Fading Techniques in Wireless Communication and their Appropriate Solution A Review

International Journal of Trend in Scientific Research and Development (IJTSRD)
Volume 6 Issue 7, November-December 2022 Available Online: www.ijtsrd.com e-ISSN: 2456 – 6470
@ IJTSRD | Unique Paper ID – IJTSRD52381 | Volume – 6 | Issue – 7 | November-December 2022 Page 1275
Fading Techniques in Wireless Communication
and their Appropriate Solution- A Review
Prof. Sukhjinder Singh1
, Dr. Hitanshu Kumar2
, Sarita Devi3
, Dr. Arashdeep Singh2
1
Assistant Professor, Modern Group of Colleges, Mukerian, Punjab, India
2
Associate Professor, Modern Group of Colleges, Mukerian, Punjab, India
3
B Tech EE Student, Modern Group of Colleges, Mukerian, Punjab, India
ABSTRACT
In this paper, fading models are considered. Fading is deviation of the
attenuation of signal affecting certain parameters and various
components. In this paper, I represent the disadvantages of fading.
Fading can cause poor performance in a communication system
because it can result in a loss of signal power without reducing the
power of the noise. This signal loss can be over all of the signal
bandwidth. Furthermore this review paper also describes its
appropriate solution OFDM that will reduce fading in some extent.
General Terms
SLM, PAPR, OFDM, MIMO, 4G, 5G, ISI
KEYWORDS: FDMA, OFDM, SLM, PAPR, PTS, MIMO, ISI, BER
How to cite this paper: Prof. Sukhjinder
Singh | Dr. Hitanshu Kumar | Sarita Devi
| Dr. Arashdeep Singh "Fading
Techniques in Wireless Communication
and their Appropriate Solution- A
Review" Published
in International
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and Development
(ijtsrd), ISSN: 2456-
6470, Volume-6 |
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2022, pp.1275-1280, URL:
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INTRODUCTION
Fading is the time variation of received signal power
due to change in transmission medium or path known
as fading. Fading depends on various factors as
mentioned above. In fixed scenario, fading depends
on atmospheric condition such as rainfall, lightning
etc. In mobile scenario, fading depends on obstacles
over the path which is varying with respect to time.
These obstacles create complex transmission signal.
The figure -1 depicts amplitude chart for slow
fading and fast fading types
TYPES OF FADING:
FAST FADING:
The phenomenon of fast fading is represented by
rapid fluctuations of signal over small areas (i.e.,
Bandwidth). When the signal arrives from all the
directions in the plane, fast fading will be observed
for all directions of motion.
Fast fading occurs when channel implies response
changes very rapidly within the symbol duration.
High Doppler spread
Symbol period > Coherence time
Signal variation < Channel variation
Fast fading is a result of reflections of local objects
and motion of objects relative to those objects.
SLOW FADING:
Slow fading is the result of shadowing by buildings,
hills, mountains and other objects over the path.
IJTSRD52381

International Journal of Trend in Scientific Research and Development @ www.ijtsrd.com eISSN: 2456-6470
Low Doppler Spread
Symbol period << Coherence Time
Signal Variation >>Channel Variation
Slow fading results in a loss of SNR Error correction
coding and receiver diversity techniques are used to
overcome effects of slow fading.
Implementation of Fading models or fading
distributions:
Implementations of fading models or fading
distributions include Raleigh fading and Rican fading.
These channel distributions or models are designed to
incorporate fading in the baseband data signal as per
fading profile requirements.
RAYLEIGH FADING:
In relay model, only non-Line of slight (NLOS)
components simulated between transmitter and
receiver.
MATLAB provides “Rayleigh Chan” function to
simulate Rayleigh channel model.
The power is exponentially distributed.
The phase is uniformly distributed and independent
from the amplitude. It is the most used type of fading
in wireless communication.
RICIAN FADING:
In Ra model, both line of sight (LOS) and non-lines
light (NLOS) components are simulated between
transmitter and receiver.
MATLAB provide “Rican Chan” function to simulate
Rican channel model.
