3 Logical channels
3GPP45.002GSM/EDGE Multiplexing and multiple access on the radio pathRelease 17TS
3.1 General
This subclause describes the logical channels that are supported by the radio subsystem.
3.2 Traffic channels
3.2.1 General
Traffic channels (TCH’s) are intended to carry either encoded speech or user data in circuit switched mode. Five general forms of traffic channel are defined:
i) Full rate traffic channel (TCH/F). This channel carries information at a gross rate of 22,8 kbit/s.
ii) Half rate traffic channel (TCH/H). This channel carries information at a gross rate of 11,4 kbit/s.
iii) Enhanced circuit switched full rate traffic channel (E-TCH/F). This channel carries information at a gross rate of 69,6 kbit/s including the stealing symbols.
iv) 8-PSK full rate traffic channel (O-TCH/F). This channel carries information at a gross rate of 68,4 kbit/s.
v) 8-PSK half rate traffic channel (O-TCH/H). This channel carries information at a gross rate of 34,2 kbit/s.
Packet data traffic channels (PDTCH’s) are intended to carry user data in packet switched mode. For the purpose of this Technical Specification, any reference to traffic channel does not apply to PDTCH unless explicitly stated.
All traffic 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.
Multiple full rate channels can be assigned to the same MS. This is referred to as multislot configurations, which is defined in subclause 6.4.2.1.
Multiple packet data traffic channels can be assigned to the same MS or, in the case of point-to-multipoint transmission, a group of MSs. This is referred to as multislot packet configurations, as defined in subclause 6.4.2.2 and subclause 6.4.2.3a.
A combination of a half rate traffic channel and a half rate packet data traffic channel on the same basic physical channel can be assigned to the same MS as defined in subclause 6.4.2.3.
A combination of a traffic channel and one or more full rate packet data traffic channels can be assigned to the same MS.
A pair of speech traffic channels along with their associated control channels sharing the same timeslot number (see subclause 4.3), ARFCN (see subclause 6.2.3) and TDMA frame number (see subclause 4.3) is referred to as a VAMOS pair. The speech traffic channels along with their associated control channels in a VAMOS pair are said to be in VAMOS mode and are referred to as VAMOS subchannels.
In case of speech traffic channels in VAMOS mode, up to 4 speech traffic channels can be mapped on the same basic physical channel both in downlink and uplink (see subclause 6.4.1).
The specific traffic channels available in the categories of speech and user data are defined in the subclauses following.
3.2.2 Speech traffic channels
The following traffic channels are defined to carry encoded speech:
i) full rate traffic channel for speech (TCH/FS);
ii) half rate traffic channel for speech (TCH/HS);
iii) enhanced full rate traffic channel for speech (TCH/EFS);
iv) adaptive full rate traffic channel for speech (TCH/AFS);
v) adaptive half rate traffic channel for speech (TCH/AHS);
vi) adaptive full rate traffic channel for wideband speech (TCH/WFS);
vii) adaptive half rate 8PSK traffic channel for speech (O-TCH/AHS);
viii) adaptive full rate 8PSK traffic channel for wideband speech (O-TCH/WFS);
ix) adaptive half rate 8PSK traffic channel for wideband speech (O-TCH/WHS).
3.2.3 Circuit switched data traffic channels
The following traffic channels are defined to carry user data:
i) full rate traffic channel for 9,6 kbit/s user data (TCH/F9.6);
ii) full rate traffic channel for 4,8 kbit/s user data (TCH/F4.8);
iii) half rate traffic channel for 4,8 kbit/s user data (TCH/H4.8);
iv) half rate traffic channel for 2,4 kbit/s user data (TCH/H2.4);
v) full rate traffic channel for 2,4 kbit/s user data (TCH/F2.4);
vi) full rate traffic channel for 14,4 kbit/s user data (TCH/F14.4);
vii) enhanced circuit switched full rate traffic channel for 28,8 kbit/s user data (E-TCH/F28.8);
viii) enhanced circuit switched full rate traffic channel for 32,0 kbit/s user data (E-TCH/F32.0);
ix) enhanced circuit switched full rate traffic channel for 43.2 kbit/s user data (E-TCH/F43.2).
