3GPP LTE MAC Layer
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The document discusses the MAC layer functions and channels in 3GPP LTE networks. It describes the logical and transport channels used at the MAC layer, including common control, dedicated control, dedicated traffic, multicast control and multicast traffic channels. It also explains the mapping between logical and transport channels, and lists the various downlink and uplink physical channels such as PDSCH, PDCCH, PHICH, PUSCH and PUCCH.
3GPP LTE MAC Layer
- 1. EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems 3GPP LTE Channels and MAC Layer © 2009 EventHelix.com Inc. All Rights Reserved.
- 2. EventHelix.com • telecommunication design LTE MAC Layer Functions • systems engineering • real-time and embedded systems Mapping between Error Correction Transparent and Logical Through Hybrid ARQ Channels MAC Priority Handling with Logical Channel Dynamic Scheduling Prioritization © 2009 EventHelix.com Inc. 2
- 3. EventHelix.com MAC in the LTE Protocol • telecommunication design • systems engineering Stack • real-time and embedded systems MME eNodeB UE NAS NAS RRC RRC PDCP PDCP RLC RLC MAC MAC PHY PHY © 2009 EventHelix.com Inc. 3
- 4. EventHelix.com • telecommunication design LTE Channel Architecture • systems engineering • real-time and embedded systems RLC 1. RLC layer passes data to the MAC layer as Logical Channels logical channels. 2. The MAC layer formats MAC and sends the logical channel data as Transport Channels transport channel. 3. The physical layer encodes the transport PHY channel data to Physical Channels physical channels. © 2009 EventHelix.com Inc. 4
- 5. EventHelix.com Downlink PDCP, RLC and • telecommunication design • systems engineering MAC Sublayer Organization • real-time and embedded systems Radio Bearers ROHC ROHC ROHC ROHC PDCP Security Security Security Security Segm. Segm. Segm. Segm. RLC ... ... ARQ etc ARQ etc ARQ etc ARQ etc CCCH BCCH PCCH Logical Channels Scheduling / Priority Handling MAC Multiplexing UE1 Multiplexing UEn HARQ HARQ Transport Channels © 2009 EventHelix.com Inc. 5
- 6. EventHelix.com Uplink PDCP, RLC and MAC • telecommunication design • systems engineering Sublayer Organization • real-time and embedded systems Radio Bearers ROHC ROHC PDCP Security Security Segm. Segm. RLC ... ARQ etc ARQ etc CCCH Logical Channels Scheduling / Priority Handling MAC Multiplexing HARQ Transport Channels © 2009 EventHelix.com Inc. 6
- 7. EventHelix.com • telecommunication design LTE Downlink Channels • systems engineering • real-time and embedded systems PCCH BCCH CCCH DCCH DTCH MCCH MTCH Downlink Logical channels Downlink Transport PCH BCH DL-SCH MCH channels Downlink Physical PBCH PDSCH PMCH PDCCH PHICH channels © 2009 EventHelix.com Inc. 7
- 8. EventHelix.com LTE Downlink Logical • telecommunication design • systems engineering Channels 1 • real-time and embedded systems Paging Control • A downlink channel that transfers paging information and system information change notifications. Channel • This channel is used for paging when the network does not (PCCH) know the location cell of the UE. Broadcast Control • A downlink channel for broadcasting system control Channel information. (BCCH) Common Control • Channel for transmitting control information between UEs and network. Channel • This channel is used for UEs having no RRC connection with (CCCH) the network. © 2009 EventHelix.com Inc. 8
- 9. EventHelix.com LTE Downlink Logical • telecommunication design • systems engineering Channels 2 • real-time and embedded systems Dedicated Control • A point-to-point bi-directional channel that transmits dedicated control Channel information between a UE and the network. • Used by UEs having an RRC connection. (DCCH) Dedicated Traffic • A point-to-point channel, dedicated to one UE, for the transfer of user Channel information. • A DTCH can exist in both uplink and downlink. (DTCH) Multicast Control • A point-to-multipoint downlink channel used for transmitting MBMS Channel control information from the network to the UE, for one or several MTCHs. • This channel is only used by UEs that receive MBMS. (MCCH) Multicast Traffic Channel • A point-to-multipoint downlink channel for transmitting traffic data from the network to the UE. (MTCH) • This channel is only used by UEs that receive MBMS. © 2009 EventHelix.com Inc. 9
