FADING EFFECTS IN MANET

Abstract

ABSTRACT Fading is a natural phenomenon where the transmitted signal strength is gradually reduced before it reaches the receiver. There are various reasons for fading, many of which cannot be avoided but can only be managed. The fading effect will cause a dip in signal strengthand sometimes it increases the signal strength. The frequency range of Mobile ad hoc networkis 30 MHz to 5 GHz this means we can expect a range of .06 meters (6 Centimetres) to 10 meters. Reduction of signal strength due to fading will also adversely affect the range of transmission. Thus,_ once the signal strength goes below a certain threshold value we can switchover to the available alternate path, thereby the data transmission can continue unhindered. Also, the effects of fading will diminish the received power to such a small amount that it appears as if there is no packet transmitted by the neighbouring node. Thus, we need to switchover to an alternate path and wait for a fixed amount of time before calling any node, selfish.

Specification

FADING EFFECTS IN MANET
PREAMBLE TO THE DESCRPTION
THE FIELD OF INVENTION (WIRELESS COMMUNICATION)
The invention pertains to innovative analysis of Mobile Ad Hoc Networks and its data transmission.
BACKGROUND OF THE INVENTION
The world is moving towards wireless communication and away from wired communications,in so many
ways. There are quite a few distinct technical advantages wired conununications has over wireless that makes
wired communication exist, one being the less amount of randomness associated with the wired
conununication. One of the reasons for the randomness in wireless which we include in the calculations of
bit error rate (BER) and signal-to-noise (SNR) ratio is the fluctuations in the signal strength, on the way to
the receiver from the transmitter. This phenomenon of signal strength variation is called fading, which exists
in various forms.
The signal strength variation caused due to fading can be due to many reasons of which the prime
factors are the location ofthe mobile nodes, the arrival time of signals and the frequency of the transmitted
signal. A transmitted signal from the source antenna travels in .various directions as it moves away from lhe
source and towards the destination antenna. Thesignals may get reflected by different surfaces and reach the
receiving antenna via multiple paths.
Many types of radio wave communications are affected by the multi path fading. Anytransmissions
using signals from low frequency range of the electromagnetic spectrum even up -
to microwave frequencies will experience mullipalh fading effect. In multipath propagation, asthc path length
changes the relative strength and the phase of the signal also varies. This can create distortion of the
transmitted signals. As the path length changes the signal arrival at thereceiver will spread over time,
resulting in distortion and interference.
MANET Routing protocol design and implementation should take into account the effects of
multipath fading. In Mobile ad hoc networks the transmitted signal will reach the receiver not only through
the direct path but also through reflections from many objects around MANET nodes. The multipath
propagation can give rise to interference in a variety of ways including distortion of the signal, loss of data
and fading. Multipath ·causes constructive and destructive interference, phase shifting of the signal.
Destructive interference causes fading. Nodes in MANET can change location and direction based on their
free will, resulting in changes in signal path length.
The signal strength received by the destination node is the sununation of the signals from direct as
well as the indirect paths. Based on the path lengths the signals will either increase or decrease the received
signal strength. Fading can be broadly classified into two main types known as large scale fading and smallscale
fading. The term large scale fading is used to represent the signal loss due to multipath propagation
over large areas. Small scale fading is used to represent the signal loss due to obstacles near the receiver. In
this research work on MANET the main focus is on the small scale fading which can be described using
. either Rayleigh or Ricean distribution.
SUMMARY OF THE INVENTION
FADING EFFECTS IN MANET
COMPLETE SPECIFICATION
Specifications
• The MANET network consisting of 15 nodes is simulated using Qua!Net simulatorversion 5.0.2.
• All MANET nodes are transceiver nodes, which does the function of Routing too.
• The fading considered is based on either Rayleigh or Ricean distribution
NETWORK SETUP FOR ANALYTICAL AND EXPERIMENTAL ANALYSIS
The simulation is done using 15 mobile nodes with random waypoint mobility model and AODV protocol.
The channel path loss model is Two Ray, the channel frequency is 2.4GHz, the maximum velocity of nodes
is I 0 Meters/Sec and we have used Rayleigh fading model. The Rayleigh fading effect impacts the total bytes
received by the destination. As the number of received bytes goes low, the packet loss is becoming high and
the throughput takes a majorhit. The source node may appear to be selfish, if the fading effect is not
recognized. At this
·juncture, the protocol should go for an alternate route without terming the source as a selfish node. The
network can be sustained·by using· the original route after some time interval.
: This experiment is repeated in a Cartesian coordinate system terrain of size 1500 * 600 Meters, with two ray
path loss model. This network consists of I 00 Mobile Nodes placed randomly throughout the network area.
The scenario is validated without fading and also with Rayleigh,Ricean and fast Rayleigh fading. In this
. validation, the packets sent and received through the MANET nodes are measured. Rayleigh fading is a
•. model that can be applied and observed in metropolis where there are many buildings and line of sight
. propagation is almost not possible.Ricean fading on the other hand is a phenomenon happening in outdoor
areas where line of sight propagation plays a more dominant role.
FADING EFFECTS IN MANET
DESCRIPTION
Even though Rayleigh and Ricean fading varies in nature, during the simulation of MANET using Qualnet
it was found that the packets received for both types of fading to be only around60% of the total sent packets.
Two observations are made here, first is the drastic packet loss, the second is the similarity between the
Rayleigh and Ricean fading. The main reason for the similarity between the throughput in case of Rayleigh
and Ricean fading can be the highly mobile nature ofMANET nodes. This mobility of the nodes in MANET
may have neutralizedthe inherent difference in the nature of Rayleigh and Ricean fading.
Fading Comparison
• Average Packets
Received
It was also observed that the fast Rayleigh fading affects the throughput to a greater extent having only 40%
packet delivery ratio. Fast fading occurs when the coherence time of the channel is small relative to the delay
requirement of the application. It originates due to effects of constructive and destructive interference patterns
which are caused due to multi path. The variation in the signal strengih is the main reason behind the reduction
in number of packets delivered. Due to poor signal quality the receiver is not able to receive the incoming
packets. These problems are common to all MANET Routing Protocols .
All these observations as shown in fading comparison should play an important role inany analysis
of MANET routing protocols and should be studied through real time experimentation, to establish more
clarity and insights on the effects of fading. This fading is a common issue for all protocols in MANET so
any solution along with the alternate path solution, which results from lh~ eff01ts of the research
communities, can be treated as a,common solution and needs to be implemented in all MANET protocols.

CLAIM
We Claim
I. Even though Rayleigh and Ricean fading varies in nature, during the simulation ofMANET
using Qualnet it was found that the packets received for both types of fading to be only
around 60% of the total sent packets.
2. Two observations are made here, first is the drastic packet loss, the second is the similarity
between the Rayleigh and Ricean fading.
3. The main reason for the similarity between the throughput in case of Rayleigh and Ricean
fading can be the highly mobile nature of MANET nodes.
4. This mobility of the nodes in MANET may have neutralized the inherent difference in the
nature of Rayleigh and Rict:an fading.
5. It was also observed that the fast Rayleigl:l!admg affects~thetliroTtghpuno·a·grt:alt:t-t:xtcut
having only 40% packet delivery ratio.
6. Fast fading occurs when the coherence time of the channel is small relative to the delay
requirement of the application.
7. The variation in the signal strength is the main reason behind the reduction in number of
packets delivered.
8. Due to poor signal quality the receiver is not able to receive the incoming packets.

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