Air interface framing is illustrated as in figure below. A super frame is made up of 4096 radio frames. Each radio frame is made up of 15 timeslots. A timeslot can be allocated to either UL (uplink) and DL (downlink) transmission.

Within each timeslot several Resource Units (RUs) (sometime termed “codes” or “bursts”) can be supported. An RU is defined as a single code within a single timeslot. As defined in 3GPP TD-CDMA downlink supports two spreading factor, SF1 and SF16. IPWireless implements both SF1 and SF16 for the downlink.

Thus, the maximum number of codes supported in the DL is 16xSF16 or 1xSF1 code per time slot. When using SF16, the minimum code granularity on the downlink is 4, meaning that each user gets assigned at least 4 codes. The upper bound on the number of multiples of 4 codes allocated per slot is determined by C/I conditions and traffic conditions. On the uplink, spreading factor 1, 2, 4, 8, and 16 are allowed.
In a public wide-area TDD system such as that of IPWireless the UL and DL transmissions are synchronized to eliminate the possibility of NodeB-to-NodeB and UE-to-UE interference.