## 4.2.9 Insertion of discontinuous transmission (DTX) indication bits

25.2123GPPMultiplexing and channel coding (FDD)Release 17TS

In the downlink, DTX is used to fill up the radio frame with bits. The insertion point of DTX indication bits depends on whether fixed or flexible positions of the TrCHs in the radio frame are used. It is up to the UTRAN to decide for each CCTrCH whether fixed, pseudo-flexible (Subclause 4.2.7.2.1A), or flexible positions are used during the connection. DTX indication bits only indicate when the transmission should be turned off, they are not transmitted. Pseudo-flexible rate matching is always used when DL_DCH_FET_Config is configured by higher layers. Otherwise pseudo-flexible rate matching is not used.

#### 4.2.9.1 1^{st} insertion of DTX indication bits

This step of inserting DTX indication bits is used only if the positions of the TrCHs in the radio frame are fixed. With fixed position scheme a fixed number of bits is reserved for each TrCH in the radio frame.

The bits from rate matching are denoted by , where *G _{i}* is the number of bits in one TTI of TrCH

*i*. Denote the number of bits in one radio frame of TrCH

*i*by

*H*. Denote

_{i}*D*the number of bits output of the first DTX insertion block.

_{i}In TTIs containing no compressed frames or frames compressed by spreading factor reduction, *H _{i} *is constant and corresponds to the maximum number of bits from TrCH

*i*in one radio frame for any transport format of TrCH

*i*and

*D*

_{i}*=*

*F*

_{i}*H*.

_{i}The bits output from the DTX insertion are denoted by *h _{i1}, h _{i2}, h _{i3}, …, h _{iDi}*

_{ }Note that these bits are three valued. They are defined by the following relations:

* k = *1, 2, 3, …,* G _{i}*

* k = G _{i}+*1

*, G*2

_{i}+*, G*3

_{i}+*, …, D*

_{i}where DTX indication bits are denoted by **. Here *g _{ik} *{0, 1}

*and*

**{0, 1}.

In pseudo-flexible rate matching, the 1^{st} insertion of DTX indication bits is the same as the above for fixed position rate matching, with a difference that the above procedure is applied to each TTI independently of others.

#### 4.2.9.2 2^{nd} insertion of DTX indication bits

The DTX indication bits inserted in this step shall be placed at the end of the radio frame. Note that the DTX will be distributed over all slots after 2^{nd} interleaving.

The bits input to the DTX insertion block are denoted by ,where *S* is the number of bits from TrCH multiplexing. The number of PhCHs is denoted by *P* and the number of bits in one radio frame, including DTX indication bits, for each PhCH by *R*..

In non-compressed frames, , where *N _{data}*

_{1}and

*N*

_{data}_{2}are defined in [2].

For compressed frames, *N’ _{data,*}* is defined as . and are the number of bits in the data fields of the slot format used for the current compressed frame, i.e. slot format A or B as defined in [2] corresponding to the spreading factor and the number of transmitted slots in use.

In frames compressed by higher layer scheduling, additional DTX with respect to normal mode shall be inserted if the transmission time reduction does not exactly create a transmission gap of the desired *TGL*.

The number of bits available to the CCTrCH in one radio frame compressed by spreading factor reduction or by higher layer scheduling is denoted by and .

For frames compressed by spreading factor reduction .

For frames compressed by higher layer scheduling the exact value of is dependent on the *TGL* which is signalled from higher layers. It can be calculated as.

*N _{TGL}* is the number of bits that are located within the transmission gap and defined as:

, if , in first frame if , in second frame if |

*N _{first}* and

*TGL*are defined in subclause 4.4.

The bits output from the DTX insertion block are denoted by . Note that these bits are three valued. They are defined by the following relations:

k = 1, 2, 3, …, S

k = S+1, S+2, S+3, …, *PR*

where DTX indication bits are denoted by **. Here *s*_{k} {0,1, p}and ** {0,1}.