CARRIER FREQUENCY OFFSET ESTIMATION FOR OFDM SYSTEMS

Abstract

Synchronization is an essential task for any digital communication system. Without a proper and accurate synchronization method, it is not possible to reliably receive the transmitted data. Synchronization is the first and most important task that must be performed at the receiver. So, whole receiver architecture depends on the synchronization method that is used. Orthogonal frequency division multiplexing (OFDM) is one of the most promising techniques for achieving high speed wireless data communication. OFDM is a multicarrier transmission technique, which divides the single wideband channel into a number of narrowband channels called sub-channels; each subcarrier in each sub-channel is being modulated by a low rate data stream and sub-carriers are transmitted in parallel over the channel. The increased symbol duration reduces the impact of ISI. When the synchronization in an OFDM system is not perfect, the orthogonality among different subcarriers is destroyed and the ICI will be introduced. Therefore in OFDM system CFO estimation is an important issue that needs to be considered. In this dissertation work, we have used repeated data symbols to estimate the carrier frequency offset for OFDM system, which is one of the earliest CFO estimation schemes for OFDM system. Following that we will discuss a Numerical technique for estimation of CFO for OFDM system. The technique is a blind maximum likelihood (ML) estimate of frequency offset using the Newton - Raphson method. Reduced complexity CFO estimation technique for OFDM systems which use null subcarriers is also been exploited. For simulation MATLAB is used and it is demonstrated through simulation results that the performance of CFO estimation using null subcarriers approach is close to the Cramer Rao bound.