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Clipping is a simple and convenient PAPR (peak-to-average power ratio) reduction method to prevent the high-speed OFDM (orthogonal frequency division multiplexing) communication system from nonlinear distortion. However, clipping method inherently produces clip noise so that BER performance can be degraded. Clipping noise can be divided into in-band and out-of-band clipping noise. In this paper, we study the clipping effect on the forward link of the OFDM-FDMA (frequency division multiple access) communication system. BER (bit error rate) performance of OFDM-FDMA system using clipping method is theoretically analyzed. We also investigate the BER performance of the clipped OFDM-FDMA signal including the HPA and quantify the appropriate IBO (input back-off) in HPA. From the simulation results, it can be found that the BER performance of the OFDM-FDMA system is degraded by the clipping process. When clipping ratio is about 2, BER of the clipped OFDM-FDMA with only in-band noise and in-band plus out-of-band noise closely approaches to the BER of OFDM-FDMA without clipping. The simulation results also show that when the number of subcarriers for each user in OFDM-FDMA system is 16, with clip ratio 2 and IBO of 3 dB, the BER curve with in-band plus out-of-band noise is very similar to that of the linear amplifier. So, we can choose the appropriate IBO value and CR (clip ratio) to get the desired BER performance.