Symbol merging approach for intercell interference mitigation in wireless OFDM systems

Out-of-band power emissions impose stringent limits on the performance that new techniques, such as intercell interference coordination (ICIC) and cognitive radio (CR), provide over wireless systems with OFDM-based air interfaces. To tackle this problem, in this work we consider the use of a simple symbol merging (SM) approach, to enable the reduction of adjacent channel interference when generating the OFDM signal. The basic idea behind this proposal is simple: implement an inverse discrete Fourier transform (IDFT) calculation with double length, to merge OFDM symbols in pairs and reduce by half the number of points with discontinuities in time domain (compared to a conventional OFDM transmission). In addition, a spectral precoding technique is also introduced, to provide a continuous time behavior in the concatenation points that remain after the merging. Based on different performance analyses it is possible to conclude that, our proposed spectral precoding method guarantees a reduced distortion level in the frequency domain, when compared to traditional N-continuous OFDM techniques reported in the literature. Finally, the effect of avoiding the use of cyclic prefix (CP) in part of the OFDM symbols is also studied.