Method and apparatus for obtaining synchronization for communication between devices

Abstract

A method and an apparatus for obtaining synchronization of a terminal for communication between devices when a base station collapses are provided. The method includes, when a preamble signal is not received from the base station, maintaining a first synchronization for a predetermined time using a timer, transmitting a first preamble signal at a first synchronization point, performing a synchronization procedure with at least one neighbor terminal based on the first preamble signal, and, after the synchronization procedure, performing communication with the at least one neighbor terminal. In addition, when a preamble signal is not received from a base station, a first preamble signal from a relevant neighbor terminal is monitored for a predetermined time. When the first preamble signal is not received from the relevant neighbor terminal for the predetermined time, a second preamble signal is transmitted at an arbitrary point.

What is claimed is: 
     
         1 . A method for operating a terminal, the method comprising:
 monitoring a synchronization signal from a base station;   transmitting a first synchronization signal based on a synchronization with the base station; and   performing communication with a neighbor terminal which receives the first synchronization signal from the terminal.   
     
     
         2 . The method of  claim 1 , wherein the first synchronization signal indicates that the terminal fails to receive the synchronization signal from the base station. 
     
     
         3 . The method of  claim 1 , further comprising:
 monitoring the synchronization signal received from the base station;   if the synchronization signal is received from the base station, performing synchronization based on the synchronization signal; and   performing communication with the base station.   
     
     
         4 . The method of  claim 1 , wherein the first synchronization signal comprises a sequence which is different from sequences for the synchronization signal transmitted by the base station. 
     
     
         5 . The method of  claim 1 , wherein the transmitting the first synchronization signal comprises transmitting the first synchronization signal, if the terminal fails to receive the synchronization signal from the base station. 
     
     
         6 . The method of  claim 1 , wherein the performing communication comprises performing communication directly between devices. 
     
     
         7 . The method of  claim 1 , wherein the first synchronization signal indicates that the base station has collapsed. 
     
     
         8 . The method of  claim 1 , wherein the synchronization signal from the base station is used to as a synchronization signal and as information for distinguishing the base station. 
     
     
         9 . A method for operating a terminal, the method comprising:
 monitoring a synchronization signal from a base station;   monitoring a first synchronization signal from a neighbor terminal;   transmitting a second synchronization signal, if the terminal fails to receive the first synchronization signal; and   performing communication with a first neighbor terminal which receives the second synchronization signal.   
     
     
         10 . The method of  claim 9 , wherein the first synchronization signal indicates that the terminal fails to receive the synchronization signal from the base station. 
     
     
         11 . The method of  claim 9 , further comprising:
 monitoring a synchronization signal from a base station; and   if the synchronization signal is received from the base station, performing synchronization based on the synchronization signal to communicate with the base station.   
     
     
         12 . The method of  claim 9 , further comprising:
 monitoring a first synchronization signal from a second neighbor terminal; and   if the first synchronization signal is received from the second neighbor terminal, performing synchronization based on the first synchronization signal to communicate with the second neighbor terminal.   
     
     
         13 . The method of  claim 12 , further comprising:
 monitoring a synchronization signal from a base station; and   if the synchronization signal is received from the base station, performing synchronization based on the synchronization signal to communicate with the base station.   
     
     
         14 . The method of  claim 9 , further comprising:
 monitoring a synchronization signal from a base station and a first synchronization signal from a relevant neighbor terminal; and   maintaining synchronization with the first neighbor terminal, if the terminal fails to receive the synchronization signal from the base station and the first synchronization signal from the neighbor terminal.   
     
     
         15 . The method of  claim 9 , wherein the transmitting a first synchronization signal comprises transmitting the first synchronization signal, if the terminal fails to receive the synchronization signal from the base station. 
     
     
         16 . The method of  claim 9 , wherein the performing communication comprises performing communication directly between devices. 
     
     
         17 . The method of  claim 9 , wherein the first synchronization signal indicates that the base station has collapsed. 
     
     
         18 . The method of  claim 9 , wherein the synchronization signal from the base station is used to as a synchronization signal and as information which is used for distinguishing the base station. 
     
     
         19 . The method of  claim 9 , wherein the second synchronization signal comprises a sequence which is different from sequences for the synchronization signal transmitted by the base station. 
     
