A base station (BS) of a mobile communication system receives a candidate list including a candidate remote radio head (RRH) adjacent to the UE, excluding at least one serving RRH connected to the UE, among a plurality of RRHs, from the UE, allocates a random access code index to at least one candidate RRH included in the candidate list, and subsequently transmits the random access code index allocated to the at least one candidate RRH to the UE.