02-07-2012, 12:15 PM
PERFORMANCE OF BER IN OFDM SYSTEM FOR AWGN AND RAYLIEGH CHANNELS
[attachment=26416]
INTRODUCTION
New Technologies and there by various applications are emerging in the wireless area in the last few years.
The minimum target data rate for the 4G system is expected to be at 10-20 Mbps
A promising modulation technique that is increasingly
being considered for adoption by 4G community is Orthogonal Frequency Division Multiplexing(OFDM).
WHAT IS OFDM
OFDM also known as Multi-Carrier or Multi-Tone
Modulation
It is a special kind of FDM
The spacing between carriers are such that they are orthogonal to one another
By using ofdm inter symbol interference(ISI) can be reduced
ISI has very small or no effect on the OFDM systems hence an equalizer is not needed at the receiver side.
OFDM
It is the combination of modulation and multiplexing
OFDM has been adopted in the Wi-Fi arena where the 802.11a standard uses it to provide data rates up to 54 Mbps in the 5 GHz ISM band
It is being used for WiMAX and is also the format of choice for the next generation cellular radio communications systems including 3G LTE and UMB.
It utilises many carriers together to provide many advantages over simpler modulation formats.
An OFDM signal consists of a number of closely spaced modulated carriers.
In addition the sub-carriers in an OFDM system are overlapping to maximize spectral efficiency
OFDM is a technique for transmitting data in parallel by using a large number of modulated sub-carriers
OFDM can provide large data rates with sufficient robustness to radio channel impairments
AWGN CHANNEL
simplest mathematical model of the radio channel is the additive white Gaussian noise (AWGN) channel.
The AWGN channel is a good model for many satellilite and deep space communication links
An AWGN channel adds white Gaussian noise to the signal that passes through it
The noise is additive
The noise is white
The noise sample have a Gaussian distribution
RAYLIEGH FADING CHANNEL
Rayleigh fading is a statistical model for the effect of a propagation environment on a radio signal such as that used by wireless devices.
Rayleigh fading is most applicable when there is no line of sight between the transmitter and receiver.
It is reasonable model for tropospheric and ionospheric signal propagation
It assumes that the power of a signal that has passed through such a transmission medium (also called a communications channels will vary randomly or fade according to a Rayleigh distributuion )
CONCLUSION
The ber performance of awgn and rayliegh fading are simulated.It showed that awgn has better performance compared to rayliegh fading channel . More research can be carried out on realizing the application of OFDM in the future wireless communications.
[attachment=26416]
INTRODUCTION
New Technologies and there by various applications are emerging in the wireless area in the last few years.
The minimum target data rate for the 4G system is expected to be at 10-20 Mbps
A promising modulation technique that is increasingly
being considered for adoption by 4G community is Orthogonal Frequency Division Multiplexing(OFDM).
WHAT IS OFDM
OFDM also known as Multi-Carrier or Multi-Tone
Modulation
It is a special kind of FDM
The spacing between carriers are such that they are orthogonal to one another
By using ofdm inter symbol interference(ISI) can be reduced
ISI has very small or no effect on the OFDM systems hence an equalizer is not needed at the receiver side.
OFDM
It is the combination of modulation and multiplexing
OFDM has been adopted in the Wi-Fi arena where the 802.11a standard uses it to provide data rates up to 54 Mbps in the 5 GHz ISM band
It is being used for WiMAX and is also the format of choice for the next generation cellular radio communications systems including 3G LTE and UMB.
It utilises many carriers together to provide many advantages over simpler modulation formats.
An OFDM signal consists of a number of closely spaced modulated carriers.
In addition the sub-carriers in an OFDM system are overlapping to maximize spectral efficiency
OFDM is a technique for transmitting data in parallel by using a large number of modulated sub-carriers
OFDM can provide large data rates with sufficient robustness to radio channel impairments
AWGN CHANNEL
simplest mathematical model of the radio channel is the additive white Gaussian noise (AWGN) channel.
The AWGN channel is a good model for many satellilite and deep space communication links
An AWGN channel adds white Gaussian noise to the signal that passes through it
The noise is additive
The noise is white
The noise sample have a Gaussian distribution
RAYLIEGH FADING CHANNEL
Rayleigh fading is a statistical model for the effect of a propagation environment on a radio signal such as that used by wireless devices.
Rayleigh fading is most applicable when there is no line of sight between the transmitter and receiver.
It is reasonable model for tropospheric and ionospheric signal propagation
It assumes that the power of a signal that has passed through such a transmission medium (also called a communications channels will vary randomly or fade according to a Rayleigh distributuion )
CONCLUSION
The ber performance of awgn and rayliegh fading are simulated.It showed that awgn has better performance compared to rayliegh fading channel . More research can be carried out on realizing the application of OFDM in the future wireless communications.