In a digital time division multiple access (TDMA) radio system, the transmission times of mobile stations in a cell are advanced in relation to the base station of the cell each by a timing advance which compensates for the transmission delay caused by the distance between the base station and the respective mobile station. Part of the radio capacity of the cell is arranged to serve only within a first given timing advance range, and thereby to serve mobile stations located within a first given area of the cell, and another part of the radio capacity is arranged to serve only within a second given timing advance range, which is different from the first timing advance range, and thereby to serve mobile stations located with a second given area of the cell. The first and second areas may partially overlap. Handoffs between channels of the capacity are accomplished on the basis of exceeding or falling below threshold timing advance values.