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A PROPOSAL ON THE SOLUTIONS TO NOISE IN DATA
COMMUNICATIONS
BY
AROH SIXTUS OLISAEMEKA
13/ENG04/006
A PROPOSAL SUBMITTED TO
CIVIL ENGINEERING DEPARTMENT
COLLEGE OF ENGINEERING
AFE BABALOLA UNIVERSITY ADO-EKITI
EKITI STATE, NIGERIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE COURSE
TECHNICAL REPORT WRITING AND PRESENTATION
November 2015
ABSTRACT
Data communications is a very important part of the computer engineering discipline as
technology advances data communication gets broadened from the early stages of walkie talkies
to mobile phones where text messages, voice calls, emails and the likes can all be transmitted
simultaneously. It is therefore important that data transmitted should be if not 100% free from
errors but close enough to prevent loss of information data corruption misinformation and so on.
Noise as simple as it sounds is a problem in data communications as it distorts data in many
ways through its transmission. It affects the signal being transmitted and hence a solution to this
is a top priority.
TABLE OF CONTENTS
ABSTRACT ..................................................................................................................................... I
1.
INTRODUCTION ................................................................................................................... 1
1.0
NOISE .............................................................................................................................. 1
2.
REVIEW OF RELATED LITERATURE ............................................................................... 3
3.
SOLUTIONS TO NOISE IN DATA COMMUNICATIONS ................................................ 7
4. CONCLUSION ......................................................................................................................... 11
REFERENCES ............................................................................................................................. 12
1. INTRODUCTION
1.0
NOISE
Computer engineering is the discipline that drives technological advancement, from conception
time computer engineering has lead the world in innovations and research due to the simplicity
in undergoing research through simulations, hence data must be exchanged a=from one computer
and another. Therefore, noise must be checked and controlled or its effects detected and
corrected.
In electronics, noise is a random fluctuation in an electrical signal, a characteristic of all
electronic circuits. Noise generated by electronic devices varies greatly as it is produced by
several different effects. Noise is an unwanted electrical disturbance or signal which causes
distortions to audio, visual or any type of signal and digital communications. Noises are
inevitable in communication systems that is, an ever part of all systems.
Sources of noise:
1. Natural source: Electronic storms, solar flares and radiation
2. Man-made: Electric motors, ignition systems of automobiles, from electrical devices.
3. Fundamental source (Internal): Noise within the electronic equipment because they are
integral parts of the physical nature of the material used for making electronic
components.
Classification of noise(Internal):
1. Thermal noise (sometimes thermal, Johnson or Nyquist noise): is unavoidable, and
generated by the random thermal motion of charge carriers (usually electrons), inside an
electrical conductor, which happens regardless of any applied voltage.Thermal noise is
approximately white, meaning that its power spectral density is nearly equal throughout
the frequency spectrum.
2. Shot noise: The shot noise is produced due to shot effect. Shot noise is produced in all
amplifying devices rather than in all active devices. A shot noise is produced as a result
of a random variation in the arrival of electrons or holes at the output electrode of an
amplifying device. Also the fluctuation in electric currents due to the random passage of
discrete electric charge. The shot noise has a uniform spectral density and hence
classified as white noise.
3. Flicker noise: Flicker noise, also known as 1/f noise, is a signal or process with a
frequency spectrum that falls off steadily into the higher frequencies, with a pink
spectrum. It occurs in almost all electronic devices, and results from a variety of effects,
though always related to a direct current.
4. Transit-time noise: If the time taken by the electrons from traveling from emitter to
collector becomes comparable to the period of the signal being amplified, that is, at
frequencies above VHF and beyond, so-called transit-time effect takes place and noise
input admittance of the transistor increases. From the frequency at which this effect
becomes significant it goes on increasing with frequency and quickly dominates over
other terms.
2. REVIEW OF RELATED LITERATURE
1. Message: it is the information or data to be communicated. It is in some form of
information e.g. text, numbers, pictures, video, audio.
