Transmission Overview

Sept 22-23

-S.Naga Kishore

1. Schedule2. Purpose3. Transmission required? 4. Day 1, 2 sessions5. Conclusions

INDEX

Morning session:

• Fundamentals of Transmission• What is E1?• Summary

Post Lunch session:

• PDH/SDH• Summary

Day 1

Morning session:• Fundamentals of Fiber optics• Link Budgeting• Measurements• DWDM• Summary

Post Lunch session:• Fundamentals of Microwave• Link Budgeting• Measurements• Summary

Day 2

The Purpose

This training is intended to give overview on the following: 1. Transmission principles - Modulation, Multiplexing, Digital

modulation

2. Media of Transmission - Microwave, Fiber Optic, Satellites

3. Measurements & Test instruments of Transmission

4. Equipments of Transmission

5. Over view of PDH, SDH

6. Link budgeting

1. Is Transmission required?

“Mr.Watson come here, I want you”- This is the first sentence delivered(transmitted) by A.G.Bell on Mar 10th 1876.

If there are three phones the connection could be

A -- B -- C—|

|_ _ _ _ _|

If there are three thousand? I don’t think it is easy!! Will you!!!

Fundamentals

Transmission made Simple:

1. Frequency (Lamda)2. Power3. Band width

FREQUNCY WAVE LENGTHOLD NEW GHz

3-30 MHz

0-250MHz 0.1 3m0.15 2m

300-1000MHz 0.2 1.5m0.3 100cm

250-500MHz0.5 60cm

300-1000MHz500-1000MHz 0.75 40cm

1.0 30Ccm1-2 GHz 1-2 GHz 1.5 20cm

2.0 1.5cm2-3 GHz 3 10cm

3-4 GHz 4 7.5cm5 6cm

4-6 GHz 6 5cm

6-8 GHz 8 3.75cm

8-10 GHz 10 3cm8-12.4GHz

12.4GHz-18GHz 10-20 GHz 15 2cm

18-26.5GHz 20 1.5cm20-40 GHz 30 10mm

26.5-40 GHz40 7.5mm

33-50 40-60 40-60GHz 50 6mmGHz GHz

60 5mm50-75 60-90 GHz GHz 60-140GHz 75 4mm

100 3mm75-110GHz 110

110-170GHz 140 2mm

BAND DESIGNATIONS

HF A

VHF

BUHF

C

L D

S E

F

C G

H

X I

JI Ka

KK

Q Ka

U L

V E O M

W

T

Frequency - Band Designation, Old and New

0 +40

-10 +30

-20 +20

-30 +10

-40 0

1 mW 10 mW 100 mW 1 W 10W

100nW 1mW 10mW 10mW 10mW

dBM Watts Vs. dBM

POWER: Power Ratio dBm –mW - W

Bandwidth:

It is the width of the channel. Form Freq. X to Freq. Y

Bandwidth = X(8 Khz) ~ Y(4 Khz) = 4 Khz

Bandwidth

12

3 n-1n-2

0 f4KHz 8KHz 12KHz

Bandwidth used = n x 4 kHz

Multiplexing:Channel multiplexing is essential for telephone transmission. This technique makes it possible to reduce, very substantially, the number of links required to connect the subscribers.

Frequency Division Multiplex:This system is based on the position of the different channels to be transmitted in terms of frequency. Each channel uses a maximum frequency band of 4 KHz. The no. of channels transmitted is thus calculated by dividing the multiplexed frequency band by 4 KHz.This multiplexing mode makes it possible to obtain a high number of channels in a restricted bandwidth but involves a number of disadvantages which tend to cause relatively rapid degradation of the data transmitted: high sensitivity to external interference and aggregation and amplification of distortion up to the final destination.

PRINCIPLES OF DIGITAL TRANSMISSION

12

3 n-1n-2

0 f4KHz 8KHz 12KHz

Bandwidth used = n x 4 kHz

Time Division Multiplex (TDM)Principle: The signal to be transmitted is fully defined by its instantaneous values sampled at regular intervals, subject to certain conditions (Shannon Theorem). It is therefore possible to Insert samples of n-1 other channels between two samples of a particular channel, to constitute aTime Division Multiplex (TDM) frame of n channels.The sampling of the original voice signal is made at 8 KHz I.e. twice the maximum frequencyIn the signal being transmitted (300 Hz – 3400 Hz).

1

2

1

2

nn t

Channel Repetition (Te) Frame of n channels (Te)

Te Te

32 analogchannels

32 analogchannels

J

U

N

C

T

I

O

N

J

U

N

C

T

I

O

N

TNE 1 TNE 1

BIN

BIN

2.048 M

HDB 3

HDB 3

DIGITIZATION PRINCIPLE Component elements of a low rate link:

A low rate link multiplexes 32 telephone channels giving a digital transmission rate of 2.048 Mbps. This type of link has two basic elements, these being the PCM multiplexer (TNE1) and the line terminal (TNL). The CCITT recommendations, designed to define standards common to all equipment, apply at line terminal junction level.

The TNE1 provides the five basic ADC or DAC operations:

Sampling / quantification / compression / coding / time-division multiplexing

The TNL provides the following three functions:

Junction between multiplexer and telephone link / transcoding / junction and line testing.

Modulating Signal

Amplitude modulated pulsesTe

Sh

Se Ss

t

t

Sampling pulses

SamplingAnalog signal Se, already compressed in order to limit its dynamic range, is sampled by clock Signal Sh. Resultant signal Ss comprises a series of pulses, the amplitudes of which represent the levelsOf input signal Se when the sampling gate opens.

A/D CONVERSION

S / N

50 dB

40 dB

33 dB30 dB

20 dB

10 dB

- 70 - 60 -50 - 40 - 30 - 20 - 10 0

dBM

98% of cases

Compression:

As the majority of levels to be transmitted are between – 30dBM and 0 dBM, a compression law must be found where the S/N ratio is satisfactorily throughout this amplitude range. The optimum result is obtained by reducing the size of the steps for weak signals. The compression law therefore has a linear part, comprising a series of small, equal steps, followed by a logarithmic part for the other steps.

s A B C W X Y Z

Sign Segment Position in segment

Coding:

When the first signal has been quantified, the value of the steps which it occupies at the sampling times isTransmitted in binary code form. The coding law uses 12 straight line segments, each with 16 ranges (giving a total of 256 ranges). The ranges occupied are coded in 8-bit binary word form as mentioned above.

10

1

0 01 1 1 0 0 0 0 0 0

1 0 1 0 0 1 1 1 0 0 0 V 0 1

Binary Code

HDB3Code

Binary Code

HDB3Code

1 0 0 0 01 1

0 0 0 0 0 0 0 0

1 0 0 0 V VV PP1 1 0 0 0 0 1

HDB3 Code:(third other high density binary code)

This code must comply with the following rules:• bipolarity rule: “1” bits coded alternately +1 and –1, with RZ in the next half-period. When two successive “1” bits have the same polarity this corresponds to violation of the bipolarity rule.• there must not be more than 3 consecutive “0” bits. To achieve this, the 4 th “0” bit is replaced by a “1” bit. To detect this substitution for deletion of the spurious “1” bit at the reception end, it is sent a violation of the bipolarity rule (V), as shown in the following example.

• successive violations must be of opposite polarity. If all violations in a sequence of “0” bits have the same polarity, the mean value of the signal would be non-zero. When the number of “1” bits between two violations is not odd, a packing bit at “1” (P) is added in place of the first “0” bit.

HDB 3 Code

Bipolar RZ Code

1T

Frequency

W (f)

Nevertheless, the redundancy of the HDB3 code allows detection of line transmission errors.

The HDB3 code shows slightly modified spectral distribution with respect to the binary RZ code.

PCM / MEOrder 1

2.048 Mpbs

PCM / ME2/8

PCM / ME8/34

PCM / ME34/140

34.368Mbps

PCM / MEOrder 1

4xME 1 139.264Mbps

8.448Mbps

2.048 Mpbs

High rate link.

A high rate link is the result of a succession of PCM/ME multiplexing stages, serving to increase:

• digital transmission rate

• link channel capacity.

32 channels

32 channels

SATELLITE

R F LINK

COAXIAL CABLE

HIGHER ORDERMULTI-PLEXER

HIGHER ORDERMULTI-PLEXER

OPTICAL FIBER CABLE

OPTICAL FIBER:

Synchronous Digital Hierarchy

PLESIOCHRONOUS DIGITAL HIERARCHY (PDH)

Telephone

Telephone

Primary

PCM

Multiplex

Audio

1

30

1 1 1 1

4 4 11

M 1-2 M 2-3 M 3-4

2.048 Mb/sHD B3Primary

8.448 Mb/sHD B3

Secondary

34.368 Mb/sHD B3Tertiary

139.264 Mb/sHD B3

Quaternary

280Mb/s

280Mb/s

1.2Gb/sEtc.

