The present invention relates to cell plans and cell plan changes in point to multipoint systems (PMP). A cell plan arrangement is provided comprising cells having four 90.degree. sectors to which individual sector at least one of four orthogonal channels, such as channels distinguished by two frequencies and two polarisations, are allocated. A method is furthermore provided allowing gradual sector-by-sector migration into a 45.degree. sector cell plan. The cell plan offers advantageous carrier to interference ration (C/I) improvements.