FADING MITIGATION TECHNIQUES IN
WIRELESS MOBILE COMMUNICATION
SYSTEM:
INTRODUCTION
In wireless communication, multipath is the
propagation phenomena that results in radio signals
reaching the receiving antenna by two or more paths.
The causes of Considered various channel related
impairments and position of transmitter/receiver
following are the types of fading in wireless
communication system. Large scale fading, small
scale fading and fading models. As we know, fading
signals from ground and surrounding buildings as
well as scattered signals from trees, people and
towers present in the large area. There are two types
of fading viz. large scale fading and slow scale
fading.
LARGE SCALE FADING:
Large scale fading occurs when an obstacle comes in
between transmitter and receiver. This interference
types causes significant amount of signal strength
reduction. This is because EM wave is shadowed or
blocked by the obstacle. It is related to large
fluctuations of the signal over distance.
SMALL SCALE FADING:
Small scale fading is concerned with rapid
fluctuations of received signal strength over very
short distance and short time period. Based on
multipath delay spread there are two types of small
scale fading viz. flat fading and frequency selective
fading. These multipath fading types depend on
propagation environment.
FLAT FADING:
The wireless channel is said to be flat fading if it has
constant gain and linear phase response over a
bandwidth of the transmitted signal.In these types of
fading all the frequency components of received
signal fluctuate in same proportions simultaneously.
It is also known as non-selective fading.
Signal BW<< Channel BW
Symbol period >> Delay spread
The effect of flat fading is seen as decrease in SNR.
This flat fading channel is also known as amplitude
varying channels or narrowband channels.
FREQUENCY SELECTIVE FADING:
It affects different spectral components of a radio
signal with different amplitudes. Hence the name
selective is fading.
Signal BW > Channel BW
Symbol period < Delay Spread
Multipath includes atmospheric scattering, ionosphere
reflection, reflection from water bodies and terrestrial
objects such as mountains and buildings. Multipath
radio signal propagation occurs on all terrestrial radio
links. The radio signals not only travel by the direct
line if sight (LOS) path, but as the transmitted signal
does not leave the transmitted antenna in only the
direction of receiver, but over a range of angles even
when a directive antenna is used. Consequently, the
transmitted signal spread out from transmitter and
they will reach other object: hills, buildings,
reflections surfaces such as the ground, water etc.
When the radio signals arrive at the receiver via
variety of paths, the overall signal received is the sum
of all the signals appearing at the antenna. Sometimes
these signals may be phase with main signal and will
add to it to increase its strength at other times, they
will be out of phase with the main signal, therefore
resulting in overall signal strength reduction.
Background information:
Multipath is the propagation phenomenon that results
in radio signals reaching the receiving antenna bytwo

or more paths. Fading refers to the distortions that are
carriers modulate telecommunication signal
experiences over certain propagation media.
In wireless system, fading is due to multipath
propagation and is sometime referred to as multipath
include fading. Fading is term used to describe the
fluctuation in a received signal as a result of
multipath component. Several replicas of the signal
arrive at the receiver, having traversed different
propagation paths, adding constructively and
destructively the fading can be defined as fast fading
or slow fading. Additionally, fading can be defined as
flat or frequency Selective fading
MULTIPATH EFFECTIVE FADING:
In principle, the following are the main multipath
effects:
1. Rapid changes in signal strength over a small
travel distance or time interval.
2. Random frequency modulation due to varying
Doppler shifts on different multipath signals.
3. Time dispersion or echoes caused by multipath
propagation delays.
The following physical factors influence small-scale
fading in the radio propagation channel:
1. Multipath propagation – Multipath is the
propagation phenomenon that results in radio
signals reaching the receiving antenna by two or
more paths. The effects of multipath include
constructive and destructive interference, and
phase shifting of the signal.
2. Speed of the mobile – The relative motion
between the base station and the mobile results in
random frequency modulation due to different
doppler shifts on each of the multipath
components.
3. Speed of surrounding objects – If objects in the
radio channel are in motion, they induce a time
varying Doppler shift on multipath components.
