A simultaneous frequency up conversion of four intermediate frequency (IF) signals is carried out by utilizing a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) in a differential configuration for radio over fiber applications. A sampling signal compelled by an optical pulse clock source produces 10-ps-width pulses at a repetition rate domain that is from 7.8 to 19.5 GHz. The four IF signals carrying quadratic phase shift keying (QPSK) data at frequencies fm are up converted at the SOA-MZI output at mixing frequencies nfsk ± fm, where k and m equal 1, 2, 3, and 4 and n is the harmonic rank of the sampling signal. The simulation study for simultaneous frequency up conversion relied on the SOA-MZI sampling mixer is developed to acquire the conversion gain and the error vector magnitude (EVM) in the repetition rate range. Using the virtual photonics integrated simulator, we show that incrementing the repetition rate from 7.8 to 19.5 GHz improves the competence and merit of the optical transmission system due to a better signal level and a lower aliased noise power with a higher sampling rate. Positive conversion gains were achieved at a higher mixing frequency for each channel. Concomitantly, the benefit on the conversion gain provided by augmenting the sampling frequency is 14 dB. By increasing the repetition rate, the EVM can be ameliorated up to 12% for all channels. In addition, it degrades more when the frequency channel increases over the repetition rate range. The maximum bit rate of 25 Gbit/s with a QPSK modulation meets the forward error correction limit