4.2.3 Traffic Related Architecture – UE Side

25.3213GPPMedium Access Control (MAC) protocol specificationTS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

Figure 4.2.3-1 illustrates the connectivity of MAC entities.

The MAC-c/sh/m controls access to all common transport channels, except the HS-DSCH transport channel and the E-DCH transport channel (FDD and 1.28Mcps TDD only).

The MAC-d controls access to all dedicated transport channels, to MAC-c/sh/m and MAC-hs/ehs.

The MAC-c/sh/m controls access to MAC-is/i. (FDD and 1.28Mcps TDD only for UEs in CELL_FACH state and Idle mode).

The MAC-hs/ehs handles the HSDPA specific functions and controls access to the HS-DSCH transport channel. Upper layers configure which of the two entities, MAC-hs or MAC-ehs, is to be applied to handle HS-DSCH functionality.

The MAC-e/es or MAC-i/is controls access to the E-DCH transport channel. Upper layers configure which of the two entities, MAC-e/es or MAC-i/is, is to be applied to handle E-DCH functionality.

In case of selective combining of MTCH channels from multiple cells, the MAC-m controls access to the FACH transport channels used to carry MTCH and MSCH.

In the downlink, if logical channels of dedicated type are mapped to common transport channels then MAC-d receives the data from MAC-c/sh/m or MAC-hs/ehs via the illustrated connection between the functional entities.

In the downlink, if logical channels of common type are mapped to HS-DSCH then MAC-c/sh/m receives the data from MAC-ehs via the illustrated connection between the functional entities (FDD and 1.28 Mcps TDD only).

In the uplink, if logical channels of dedicated type are mapped to common transport channels then MAC-d submits the data to MAC-c/sh/m and MAC-is/i via the illustrated connection between the functional entities.

The mapping of logical channels on transport channels depends on the multiplexing that is configured by RRC.

The MAC Control SAP is used to transfer Control information to each MAC entity.

The associated signalling shown in the figure illustrates the exchange of information between layer 1 and layer 2 provided by primitives shown in [3].

Figure 4.2.3-1: UE side MAC architecture

4.2.3.1 MAC-c/sh/m entity – UE Side

Figure 4.2.3.1-1 shows the UE side MAC-c/sh/m entity.

The following functionality is covered:

– TCTF MUX:

– this function represents the handling (insertion for uplink channels and detection and deletion for downlink channels) of the TCTF field in the MAC header, and the respective mapping between logical and transport channels.
The TCTF field indicates the common logical channel type, or if a dedicated logical channel is used;

– add/read UE Id:

– the UE Id is added for RACH transmissions;

– the UE Id, when present, identifies data to this UE.

– read MBMS Id:

– the MBMS Id is read in case of MTCH reception;

– the MBMS Id identifies received data to an MBMS service.

– UL: TF selection:

– in the uplink, the possibility of transport format selection exists.

– ASC selection:

– For RACH, MAC indicates the ASC associated with the PDU to the physical layer. This is to ensure that RACH messages associated with a given Access Service Class (ASC) are sent on the appropriate signature(s) and time slot(s). MAC also applies the appropriate back-off parameter(s) associated with the given ASC. When sending an RRC CONNECTION REQUEST message, RRC will determine the ASC; in all other cases MAC selects the ASC;

– scheduling /priority handling

– this functionality is used to transmit the information received from MAC-d on RACH based on logical channel priorities. This function is related to TF selection.

– TFC selection

– transport format and transport format combination selection according to the transport format combination set (or transport format combination subset) configured by RRC is performed,

The RLC provides RLC-PDUs to the MAC, which fit into the available transport blocks on the transport channels.

There is one MAC-c/sh/m entity in each UE.

Figure 4.2.3.1-1: UE side MAC architecture / MAC-c/sh/m details

42.3.1b MAC-m entity – UE Side

Figure 4.2.3.1b-1 shows the UE side MAC-m entity.

