Influence of the phase relationship between direct path and interference path on XPIC performance

The article analyses the dependence of the XPIC ("cross-polar interference canceller") performance from the phase relationship between direct path and interference path in terrestrial radio relay links. By means of theoretical considerations and simulation results it is shown that the XPIC (based on minimum mean square error criterion) can totally cancel the cross-polar interference for particular values of the phase shift. For such values the XPIC can also recover the part of the useful information that, because of depolarisation phenomena, is transmitted on the opposite polarised branch. Moreover the analysis of the coefficient values allows one to demonstrate that the cancellation of the cross-polar interference and the recovery of the useful information on the other polarization branch is realized by means of the quadrature part of the canceller coefficients. In summary, the article highlights the existence of favourable propagation conditions in the XPIC operation that have to be considered in the computation of the performance of radio relay links with frequency reuse.