A Fast Algorithm to Find Generic Odd and Even Order Intermodulation Products

Abstract — Nonlinear devices, such as power amplifiers, typically generate spurious signal components known as intermodulations. This phenomenon is particularly important when multiple signals, allocated at different frequencies, pass through nonlinear devices simultaneously. In this paper we extend a known fast counting algorithm (FCA) of intermodulation components and compare it with other counting algorithms. The results obtained show significant improvement on the processing time. The carrier configuration is modelled by using indicator polynomials. We show that the distribution of high order intermodulation products can be computed in a reduced amount of time, by extending the algorithmic results relevant to third order intermodulations. In addition, we notice that in particular situations even order intermodulations are also important. They occupy the adjacent harmonic zones, generally allocated to other services, so that the achievable performance deteriorates. We extend an algorithm which computes the position of even and odd order intermodulations, and we make it faster and computationally more efficient. These results may improve both the optimisation of the spectrum shape and the analysis of the nonlinear effects. Comparisons with some other direct counting algorithms are made in terms of accuracy and speed. Index Terms — Channel allocation, counting algorithms, intermodulation distortion, multicarrier systems