This document is an assignment submission for a data communication course. It discusses various topics related to data communication including the definition of data communication, components of a data communication system, analog and digital transmission methods, modulation techniques like amplitude-shift keying and frequency-shift keying. It also defines key terms like analog signals, digital signals, modulation and describes different types of signals and transmission methods.

1. Assignment- 04
Course Title: Data Communication
Course Code: CSE 313
Submitted To:
Pranob Nath Bandhu
Lecturer
City University
Khagan, Savar, Dhaka.
Submitted By:
Md.Rasel Kabir Raju
ID: 1834902202
Batch: 49th
Program: CSE
Submission date:

2. Data Communication
Data communication refers to the exchange of data between a source and a receiver via form
of transmission media such as a wire cable. Data communication is said to be local if
communicating devices are in the same building or a similarly restricted geographical
area.The meanings of source and receiver are very simple. The device that transmits the data
is known as source and the device that receives the transmitted data is known as receiver.
Data communication aims at the transfer of data and maintenance of the data during the
process but not the actual generation of the information at the source and receiver.
Componentsof data communication system
A Communication system has following components:
1. Message: It is the information or data to be communicated. It can consist of text, numbers,
pictures, sound or video or any combination of these.
2. Sender: It is the device/computer that generates and sends that message.
3. Receiver: It is the device or computer that receives the message. The location of receiver
computer is generally different from the sender computer. The distance between sender and
receiver depends upon the types of network used in between.
4. Medium: It is the channel or physical path through which the message is carried from
sender to the receiver. The medium can be wired like twisted pair wire, coaxial cable, fiber-
optic cable or wireless like laser, radio waves, and microwaves.

3. 5. Protocol: It is a set of rules that govern the communication between the devices. Both
sender and receiver follow same protocols to communicate with each other.
Analog transmission:
Analog format is that in which information is transmitted by modulating a continuous
transmission signal, such as amplifying a signal’s strength or varying its frequency to add or
take away data
Serial Transmission
In telecommunications, serial transmission is the sequential transmission of signal elements
of a group representing a character or other entity of data. Digital serial transmissions are bits
sent over a single wire, frequency or optical path sequentially.
Parallel Transmission
In telecommunications, parallel transmission is the simultaneous transmission of the signal
elements of a character or other entity of data. In digital communications, parallel
transmission is the simultaneous transmission of related signal elements over two or more
separate paths. Multiple electrical wires are used which can transmit multiple bits
simultaneously, which allows for higher data transfer rates than can be achieved with serial
transmission.
SIGNAL
In signal processing, a signal is a function that conveys information about a phenomenon.In
electronics and telecommunications,it refers to any time varying voltage, current, or
electromagnetic wave that carries information. A signal may also be defined as an observable
change in a quality such as quantity.Any quality, such as physical quantity that exhibits
variation in space or time can be used as a signal to share messages between observers.
According to the IEEE Transactions on Signal Processing, a signal can be audio, video,
speech, image, sonar, and radar-related and so on In another effort to define signal,anything
that is only a function of space, such as an image, is excluded from the category of signals.
Also, it is stated that a signal may or may not contain any information.
In nature, signals can be actions done by an organism to alert other organisms, ranging from
the release of plant chemicals to warn nearby plants of a predator, to sounds or motions made

4. by animals to alert other animals of food. Signaling occurs in all organisms even at cellular
levels, with cell signaling. Signaling theory, in evolutionary biology, proposes that a
substantial driver for evolution is the ability for animals to communicate with each other by
developing ways of signaling. In human engineering, signals are typically provided by a
sensor, and often the original form of a signal is converted to another form of energy using a
transducer. For example, a microphone converts an acoustic signal to a voltage waveform,
and a speaker does the reverse.
Analog and digital signal
Two main types of signals encountered in practice are analog and digital. The figure shows a
digital signal that results from approximating an analog signal by its values at particular time
instants. Digital signals are quantized, while analog signals are continuous.
Analog signal
An analog signal is any continuous signal for which the time varying feature of the signal is a
representation of some other time varying quantity, i.e., analogous to another time varying
signal. For example, in an analog audio signal, the instantaneous voltage of the signal varies
continuously with the sound pressure. It differs from a digital signal, in which the continuous
quantity is a representation of a sequence of discrete values which can only take on one of a
finite number of values.The term analog signal usually refers to electrical signals; however,
analog signals may use other mediums such as mechanical, pneumatic or hydraulic. An
analog signal uses some property of the medium to convey the signal's information. For
example, an aneroid barometer uses rotary position as the signal to convey pressure
information. In an electrical signal, the voltage, current, or frequency of the signal may be
varied to represent the information.Any information may be conveyed by an analog signal;
often such a signal is a measured response to changes in physical phenomena, such as sound,
light, temperature, position, or pressure. The physical variable is converted to an analog
signal by a transducer. For example, in sound recording, fluctuations in air pressure (that is to
say, sound) strike the diaphragm of a microphone which induces corresponding electrical
fluctuations. The voltage or the current is said to be an analog of the sound.

