## 3.3 Data channel at full rate, 12.0 kbit/s radio interface rate (9.6 kbit/s services (TCH/F9.6))

3GPP45.003GSM/EDGE Channel codingRelease 17TS

The definition of a 12.0 kbit/s radio interface rate data flow for data services is given in 3GPP TS 44.021.

### 3.3.1 Interface with user unit

The user unit delivers to the encoder a bit stream organized in blocks of 60 information bits (data frames) every 5 ms. Four such blocks are dealt with together in the coding process {d(0),…,d(239)}. For non‑transparent services those four blocks shall align with one 240‑bit RLP frame.

### 3.3.2 Block code

The block of 4 * 60 information bits is not encoded, but only increased with 4 tail bits equal to 0 at the end of the block.

u(k) = d(k) for k = 0,1,…,239

u(k) = 0 for k = 240,241,242,243 (tail bits)

### 3.3.3 Convolutional encoder

This block of 244 bits {u(0),…,u(243)} is encoded with the ½ rate convolutional code defined by the following polynomials:

G0 = 1 + D3 + D4

G1 = 1 + D + D3+ D4

resulting in 488 coded bits {C(0), C(1),…, C(487)} with

C(2k) = u(k) + u(k‑3) + u(k‑4)

C(2k+1) = u(k) + u(k‑1) + u(k‑3) + u(k‑4) for k = 0,1,…,243 ; u(k) = 0 for k < 0

The code is punctured in such a way that the following 32 coded bits:

{C(11+15j) for j = 0,1,…,31} are not transmitted.

The result is a block of 456 coded bits, {c(0),c(1),…, c(455)}

### 3.3.4 Interleaving

The coded bits are reordered and interleaved according to the following rule:

i(B,j) = c(n,k) for k = 0,1,…,455

n = 0,1,…,N,N + 1,…

B = B0 +4n + (k mod 19) + (k div 114)

j = (k mod 19) + 19 (k mod 6)

The result of the interleaving is a distribution of the reordered 114 bit of a given data block, n = N, over 19 blocks, 6 bits equally distributed in each block, in a diagonal way over consecutive blocks.

Or in other words the interleaving is a distribution of the encoded, reordered 456 bits from four given input data blocks, which taken together give n = N, over 22 bursts, 6 bits equally distributed in the first and 22^{nd} bursts, 12 bits distributed in the second and 21^{st} bursts, 18 bits distributed in the third and 20^{th} bursts and 24 bits distributed in the other 16 bursts.

The block of coded data is interleaved "diagonal", where a new block of coded data starts with every fourth burst and is distributed over 22 bursts.

### 3.3.5 Mapping on a Burst

The mapping is done as specified for TCH/FS in subclause 3.1.4. On bitstealing by a FACCH, see subclause 4.2.5.