Pulse Digital Modulation & Delta Modulation | Communication System - Electronics and Communication Engineering (ECE) PDF Download

 Page 1


1 
 
 
Digital Pulse Modulation 
 
Elements of Digital Communication Systems: 
 
 
 
 
 
Fig. 1 Elements of Digital Communication Systems 
 
1. Information Source and Input Transducer: 
The source of information can be analog or digital, e.g. analog: audio or video 
signal, digital: like teletype signal. In digital communication the signal produced by 
this source is converted into digital signal which consists of 1's and 0's. For this we 
need a source encoder. 
2. Source Encoder: 
In digital communication we convert the signal from source into digital signal 
as mentioned above. The point to remember is we should like to use as few binary 
digits as possible to represent the signal. In such a way this efficient representation 
of the source output results in little or no redundancy. This sequence of binary digits 
is called information sequence. 
Source Encoding or Data Compression: the process of efficiently converting 
the output of whether analog or digital source into a sequence of binary digits is 
known as source encoding. 
Page 2


1 
 
 
Digital Pulse Modulation 
 
Elements of Digital Communication Systems: 
 
 
 
 
 
Fig. 1 Elements of Digital Communication Systems 
 
1. Information Source and Input Transducer: 
The source of information can be analog or digital, e.g. analog: audio or video 
signal, digital: like teletype signal. In digital communication the signal produced by 
this source is converted into digital signal which consists of 1's and 0's. For this we 
need a source encoder. 
2. Source Encoder: 
In digital communication we convert the signal from source into digital signal 
as mentioned above. The point to remember is we should like to use as few binary 
digits as possible to represent the signal. In such a way this efficient representation 
of the source output results in little or no redundancy. This sequence of binary digits 
is called information sequence. 
Source Encoding or Data Compression: the process of efficiently converting 
the output of whether analog or digital source into a sequence of binary digits is 
known as source encoding. 
2 
 
3. Channel Encoder: 
The information sequence is passed through the channel encoder. The 
purpose of the channel encoder is to introduce, in controlled manner, some 
redundancy in the binary information sequence that can be used at the receiver to 
overcome the effects of noise and interference encountered in the transmission on 
the signal through the channel. 
For example take k bits of the information sequence and map that k bits to 
unique n bit sequence called code word. The amount of redundancy introduced is 
measured by the ratio n/k and the reciprocal of this ratio (k/n) is known as rate of 
code or code rate. 
4. Digital Modulator: 
The binary sequence is passed to digital modulator which in turns convert the 
sequence into electric signals so that we can transmit them on channel (we will see 
channel later). The digital modulator maps the binary sequences into signal wave 
forms , for example if we represent 1 by sin x and 0 by cos x then we will transmit sin 
x for 1 and cos x for 0. ( a case similar to BPSK) 
5. Channel: 
The communication channel is the physical medium that is used for 
transmitting signals from transmitter to receiver. In wireless system, this channel 
consists of atmosphere , for traditional telephony, this channel is wired , there are 
optical channels, under water acoustic channels etc.We further discriminate this 
channels on the basis of their property and characteristics, like AWGN channel etc. 
6. Digital Demodulator: 
The digital demodulator processes the channel corrupted transmitted 
waveform and reduces the waveform to the sequence of numbers that represents 
estimates of the transmitted data symbols. 
7. Channel Decoder: 
This sequence of numbers then passed through the channel decoder which 
attempts to reconstruct the original information sequence from the knowledge of 
the code used by the channel encoder and the redundancy contained in the received 
data 
Note: The average probability of a bit error at the output of the decoder is a 
measure of the performance of the demodulator – decoder combination. 
8. Source Decoder: 
At the end, if an analog signal is desired then source decoder tries to decode 
the sequence from the knowledge of the encoding algorithm. And which results in 
the approximate replica of the input at the transmitter end. 
Page 3


1 
 
 
Digital Pulse Modulation 
 
Elements of Digital Communication Systems: 
 
 
 
 
 
Fig. 1 Elements of Digital Communication Systems 
 
1. Information Source and Input Transducer: 
The source of information can be analog or digital, e.g. analog: audio or video 
signal, digital: like teletype signal. In digital communication the signal produced by 
this source is converted into digital signal which consists of 1's and 0's. For this we 
need a source encoder. 
2. Source Encoder: 
In digital communication we convert the signal from source into digital signal 
as mentioned above. The point to remember is we should like to use as few binary 
digits as possible to represent the signal. In such a way this efficient representation 
of the source output results in little or no redundancy. This sequence of binary digits 
is called information sequence. 
Source Encoding or Data Compression: the process of efficiently converting 
the output of whether analog or digital source into a sequence of binary digits is 
known as source encoding. 
2 
 
