We use (8,13,15,23)GHz ODU at vertical &

Generally the licensing authorities would assign the frequency channel and the polarization. However if you have any choice then vertical polarisation at the higher bands (eg 15-18-23-38 GHz) would be preferable as it gives a better link performance in regards of the rain outage (something to do with the direction of the falling rain drops and their comparable size with the radio signal wavelength – there is more theoretical reading on the Web available) However, if you have some interfering signal coming over to your radio site and this signal has got, say, a vertical polarisation, then by choosing a horizontal polarisation for your link you would be able to achieve an interfering signal discrimination (say about 20dB additionally) and therefore, hopefully, overcome an interference problem.