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