- 10. EventHelix.com LTE Downlink Transport • telecommunication design • systems engineering Channels 1 • real-time and embedded systems • Supports UE discontinuous reception (DRX) to enable UE power saving Paging Channel • Broadcasts in the entire coverage area of the cell; (PCH) • Mapped to physical resources which can be used dynamically also for traffic/other control channels. Broadcast • Fixed, pre-defined transport format Channel • Broadcast in the entire coverage area of the cell (BCH) • Broadcasts in the entire coverage area of the cell; Multicast Channel • Supports MBSFN combining of MBMS transmission on multiple cells; (MCH) • Supports semi-static resource allocation e.g. with a time frame of a long cyclic prefix. © 2009 EventHelix.com Inc. 10
- 11. EventHelix.com LTE Downlink Transport • telecommunication design • systems engineering Channels 2 • real-time and embedded systems • Supports Hybrid ARQ Downlink • Supports dynamic link adaptation by varying the modulation, coding and transmit power Shared • Optionally supports broadcast in the entire cell; • Optionally supports beam forming Channel • Supports both dynamic and semi-static resource allocation • Supports UE discontinuous reception (DRX) to (DL-SCH) enable UE power saving • Supports MBMS transmission © 2009 EventHelix.com Inc. 11
- 12. EventHelix.com LTE Downlink Physical • telecommunication design • systems engineering Channels 1 • real-time and embedded systems Physical Downlink • Carries the DL-SCH and PCH Shared Channel • QPSK, 16-QAM, and 64-QAM Modulation (PDSCH) Physical Downlink • Informs the UE about the resource allocation of PCH and DL-SCH, and Hybrid ARQ information related to DL-SCH Control Channel • Carries the uplink scheduling grant (PDCCH) • QPSK Modulation Physical Hybrid ARQ • Carries Hybrid ARQ ACK/NAKs in response to uplink Indicator Channel transmissions. • QPSK Modulation (PHICH) © 2009 EventHelix.com Inc. 12
- 13. EventHelix.com LTE Downlink Physical • telecommunication design • systems engineering Channels 2 • real-time and embedded systems Physical • The coded BCH transport block is mapped to four sub-frames within a 40 ms interval. 40 ms timing is blindly detected, i.e. Broadcast there is no explicit signalling indicating 40 ms timing • Each sub-frame is assumed to be self-decodable, i.e. the BCH Channel can be decoded from a single reception, assuming sufficiently good channel conditions. (PBCH) • QPSK Modulation Physical Multicast • Carries the MCH Channel • QPSK, 16-QAM, and 64-QAM Modulation (PMCH) © 2009 EventHelix.com Inc. 13
- 14. EventHelix.com • telecommunication design LTE Uplink Channels • systems engineering • real-time and embedded systems CCCH DCCH DTCH Uplink Logical channels Uplink Transport RACH UL-SCH channels Uplink Physical channels PRACH PUSCH PUCCH © 2009 EventHelix.com Inc. 14
- 15. EventHelix.com • telecommunication design LTE Uplink Logical Channels • systems engineering • real-time and embedded systems Common Control • Channel for transmitting control information between UEs and network. Channel • This channel is used for UEs having no RRC connection with (CCCH) the network. Dedicated Control • A point-to-point bi-directional channel that transmits dedicated control information between a UE and the Channel network. (DCCH) • Used by UEs having an RRC connection. Dedicated Traffic • A point-to-point channel, dedicated to one UE, for the Channel transfer of user information. • A DTCH can exist in both uplink and downlink. (DTCH) © 2009 EventHelix.com Inc. 15
- 16. EventHelix.com LTE Uplink Transport • telecommunication design • systems engineering Channels • real-time and embedded systems Random Access • Channel carries minimal information • Transmissions on the channel may be lost due to Channel collisions (RACH) Uplink Shared • Optional support for beam forming • Supports dynamic link adaptation by varying the Channel transmit power and potentially modulation and coding • Supports Hybrid ARQ (UL-SCH) • Supports dynamic and semi-static resource allocation © 2009 EventHelix.com Inc. 16