The following functionality is covered:

– TCTF DEMUX:

– this function represents the handling (detection and deletion for downlink channels) of the TCTF field in the MAC header, and the respective mapping between logical and transport channels.
The TCTF field indicates the common logical channel type;

– read MBMS Id

– the MBMS Id is read in case of MTCH reception;

– the MBMS Id identifies received data to an MBMS service.

The MAC Control SAP is used to transfer control information to MAC-m.

If MTCH channels are selectively combined, the MAC-m entity exists in the UE. Otherwise, the MAC-m entity does not exist.

In case of selective combining of MTCH channels from multiple cells, there are one MAC-c/sh/m for the current cell and one MAC-m entity for each neighboring cell in the UE.

Figure 4.2.3.1b-1: UE side MAC architecture / MAC-m details

4.2.3.2 MAC-d entity – UE Side

Figure 4.2.3.2-1 shows the UE side MAC-d entity.

The following functionality is covered:

– Transport Channel type switching

– Transport Channel type switching is performed by this entity, based on decision taken by RRC. This is related to a change of radio resources. If requested by RRC, MAC shall switch the mapping of one designated logical channel between common and dedicated transport channels.

– C/T MUX:

– The C/T MUX is used when multiplexing of several dedicated logical channels onto one transport channel (other than HS-DSCH) or one MAC-d flow (HS-DSCH) is used. An unambiguous identification of the logical channel is included. If MAC-ehs is configured, C/T MUX toward MAC-ehs is not used.

– Ciphering:

– Ciphering for transparent mode data to be ciphered is performed in MAC-d. Details about ciphering can be found in [10].

– Deciphering:

– Deciphering for ciphered transparent mode data is performed in MAC-d. Details about ciphering can be found in [10].

– UL TFC selection:

– Transport format and transport format combination selection according to the transport format combination set (or transport format combination subset) configured by RRC is performed.

The MAC-d entity is responsible for mapping dedicated logical channels for the uplink either onto dedicated transport channels or to transfer data to MAC-c/sh/m to be transmitted via common channels.

One dedicated logical channel can be mapped simultaneously onto DCH and DSCH in TDD mode.

One dedicated logical channel can be simultaneously mapped onto DCH and HS-DSCH.

The MAC-d entity has a connection to the MAC-c/sh/m entity. This connection is used to transfer data to the MAC-c/sh/m to transmit data on transport channels that are handled by MAC-c/sh/m (uplink) or to receive data from transport channels that are handled by MAC-c/sh/m (downlink).

The MAC-d entity has a connection to the MAC-hs or MAC-ehs entity. This connection is used to receive data from the HS-DSCH transport channel which is handled by MAC-hs or MAC-ehs (downlink).

The MAC-d entity has a connection to the MAC-e/es or MAC-i/is entity. This connection is used to transmit data on the E-DCH transport channel which is handled by the MAC-e/es or MAC-i/is (uplink).

There is one MAC-d entity in the UE.

Figure 4.2.3.2-1: UE side MAC architecture / MAC-d details

4.2.3.3 MAC-hs entity – UE Side

In the model below the MAC-hs comprises the following entities. In 1.28 Mcps TDD multi-frequency HS-DSCH cell, the associated downlink control channel and uplink control channel pair controlling the HS-DSCH transmission on the certain carrier shall be allocated on the same carrier. The downlink control channel carries the HS-DSCH operation related info and the uplink control channel carries the feedback info from the UE side.

– HARQ:
The HARQ entity is responsible for handling the MAC functions relating to the HARQ protocol. The HARQ functional entity handles all the tasks that are required for hybrid ARQ. It is responsible for generating ACKs or NACKs. The detailed configuration of the hybrid ARQ protocol is provided by RRC over the MAC-Control SAP. In 1.28 Mcps TDD multi-frequency HS-DSCH cell, multiple HARQ processes are assigned for HS-DSCH operaton on every carrier independently, namely HARQ sub-entity; only one HARQ process is allowed to receive HS-DSCH in one TTI for each carrier. The maximum number of HARQ process per HS-DSCH per TTI on which an HS-DSCH transmission can be received is one.