Limitations / Disadvantages of PDH:

1. Inability to drop lower bit rates directly from 3rd or 4th order

2. Alternate Routing - Data lost during rerouting

3. Frame slip - Due to lack of Synchronization

4. Limited NMS Support - No spare signal capacity

5. Higher Bit rates are proprietary - no possibility of inter working

Multiplexer Mountain34 Mbps

8 Mbps

2 Mbps

140/34 140/34

34/8 34/8

8/2 8/2

140M 140M

Customer

SYNCHRONOUS DIGITAL HIERARCHY (SDH)

• Background/History: CCITT Study Group XVIII formed in June 1986November 1988- First SDH standards were approved

- G 707, 708 & 709.• Advantages:

1. No need for Mux banks as per hierarchy to drop lower data rates.

2. Common standard enabling multi-vendor network3. Better Management - TMN - nearly 5% of signal bandwidth4. Accommodates both existing and future services -

ATM, B-ISDN etc. 5. Fast provisioning6. Better network survivability

SDH HIERARCHY (CCITT)

• Synchronous Transport Module

STM - 1 - 155.52 Mb/s

STM - 4 - 622.08 Mb/s

STM - 16 - 2.488 Gb/s

Equivalent SONET (USA) standards are

(Optical Carrier) OC1, OC3, OC12 & OC48

SDH NETWORK ELEMENTS

• Line Terminal Mux (LTM): Can accept a no. of Tributary signals and multiplex them to the appropriate optical / electrical SDH rate carrier i.e. STM-1/4/16.

The input tributaries can be either PDH/lower rate SDH Signals.

TMs form the main gateway from the PDH to SDH network

LTM

140MB or

STM1

STM-N

(N=4 or 16)

1+1 Protection Switching

SDH NETWORK ELEMENTS

• Add Drop Mux (ADM): A particular type of Mux designed to add / drop channels from the ‘through’ signal. Generally available at STM-1/4 interface rates and signals at 2/34/140 Mb/s.

ADM function is one of the major advantages of SDH, eliminating the need for banks of hardwired back-back terminals.

EastWest

2MB 2MB

STM1

STM1

ADM

SDH NETWORK ELEMENTS

• Synchronous Digital Cross Connect (SDxC): They can function as semi-permanent switches for transmission channels and can switch at any level from 64kbps to STM-1, generally having interfaces at STM-1/4.

Can be rapidly reconfigured under software control, to provide digital leased lines and other services of varying bandwidth.

STM-1STM-1

DXC

SDH NETWORK ELEMENTS

• Regenerator: For SDH Transmission over 50km, regenerators are required with spacing dependent on transmission technology. They have alarm reporting and performance monitoring capability.

STM-NSTM-N

SDH FRAME STRUCTURE

• SDH Terms:STM-N: Synchronous Transport Module ‘n’ (n=1,4, 16) consists of ‘FRAMES’ into which data is filled.

VC-4 : Virtual Container Level 4. A defined area to carry user data;

140Mbps.

TU: Tributary Unit Signal. Subdivision of VC-4 to carry lower rate services (2,34MB)

Analogous to Road Transport System:

A

A

B

B

B

STM Frames

Optical Carrier

TU Frames

VC-4

Pallets = TU Frames

A

SDH FRAME STRUCTURE

• SDH - a transport system

The transport system adopted in SDH is analogues to a road transport system. If you need to deliver items between 2 points you need trucks. Depending on the quantity of items to be moved you need small or large trailers. Depending on the size of the items being shipped you need “pallets” to allow simple stacking with the trailer payload area. For different item types you have different pallets and different loading instructions.

SDH has exactly the same concepts wit different names:Road - Optical CarrierTruck - Synchronous Transport ModuleTrailer - Virtual Container level 4Pallets - Tributary unit frames

Synchronous Transport Frame for STM-1

F1 F2 F3 F4 F5 F6 Etc.

A1 A2

STM-1 Virtual Container(VC-4)

SECTION

OVERHEAD

Framing Bytes STM-1

155. 52Mbit/s

9 ROWS

9

810 BYTES

261

270 COLUMNS

2430 BYTES/FRAME * 8 BITS/BYTE * 8000 FRAMES/SEC = 155. 52 Mbit/s

A1 = Frame word = 11110110; B1 = 00101000

Synchronous Transport Frame for STM-1

Six Framing Bytes (3 X A1 followed by 3 X A2 Bytes) act as a marker, allowing any byte in the frame to be easily located.The concept of Transporting Tributary Signals intact across a Synchronous network has resulted in the term, ‘Synchronous Transport Frame’, consisting of two parts -

a VC part & a Section Overhead part.VC: Individual tributary signals are arranged within the VC for end-to-end transmission. VC is assembled and disassembled only once, even though it may be transferred from one transport system to another many times.Section Overhead (SOH): this provides facilities (such as alarm monitoring, BER monitoring and datacom chls.) required to support and maintain the transportation of a VC between nodes in a synchronous network. SOH pertains only to an individual transport system and is not transferred with the VC between transport systems.

Synchronous Transport Frame for STM-1

• Section Overhead (SOH): To ensure that the clock can always be recovered from the received data , all bytes in the frame except those in the first row of SOH are scrambled.

Tributary

Signal

VC ASSEMBLY NODE

Transport System ‘X’

Transport System ‘Y’

Tributary Signal

Transport Frame ‘X’

Transport Frame ‘Y’

SectionOverhead ‘X’

Section Overhead ‘Y’

SDH NETWORKNODES

VC ASSEMBLYNODE

SDH MUX HIERARCHY

STM-N AUG AU-4 VC-4 C-4

TUG-3 TU-3 VC-3

C - 3

TUG-2 TU-12 VC - 12 C - 12

xN x1140MB/ S

x3

x7

x3

34 MB/ S

2MB/ S

Admin UnitGroup

Tributary UnitGroup

C - 12 Container Tributary Unit (TU) + Overhead = + Pointer

STM-1 -> 155 52MB/S -- 63X2 MB/S -- 3 X34 MB/S -- 1X140 MB/S

= Addressing Unit (AU)

Mapping of 2Mbps into STM – Mapping of 2Mbps into STM – N signalN signal

A corresponding arrangement is used for demultiplexing

2.048 Mbps(E1)

1 2 3 32

32 Bytes

1 2 3 32VC-1235 Bytes

POH (Lower Order)

1 2 3 32C-1234 Bytes

Stuffing Bytes

Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N

TU-12

36 Bytes

Pointer

9 Rows

4 Columns

TU 12 is arranged Into Matrix of 9 X 4

Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N

TUG-2 9 Rows

12 Columns

9 Rows

4 Columns 4 Columns 4 Columns

TU-12 TU-12 TU-12

Multiplexing

Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N

7 TUG-2s

Stuffing Bytes

86 Columns 84 Columns

TUG 3

X 7 TUG-2 TUG-3(multiplexing)

Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N

PAY LOAD

RSOH

MSOH

AU Pointer

261 Columns

270 Columns

9 Columns

1-3 rows

5-9 rows

4th row

STM-1 frame structureSTM-1 frame structure

261 Columns

AU – 4 (Adding Pointer)

PO

H

Pay LoadAU Pointer

9 Columns

4 th Row

Pay LoadPO

H

VC - 4

261 Columns

9 rows

Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N

Path OverHeadPath OverHead

TCM – Tandem Connection Monitoring

SDH MUX HIERARCHY

To take care of small timing differences in the synchronous network and simplify Mux / demux and cross connection of signals, VC-4 is allowed to float; may begin in one frame and end in next.

Additional bytes called ‘AU Pointer’ in SOH, contains a Pointer value to indicate the location of the first byte of VC-4.

PAYLOAD

MAPPING

TRIBUTARY

SIGNAL

PAYLOAD

CAPACITY

140 MB/S

(C - 4)Mapped

140MB/S

at 149.76MB/S

PATH

OVERHEADSTUFF BITS

VC - 4150.34 MB/S

VC - 4Assembly Process

SYNC.VC

SDH PROTECTION

1. Hardware / Board Protection:For 2MB protection of Card failure

Switching time ~ 2 Sec.2. MS (Multiplex Section) Protection:

for TMs - DoT PoIsfor STM Aggregate protection against card failure

Switching time ~ 2 Sec

3. SNCi (Sub Network Control-inherent monitoring) Protection - ADMs:Path protection against fiber cut / node failure.STM-1 protection - data parallely sent on both directions and better one is selected or available one incase of failure.

Switching time < 100ms.

Digital Microwave

BELL Digital Multiplex Hierarchy

1

Primary

PCM

Multiplex

24

1

M1-2

4

1

M2-3

24

1

n

1

Primary

PCM

Multiplex

30

1

M1-2

4

1

M2-3

4

1

M3-4

4

1

n

1.544 Mb/sB8ZSDS1

6.312 Mb/sB6ZSDS2

44.736 Mb/sB3ZSDS3

2.048 Mb/sHDB3

Primary

8.448 Mb/sHDB3

Secondary

34.368 Mb/sHDB3

Teritary

139.264 Mb/sCMI

Quaternary

90 Mbps

180 Mbps

432 Mbps

565 Mbpsetc.

280 Mbps

565 Mbps

1.2 Gbpsetc.

Audio

Audio

European Digital Multiplex Hierarchy

BELL Digital Multiplex Hierarchy

The various digital services, whether they are digitized telephony (64 kbps PCM or 32kbps ADPCM), data, videotex or facsimile etc., are time division multiplexed (TDM) together to form higher rate bit streams. This is done in stages as shown in this slide of the North American and European digital hierarchies. These are the most commonly used hierarchy rates, different hierarchies are used in Japan and in some military systems. The output of each multiplex stage may form the tributary stream for the next stage of multiplexing in a high-capacity system, or may pass directly to the transmission system in a lower-capacity route.

Digital Transmission System

HigherOrder

Multiplex

HigherOrder

Multiplex

MEDIA

LINE (COAX CABLE)

DIGITAL Radio

SATELLITE

Terminal Terminal

OPTICAL FIBER

CCITTINTERFACE

CCITTINTERFACE

Digital Transmission SystemThe bit rates and interface codes etc are all standardized by CCITT (International Telephone and Telegraph Consultative Committee) and are independent of the particular transmission medium used. The transmission system may carry traffic at any of the bit-rates in the hierarchy, depending on the capacity through-put requirements of the system. The testing and the performance of the system at these interfaces relates to network performance in the IDN and again is specified by CCITT independent of the transmission media. These standards have been adopted by CEPT in Europe and by the ANSI/ECSA*TI Committee in North America.

