Optimization of the Resulting Characteristic for Power Amplifiers Using Predistortion

Abstract

Power amplifiers are nonlinear devices that traditionally have been tried linearized by means of predistortion. The nonlinear impact can be identified by sidelobes in the frequency domain. By accepting a certain sidelobe level, this implies that we also accept a somewhat nonlinear characteristic on the resulting cascade of our transmitter. The main question raised in this thesis is: How is the optimal nonlinear cascade that maximizes transmitted power defined when some given out-of-band spectral requirements are fulfilled? The problem has been limited such that examinations have been done on a single carrier system seen in context to a chosen set of out-of-band spectral requirements. The different nonlinear characteristics have been represented by means of B-splines. Thus, the results obtained are only the best set of parameters in the model utilized, and hence, only a sub-optimal solution to the problem. Results are presented for different spectral restrictions. Simulations performed suggest that a linear characteristic is the optimal, when restrictions are placed within the sidelobe level close to the mainlobe. When the first sidelobe is allowed to grow unlimited, a parameter set using 2-segments B-spline have proved to give the highest average transmitted