2.1 General organization

3GPP45.003GSM/EDGE Channel codingRelease 17TS

Each channel has its own coding and interleaving scheme. However, the channel coding and interleaving is organized in such a way as to allow, as much as possible, a unified decoder structure.

Each channel uses the following sequence and order of operations:

‑ the information bits are coded with a systematic block code, building words of information + parity bits;

‑ these information + parity bits are encoded with a convolutional code or a turbo code, building the coded bits;

‑ reordering and interleaving the coded bits, and adding a stealing flag, gives the interleaved bits.

All these operations are made block by block, the size of which depends on the channel. However, most of the channels use a block of either 456 coded bits or 1368 coded bits, corresponding to 456 coded symbols, which is interleaved and mapped onto bursts in a very similar way for all of them. This block of 456 coded symbols is the basic structure of the channel coding scheme. Figures 1a, 1b, 1c, 1d, 1ea, 1eb, 1f, 1g, 1h, 1i, 1j, 1k, 1l, 2 and 2aa give diagrams showing the general structure of the channel coding.

In the case of full rate speech TCH, a block of 456 coded bits carries the information of one speech frame. In case of control channels, it carries one message.

In the case of half rate speech TCH, the information of one speech frame is carried in a block of 228 coded bits.

In the case of the Enhanced full rate speech the information bits coming out of the source codec first go through a preliminary channel coding. Then the channel coding as described above takes place.

In the case of 8-PSK modulated speech TCH, the information of one speech frame is carried in a block of 1368 coded bits (456 coded symbols) for full rate channels or 684 coded bits (228 coded symbols) for half rate channels.

In the case of a packet switched channel the block of 456, 1096, 1384, 1848, 2200, 2312 or 2748 coded bits carries one RLC/MAC block.

In the case of E-TCH/F28.8 or E-TCH/F43.2, the block of 1368 coded bits (456 coded symbols) carries one radio interface data block. In the case of E-TCH/F32.0, the block of 1392 coded bits (464 coded symbols) carries one radio interface data block.

In the case of FACCH, a coded message block of 456 bits is divided into eight sub‑blocks. The first four sub‑blocks are sent by stealing the even numbered bits of four timeslots in consecutive frames used for the TCH. The other four sub‑blocks are sent by stealing the odd numbered bits of the relevant timeslot in four consecutive used frames delayed 2 or 4 frames relative to the first frame. Along with each block of 456 coded bits there is, in addition, a stealing flag (8 bits), indicating whether the block belongs to the TCH or to the FACCH. In the case of SACCH, BCCH, CCCH or CTSCCH, this stealing flag is dummy. In the case of a packet switched channel, these bits are used to indicate the coding scheme used.

In the case of E-FACCH/F, a coded message block of 456 bits is divided into four sub-blocks. The four sub-blocks are sent by stealing all symbols of four timeslots in consecutive frames used for the E-TCH and using GMSK modulation. The indication of the E-FACCH/F is based on the identification of the modulation. Along with each block of 456 coded bits there is, in addition, a stealing flag (8 bits), indicating whether the block belongs to the E-FACCH, FACCH or TCH.

Some cases do not fit in the general organization, and use short blocks of coded bits which are sent completely in one timeslot. They are the random access messages of:

– the RACH;

– or PRACH, CPRACH and MPRACH;

on uplink and the synchronization information broadcast on the SCH or CSCH on the downlink. In CTS, they are the access request message of the CTSARCH on uplink and the information broadcast on the CTSBCH-SB on downlink.

In the coding/multiplexing unit of FLO, error detection, forward error correction and rate matching is applied to each transport channel independently. However the transport channels share a common multiplexing, TFCI mapping, interleaving and burst mapping. All these operations are made every transmission time interval and the number of coded bits produced by the coding/multiplexing unit depends on the basic physical subchannel. In the case of full rate GMSK basic physical subchannel, blocks of 464 bits are produced. In the case of half rate GMSK basic physical subchannel, blocks of 232 bits are produced. In the case of full rate 8PSK basic physical subchannel, blocks of 1392 bits are produced. In the case of half rate 8PSK basic physical subchannel, blocks of 696 bits are produced.

For EC-GSM-IoT, the same nine modulation and coding schemes as for EGPRS are defined for the extended coverage packet data traffic channels (EC-PDTCH). In addition three modulation and coding schemes employing MCS-1 and blind physical layer transmissions are defined for EC-PDTCH. For extended coverage common control channels in downlink (EC-CCCH/D) and the extended coverage packet associated control channel (EC-PACCH/U and EC-PACCH/D), three coding schemes having the same structure, differing mainly in message size and puncturing, are defined. The encoded bits are mapped onto a single burst, which is transmitted using blind physical layer transmissions. The extended coverage broadcast control channel (EC-BCCH) uses the same coding scheme as the broadcast control channel (BCCH) with subsequent blind physical layer transmissions. The extended coverage synchronization channel (EC-SCH) uses the same coding scheme as the synchronization channel (SCH), with subsequent blind physical layer transmissions and cyclic bit shifting. The extended coverage random access channel (EC-RACH) uses the same coding scheme as the random access channel (RACH), with subsequent blind physical layer transmissions, with the exception of the EC-RACH used for coverage class CC5, that applies modified coding schemes with subsequent blind physical layer transmissions. Figures 1m, 1n, 2ab, 2ac, 2ad, 2ae,2af and 2ag give diagrams showing the general structure of the channel coding for EC-channels.