This slide shows the four commonly used methods of transmission. Optical fiber is the most popular for high-capacity routes in Network Operators (PTT’s Telcos and Common Carriers) where existing routes or “way-leaves” exist. However, Microwave Radio and Satellite have many applications in lower capacity routes, in difficult terrain and in private and military communication networks where the advantages of flexibility, security and speed of installation offered by Radio and particularly valuable.

MOD IF RF RF IF DEMOD

RF IF IF RFREGEN

IN OUT

FIRST REPEATER SECOND REPEATER

REPEATER

Transmit Terminal Receive Terminal

CCITT INTERFACECCITT INTERFACE

A practical Radio relay system often consist of several hops as the maximum distance between transmit and receive antennas or “hop length” is normally 30 – 60 km (20-40 miles) in a line-of-sight system. The intermediate stations are called repeater stations and the traffic data stream may not necessarily be brought down to CCITT interface at these points, but simply regenerated at the binary level. Some Radios use a direct IF repeater without regeneration. This saves cost, but some of the benefits of digital transmission are lost because of the build up of noise and distortion in a similar way to analog Radio systems.

The microwave frequency bands and the Radio channel spacing in these bands have all been standardized by CCIR (International Radio Consultative Committee) and FCC in North America. Some typical frequency bands are 2 GHz (used for lower capacity), 4,6,7,8,11 and 14 GHz. Above 11 GHz rain attenuation becomes a greater problem necessitating a shorter hop length for a given system availability. There is a new generation of Radios becoming available, operating in the range 15-50 GHz which provides low and high capacity short-haul links in cities for interconnecting business centers with main transmission centers. The small physical size of antennas at these frequencies makes this type of link very easy to install.

Digital Radio Block Diagram

CODER

~

~~

~

~~

~

~~

~

~~

~

MOD

D

ECODER

~

~~

~

~~

DEMOD~

~~

~

~

~~

UPCONVERTER

DOWNCONVERTER

Here is a simplified block diagram of a digital Radio transmitter and receiver. Those of you familiar with analog Radio will recognize a strong similarity in the block diagram, though the modulator and demodulator sections are very different as we shall see later.

Digital Radio Block Diagram

This block diagram shows IF modulation and demodulation (at the familiar 70 MHz or 140 MHz IF) with up and down conversion to the microwave transmit frequency. Most high-capacity digital Radios use this system but there are quite a number of low-capacity Radios with simple modulation schemes which use direct modulation at microwave frequencies. In this case the modulator is connected directly to the power amplifier.

Most Radios use the same receiver structure with down-conversion to the IF where the automatic gain controlled amplifier (typically 50 - 60 dB range) maintains a constant level to the demodulator during fading.

Notice the various filters through the transmitter and receiver. These are very important in the overall design as we shall see later. First we will look at the coder and decoder section sections which provide the interface to the outside world.

Coding

•STANDARD

CCITTCODED

INTERFACE

e.g. 139Mb/s CI

34Mb/S HDB3

44.7 Mb/sB3ZS

CODED/BINARY

CONVERTOR

SERVICE CHANNELS, ALARMS, ETC.

BINARY

DATA

BUFFER

STORE

CLOCK

(CCITT)

MULTIFLEXAND

FRAMING

PARITY

CHECK

SCRAMBLER DIFFERENTIAL

ENCODER

TO

MODULATOR

DATA AT

Radio CLOCK RATE

e.g. 141 MHz

CLOCK RATE

CONVERSION

TYPICAL DIGITAL Radio CODER

At first this block diagram looks rather complicated; however, its function is simply to provide the standard CCITT interface to the integrated digital network and then adapt the sequential bit stream to add the additional information used by the Radio. The result is that the Radio operates at a higher bit rate than the CCITT interface. The additional information such as digital service channels* and alarms are multiplexed into the data stream along with framing signals to allow the receiver to sort out which bit is which.

CodingAfter this, a parity circuit adds a parity bit to produce an even or odd number of ones in a given block of data. Then the signal is passed through a scrambler to randomize the data being transmitted. The parity check is used by the receiver to check for errors in transmission and to initiate protection switching. The differential encoder provides the interface to the digital modulator and decides how the binary data will be encoded on the individual phase states.

In practical Radios, two or more of these blocks may be combined into a single function or even one integrated circuit! At the receiver the decoder performs a similar function in reverse. Note at a repeater station where no CCITT interface is required, some of the blocks may not be required. Generally this digital circuitry is highly reliable and does not require testing in installation or maintenance with the exception perhaps of jitter testing at the CCITT interfaces (G823 CEPT Standards, G824 North American Standards and Bell Technical References 43501 and 43806 and ECSA TIX1.3 Committee).

*Service Channel and Alarm capabilities are typically short haul, “part-line” communication channels used for maintenance of the Radio system. Some Radios do not use digital service channels but instead frequency modulate the audio channel directly onto the carrier signal independently of the digital transmission.

Encoding the Input data

0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 1 1 1 0

0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 1 1 1 0

CCITT Standard

input Data

Binary Equivalent

Rate Conversion

Framing and

Service Channel

Scrambling

Mapping and

Differential Coding

I

Q

Here is an example of how the coding circuits of a Radio might modify an

incoming data stream. In our example, the incoming return to zero signal is

converted to a typical non-return to zero format. Depending on the rates the

signal may be TTL or ECL. The Radio will add additional information to the

incoming data. Therefore, to accommodate this additional information the

original data is converted to a higher rate. The Radio specific information is

then added. This original data may contain a long sequence of zeroes. If

transmitted this would alter the desired spectrum and confuse the receiver.

The avoid this problem, a pseudo random sequence is modulated onto the

data stream. This sequence is known by the receiver so that the original

signal can be recovered. One of the final steps is to create two signals, I and

Q, which are fed to the modulator. These signals determine the resulting

digital format of the transmitted signal.

Frequency Shift Keying

Frequency modulation and phase modulation are closely related. A static frequency shift of +1Hz means that the phase is constantly advancing at the rate of 360 degrees per second (2 rad / sec), relative to the phase of the unshifted signal.

FSK (Frequency Shift Keying) is used in many applications including cordless and paging systems. Some of the cordless systems include DECT (Digital Enhanced Cordless Telephone) and CT2 (Cordless Telephone 2).

In FSK, the frequency of the carrier is changed as a function of the modulating signal (data) being transmitted. Amplitude remains unchanged. In binary FSK (BFSK or 2FSK). A “1” is represented by one frequency and a “0” is represented by another frequency.

Analog Vs. Digital Modulation

AM

FM

PM

Digital

With digital modulation information is in the phase and amplitude of the signal.

Analog Vs. Digital Modulation

The coder and modulator work together to put the data information onto the carrier. Digital data can be put on a carrier using analog modulation like amplitude modulation (AM), frequency modulation (FM) or phase modulation (PM). Digital modulation is very similar to analog modulation in many respects. In fact, digital or I-Q modulation is a combination of amplitude and phase modulation. However, I-Q modulation transmits data more efficiently than analog modulation and is more immune to noise.

QPSK Modulation4 Possible States

Q

V q01

1110

00

V j

I

Quadrature Phase Shift Keying (QPSK or 4-PSK) again uses constant carrier magnitude but now four different phase values (I.e. 450 , 1350 , 2250 and 3150) are used. The modulation phase states can be generated by adding together appropriate amplitudes of in-phase and quadrature carrier (Vi and Va), or alternatively by phase – shifting the microwave carrier directly using an electronically switched phase shifter such as wave guide stubs or delay lines.

because we have four discrete states or symbols, we can transmit more information per state – in this case, as you can see, 2-bits of binary data, or a symbol, are encoded on each of the states. Because the serial data is taken 2 bits at a time to form the symbol, the symbol, the symbol-rate is half the bit-rate is half. This is because the bandwidth required is proportional to the “symbol rate” not the “data rate”.

QPSK Modulation – 4 Possible States

Some Typical Modulation Formats

·

• •

•

• •

• •

•

•

•

•

•

•

•

•

•

•

•

• •

• •••

••

• •• •

····

······

· ···

·· · · ··

··

··

·

··

··

·

··

····

·

···

· · ·· · ·· · ·· · ·· ·

··

···

····

BPSK QPSK 8PSK

16QAM 64QAM

Some Typical Modulation Formats

In summary here are some common digital Radio modulation

schemes from simple BPSK to complex 64QAM. It is interesting to

compare the bandwidth efficiency of these schemes with analog

FM Radio when transmitting telephony. When carrying 64Kbit

PCM, only 64QAM can match an FDM/FM Radio! So why does

anyone bother with simple modulation schemes? The answer is

that with 64 QAM the states are so close together that the immunity

to noise and interference is greatly reduced compared with BPSK

and QPSK. In hostile or noisy conditions (e.g. satellite) the simple

schemes are favored. In high-capacity line-of-sight systems where

signals are strong, bandwidth efficiency is often considered more

important, 256 QAM systems are now being put into use.

Symbol Rate:

“The rate at which the carrier

moves from one point in the

constellation to the next point”

The symbol rate is important because it tells you the bandwidth required to transmit the signal.