– Reordering Queue distribution:
The reordering queue distribution function routes the MAC-hs PDUs to the correct reordering buffer based on the Queue ID.For 1.28 Mcps TDD, the reordering queue distribution function discards the MAC-hs PDU if the N field in MAC-hs header is zero.

– Reordering:
The reordering entity reorders received MAC-hs PDUs according to the received TSN. MAC-hs PDUs with consecutive TSNs are delivered to the disassembly function upon reception. MAC-hs PDUs are not delivered to the disassembly function if MAC-hs PDUs with lower TSN are missing. There is one reordering entity for each Queue ID configured at the UE.

– Disassembly:
The disassembly entity is responsible for the disassembly of MAC-hs PDUs. When a MAC-hs PDU is disassembled the MAC-hs header is removed, the MAC-d PDUs are extracted and any present padding bits are removed. Then the MAC-d PDUs are delivered to higher layer.

The associated signalling shown in the figure illustrates the exchange of information between layer 1 and layer 2 provided by primitives shown in [3].

Figure 4.2.3.3-1: UE side MAC architecture / MAC-hs details

Figure 4.2.3.3-2: UE side MAC architecture/MAC-hs details (1.28Mcps TDD multi-frequency HS-DSCH operation mode only)

4.2.3.4 MAC-e/es entity – UE Side

The split between MAC-e and MAC-es in the UE is not detailed. In the model below the MAC-e/es comprises the following entities:

– HARQ:
The HARQ entity is responsible for handling the MAC functions relating to the HARQ protocol. It is responsible for storing MAC-e payloads and re-transmitting them. The detailed configuration of the hybrid ARQ protocol is provided by RRC over the MAC-Control SAP.

– For FDD: The HARQ entity provides the E-TFC, the retransmission sequence number (RSN), and the power offset to be used by L1. Redundancy version (RV) of the HARQ transmission is derived by L1 from RSN, CFN and in case of 2 ms TTI from the sub-frame number.

– For TDD: The HARQ entity provides the HARQ process identity, the E-TFC, the retransmission sequence number (RSN) and an indication of the power offset to be used by L1. The redundancy version (RV) of the HARQ transmission is derived by L1 from RSN. RRC signalling can also configure the L1 to use RV=0 for every transmission.

– Multiplexing and TSN setting:
The multiplexing and TSN setting entity is responsible for concatenating multiple MAC-d PDUs into MAC-es PDUs, and to multiplex one or multiple MAC-es PDUs into a single MAC-e PDU, to be transmitted in the next TTI, as instructed by the E-TFC selection function. It is also responsible for managing and setting the TSN per logical channel for each MAC-es PDU.

– E-TFC selection:
This entity is responsible for E-TFC selection according to the scheduling information, Relative Grants (FDD only) and Absolute Grants, received from UTRAN via L1 and Serving Grant value signalled through RRC, and for arbitration among the different flows mapped on the E-DCH. The detailed configuration of the E-TFC entity is provided by RRC over the MAC-Control SAP. The E-TFC selection function controls the multiplexing function.

– Scheduling Access Control (TDD only):

The Scheduling Access Control entity is responsible for routing associated uplink signalling via E-UCCH and MAC-e PDU (in the case that E-DCH resources are assigned) or via E-RUCCH (in the case that no E-DCH resources are assigned). It is also responsible for obtaining and formatting the appropriate information to be carried on E-UCCH/E-RUCCH.

NOTE: HARQ process ID and RSN are carried on E-UCCH.

Figure 4.2.3.4-1a: UE side MAC architecture / MAC-e/es details (FDD)

Figure 4.2.3.4-1b: UE side MAC architecture / MAC-e/es details (TDD)

4.2.3.5 MAC-ehs entity – UE Side

In the model below the MAC-ehs comprise the following entities, In 1.28 Mcps TDD multi-frequency HS-DSCH cell, the associated downlink control channel and uplink control channel pair controlling the HS-DSCH transmission on the certain carrier shall be allocated on the same carrier. The downlink control channel carries the HS-DSCH operation related info and the uplink control channel carries the feedback info from the UE side.

