A method of operating a time division multiple access (TDMA) radio system having multi-slot capabilities and utilizing half-duplex transmission/reception where uplink and downlink user data transmissions between a mobile station (MS) 2 and a base station (BS) 3 are made in separate TDMA frames. A greater number of time slots are allocated to the mobile station 2 in each downlink TDMA frame than in each uplink TDMA frame to improve the efficiency of radio resource allocation and of the radio module 4 of the mobile station 2.