WIRELESS COMMUNICATION COMBATING FADING CHANNEL

WIRELESS COMMUNICATION•Wireless communication is among technology’s biggest contributions to mankind.

• Wireless communication involves the transmission of information over a distance without help of wires, cables or any other forms of electrical conductors. The transmitted distance can be anywhere between a few meters.

•Some of the devices used for wireless communication are cordless telephones, mobiles, GPS units, wireless computer parts, and satellite television.

SOURCESOURCE

ENCODERCHANNEL ENCODER MODULATOR

TRANSMITTER ANTENNA

RECEIVER ANTENNA

DEMODULATORCHANNELDECODER

SOURCE DECODER

DESTINATION

WIRELESS CHANNEL

INTERFERENCES1.Noise, 2.Fading,

3.Shadowing

BLOCK DIAGRAM OF WIRELESS COMMUNICATION SYSTEM

An introduction to fading!

•In wireless communications, fading is deviation of the attenuation affecting a signal over certain propagation media.Fading may vary with time, geographical position or radio frequency and is often modeled as a random process.

•It is used to describe the rapid fluctuations of the amplitudes, phase or multipath delays of a radio signal over a short period of time or travel distance.

•Fading is caused by interference between two or more versions of transmitted signal which arrive at the receiver at slightly different times, it results in a such output signal which may largely vary in amplitude and phase depending on the distribution of the intensity, relative propagation of the waves and the bandwidth of the transmitted signal.

CAUSES OF FADING

MULTIPATH PROPAGATION

In wireless communication, multipath propagation is the phenomenon that results the radio signals reaching receiving antenna by two or more paths.

CAUSES OF FADING

SHADOWING

Shadowing is the effect due to which the received signal power fluctuates due to objects obstructing the propagation pathbetween transmitter and receiver.

CLASSIFICATIONS OF FADINGFADING

(BASED ON MULTIPATH TIME DELAY SPREAD)

FLAT FADING

FREQUENCY SELECTIVE FADING

FADING(BASED ON DOPPLER

SPREAD)

FAST FADING

SLOW FADING

CLASSIFICATIONS OF FADING(A BRIEF DISCUSSION)

• Low Doppler spread• Coherence time > Symbol

period

• High Doppler spread• Coherence time < Symbol

period

• BW of signal > BW of channel

• Delay spread > Symbol period

• BW of signal < BW of channel

• Delay spread<Symbol period

FLAT FADING

FREQUENCY SELECTIVE

FADING

SLOW FADING

FAST FADING

•

MODULATION TO COMBAT FADING

Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information be transmitted. The basic schemes for modulations are as follows:

Amplitude Modulation Amplitude Shift Keying

Frequency Modulation Frequency Shift Keying

Phase Modulation Phase Shift keying

TYPES OF FADING CHANNEL

FADING CHANNELS

RAYLEIGH RICIAN

RICIAN FADING

Rician fading is a model for radio propagation abnormally caused by partial cancellation of the signal itself. The signal arrives by several different parts. It occurs when one of the paths is typically much stronger than the others.

RICIAN FADING• Rician fading or Ricean fading is a stochastic model for radio propagation

anomaly caused by partial cancellation of a radio signal by itself — the signal arrives at the receiver by several different paths (hence exhibiting multipath interference), and at least one of the paths is changing (lengthening or shortening). Rician fading occurs when one of the paths, typically a line of sight signal, is much stronger than the others. In Rician fading, the amplitude gain is characterized by a Rician distribution.

• Rayleigh fading is the specialised model for stochastic fading when there is no line of sight signal, and is sometimes considered as a special case of the more generalised concept of Rician fading. In Rayleigh fading, the amplitude gain is characterized by a Rayleigh distribution.

code and model

BIT ERROR RATE:BERBit error rate is a key parameter that is used in assessing systems that transmit di

gital data from one location to another. BER is applicable to radio data links.

When data is transmitted over a data link, there is a possibility of errors being introduced into the system. If this is so, the integrity of the system may be compromised. As a result, it is necessary to assess the performance of the system, and BER provides an ideal way in which this can be achieved. BER assesses the full end to end performance of a system including the transmitter, receiver and the medium between the two.

BER is defined as the rate at which errors occur in a transmission system. the formulae is:-

PERFORMANCE OF BPSK MODULATION IN RAYLEIGH FADING CHANNEL

RAYLEIGH FADING

Rayleigh fading is the name given to the form of fading that is often experienced in an environment where there is a large number of reflections present.

RAYLEIGH DISTRIBUTION

SIMULATION USING RAYLEIGH• The simulation of the model under study was carried out using MATL

AB application package.The simulation was carried out with BPSK modulation.The following parameters and system configurations were used:

• Modulation: BPSK.• Carrier frequency: 900 MHz.• Bandwidth of signal: 200 ns.• Noise: AWGN.• Mobile speed: 90 km/h.• Fading type: Rayleigh fading

• the results obtianed by the simulation using Rayleigh channel is:

FADING CHANNELS IMPACTS• From the beginning of wireless communication, there is a

high demand for realistic models for wireless fading channels. The reason for the demand is that channel models are essential for the performance evaluation, parameter optimisation, and test of mobile communication systems.

• Design methods for fading channels are therefore of great importance for system engineers who are involved in the development of present and future communication systems. All presented channel models have in common that they are derived from a superposition of a finite number of complex sinusoids.

FUTURE WORK• In this project, we will choose BPSK modulation to test

the effect of different channels to the received data. So, we only use the channel phase information.

• We may add more modulation techniques in our model, such as ASK and QAM with different modulation orders. Then we will need to estimate both the channel phase information and amplitude information.

FUTURE WORK –CONT.• In this project, we may produce two different scenarios

by simulate a GSM carrier frequency and bandwidth, and use pilot data to estimate the channel phase. All of these are simulated in Matlab at present.

• In our future model, we may integrate our model into Qualnet, which will give a better environment to simulate a wireless network model.

OUR KNOWLEDGE POOL

www.wikipedia.org

www.mathworks.com

www.slideshare.net

ACKNOWLEDGEMENTS

We are Thankful to Our H.O.D

Prof. MOUSUMI BANERJEE

And Our Mentor Prof. Arpita Chakraborty

25

THANK YOU