5A Physical channels for the 1.28 Mcps option
25.2213GPPPhysical channels and mapping of transport channels onto physical channels (TDD)Release 17TS
All physical channels take three-layer structure with respect to timeslots, radio frames and system frame numbering (SFN), see [14]. Depending on the resource allocation, the configuration of radio frames or timeslots becomes different. All physical channels need guard symbols in every timeslot. The time slots are used in the sense of a TDMA component to separate different user signals in the time and the code domain. The physical channel signal format for 1.28Mcps TDD is presented in figure 18A.
A physical channel in TDD is a burst, which is transmitted in a particular timeslot within allocated Radio Frames. The allocation can be continuous, i.e. the time slot in every frame is allocated to the physical channel or discontinuous, i.e. the time slot in a subset of all frames is allocated only. A burst is the combination of a data part, a midamble and a guard period or only a midamble for standalone midamble channel. The duration of a burst is one time slot. Note when in the entire carrier dedicated to MBSFN operation, a burst is the combination of a preamble and a data part. Several bursts can be transmitted at the same time from one transmitter. In this case, the data part must use different OVSF channelisation codes, but the same scrambling code. The midamble part has to use the same basic midamble code, but can use different midambles. In a multi-frequency cell the midamble parts in different carrier shall also have to use the same basic midamble code, but can use different midambles. Note when in MBSFN operation, a midamble or preamble is not necessarily cell-specific.
Figure 18A: Physical channel signal format for 1.28Mcps TDD option
The data part of the burst is spread with a combination of channelisation code and scrambling code. The channelisation code is a OVSF code, that can have a spreading factor of 1, 2, 4, 8, or 16. The data rate of the physical channel is depending on the used spreading factor of the used OVSF code.
So a physical channel is defined by frequency, timeslot, channelisation code, burst type and Radio Frame allocation. The scrambling code and the basic midamble code or preamble code are broadcast and may be constant within a cell. When a physical channel is established, a start frame is given. The physical channels can either be of infinite duration, or a duration for the allocation can be defined.