750 – 13,250 ITU-R Rec F.497-6 (2007)

July 2013

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RF Atmospheric Attenuation

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B.2 A TERRESTRIAL MICROWAVE LINK

AND APPLICATIONS

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Data

Equipment

Outdoor RF/Antenna

Gigabit

Ethernet NxDS1/E1

PABX

Equipment

Data

Equipment

Outdoor RF/Antenna

Gigabit

Ethernet NxDS1/E1

PABX

Equipment

6 to 360 Mbit/s

QPSK to 256 QAM

July 2013

One "hop" of Microwave

Radio Node Hardware Example - Eclipse

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Cellular Site MSC-BSC-BTS IP/TDM Interconnectivity

MSC (MTSO) - Switching Office (POP)

BTS - Base Station

BSC - Base Station Controller

BSC

18/23 GHz (NxDS1/E1)

23/38 GHz (NxDS1/E1)

18 GHz (NxDS1/E1) 18 GHz (DS3/E3) Eclipse Eclipse

BTS

BSC

Eclipse

MSC

(MTSO)

Eclipse

BTS BTS

BTS

Eclipse IRU 600 Self-Healing STM-1/OC-3/Ethernet /IP Ring

Typical TDM Capacity Requirements

OC-3/STM-1 to

OC-12/STM-4

16xDS1/E1 to

OC-3/STM-1 BSC to MSC

2-16xDS1/E1 1-2xDS1/E1 BTS to BSC

3G 2G Hops

BTS to BTS 1-2xDS1/E1 2-16xDS1/E1

July 2013

Mobile RAN and Backhaul Transport

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IEEE, Oct. 2010

Carrier Ethernet MPLS-TP

Outdoor Networked Radio (4-QAM through 1024-QAM)

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B.3 HOW FAR CAN TERRESTRIAL

MICROWAVE GO?

Typical Relative Path Lengths with Clear Line of Sight (LOS)

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Path Length, mi (km)

6/7/8 GHz

11 GHz

18 GHz

23/38 GHz

100(160) 5(8) 10(16)

• Path lengths in the different RF

bands are estimates only

• A path analysis is required to

calculate the reliability and

availability criteria.

Maximum EIRP (Effective

Isotropic Radiated Power) =

+55 dBW = +85 dBm

3(5)

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80 GHz

21

Examples of Very Long IP Microwave Links for Air Traffic Control

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B.4 HOW MICROWAVE RADIOS

COMMUNICATE

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Adaptive Coding and Modulation for IP Backhaul

Throughput

[Mbit/s @ 7 MHz Ch BW]

(QPSK) 10

(16QAM) 20

(64QAM) 30

Example: 99.990% 99.995% 99.999% Rain Availability or Path Reliability

Fade Margin: 24 dB (20%) 31 dB (55%) 40 dB (25%)

Time

Fast Multipath or Slow Rain Fade

Best Effort Traffic Less Critical

Traffic Critical Traffic

(256QAM) 40

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Coding Gain in AWGN Channels

• Coding gain in AWGN (Additive White Gaussian Noise) channels is defined as

the amount that the bit energy or S/N power ratio can be reduced under the coding

technique for a given Pb (bit error probability) or Pbl (block error probability)

Shannon Limit: Threshold, Eb/N0, below which

reliable communication can not be maintained! This

ratio can be considered a metric that characterizes the

performance of one system vs. another. The smaller

the ratio, the more efficient is the modulation and

detection process for a given Pb.

Pb

10-2

10-4

10-6

Uncoded

Coded

-1.6 dB -8 dB 16 dB

X dB of Coding Gain depending on modulation and BW

Eb/N

0

mNoEbNC log10//

With concatenated coding, the coded curve is steeper

than with Reed-Solomon alone.

Example: The C/N of a p-t-p radio featuring

4DS1/16QAM and Eb/N0 = 11.9 dB @ 10-6

equals: 11.9 dB + 10 log4 = 17.9 dB

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MLCM Signal Constellation d

√ 2 d 1 0

Level 1

1 0

2d

1 0

Level 2

A set of 64 symbols is divided into subsets B0 & B1 with

increased minimum square distance. Error performance

of level 1 is determined by the minimum square distance

of the original partition. Then in order to increase “free

Euclidean distance,” coding (combination of block or

convolutional) is performed to the lower level. Hence the

total error performance is improved. Example (16QAM):

Code rate, R = (1/2+3/4+23/24+1)/4=3.2/4

B1 B0

C2 C0 C1 C3

Level 3

B.5 HOW REPEATERS EXTEND THE

RANGE

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Passive Reflector

"Billboard"

