Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

RF Issues 193hence reduce, for instance, infrastructure costs by installing fewer base stations. Unfortunately,high power amplifiers are non-linear devices, where the maximum efficiencyis achieved at the saturation point. Furthermore, at high carrier frequencies (e.g. IEEE802.11h at 5 GHz) low cost RF transmit and receive oscillators can be applied at theexpense of higher phase noise.The main objective of this section is to analyze the performance of multi-carrier andmulti-carrier CDMA transmission with a high number of sub-carriers in the presence oflow cost oscillators with phase noise and HPAs with both AM/AM and AM/PM nonlinearconversions. First, a commonly accepted phase noise model is described. Afteranalyzing its effects in multi-carrier transmission with high order modulation, measuresin the digital domain based on common phase error (CPE) correction are discussed. Theeffects of two classes of non-linear power amplifiers are presented, namely traveling wavetube amplifiers (TWTAs) and solid state power amplifiers (SSPAs). Two techniques toreduce the effects of non-linear HPAs based on pre-distortion and spreading code selectionare discussed. Finally, in order to estimate the required transmit RF power for a givencoverage area, a link budget analysis is carried out.4.7.1 Phase NoiseThe performance of multi-carrier synchronization tracking loops depends strongly on theRF oscillator phase noise characteristics. Phase noise instabilities can be expressed andmeasured in the time and/or frequency domain.4.7.1.1 Phase Noise ModelingVarious phase noise models exist for the analysis of phase noise effects. Two often-usedphase noise models that assume instability of the phase only are described in the following.Lorenzian power density spectrumThe phase noise generated by the oscillators can be modeled by a Wiener–Lèvy process[68], i.e.θ(t) = 2π∫ t0µ(τ) dτ, (4.79)where µ(τ) represents white Gaussian frequency noise with power spectral density N 0 .The resulting power density spectrum is Lorenzian, i.e.2H(f) = ( ( ) 2πf 2). (4.80)πβ +βThe two-sided 3 dB bandwidth of the Lorenzian power density spectrum is given by β,also referred to as the line-width of the oscillator.Measurement-Based power density spectrumAn approach used within the standardization of DVB-T is the application of the powerdensity spectrum defined by [74]