PART 1Microwave Communication Principle

NEC CorporationNEC Corporation

CONTENTS

1. Introduction to microwave system

2. Block diagram for microwave communication system

3. System hierarchy

1. Introduction to microwave system

1.1 DIFFERENT TRANSMISSION METHODS

MUX

Satellite

Fiber-optics cable

Radio link

Coaxial cable

MUX

1.2 Frequency for microwave ：300MHZ ～ 300GHZ

Wavelength ：1m~1mmSubband：UHF: 0.3-1.12G X：8.2-12.4G L: 1.12-1.7G KU：12.4-18G LS：1.7-2.6 G K: 18-26G S：2.6-3.95 G Ka:26.5-40G C：3.95-5.85G U: 40-60G XC：5.85-8.2G

10Km 1Km 100m 10m 1m 10cm 1cm 1mm

f 30KHz 300KHz 3MHz 30MHz 300MHz 3GHz 30GHz 300GHz

LF MF HF VHF UHF SHF EHF

microwave

1.3 Features:

1. Short wavelength / high frequency easy to design compact and light aerial system and wide bandwidth, large capacity

2. Frequency plan

3. Line of sight propagation, reflection, diffraction and scattering etc.

4. Free space loss

5. Fade caused by other types of path loss. Multipath.

6. Interference

85432 10 201 30 40 50

1.5 2.5Regional network

National network

Regional and local area network

2834

Mbit/s34140155

Mbit/s

28

34140155

Mbit/s

3.3 11 GHz

GHz

1.3.1RADIO-FREQUENCY USE

1.3.2FREQUENCY PLAN

Channel number

Frequency

F3

F1F2

Fo

1 2 n 1' n'

Lower half band Upper half band

Center frequency

Fo: Center frequency

2'

1.3.2 FREQUENCY SHIFT BETWEEN CHANNELS

ANALOG

DIGITAL

1800 channels MF 140 kHz rms/channel 30 MHz

CAPACITY MODULATION DEVIATION

2700 channels MF 140 kHz rms/channel 40 MHz

30 channels 2 Mbit/s 4 PSK 3.5 MHz

120 channels 8 Mbit/s 4 PSK 7 MHz

480 channels 34 Mbit/s4 QAM 30 MHz

16 QAM 14 MHz

1920 channels 140 Mbit/s16 QAM 40 MHz

64 QAM 30 MHz

1.3.3/4 RADIO PROPAGATION

The radio link propagation follows the line of sight: it requires a perfect clearing between transmitingand receiving antennas. The propagation medium is made of the lower layers of the atmosphere(a few meters to a few hundred of meters above ground)

The non homogeneity of the atmosphere influences the waves propagation:1°) Path curvature2°) Reflecting, diverging, focusing intermittent events

Free space loss=92.4+20*log(f*d) (dB)

among them, f:GHz, d:km

Atmosphere influence

Refraction Partial reflection Absorption Diffusion

i.1

i.2

n1

n2

n1*sin i.1 = n2*sin i.2

n1

n2

Almost horizontal height

Gaz and water vapor

Frequ. < 15 GHz : insignificant20 GHz : 0.1 dB / km

Rain

Frequ. > à 10 GHz

Diffusion volume

500Km

RADIO PROPAGATION

Ground influence

DiffractionReflection

Diffraction on a ridge

Spherical diffraction

RADIO PROPAGATION

RImaginary EarthReal Earth

Ro

Standard atmosphere N = - 39 N.units Km

K = R/Ro = 4/3h

h

Radio path

Air refraction index at sea level : n = 1,000 315

N = 315 N units

N : Gradient of air refraction indexN may reach more extreme values than + 250 or - 350, during short percentage of time

Using an imaginary earth with a radius of 8500 km, allows to simplify the radio hop perception

RADIO PROPAGATION

Changes of transmitting media,such as, atmosphere, link, time, altitude,climate etc.

Fading due to multipath arising from surface reflection

Attenuation due to atmospheric gases;

Attenuation due to precipitation

Type of fading:

fast fading and slow fading;

fast fading: the channel impulse response changes rapidly within the symbol duration.

slow fading:the channel impulse response changes at a rate much lower than the

trasnsmitted baseband signal.

up fading and down fading;

up fading: direct wave arrives later than reflecting wave; down fading: virse versa

frequency selective fading and flat fading

the received signal spectrum remains a close replica of the transmitted signal spectrum

except for a change in amplitude.