2. Sender/Transmitter: a device used in communication system which uses electromagnetic
waves (radio waves) to transport information (in this case sound) over a distance.In
electronics and telecommunications, a transmitter or radio transmitter is an electronic
device which generates a radio frequency alternating current. When a connected antenna
is excited by this alternating current, the antenna emits radio waves.In addition to their
use in broadcasting, transmitters are necessary component parts of many electronic
devices that communicate by radio, such as cell phones, wireless computer networks,
Bluetooth enabled devices, garage door openers, two-way radios in aircraft, ships,
spacecraft, radar sets and navigational beacons.
3. Receiver: it is a device that receives the message sent from the transmitter. It can be a
computer, workstation, telephone, T.V etc.
4. Transmission medium: It is the physical path by which the message travels from sender
to receiver. Examples twisted pair cables, coaxial cable, optical fibre cable, wave guide,
radio waves (free space).
5. Spectral density: ratio of power to frequency in signals.
Some other types of noise:
1. Burst noise: Burst noise consists of sudden step-like transitions between two or more
levels (non-Gaussian), as high as several hundred microvolts, at random and
unpredictable times. Each shift in offset voltage or current lasts for several milliseconds,
and the intervals between pulses tend to be in the audio range (less than 100 Hz), leading
to the term popcorn noise for the popping or crackling sounds it produces in audio
circuits.
2. Coupled noise: Energy external of the receiver can couple noise, also by energy
conversion. Generally, this is done by fundamental interaction, in electronics mainly by
inductive coupling and/or capacitive coupling.
3. Intermodulation noise: Intermodulation noise is caused when signals of different
frequencies share the same non-linear medium.
4. Crosstalk: Phenomenon in which a signal transmitted in one circuit or channel of a
transmission systems creates undesired interference onto a signal in another channel.
5. Interference: Modification or disruption of a signal travelling along a medium.
6. Atmospheric noise (static noise):
7. This noise is also called static noise and it is the natural source of disturbance caused by
lightning discharge in thunderstorm and the natural (electrical) disturbances occurring in
nature.
8. Industrial noise: Sources such as automobiles, aircraft, ignition electric motors and
switching gear, High voltage wires and fluorescent lamps cause industrial noise. These
noises are produced by the discharge present in all these operations.
9. Extra-terrestrial noise: Noise from outside the Earth includes:
1. Solar noise: Noise that originates from the Sun is called solar noise. Under normal
conditions there is constant radiation from the Sun due to its high temperature.
Electrical disturbances such as corona discharges, as well as sunspots can produce
additional noise.
2. Cosmic noise: Distant stars generate noise called cosmic noise. While these stars
are too far away to individually affect terrestrial communications systems, their
large number leads to appreciable collective effects. Cosmic noise has been
observed in a range from 8 MHz to 1.43 GHz.
QUANTIFICATION
The noise level in an electronic system is typically measured as an electrical power N in watts or
dBm, a root mean square (RMS) voltage (identical to the noise standard deviation) in volts,
dBμV or a mean squared error (MSE) in volts squared. Noise may also be characterized by its
probability distribution and noise spectral density N0(f) in watts per hertz.
A noise signal is typically considered as a linear addition to a useful information signal. Typical
signal quality measures involving noise are signal-to-noise ratio (SNR or S/N), signal-toquantization noise ratio (SQNR) in analog-to-digital conversion and compression, peak signalto-noise ratio (PSNR) in image and video coding, Eb/N0 in digital transmission, carrier to noise
ratio (CNR) before the detector in carrier-modulated systems, and noise figure in cascaded
amplifiers.