QPSK Modulator

SERIAL TOPARALLEL

CONVERTERCARRIER

PHASE SHIFT

COMBINER BPF

SYMBOL RATE:Fs = fb / 2

BALANCEDMODULATOR

I

fb

Fs = fb / 2

BINARYNRZ

INPUTSIGNAL

I.F

00

900

900Q

COMBINED VECTORSTATE DIAGRAM

BALANCEDMODULATOR

QUADRATURE DATA STREAM

01 00

11 10

QPSK Modulator

In QPSK the incoming bit-stream is divided into two parallel streams so that one bit is fed simultaneously to both I & Q balanced modulators to construct the 2 bit symbols. The carrier output from the modulator is switched under the control of the digital bit-stream and by adding together the I and Q outputs the phase state diagram is generated. In this case the band limiting filter is a band pass filter if IF, though, provided the modulators are linear, the filtering could have been implemented with LPF filters before the balanced modulators, thereby shaping the spectrum of the incoming pulses. Practically, some band-limiting is required before the modulators, otherwise the very wide sin x/x spectrum will fold around de and overlay the desired central lobe of the spectrum

QPSK Demodulator

BPFPowerSplitter

CarRec.

PhaseSplitter

SymbolTiming

Rec. (STR)

Parallel toSerial

Convertor

LPFThreshComp.

LPFThreshComp.

PhaseDemodulator

PhaseDemodulator

O O

I

OO

900

BinaryNRZ

Fb/2

fb

Fb/2

IFInput

QPSK Demodulator

The QPSK demodulator works in a similar way to the modulator, extracting the I and Q streams by demodulation using in-phase and quadrature carrier signals. The demodulator is more complicated because it must recover a carrier signal and timing signal from the incoming IF. Carrier recovery is usually implemented using a non-linear process such as frequency multiplication followed by a phase-locked loop. Symbol-timing is recovered from the demodulated data stream by a tuned circuit or phase-locked loop filtering out the clock component in the data stream. The scrambler in the transmitter ensures there is always a clock component independent of the data fed to the Radio input.

The demodulator I and Q streams are filtered to remove unwanted IF signals and then passed into threshold detectors where a signal is sampled by the symbol-timing clock to determine whether a ‘1’ or ‘0’ is present and to regenerate the data stream. It is during this sampling and regeneration process that errors occur as we shall see later when we consider the effects of noise.

I, Q, Eye Diagram and Constellation

••

• •

EYE

CONSTELLATION

I

Q

+1

-1

+1

-1

1 2 3 4 5 6 7

1,4

5

3

2Q

I, Q, Eye Diagram and Constellation

Notice in the previous picture that the modulator uses an I and a Q signal. These signals determine the type of modulation created by the modulator. In this picture both the I and Q signals carry one bit of information. This means that each signal has two levels. This tells us that the output will be QPSK. The top two waveforms are I vs. time and Q vs. time. They are marked at equally spaced “timing instants”. At these instants the waveform has settled to one of its predefined levels (two possible levels for QPSK). If we plot I vs. Q we see the constellation. I and Q each have two possible states so there are four states in the constellation.

The EYE diagrams are simply I vs. Time and Q vs. time as these waveforms appear on an oscilloscope which is triggered at the timing instants.

Required Bandwidths

As we shall shortly see, the spectrum used by a digital Radio is a percentage of its main lobe. Therefore, if this lobe is wider, more spectrum is used in transmission. Filters are used throughout the Radio to limit the spectrum and the minimum tolerable bandwidth is determined by the symbol rate.

Unfiltered Digital Radio Spectrum

The unfiltered output of the digital Radio modulator occupies a very wide bandwidth, theoretically infinite defined by the sin x/x characteristic. The digital signal modulating the Radio is random, so the spectrum analyzer shows a noise spectrum picture with a spectral density shown in the side. In fact, the spectrum of Radio should be independent of the data input to the Radio - this is the purpose of the scrambler. The nulls in the spectrum occur at multiples of the symbol rate of the Radio. The absence of the scrambler could cause a line spectrum to appear with some repetitive incoming data streams.

fc-5F8 fc-4F8 fc-3F8 fc-2F8 fc-F8 fc fc+F8 fc+2F8 fc+3F8 fc+4F8 fc+5F8

A FILTERED Radio

CODER

MOD U/C

DECODER

DEMODD/C

Signal requires less bandwidth but data is filtered.

A FILTERED Radio

For practical application the Radio spectrum must be restricted to avoid interference with adjacent channels. The Radio filters are designed to do this while, at the same time, not degrading the data transmission.

Our signal is filtered so that it is completely contained in a relatively small bandwidth. In this way, other Radios can transmit at frequencies close to our transmit frequency. However, filtering our signal will make it difficult to decode. In fact, without careful attention to the pulse shaping effects of filters, the error rate can increase dramatically.

The Filtering is Distributed in the Radio

CODER

~

~~

~

~~

~

~~

~

~~

~

MOD

D

ECODER

~

~~

~

~~

DEMOD~

~~

~

~

~~

UPCONVERTER

DOWNCONVERTER

The Filtering is Distributed in the RadioThe overall filtering function we have been considering is the effect of cascading all the filters in the transmitter and receiver from the output of the coder in the transmitter to the input of the regenerator in the receiver. The overall response must have flat group-delay. The main band shaping is usually shared between transmitter and receiver, for example a square-root raised cosine filter characteristic in each.

This shaping is often done by the IF filters and BB low-pass filters with RF sections being flat. Individual filters will not necessarily have the raised cosine response we have discussed and of course, will not always have a flat amplitude response familiar in analog Radio.

Comment:

Practical Radio filters may not have exactly are the theoretical response described in this section. Modern computer optimization techniques enable a variety of amplitude and group delay characteristics to be synthesized which approximate to the zero ISI requirement.

Another variant in filter design is the so-called partial response system (PRS) or correlative system. In this design the channel bandwidth is deliberately restricted to less than the Nyquist bandwidth so that controlled ISI produces a multi-level signal. An adaptive filter or correlative detector issued in the receiver. Examples of these systems are 9 QPR (filtered QPSK) and 40 QPR (filtered 16 QAM). In common with other complex modulation schemes, greater bandwidth efficiency is achieved at the expense of noise immunity.

Spectral Efficiency Theoretical Limit

BPSK 1 bit/sec/Hz

QPSK 2 bit/sec/Hz

16 QAM 4 bit/sec/Hz

64 QAM 6 bit/sec/Hz

256 QAM 8 bit/sec/Hz

AM Radio is not a very efficient way to send digital information. The 16 QAM Radio in the previous example doesn’t use all of its potential efficiency. However, wasting a little capacity could make the des.ign easier to implement and more reliable, and for many applications this type of Radio is quire adequate. In general, analog Radio is more efficient at transmitting voice channels than digital Radios. However, digital Radios are far more efficient for transmitting digital information and the signal quality is higher.

Block Diagram of a Radio Link with Impairments

MODERN IMPAIRMENTS

INTERSYMBOL INTERFERENCEDATA

SOURCE

DECISIONDEVICE

MOD DEMOD

BRANCHINHFILTERS

BRANCHINHFILTERS

FADING

INTERFERERS

IFFILTER

IFFILTER

NON LINEARITIES

LO

PHASENOISE

TERMINALNOISE

LO

f or ff or f

Block Diagram of a Radio Link with Impairments

A practical digital Radio can suffer from a number of impairments which give rise to error generation in the system. The most common causes of degradation are illustrated on this slide*.

As you can see, some of these impairments are due to propagation and interference effects and are external to the Radio equipment, while others are due to imperfections in the digital Radio itself.

First we will look at how we characterize the performance of a Radio. After this we will stress the Radio to predict its ability to cope with transmission impairments, and finally we will measure individual impairments.

*”Comparison of High-Level Modulation Schemes for High-Capacity Digital Radio Systems” by Michel Borgne. IEEE Transactions on communication,

Vol. Comm-33 No.5 May 1985. pp 442-449.

Frequency / Power

CODER

MODULATOR

Fader O

O O

Power Meter RF

TTS

Frequency / Power

A power meter and frequency counter are probably the two most commonly used pieces of test equipment used on a digital Microwave Radio. Initial alignment procedures include adjusting LO frequencies. Therefore, monitor points are readily available. Transmitted power frequency are logged on a routine basis for virtually every Radio.

Radio transmitters carry high power levels often in excess of 30 dBm. Therefore, use the appropriate attenuators to avoid destroying test equipment. In general, the IF section of the Radio will have 75 terminations while the RF section will have 50 . Use a 50 to 75 adapter where appropriate to assure accurate power measurements.

Error Performance Testing

PATTERNGENERATOR

TRANS-MITTER

RECEIVERERROR

DETECTOR

TRANS-MITTER

RECEIVER

DIGITAL Radio SYSTEM

PRBS OUT-OF SERVICE

IN-SERVICE

OOO

PARITY OUTPUT

PULSES

ERRORANALYSER

TRAFFICTRAFFIC

Radio ALARM PANEL

PARITY CHECK

Error Performance TestingError Performance measurements can be made in two ways:

– Out-of Service, where the traffic is removed and a Pseudo-Random Binary Sequence (PRBS) is applied to the transmit terminal, and the received data stream checked bit by bit for errors. Sequence lengths of 215-1and 223-1 are specified by CCITT. This is the preferred method for assessing the performance of the Radio particularly during commissioning since every bit is checked for errors. Normally the pattern-generator and error-detector are connected at the coded CCITT interface on the terminal. Alternatively, the connection may be made at a binary data and clock interface depending on the terminal design.

– In-service, where the Radio operates normally carrying revenue-earning traffic and the error performance is measured internally by parity checking on data blocks. This works quite well at moderate or low error ratios, but becomes inaccurate during bursts of errors, for example during multi path fading, when there is a possibility of parity error cancellation in the data block. The result of this simple test is usually displayed on the Radio Control Panel. Alternatively the parity error detection may be available as an electrical pulse which can be connected to the “external error input” of the error analyzer. ‘Through-data’ options of the HP3764A AND HP3784A offer through data jitter modulation. This allows the user to make measurements of jitter tolerance on equipment which needs framing bits to be present in the test signal eg. Demultiplexers.