1.3.5 FADING

SELECTIVE FADING

Cause: Multipath propagation

Refraction

ReceiverTransmitter

A max

A minFrequency

Radio channel > 1 non-minimal phase fading

A

F0F

A

AA

For A1 = A2 A max dB = + 6A min dB = -

A

F = 1

1

1

1

2

- A+ A

2

2

8

= T

=AA

2

2

1

- T 1

Reflection

A ,T2 2A ,T 11

< 1 minimal-phase fading

The direct signal is larger than the reflected signal.

FADINGMain cause: Rain snow for frequencies > 10 GHz

Transmitter

FI

-80 < Pr < -20 dBm

Receiver Demodulator

DigitalSignal

IF

A B

CAG

A

Time

dBm

W 0

Noise

WSignal

Noise

B

dBm

Time

IF Level 0 dBr ± 2dB

CN

COUNTER-FADING MEASURES

A. Techniques without diversity

• reduction of the levels of ground reflection

• increase of path inclination

• various equalizers

B. Diversity techniques

• FD

• SD H

10.2/F1/2<H<37/F1/2

1.3.6 INTERFERENCE

A. Co-channel interference

Caused by other signal residing at the same frequency as the desired signal

B. Adjacent channel interference

Caused by RF leakage on the operational channel from a neighbouring RF equipment using an adjacent frequency. This can occur when an adjacent channel user is operating in close proximity to the user’s receiver, or when the user's signal is much weaker than that of the adjacent channel user.

COUNTER-INTERFERENCE MEASURESA. Increase Transmit Power

B. Bandpass filter, sharp cut off filter

MICROWAVE RADIO LINK

TX/Rx

TerminalStation

Relay station(Active)

Hop NO.1

or

Relay station(Passive)

TX/Rx

TerminalStation

Cable CableRadio link

Distance between the transmitter and the receiver, some km < D < 100 km

Availability and quality are depending on distance according I.T.U.R. rules

Hop NO.2

Hop No.n

TX/Rx TX/Rx

2. Block diagram for microwave communication system

• Block diagram for microwave system

Source encode TX BB MOD UP CONV

PWR AMP

BR CKT

SYN

RX decode RX BB DEM DOWN CONV LNA BR

CKT

(Modulator )

(Demodulator )

TX Rx

Antennas

IFUHF/SHF

BB : Base band

Base band

IF : Intermediate Frequency

UHF : Ultra-High Frequency (300 - 3000 MHz)

SHF : Super-High Frequency (3000 - 30.000 MHz)

MICROWAVE LINK STRUCTURE

MODULATOR

Auxiliary rates

Digitaljunction

Microwaveframe Modulator

organisation

IF output

Zc = 75

- Serial/parallel conversion- Data scrambling

- Forward Error Correction code (F.E.C)- Calculation & coding of parity bit

- Cable correction- Clock recovery- Regeneration- Code x NRZ transcoding

- Coding- Filtering

2/8/34/140/155 Mbit/s

Zc = 75

CCITTG.703

32/64/704/2048 kbit/s

- Sync. clock/microwave frame

- AIS switching

- 2 state modulationn

- Auxiliary rate adaptation- Multiplexing

MODULATOR PRINCIPLE

PSK 4 MODULATOR BLOCK DIAGRAM

PSK 4 - COHERENT DEMODULATOR PRINCIPLE

PSK4 - COHERENT DEMODULATOR - DECISION CIRCLES

PSK 4 - COHERENT DEMODULATOR BLOCK DIAGRAM

MODULATOR / DEMODULATOR - COMPLETE BLOCK DIAGRAM

16 QAM PRINCIPLE

16 QAM MODULATOR BLOCK DIAGRAM

16 QAM DEMODULATOR PRINCIPLE - DECISION LEVELS

16 QAM DEMODULATOR - BLOCK DIAGRAM

DIGITAL RADIO TRANSMISSION EQUIPMENT

- Microwave frame- Multiplexing- Modulation

- Translation- Amplification

- Demodulation- Microwave frame

.Demultiplexing

.Measurements of B.E.R.- Distorsion correction

- Translation- Amplification

Modulator Transmitter Receiver Demodulator

Transmission Reception

Main

rate

MICROWAVE FRAME

Microwave frame object:

