New receiver structures for subcarrier synchronization in OFDM systems over frequency-selective channels

In this paper, subcarrier synchronization techniques for OFDM systems are studied. These techniques are evaluated for frequency dispersive, frequency nondispersive, time varying, and time invariant channels. DVB-T parameters are taken as reference. It has been observed that one needs an effective subcarrier synchronization measure in order to combat degrading effects of dispersive, time varying channels. Because of this reason, we propose new receiver structures to solve synchronization problems for such channels. In the proposed receiver structure, PLL trackers for subcarriers synchronization are used. The PLL´s are operated by using an expectation maximization (EM) based phase offset estimation algorithm. According to the performance evaluations made by computer simulations, the proposed receivers improve the system performance on a large scale.