3.2.4 Packet data traffic channels (PDTCH and EC-PDTCH)
A PDTCH/F corresponds to the resource assigned to a single MS or, in the case of point-to-multipoint transmission, to multiple MSs for user data transmission. An EC-PDTCH/F always corresponds to the resource assigned to a single MS in BTTI configuration.
In BTTI configuration, an (EC-)PDTCH/F is mapped onto one physical channel (see subclause 6.3.2.1). Due to the dynamic multiplexing onto the same physical channel of different logical channels (see subclause 6.3.2), an (EC‑)PDTCH/F in BTTI configuration carries information at an instantaneous bit rate ranging from 0 to a maximum value dependent on the modulation and on the symbol rate, as given in table 3.2.4-1.
Table 3.2.4-1: Maximum instantaneous bit rate (kbit/s) for different modulations
|
Modulation |
Maximum instantaneous bit rate (kbit/s) |
|
|
Normal symbol rate1 |
Higher symbol rate1 |
|
|
GMSK |
22,8 |
– |
|
QPSK |
– |
55,2 |
|
8-PSK |
69,6 |
– |
|
16QAM |
92,8 |
110,4 |
|
32QAM |
116,0 |
138,0 |
|
NOTE: see 3GPP TS 45.004 [14] |
||
In RTTI configuration, a PDTCH/F is mapped onto two physical channels, i.e. a PDCH-pair (see subclause 6.3.2.1). A PDTCH/F in RTTI configuration carries information at an instantaneous bit rate ranging from 0 to a maximum value which is double the corresponding value for that modulation and the symbol rate.
A PDTCH/H corresponds to the resource assigned to a single MS on half a physical channel for user data transmission. The maximum instantaneous bit rate for a PDTCH/H is half that for a PDTCH/F. A PDTCH/H is only possible in BTTI configuration if FANR is not activated (see 3GPP TS 44.060 [11]).
All packet data traffic channels are uni-directional, either uplink ((EC-)PDTCH/U), for a mobile originated packet transfer or downlink ((EC-)PDTCH/D) for a mobile terminated packet transfer.
In the case of point-to-multipoint transmission, a PDTCH/D can be used for communication with multiple MSs.
3.3 Control channels
3.3.1 General
Control channels are intended to carry signalling or synchronization data. Four categories of control channel are defined: broadcast, common, dedicated and CTS control channels. Specific channels within these categories are defined in the subclauses following.
3.3.2 Broadcast channels
3.3.2.1 Frequency correction channels (FCCH and CFCCH)
The frequency correction channel carries information for frequency correction of the mobile station. It is required only for the operation of the radio sub‑system. Different mapping is used for FCCH and COMPACT CFCCH (see clause 7).
3.3.2.2 Synchronization channels
3.3.2.2.0 General
The synchronization channel carries information for frame synchronization of the mobile station and identification of a base transceiver station. It is required only for the operation of the radio sub‑system. Different channels are used for SCH, EC-SCH and COMPACT CSCH.
3.3.2.2.1 Synchronization channel (SCH)
Specifically the synchronization channel (SCH) shall contain two encoded parameters:
a) Base transceiver station identity code (BSIC): 6 bits (before channel coding) consists of 3 bits of PLMN colour code with range 0 to 7 and 3 bits of BS colour code with range 0 to 7 as defined in 3GPP TS 23.003 [2].
b) Reduced TDMA frame number (RFN): 19 bits (before channel coding) =
T1 (11 bits) range 0 to 2047 = FN div ( 26 x 51)
T2 (5 bits) range 0 to 25 = FN mod 26
T3′ (3 bits) range 0 to 4 = (T3 ‑ 1) div 10
where
T3 (6 bits) range 0 to 50 = FN mod 51
and
FN = TDMA frame number as defined in subclause 4.3.3.
3GPP TS 44.006 [9] and 3GPP TS 44.018 [10] specify the precise bit ordering, 3GPP TS 45.003 [13] the channel coding of the above parameters and 3GPP TS 45.010 [17] defines how the TDMA frame number can be calculated from T1, T2, and T3′.