Site A

Single

Reflector

Site B

Terrain

Obstruction

Passive Repeater Arrangements

Site B

Site A

Terrain

Obstruction

Terrain

Obstruction

Double

Reflector

Double Reflector

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Site A Beam Bender

(Back-To-Back

Parabolics)

Terrain

Obstruction

Site B

Beam Bender

Back-To-Back Parabolic Antennas

"Beam Bender"

Other Passive Repeater Arrangements

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B.6 MICROWAVE TOWER ISSUES

Twist and Sway

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A B C

Antennas: HSX12-77 Antennas: HSX12-77

Beamwidth: ±0.35o Beamwidth: ±0.35o

425ft/130m

200ft/60m

425ft/130m

Daytime Tower Twist: ±10

±0.50 deflection angle

at 10 dB point

B.7 CAUSES OF MICROWAVE

DISCONNECT PERIODS

Causes of Traffic Disconnect - Outage

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• Rain outage (predictable and therefore acceptable) in access links above

about 10 GHz

• Equipment failure within the MTBF (Mean Time Between Failure) period

• Maintenance error or manual intervention (e.g., failure of a locked-on

module or path)

• Infrastructure failure (e.g., antenna, batteries, towers, power system)

• Low fade margin in non-diversity links

• Power fade (long-term loss of fade margin) in paths above about 6 GHz

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C. SOME EXAMPLES OF L2 RADIO

TECHNOLOGY

Eclipse Intelligent Node Unit

• The most compact nodal

solution on the market

• Single indoor unit

supporting multiple radio

paths

• Hot-swappable radio and

data access modules

• Support for all traffic types

• Cable-less traffic

connections

• Complete solution in one

box

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• Lower Losses than Couplers • More ODUs per Antenna feed

• Fewer Antennas

• Increased system gain • Reduces antenna sizes

• Less Tower Loading

• Radios’ features • 5 to 38 GHz licensed operation

• Fully transparent to payload

• Up to 500 Mbit/s of TDM, Hybrid TDM/Ethernet/IP, or all-IP throughput

• QPSK to 256-QAM

Networked Radios

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D. WHY PROPAGATION?

Radio Wave Propagation

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GEO, MEO,

and LEO

Satellites

Sky Wave

(MF, HF only)

REFRACTED WAVE

NON-REFRACTED (k=1) WAVE Transmitting

Antenna

Receiving

Antenna

Troposphere

Ionosphere

Microwave link propagation is

influenced by REFRACTION,

REFLECTION, and DIFFRACTION

(not shown) wave propagation.

Ground Wave

(LF/MF only)

True Earth’s Curvature

MULTIPATH RAYS

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Ray Tracing Along a Profile

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• Not unlike outbound ripples from a pebble

tossed into a quiet pond, the outgoing microwave

wave front is circular. However, the only part of

the wave of interest is equal to the diameter

(aperture) of the antenna. Beyond the antenna’s

near field, and into the far field, the wave front is

flat, as shown. The ray(s), one direct (shown)

plus multipath rays (if any), are always

perpendicular (90o) to the wave front - thus only

one ray is assigned to each direct or multipath

route. All path profiles and engineering are based

upon ray analysis.

• Antennas serve only to provide maximum

coupling of the direct ray energy into the

waveguide feeder, to the exclusion of multipath

rays. Thus, optimum dish alignment is crucial

for minimum fading.

k = 1 (True Earth’s Radius)

Superrefraction (k>3)

Wavefront Ray 90o

Substandard Refraction (k<1)

Possible

Obstruction

Possible

Decoupling,

Defocusing, or

Entrapment

Dry and High Valleys

Humid Wetlands

Carrier Ethernet Link Design Parameters

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• NETWORK LAYOUT

• FIELD VERIFICATION

• MICROWAVE EQUIPMENT (Backhaul

Capacity, Link Aggregation, RF Band,

Diversity)

• LINK ANALYSIS (Google Map Study, Field

Survey, Geometry, Weather Patterns)

• LINK PERFORMANCE CALCS (ITU, Vigants)

• LINK AVAILABILITY CALCS (RF Protection,

Rain Outage)

• ACTIVE NODES and PASSIVE REPEATERS

• FREQUENCY STUDY (Interference,

Licensing, Antenna Selection)

• INFRASTRUCTURE (Shelter, AC/DC Power,

Site Security, Towers, Ice Shield, Air Con, etc.)