5. Digital signal
A digital signal is a signal that is constructed from a discrete set of waveforms of a physical
quantity so as to represent a sequence of discrete values .A logic signal is a digital signal with
only two possible values, and describes an arbitrary bit stream. Other types of digital signals
can represent three-valued logic or higher valued logics.
Alternatively, a digital signal may be considered to be the sequence of codes represented by
such a physical quantity. The physical quantity may be a variable electric current or voltage,
the intensity, phase or polarization of an optical or other electromagnetic field, acoustic
pressure, the magnetization of a magnetic storage media, etc. Digital signals are present in all
digital electronics, notably computing equipment and data transmission.With digital signals,
system noise, provided it is not too great, will not affect system operation whereas noise
always degrades the operation of analog signals to some degree.Digital signals often arise via
sampling of analog signals, for example, a continually fluctuating voltage on a line that can
be digitized by an analog-to-digital converter circuit, wherein the circuit will read the voltage
level on the line, say, every 50 microseconds and represent each reading with a fixed number
of bits. The resulting stream of numbers is stored as digital data on a discrete-time and
quantized-amplitude signal. Computers and other digital devices are restricted to discrete
time.

6. MODULATION
In electronics and telecommunications, modulation is the process of varying one or more
properties of a periodic waveform, called the carrier signal, with a separate signal called the
modulation signal that typically contains information to be transmitted.
Digital modulation
In digital modulation, an analog carrier signal is modulated by a discrete signal. Digital
modulation methods can be considered as digital-to-analog conversion and the corresponding
demodulation or detection as analog-to-digital conversion. The changes in the carrier signal
are chosen from a finite number of M alternative symbols According to one definition of
digital signal,the modulated signal is a digital signal. According to another definition, the
modulation is a form of digital-to-analog conversion. Most textbooks would consider digital
modulation schemes as a form of digital transmission, synonymous to data transmission; very
few would consider it as analog transmission.
Amplitude-shift keying (ASK)
Is a form of amplitude modulation that represents digital data as variations in the amplitude
of a carrier wave. In an ASK system, a symbol, representing one or more bits, is sent by
transmitting a fixed-amplitude carrier wave at a fixed frequency for a specific time duration.
For example, if each symbol represents a single bit, then the carrier signal will be transmitted
when the input value is 1, but will not be transmitted when the input value is 0.
Any digital modulation scheme uses a finite number of distinct signals to represent digital
data. ASK uses a finite number of amplitudes, each assigned a unique pattern of binary digits.
Usually, each amplitude encodes an equal number of bits. Each pattern of bits forms the
symbol that is represented by the particular amplitude. The demodulator, which is designed
specifically for the symbol-set used by the modulator, determines the amplitude of the
received signal and maps it back to the symbol it represents, thus recovering the original data.
Frequency and phase of the carrier are kept constant.

7. Frequency-shift keying (FSK)
Is a frequency modulation scheme in which digital information is transmitted through
discrete frequency changes of a carrier signal.The technology is used for communication
systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and
low frequency radio transmission in the VLF and ELF bands. The simplest FSK is binary
FSK (BFSK). BFSK uses a pair of discrete frequencies to transmit binary (0s and 1s)
information. With this scheme, the 1 is called the mark frequency and the 0 is called the
space frequency.
Phase-shift keying (PSK)
Is a digital modulation process which conveys data by changing (modulating) the phase of a
constant frequency reference signal (the carrier wave). The modulation is accomplished by
varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs,
RFID and Bluetooth communication.Any digital modulation scheme uses a finite number of

8. distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a
unique pattern of binary digits. Usually, each phase encodes an equal number of bits. Each
pattern of bits forms the symbol that is represented by the particular phase. The demodulator,
which is designed specifically for the symbol-set used by the modulator, determines the phase
of the received signal and maps it back to the symbol it represents, thus recovering the
original data. This requires the receiver to be able to compare the phase of the received signal
to a reference signal – such a system is termed coherent (and referred to as CPSK).CPSK
requires a complicated demodulator, because it must extract the reference wave from the
received signal and keep track of it, to compare each sample to. Alternatively, the phase shift
of each symbol sent can be measured with respect to the phase of the previous symbol sent.
Because the symbols are encoded in the difference in phase between successive samples, this
is called differential phase-shift keying (DPSK). DPSK can be significantly simpler to
implement than ordinary PSK, as it is a 'non-coherent' scheme, i.e. there is no need for the
demodulator to keep track of a reference wave. A trade-off is that it has more demodulation
errors.
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