The present document is an introduction to the 45 series of the digital cellular telecommunications systems GSM technical specifications. It is not of a mandatory nature, but consists of a general description of the organization of the physical layer with reference to the technical specifications where each part is specified in detail. It introduces furthermore, the reference configuration that will be used throughout this series of technical specifications.

The radio subsystem provides a certain number of logical channels that can be separated into two categories according to TS 44.003, TS 43.064 and TS 43.052:

1. The traffic channels (TCH): they are intended to carry two types of user information streams: encoded speech and data. The following types of traffic channels are defined: Bm or full rate (TCH/F), Lm or half rate (TCH/H), cell broadcast (CBCH), full rate packet data ((EC-)PDTCH/F) and half rate packet data (PDTCH/H) traffic channels. For the purpose of this series of technical specifications, the following traffic channels are distinguished:
   • full rate speech TCH (TCH/FS);
   • enhanced full rate speech TCH (TCH/EFS)
   • half rate speech TCH (TCH/HS);
   • adaptive full rate speech TCH (TCH/AFS);
   • adaptive half rate speech TCH (TCH/AHS);
   • adaptive half rate 8-PSK speech TCH (O-TCH/AHS);
   • adaptive full rate wideband speech (TCH/WFS)
   • adaptive full rate 8-PSK wideband speech (O-TCH/WFS)
   • adaptive half rate 8-PSK wideband speech (O-TCH/WHS)
   • 28,8 kbit/s full rate data E-TCH (E-TCH/F28.8);
   • 32,0 kbit/s full rate data E-TCH (E-TCH/F32.0);
   • 43,2 kbit/s full rate data E-TCH (E-TCH/F43.2);
   • 14,4 kbit/s full rate data TCH (TCH/F14.4);
   • 9,6 kbit/s full rate data TCH (TCH/F9.6);
   • 4,8 kbit/s full rate data TCH (TCH/F4.8);
   • 4,8 kbit/s half rate data TCH (TCH/H4.8);
   • * 2,4 kbit/s full rate data TCH (TCH/F2.4);
   • * 2,4 kbit/s half rate data TCH (TCH/H2.4);
   • cell broadcast channel (CBCH);
   • full rate packet data traffic channel (PDTCH/F);
   • extended coverage full rate packet data traffic channel (EC-PDTCH/F);
   • half rate packet data traffic channel (PDTCH/H).
   Adaptive speech traffic channels are channels for which part of the radio bandwidth is reserved for transmission of in band signalling to allow in call adaptation of the speech and channel codec. 8 full rate block structures for TCH/AFS, 8 half rate block structures for O-TCH/AHS, 6 half rate block structures for TCH/AHS, 3 full rate block structures for TCH/WFS, 5 full rate block structures for O-TCH/WFS and 3 half rate block structures for O-TCH/WHS are defined.
   All channels are bi directional unless otherwise stated. Unidirectional downlink full rate channels, TCH/FD are defined as the downlink part of the corresponding TCH/F. Unidirectional uplink full rate channels are FFS.
   The assigned uplink and downlink (EC-)PDTCHs are used independently of each other. Dependent assignment of uplink and downlink is possible. A PDTCH/F may be defined either in BTTI configuration or in RTTI configuration. An EC-PDTCH/F shall be defined in BTTI configuration. When blind physical layer transmissions are used on EC-PDTCH, variants of the BTTI configuration are used, see TS 43.064 and TS 45.003.
   Multislot configurations for circuit switched connections are defined as multiple (1 up to 8) full rate channels assigned to the same MS. At least one channel shall be bi directional (TCH/F). The multislot configuration is symmetric if all channels are bi directional (TCH/F) and asymmetric if at least one channel is unidirectional (TCH/FD).
   High Speed Circuit Switched Data (HSCSD) is an example of multislot configuration, in which all channels shall have the same channel mode.
   Multislot configurations for packet switched connections are defined as multiple (1 up to 8) (EC-)PDTCH/Us and one (EC-)PACCH for one mobile originated communication, or multiple (1 up to 8) (EC-)PDTCH/Ds and one (EC-)PACCH for one mobile terminated communication respectively, assigned to the same MS. In this context "assignment" refers to the list of PDCHs in BTTI configuration or PDCH-pairs in RTTI configuration that may dynamically carry the (EC-)PDTCHs for that specific MS. One exception applies in case of EC operation where the PDCHs of a mobile originated communication carry the EC-PDTCHs by means of a fixed uplink allocation.
   The (EC-)PACCH shall have the same TTI configuration as the (EC-)PDTCH that it is associated with. The rules for mapping of (EC-)PACCH onto physical channels are specified in TS 44.060. In the case of point-to-multipoint transmission for MBMS, multiple (1 up to 5) PDTCH/Ds and one PACCH can be assigned for simultaneous communication with multiple mobiles.
   Multislot configurations for dual transfer mode are defined as one bi-directional, traffic channel (TCH/H, O TCH/H, TCH/F, O-TCH/F or E-TCH/F) and one packet channel combination. The packet channel combination may consist of multiple PDTCH/Us and one PACCH for one mobile originated communication, or multiple PDTCH/Ds and one PACCH for one mobile terminated communication respectively, assigned to the same MS. The PDTCHs may be transmitted either in BTTI configuration or in RTTI configuration. The rules for mapping of PACCH onto physical channels are specified in TS 44.060.
   An MS capable of dual transfer mode (DTM) shall support, as a minimum, DTM multislot class 5, which utilises the two-timeslot channelization method, i.e. a single TCH/F or O TCH/F plus a single PDTCH/F. In addition, the MS supporting DTM shall support TCH/H + PDCH/F configuration with the adaptive multirate (AMR) speech coder for voice coding.
2. The signalling channels: these can be sub divided into BCCH (broadcast control channel, including packet broadcast control channel (PBCCH), see sub clause 1.3, and extended coverage broadcast control channel (EC-BCCH)), CCCH (common control channel, including packet common control channel (PCCCH), see sub clause 1.3, and extended coverage common control channel (EC-CCCH)), SDCCH (stand alone dedicated control channel), (P)ACCH ((packet) associated control channel, including extended coverage packet associated control channel (EC-PACCH)), packet timing advance control channel (PTCCH) and CTSCCH (CTS control channel). An associated control channel is always assigned in conjunction with, either a TCH, or an SDCCH. A packet associated control channel is always assigned in conjunction to one or multiple (EC-)PDTCH, concurrently assigned to one MS. Two types of ACCH for circuit switched connections are defined: continuous stream (slow ACCH) and burst stealing mode (fast ACCH). For the purpose of this series of technical specifications, the following signalling channels are distinguished:
   • stand-alone dedicated control channel, four of them mapped on the same basic physical channel as the CCCH (SDCCH/4);
   • stand-alone dedicated control channel, eight of them mapped on a separate basic physical channel (SDCCH/8);
   • full rate fast associated control channel (FACCH/F);
   • enhanced circuit switched full rate fast associated control channel (E-FACCH/F);
   • half rate fast associated control channel (FACCH/H);
   • full rate octal fast associated control channel (O FACCH/F);
   • half rate octal fast associated control channel (O FACCH/H);
   • slow, TCH/F, O-TCH/F or E-TCH/F associated, control channel (SACCH/TF);
   • slow, TCH/F or O-TCH/F associated, control channel for enhanced power control (SACCH/TPF);
   • slow, TCH/H or O TCH/H associated, control channel (SACCH/TH);
   • slow, TCH/H or O TCH/H associated, control channel for enhanced power control (SACCH/TPH);
   • slow, TCH/F, O-TCH/F or E-TCH/F associated, control channel for multislot configurations (SACCH/M);
   • slow, TCH/F or O-TCH/F associated, control channel for enhanced power control in multislot configurations (SACCH/MP);
   • slow, TCH/F associated, control channel for CTS (SACCH/CTS);
   • slow, SDCCH/4 associated, control channel (SACCH/C4);
   • slow, SDCCH/8 associated, control channel (SACCH/C8);
   • packet associated control channel (PACCH);
   • extended coverage packet associated control channel (EC-PACCH);
   • packet timing advance control channel (PTCCH);
   • broadcast control channel (BCCH);
   • packet broadcast control channel (PBCCH);
   • extended coverage broadcast control channel (EC-BCCH);
   • random access channel (i.e. uplink CCCH) (RACH);
   • packet random access channel (i.e. uplink PCCCH) (PRACH);
   • extended coverage random access channel (i.e. uplink EC-CCCH) (EC-RACH);
   • paging channel (part of downlink CCCH) (PCH);
   • extended coverage paging channel (part of downlink EC-CCCH) (EC-PCH);
   • packet paging channel (part of downlink PCCCH) (PPCH);
   • access grant channel (part of downlink CCCH) (AGCH);
   • packet access grant channel (part of downlink PCCCH) (PAGCH);
   • extended coverage access grant channel (part of downlink EC-CCCH) (EC-AGCH);
   • extended coverage paging indication channel (EC-PICH);
   • notification channel (part of downlink CCCH) (NCH);
   • CTS beacon channel (part of downlink CTSCCH) (CTSBCH-FB and CTSBCH-SB);
   • CTS paging channel (part of downlink CTSCCH) (CTSPCH);
   • CTS access request channel (part of uplink CTSCCH) (CTSARCH);
   • CTS access grant channel (part of downlink CTSCCH) (CTSAGCH);
   • enhanced inband associated control channel (E-IACCH);
   • enhanced power control channel (EPCCH);
   • enhanced power control channel for multislot configurations (EPCCH/M);
   • packet random access channel for MBMS (MPRACH).
   All associated control channels have the same direction (bi directional or unidirectional) as the channels they are associated to. The unidirectional SACCH/MD, SACCH/MPD or EPCCH/MD are defined as the downlink part of SACCH/M, SACCH/MP or EPCCH/M respectively.

