Digital, Microwave & Optical Communications Portfolio - CIS117-6

This portfolio provides a comprehensive overview of digital, microwave, and optical communication systems, addressing key concepts and components. It begins by explaining entropy in digital communications, emphasizing its role in optimizing bandwidth usage through efficient code mapping. The portfolio then details the essential components of a digital communication system, including input transducers, source encoders, channel encoders, digital modulators, demodulators, and output transducers, highlighting the importance of converting analog data into digital signals for noise-resistant transmission. Furthermore, it discusses the role of digital modulation in enhancing signal reproduction over long distances, differentiating it from analog modulation and detailing various techniques like Amplitude Shift Keying, Phase Shift Keying, and Frequency Shift Keying. The document explains how digital modulation helps in faithful and convenient signal reproduction, particularly beneficial for long-distance communication with repeaters.

Submission Deadline Marks and Feedback
Before 10am on:
22/03/2019
20 working days after deadline (L4, 5 and 7)
15 working days after deadline (L6)
10 working days after deadline (block delivery)
05/04/2019
Unit title & code Digital, Microwave and Optical Communications (CIS117-6)
Assignment number and title One – Digital , Microwave and Optical Communications
Assessment type Portfolio
Weighting of assessment 100%
Unit learning outcomes 1.Demonstrate a systematic understanding of the fundamental
underpinning scientific principles of digital, microwave and optical
communications and the corresponding system components.
2. Criticallyanalyse and assess digital, microwave and optical
communication technologies, techniques, models and system design
and performance
What am I required to do in this assignment?
You are required to complete the exercises that outlined below. There are exercises for each of the three components: Digital, Microwave
and Optical Communications. The exercises are also included below for completeness. Each exercise has a number of marks associated with
it, and you will need to answer all of the sub question for each component.
Digital communications
Q1 a) Explain the concept of entropy (information theory) with respect to digital communications (5 marks)
In every digital communication, the message or information is transferred as series of codes. Each code represents a
unique character or symbol of the language in which information is being exchanged. However, in every language
some symbols or characters repeat more often than others do.
Digital communication always tries to send more and more information consuming as minimum bandwidth as

possible. Therefore, engineers always try to evaluate the structure of the information to be transmitted, so that
mapping of codes to symbols can be made in optimal manner.
This means choosing short quotes for symbols that occur more often that would have maximum effective usage of
bandwidth. Mathematically, this is termed as entropy. Average information on message of entropy of a source this can
be represented as this, where Information content Ii of a message is presented as mi :
(Modern digital and Analog Communication Systems, 2010, p. 737)
Entropy is therefore dependent upon probability or frequency of a message being repeated in the entire piece of
information. So this can be related as inverse of information content. Higher entropy means lower information value
for each message. Alternatively, it can be seen, as more bits are required to send certain message when the
randomness of individual symbols in a message is high. On the other hand, if the randomness among symbols is small,
entropy would be small and more information can be sent using less number of bits.
Talking about entropy in communication background, it is beneficial to have messages with low entropy rates or
message being more predictable. This allows for easier recovery of a message at receiver from a corrupted message
faithfully because outcome of a message is predictable. A message with high entropy on the other hand has high level
of randomness and hence is least predictable in case it is received as corrupted signal.
Q1 b) Using a diagram, explain the key components of a digital communications system (10 marks)
The term Digital communication system is two definitions in one word. The word digital is counterpart of the word
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analog. There are two differentiating aspects to these two types. Digital has fixed levels of magnitude at regular
interval from each other like integer values. Analog on the other hand has continuous levels of magnitude like decimal
numbers. The same when applied to time domain, Digital signal often exists on certain fixed time intervals while
analog signal is continuous over a period of time.
Communication system is simple mechanism that allows for transfer of messages between two points. Combining the
two definitions, when we use digital signals for representation of messages and perform communication using those
signals, the system is termed as Digital Communication System. A high level view of the system can be seen here. A
Signal is sent by transmitting end over a medium or channel that is susceptible to noise. The other end receives this
signal and tries to recover original message.
