A method of communicating data in a wireless communications system, the method comprising: receiving, by a mobile terminal, first control information, wherein the first control information is related to bitmap configuration information, wherein the bitmap configuration information indicates a number of groups created by dividing all of a plurality of random access preambles, wherein the one or more of the plurality of random access preambles in each of the groups are indicated by the bitmap configuration information, and wherein the bitmap configuration information is received from a network via a radio resource control signal; transmitting, by the mobile terminal, a first random access preamble; receiving, by the mobile terminal, second control information via a control channel within a time window, wherein the second control information is related to bitmap information and the control channel is a physical downlink control channel, and wherein the second control information consists of 16 bits radio network temporary identity implicitly encoded in 16 bits cyclic redundancy check, 3 bits modulation and coding scheme, 2 bits retransmission sequence number, and a number of reserved bits; determining, by the mobile terminal, whether a group including the transmitted first random access preamble is matched with a group indicated by the received second control information, wherein the group including the transmitted first random access preamble is classified by the first control information; and transmitting, by the mobile terminal, a second random access preamble if it is determined that the group including the transmitted first random access preamble is not matched with the group indicated by the received second control information. receiving, by a mobile terminal, first control information, wherein the first control information is related to bitmap configuration information, wherein the bitmap configuration information indicates a number of groups created by dividing all of a plurality of random access preambles, wherein the one or more of the plurality of random access preambles in each of the groups are indicated by the bitmap configuration information, and wherein the bitmap configuration information is received from a network via a radio resource control signal; transmitting, by the mobile terminal, a first random access preamble; receiving, by the mobile terminal, second control information via a control channel within a time window, wherein the second control information is related to bitmap information and the control channel is a physical downlink control channel, and wherein the second control information consists of 16 bits radio network temporary identity implicitly encoded in 16 bits cyclic redundancy check, 3 bits modulation and coding scheme, 2 bits retransmission sequence number, and a number of reserved bits; determining, by the mobile terminal, whether a group including the transmitted first random access preamble is matched with a group indicated by the received second control information, wherein the group including the transmitted first random access preamble is classified by the first control information; and transmitting, by the mobile terminal, a second random access preamble if it is determined that the group including the transmitted first random access preamble is not matched with the group indicated by the received second control information.