When there is no need to distinguish between different sub categories of the same logical channel, only the generic name will be used, meaning also all the sub categories, irrespective of modulation used (SACCH will mean all categories of SACCHs, SACCH/T will mean both the slow, TCH associated, control channels with and without enhanced power control, etc.). Also EC-channels are considered to be a sub-category of the same logical channels as non-EC-channels, unless otherwise stated. The logical channels mentioned above are mapped on physical channels that are described in this set of technical specifications. The different physical channels provide for the transmission of information pertaining to higher layers according to a block structure.

For the purpose of elaborating the physical layer specification, a reference configuration of the transmission chain is used as shown in annex A. This reference configuration also indicates which parts are dealt with in details in which technical specification. It shall be noted that only the transmission part is specified, the receiver being specified only via the overall performance requirements. With reference to this configuration, the technical specifications in the 45 series address the following functional units:

• 3GPP TS 45.002: burst building, and burst multiplexing;
• 3GPP TS 45.003: coding, reordering and partitioning, interleaving, and for EC-channels blind physical layer transmissions;
• 3GPP TS 45.004: differential encoding, modulation, and for EC-GSM-IoT overlaid CDMA;
• 3GPP TS 45.005: transmitter, antenna, and receiver (overall performance).

This reference configuration defines also a number of points of vocabulary in relation to the name of bits at different levels in the configuration. It must be outlined, in the case of the encrypted bits, that they are named only with respect to their position after the encryption unit, and not to the fact that they pertain to a flow of information that is actually encrypted.