DIGITALTRANSMISSION TECHNOLOGY BY V.S.ARJUN

1. PRESENTATION BY :

2. Transmission systems interconnect
communication devices by guiding signal
energy in a particular direction or directions
through a transmission medium such as
copper, air, or glass.
DIGITAL TRANSMISSION is the
transmission of digital signals between two
or more points in a communications system.
DTS use both metallic and optical fiber
cables for their transmission medium.

3. Noise immunity
Long distance communication
Easy Storage & processing
Errors can be easily detected & corrected
More accurate
ADVANTAGES

4. DISADVANTAGES
• More bandwidth required
• Additional encoding & decoding circuitary
required.
• synchronization of transmitter & receiver
clocks required

5. Multiplexing (also known as muxing)
is a method by which multiple analog
message signals or digital data streams
are combined into one signal over a
shared medium.
The aim is to share an expensive
resource
For example, in telecommunications, several telephone
calls may be carried using one wire.
•George Owen Squier is credited with the
development of multiplexing in 1910.

6. MULTIPLEXING
• can extract the original
channels on the receiver side.
DEMUX
(Demultiplexing )
• A device that performs the
multiplexingMULTIPLEXER
• A device that performs the
demultiplexingDEMULTIPLEXER

7. MULTIPLEXING (MUX)
General multiplex scheme: the ν input lines-channels are
multiplexed into a single fast line. The de multiplexer receives
the multiplexed data stream and extracts the original channels
to be transferred

8. MULTIPLEXING (MUX)
SPACE-Division Multiplexing (SDM)
FREQUENCY-Division Multiplexing (FDM)
TIME-Division Multiplexing (TDM)
CODE Division Multiplexing(CDM)
Multiplexing technologies may be
divided into several types

9. SPACE-DIVISION MULTIPLEXING
• In wired communication, space-division
multiplexing simply implies different point-to-
point wires for different channels.
• Examples include an analogue stereo audio
cable, with one pair of wires for the left
channel and another for the right channel,
and a multipair telephone cable.

10. Examples

11. FREQUENCY-DIVISION
MULTIPLEXING
• The spectrum of each input signal is
shifted to a distinct frequency range.
• It is an analog technology
• One of FDM's most common
applications is cable television.

13. TIME-DIVISION MULTIPLEXING
• Time-division multiplexing (TDM) is a digital
(or in rare cases, analog) technology.
• TDM involves sequencing groups of a few bits
or bytes from each individual input stream,
one after the other, and in such a way that
they can be associated with the appropriate
receiver.

14. Fig. Time-division multiplexing (TDM)

15. CODE-DIVISION MULTIPLEXING
• Code division multiplexing (CDM) or spread
spectrum is a class of techniques where
several channels simultaneously share the
same frequency spectrum, and this spectral
bandwidth is much higher than the bit rate.
• One form is frequency hopping, another is
direct sequence spread spectrum.
• Advantages over conventional techniques are
that variable bandwidth is possible

16. • Code Division Multiplex techniques are used
as an channel access scheme, namely Code
Division Multiple Access (CDMA), e.g. for
mobile phone service and in wireless
networks.
• Another important application of CDMA is the
Global Positioning System (GPS).

17. FOUR Methods of pulse modulation:
• Pulse Amplitude
Modulation
• Pulse Width Modulation
• Pulse Position
Modulation
• Pulse Code Modulation
PULSE MODULATION
The process of transmitting signals in the form of
pulses (discontinuous signals) by using special
techniques.

18. Analog Pulse Modulation Digital Pulse Modulation
Pulse Amplitude (PAM)
Pulse Width (PWM)
Pulse Position (PPM)
Pulse Code (PCM)
Delta (DM)
Pulse Modulation
Pulse Amplitude Modulation (PAM):
* The signal is sampled at regular intervals such that each sample
is proportional to the amplitude of the signal at that sampling
instant. This technique is called “sampling”.
* For minimum distortion, the sampling rate should be more than
twice the signal frequency.

19. AND
Gate
Pulse Shaping
Network
FM
Modulator
Analog
Signal
PAM - FM
Pulses at sampling frequency HF Carrier Oscillator
PAM
Pulse Amplitude Modulator
Analog Signal
Amplitude Modulated
Pulses

20. * In this type, the amplitude is maintained constant but the duration
or length or width of each pulse is varied in accordance with
instantaneous value of the analog signal.
* The negative side of the signal is brought to the positive side by
adding a fixed d.c. voltage.
Analog Signal
Width Modulated Pulses
Pulse Width Modulation (PWM or PLM or PDM):

21. * In this type, the sampled waveform has fixed amplitude and
width whereas the position of each pulse is varied as per
instantaneous value of the analog signal.
* PPM signal is further modification of a PWM signal. It has
positive thin pulses (zero time or width) corresponding to the
starting edge of a PWM pulse and negative thin pulses
corresponding to the ending edge of a pulse.
* This wave can be
further amended
by eliminating the
whole positive
narrow pulses.
The remaining
pulse is called
clipped PPM.
PWM
PPM
Pulse Position Modulation (PPM):

22. PAM, PWM and PPM at a glance:
Analog Signal
Amplitude Modulated Pulses
Width Modulated Pulses
Position Modulated Pulses