(Arkin)
The main advantage of using a digital communication system is its ability to accommodate noise without affecting its
accuracy to unrecoverable extent. However, original data is still analog in nature like voice, video or other sensed
inputs. This analog input has to be converted into digital signal for transmission. This conversion has a drawback of
not being précised enough. Therefore, any advantage we have from using digital signal in terms of noise immunity is
countered by its inability to precisely reflect an actual analog signal. This is one aspect of comparison. But even with
this disadvantage of being non –précised, digital communication is better because loss of precision is known and can
be made up for at the receiver by extrapolations. But there is no way to know effect of noise on a signal in transit and
reverse the effects of it on a received value. So this makes digital communication a method of choice.
This process of converting source of information into digitally represented symbols and transmission of such data over
a medium is shown here using a block diagram. The information from source is captured and converted into an
electrical signal. The signal is then encoded into digital symbols using a Source encoder and some predefined
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quantization algorithms like PCM. This low rate digital data is then further encoded to be suitable for transmission
over a channel. This involves addition of error correction/ detection codes and other header information to the original
message packet. Finally, we get a bit stream that is used to modulate the actual channel. Modulation is process of
altering at least one of the three features of a channel, namely its amplitude, Frequency or phase or any combination of
these. Once channel encoded bit stream is used to alter channel signal, the modulated signal is transmitted over a
medium.
Explanation of the key
components illustrated
in the figure 1.1
above:
1. Input
Transducer:
The source of
data can be
simple or
digital, for
example
simple: sound or video signal, computerized: like print signal. It is a device called transducer which converts
over one type of energy or signal into another type of energy. The transducer is situated at the input side and
output side of the communication framework. The transducer that is situated at the information side of the
communication framework is called input transducer. For the most part, the input transducer changes over the
non-electrical flag (sound signal or light signal) into an electrical signal. The best case of an input transducer is
the microphone which is put between the data source and the transmitter area. An amplifier is a gadget which
changes over your voice signals (sound signals) into electrical signals.
2. Source Encoder:
The signal delivered by source is changed over into digital signal comprises of 0′s and 1's. For this we need
source encoder. We should jump at the chance to use as couple of binary digits as conceivable to speak to the
signal. In such a way this effective portrayal of the source yield results in next to zero redundancy. This
grouping of binary digits is called data sequence. The process of efficiently and significantly converting the
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output of analog or digital source into a sequence of binary digits is known as source encoding.
3. Channel Encoder:
The data sequence is passed through the channel encoder. The motivation behind the channel encoder is to
presented, in controlled way, some vagueness in the binary data sequence that can be utilized at the recipient to
beat the impacts of commotion and impedance experienced in the transmission on the signal through the
channel. For example take k bits of the data information and map that k bits to distinct n bit arrangement called
code word. The measure of redundancy introduced is estimated by the proportion n/k and the complementary
of this proportion (k/n) is known as rate of code or code rate.
4. Digital Modulator and D/A converter:
The binary arrangement is passed to digital modulator which in return converts the sequence into electric
signals with the goal that we can transmit them on channel. The digital modulator maps the binary sequence
into flag wave shapes, for instance in the event that we speak to 1 by sin x and 0 by cos(x), at that point we
will transmit sin x for 1 and cos(x) for 0. An A/D converter is a gadget that changes over simple signals
(normally voltage) got from natural (physical) wonders into digital design, transformation includes a
progression of steps, including inspecting, quantization, and coding.
5. Digital Demodulator:
The digital demodulator forms the channel tainted transmitted waveform and decreases the waveform to the
succession of numbers that shows to estimate of the transmitted information symbols.
6. Channel Decoder:
This sequence of numbers then passed through the channel decoder which tries to do the construction from the
beginning basically it means reconstruct the original data sequence from the information of the code used by
the channel encoder and the redundancy contained in the received data. Average probability of a bit error at the
output of the decoder is a measure of the performance of the demodulator – decoder combination
7. Source Decoder:
Source decoder endeavors to decipher the sequence from the information of the encoding algorithm related to
the encoding schemes. Furthermore, this results in the inexact copy of the contribution at the transmitter end.
