Communication system, base station, user equipment and timing synchronization method for base station thereof

Abstract

A communication system, a base station, a user equipment (UE), and a timing synchronization method for the base station thereof are provided. The communication system includes a first base station, a second base station and the user equipment. The UE is located within coverage of the first base station and the second base station. The first base station and the second base station respectively measure signal stability of the user equipment so that the second base station selects the user equipment based on the measurements for the stability of the signals. The first base station computes a first timing error for transmitting or receiving message between the first base station and the user equipment then transmits the first timing error to the second base station. The second base station adjusts a timing difference between the first base station and the second base station through the first timing error.

What is claimed is: 
     
         1 . A user equipment (UE), located in a communication coverage of a first base station and a second base station, comprising:
 a transceiver, exchanging information with the first base station and the second base station; and   a processor, coupled to the transceiver,   wherein the processor exchanges information with the first base station through the transceiver, the transceiver receives a first instruction message from the first base station, the processor transmits a reference message to the second base station through the transceiver according to the first instruction message, the transceiver receives a synchronization message from the second base station and receives a second instruction message from the first base station, the processor records a round-trip time (RTT) of transmitting and receiving the reference message and the synchronization message with the second base station according to the second instruction message and transmits the RTT to the first base station through the transceiver, wherein the reference message and the synchronization message are periodic signals.   
     
     
         2 . The user equipment according to  claim 1 , wherein the RTT comprises a time required by the UE for transmitting the reference message to the second base station, a time required by the second base station for transmitting the synchronization message to the UE and a time required by the second base station for processing the reference message. 
     
     
         3 . A timing synchronization method for base stations, adapted to a user equipment (UE) located in a communication coverage of a first base station and a second base station, the method comprising:
 exchanging information with the first base station;   receiving a first instruction message from the first base station and transmitting a reference message to the second base station according to the first instruction message, where the reference message is a periodic signal;   receiving a synchronization message from the second base station, wherein the synchronization message is a periodic signal;   receiving a second instruction message from the first base station and recording a round-trip time (RTT) of transmitting and receiving the reference message and the synchronization signal with the second base station according to the second instruction message; and   transmitting the RTT to the first base station.   
     
     
         4 . The method according to  claim 3 , wherein the RTT comprises a time required by the UE for transmitting the reference message to the second base station, a time required by the second base station for transmitting the synchronization message to the UE and a time required by the second base station for processing the reference message.