Jitter Measurements in the Digital Network

JITTERGENERATOR

JITTERRECEIVER

PATTERNGENERATOR

Rx

ERRORDETECTOR

Tx

JTF

DIGITAL RADIOLINK

MTIJMOJ/MIOJ

MTIJ = Maximum Tolerable Input Jitter MIOJ = Maximum Intrinsic Output JitterMOJ = Maximum Output Jitter JTF = Jitter Transfer Function

Jitter Measurement in the Digital Network

Perhaps the most common Jitter measurements are made at the standard CCITT interface on the Radio which connects with the Digital Network. A number of Jitter specifications have been laid down by CCITT for the CCITT standard hierarchy rates. The idea is that if a piece of equipment meets the specifications at its input and output, then it can be connected freely within the Digital Network without degrading Jitter performance and causing errors.

There are three classes of Measurements:– Maximum Tolerable Input Jitter: Which is tested by applying

increasing Jitter to an input data stream and determining the onset of bit errors.

– Maximum Output Jitter(AND Intrinsic Output Jitter: Which is the level of output jitter with a jittered (or jitter-free) input signal.

– Jitter Transfer Function: Which is a measure of how the Jitter is attenuated by passing through the system, a necessary specification to prevent jitter accumulation in the network.

Jitter Measurement in the Digital Network

Although Jitter measurements are mostly made within the factory where equipment should be fully checked to the appropriate specification, they are sometimes made in the field, particularly with large networks where there may be a chance of Jitter accumulation.

The Jitter options of the HP 3764A and HP3784A perform these measurements to the CCITT standards, so are well suited to performing these jitter measurements.

Return Loss

Fader O

O O

Power Meter RF

TTS

CRYSTAL DETECTOR

WG to Coax Adapters

LEVELLINGHEAD

DIRECTIONALCOUPLER

ANTENNAFEED

LOCATE DAMAGE PREVENT DISPERSION

Return Loss

Even a perfectly adjusted Radio may not operate properly if attached to a damaged or poorly installed antenna system. Multiple reflections within the antenna feeder system can recombine and cause dispersive fading (a non-flat transfer function). Return loss is a common measure of the health of an antenna feeder network. A minimum acceptable return loss is often specified in the radio manual. For example, 64 QAM radios often require that the antenna have a return loss of 24dB or better.

DRTS is ideal to measure return loss. For a description of the measurement see AN 379-2 “Measuring Microwave Radio Antenna Return Loss using the HP 11758T Digital Radio Test System”.

Practical C/N Vs BER Curves

ImplementationMargin

RFBACK TO BACK

IFBACK TO BACK

Background BER

IDEAL

(Theoretical or

Design

BER

36

10-3

10-6

10-4

10-5

10-7

10-8

10-9

10-10

10-11

10-12

20 22 24 26 28 30 32 34 38 40

C/N RATIO (dB)

Practical C/N Vs BER Curves

When we look at the performance of an actual Radio, the results depart from the theoretical values in the way shown in this slide*. The difference between theory and practice is sometimes called the implementation margin and results from all the imperfections that can occur in practical Radio.

The poorer the performance, the greater the required C/N for a given bit error ratio (BER). At high C/N ratio the digital Radio performance becomes asymptotic to the low-level background (or dribble) BER.

* The practical results shown, are for a 64-QAM Radio, and are plotted on “error-function” paper which has a vertical scale such that the theoretical curve plots as a straight line. Deviations from this line for practical systems are then clearly seen.

Comment

Normally a Radio will be worse than the theoretical curve, I.e. it will require a higher C/N ratio for a given BER. The exception is for systems using forward error correction (FEC) when the practical system can have an overall performance better than theoretical, in which case, bandwidth is being exchanged for better BER. Some line-of-sight Radios use this technique, and it is quire common in satellite systems.

Inter-symbol Interface

•

•

•

•

•••••

Inter-symbol Interface

We wish to send a signal which has only a specific number of

possible values at the timing instants. If we poorly filter our data

stream the result will be many possible levels on the output. In fact,

the output level resulting from a ‘1’ being transmitted can change

depending on the data which preceded it. This problem is called

inter symbol interference.

Adjacent Channel Interference andSpectral Occupancy Tests

CODER

~

~~

~

~~

~

~~

~

~~

~

MOD

D

ECODER

~

~~

~

~~

DEMOD

~

~~

~

~

~~

UPCONVERTER

DOWNCONVERTER

SPECTRUM ANALYSER

SPECTRUM ANALYSER

Adjacent Channel Interference andSpectral Occupancy Tests

These two tests are generally made with a Spectrum Analyser. The Spectral Occupancy test is a measure of how well unwanted sidebands and spurious signals have been suppressed by the successive filters in the transmitter. To minimize interference to adjacent radio channels it is very important that the Radio complies with the occupancy mask laid down by the local regulating authority (e.g. the FCC in the USA or a PTT in a European country etc.).

The levels of interface present at the receiver can also be checked using a spectrum analyzer with the associated transmitter switched off. Sources of interference include:

• Adjacent Channel - due to poor out-of-band suppression from adjacent transmitters.

• Co-channe - from another Radio on the same frequency possibly using an opposite polarization.

• External Sources - such as Radar Systems.

Interference causes eye-closure in the demodulator and results in a C/N penalty or loss of receiver sensitivity.

Nyquist Filtering

•

•

•

•

Raised Cosine

Nyquist Filtering

There are certain types of filters which don’t cause inter-symbol

interference (ISI). These filters limit the spectrum to provide

high spectral efficiency. In addition, these filters resonate in

such a way that, although the path between timing instants

varies depending on the data sequence, the number of possible

states at the timing instant remains unchanged. The result is

that the output signal can be decoded once the timing instants

are determined by the receiver.

Digital Radio Links • Planning Objectives:

The main goal of Radio link route planning is to achieve in the most economical way, the transmission performance corresponding to the users needs. The criteria for this are set by the requirements for the total connection based either on the CCIR recommendations and national specifications (public telephone networks) or the users’ own performance requirements (dedicated networks).

• Availability Objectives:A digital Radio-relay system is considered to be in an unavailable state if in at least one direction of transmission, one or both of the following conditions occur for at least 10 consecutive seconds.1. The digital signal is interrupted (including alignment and timing losses).2. The BER is greater than 10-3

This unavailability may be caused by equipment failures, adverse propagation conditions, interference or other reasons.

the CCIR HAS GIVEN Rec.557 for availability objectives in the high grade portion of an ISDN/3/. For medium and low grade circuits there exist no recommendations for the present.For the high grade portion of ISDN (2500KMHRDP) the availability objective is 99.7% of the time corresponding 0.033% unavailability for a 280KM section.

• Clearance:

To determine the clearance the terrain profile of the hop is usually drawn on a hop profile chart, made for the value of k equal to 4/3. In this case, the Radio wave propagation path during normal conditions forms a straight line on the chord. The clearance at a given point is then the distance between the terrain surface and the chord joining the transmitting and receiving antennas. When calculating the clearance one should take into account buildings and they average height of trees (in temperate climates typically 10…20 m in tropic 20…40 m.)

rF = 17.3 * d1 * d2 (d*f)

rF is the radius of the first Fresnel zone (m),F is the Radio frequency (in GHz).d is the total hop length (km)d1 andd2 are the distances from the point under consideration to the end points (km); d = d1 + d2

For f > 3 GHz

i) 100% of the radius of the first Fresnel zone is free for k = 4/3

ii) At least zero clearance for the first Fresnel zone is obtained for a small value of k (i.e grazing path).

• Space diversity reception:

On long (> 30 km) hops with large reflecting surfaces, the only efficient countermeasure against reflection fadings is space diversity reception. The optimum vertical distance is between the centres of the diversity antennas is given by Eq. (2.8).

S = 75 * d / (f * ht)

s is the optimum distance between the space diversity antennas

(m)

d is the hop length (km)

f is the Radio frequency (GHz)

ht is the height of the opposite transmitting antenna

above the reflecting surface (m)

Lho = Lo+Lad+Lbr+Lc1+Lc2-Ga1-Ga2

Lho is unfaded hop loss

Lo is free space loss

Lad is additional terrain loss

Lbr is antenna branching loss

Lc1 and

Lc2 are antenna feeder losses

Ga1 and

Ga2 are antenna gains

(all quantities are expressed in decibels)

Lho = 20*log(Da) + 17.8

Ga is the antenna gain (dB)

Da is the antenna diameter (m)

F is the Radio frequency (GHz)

ANTENNA GAINS

• Examples of Hop DesignIsolated (no interference) hop: This situation is common in practice because by proper design interference may often be kept small for example by selecting high gain antennas for star points and small interference has only minor effect on systems using modulation methods with few signal states (e.g. 2PSK, 4PSK, MSK). The first example also demonstrates use of space diversity on overwater paths.The second example sketches the calculations procedure under the presence of non-correlated interference. The actual case deals with adjacent channel interference at a star point.

• Ordinary Hop:The phases of a normal route calculation are:– selecting the antenna heights– Calculating the fading margin– Calculating the outage time– Repeating steps 2 and 3 with varying combinations of antennas and

feeders and possibly using diversity until an economic solution which gives the required performance is achieved.