- 17. EventHelix.com LTE Uplink Physical • telecommunication design • systems engineering Channels • real-time and embedded systems Physical Radio • Carries the random access preamble Access Channel • The random access preambles are generated from Zadoff-Chu sequences with zero correlation zone, generated from one or several (PRACH) root Zadoff-Chu sequences. Physical Uplink • Carries the UL-SCH Shared Channel • QPSK, 16-QAM, and 64-QAM Modulation (PUSCH) Packet Uplink • Carries Hybrid ARQ ACK/NAKs in response to downlink transmission • Carries Scheduling Request (SR) Control Channel • Carries CQI reports (PUCCH) • BPSK and QPSK Modulation © 2009 EventHelix.com Inc. 17
- 18. EventHelix.com • telecommunication design RNTI Mapping • systems engineering • real-time and embedded systems • When MAC uses the PDCCH to indicate radio resource allocation, the RNTI that is mapped on the PDCCH depends on the logical channel type: DTCCH RA Resp. PCCH CCCH BCCH and DTCH on DL-SCH Temporary C-RNTI P-RNTI RA-RNTI SI-RNTI C-RNTI Temporary C-RNTI Semi Persistent C-RNTI © 2009 EventHelix.com Inc. 18
- 19. EventHelix.com • telecommunication design Random Access Procedure • systems engineering • real-time and embedded systems Random Access Resource Selection Select Random Access Preamble Determine the next available PRACH Sub-frame Random Access Preamble Transmission Set Preamble Target Power Ask Physical Layer to Transmit Preamble Random Access Response Reception on PDCCH Match the preamble to receive the Apply the timing advance in the message Process uplink resource grant response Contention Resolution Uplink control message is transmitted on the granted uplink The contention resolution timer is stopped when the lower resource and the contention resolution timer is started layers indicate that the message has been acknowledged © 2009 EventHelix.com Inc. 19
- 20. EventHelix.com • telecommunication design DL-SCH Data Transfer • systems engineering • real-time and embedded systems Downlink Assignment Received on PDCCH Message indicates if there is transmission on the DL- New Data Indicator (NDI) is updated SCH for the UE. Hybrid ARQ Operation If received NDI != previous NDI or first transmission: If received NDI == previous NDI: Soft buffer contents are replaced with new data Soft buffer data is chase combined with the new data Data Delivery and Acknowledgement If data in the Soft buffer is successfully decoded and If data decoding in the Soft buffer results in an error, a no error is detected, send positive acknowledgement negative acknowledgement is sent. © 2009 EventHelix.com Inc. 20
- 21. EventHelix.com • telecommunication design UL-SCH Data Transfer • systems engineering • real-time and embedded systems Scheduling Request (SR) is sent to initiate uplink data transfer. Buffer Status Report (BSR) is sent to report pending data in uplink buffers. Power Headroom Report (PHR) communicates the additional return power available at the UE. Uplink Grant assigns uplink resources for transmission UE transmits the uplink data on the assigned resources. Hybrid ARQ is used. © 2009 EventHelix.com Inc. 21
- 22. EventHelix.com • telecommunication design Explore More • systems engineering • real-time and embedded systems Specification Title 3GPP TS 36.300 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 3GPP TS 36.321 Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification 3GPP TS 36.211 Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation © 2009 EventHelix.com Inc. 22
- 23. EventHelix.com • telecommunication design Thank You • systems engineering • real-time and embedded systems Thank you for visiting EventHelix.com. The following links provide more information about telecom design tools and techniques: Links Description EventStudio System Designer 4.0 Sequence diagram based systems engineering tool. VisualEther Protocol Analyzer 1.0 Wireshark based visual protocol analysis and system design reverse engineering tool. Telecom Call Flows GSM, SIP, H.323, ISUP, LTE and IMS call flows. TCP/IP Sequence Diagrams TCP/IP explained with sequence diagrams. Real-time and Embedded System Real-time and embedded systems, call flows and Articles object oriented design articles. © 2009 EventHelix.com Inc. 23