Research On ICI Self-cancellation Algorithm And Dynamic Allocation For OFDM Systems

With the development of the mobile communication technology, the Orthogonal Frequency Division Multiplexing (OFDM) system has become the hotspot. It modulates the signals to sub-carriers which are orthogonal and increase the time for sending signals, so it can reduce the effect of inter-symbol interference (ISI) effectively. But OFDM is sensitive to the frequency offset because the orthogonality between sub-carriers resulting inter-carrier interference (ICI) which gives rise to an irreducible error floor of the system's bit error rate (BER). At the same time, in broadband OFDM system over mobile fading channels, which have different channel capacity, if a fixed modulation scheme is applied to all sub-channels, the whole system's capacity and the transmitted power have not been full used. This problem can be mitigated if adaptive modulation schemes are employed for individual OFDM sub-channels. In this paper, a dynamic bit allocation scheme is discussed. This algorithm distributes the information bits, the signal constellations and transmitting power adaptively to different sub-channels according to channel instantaneous attenuations to satisfy average power and BER constraints. Otherwise, ICI self-cancellation is a very simple way for suppressing ICI in OFDM system. A self-cancellation algorithm to reduce ICI to realize for OFDM systems is proposed here. Without any additional hardware nor great loss in bandwidth efficiency, it just bases on the DFT modules to reduce the sensitivity to frequency offset and can get a proper gain in CIR compared with the standard OFDM system. We use this ICI self-cancellation algorithm in dynamic bit allocating OFDM system with different parameters. The results of computer simulation prove the correctness.