3.3.2.2.2 COMPACT synchronization channel (CSCH)
The COMPACT packet synchronization channel CSCH shall contain two encoded parameters:
a) Base transceiver station identity code (BSIC): 6 bits (before channel coding) consists of 3 bits of PLMN colour code with range 0 to 7 and 3 bits BS colour code with range 0 to 7 as defined in 3GPP TS 23.003 [2].
b) Reduced TDMA frame number (RFN): 19 bits (before channel coding) =
R1 (10 bits) range 0 to 1023 = FN div (51 x 52)
R2 (6 bits) range 0 to 50 = (FN div 52) mod 51
TG (2 bits) range 0 to 3
Reserved (1 bit)
where
FN = TDMA frame number as defined in subclause 4.3.3
and
TG = time group as defined in subclause 4.3.4.
3GPP TS 44.006 [9] and 3GPP TS 44.018 [10] specify the precise bit ordering, 3GPP TS 45.003 [13] the channel coding of the above parameters and 3GPP TS 45.010 [17] defines how the TDMA frame number can be calculated from R1 and R2.
3.3.2.2.3 Extended Coverage synchronization channel (EC-SCH)
The extended coverage synchronization channel (EC-SCH) shall contain six encoded parameters, and three spare bits:
a) Base transceiver station identity code (BSIC): 9 bits (before channel coding) consists of 3 bits of PLMN colour code with range 0 to 7, 3 bits of BS colour code with range 0 to 7 and 3 bits of Radio frequency Colour Code with range 0 to 7 as defined in 3GPP TS 23.003 [2].
b) Parameters used to identify the Reduced TDMA frame number per quarter hyperframe (RFNQH): 12 bits (before channel coding) =
T1′ (8 bits) range 0 to 255 = (FN div (51*26*2)) mod 256
NOTE 1: T1′ identifies one of 256 pairs of superframes within a quarter hyperframe
T2′ (4 bits) range 0 to 12 = (FN div (51*4)) mod 13
NOTE 2: T2′ identifies a specific set of four contiguous 51-multiframes within a pair of superframes, i.e. 52 51-multiframes.
c) Implicit Reject Status: 2 bits
See 3GPP TS 44.018 [10].
d) EC-BCCH CHANGE MARK: 3 bits
See 3GPP TS 44.018 [10].
NOTE 2a: Indicating a new value for the EC-BCCH CHANGE MARK in the EC-SCH shall start within the same 51-multiframe used to begin the transmission of the corresponding new EC SI information.
e) RACH Access Control: 1 bit
See 3GPP TS 44.018 [10].
In addition, the following parameters are required to derive the Reduced frame number per quarter hyperframe (RFNQH):
f) T2” (2 bits) range 0 to 3 = (FN div 51) mod 4
NOTE 3: T2” identifies the specific 51-multiframe in the set of four contiguous 51-multiframes. T2” is signalled through the cyclic shift pattern used on the EC-SCH, see 3GPP TS 45.003 [13].
g) T3 (see subclause 3.3.2.2.1) will be determined by the device through the identification of the mapping of the FCCH onto the specific TDMA frames within the 51-multiframe, see Table 3.
After the decoding of EC-SCH and the determination of T3, the MS will have knowledge about the frame structure within a quarter hyperframe. The QUARTER_HYPERFRAME_INDICATOR is acquired when receiving an Immediate Assignment, see 3GPP TS 44.018 [10].
QUARTER_HYPERFRAME_INDICATOR (2 bits) range 0…3 = FN div (26*51*512)
After acquisition of the QUARTER_HYPERFRAME_INDICATOR, the MS will have knowledge about the frame structure within a hyperframe.
3GPP TS 44.006 [9] and 3GPP TS 44.018 [10] specify the precise bit ordering, 3GPP TS 45.003 [13] the channel coding of the above parameters and 3GPP TS 45.010 [17] defines how the TDMA frame number (FN as defined in subclause 4.3.3) can be calculated from T1′, T2′, T2”, T3 and the QUARTER_HYPERFRAME_INDICATOR.
