IFDM Communication Systems

2007 WordsFeb 22, 20188 Pages
OFDM is a great technique to handle impairments of wireless communication channels such as multipath propagation. Hence, OFDM is a practical candidate for future 4G wireless communications techniques [1]-[4]. On the other hand, one of the major drawbacks of the OFDM communication system is the drift in reference carrier. The offset present in received carrier will lose orthogonality among the carriers. Hence, the CFO causes a reduction of desired signal amplitude in the output decision variable and introduces ICI. Then it brings up an increase of BER. The effect caused by CFO for OFDM system was analyzed in [7]-[9]. In [7] BER upper bound of OFDM system is analyzed without ICI self-cancellation and BER of OFDM system is analyzed using self-cancellation, but this method is less accurate. In [9], it is indicated that CFO should be less than 2% of the bandwidth of the sub-channel to guarantee the signal to interference ratio to be higher than 30 dB. A critically sampled OFDM system/OQAM system is also not robust to CFO [9], even when optimal pulses are used as shaping filters. Thus, carrier frequency offset greatly degrades system performance. Therefore, practical OFDM systems need the CFO to be compensated with sufficient accuracy, and this has led to a whole lot of literature on CFO estimation algorithms. Most of the existing CFO estimators for OFDM are based on periodically transmitted pilot symbols. Yet, the pilot symbols transmission loses a significant bandwidth,

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