GSM Noncombined Channel Configuration

This page details the GSM Noncombined channel configuration for Time Slots TS0 and TS1. It covers the 51-frame multiframe structure, mentioning the mapping of FCCH, SCH, BCCH, CCCH, and SDCCH channels on TS0 and TS1 for both downlink and uplink.

As mentioned in the GSM Channel Types documentation, in noncombined channel configurations, the signaling channels (SDCCH) are not combined with (FCCH+SCH+BCCH+CCCH) on time slot TS0. Instead, they are mapped on a separate time slot, TS1, as illustrated in the figure below.

In the noncombined case, there are nine CCCH blocks, labeled CCCH(0) to CCCH(8). If the System Information messages (SIs) are extensive and cannot be accommodated within the BCCH block, then the first CCCH block, CCCH(0), can also be utilized for BCCH, and the SIs are transmitted on it.

In a GSM system, the BS_AG_BLKS_RES parameter determines how many CCCH blocks are reserved for AGCH and how many are used for PCH. This parameter is a 3-bit field and is transmitted on BCCH SI-3. It ranges from 0 to 7. A value of 2 indicates that 2 blocks are reserved for AGCH, and the remaining 7 blocks are for PCH.

For more details, please visit the GSM Terminology page.

The GSM Noncombined channel configuration for TS0 is shown in the figure below.

As depicted in Figure 1, BCCH/CCCH is mapped in TS0. Figure 2 shows SDCCH mapped to TS1.

A total of 8 users can share a time slot. This is referred to as an SDCCH/8 combination. The “8” signifies that there are 8 total subchannels, and each is used by a different SDCCH user.

Figure 2 illustrates that there are 8 SDCCHs and 4 SACCHs in the downlink multiframe. This is because the rate of SDCCH is twice that of the SACCH channel.

The GSM Noncombined channel configuration for TS1 is illustrated in the figure above.