3.3.2.3 Broadcast control channel (BCCH)
The broadcast control channel broadcasts general information on a base transceiver station per base transceiver station basis. Of the many parameters contained in the BCCH, the use of the following parameters, as defined in 3GPP TS 44.018 are referred to in subclause 6.5:
a) CCCH_CONF which indicates the organization of the common control channels:
From this parameter, the number of common control channels (BS_CC_CHANS) and whether or not CCCH or SDCCH are combined (BS_CCCH_SDCCH_COMB = true or false) are derived as follows:
|
CCCH_CONF |
BS_CC_CHANS |
BS_CCCH_SDCCH_COMB |
|
000 |
1 |
false |
|
001 |
1 |
true |
|
010 |
2 |
false |
|
100 |
3 |
false |
|
110 |
4 |
false |
b) BS_AG_BLKS_RES which indicates the number of blocks on each common control channel reserved for access grant messages:
3 bits (before channel coding) range 0 to 7.
In a routing area where eDRX is supported, the number of blocks per 51-multiframe reserved for AGCH is subject to the requirement that all cells in the routing area shall have the same number of paging blocks per 51-multiframe.
c) BS_PA_MFRMS which indicates the number of 51-multiframes between transmission of paging messages to mobiles of the same paging group:
3 bits (before channel coding) range 2 to 9.
An exception is the case where a MS has negotiated the use of eDRX in a Routing Area where eDRX is supported (see 3GPP TS 44.018 [10]) in which case the BS_PA_MFRMS does not apply. In this case the number of 51-multiframes between transmissions of paging messages is based on the eDRX value negotiated between the MS and the network – see Table 6.5.6a-1.
d) support of GPRS
The BCCH shall indicate whether or not packet switched traffic is supported. If packet switched traffic is supported and if the PBCCH exists, then the BCCH shall broadcast the position of the packet data channel (PDCH), as defined in subclause 6.3.2.1, carrying the PBCCH. (See sub-clause 1.3).
3.3.2.3a Extended coverage broadcast control channel (EC-BCCH)
The extended coverage broadcast control channel broadcasts general information on a base transceiver station per base transceiver station basis. Of the many parameters contained in the EC-BCCH, the use of the following parameter, as defined in 3GPP TS 44.018 [10] is referred to in subclause 6.5:
a) EC_BS_CC_CHANS which indicates the number of extended coverage common control channels.
3.3.2.4 Packet Broadcast Control Channels
3.3.2.4.1 Packet Broadcast Control Channel (PBCCH)
The PBCCH broadcasts parameters used by the MS to access the network for packet transmission operation. In addition to those parameters the PBCCH reproduces the information transmitted on the BCCH to allow circuit switched operation, such that a MS in GPRS attached mode monitors the PBCCH only, if it exists. The existence of the PBCCH in the cell is indicated on the BCCH. (See sub-clause 1.3). In the absence of PBCCH, the BCCH shall be used to broadcast information for packet operation.
Of the many parameters contained in the PBCCH, the use of the following parameters, as defined in 3GPP TS 44.060 are referred to in subclauses 6.5 and 6.3.2:
a) BS_PBCCH_BLKS (1,…,4) indicates the number of blocks allocated to the PBCCH in the multiframe (see subclause 6.3.2.3.3).
b) BS_PCC_CHANS indicates the number of physical channels carrying PCCCHs including the physical channel carrying the PBCCH
c) BS_PAG_BLKS_RES indicates the number of blocks on each PDCH carrying PCCCH per multiframe where neither PPCH nor PBCCH should appear (see subclause 6.3.2.3.4). The BS_PAG_BLKS_RES value shall fulfil the condition : BS_PAG_BLKS_RES <= 12 – BS_PBCCH_BLKS – 1.
d) BS_PRACH_BLKS indicates the number of blocks reserved in a fixed way to the PRACH channel on any PDCH carrying PCCCH (see subclause 6.3.2.2.3).
The PBCCH channel of a cell shall be allocated on the same frequency band (see 3GPP TS 45.005) as the BCCH channel of that cell.
3.3.2.4.2 COMPACT Packet Broadcast Control Channel (CPBCCH)
The CPBCCH is a stand-alone packet control channel for COMPACT. The CPBCCH broadcasts parameters used by the MS to access the network for packet transmission operation.
