Abstract: The present invention relates to an arrangement for point-to-point transmission over links between first and second link (end) terminals in a system implementing time division duplex (TDD) and wherein information is sent over the links in frames divided into time slots. It is adapted to determine the lengths of the frames on a per link basis using one or more link parameters, the frame length hence being variable.

Abstract: The present invention concerns calibration of a group antenna system (11) with a number of radiation elements (X1, . . . , XN) and a number of controllable transmitters (T1, . . . , TN), in which the transmitters at the reception of an input signal transmit output signals for feeding the radiation elements. The calibration is done to be able to obtain a time varying antenna diagram at transmission and should be able to perform under operation without interrupting the normal operation of the group antenna system (11). The group antenna system comprises a control system for automatically correcting the control of the transmitters (T1, . . . , TN) for error deviations thereof. The group antenna system (11) comprises means (37) for generating a sum signal corresponding to the sum of the output signals. The control system generates error signals, giving information about the error deviations, employing the sum signal, the input signal and the complex amplifications varying with time for the transmitters.