Antenna selection in a diversity system, which operates correctly even when switching times are asynchronous with a received signal

摘要

This application relates to antenna selection methods of the type which initially switch between a plurality of antennae at predetermined regular intervals, until quality metrics of received signals can be used to determine which antenna to select. Received preamble signals, from which quality metrics are extracted, are asynchronous with predetermined antenna switching times. This lack of synchronicity has led to antenna selection errors in prior art systems. In a first embodiment (improvement 2), if, following a first antenna switch operation, it is determined that a quality metric of a received signal initially continuously exceeds a predetermined threshold before falling below the threshold within a predetermined time interval, then it is concluded that the first switch was made in error and a switch is made back to the antenna used prior to the first switch. In a second embodiment (improvement 1), when a quality metric is below a first threshold corresponding to a level required to permit detection of the signal, a switch from a first antenna to a second antenna is made at a predetermined switching time only if at that time the quality metric exceeds a second threshold which is less than a first threshold. The quality metric may be a correlation value, intensity value or power value. In claim 1 the first embodiment is expressed in terms of an "antenna stay time" and an "error available time".