Pseudo-duplex digital radio

A digital radio in time division duplex communication with a second digital radio derives a source signal activity parameter which indicates the likelihood of there being a source (which may be voice) signal for transmission by the digital radio to the second digital radio over a single radio channel. The digital radio also derives a first value of a signal direction parameter direction parameter in dependence on both the value of the signal activity parameter for the digital radio and a second value of the signal direction parameter received from the second digital radio. The digital radio selects the proportions of time for transmission and reception over the single radio channel in dependence on the first value of the signal direction parameter. The digital radio also transmits the first value of the signal direction parameter to the second digital radio to perform an analogous update of its value of the signal direction parameter. The arrangement is robust to radio channel and source signal activity parameter value imperfections.