Intermodulation product statistics in multi-carrier radio systems

The authors study the probability distribution function (PDF) and cumulative probability distribution function (CPDF) of the IM (intermodulation) products in several nonlinearly amplified systems by computer simulations and hardware measurements. The statistics of the in-band and out-of-band IM products are found. Particular emphasis is given to the study of the CPDF of out-of-band IM products since it is shown that these can be the major cause of adjacent-channel-interference (ACI). It is demonstrated that the PDF of the out-of-band IM interference is not necessarily Gaussian and that this out-of-band IM noise may lead to more frequent peaks and to higher peaks or crest factors than practical Gaussian noise sources. Thus the BER (bit error rate) will be worse than that in the WGN (white Gaussian noise) case. On the contrary, in the case of in-band IM noise, the BER performance is better than that of the WGN case when C/N (carrier/noise ratio) is high enough.<>