Method, apparatus and system for controlling a transmit diversity device

A method of controlling a mobile communication apparatus comprising:

• transmitting a plurality of signals using a plurality of antennas, wherein signals respectively transmitted on the antennas differ by a plurality of phase differences respective to the plurality of transmissions, wherein in said plurality of transmissions, signals transmitted by the plurality of antennas have a first power ratio therebetween;
• detecting a phase instability condition based at least on said plurality of phase differences by detecting that the plurality of phase differences comprise a progression of phase differences substantially in the same direction;
• and
• if said phase instability condition is detected, then in a subsequent transmission, transmitting a signal on the plurality of antennas using a second power ratio between said antennas, different from said first power ratio.