BER PERFORMANCE OF OFDM SYSTEM WITH ADAPTIVE MODULATION
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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..,
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
Adaptive modulation comparison is made with fixed modulation system under various IFFT size(N).
BER is calculated using following formula:
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
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…..