If the surrounding objects move at a greater rate
than the mobile, then this effect dominates fading.
4. Transmission Bandwidth of the signal – If the
transmitted radio signal bandwidth is greater than
the “bandwidth” of the multipath channel
(quantified by coherence bandwidth), the received
signal will be distorted.
Orthogonal Frequency Division
Multiplexing:
Orthogonal frequency division multiplexing (OFDM)
is the method of data transmission where a single
information stream is split among several closely
spaced narrowband sub channel frequencies instead of
a signal wideband channel frequency and it is mostly
used in wireless data transmission.
In a traditional single-channel modulation scheme,
each data bit is sent serially or sequentially one after
another. In OFDM, several bits can be sent in parallel,
or at the same time, in separate sub stream channels.
This enables each sub stream’s data rate to be lower
than would be required by a single stream of similar
bandwidth. This makes the system less susceptible to
interference and enables more efficient data
bandwidth.fig1. Show an OFDM spectrum.
Fig. 1OFDM SPECTRUM
OFDM is a form of multicarrier modulation. An
OFDM signal consists of a number of closely spaced
modulated carriers. When modulation of any form –
voice, data, etc. is applied to a carrier, then sidebands
spread out either side. It is necessary for a receiver to
be able to receive the whole signal to be able to
successfully demodulate the data. As a result when
signals are transmitted close to one
Another they must be spaced so that the receiver can
separate them using a filter and there must be a guard
band between them. This is not the case with OFDM.
Although the sidebands from each carrier overlap,
they can still be received without the interference that
might be expected because theyare orthogonal to each
another. This is achieved by having the carrier spacing
equal to the reciprocal of the symbol.
OFDM Signals
DATA ON OFDM:
The data to be transmitted on an OFDM signal is
spread across the carriers of the signal, each carrier
taking part of the payload. This reduces the data rate
has the advantage that interference from reflections is
much less critical.
This is achieved by adding a guard band time or guard
interval into system. This ensure that the data is only
sampled when the signal is stable and no new delayed
signals arrive that would alter the timing and phase of
the signal.

OFDM guard interval
The distribution of the data across a large number of
carriers in the OFDM signal has some further
advantages. Null caused by multipath effects or
interference ones being many or all of the corrupted
data to be done because the error correction code is
transmitted in a different part of the signal.
Received correctly. By using error coding techniques,
which does mean adding further data to the
transmitted signal, it enables
ORTHOGONALITY:
In OFDM the sub-carrier frequencies are chosen so
that the sub-carriers are orthogonal to each other,
meaning that cross-talk between the sub-channels is
eliminated and inter in OFDM spectrum, multiple
closely spaced orthogonal subcarrier signals with
overlapping spectra are transmitted to carry data in
parallel this is greatly simplifies the design of both the
transmitter and the receiver; unlike conventional
FDM, a separate filter for each sub-channel is not
required.
1. OFDM TRANSCEIVE EXPLANATION
OFDM is a Multi-Carrier Modulation (MCM)scheme,
which uses closely spaced multiple subcarriers to
transmit data. Data to be transmitted is split and
transmitted using multiple subcarriers instead of using
a single carrier. The key idea is instead of transmitting
at a very high bit rate, the data is transmitted over
multiple sub channels each carrying lower bit rates.
To generate OFDM successfully their relationship
between all the carriers must be carefullycontrolled to
maintain the orthogonality of the carriers. For this
reason, OFDM is generated by firstly choosing the
spectrum required based on the input data, and
modulation scheme used. Each carrier to be produced
is assigned same data to transmit. The required
amplitude and phase of them are calculated based on
the modulation scheme. OFDM system involves
mapping of symbols onto a set of orthogonal
subcarriers that are multiples of the base frequency.
