A method, apparatus and system for increasing cell capacity through optional signal combining between Relay Stations (RSs) in a cellular system using wired RSs is disclosed. The method includes receiving, by a Base Station (BS), an average Carrier-to-Interference ratio (C/I) value of transmission signals from Mobile Stations (MSs) located inside each coverage area, being fed back from the RSs or the MSs in its corresponding cell; classifying the MSs into two groups according to the C/I value; performing resource allocation satisfying a minimum data rate from a corresponding RS, for MSs belonging to a group having a C/I value greater than a preset threshold Γ among the classified groups; performing resource allocation by applying an optional signal combining scheme taking into account two RSs having a highest C/I value, for MSs belonging to a group having a C/I value below the threshold among the classified groups; and allocating all unallocated subchannels of each individual RS in an order of an MS having a high C/I value among MSs of a corresponding RS until there is no more unallocated subchannel of each RS.