Design Formulae

•Radius of the first Fresnel zonerF = 17.3 * d1 * d2 (d*f)

•Fading MarginM = Ptx – Lho – Prxth

•Total Hop LossLho = Lo+Lad+Lbr+Lc1+Lc2-Ga1-Ga2

•Free Space LossLo = 92.5+20 * log(d) + 20 * log(f)

•Antenna gainGa = 20 * log (Da) + 20 * log (f) + 17.8

MW LINK BUDGET CALCULATION

INITIAL SURVEY• LOS Survey to be done • Collect information – Coordinates, Ht. Of the bldng., Connectivity to nearby sites etc.

PATHLOSS TOOL for LINK ANALYSIS• Load them in the Pathloss tool• Check for the path profile between the 2 sites and adjust the antenna hts. so that there is enough clearance. The Pathloss gives Distance and the Azimuths between the 2sites.

PARAMETERS TO BE CONSIDERED• Determine the type of Antenna 0.6 / 0.8 / 1.2 / 1.8 mtr.

• Determine the Frequency 18 /15 / 7 GHZ

• Hi – Lo frequencies, of a particular spot freq., at the 2 sites of the link to be decided. (No Hi-Lo violations allowed at a particular site.)

• Input the values for Antenna Model, Antenna gain(dBi), TX Power(16/17 dB ), Emission Designator, Rx Threshold level(-66/-71dB), Max. Receive signal(-20dB) All Vendor Specific

MW LINK BUDGET CALCULATIONPARAMETERS TO BE CONSIDERED • Determine Polarization – Vertical / Horizontal

• Add the Rain fall of that region

• Run the Interference Analysis

• See for any Errors in Error log, Hi-Lo violations and Interference.

• If any Interference check/change the following parameters i)HEIGHT ii)POLARIZATION iii)FREQUENCY iv) TX POWER

• Following are the important parameters to be checked for in the result: Availability 99.995 % Thermal Fade Margin around 35 dB Receive Signal Level around -30 dB

Sithaphal Mandi NallakuntaMW=G+5+17.5 MW=G+4+6mtr

Total=35.5 mtr Total = 21mtr

Elevation (m) 523.76 476.14Latitude 17 25 46.00 N 17 23 55.00 N

Longitude 078 30 58.00 E 078 30 26.00 ETrue azimuth (°) 195.47 15.47

Vertical angle (°) -1.03 1.01

Antenna model 1.2--VHLP4-142 0.6--VHLP2-142Antenna height (m) 35.69 20.43Antenna gain (dBi) 42.90 37.10

Circ. branching loss (dB) 0.50 0.50TX filter loss (dB) 0.00 0.00RX filter loss (dB) 0.00 0.00Other RX loss (dB) 0.00 0.00

Frequency (MHz) 15000.00Polarization Horizontal

Path length (km) 3.54Free space loss (dB) 126.97

Atmospheric absorption loss (dB) 0.10Field margin (dB) 1.00

Net path loss (dB) 49.07 49.07

Radio model DMC-ALTIUM DMC-ALTIUMTX power (watts) 0.05 0.05TX power (dBm) 17.00 17.00

EIRP (dBm) 59.40 53.60Emission designator 28MOD7W 28MOD7W

TX Channels 13 A -H 15271.0000H 13A-L 14851.0000HRX threshold criteria BER 10-3 BER 10-3

RX threshold level (dBm) -68.00 -68.00Maximum receive signal (dBm) -20.00 -20.00

RX signal (dBm) -32.07 -32.07Thermal fade margin (dB) 35.93 35.93

Dispersive fade margin (dB) 43.00 43.00Dispersive fade occurrence factor 1.00

Effective fade margin (dB) 35.15 35.15

Geoclimatic factor 1.41E-03Grazing angle (mr) 18.93

Path inclination (mr) 17.76Average annual temperature (°C) 30.00

Worst month - multipath (%) 100.00000 100.00000(sec) 0.01 0.01

Annual - multipath (%) 100.00000 100.00000(sec) 0.05 0.05

(% - sec) 100.00000 - 0.10

Rain region ITU Region N0.01% rain rate (mm/hr) 95.00

Flat fade margin - rain (dB) 35.93Rain rate (mm/hr) 174.72

Rain attenuation (dB) 35.93Annual rain (%-sec) 99.99884 - 364.53

Annual multipath + rain (%-sec) 99.99884 - 364.63

Thu, Sep 19 2002Sithaphal Mandi (H1.2) Nallkunta(L0.6).pl4Reliability Method - ITU-R P.530-6

Rain - ITU-R P530-7

15GHz Link Analysis

18GHz Link AnalysisTIRUMAL ALWAL

MW =27 mtr MW = 25 mtr

Elevation (m) 552.30 570.13Latitude 17 28 04.20 N 17 30 13.60 N

Longitude 078 30 31.70 E 078 30 48.70 ETrue azimuth (°) 7.19 187.19

Vertical angle (°) 0.26 -0.29

Antenna model VHLP2-180 VHLP2-180Antenna height (m) 25.00 26.24Antenna gain (dBi) 38.70 38.70

Miscellaneous loss (dB) 0.50 0.50

Frequency (MHz) 18000.00Polarization Vertical

Path length (km) 4.01Free space loss (dB) 129.63

Atmospheric absorption loss (dB) 0.22Net path loss (dB) 53.45 53.45

Radio model Nera Citylink Nera CitylinkTX power (watts) 0.04 0.04

TX power (dBm) 16.50 16.50EIRP (dBm) 54.70 54.70

Emission designator 28MOD7W 28MOD7WTX Channels F8 -L 17865.0000V F8 - H 18875.0000V

RX threshold criteria BER 10-6 BER 10-6RX threshold level (dBm) -72.00 -72.00

RX signal (dBm) -36.95 -36.95Thermal fade margin (dB) 35.05 35.05

Dispersive fade margin (dB) 43.00 43.00Dispersive fade occurrence factor 1.00

Effective fade margin (dB) 34.40 34.40

Geoclimatic factor 4.45E-05Grazing angle (mr) 12.65

Path inclination (mr) 4.76Average annual temperature (°C) 30.00

Worst month - multipath (%) 100.00000 100.00000(sec) 4.23e-03 4.23e-03

Annual - multipath (%) 100.00000 100.00000(sec) 0.02 0.02

(% - sec) 100.00000 - 0.04

Rain region ITU Region NFlat fade margin - rain (dB) 35.05

Rain rate (mm/hr) 138.23Rain attenuation (dB) 35.00

Annual rain (%-sec) 99.99685 - 992.05Annual multipath + rain (%-sec) 99.99685 - 992.09

Fri, Sep 20 2002TIRUMAL-ALWAL.pl4Reliability Method - ITU-R P.530-6

Rain - Crane

Fiber Optics

Why Use Fiber Optics?

1. Wide Bandwidh

• High carrying capacity including voice, data and Video

• WDM Technology supports lakhs of channels on a pair of optical fiber

• Can carry hundreds of HDTV Channels.

2. Why Use Fiber Optics?

• Digital Transmission is superior to analog transmission because the original signal transmitted can be faithfully reproduced at the receiving stations.

• Light pulses spread much less compared to other signals

• Low Bit error rates.

3. Low Attenuations

• Spacing between the repeater stations can be increased.

• Speed of transmission increases as the number of repeater stations is reduced

• Cost of the systems will reduce with the reduction in repeater stations.

• Reliability increases as the no. of repeater stations is reduced

4. Electro Magnetic Immunity

• Not affected by stray magnetic fields.

• Does not create electro-magnetic radiation

• Extremely good for applications in areas with high magnetic field like induction equipment, high tension over head lines etc.

• Ideal for computer networking process control etc.

5. Small Size

• Fiber Optic cable is only one tenth the size of co-axial cable for the same carrying capacity.

• Can replace co-axial systems in underground ducts directly.

• Replacement of co-axial cable by fiber optic cable of the same size, the capacity increases by many folds.

6. Light Weight

• Easy to install and maintain

• Ideal for applications like airplanes, rockets, satellites, submarines etc.

7. Safety

• Superior resistance to most of the acids, alkalis, water, nuclear radiation etc.

• Best suited for applications in hazardous areas and difficult terrain.

8. Security

• Fiber optic cables do not radiate any electro magnetic energy. So, it is very difficult to tap the same.

• Extremely good for applications like security agencies, Defense etc.

9. Reliability

• Does not react with most of the known chemicals

• Does not react with water

• High resistance to nuclear radiation and heat

• Very few breakdowns

• No insulation failures

10. Ease of Installation & Maintenance

• Easier to install in comparison to a copper cable.

• Automatic splicing machines have improved the splice loss to 0.02dB per splice

• Latest joint closures, termination boxes, splice trays etc. are extremely easy to handle.

• Advanced test instruments can localize the faults within 1m in a few minutes.

11. Upgradability

• Capacity can be increased considerably by just changing the terminal equipment

• No need to replace the cables

• Same fiber can also operate at different wavelengths using WDM technology increase the capacity further.

12. Price

• Very good price to performance ratio

• Prices of cables, equipment, accessories and test instruments are steadily coming down due to high volumes.

• Multimedia and more such services in the same fiber will bring down the cost further in the future.

Fiber Optics - Basics

Optical Fiber - Medium of Communication

Light - Carrier of Information

Optical Fiber - Core and Cladding(Core inner part and Cladding outer part)

Speed of light and refractive index in different media

Refractive Index(n) of a medium = Speed of light in vacuum/speed of light in the medium.

