A method of obtaining resource allocation at a user equipment in a mobile communication system using a plurality of subcarriers, the method comprising: generating a preamble sequence according to a user equipment identifier to identify the user equipment if a signaling message to be transmitted is generated by the user equipment; being characterized in that the method further comprises: transmitting an Orthogonal Frequency Division Multiplexing, OFDM, subframe including the preamble sequence and the signaling message to a base station without a scheduling from the base station, wherein the preamble sequence is included in a first OFDM symbol of the OFDM subframe and the signaling message is included in an OFDM symbol behind the first OFDM symbol; and receiving from the base station an acknowledgement signal for the preamble sequence and resource allocation information for an uplink shared channel, after transmitting the preamble sequence and the signaling message, wherein the acknowledgement signal is generated according to the user equipment identifier, wherein the signaling message includes buffer status information, power headroom information and service type information, wherein the service type information indicates whether data to be transmitted needs a real-time transmission or not. generating a preamble sequence according to a user equipment identifier to identify the user equipment if a signaling message to be transmitted is generated by the user equipment; being characterized in that the method further comprises: transmitting an Orthogonal Frequency Division Multiplexing, OFDM, subframe including the preamble sequence and the signaling message to a base station without a scheduling from the base station, wherein the preamble sequence is included in a first OFDM symbol of the OFDM subframe and the signaling message is included in an OFDM symbol behind the first OFDM symbol; and receiving from the base station an acknowledgement signal for the preamble sequence and resource allocation information for an uplink shared channel, after transmitting the preamble sequence and the signaling message, wherein the acknowledgement signal is generated according to the user equipment identifier, wherein the signaling message includes buffer status information, power headroom information and service type information, wherein the service type information indicates whether data to be transmitted needs a real-time transmission or not. transmitting an Orthogonal Frequency Division Multiplexing, OFDM, subframe including the preamble sequence and the signaling message to a base station without a scheduling from the base station, wherein the preamble sequence is included in a first OFDM symbol of the OFDM subframe and the signaling message is included in an OFDM symbol behind the first OFDM symbol; and receiving from the base station an acknowledgement signal for the preamble sequence and resource allocation information for an uplink shared channel, after transmitting the preamble sequence and the signaling message, wherein the acknowledgement signal is generated according to the user equipment identifier, wherein the signaling message includes buffer status information, power headroom information and service type information, wherein the service type information indicates whether data to be transmitted needs a real-time transmission or not.