23. PULSE CODE MODULATION
It was only in 1938,Mr. A.M. Reaves (USA) developed a Pulse
Code Modulation (PCM) system to transmit the spoken word in digital form.
 Pulse-code modulation (PCM) is a method used to digitally represent
sampled analog signals. It is the standard form of digital audio in
computers, Compact Discs, digital telephony and other digital audio
applications
In a PCM stream, the amplitude of the analog signal is sampled regularly
at uniform intervals, and each sample is quantized to the nearest value
within a range of digital steps
To develop a PCM signal from several analogue signals, the following
processing steps are required
• Filtering
• Sampling
• Quantization
• Encoding
• Line Coding

24. * Analog signal is converted into digital signal by using a digital
code.
* Analog to digital converter employs two techniques:
1. Sampling: The process of generating pulses of zero width
and of amplitude equal to the instantaneous amplitude of the
analog signal. The no. of pulses per second is called
“sampling rate”.
2. Quantization: The process of dividing the maximum value
of the analog signal into a fixed no. of levels in order to
convert the PAM into a Binary Code.
The levels obtained are called “quanization levels”.
* A digital signal is described by its „bit rate‟ whereas analog
signal is described by its „frequency range‟.
* Bit rate = sampling rate x no. of bits / sample
Pulse Code Modulation (PCM):

25. Time
V
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a
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e
7
6
5
4
3
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1
0
111
110
101
100
011
010
001
000
L
e
v
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l
s
B
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y
C
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s
Time
Time
V
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0 1 0 1 0 1 1 1 0 1 1 1 1 1 0 1 0 1 0 1 0
Sampling,
Quantization and
Coding

26. EVOLUTION OF DIGITAL
MULTIPLEXING
Fig. Transport Technologies Evolution

27. Plesiochronous digital hierarchy (PDH)
PDH is a Multiplex hierarchy.
The PDH signals are the 2.048 Mbit/s signal
that carries 30 voice channels, the 8.488
Mbit/s signal that multiplexes four 2.048
Mbit/s signals, the 34.368 Mbit/s signal that
multiplexes four 8.488 Mbit/s signals,
and the 139.264 Mbit/s signal that
multiplexes four 34.368 Mbit/s signals.

28. PDH MULTIPLEXING
STRUCTURE

29. PDH Bit Rates

30.  COMPLICATED MUX/DMUX TECHNIQUE
 NO COMMON STANDARD
 POOR MANAGEMENT
• NO PROTECTION & PROBLEM OF INTER NETWORKING
• VENDER DEPENDENT
• PROBLEM OF CROSS-CONNECTION
• NEARLY SYNCHRONOUS
DRAWBACK OF PDH SYSTEM

31. Synchronous Digital Hierarchy (SDH)
• Synchronous Digital Hierarchy (SDH) is standardized
protocols that transfer multiple digital bit streams over
optical fiber using lasers or highly coherent light from
light-emitting diodes (LEDs).
• SDH IS AN ITU-T STANDARD FOR A
HIGH CAPACITY TELECOM NETWORK.
• SDH IS A SYNCHRONOUS DIGITAL
TRANSPORT SYSTEM, AIM TO PROVIDE A
SIMPLE, ECONOMICAL AND FLEXIBLE TELECOM
INFRASTRUCTURE.

32. WHY SDH SYSTEM
• GLOBAL STANDARD
• MULTI-VENDER DEPENDENT
• SIMPLIFIED MUX/DMUX TECHNIQUE
• POWERFUL MANAGEMENT
• POWERFUL PROTECTION

33. SDH SYSTEMS
SYSTEM BITE RATE No. OF CHANNELS
STM-1 155.52 Mbps 1890
STM-4 622.08 Mbps 7560
STM-16 2.5 Gbps 30240
STM-64 10 Gbps 120960
STM-256 40 Gbps 483840

34. SDH/PDH RATES
SDH
140 Mbit/s
34 Mbit/s
8 Mbit/s
2 Mbit/s
Nx45 Mbit/s 100 Mbit/s
45Mbit/s
6,3 Mbit/s
1,5 Mbit/s
32 Mbit/s
6,3 Mbit/s
1,5 Mbit/s
400 Mbit/s
PDH
PDH
EUROPE
PDH
JAPAN
PDH
NOTH AMERICA
Level 1
Level 4
Level 3
Level 2
STM64 10Gbit/s
STM4 620Mbit/s
STM1 155Mbit/s
STM16 2,48Gbit/s

35. ADVANTAGES OF SDH
• HIGH TRANSMISSION RATES
• SIMPLIFIED ADD &DROP FUNCTION
• HIGH AVAILABILITY AND CAPACITY
MATCHING
• RELIABILITY
• FUTURE-PROOF PLATFORM FOR NEW
SERVICES
• INTERCONNECTION
• SDH SUPPORTS PDH SIGNALS

36. SDH APPLICATION AREAS
• SDH systems are used in almost all areas of
telecommunication network. Some of the
applications areas are given below.
• Access Network
• Aggregation Network
• Metro Network
• Long distance National as well as International
• Wireless Backhauling
• SCADA (Supervisory Control and Data Acquisition)

39. Racks of Alcatel STM-16 SDH add-drop
multiplexers

41. Thank you!!