Book excerpt: As a promising technique, OFDM has been widely used in emerging broadband communication systems, such as digital audio broadcasting (DAB), high-definition television (HDTV), and wireless local area network (IEEE 802.11a and HIPERLAN/2). However, as the OFDM signals are the sum of signals with random amplitude and phase, they are likely to have large PAPR that require a linear high-power- amplifier (HPA) with an extremely high dynamic range which is expensive and inefficient. Furthermore, any amplifier nonlinearity causes intermodulation products resulting in unwanted out-of-band power. A number of approaches have been proposed to deal with the PAPR problem, including amongst others, clipping, clipping-and-filtering (CF), coding, companding transform, active constellation extension (ACE), selected mapping (SLM), and partial transmit sequence (PTS). This book proposes an improvement in the selected mapping technique. The resulting scheme can also be applied to the multiple transmitting antenna cases. Further, it compares the simulation results to the existing techniques namely exponential companding transform, repeated clipping and filtering, and adaptive active constellation extension.