Noise is a random process, characterized by stochastic properties such as its variance,
distribution, and spectral density. The spectral distribution of noise can vary with frequency, so
its power density is measured in watts per hertz (W/Hz). Since the power in a resistive element is
proportional to the square of the voltage across it, noise voltage (density) can be described by
taking the square root of the noise power density, resulting in volts per root hertz. Integrated
circuit devices, such as operational amplifiers commonly quote equivalent input noise level in
these terms (at room temperature).
Noise power is measured in watts or decibels (dB) relative to a standard power, usually indicated
by adding a suffix after dB. Examples of electrical noise-level measurement units are dBu,
dBm0, dBrn, dBrnC, and dBrn (f1 − f2), dBrn.
Noise levels are usually viewed in opposition to signal levels and so are often seen as part of a
signal-to-noise ratio (SNR). Telecommunication systems strive to increase the ratio of signal
level to noise level in order to effectively transmit data. In practice, if the transmitted signal falls
below the level of the noise (often designated as the noise floor) in the system, data can no
longer be decoded at the receiver. Noise in telecommunication systems is a product of both
internal and external sources to the system.
In a carrier-modulated passband analog communication system, a certain carrier-to-noise ratio
(CNR) at the radio receiver input would result in a certain signal-to-noise ratio in the detected
message signal. In a digital communications system, a certain Eb/N0 (normalized signal-to-noise
ratio) would result in a certain bit error rate.
3. SOLUTIONS TO NOISE IN DATA COMMUNICATIONS
Noise reduction
Noise reduction is the process of reducing noise in a signal.All active devices, both analog and
digital, have characteristics that make them susceptible to noise. Noise can be random or white
noise with no coherence, or coherent noise introduced by the device's mechanism or processing
algorithms.
REDUCTION OF ELECTROMAGNETIC NOISE COUPLING
In mostsituations noise on a signal in a circuit is unwanted. A circuit should provide a true output
of the desired goal of its construction. There are many different noise reduction techniques that
can change a noisy altered output signal to a more theoretical output signal.
1. Faraday cage: A Faraday cage is a good way to reduce the overall noise in a complete
circuit. The Faraday cage can be thought of as an enclosure that separates the complete
circuit from outside power lines and any other signal that may alter the true signal. A
Faraday cage will usually block out most electromagnetic and electrostatic noise.
2. Capacitive coupling: A current through two resistors, or any other type of conductor,
close to each other in a circuit can create unwanted capacitive coupling. If this happens
an AC signal from one part of the circuit can be accidentally picked up in another part.
The two resistors (conductors) act like a capacitor thus transferring AC signals. There
may be other reasons for which capacitive coupling is wanted but then it would not be
thought of as electronic noise.
3. Ground loops: When grounding a circuit, it is important to avoid ground loops. Ground
loops occur when there is a voltage drop between the two ground potentials. Since
ground is thought of as 0V, the presence of a voltage is undesirable at any point of a
ground bus. If this is the case, it would not be a true ground. A good way to fix this is to
bring all the ground wires to the same potential in a ground bus.
4. Shielding cables: In general, using shielded cables to protect the wires from unwanted
noise frequencies in a sensitive circuit is good practice. A shielded wire can be thought of
as a small Faraday cage for a specific wire as it uses a plastic or rubber enclosing the true
wire. Just outside the rubber/plastic covering is a conductive metal that intercepts any
noise signal. Because the conductive metal is grounded, the noise signal runs straight to
ground before ever getting to the true wire. It is important to ground the shield at only
one end to avoid a ground loop on the shield.
5. Twisted pair wiring: Twisting wires very tightly together in a circuit will dramatically
reduce electromagnetic noise. Twisting the wires decreases the loop size in which a
magnetic field can run through to produce a current between the wires. Even if the wires
are twisted very tightly, there may still be small loops somewhere between them, but
because they are twisted the magnetic field going through the smaller loops induces a
current flowing in opposite ways in each wire and thus cancelling them out.