• ANTENNA FEEDER SYSTEM, (Structures,

Aesthetics, Transmission Lines)

• GROUNDING AND SAFETY

Towers >200ft (60-m)

Require Lighting,

Painting

Sections:

20-ft guyed,

25-ft Self Supp Shelter

Elliptical

Waveguide, Coax

Atmospheric

Multipath

Millimeter Wave

Rain Attenuation

Refraction, k-Factor

Variations

Antenna Sizes,

Types, Alignment

Diversity

Type, Ant.

Spacing, XPIC

Path

Clearance

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Dust Cloud

Multipath Propagation

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Excessive Path

Clearance

Elevated Super-refractive

Layer

Specular Reflection

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E. ANTENNAS AND FEEDER SYSTEMS

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Reflector Antennas

Photos courtesy of Andrew Corporation

July 2013

Standard parabolic

Standard parabolic

(with radome) Shielded with radome

(high performance)

Higher F/B ratio

Spillover Effect Scattering Effect Diffraction Effect

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Antennas

• Used to efficiently radiate/receive the energy towards/from

the far-end of the link

• Important characteristics

– Gain / directivity / beamwidth

– Side lobe level

– Front-to-back ratio (F/B)

– Polarization (linear V/H, circular, dual V/H)

– Cross-polar discrimination

– VSWR

– Frequency operating range

– Mounting, weight, and wind loading

– Aesthetics

July 2013

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Antenna Alignment Issues

Antenna aligned on a side-lobe

Correct antenna alignment

July 2013

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Antenna Decoupling

• Angle of arrival may vary by as much as 1° on long paths

in humid areas at night; therefore larger antennas are

typically slightly uptilted during daytime periods

• Such variations may cause power fades and degraded

performance (loss of fade margin, increased outage) if

antennas are very directive

Variation in arrival angle

K=

K=4/3

K=-2

July 2013

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PRESSURIZED (AIR)

COAXIAL CABLE

UNPRESSURIZED (FOAM)

COAXIAL CABLE

ELIPTICAL

WAVEGUIDE

RECTANGULAR (RIGID)

WAVEGUIDE

CIRCULAR (RIGID)

WAVEGUIDE

Transmission Lines

July 2013

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Transmission Lines (Feeder Systems)

• Coaxial cable

• Air dielectric (lower loss)

• Foam dielectric (higher loss)

• Works from DC, but losses increase very rapidly above 2GHz

• Waveguide

• Elliptical (very common)

• Circular (very low loss)

• Rectangular (now rarely used)

• Flexible/twistable waveguide

• Frequencies below cut-off do not propagate through waveguide

July 2013

F. RF PROTECTION

Definitions

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• Protection Schemes provide a level of security from long-

term (>10 CSES/event – Consecutive Severely Errored

Seconds) outages and loss of data throughput, and

therefore improve Availability and reduce traffic

disconnects.

• Diversity Arrangements reduce the number and duration

of short-term (<10 CSES/event) outages (no traffic

disconnects) and therefore improve Performance.

July 2013

F.1 MONITORED HOT STANDBY

1+1 Monitored Hot Standby Outdoor Node (cont’d)

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Tribs 1-20

Protection

Cable

ODU 600sp/hp/ep

Y-Cables

1+1 Monitored Hot Standby Outdoor Node

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Equal split (3dB)

RF Splitter is also

possible with the

consequence of a

2dB link gain

penalty which

translates into a

58% degradation in

the hop’s error

performance and

perhaps larger

antennas!

ANTENNA

DATA

OUT

DATA IN

-1.6dB

-6.6dB

Tx A

Rx A

Tx B

Rx B

Asymmetric

RF

Coupler

INU/IDU errorless data

selection is frame-by-frame

-1.6dB

-1.6dB

Tx A or Tx B is on line

H.2 MONITORED HOT STANDBY WITH

SPACE DIVERSITY

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Space Diversity with Horizontal Offset

1+1 Monitored Hot Standby Space Diversity - Outdoor Node

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Multipath forms essentially

in the vertical plane;

consequently, the antennas

should always be placed

vertically to achieve de-

correlated paths !

Main ANTENNA

DATA

OUT

DATA IN

Tx A

Rx A

Tx B

Rx B

INU errorless data

selection is frame-by-frame

Diversity ANTENNA

300 ms

Vertical antenna spacing from 3 – 23m

ITU-R P.530-13

RSLM

RSLD

-40 dB fade

-20 dB fade

THANKS YOU AND SUGGESTIONS

Suggestions

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