This can be implemented in digital domain using Fast
Fourier Transform (FFT) and Inverse Fast Fourier
Transform (IFFT). These transforms are important
from OFDM perspective as they can be viewed as
mapping digital input data onto orthogonal
subcarriers. The IFFT takes frequency-domain input
data and converts it to the time-domain output data
(analog OFDM symbol waveform). This waveform is
transmitted by the OFDM transmitter. The receiver
receives the waveform and uses FFT transform to
convert the data back from time-domain into
frequency domain to recover the data back. This is
done by finding the equivalent wave for, generated by
a sum of orthogonal sinusoidal components. The
amplitude and phase of the sinusoidal components
represent the frequency spectrum of the time domain
signal. The IFFT performs the reverse process
transforming a spectrum (amplitude and phase of each
component) into a time domain signal. An IFFT
converts a number of complex data points, of length
that is a power of 2, into the time domain signal of the
same number of point’s .Each data point in frequency
spectrum used for an FFT or IFFT is called a bin. The
orthogonal carrier required for the OFDM signal can
be easily generated by setting the amplitude and phase
of each frequency.
2. PROBLE M OF PEAK-TO-AVERAGE
POWER RATIOIN OFDM SYSTEM
One of the most serious problems is the high peak to
average power ratio (PAPR) of the transmitted FDM
signal, since these large peaks introduce a serious
degradation in performance when the signal passes
through a nonlinear high power amplifier (HPA).
High PAPR results from the nature of the modulation
where multiple subcarriers/sinusoids are added
together to form the signal to be transmitted .When
sinusoid the peak magnitude.
Fig.2.OFDM Trans receiver Structure
Fig2 shows the configuration for a basic OFDM
Transmitter and Receiver
For an OFDM system with N sub-carriers, the peak
power of received signals is N times the average
power when phase values are the same .The PAPR of
baseband signal will reach its theoretical maximum
at( ) = 10log . For example, for a 16 sub-carrier
system, the maximum PAPR is 12 dB. Never the less,
this only a theoretically .In reality the probability of
reaching this maximum is very low.

SPATIAL MULTIPLEXING:
Spatial multiplexing or space division multiplexing is
a multiplexing technique in MIMO wireless
communication, fiber-optic communication and other
communications technologies used to transmit
independent channels separated in space. It is MIMO
wireless protocol that sends separate data signals or
streams between antennae to enhance wireless signal
performance or functionality. It is a type of “spatial
diversity” and an engineering trick that helps to
increase the possibilities for various types of end- to-
end transmission.
Spatial multiplexing takes advantage of the
differences in the channels between transmitting and
receiving antennas pair to provide multiple
independent streams between the transmitting and
receiving antennas, increasing throughput by sending
data over parallel streams.
SPATIAL MULTIPLEXING FOR 5G
WIRELESS COMMUNICATIION:
In spatial multiplexing, is used in slow fading for 5G
wireless communication. Increased demand for higher
data rates and channel capacity is driving the need to
use the RF spectrum more efficiently. As a result, 5G
wireless system will use mm Wave frequency bands
to take advantage of the increased bandwidth. The
higher operating frequencies enable large-scale
antennae arrays, which can be used to mitigate serve
propagation loss in the mm wave band. Large arrays
can also be used to implement a MIMO system in
which unique signals can be transmitted from different
antenna elements in the array. MIMO system enables
spatial multiplexing technique that can be used to
improve data throughput.
5G system require a large antenna arrays, applying
digital weights on each antennae element is not always
practical due to cost and space limitations, so we use
hybrid beam forming techniques can be applied in a
mixed RF and digital beam forming system to
alleviate these restrictions. In a hybrid beam form
system, both the precoding weights and the combining
weights are combinations of baseband digital weights
and RF band analog weights. On transmit side, the
baseband digital weights modulate the incoming data
streams to form input signals at each RF chain and the
analog weights then translate the signal at each RF
chain to signal at each antennae element. The process
is reversed on the revive side.
CONCLUSION:
In this paper, we are find the solution of fading
reduce techniques. The first technique is OFDM
(orthogonal frequency diversity multiplexing), this
technique is the method of data transmission and is
used wireless data transmission. The second
technique is spatial multiplexing that is used to
transmit independent cannel separated in space. These
technologies are reduce fading problem.
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