Effective schemes for OFDM sidelobe control in fragmented spectrum use

OFDM as multicarrier scheme provides adaptive functionality that is required to implement waveform processing for cognitive radio, dynamic spectrum use and fragmented coexistence scenarios. However, OFDM faces some difficulties due to the relatively strong sidelobes around the active subcarriers, which introduces interference effects between adjacent frequency slots intended to be used independently in non-synchronized way. In this paper we consider edge windowing and cancellation carrier approaches for controlling the spectrum leakage in a practicadl 5 MHz 3GPP LTE scenario. The focus is on minimizing the OFDM signal leakage to narrow unused gaps in the used frequency band, using low-complexity algorithms and minimized overheads in terms of power and spectral efficiency. We develop a simplified version of the cancellation carrier scheme which is suitable for non-contiguous subcarrier allocation in OFDM. It is shown that with relatively narrow unused gaps in the spectrum, it is possible to reach good level of sidelobe suppression with significantly reduced computational complexity.