A New TD-EAIC Approach for Steep OFDM Sidelobe Suppression with Linear Complexity

Abstract

In communication channels with frequency selective attenuation or frequency dependent noise, like data wires, power line communication (PLC) or wireless channels, OFDM is known to be more suitable than single channel modulation, because it can allocate the frequency channels with different power levels and different degrees of modulation. Aside of high peak-to-average power ratio (PAPR), the sidelobes of OFDM which use excess bandwidth are one of its drawbacks. The recently introduced method of time domain extended active interference cancellation (TD-EAIC) for non-guarded (NG-) OFDM was shown to achieve a combination of low selfinterference and high sidelobe attenuation. This paper addresses the relatively high computational effort of original TD-EAIC and presents several adaptations that lead to significant improvements in terms of computational complexity and memory usage. With a symmetric time-grid FFT an additional symmetry is achieved. This enables the decomposition of the cancellation signal into a native spectral precoding and a fully differential signal part which only depends on the signal difference between two consecutive OFDM symbols. Skipping the precoding part leaves a purely differential TD-EAIC (D-TD-EAIC) which has a marginally smaller performance but is even easier to implement. Finally a truncated singular value decomposition (SVD) is used to achieve linear complexity. It is shown that the resulting computational effort is at a competitive level, while the achieved sidelobe suppression can be designed for specific demands. Together with the transparency of the cancellation signal, which allows for an unchanged receiver, this makes (D-)TD-EAIC a suitable method for bandwidth restricted channels.