Of the many parameters contained in the CPBCCH, the use of the following parameters, as defined in 3GPP TS 44.060 are referred to in subclauses 6.5 and 6.3.3:
a) BS_PBCCH_BLKS (1,…,4) indicates the number of blocks allocated to the CPBCCH in the multiframe (see subclause 6.3.2.3.3a).
b) BS_PCC_CHANS indicates the number of radio frequency channels per cell carrying CPCCCHs including the radio frequency channel carrying the CPBCCH.
c) BS_PAG_BLKS_RES indicates the number of blocks on each radio frequency channel carrying CPCCCH per multiframe where neither CPPCH nor CPBCCH should appear (see subclause 6.3.2.3.4a). BS_PAG_BLKS_RES cannot be greater than 8.
d) BS_PRACH_BLKS indicates the number of blocks reserved in a fixed way to the CPRACH channel on any radio frequency channel carrying CPCCCH (see subclause 6.3.2.2.3a).
e) NIB_CCCH_0, NIB_CCCH_1, NIB_CCCH_2, and NIB_CCCH_3 indicate the number of downlink blocks per multiframe designated as idle to protect CPBCCH and CPCCCH blocks for non-serving time groups (see subclause 6.5.1).
f) LARGE_CELL_OP indicates which type of cell size is used: nominal or large.
3.3.3 Common control type channels
3.3.3.1 Common control type channels, known when combined as a common control channel (CCCH)
i) Paging channel (PCH): Downlink only, used to page mobiles.
ii) Random access channel (RACH): Uplink only, used to request assignment of a SDCCH or to request assignment of one or several (EC-)PDTCHs.
iii) Access grant channel (AGCH): Downlink only, used to assign a SDCCH or directly a TCH. Also used to assign one or several (EC-)PDTCHs.
iv) Notification channel (NCH): Downlink only, used to notify mobile stations of voice group and voice broadcast calls.
3.3.3.2 Packet Common control channels
3.3.3.2.1 Packet Common Control Channels (PCCCH)
i) Packet Paging channel (PPCH): Downlink only, used to page MS.
ii) Packet Random access channel (PRACH): Uplink only, used to request assignment of one or several PDTCHs (for uplink or downlink direction).
iii) Packet Access grant channel (PAGCH): Downlink only, used to assign one or several PDTCH.
If a PCCCH is not allocated, the information for packet switched operation is transmitted on the CCCH. If a PCCCH is allocated, it may transmit information for circuit switched operation. (See sub-clause 1.3).
The PCCCH channel of a cell shall be allocated on the same frequency band (see 3GPP TS 45.005 [15]) as the BCCH channel of that cell.
3.3.3.2.2 COMPACT Common Control Channels (CPCCCH)
i) Packet Paging channel (CPPCH): Downlink only, used to page MS.
ii) Packet Random access channel (CPRACH): Uplink only, used to request assignment of one or several PDTCHs (for uplink or downlink direction).
iii) Packet Access grant channel (CPAGCH): Downlink only, used to assign one or several PDTCH.
3.3.3.2.3 MBMS Common Control Channels
i) MBMS Packet Random access channel (MPRACH): Uplink only, used during the initial counting procedure for MBMS (see 3GPP TS 44.060).
3.3.3.3 Extended Coverage Common Control Channels
i) Extended Coverage Paging channel (EC-PCH): Downlink only, used to page MS.
ii) Extended Coverage Random access channel (EC-RACH): Uplink only, used to request assignment of one or several EC-PDTCH’s (for uplink direction).
iii) Extended Coverage Access grant channel (EC-AGCH): Downlink only, used to assign one or several EC-PDTCH’s.
3.3.4 Dedicated control channels
3.3.4.1 Circuit switched dedicated control channels
i) Slow, TCH/F or E-TCH/F associated, control channel (SACCH/TF).
ii) Fast, TCH/F associated, control channel (FACCH/F).
iii) Slow, TCH/H or O-TCH/H associated, control channel (SACCH/TH).
iv) Fast, TCH/H associated, control channel (FACCH/H).
v) Stand alone dedicated control channel (SDCCH/8).
vi) Slow, SDCCH/8 associated, control channel (SACCH/C8)
vii) Stand alone dedicated control channel, combined with CCCH (SDCCH/4).
viii) Slow, SDCCH/4 associated, control channel (SACCH/C4).
ix) slow, TCH/F, O-TCH/F or E-TCH/F associated, control channel for multislot configurations (SACCH/M).
