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Generalized frequency division multiplexing (GFDM) is a flexible non-orthogonal waveform candidate for 5G which can offer some advantages such as low out-of-band emission and high spectral efficiency. This paper investigates the effects of nonlinear behavior of practical power amplifier (PA) on the GFDM spectrum. A closed form expression for power spectral density (PSD) of GFDM signal is extracted. Then, PSD at the output of PA as a function of input power and the coefficients of nonlinear polynomial PA model is derived. In addition, the adjacent channel power (ACP) and ACP ratio, as two important performance metrics, are evaluated. The simulation results confirm the accuracy of derived analytical expressions. Moreover, to validate the performance of GFDM modulation after nonlinear PA, it is compared with orthogonal frequency division multiplexing modulation. [ABSTRACT FROM AUTHOR]

The nonlinear behavior of power amplifier (PA) in orthogonal frequency-division multiplexing (OFDM)-based cognitive radio (CR) system introduces in-band and adjacent channel interferences. The power in the adjacent channels is an important issue in the CR because it can act as interference to primary users. In this paper, we derive a closed-form expression for the leakage power at adjacent channels when CR devices use OFDM modulation. Moreover, the PA nonlinearity creates in-band distortion that produces intercarrier interference and reduces the secondary system capacity. To control this effect, we derive the optimum power scaling factor for the input signal that maximizes the secondary user rate. The optimization process is executed by considering nonlinear effects on signal-to-interference-and-noise ratio under the constraints of the powers in the adjacent channels. The power in the adjacent channels should not exceed the interference temperature limit. The analytical results are verified by simulation studies. [ABSTRACT FROM AUTHOR]

Abstract: Generalized frequency division multiplexing (GFDM) is suitable for cognitive radio networks due to its low out‐of‐band emission and high spectral efficiency. In this paper, we thus consider the use of GFDM to allow an unlicensed secondary user (SU) to access a spectrum hole. However, in extremely congested spectrum scenarios, both active incumbent primary users on the left and right channels of the spectrum hole will experience out‐of‐band interference. While constraining this interference, we thus investigate the problem of power allocation to the SU transmitter to maximize the overall data rate where the SU receiver is employing a matched filter or zero‐forcing receiver. The power allocation problem is thus solved as a classic convex optimization problem. Finally, total transmission rate of GFDM is compared with that of orthogonal frequency division multiplexing. For instance, when right and left interference should be below 10 dBm, the capacity gain of GFDM over OFDM is 400%. [ABSTRACT FROM AUTHOR]