– Extra-bit insertion/extraction:

Service channel Supervision of quality Auxiliary rates

– Data scrambling

TS/RC function

Digital junction

MODULATOR

2/8/34/140/155 Mbit/s

NRZ

CkSwitch

Clockrecovery

RegeneratorTranscoder

AISGenerator

Cablecorrection

Digitalaccess

G703

Signalling

f

MODULATOR

Frame and modulator

Scrambler

NRZ

Ck

Multiplexer

ParityECC

Calculator

Serial

Converter

Encoder

1

BB Filter

Modulator

IFOutput

IF oscillator

Auxiliary data

F.A.W

SHAPING FILTERS

Eye diagram

Forced-up cosinus responseH (f)

T

T2

0 f12T

1TUseful band

(Nyquist)

= 0

= 0.5

= 1

1

0 T-T-2T-3T 2T 3T

12

Transcient response

= 0

= 0.5

= 1

t

with noiseIdeal

TRANSMITTER

Principle

IF

Oscillator: Fn±FI

Amplifier Converter Amplifier

Frequency

A

IF Fn SHF Canal

Translation

RECEIVER

Principle

Fn Fn'

dB dB

Fn

Oscillator Fn'

Converter Amplifier

IF

IF

IF

Frequency Frequency

DEMODULATOR

Equalizer Demodulator Digitalprocessing

Auxiliary rates

Digital

Signal

- MVT search- Demultiplexing- Descrambling- Parallel/serial conversion- NRZ/code x transcoding- Quality analysis

- Demodulation- Clock recovery- Regeneration

Selective fading dynamic correction

(B.E.R. 1.10 ; 1.10 )-6 -4

MINIMUM PHASE EQUALIZATION SYSTEM

Minimal phase

Processor

IF Receivedconstellation

Regeneration+

Digitalprocessing

Digital

output

Demodulator

Tb2

A'1

A 2

A1

(T2)

T 2 T 1-A2

Delay = Tb2 +

A1

A'1 = A1

= 1A

A 2

1A A 2+

Recursive filter(T1)

< 1

EQUALIZATION SYSTEM

Non-minimal phase

Demodulator

A

Processor

+ A 1 2 2

Tb

A1

A2

A1

A2

A' 2

A' 1

+

A' 1A2

= 2t' = t +

T b

2+ O

A' 1 = A1

A2

A1= , t = T 2 - T 1

= A2

A1> 1

A2, T 2

A1, T 1

A2 +( T b

2O

(

A2 + A1( ) T b

2+ O

A2 + A1( ) 1

Transversal filter1

SELECTIVE FADING: CORRECTION SYSTEM

Signature description

The signature is the performance achieved by an equalizer circuit

for a given BER (10 ) -3

S = 20 log (1 - = AA

Rx Equ. Demod. 1.10 -3

A

0

A

R

A

+-

20 log (1 -

0 dBr

A

A

= K avec K impair

MHz

)

)

1

1

1

2

2

2

2

measurementBER

= 6,3 ns

F

F

3. System hierarchy

DIGITAL SYSTEM HIERARCHY

2400/19200 bit/sData VF

TN 1

64 kbit/s

2.048 Mbit/s

8.448 Mbit/s

34.268 Mbit/s

139.264 Mbit/s

TN 2

TN 3

TN 44 x 480 channels

1920 channels

4 x 120 channels

480 channels

4 x 30 channels

120 channels

+ frame + stuffing

30 channels 64 kbit/s + 64 kbit/s signalling + 64 kbit/s frame32 x 64 = 2.048 kbit/s

Data

MUX PCM

TRT PRODUCTS

Tx/RxCMI

Tx/RxHDB3

Tx/RxHDB3

Tx/RxHDB3

1

432

1

432

TN21

432

1

30

140 Mbit/s34,268 Mbit/s

8,448 Mbit/s

2,048 Mbit/s

64 kbit/s

34 Mbit/s

8 Mbit/s

2 Mbit/s

Tx/Rx

TN4

2/34 Mbit/s PDHADM155

155 Mbit/s

CMI

4x2 Mbit/s

or 4x2 Mbit/s

or 16x2 Mbit/s

TN3

TN1