5B.1 General

25.2213GPPPhysical channels and mapping of transport channels onto physical channels (TDD)Release 17TS

All physical channels take a three-layer structure with respect to timeslots, radio frames and system frame numbering (SFN). Depending on the resource allocation, the configuration of radio frames or timeslots becomes different. All physical channels need a guard period in every timeslot. The time slots are used in the sense of a TDMA component to separate different user signals in the time domain. The physical channel signal format is presented in figure 18AA.

A physical channel in the 7.68Mcps TDD option 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 two data parts, a midamble part and a guard period. The duration of a burst is one time slot. Several bursts can be transmitted at the same time from one transmitter. In this case, the data parts must use different OVSF channelisation codes, but the same scrambling code. The midamble parts are either identically or differently shifted versions of a cell-specific basic midamble code, see section 5B.3.3. Note when in MBSFN operation, a midamble is not necessarily cell-specific.

Figure 18AA: Physical channel signal format

The data part of the burst is spread with a combination of channelisation code and scrambling code. The channelisation code is an OVSF code, that can have a spreading factor of 1, 2, 4, 8, 16 or 32. The data rate of the physical channel depends on the used spreading factor of the used OVSF code.

The midamble part of the burst can contain two different types of midambles: a short one of length 512 chips, or a long one of length 1024 chips. The data rate of the physical channel depends on the used midamble length. Additionally, when in MBSFN operation a midamble of length 640 chips is used.

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 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 of a duration defined by allocation.