– HARQ:
The HARQ entity is responsible for handling the HARQ protocol. There shall be one HARQ process per HS-DSCH per TTI for single stream transmission, two HARQ processes per HS-DSCH per TTI for dual stream transmission, three HARQ processes per HS-DSCH per TTI for three stream transmission (FDD only) and four HARQ processes per HS-DSCH per TTI for four stream transmission (FDD only). There shall be one HARQ entity per HS-DSCH (FDD only). The HARQ functional entity handles all the tasks that are required for hybrid ARQ. It is for example responsible for generating ACKs or NACKs. The detailed configuration of the hybrid ARQ protocol is provided by RRC over the MAC-Control SAP.In 1.28 Mcps TDD multi-frequency HS-DSCH cell, multiple HARQ processes are assigned for HS-DSCH operaton on every carrier independently, namely HARQ sub-entity; only one HARQ process is allowed to receive HS-DSCH in one TTI for each carrier. The maximum number of HARQ process per HS-DSCH per TTI on which an HS-DSCH transmission can be received is one.

– Disassembly:
The disassembly entity disassembles the MAC-ehs PDUs by removing the MAC-ehs header and possible padding. For 1.28 Mcps TDD, the disassembly entity discards the MAC-ehs PDU if the L field in MAC-ehs header is zero.

– Reordering queue distribution:
The reordering queue distribution function routes the received reordering PDUs to correct reordering queues based on the received logical channel identifier.

– Reordering:
The reordering entity organises received reordering PDUs according to the received TSN. Data blocks with consecutive TSNs are delivered to reassembly entity upon reception. A timer mechanism determines delivery of non-consecutive data blocks to higher layers. There is one reordering entity for each MAC-ehs Queue ID configured at the UE. For the logical channels BCCH and PCCH no re-ordering is applied.

– Reassembly:
The reassembly entity reassembles segmented MAC-ehs SDUs (corresponding to either MAC-c or MAC-d PDUs) and forwards the MAC PDUs to LCH-ID demultiplexing entity.

– LCH-ID demultiplexing:
The demultiplexing entity routes the MAC-ehs SDUs to correct logical channel based on the received logical channel identifier.

The following is allowed:

– The MAC-ehs SDUs included in a MAC-ehs PDU can have a different size and a different priority and can be mapped to different priority queues.

In case of Multiflow, there can be two MAC-ehs entities, if so configured by upper layers.

Figure 4.2.3.5-1: UE side MAC architecture/MAC-ehs details.

Figure 4.2.3.5-2: UE side MAC architecture/MAC-ehs details (1.28Mcps TDD multi-frequency HS-DSCH operation mode only)

4.2.3.6 MAC-i/is entity – UE Side

The split between MAC-i and MAC-is in the UE is not detailed. In the model below the MAC-i/is comprises the following entities:

– HARQ:
The HARQ entity is responsible for handling the MAC functions relating to the HARQ protocol. It is responsible for storing MAC-i payloads and re-transmitting them. The detailed configuration of the hybrid ARQ protocol is provided by RRC over the MAC-Control SAP.

– For FDD: There shall be one HARQ entity per E-DCH. The HARQ entity provides the E-TFC, the retransmission sequence number (RSN), and the power offset to be used by L1. If uplink MIMO is configured by upper layers, then this information is provided independently for the primary and secondary stream. Redundancy version (RV) of the HARQ transmission is derived by L1 from RSN, CFN and in case of 2 ms TTI from the sub-frame number.

– For TDD: There shall be one HARQ entity per E-DCH for 1.28Mcps TDD. The HARQ entity provides the HARQ process identity, the E-TFC, the retransmission sequence number (RSN) and an indication of the power offset to be used by L1. The redundancy version (RV) of the HARQ transmission is derived by L1 from RSN. RRC signalling can also configure the L1 to use RV=0 for every transmission.