Material Refractive Index(n) Speed of light (kmps)

Vacuum 1.0 300.000Air 1.0003(I) 300.000Water 1.33 225.000Fused Quartz 1.46 205.000Glass 1.5 200.000Diamond 2.5 120.000

ReflectionNormal

Angle of Incidence Angle of Reflection

Reflecting Surface

Angle of Incidence = Angle of Reflection

Refraction

Refraction

NormalAngle of Incidence

Angle of Refraction

n1

n2

n2>n1

NormalAngle of Incidence

Angle of Refraction

n1

n2

n1>n2

How Fibre Works

The operation of an Optical Fibre is based on the principle of Total Internal Reflection (TIR).

Light reflects or refracts (bends) depending on the angle at which it strikes a surface. This occurs because different interfaces between materials refract light in different ways.

Critical Angle

Normal

Critical Angle ofIncidence

Angle of Refraction

n1

n2

Total Internal Reflection

Normal

Angle of Incidence Angle of Reflection

n1

n2

n1 n2

Propagation of Light in Optical Fibre

818181

81

n1

n2

n3n=1.49

n=1.48

n=1.8

Core and Cladding

CORE CLADDING

GLASS

GLASS

PLASTIC

GLASS

GLASS

PLASTIC

CORE CLADDING

Different Types of Optical Fibres

TYPES OFOPTICAL FIBRES

MULTIMODE

GRADEDINDEX

STEPINDEX

SINGLE MODE

DEPRESSEDCLAD

MATCHEDCLAD

DISPERSIONSHIFTED

DISPERSIONFLATTERED

Core and Cladding

An Optical fibre consists of two different types of highly pure, solid glass to form the core and cladding, over which a dual layer protective coating is applied to protect the fibre during

cabling / laying / terminating process.

Cl adding

Cl adding

Core

Reflected

n2

n1

Refractive Index

FIG - 1 n1> n2 - Total Internal Reflection

n = Velocity of light in a Vaccum

Velocity of light in the Medium Vaccum = 1.0; Pure Silica = 1.4469 (@1300nm)

Refracted

Single Mode and Multi Mode Fibres• MULTI MODE:

Multi mode fibre was the first type of commercial fibre, which has larger core diameter (50 or 62.5nm) allowing multiple modes of light to propagate through the fibre simultaneously.

It is used primarily for short distances (<2KM) such as LAN communication, due to more loss and less bandwidth capacity.

• SINGLE MODE:

Single Mode fibre has a much smaller core (8-10nm) that allows only one mode of light at a time to propagate through the core.

This is widely used for all voice/data transmission applications over long distances and high capacities.

125micrometre

8-10 micrometre

125 micrometre

50 - 62.5 micrometre

Single Mode Multi Mode

SINGLE MODE FIBRE PERFORMANCE CHARACTERSTICS:

The two key parameters are:

1) Attuenuation and 2) Dispersion

1) Attenuation: It is the reduction of signal strength or light power over the length of the fibre and is measured in dB/KM. Lower attenuation (loss) means lesser repeaters, thus reducing cost and increasing reliability. Typical values are 0.35dB at 1310nm and 0.25dB at 1550nm.

2) Dispersion: It is the smearing or broadening of an optical signal that results from the many wavelength components travelling at different rates. This limits the max. data rate carrying capacity of a SM fibre link.

Amp

Distance

Input Output

2) Dispersion (Contd....)

The wavelength at which the Dispersion equals zero is called

the ‘Zero-Dispersion Wavelength’, which is the wavelength at

which the fibre has its max. information carrying capacity.

For SM fibres, it is around 1310nm. It is measured in

Pico-seconds / nm-KM. It is possible to shift the zero dispersion

wavelength to 1550nm by manufacturing techniques, to allow

more bandwidth and longer distances.

Cut Off Wavelength

• It is the wavelength at which a single mode fibre will start acting as multimode fibre. This is lower than the operating wavelength.

Related Accessories / Terminology

Fusion Splice: To form permanent connections between fibres in the system using fusion (arc) Technique.

Typical Loss - 0.04 to 0.1dB.

Mechanical Splice: Alternate method for emergency restoration.

Higher loss - 0.1 to 0.5dB.

Connectors: Provide remateable connections, typically at termination points.

Pigtails, Patch cords: Short length of flexible fibre optic cables for

terminations at the Equipments .

Fusion Splicer• Inset heat shrinkable sleeve to one of the fibres• Mount the prepared fibre in the Splicing machine• Align the fibres• Fuse the fibres• Check the splice loss using OTDR• If the plice loss is within thelimit, remove the splice put the splice protector• After the sleeve shrinks remove the same fix it in the splice protection tray• Keep the splice protection tray in the joint closure of fibre distribution frame frame and close it.

Factors which can affect the loss of a Fusion splice?

• External factors like dirt, dust etc.• Cleave angle• Fibre positioning or view angle• Geometry of the fibres• Eccentrically positioned fibre cores• Problems with the machine itself

How to identify the factors which gives high loss?

1. Clean the fibre and the V-Grooves weel to ensure that the external parametersare not affecting the splice loss.

2. View the splice parameters while splicing so that the cleave angle, view angle and geometry of the fibre can be verified.

3. Check whether the machine is okay.

Mechanical Splice

• Install mechanical splice in the splice tool

• Insert the prepared fibre into one side of the mechanical splice

• Insert the second prepared fibre to the other side of the mechanical splice.

• Push both the fibres till they touch each other and fix the fibre on the tool

to avoid movement.

• Check the insertion loss using an OTDR

• Press the top of the mechanical splice loss using the tool if the splice loss

is within the limits

• Remove the mechanical splice and fibres from the tool and put the same

in a splice holding tray.

• Close the splice holding tray and transfer the same to joint closure or fibre

distribution frame depending on the application.

Fibre preparation for splicing and connectorisation

OPERATION TOOL USED

1. Remove cable outer coating to the required length Cable Slitter

2. Remove loose tube or tight tube jacket to the Loose tube stripper or

required length. Cord stripping pliers.

3. Cut the Kevlar in the case of tight jacket Ceramic Scissors.

fibre to the required length

4. Remove jelly using isopropyl alcohol in case of Isopropyl Alcohol dispenser and

5. loose jacked fiber tissuepaper

5. Strip the fiber to the required length Fiber stripper 250/125um, 900/125um

6. Cleave the fibre to the required length High Precision or Ordinary Cleaver

7. Clean the Fibre Isopropyl Alocohol

Test Instruments

• OTDR : Optical Time Domain Reflectometer -To detect faults/breaks in the FO links.

• Optical Power Meter : To measure the optical power at the end of Fibre.

• Optical Source : To send light source in to the Fibre for testing- Laser/LED.

Application in TTL Netowork

1. To all the DoT PoIs

2. From Main Switch to Concentrator sites

3. Main Switch to a few CDMA Cell sites.

4. In future to Customers (ISPs) for high capacity leased lines.

Present Intracity capacity - STM-1 (155MB/s 1890 voice chls)

STM-4 (622MB/S 7560 voice chls)

Future Backbone Capacity - STM-16 (2.5Gb/S)

DWDM - Dense Wavelength Division

Multiplexing (n x STM-16)

A presentation on

DWDM

11.06.2003

Dense

Some times called stacked SDH/SONET

Wavelength DivisionMultiplexing

DWDM

…What is DWDM ?

A multi channel fiber optic transmission system in which one fiber transmits No of client signals provided by different Wavelength optical carriers

Why DWDM ?

a) Overcome fiber exhaust / lack of fiber availability problems (Better utilization of available fiber)

d) Cost effective transmission

e) No O-E-O conversion delays

f) Wave length leasing instead of Bandwidth leasing

b) Space & Power savings at intermediate stations

c) Easier capacity expansion

…Why DWDM ?

LTELTE

LTELTE

LTELTE

LTELTE

Traditional Network with Repeaters, no WDM

75% fewer fibersWDM Networkwith Repeaters

LTELTE

LTELTE

LTELTE

LTELTE

75% less equipmentWDM Network withOptical Amplifiers

LTELTE

LTELTE

LTELTE

LTELTE

Any Disadvantages of this Technology ?

Yes of course…

a) Multi channel failure due to line failure

b) Requirements for more deliberate design of Dispersion management, gain profile management & launched power due to broader Wavelength range to be handled

WDM Classification:

WDM Classification is based on the Channel spacing between 2 Wave lengths

Channel spacing > 200GHz is called CWDM

Channel spacing > 100 GHz is called WDM

Channel spacing < 100GHz is called DWDM

Channel spacing < 25GHz is called UDWDM

100 GHz is equal to 0.8 nm

Infrared Spectrum

O-Band E-Band S-Band C-Band L-Band

1260-1360nm

1360-1460nm

1460-1530nm

1530-1565nm

1565-1625nm

CWDM CWDMFuture DWDM DWDM DWDM

Low-loss range

0.1

0.2

0.3

0.01300 1400 1500 1600 Wavelength (nm)

LOSSdb/km C-Band L-Band

(nm)

15

32

.68

15

33

.47

15

34

.25

15

35

.04

15

35

.82

15

36

.61

15

37

.40

15

38

.19

15

38

.98

15

39

.77

15

40

.56

15

41

.35

15

42

.14

15

42

.94

15

43

.73

15

44

.53

15

45

.32

15

46

.12

15

46

.92

15

47

.72

15

48

.52

15

49

.32

15

50

.12

15

50

.92

15

51

.72

15

52

.52

15

53

.33

15

54

.13

15

54

.94

15

55

.75

15

56

.56

15

57

.36

15

58

.17

15

58

.98

15

59

.79

15

60

.61

15

61

.42

15

62

.23

15

30

.33

15

31

.12

15

31

.90

(THz)

19

5.7

19

5.6

19

5.5

19

5.4

19

5.3

19

5.2

19

5.1

19

5.0

19

4.9

19

4.8

19

4.7

19

4.6

19

4.5

19

4.3

19

4.2

19

4.1

19

4.0

19

3.9

19

3.8

19

3.7

19

3.6

19

3.5

19

3.4

19

3.3

19

3.2

19

3.1

19

3.0

19

2.9

19

2.8

19

2.7

19

2.6

19

2.5

19

2.4

19

2.3

19

2.2

19

2.1

19

2.0

19

1.9

19

6.0

19

5.9

19

5.8

C3

7C

36

C3

5C

34

C3

3C

32

C3

1C

30

C2

9C

28

C2

7C

26

C2

5C

24

C2

3C

22

C2

1T

on

e c

h.

