Sidelobe Suppression for Cyclic Prefix OFDM with Time Domain Extended Active Interference Cancellation

Abstract

In recent papers it has been demonstrated, that Time Domain Extended Active Interference Cancellation (TD-EAIC) can provide a significant sidelobe suppression at acceptable self-interference level and feasible computational effort in a non-guarded (NG)-OFDM system. Meanwhile much simulation research has been made to find the best adaption to use it within a cyclic prefix (CP)-OFDM system as well. This paper presents two configurations that were found to be best, concerning either the aspect of coding redundancy or the aspect of signal latency. Both can provide a spectral shaping which reduces out-of-band energy (OOBE) to a negligible level and with self-interference levels below the interference that can be expected from a typical CP-OFDM channel. Compared to previously published, similar EAIC-approaches, they show significant lower self-interference with identical sidelobe suppression. The first configuration uses the differential (D-) version of TD-EAIC that was presented in the last paper, but with necessary adaption to the carrier phase. The second configuration works without any latency to the signal path, making it the stringent choice for transmission systems with a minimal roundtrip requirement. The truncated singular value decomposition (SVD) approach, as presented in the last paper, is again used to make the computational complexity linear and thus practically implementable regardless of FFT size and carrier count. The usage of the proposed methods includes, achieving deep notches in the transmission spectrum of Cognitive Radio systems. Furthermore, steep spectral edges can be accomplished to reduce spectral guard bands between different transmitters and exploit bandwidth efficiently without mutual interference.