Reduction of subcarriers spectrum sidelobes and intermodulation in NC-OFDM systems

The paper tackles the problem of efficient reduction of the out-of-band (OOB) radiation in multi-carrier systems when considering the presence of a nonlinear power amplification. It is important to provide “green” transmitters producing less electromagnetic “pollution” out of its nominal frequency band and obtaining at the same time high energy efficiency of the used power amplifier. One of the known methods assumes appropriate modulation of dedicated subcarriers by specially calculated symbols reducing OOB radiation. The solution proposed in this paper combines two approaches, among which the first, called cancellation carriers, is used traditionally for subcarrier sidelobes minimization, and the second, called tone reservation, for peak to average power ratio reduction. The novelty of this work is in joint minimization of both aforementioned metrics in the near optimal way while keeping low computational complexity. The result is seen as a decreased power of the OOB radiation observed after signal passing through the power amplifier. The obtained results confirm that the proposed algorithm outperforms the approaches in which those metrics are minimized separately. Additionally, a number of simulations has been carried out to investigate the influence of the proposed algorithm parameters on the resultant out-of-band radiation performance.