The present invention relates to a method and arrangement for switching between different modes in a communications network. The network comprises a number of transmit and a number of receive antennas, said modes comprising a single user mode and a multiple user mode. The method including the steps of: transmitting reference signals or predetermined sequences corresponding to both said modes comprising respective weighting matrices for said modes during a preparation phase, which comprises of one or more transmission time intervals (TTI), transmitting on a common channel, signalling information indicating start and duration of said preparation phase to all receiving equipments in a reception area.