Constant Envelope OFDM Phase Modulation - Dr. James R. Zeidler

Chapter 2OFDMIn Sections 1.1 and 1.2 the basic properties of OFDM are identified. In this chapter,OFDM is studied in more detail. Section 2.1 covers key properties of OFDM. In Section2.1.1, the cyclic prefix is studied. In Section 2.1.2, the processing of the discrete-timesamples is described, and the equivalence of linear channel convolution and circularchannel convolution is explained. In light of this property, OFDM is considered a specialcase of the more general block modulation with cyclic prefix scheme, as discussed inSection 2.1.3. Finally, in Section 2.1.4 the main functional blocks of the OFDM systemare described.The PAPR statistics are analyzed in Section 2.2 and power amplifier models usedto evaluated system performance are described in Section 2.3. Then in Section 2.4 theeffect of nonlinear power amplification on OFDM systems is studied in terms of spectralleakage (Section 2.4.1), performance degradation (Section 2.4.2), and system range andefficiency (Section 2.4.3). Lastly, the various PAPR mitigation techniques found in theresearch literature are categorized in Section 2.5, and a technique called signal clippingis evaluated in terms of its effectiveness to improve system performance.15