8. Output Transducer:
At last we get the ideal or desired signal in wanted configuration simple or digital, channels for digital
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Interchange communication. The adjustment and coding utilized in a digital communication framework rely
upon the attributes of the channel. The two principal qualities of the channel are Data transmission and
POWER. What's more alternate qualities are whether the channel is direct or nonlinear, and how free the
channel is free from the outer impedance.
Q2 a) What is digital modulation used for within a digital communications system? (5 marks)
In a communication system, there are two types of signals. A data stream and a carrier. When data stream is Analog in
nature and is used to modulate, i.e. alter at least one of the attributes of a carrier signal it is called Analog modulation.
However this type of modulation suffers from noise related degradation of quality and also suffers due to non-linearity
in underlying circuits involved in communication.
To overcome these channel noise and distortion effects, Data stream is converted into digital bit stream that is then
used to modulate a carrier. This is called as Digital modulation. It has a major advantage of being reproduced at a
distance using regenerative repeaters without loss of quality which is not possible in analog communication due to
inherent losses related to transmission. Or it can said reproduction of a digitally modulated signal is more faithful and
convenient in comparison to analog modulated signal. Digital Modulation is particularly suitable for long distance
communication with repeaters in between.
To differentiate Digital modulation from
Analog modulation, the modulation term
is replaced with “keying”. Like Analog
modulation, digital modulation also has
three flavors, namely:
i. Amplitude Shift Keying: The
amplitude of the carrier is altered on
basis of Digital signal turning it on
and off depending upon bit value.
This is also known as OOK for On-
Off keying.
(Modern digital and Analog Communication
Systems, 2010, p. 373)
ii. Phase Shift Keying: This is another type of modulation where phase of the carrier is changed in accordance to
digital input stream. The carrier is turned by 180 in phase when digital signal transforms from one level to another.
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As shown in figure below for PSK and FSK.
(digicoms)
iii. Frequency Shift Keying: The frequency of the carrier is increased or slowed down based on incoming data bit
value. The amplitude of the carrier is not changed in this scheme neither is the phase of the carrier altered in any
manner, only the frequency is varied over time to indicate change of value in input signal.
Q2 b) Explain three different ways of modulating a signal when only one degree of freedom is modulated (10 marks)
In communication terms it is important to understand two types of signals, the modulating signal and modulated
signal. The low frequency signal that is actual information is called the baseband signal but owing to its low frequency
it is difficult to transmit it over long distance with wires. So it needs another high frequency signal called the Carrier
on which this baseband signal can piggyback to reach its destination. This carrier signal is orders of magnitude higher
in terms of frequency and is suited for wireless transmission.
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All kinds of signals have three independent attributes that can be modified in a manner relative to another signal so
that modified signal can be identified to have been changed under a known sequence of input or pattern. The three
attributes are its amplitude, its frequency and its phase. Based on these three attributes, there exists three basic
modulation techniques. They are:
i. Amplitude Modulation or AM: Amplitude is the maximum value the signal can achieve in its either polarity
levels. When this Amplitude of the carrier signal
is muted to a certain extent due to a change in
input sequence of baseband signal being used for
modulation, the process is called Amplitude
modulation.
The amount of modulation of carrier is defined in
terms of modulation index. The index defines
what is the maximum amount of deviation in
amplitude of carrier signal due to maximum
change in amplitude of the baseband signal. An
index value of 1 would mean amplitude varies
between zeros to maximum.
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Baseband Signal
Modulated Carrier

ii. Frequency Modulation: When instead of amplitude,
frequency of the carrier signal is modulated under influence
of baseband signal, it is called frequency modulation. The
FM has advantage of being more resistant of effects of
noise and distortion but it occupies much larger bandwidth
as compared to AM technique. Also devices for the FM are
more complicated and expensive compared to the AM. Still
its SNR ratio makes it more suitable for broadcast
communication and is widely used in all commercial
systems.
