5 Mapping of packet data logical channels onto physical channels

03.643GPPGeneral Packet Radio Service (GPRS)Overall description of the GPRS radio interfaceStage 2TS

NOTE: The text in this clause is informative. The normative text is in 3GPP TS 05.02 [11]. Where there is a conflict between these descriptions, the normative text has precedence.

5.1 General

Different packet data logical channels can occur on the same physical channel (i.e. PDCH). The sharing of the physical channel is based on blocks of 4 consecutive bursts, except for PTCCH. The mapping in frequency of PDCH on to the physical channel shall be as defined in GSM 05.02 [11].

A PDCH may be either full-rate (PDCH/F) or half-rate (PDCH/H). PDCH/H is only applicable to DTM. See GSM 05.02 [11].

GPRS and EGPRS employ the same physical layer, except for the PDTCH.

On PRACH, CPRACH and PTCCH/U, access bursts are used. On all other packet data logical channels, radio blocks comprising 4 normal bursts are used. The only exception is some messages on uplink PACCH which comprise 4 consecutive access bursts (to increase robustness).

5.2 Packet Common Control Channels (PCCCH and CPCCCH)

At a given time, the logical channels of the PCCCH are mapped on different physical resources than the logical channels of the CCCH.

The PCCCH and CPCCCH do not have to be allocated permanently in the cell. Whenever the PCCCH is not allocated, the CCCH shall be used to initiate a packet transfer. For Compact, CPCCCH shall be allocated.

One given MS may use only a subset of the PCCCH and CPCCCH, the subset being mapped onto one physical channel (i.e. PDCH).

The PCCCH, when it exists:

– is mapped on one or several physical channels according to a 52-multiframe, In that case the PCCCH, PBCCH and PDTCH share same physical channels (PDCHs).

The existence and location of the PCCCH shall be broadcast on the cell.

Since GSM phase 1 and phase 2 MS can only see and use the CCCH, the use on the PCCCH can be optimised for GPRS e.g. a PRACH of 11 bits can be used on uplink.

For Compact, one radio frequency channel of the cell allocation shall be used to carry synchronization information and the CPBCCH, this shall be known as the primary Compact carrier. All other radio frequency channels of the cell allocation shall be known as secondary Compact carriers.

For primary and secondary Compact carriers, CPCCCHs shall be allocated on only one timeslot (which is associated with a time group as defined in GSM 05.02 [11]). This time group is known as the serving time group and rotates over odd timeslot numbers as follows: 7, 5, 3, 1, 7, 5, . The CPCCCH is mapped according to a Compact 52-multiframe and the serving time group rotation occurs between frame numbers (FN) mod 52 = 3 and 4.

5.2.1 Packet Random Access Channel (PRACH and CPRACH)

The PRACHand CPRACH are mapped on one or several physical channels. The physical channels on which the PRACH is mapped are derived by the MS from information broadcast on the PBCCH or BCCH. The physical channels on which the CPRACH is mapped are derived by the MS from information broadcast on the CPBCCH.

PRACH and CPRACH are determined by the Uplink State Flag marked as free that is broadcast continuously on the corresponding downlink (see subclause 6.6.4.1). Additionally, a predefined fixed part of the multiframe structure for PDCH can be used as PRACH or CPRACH only and the information about the mapping on the physical channel is broadcast on PBCCH or CPBCCH. During those time periods an MS does not have to monitor the USF that is simultaneously broadcast on the downlink.

5.2.2 Packet Paging Channel (PPCH and CPPCH)

The PPCH and CPPCH are mapped on one or several physical channels. The exact mapping on each physical channel follows a predefined rule (see subclause 6.1.2), as it is done for the PCH.

The physical channels on which the PPCH or CPPCH are mapped, as well as the rule that is followed on the physical channels, are derived by the MS from information broadcast on the PBCCH or CPBCCH.

5.2.3 Packet Access Grant Channel (PAGCH and CPAGCH)

The PAGCH and CPAGCH are mapped on one or several physical channels. The exact mapping on each physical channel follows a predefined rule (see subclause 6.1.2).

The physical channels on which the PAGCH or CPAGCH are mapped, as well as the rule that is followed on the physical channels, are derived by the MS from information broadcast on the PBCCH or CPBCCH.

5.2.4 Packet Notification Channel (PNCH and CPNCH)

The PNCH and CPNCH are mapped on one or several blocks on PCCCH and CPCCCH. The exact mapping follows a predefined rule. The mapping is derived by the MS from information broadcast on the PBCCH or CPBCCH.

5.3 Packet Broadcast Control Channel (PBCCH and CPBCCH)

The PBCCH and CPBCCH shall be mapped on one or several physical channels. The exact mapping on each physical channel follows a predefined rule (see subclause 6.1.2), as it is done for the BCCH. For Compact, CPBCCH shall be allocated. CPBCCH and BCCH are mutually exclusive.

