5.3 Channel organization

3GPP45.001General descriptionGSM/EDGE Physical layer on the radio pathRelease 17TS

The channel organization for the traffic channels (TCH), FACCHs and SACCH/T uses the 26‑frame multiframe. It is organized as described in figure 2, where only one time slot per TDMA frame is considered.

Figure 2: Traffic channel organization.

The FACCH is transmitted by pre-empting half or all of the information bits of the bursts of the TCH to which it is associated (see 3GPP TS 45.003).

The channel organization for the control channels (except FACCHs and SACCH/T) uses the 51‑frame multiframe. It is organized in the downlink and uplink as described in figure 3.

The channel organization for packet data channels uses the 52- multiframe. Full rate packet data channels in BTTI configuration are organized as described in figure 2a1, and in RTTI configuration in figure 2a3. Half rate packet data channels can be organized as described in figure 2a2.

52 TDMA Frames

X = Idle frame
T = Frame used for PTCCH
B0 – B11 = Radio blocks

Figure 2a1: 52- multiframe for PDCH/Fs in BTTI configuration.

Figure 2a2: 52- multiframe for PDCH/Hs.

Figure 2a3: 52- multiframe for a PDCH-pair in RTTI configuration.

In case of EC operation the multiframe structure for PDCH consists of 52 TDMA frames, divided into 12 blocks (of 4 frames) and 4 idle frames, see Figure 2a4. In EC operation, BTTI (and variants thereof, see 3GPP TS 43.064 [8] and 3GPP TS 45.003 [14]) is always used, and no frames are allocated for the PTCCH. In case blind physical layer transmissions are used, multiple BTTI blocks constitute the block that is mapped onto the physical channel, see Figure 2a4 to Figure 2a7, resulting in an effective TTI that is a multiple of the basic TTI of 20 ms. For an EC TBF assigned four consecutive PDCHs, the effective TTI is 20 ms for CC2, 40 ms for CC3, 80 ms for CC4 and 240 ms for CC5 (uplink only). For an EC TBF assigned two consecutive PDCHs, the effective TTI is 40 ms for CC2, 80 ms for CC3, 160 ms for CC4 and 480 ms for CC5 (uplink only).

Figure 2a4: Multiframe structure for EC-GSM-IoT using one PDCH for CC1 and four PDCHs for CC2 to CC4 in EC operation.

Figure 2a5: Multiframe structure for EC-GSM-IoT using two PDCHs for CC2 to CC4 in EC operation.

Figure 2a6: Multiframe structure for EC-GSM-IoT using four PDCHs for CC5 in EC operation

Figure 2a7: Multiframe structure for EC-GSM-IoT using two PDCHs for CC5 in EC operation.

For an uplink EC TBF assigned two consecutive PDCHs, compact burst mapping shall be used on an EC-PDTCH (see 3GPP TS 43.064 [8] and 3GPP TS 45.003 [14]).

The channel organization for CTS control channels uses the 52-multiframe. It is organized as described in figure 2b.

52 TDMA Frames

A: TDMA frame for CTSARCH

B: TDMA frame for CTSBCH

P: TDMA frame for CTSPCH

G: TDMA frame for CTSAGCH

X: Idle frame

Figure 2b: 52-multiframe for CTS.

Figure 3: Channel organization in the 51‑frame multiframe

Figure 3a: Channel organization in the 51‑frame multiframe for EC-GSM-IoT (TN1).