C2

0C

19

C1

8C

17

C1

6C

15

C1

4C

13

C1

2C

11

C1

0C

09

C0

8C

07

C0

6C

05

C0

4C

03

C0

2C

01C

40

C3

9C

38

Carrier wavelength

Carrier frequency

Channel number

Note 1: Optical carriers are allocated on ITU-T 100 GHz (0.1 THz) grid in Rec. G. 692.

2: Tone channel is dedicated for operation & maintenance support.

3. C13 is the Centre Wavelength

Wavelength allocation in C-Band

Main Components in DWDM

1) Transponder

2) Omux/Odmux

3) Optical Amplifier

4) OADM

5) Regenerator

Client signals Client signalsWDM aggregate signals

IL-AMP span

IL-AMP#1

IL-AMP#n

IL-AMP#1

IL-AMP#n

TERM system

TERM system

Intermediate regenerator

(n-1)IL-AMP spans

Wav

elen

gth

co

nve

rsio

nO

pti

cal m

ux/

dem

ux

Wav

elen

gth

co

nve

rsio

nO

pti

cal m

ux/

dem

ux

Op

tica

l mu

x/d

emu

xC

h-s

ign

al r

egen

erat

ion

Line system

…DWDM Components

Transponder

A device that takes an optical signal, performs electrical3R regeneration & re-transmits the signal in optical formIn to Wavelength grid as per G.192

It allows any Wavelength as input to DWDM

For every input Wavelength, one transponder is required

Its very useful for Wavelength leasing, as customer can Send any wavelength

Omux/Odmux

Various Transponder outputs (Wavelengths) will be provided as Inputs to Mux. Each input is equipped with A selective filter of certain Wavelength. The output of these filters are coupled to a Single Mode fiber

At the Receiver end, these Wavelengths are separated again by a Demux & directs them to individual Transponders

Both Mux & Demux are identical components, only difference is that they are driven in opposite direction

OMUX

TransmitAmplifier(TXA)

OMUX

Aggregate Signal over n-channels with wavelengths ranging from λ1 to λn.

Channel spacing is 100 GHz and even.

Channel

#1#2#3

#(n-1)#(n-2)

#n

Wavelength

λ1λ2λ3

λ(n-1)λ(n-2)

λnλ1 λ2 λnλ(n-1)

100 GHz

Clie

nt

OMUX

Optical Amplifier

Where do we require Optical Amps ?

a) Booster/Post AmpBoosts the signal at Transmitter end to compensate relatively low output power of laser transmitters

b) Line Amp

Used at regular intervals to compensate fiber transmission loss

c) Pre Amp

Boosts signal prior to Optical detectors to increase the Rx sensitivity

…Optical Amplifier

Tx Rx

PreamplifierTx Rx

Line amplifier

Tx Rx

Booster/Post Amplifier

…Optical Amp

Erbium Doped Fiber Amp (EDFA)

1) EDFA Characteristics:

It is simply an Optical Amp

Supports both C-Band & L-Band

EDFA changed the WDM world

One device amplifies all the Wavelengths & hence extended distance between Regenerators

…EDFA

Gain Flattening

Art of getting equal amount of amplification over a Range of Wavelengths

Gain profile depends on input Wavelengths & signal power

Amp gain is not constant for all Wavelengths

Does not correct Dispersion

Does not reshape or retime the signal

…Optical Amps

EDFA Operation:

Erbium is a rare metallic earth element that is used to amplify light signals sent along fiber optic cable

When Erbium is doped to a fiber optic material like glass, and light is pumped through it at 980/1480nm, result is An EDFA

If photon of light in 1550nm range collide with excited electrons, the electrons give off photons of the same Wavelength, same phase & direction as the original photon

…EDFA

OADM

Hence A special type of Mux is designed called Optical Add/Drop Mux

With an Add/drop facility, new channels can be added to & others can be dropped off the transmission link

In general, not all transmission channels have the same start & destination

This Add/Drop function is completely in Optical form

…OADM

Regenerator

Regenerator is nothing but an Amplifier, with addition of3R function

Since noise level also amplifies along with original signal in an ordinary amplifier, it requires to supress this noiseat intermediate stations

No need to convert the original signal in to electrical formwhile regeneration

Regeneration requires at every 600kms distance

Amplifier Vs Regenerator

What is 3R generation ?

Re-amplification – 1R

Re-shaping – 2RCorrecting noise & dispersion

Remove noise from a digital signal & shape it in to clear 1’s & 0’s

Boost up the received weak signals to transmit further

It is done by Optical Amps

Done by DCF & OEO

Re-timing – 3R

Synchronizing with Network clock

Adjusting the precise location of 1’s & 0’s in a detected signal in order to match them to the bit rate of system

By using PLL & optical clock recovery

Here is a list of parameters to be considered for a Optical Link Budget: Find out the Route Distance “d” between Node A & Node B & Consider 3% excess of this distance for bends & loops , of this Distance “d”. The New Distance = “D” in Kms Choose the Optimal Drum Length of OFC in case the distances are more viz a Backbone Case Understand how many Splices “N” are expected between both nodes over the distance D

In Case of Backbone it is for every 3.85 KmsIn Case of access it is for every 280 Mtrs.

Choose Fiber type – G.652 or G.655. At Present TTL has G.652 Fibers live in it’s network both on BB Choose Laser Wavelength window based on application

Backbone – since “D” is always more than 50 Kms, 1550 nm Window is chosenAccess – Since “D” is always less than 30 Kms, 1310 nm Window is chosen

Assumptions: Loss per Km @ 1310 nm Operation on a G.652 Fiber = 0.4 dB = LF

Loss per Km @ 1550 nm Operation on a G.652 Cable = 0.22 dB = LF

No. of Splices between 2 Nodes = “ N”( N=1+ (D/0.280) for access & N=1+(D/3.85) for BB Networks) Average Splice Loss LN = 0.05 dB per splice Optical Penalty due to dispersion (Applicable practically to Backbone systems only) = LD = 2 dB Max Insertion Loss of Fiber optic Patch cords per hop = L I = 1 dB Max. No. of Cuts expected to happen per year (applicable for Backbone) = 2 No’s Life period of the OFC = 20 Years Total Losses expected between 2 Stations on Fiber over a period of 20 Years = LT

LT = LN*N + LF*D + 0.05*2*20 + LD + L I LT = LN*N + LF*D + 5 dB

Example of a Backbone Link Budget:

Route Distance between Both Stations = d = 80 kms Wavelength of Operation = 1550 nM Fiber Cable Type – G.652 OFC Distance = D = 80*1.03 = 82.4 Kms No. of Splices = N = 1+ (D/3.85) = 1+ (82.4/3.85) = 1+ 22 = 23 Total Losses on OFC LT = LN*N + LF*D + 5 = 0.05*23 + 0.22*82.4 + 5 = 24.278 dB

Minimum Launch Power = S = -2 dBm (Manufacturer Spec. sheet) Receiver sensitivity = R = -30 dBm (Manufacturer Spec. Sheet) S-R Delta = 28 dB Margin available = S-R Delta – LT

Margin available = 28 – 24.5 = 3.5 dB (Even after considering @ 2 Cuts per year between nodes)

Example of a Access Link Budget:

Route Distance between Both Stations = d = 20 kms Wavelength of Operation = 1310 nM Fiber Cable Type – G.652 OFC Distance = D = 20*1.03 = 20.6 Kms No. of Splices = N = 1+ (D/0.280) = 1+ (20.6/0.280) = 1+ 73 = 74 Total Losses on OFC LT = LN*N + LF*D + 3(No LD in this case)

= 0.05*74 + 0.40*20.6 + 3 = 14.94 dB

Minimum Launch Power = S = -10 dBm (Manufacturer Spec. sheet) Receiver sensitivity = R = -30 dBm (Manufacturer Spec. sheet) S-R Delta = 20 dB Margin available = S-R Delta – LT

Margin available = 20 – 15 = 5 dB (Even after considering @ 2 Cuts per year between nodes)

Backbone OFC link Budget as per Distances

Section Name Actual Fiber

lengths

Total link attenuation in

dB except connector

loss - as per actual

Lengths & Design

Criterion

Total Splice Losses as per actual Lengths &

Design Criterion

Total link attenuation

in dB including connector loss-as per Designed Distances

Equipment S - R dB [w/o

optical penalty due to

dispersion]

Net attenuation allowed in dB [incl.

Dispersion tolerance]

Link Margin in dB as per

actual Lengths &

design criterion

Remarks

Ongole - Kavali 81.0 17.8 1.16 20.0 26 24 4.02

Assumptions :

1. Fiber attenuation @ 1550 nm per Km 0.222. Av. Splice loss per splice 0.053. OFC drum length 4.04. Total connetor loss per hop 15. Optical penalty due to dispersion (dis. tolerance) 26. No. of cuts / 1000 Km / Year 207. Total age of OFC 258. Net Hop length (for link attenuation) = 3% in excess of actual hop length.