On the Spectral Content of Nonlinear Carrier Aggregated Windowed OFDM Systems

Orthogonal frequency division multiplexing (OFDM) and its variants have become the most favorable multi-carrier modulation scheme in various wireless communications standards, such as long-term evolution (LTE), LTE-Advanced, 5G New Radio (5G). They are also bound to play a crucial role in shaping the standards of next-generation cellular networks. However, the slow spectral sidelobe decay rate of OFDM makes it vulnerable to larger out-of-band (OOB) emission, especially in the presence of nonlinear high power amplifiers (HPA). Various methods have been proposed to eliminate this shortcoming and reduce the OOB emission of the OFDM signals. However, these schemes are only analyzed assuming HPA to be linear. In this paper, we studied the nonlinearity effect due HPA on the spectral content of carrier aggregated (CA) windowed OFDM signal. Specifically, we show that windowing lowers the noise floor substantially, however, due to the nonlinearity of HPA, the effect of windowing on the OOB emission is negligible. As a consequence, the nonlinear characteristics of HPA should be taken into account while evaluating the performance of windowing for a CA as well as non-aggregated OFDM signals. Simulation results have been presented for both dual as well as single band CA Windowed OFDM signal along with nonlinear HPA.