6. Notch filters: Notch filters or band-rejection filters are essential when eliminating a
specific noise frequency. For example, in most cases the power lines within a building
run at 60 Hz. Sometimes a sensitive circuit will pick up this 60 Hz noise through some
unwanted antenna (could be as simple as a wire in the circuit). Running the output
through a notch filter at 60 Hz will amplify the desired signal without amplifying the 60
Hz noise. So in a sense the noise will be lost at the output of the filter.
Error Detection and Correction Techniques
Though the above techniques are effective in constraining noise but it is almost impossible to
protect signals from noise over the air, hence it is imperative that we learn how to detect and
correct the errors created by noise on our signals during transmission.
Error detection schemes
Error detecting techniques operate on the following principles; for a given frame of bits,
additional bits that constitute an error detecting code are added by the transmitter. This code is
calculated as a function of the other transmitted bits. The receiver performs the same calculation
and compares the two results =. An error occurred if and only if these two results are different.
1. Parity bits: the simplest bit error scheme is to append the parity bit at the end of each
word in a frame. A typical example is ASCII transmission which a parity bit is attached
to each 7 bit ASCII character. The value of the bit is selected so that the word has an even
number of 1s for even parity or odd number of 1s for odd parity. Typically, even parity is
used for asynchronous transmission and odd parity for synchronous transmission.
2. Cyclic redundancy checks (CRCs): A cyclic redundancy check (CRC) is a non-secure
hash function designed to detect accidental changes to digital data in computer networks;
as a result, it is not suitable for detecting maliciously introduced errors. It is characterized
by specification of what is called a generator polynomial, which is used as the divisor in a
polynomial long division over a finite field, taking the input data as the dividend, such
that the remainder becomes the result.A cyclic code has favourable properties that make
it well suited for detecting burst errors. CRCs are particularly easy to implement in
hardware, and are therefore commonly used in digital networks and storage devices such
as hard disk drives.Even parity is a special case of a cyclic redundancy check, where the
single-bit CRC is generated by the divisor x + 1.
Error correction
Error correction may generally be realized in two different ways:
1. Automatic repeat request (ARQ) (sometimes also referred to as backward error
correction): This is an error control technique whereby an error detection scheme is
combined with requests for retransmission of errored data. Every block of data received
is checked using the error detection code used, and if the check fails, retransmission of
the data is requested, this is done repeatedly, until the data can be verified. Automatic
Repeat Request (ARQ) is an error control method for data transmission that makes use of
error-detection codes, acknowledgment and/or negative acknowledgment messages, and
timeouts to achieve reliable data transmission. An acknowledgment is a message sent by
the receiver to indicate that it has correctly received a data frame. Usually, when the
transmitter does not receive the acknowledgment before the timeout occurs (i.e., within a
reasonable amount of time after sending the data frame), it retransmits the frame until it is
either correctly received or the error persists beyond a predetermined number of
retransmissions. Three types of ARQ protocols are Stop-and-wait ARQ, Go-Back-N
ARQ, and Selective Repeat ARQ.
2. Forward error correction (FEC): The sender encodes the data using an error-correcting
code (ECC) prior to transmission. The additional information (redundancy) added by the
code is used by the receiver to recover the original data. In general, the reconstructed data
is what is deemed the "most likely" original data.
ARQ and FEC may be combined, such that minor errors are corrected without retransmission,
and major errors are corrected via a request for retransmission: this is called hybrid automatic
repeat-request (HARQ).
4. CONCLUSION
Since noise is unavoidable we strive to minimize the signal to noise ratio (SNR) in a
communications system. By using the above outlined ways to reduce, detect and correct noise
our signals in data communications will be more protected and information shared is safe and
error free.
REFERENCES
1. Low-noise electronic system design. Wiley Interscience.
2. "Noise in nanotechnology". Microelectronics Reliability. Elsevier
3. Noise Reduction Techniques in Electronic Systems, John Wiley.
4. "Observation of Hot-Electron Shot Noise in a Metallic Resistor" H.M Hoffman