3. Channel Encoder: 
The information sequence is passed through the channel encoder. The 
purpose of the channel encoder is to introduce, in controlled manner, some 
redundancy in the binary information sequence that can be used at the receiver to 
overcome the effects of noise and interference encountered in the transmission on 
the signal through the channel. 
For example take k bits of the information sequence and map that k bits to 
unique n bit sequence called code word. The amount of redundancy introduced is 
measured by the ratio n/k and the reciprocal of this ratio (k/n) is known as rate of 
code or code rate. 
4. Digital Modulator: 
The binary sequence is passed to digital modulator which in turns convert the 
sequence into electric signals so that we can transmit them on channel (we will see 
channel later). The digital modulator maps the binary sequences into signal wave 
forms , for example if we represent 1 by sin x and 0 by cos x then we will transmit sin 
x for 1 and cos x for 0. ( a case similar to BPSK) 
5. Channel: 
The communication channel is the physical medium that is used for 
transmitting signals from transmitter to receiver. In wireless system, this channel 
consists of atmosphere , for traditional telephony, this channel is wired , there are 
optical channels, under water acoustic channels etc.We further discriminate this 
channels on the basis of their property and characteristics, like AWGN channel etc. 
6. Digital Demodulator: 
The digital demodulator processes the channel corrupted transmitted 
waveform and reduces the waveform to the sequence of numbers that represents 
estimates of the transmitted data symbols. 
7. Channel Decoder: 
This sequence of numbers then passed through the channel decoder which 
attempts to reconstruct the original information sequence from the knowledge of 
the code used by the channel encoder and the redundancy contained in the received 
data 
Note: The average probability of a bit error at the output of the decoder is a 
measure of the performance of the demodulator – decoder combination. 
8. Source Decoder: 
At the end, if an analog signal is desired then source decoder tries to decode 
the sequence from the knowledge of the encoding algorithm. And which results in 
the approximate replica of the input at the transmitter end. 
3 
 
9. Output Transducer: 
Finally we get the desired signal in desired format analog or digital. 
 
Advantages of digital communication: 
 
 
 
Page 4


1 
 
 
Digital Pulse Modulation 
 
Elements of Digital Communication Systems: 
 
 
 
 
 
Fig. 1 Elements of Digital Communication Systems 
 
1. Information Source and Input Transducer: 
The source of information can be analog or digital, e.g. analog: audio or video 
signal, digital: like teletype signal. In digital communication the signal produced by 
this source is converted into digital signal which consists of 1's and 0's. For this we 
need a source encoder. 
2. Source Encoder: 
In digital communication we convert the signal from source into digital signal 
as mentioned above. The point to remember is we should like to use as few binary 
digits as possible to represent the signal. In such a way this efficient representation 
of the source output results in little or no redundancy. This sequence of binary digits 
is called information sequence. 
Source Encoding or Data Compression: the process of efficiently converting 
the output of whether analog or digital source into a sequence of binary digits is 
known as source encoding. 
2 
 
3. Channel Encoder: 
The information sequence is passed through the channel encoder. The 
purpose of the channel encoder is to introduce, in controlled manner, some 
redundancy in the binary information sequence that can be used at the receiver to 
overcome the effects of noise and interference encountered in the transmission on 
the signal through the channel. 
For example take k bits of the information sequence and map that k bits to 
unique n bit sequence called code word. The amount of redundancy introduced is 
measured by the ratio n/k and the reciprocal of this ratio (k/n) is known as rate of 
code or code rate. 
4. Digital Modulator: 
The binary sequence is passed to digital modulator which in turns convert the 
sequence into electric signals so that we can transmit them on channel (we will see 
channel later). The digital modulator maps the binary sequences into signal wave 
forms , for example if we represent 1 by sin x and 0 by cos x then we will transmit sin 
x for 1 and cos x for 0. ( a case similar to BPSK) 
5. Channel: 
The communication channel is the physical medium that is used for 
transmitting signals from transmitter to receiver. In wireless system, this channel 
consists of atmosphere , for traditional telephony, this channel is wired , there are 
optical channels, under water acoustic channels etc.We further discriminate this 
channels on the basis of their property and characteristics, like AWGN channel etc. 
6. Digital Demodulator: 
The digital demodulator processes the channel corrupted transmitted 
waveform and reduces the waveform to the sequence of numbers that represents 
estimates of the transmitted data symbols. 
7. Channel Decoder: 
This sequence of numbers then passed through the channel decoder which 
attempts to reconstruct the original information sequence from the knowledge of 
the code used by the channel encoder and the redundancy contained in the received 
data 
Note: The average probability of a bit error at the output of the decoder is a 
measure of the performance of the demodulator – decoder combination. 
8. Source Decoder: 
At the end, if an analog signal is desired then source decoder tries to decode 
the sequence from the knowledge of the encoding algorithm. And which results in 
the approximate replica of the input at the transmitter end. 
3 
 
9. Output Transducer: 
Finally we get the desired signal in desired format analog or digital. 
 
Advantages of digital communication: 
 
 
 
4 
 
Introduction to Pulse Modulation 
 
What is the need for Pulse Modulation? 
 
