Where an is the data symbol on the nth subcarrier. Equation (1) is equivalent to the N-point inverse discrete Fourier transform (IDFT). The subcarrier spacing and frequencies are carefully selected to achieve the orthogonality of the subcarrier.1/T ∫_0^T▒〖x(t) y(t) dt =0〗 (2)Equation (2) means that the signals are not correlated, that is, they are two different and independent signals. In OFDM, sync-shaped pulses are used as subcarrier spectra. According to the properties of synchronous pulses, zero crossings are found at multiples of 1/T. Using synchronous pulses and selecting the center frequency fi of the subcarrier with equation (3) ensures that the orthogonality of the subcarrier is maintained.f_i= f_c + i/T i= (-N)/2……N/ 2 (3)Where fc is the center frequency of the channel and N is the number of subchannels. In this way each subcarrier has a maximum at its own center frequency and zero at the center frequency of the other subcarrier.Fig.2. OFDM transmitter modelAfter serial to parallel conversion, the inverse discrete Fourier transform (IDFT) is applied to each stream. In practice, this transformation can be implemented very efficiently using the inverse fast Fourier transform (IFFT). This is equivalent to the transition from the frequency domain to the time domain. After IFFT, all parallel data is added and transmitted. CHALLENGES IN USING OFDM One of the major problems with the OFDM system is the high peak-to-average power ratio (PAPR) that occurs in the modulated signal. A high PAPR occurs when the signal in the subchannels constructively sums in phase. High peaks are produced due to modulation. Once multiple sinusoids, which are in phase, are added together to form high peaks of the multicarrier signal. On the other hand, the... center of the card... region. However, this solution decreases the energy efficiency of the PA. On the other hand, the PAPR reduction technique offers a more energy-efficient solution. POWER AMPLIFIER BACK-OFF OPERATION To ensure that the PA operates in its linear region, the input signal is attenuated and is said to be in power back-off mode. This application of power back-off results in an increase in the power specification of the PA. As a result, the PA design is oversized, resulting in reduced energy efficiency. This is the main reason why power back-off is limited to applications where low PA efficiency requirements are required. The quantities to measure the level of power back-off are: input power back-off (IPBO) and output power back-off (OPBO). They are defined by equations (4) and (5).IPBO=10 〖log〗_(10 ) P_(i,sat)/P_i (4)