Figure 1a: Channel Coding and Interleaving Organization for speech, circuit switched data and GPRS packet data channels

In each box, the last line indicates the subclause defining the function. In the case of data TCHs, N0, N1 and n depend on the type of data TCH. In the case of PDTCH, Q0, Q1 and n depend on the coding scheme.

Interfaces:

0) speech bits from the speech encoder (s);

1) information bits (d);

2) information + parity + tail bits (u);

3) coded bits (c);

4) interleaved bits (e).

Figure 1b: Channel Coding and Interleaving Organization, adaptive multi-rate speech

In each box, the last line indicates the subclause defining the function.

Interfaces:

0) speech bits from the speech encoder (s);

1) reordered speech bits (d);

2) speech + parity + tail bits (u);

3) coded bits (c);

4) interleaved bits (e).

Figure 1c: Channel Coding and Interleaving Organization, wide-band adaptive multi-rate speech

Figure 1d: Channel Coding and Interleaving Organization for ECSD 8-PSK modulated signals

In each box, the last line indicates the subclause defining the function.

Figure 1ea: Channel Coding and Interleaving Organization for EGPRS Uplink Packet Data Channels

In each box, the last line indicates the subclause defining the function.

Figure 1eb: Channel Coding and Interleaving Organization for EGPRS Downlink Packet Data Channels

In each box, the last line indicates the subclause defining the function.

Figure 1f: Channel Coding and Interleaving Organization for EGPRS2-A Uplink Packet Data Channels

In each box, the last line indicates the subclause defining the function.

Figure 1g: Channel Coding and Interleaving Organization for EGPRS2-B Uplink Packet Data Channels, UBS-5 to UBS-9

In each box, the last line indicates the subclause defining the function.

Figure 1h: Channel Coding and Interleaving Organization for EGPRS2-B Uplink Packet Data Channels, UBS-10 to UBS-12

In each box, the last line indicates the subclause defining the function.

Figure 1i: Channel Coding and Interleaving Organization for EGPRS2-A Downlink Packet Data Channels, DAS-5 to DAS-9

In each box, the last line indicates the subclause defining the function.

Figure 1j: Channel Coding and Interleaving Organization for EGPRS2-A Downlink Packet Data Channels, DAS-10 to DAS-12

In each box, the last line indicates the subclause defining the function.

Figure 1k: Channel Coding and Interleaving Organization for EGPRS2-B Downlink Packet Data Channels, DBS-5 to DBS-9

Figure 1l: Channel Coding and Interleaving Organization for EGPRS2-B Downlink Packet Data Channels, DBS-10 to DBS-12

In each box, the last line indicates the subclause defining the function.

Figure 1m: Channel Coding and Interleaving Organization for EC-GSM-IoT Downlink Packet Data Traffic Channels

Figure 1n: Channel Coding and Interleaving Organization for EC-GSM-IoT Uplink Packet Data Traffic Channels (MCS-1/M is used for CC1 to CC4, MCS-1’/48 for CC5.)

In each box, the last line indicates the subclause defining the function. M denotes the number of blind physical layer transmissions, see subclause 5.1b.2.2 and 5.1b.3.2 for the downlink and uplink respectively.

Figure 2: Channel Coding and Interleaving Organization for control channels except PACCH, EC-BCCH, EC-SCH, EC-CCCH and EC-PACCH

In each box, the last line indicates the subclause defining the function. In the case of RACH, PRACH and of MPRACH using Packet Access Burst, P0 = 8 and P1 = 18; in the case of PRACH and of MPRACH using Extended Packet Access Burst, P0 = 11 and P1 = 21; in the case of SCH, CSCH, CTSBCH-SB and CTSARCH, P0 = 25 and P1 = 39.

Figure 2aa: Channel Coding and Interleaving Organization for PACCH

In each box, the last line indicates the subclause defining the function.

Figure 2ab: Channel Coding and Interleaving Organization for EC-BCCH

Figure 2ac: Channel Coding and Interleaving Organization for EC-SCH

Figure 2ad: Channel Coding and Interleaving Organization for EC-CCCH/D and EC-PACCH/U

Figure 2ae: Channel Coding and Interleaving Organization for EC-PACCH/D

Figure 2af: Channel Coding and Interleaving Organization for EC-RACH (M=1, 4, 16, 48 is used for CC1, CC2, CC3, CC4 and M=132 for CC5).

Figure 2ag: Channel Coding Organization for EC-RACH (M=66)

In each box, the last line indicates the subclause defining the function. M denotes the number of blind physical layer transmissions.