3.4 Data channel at full rate, 6.0 kbit/s radio interface rate (4.8 kbit/s services (TCH/F4.8))

3GPP45.003GSM/EDGE Channel codingRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

The definition of a 6.0 kbit/s radio interface rate data flow for data services is given in 3GPP TS 44.021.

3.4.1 Interface with user unit

The user unit delivers to the encoder a bit stream organized in blocks of 60 information bits (data frames) every 10 ms, {d(0),d(1),…,d(59)}.

In the case where the user unit delivers to the encoder a bit stream organized in blocks of 240 information bits every 40 ms (e.g. RLP frames), the bits {d(0),d(1),…,d(59),d(60),…,d(60+59), d(2*60),…,d(2*60+59), d(3*60),…,d(3*60+59)} shall be treated as four blocks of 60 bits each as described in the remainder of this clause. To ensure end‑to‑end synchronization of the 240 bit blocks, the resulting block after coding of the first 120 bits {d(0),d(1),…,d(60+59)} shall be transmitted in one of the transmission blocks B0, B2, B4 of the channel mapping defined in 3GPP TS 45.002.

3.4.2 Block code

Sixteen bits equal to 0 are added to the 60 information bits, the result being a block of 76 bits, {u(0),u(1),…,u(75)}, with:

u(19k+p) = d(15k+p) for k = 0,1,2,3 and p = 0,1,…,14;

u(19k+p) = 0 for k = 0,1,2,3 and p = 15,16,17,18.

Two such blocks forming a block of 152 bits {u'(0),u'(1),…,u'(151)} are dealt with together in the rest of the coding process:

u'(k) = u1(k), k = 0,1,…,75 (u1 = 1^st block)

u'(k+76) = u2(k), k = 0,1,…,75 (u2 = 2^nd block)

3.4.3 Convolutional encoder

This block of 152 bits is encoded with the convolutional code of rate 1/3 defined by the following polynomials:

G1 = 1 + D + D3 + D4

G2 = 1 + D2 + D4

G3 = 1 + D + D2 + D3 + D4

The result is a block of 3 * 152 = 456 coded bits, {c(0),c(1),…,c(455)}:

c(3k) = u'(k) + u'(k‑1) + u'(k‑3) + u'(k‑4)

c(3k+1) = u'(k) + u'(k‑2) + u'(k‑4)

c(3k+2) = u'(k) + u'(k‑1) + u'(k‑2) + u'(k‑3) + u'(k‑4) for k = 0,1,…,151;

u'(k) = 0 for k < 0

3.4.4 Interleaving

The interleaving is done as specified for the TCH/F9.6 in subclause 3.3.4.

3.4.5 Mapping on a Burst

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