? Many Signals in Modern Communication Systems are digital 
? Also, analog signals are transmitted digitally. 
? Reduced distortion and improvement in signal to noise ratios. 
? PAM, PWM, PPM, PCM and DM. 
? In CW modulation schemes some parameter of modulated wave varies continuously with 
message. 
? In Analog pulse modulation some parameter of each pulse is modulated by a particular 
sample value of the message. 
? Pulse modulation is of two types 
o Analog Pulse Modulation 
? Pulse Amplitude Modulation (PAM) 
? Pulse width Modulation (PWM) 
? Pulse Position Modulation (PPM) 
o Digital Pulse Modulation 
? Pulse code Modulation (PCM) 
? Delta Modulation (DM) 
 
Pulse Code Modulation: 
 
Three steps involved in conversion of analog signal to digital signal 
? Sampling 
? Quantization 
? Binary encoding 
Page 5


1 
 
 
Digital Pulse Modulation 
 
Elements of Digital Communication Systems: 
 
 
 
 
 
Fig. 1 Elements of Digital Communication Systems 
 
1. Information Source and Input Transducer: 
The source of information can be analog or digital, e.g. analog: audio or video 
signal, digital: like teletype signal. In digital communication the signal produced by 
this source is converted into digital signal which consists of 1's and 0's. For this we 
need a source encoder. 
2. Source Encoder: 
In digital communication we convert the signal from source into digital signal 
as mentioned above. The point to remember is we should like to use as few binary 
digits as possible to represent the signal. In such a way this efficient representation 
of the source output results in little or no redundancy. This sequence of binary digits 
is called information sequence. 
Source Encoding or Data Compression: the process of efficiently converting 
the output of whether analog or digital source into a sequence of binary digits is 
known as source encoding. 
2 
 
3. Channel Encoder: 
The information sequence is passed through the channel encoder. The 
purpose of the channel encoder is to introduce, in controlled manner, some 
redundancy in the binary information sequence that can be used at the receiver to 
overcome the effects of noise and interference encountered in the transmission on 
the signal through the channel. 
For example take k bits of the information sequence and map that k bits to 
unique n bit sequence called code word. The amount of redundancy introduced is 
measured by the ratio n/k and the reciprocal of this ratio (k/n) is known as rate of 
code or code rate. 
4. Digital Modulator: 
The binary sequence is passed to digital modulator which in turns convert the 
sequence into electric signals so that we can transmit them on channel (we will see 
channel later). The digital modulator maps the binary sequences into signal wave 
forms , for example if we represent 1 by sin x and 0 by cos x then we will transmit sin 
x for 1 and cos x for 0. ( a case similar to BPSK) 
5. Channel: 
The communication channel is the physical medium that is used for 
transmitting signals from transmitter to receiver. In wireless system, this channel 
consists of atmosphere , for traditional telephony, this channel is wired , there are 
optical channels, under water acoustic channels etc.We further discriminate this 
channels on the basis of their property and characteristics, like AWGN channel etc. 
6. Digital Demodulator: 
The digital demodulator processes the channel corrupted transmitted 
waveform and reduces the waveform to the sequence of numbers that represents 
estimates of the transmitted data symbols. 
7. Channel Decoder: 
This sequence of numbers then passed through the channel decoder which 
attempts to reconstruct the original information sequence from the knowledge of 
the code used by the channel encoder and the redundancy contained in the received 
data 
Note: The average probability of a bit error at the output of the decoder is a 
measure of the performance of the demodulator – decoder combination. 
8. Source Decoder: 
At the end, if an analog signal is desired then source decoder tries to decode 
the sequence from the knowledge of the encoding algorithm. And which results in 
the approximate replica of the input at the transmitter end. 
3 
 
9. Output Transducer: 
Finally we get the desired signal in desired format analog or digital. 
 
Advantages of digital communication: 
 
 
 
4 
 
Introduction to Pulse Modulation 
 
What is the need for Pulse Modulation? 
 
? Many Signals in Modern Communication Systems are digital 
? Also, analog signals are transmitted digitally. 
? Reduced distortion and improvement in signal to noise ratios. 
? PAM, PWM, PPM, PCM and DM. 
? In CW modulation schemes some parameter of modulated wave varies continuously with 
message. 
? In Analog pulse modulation some parameter of each pulse is modulated by a particular 
sample value of the message. 
? Pulse modulation is of two types 
o Analog Pulse Modulation 
? Pulse Amplitude Modulation (PAM) 
? Pulse width Modulation (PWM) 
? Pulse Position Modulation (PPM) 
o Digital Pulse Modulation 
? Pulse code Modulation (PCM) 
? Delta Modulation (DM) 
 
Pulse Code Modulation: 
 
Three steps involved in conversion of analog signal to digital signal 
? Sampling 
? Quantization 
? Binary encoding 
5 
 
 
 
Fig. 2 Conversion of Analog Signal to Digital Signal 
 
Note: Before sampling the signal is filtered to limit bandwidth. 
 
Elements of PCM System: 
 
Fig. 3 Elements of PCM System 
 
Sampling: 
 
? Process of converting analog signal into discrete signal. 
? Sampling is common in all pulse modulation techniques