• Ankita Vyas
• Brajlata Chourasiya

Orthogonal Frequency Division Multiplexing (OFDM) suffers from severe performance degradation in the presence of carrier frequency offset (CFO). Specifically, frequency offset leads to common phase error (CPE) & become cause of inter carrier interference (ICI), results reduction in the signal to noise ratio (SNR). In OFDM technique, some of the subcarriers undergo a deep fading. Adaptive technique can be used to mitigate the deep fading effect if the channel state information (CSI) is available at the transmitter. Generally, CSI is estimated from the average signal to noise ratio. The performance of adaptive modulation technique relies on the perfect estimation of CSI. But in general the CFO makes the estimated CSI to deviate from the actual CSI. In this paper the effects of CFO, CFO estimation & correction techniques are analyzed. Various adaptive modulation techniques to improve the spectral efficiency are also analyzed. In this paper a CFO correction technique for adaptive modulation has been proposed. In this proposed method CFO is estimated using Maximum Likelihood Estimation (MLE) & it is compensated. It shows that the proposed adaptive modulation scheme maximizes the average spectral efficiency up to 6 bps/Hz for the target BER of 10-3 & up to 8 bps/Hz for the target BER of 10-5. Thus the proposed method maximizes the spectral efficiency with an acceptable BER than direct estimation of CSI.

Orthogonal Frequency Division Multiplexing, Carrier Frequency Offset, Inter Carrier Interference, Channel State Information, Bit Error Rate, Maximum likelihood Estimation.

"CFO ESTIMATION USING ADPATIVE MODULATION TECHNIQUES", International Journal of Emerging Technologies and Innovative Research (www.jetir.org), ISSN:2349-5162, Vol.2, Issue 12, page no.183-192, December-2015, Available :http://www.jetir.org/papers/JETIR1512032.pdf

"CFO ESTIMATION USING ADPATIVE MODULATION TECHNIQUES", International Journal of Emerging Technologies and Innovative Research (www.jetir.org | UGC and issn Approved), ISSN:2349-5162, Vol.2, Issue 12, page no. pp183-192, December-2015, Available at : http://www.jetir.org/papers/JETIR1512032.pdf