A new analog predistortion criterion with application to high efficiency digital radio links

This paper describes a new approach for designing analog cubic predistorters in view of minimizing non linear distortion introduced by the high power amplifier (HPA) in microwave radio links. The approach is based on a global mean squared error minimization between the input to the predistorter and the output of the power amplifier, rather than on the elimination of the cubic term. In this manner, two advantages are obtained. Firstly, the off-band distortion terms are reduced so that it is possible to eliminate the HF transmission filter. Secondly, the interference produced by the nonlinear distortion can be uniformly distributed over the entire constellation so that it is possible to reduce the back-off value of the HPA. Results of the application of the method proposed to some high spectrally efficient QAM systems, such as the 512-QAM system, are presente

The separation of multiple mutually interfering FM signals and the use of predistortion to compensate for nonlinear RF amplifiers

This thesis covers two fairly different topics, separation of multiple FM signals, emphasizing on the case of three FM signals, and pre-distortion for compensation of non-linear amplifiers. The thesis shows that given a received signals that is the sum of three or more interfering FM signals whose phases are bandlimited, there is strong reasons to believe that there is unique solution. I.e., it is probably not possible for any other FM signals that are bandlimited to add to the same received signal. The research also shows that the solution is stable, a small error will not cause a divergence from the solution. Furthermore, a series expansion of the received phase in the case of three interfering FM signals is derived that shows the phase error is wideband compared to the bandwidth of the phase, provided that the strongest signal is strictly dominating. This shows that there is a capture effect on the strongest signal, it also shows that it is not always be possible to separate the three FM signals through cross coupled phased locked loop (CCPLL) techniques. It is also shown that the amplitudes of the signals can be found and how this can be done. An iterative method is presented for separating the three FM signals together with some simulations. The simulations support the theoretical findings;In the pre-distorter research, high order pre-distorters have been found for a fairly wide class of amplifiers. The technique circumvents the Volterra series approach and its associated problems. As the implementation of these pre-distorters are very simple, there is not any practical limitations on the order. For example, an 11th order pre-distorter is easily implemented. The theory behind these types of pre-distorter is developed and is supported through simulations