Multiple field units in a CDMA system are synchronized for communication with a base station using a shared forward and reverse link channel. Each field unit is assigned a time slot in a forward link channel to receive messages from the base station. Likewise, each field unit is assigned a time slot...http://www.google.com.hk/patents/US8175120?utm_source=gb-gplus-share專利 US8175120 - Minimal maintenance link to support synchronization
