Comparison of four OFDM signal representations approaches for high dynamic range nonlinear PA behavioural modelling

Abstract

This paper 1 presents advances in techniques for representing OFDM signals in nonlinear RF power amplifier behavioural modelling. OFDM is significantly sensitive to nonlinear distortion because of the high peak to average power ratio (PAPR) of its envelope. Four signal representation techniques are presented and compared. These are Direct Time Domain method (DTD), Mixed Frequency and Time Domain method (MFTD), Statistical approach (Stat), and MFTD combined with a Modified Stat approach (MFTD-MS). All four are applied to a Bessel Fourier behavioural model for a GaN nonlinear PA. This model is a particularly suitable tool for large dynamic range nonlinearity analysis of certain classes of multicarrier signals. The goal is to compare accuracy, preservation of modulation information, complexity and computer resource consumption.

Behavioural Analysis of Internal Mechanism of Nonlinear Distortion in OFDM Signal Systems

“…This PSD estimation method is found to have little or no dependency on neither the specific PA nonlinearity characteristic nor the PA operating point. This result is verified by simulation results using a previously published statistical simulation approach, 'Stat' approach [11,12], where the OFDM signal is characterized as a zero mean complex Gaussian process.…”

“…M and N denote the number of input frames and number of input subcarriers, respectively. The PA output may be shown to be, [10,11]: …”

“…The reference power used in the normalization at each OP is the total output power at that OP. Figure 4 is obtained from model simulation results using Stat approach, [11,12], with the same PA input signal configuration and the same GaN PA. In figure 5, the simulated PSD 3 (0,σ 2 ) and PSD 5 (0,σ 2 ) are presented for comparison with predicted PSD 3 (0,σ 2 ) and PSD 3 (0,σ 2 ).…”

“…This then is quite suitable for the analysis of the nonlinear amplification of OFDM signals. The PA input OFDM signal may be written, [11,12]:…”

“…DDF is determined by the OFDM signal standard used (or more specifically on the number of active subcarriers); it is naturally independent of either the PA characteristic or PA OP. The DDF findings observed in figure 3 may be expressed as follows, (11) and (12) ) (…”