dio frames). Several bursts can be transmit- ted at the same time from one transmitter. In this case, the data part must use different OVSF channelization codes, but the same scrambling code. The midamble part has to use the same basic midamble code, but can use different midambles [6]. The data part of the burst has a combined spread of channelization and scrambling codes. The OVSF channelization code can have a spreading factor of 1, 2, 4, 8, or 16, where the data rate of the physical channel will depend on the spreading factor used. The midamble part of the burst may contain two different types of midambles, i.e. a short one with a length of 256 chips, or a long one with 512 chips. The midamble size also has an impact on the data rate of the physical channel. In the absence of AICH the terminal resends preamble with higher power in the next available slot. 11 When the RACH transmits data, the SF and thereby the data rate fluctuate. 12 Identical to all cells. The UMTS Network and Radio Access Technology Thus, we define a TDD physical channel by frequency, time slot, channelization code, burst type and radio frame allocation. Scrambling and basic midamble codes broadcast may be constant within a cell. After the physical channel establishment a frame start event occurs with infinite or limited duration. Radio Frame (10ms) frame #i frame #i+1 Time Slot (2560*Tc) timeslot #0 timeslot #1 timeslot #2 timeslot #13 timeslot #14 Figure 4.40 Physical channel signal format. 4.4.1 Frame Structure As in the FDD mode, a TDMA frame in the TDD mode has a duration of 10 ms with a sub-division into 15 time slots (TS) of 2560 X T duration each. Hence, a TS corre- sponds to 2560 chips, each allocated to either the uplink or the downlink as illustrated in Figure 4.41. This flexibility allows the TDD mode to adapt itself to different environ- ments and deployment scenarios. Nonetheless, in any configuration there must be at least one time slot on the downlink and at least one time slot in the uplink. Frequency 10 ms Mchip/s 2560*T 1