The existence of the PCCCH, and consequently the existence of the PBCCH, is indicated on the BCCH.

For Compact, one radio frequency channel of the cell allocation shall be used to carry synchronization information and the CPBCCH, this shall be known as the primary Compact carrier. All other radio frequency channels of the cell allocation shall be known as secondary Compact carriers.

The CPBCCH shall be mapped on only one timeslot (which is associated with a time group as defined in GSM 05.02 [11]). This time group is known as the serving time group and rotates over odd timeslot numbers as follows: 7, 5, 3, 1, 7, 5, . The CPBCCH is mapped according to a Compact 52-multiframe and the serving time group rotation occurs between frame numbers (FN) mod 52 = 3 and 4. The exact mapping follows a predefined rule (see subclause 6.1.2).

5.3a Compact Frequency Correction Channel (CFCCH)

The CFCCH is the same as the FCCH with one exception  the FCCH is mapped onto a 51-multiframe as defined in GSM 05.02 [11].

5.3b Compact Synchronization Channel (CSCH)

The CSCH is similar to the SCH. The major difference is that the SCH is mapped onto a 51-multiframe as defined in GSM 05.02 [11]. This results in a different layout for the reduced TDMA frame number (RFN).

5.4 Packet Timing advance Control Channel (PTCCH)

Two defined frames of multiframe are used to carry PTCCH (see subclause 6.1.2). The exact mapping of PTCCH/U sub-channels and PTCCH/D shall be as defined in GSM 05.02 [11].

On PTCCH/U, access bursts are used. On PTCCH/D, four normal bursts comprising a radio block are used.

5.5 Packet Traffic Channels

5.5.1 Packet Data Traffic Channel (PDTCH)

One PDTCH is mapped onto one physical channel.

Up to eight PDTCHs, with different timeslots but with the same frequency parameters, may be allocated to one MS at the same time.

5.5.2 Packet Associated Control Channel (PACCH)

PACCH is dynamically allocated on the block basis on the same physical channel as carrying PDTCHs.However, one block PACCH allocation is used on the physical channel carrying only PCCCH, when the MS is polled to acknowledge the initial assignment message.

PACCH is of a bi-directional nature, i.e. it can dynamically be allocated both on the uplink and on the downlink regardless on whether the corresponding PDTCH assignment is for uplink or downlink.

When PDTCH(s) is assigned on the uplink, the corresponding downlink timeslots have continuously to be monitored by the MS for possible occurrences of PACCH. The MS can use the uplink assignment for sending PACCH blocks whenever needed. In case of extended dynamic allocation (see subclause 6.6.4.4), if the resource assigned by the network does not allow the multislot MS (see GSM 05.02 [11] , annex B) to monitor the USF on all the assigned PDCHs, the PACCH blocks shall be mapped on one PDCH in the list of assigned PDCHs.

When PDTCH(s) is assigned on the downlink, every occurrence of an uplink PACCH block is determined by polling in one of the preceding downlink blocks (transferred on the same PDCH). The network can use the downlink assignment for sending PACCH blocks whenever needed.

During an uplink allocation a MS using a fixed allocation (see subclause 6.6.4.4) must monitor the assigned PACCH timeslot during all blocks where the uplink is unassigned a number ofconsecutive timeslots. The number of consecutive timeslots depends upon the multislot class of the MS. The network shall transmit a PACCH block to a MS using a fixed allocation only during the same size timeslot gap in the uplink allocation on the PACCH.

During a downlink transmission the network shall not send downlink data to a MS during uplink PACCH timeslots or in a number of timeslot preceding and following the uplink PACCH block. The number of timeslot preceding and following the uplink PACCH timeslots depends upon the multislot class of the half duplex MS.

5.6 Downlink resource sharing

Different packet data logical channels can be multiplexed on the downlink on the same physical channel (i.e. PDCH). See details in GSM 05.02 [11]. The type of message which is indicated in the radio block header allows differentiation between the logical channels. Additionally, the MS identity allows differentiation between PDTCHs and PACCHs assigned to different MSs.

In addition, in dual transfer mode the network may allocate a PDCH dedicated to the MS. Even in the case of exclusive allocation, the network shall use the MS identity and the type of message in the radio block header.

5.7 Uplink resource sharing

Different packet data logical channels can be multiplexed on the uplink of the same physical channel (i.e. PDCH). See details in GSM 05.02 [11]. The type of message which is indicated in the radio block header, allows differentiation between the logical channels. Additionally, the MS identity allows differentiation between PDTCHs and PACCHs assigned to different MSs.

In addition, in dual transfer mode the network may allocate a PDCH dedicated to the MS.