Baton passing method and apparatus for maintaining synchronization in a

Abstract

In a TDMA satellite communication system, one of the stations is elected the primary station which transmits a reference burst to all other stations to synchronize the local clocks in each station. Each subsidiary station in turn responds by transmitting a local transmit reference burst to enable synchronization of the local transmit clocks. In order to assure that the synchronous operation of the network will continue when the reference station experiences a failure, an alternate reference station is designated in the network which will assume the role of the primary reference station in a baton passing operation in the event that the existing primary reference station must abdicate its reference role. An improved method and apparatus for carrying out the baton passing operation monitors the channel error rate at the reference station and the alternate station. The error rate is measured by detecting FEC from assessing the error syndromes in the reference bursts from the reference station as received at the reference and alternate stations. This refined monitoring technique is combined with the coarser technique of monitoring the number of negative acknowledgement signals from the subsidiary stations indicating that they have not correctly received reference bursts, to yield a more refined determination at the reference station of its effectiveness as a reference station. The alternate station uses a similar technique to determine if it is sufficiently healthy to play the role of alternate station.