x) slow, TCH/F associated, control channel for CTS (SACCH/CTS).
xi) Fast, E-TCH/F associated, control channel (E-FACCH/F).
xii) Inband, E-TCH/F associated, control channel (E-IACCH/F).
xiii) Slow, TCH/F or O-TCH/F associated, control channel for enhanced power control (SACCH/TPF).
xiv) Slow, TCH/F or O-TCH/F associated, control channel for enhanced power control in multislot configurations (SACCH/MP).
xv) Slow, TCH/H or O-TCH/H associated, control channel for enhanced power control (SACCH/TPH).
xvi) Enhanced power control, TCH/F or O-TCH/F associated channel (EPCCH/F).
xvii) Enhanced power control, TCH/F or O-TCH/F associated channel in multislot configurations (EPCCH/M).
xviii) Enhanced power control, TCH/H or O-TCH/H associated channel (EPCCH/H);
xix) Fast, O-TCH/H associated, control channel (O-FACCH/H);
xx) Fast, O-TCH/F associated, control channel (O-FACCH/F).
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 and EPCCH/MD are defined as the downlink part of SACCH/M, SACCH/MP and EPCCH/M respectively.
3.3.4.2 Packet dedicated control channels
i) The Packet Associated Control channel (PACCH): The PACCH is bi-directional. For description purposes PACCH/U is used for the uplink and PACCH/D for the downlink. The PACCH shall be transmitted using the same configuration (BTTI or RTTI) of the PDTCH that it is associated with.
ii) Packet Timing advance control channel uplink (PTCCH/U): Used to transmit random access bursts to allow estimation of the timing advance for one MS in packet transfer mode.
iii) Packet Timing advance control channel downlink (PTCCH/D): Used to transmit timing advance updates for several MS. One PTCCH/D is paired with several PTCCH/U’s.
3.3.4.3 Extended Coverage Packet dedicated control channels
i) The Extended Coverage Packet Associated Control channel (EC-PACCH): The EC-PACCH is bi-directional. For description purposes EC-PACCH/U is used for the uplink and EC-PACCH/D for the downlink. Both the EC-PACCH and EC-PDTCH shall be transmitted using the Coverage Class of the direction they are transmitted in. The Coverage Class need not be the same on uplink and downlink.
3.3.5 Cell Broadcast Channel (CBCH)
The CBCH, downlink only, is used to carry the short message service cell broadcast (SMSCB). The CBCH uses the same physical channel as the SDCCH.
3.3.6 CTS control channels
Four types of CTS control channels are defined:
3.3.6.1 CTS beacon channel (BCH)
The BCH is used to provide frequency and synchronization information in the downlink. It is made up of a pair of CTSBCH-SB (Synchronization burst) and CTSBCH-FB (Frequency correction burst).
The CTSBCH-FB carries information for frequency correction of the mobile station. It is required only for the operation of the radio sub‑system.
The CTSBCH-SB carries signalling information and identification of a CTS-FP. Specifically the CTSBCH-SB shall contain five encoded parameters:
a) status of the CTS-FP radio resources : 1 bit (before channel coding;
b) flag indicating the presence of CTSPCH in the next 52-multiframe : 1 bit (before channel coding);
c) flag indicating whether the CTS-FP is currently performing timeslot shifting on CTSBCH: 1 bit (before channel coding);
d) CTS control channels (except CTSBCH) timeslot number for the next 52-multiframe (TNC): 3 bits (before channel coding);
e) CTS-FP beacon identity (FPBI) : 19 bits (before channel coding), as defined in 3GPP TS 23.003.
3GPP TS 44.056 specifies the precise bit ordering and 3GPP TS 45.003 the channel coding of the above parameters.
3.3.6.2 CTS paging channel (CTSPCH)
Downlink only, used to broadcast information for paging.
3.3.6.3 CTS access request channel (CTSARCH)
Uplink only, used to request assignment of a dedicated RR connection.
3.3.6.4 CTS access grant channel (CTSAGCH)
Downlink only, used to grant a dedicated RR connection.
3.4 Combination of channels
Only certain combinations of channels are allowed as defined in 3GPP TS 44.003. Subclause 6.4 lists the combinations in relation to basic physical channels.