Disclosed is a method in a base station for providing a network access service to terminals. Where one of the terminals is selected as a source terminal and at least one of the other terminals is used as a relay node for relaying communication between the base station and the source terminal. Parameters for relay communication are initialized. A relay communication request message including that the parameters is transmitted. In response to the message, a terminal independently sets and performs the relay communication between the base station and the source terminal. Uplink signals are received from the source and relay terminals. The uplink signals received from the source and relay terminals are combined and decoded. A transmit diversity gain is obtained in uplink transmission of a terminal with a single antenna because relay nodes retransmit the source terminal's signal.