     
         20 . The method of  claim 9 , wherein the first synchronization signal is transmitted based on a synchronization with the base station. 
     
     
         21 . The method of  claim 9 , wherein the second synchronization signal indicates that the terminal fails to receive the synchronization signal from the base station. 
     
     
         22 . An apparatus for a terminal, the apparatus comprising:
 a controller configured to monitor a synchronization signal from a base station; and   a transmitter configured to, transmit a first synchronization signal based on synchronization with the base station,   wherein the controller is further configured to perform communication with a neighbor terminal which receives the first synchronization signal from the terminal.   
     
     
         23 . The apparatus of  claim 22 , wherein the first synchronization signal indicates that the terminal fails to receive the synchronization signal from the base station. 
     
     
         24 . The apparatus of  claim 22 , wherein the controller is further configured to:
 monitor the synchronization signal received from the base station;   perform synchronization based on the synchronization signal if the synchronization signal is received from the base station; and   perform communication with the base station.   
     
     
         25 . The apparatus of  claim 22 , wherein the first synchronization signal comprises a sequence which is different from sequences for the synchronization signal transmitted by the base station. 
     
     
         26 . The apparatus of  claim 22 , wherein the transmitter transmits the first synchronization signal based on a synchronization with the base station if the terminal fails to receive the synchronization signal from the base station. 
     
     
         27 . The apparatus of  claim 22 , wherein the controller is further configured to perform communication directly between devices. 
     
     
         28 . The apparatus of  claim 22 , wherein the first synchronization signal indicates that the base station has collapsed. 
     
     
         29 . The apparatus of  claim 22 , wherein the synchronization signal from the base station is used to as a synchronization signal and as information which is used for distinguishing the base station. 
     
     
         30 . An apparatus for a terminal, the apparatus comprising:
 a controller configured to monitor a synchronization signal from a base station, and, to monitor a first synchronization signal from a neighbor terminal, if the terminal fails to receive the synchronization signal from the base station; and   a transmitter configured to transmit a second synchronization signal,   wherein the controller is further configured to perform communication with the at least one neighbor terminal which receives the second synchronization signal.   
     
     
         31 . The apparatus of  claim 30 , wherein the first synchronization signal indicates that the terminal fails to receive the synchronization signal from the base station. 
     
     
         32 . The apparatus of  claim 30 , wherein the controller is further configured to monitor a synchronization signal from a base station; and
 to perform synchronization based on the synchronization signal to communicate with the base station if the synchronization signal is received from the base station.   
     
     
         33 . The apparatus of  claim 30 , wherein the controller is further configured to monitor a first synchronization signal from a second neighbor terminal, and to perform synchronization based on the first synchronization signal to communicate with the second neighbor terminal if the first synchronization signal is received from the second neighbor terminal. 
     
     
         34 . The apparatus of  claim 33 , wherein the controller is further configured to monitor a synchronization signal from a base station, and, to perform synchronization based on the synchronization signal to communicate with the base station if the synchronization signal is received from the base station. 
     
     
         35 . The apparatus of  claim 30 , wherein the controller is further configured to monitor a synchronization signal from a base station and a first synchronization signal from a neighbor terminal, and to maintain synchronization with the first neighbor terminal if the terminal fails to receive the synchronization signal from the base station and the first synchronization signal from the neighbor terminal. 
     
     
         36 . The apparatus of  claim 30 , wherein the second synchronization signal comprises a sequence which is different from sequences for the synchronization signal transmitted by the base station. 
     
     
         37 . The apparatus of  claim 30 , wherein the first synchronization signal is transmitted based on a synchronization with the base station. 
     
     
         38 . The apparatus of  claim 30 , wherein the second synchronization signal indicates that the terminal fails to receive the synchronization signal from the base station. 
     
     
         39 . The apparatus of  claim 30 , wherein the transmitter transmits the first synchronization signal based on a synchronization with the base station if the terminal fails to receive the synchronization signal from the base station. 
     
     
         40 . The apparatus of  claim 30 , wherein the controller is configured to perform communication directly between devices. 
     
     
         41 . The apparatus of  claim 30 , wherein the first synchronization signal indicates that the base station has collapsed. 
     
     
         42 . The apparatus of  claim 30 ,
 wherein the synchronization signal from the base station is used to as a synchronization signal and as information which is used for distinguishing the base station.