BER PERFORMANCE OF OFDM SYSTEM WITH ADAPTIVE MODULATION

Presented by:

Harish RajulaP14EC009

SV_NIT-Suratharish.rajula91@gmail.com

Ieee Explorer search:BER Performance of OFDM System with

Adaptive Modulation

Challenges in Designing OFDM Transmitter:1. The Number of subcarriers required

to send the given data

Each subcarriers are centered at frequencies that are orthogonal to each other (usually multiples of frequencies).

2. The second design parameter could be the

Modulation format that we wish to use

An OFDM signal can be constructed using anyone of the

following digital modulation techniques namely BPSK, QPSK, QAM etc..,

OFDM Trasmitter:

In an OFDM transmission system if the same

fixed transmission scheme is used for all OFDM subcarriers, Each subcarrier is attenuated

individually under the frequency-selective and fast fading channel

It results in highest attenuation and hence poor performance

Defining the problem

Proposing Technique->

Adaptive Modulation

Block diagram:

Adaptive modulation comparison is made with fixed modulation system under various IFFT size(N).

BER is calculated using following formula:

Key ponts:

Adaptive modulation is introduced by presenting some

of the simpler adaptive Quadrature Amplitude Modulation(QAM) schemes and their performance for both perfectly known and predicted channels.

ADAPTIVE MODULATION ALGORITHM

Simulation Results:

Here IFFT size is denoted by N. For IFFT size N=64,128, 256,512 ,1024,2048 BER performance has shown

Conclusion:In adaptive modulation, modulation rate

changes based upon value of an instantaneous SNR.

The BER performance comparison between fixed and adaptive modulation shows that BER performance for all modulation techniques is better, when IFFT size is greater than 512.

For all values of IFFT sizes, average BER of Adaptive modulation is approximately 0.203568 and for higher order fixed modulation it is approximately 0.913545 .

Hence, it concludes that BER performance of adaptive modulation is better than fixed modulation with the cost of more execution time.

To be continue…….Effect of Channel Prediction on

Automatic Modulation Classification for Adaptive OFDM Systems…

Adaptive OFDM for Wireless Interconnect in Confined Enclosures…..