– Multiplexing and TSN setting:
The multiplexing and TSN setting entity is responsible for concatenating multiple MAC-d PDUs into MAC-is PDUs, and to multiplex one or multiple MAC-is PDUs into a single MAC-i PDU, or, for FDD when more than one uplink frequency or uplink MIMO is activated, one or two MAC-i PDUs, to be transmitted in the next TTI, as instructed by the E-TFC selection function, and for 1.28Mcps TDD when multi-carrier E-DCH operation is activated, one or up to 6 MAC-i PDUs, to be transmitted in the next TTI, as instructed by the E-TFC selection function. It is also responsible for managing and setting the TSN per logical channel for each MAC-is PDU.
In FDD and 1.28 Mcps TDD, the multiplexing and TSN setting entity is responsible for multiplexing MAC-c PDUs or segments of MAC-c PDUs into a single MAC-is PDU, and for multiplexing MAC-is PDUs into a single MAC-i PDU, to be transmitted in the next TTI, as instructed by the E-TFC selection function. It is also responsible for managing and setting the TSN for the common control channel for each MAC-is PDU.

– Segmentation:
The segmentation function is responsible for segmenting MAC-d PDUs and MAC-c PDUs (FDD and 1.28 Mcps TDD only).

– CRC Attachment (FDD and 1.28 Mcps TDD only):
If segmentation is performed for MAC-c PDUs, a CRC is appended to the MAC-c PDU and segmentation is then performed for the entire MAC-c PDU including CRC. The size of the CRC field is 8 bits and the CRC is calculated as specified in section 4.2.1.1 in [16] or [19]. In the CRC field, the generated parity bits, denoted as p_im1, p_im2, p_im3, …, p_im8, shall be appended to the MAC-c PDU sequentially such that p_im1 is the leftmost bit and p_im8 is the rightmost bit (see Figure 9.1.5.4d).

– Add UE ID (FDD only):
In CELL_DCH state, no E-RNTI is included in the MAC-PDU header.
In CELL_FACH, the E-RNTI is added in all MAC-i PDUs for DCCH/DTCH and NodeB triggered HS-DPCCH transmission at the UE side until the UE receives an E-AGCH with its E-RNTI (through an E-RNTI-specific CRC attachment).
In CELL_FACH state and in Idle mode, no E-RNTI is added in MAC-i PDUs for CCCH data transmission.

– E-TFC selection:
This entity is responsible for E-TFC selection according to the scheduling information, Relative Grants (FDD only) and Absolute Grants, transmission rank indication and offset received from UTRAN via L1 and Serving Grant value signalled through RRC, and for arbitration among the different flows mapped on the E-DCH. The detailed configuration of the E-TFC entity is provided by RRC over the MAC-Control SAP. The E-TFC selection function controls the multiplexing function.

– ASC selection (FDD and 1.28 Mcps TDD only):
At the start of the Enhanced Uplink in CELL_FACH state and Idle mode, MAC-is/i applies the appropriate back-off parameter(s) associated with the given ASC. When sending an RRC CONNECTION REQUEST message, RRC will determine the ASC; in all other cases MAC-is/i selects the ASC.

– Scheduling Access Control (TDD only):

The Scheduling Access Control entity is responsible for routing associated uplink signalling via E-UCCH and MAC-i PDU (in the case that E-DCH resources are assigned) or via E-RUCCH (in the case that no E-DCH resources are assigned). It is also responsible for obtaining and formatting the appropriate information to be carried on E-UCCH/E-RUCCH.

NOTE: HARQ process ID and RSN are carried on E-UCCH.

Figure 4.2.3.6-1: UE side MAC architecture / MAC-i/is details (FDD)

Figure 4.2.3.6-1a: UE side MAC architecture / MAC-i/is details (uplink MIMO is configured, FDD)

Figure 4.2.3.6-2: UE side MAC architecture / MAC-i/is details (TDD)

Figure 4.2.3.6-2a：UE side MAC architecture/MAC-i/is details (1.28Mcps TDD multi-carrier E-DCH carrier is configured)