Generalized Frequency Division Multiplexing (GFDM) has been recently proposed for next generation 5G mobile networks. A disadvantage of GFDM, similarly to the other multicarrier signals, is its high peak-to-average-power ratio (PAPR), Large PAPR signals can easily saturate the transmit power amplifier and cause degradation in BER performance and out-of-band emissions. In this work we investigate the performance of GFDM in presence nonlinearity effects in the transmission channel, with the aim to explore the effectiveness of some PAPR reduction techniques to mitigate OOB radiation and error performance degradation. To reduce PAPR we consider clipping techniques with iterative receiver, companding and selective mapping techniques, and for performance comparison we also evaluate IFDMA. The simulation results show that Clipping techniques delivers the best result, whereas IFDMA is able to maintain an acceptable performance level with low complexity in the receiver.