One major drawback of OFDM is the large Peak to Average Power Ratio (PAPR). OFDM is a linear modulation, therefore large PAPR requires large linear dynamic range of the transmitter (TX) as well as the receiver (RX) paths. The weak point in the TX-RX chain is the Power Amplifier (PA). As known, a linear PA which is able to amplify signals with large PAPR has to have a large dynamic range that results with low power efficiency, thus by reducing PAPR one may improve the efficiency of PA. A PAPR reducing method in OFDM, based on SeLective Mapping (SLM) is considered. As known, SLM requires transmitting a Side Information (SI). Increasing the SLM order reduces the PAPR but increases the size of SI. In order to transmit the SI some power and bandwidth are needed, those are taken from the total power and bandwidth budget and thus lowering the capacity. On the other hand the reduced PAPR improves the PA efficiency, thus increases the channel capacity. Accordingly maximal value of channel capacity is expected as well as an optimal SLM order.