(what-are-the-applications-of-frequency-modulation, 2017)
iii. Phase Modulation: In this form of modulation, amplitude and
frequency of the carrier are not altered but only the phase of the
carrier is modulated as per changes in amplitude of the baseband
signal. The PM also called as angle modulation is resistant to
Each time the baseband signal reaches its maximum value, the
phase of the carrier is reversed by 180◦. The same happens when
baseband reaches in negative peak; the phase again shifts by
180.
However, it is Phase modulation but it inherently does bring a
change in frequency of the carrier by small amount.
Depending upon requirement of the communication environment any of the three techniques can be utilized to form a
mode of communication between the transmitter and receiver or multiple receivers in case of broadcast.
Q3) Consider a DMS where output is generated from an alphabet {a,b,c,d,e,f,g,h} with respective with probabilities {0.25,
0.1, 0.02, 0.05, 0.25, 0.03, 0.25, 0.05}.
a) Design a Huffman code and sketch the corresponding coding tree. Explain the codewords for each character in the alphabet (10 marks)
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b) Calculate the average length of the codeword if the Huffman code you generated (5 marks)
Huff man codes: a – 0,e - 10, g - 111, b-1100, d – 11010, h – 110110, c – 1101110, f – 1101111
Average Length of codes = 0.25 * 1 + 0.25 * 2 + 0.25 * 3 + 0.1 * 4 + 0.05*5 + 0.05*6 + 0.02 * 7 + 0.03 * 8 = 2.8
bits / symbol
c) Calculate the efficiency of your Huffman code (5 marks)
Efficiency is = H / L
H = ∑
k=0
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Px ( i ) ∗log 2[ 1
Px (i) ¿] ¿ = 2.56 / 2.8 = 0.914285
Q4) Design a Shannon-Fano code and sketch the corresponding coding tree where the alphabet is {a,b,c,d,e,f} with corresponding
probabilities {0.5, 0.1, 0.05, 0.05, 0.25, 0.25} (10 marks)
Write all probabilities in decreasing order:
a 0.5 0 0
e 0.25 1 0 0 100
f 0.25 1 0 1 101
b 0.1 1 1 0 110
10
Root
a (0.25) 0.75
e(0.25) 0.50
g(0.25) 0.25
b (0.1) 0.15
d (0.05) 0.10
h (0.05) 0.05
f (0.03) c (0.02)

c 0.05 1 1 1 0 1 11101
d 0.05 1 1 1 1 1 11111
Microwave communications
Q1) Antennas play a vital role in the performance of wireless communications systems. Microstrip patch
antennas are very widely used in wireless applications due to their inherent features of simple design,
low complexity, ease of fabrication and low cost to meet the design requirements.
The objective of this assignment is the design of a microstrip patch antenna for a practical Wireless
Local Area Network (WLAN) application operating at ISM band in the range of 2.45 GHz. The antenna
is excited using a microstrip transmission line.
a) The important dimensions that need to be optimised include length and width of the ground plane,
patch and feed, and width and length of the two matching cuts on each side of the feed.
1. You need to design an antenna that needs to be matched such that the resonance frequency
is:
fr = 2.45GHz + (last 3 digits of your student ID / 2)Mhz
For example, if your student ID number is 1322350 then the antenna working frequency should
be as follows:
350⎛ ⎞
f r = 2.45GHz + (300/2)MHz
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1
a(0.5) 0.5
e f 0.1
0.1
d c
b

= 2.45GHz +150MHz = 2.6GHz
(20 marks)
Antenna Frequency : - =
PROPOSED ANTENNA GEOMETRY :
Given: Frequency of operation for antenna = 2.45GHz + 295.5MHz = 2.745.5GHz
First we calculate λ=C /f
Where C = speed of light 3 X 108m/sec and f = Resonant Frequency 2.7455GHz
Substituting values gives λ=¿0.109m
Selecting a substrate for ground plane ; assuming FR4 Epoxy dielectric substrate with relative
Permittivity of ∈𝑟 =4.4
Then width of the patch can be calculated as W =
Wp =
C
2 f √ ϵr+ 1
2
Where, C = frequency of light and f = resonant frequency, ϵr is substrate permittivity
Substituting the values gives
W0 = 33.255 mm
Length of the patch is calculated based on Leff as
L = Leff - 2∆L
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