According to the present invention there is provided a method of transmitting user data in a TDMA system in which the number of channels is increased by partitioning at least one time-slot in a TDMA frame into at least two sub-time-slots. Each sub time-slot may be allocated to a different user. User data may be transmitted in each time slot in a burst structure, user data being transmitted in each sub time-slot in a corresponding burst structure. User data may be transmitted in each time slot in a burst structure having n bits and wherein each time slot is partitioned into m sub time slots, user data being transmitted in each sub time-slot in a corresponding burst structure having n/m bits.