1. Technology training (Session 4)
Long Term Evolution
Technology training
(Session 4)

2. Outline LTE major interfaces Physical, transport and logical channels
Physical channel supporting DL transmission

3. Part 1
LTE major interfaces

4. SAE-Architecture LTE Network layout
SAE – flat architecture
Core network,
RAN
RAN consist of single elements: eNode B
Single element simplifies RAN
No single point of failure
Core network provides two planes
User plane (through SGSN)
Control plane (through MME)
Interfaces
S1-UP (eNode B to SGSN)
S1-CP (eNode B to MME)
X2 between two eNode Bs (required for handover)
Uu (UE to eNode B)
LTE Network layout
UE – user equipment (i.e. mobile)
eNode B – base station
SGSN – Support GPRS Serving Node
GGSN – Gateway GPRS Serving Node
MME – Mobility Management Entity
PCRF - Policy and Charging Rules function
SAE = System Architecture Evolution

5. OSI Communication model
LTE interfaces described using OSI model
OSI = Open System Interconnect
Developed by ISO as a general model for computer communication
Used as a framework for development and presentation of most contemporary communication standards
Each layer communicates only with two adjacent layers and its peer on the other side
Each layer receives services from the layer below and provides services to the layer above
Intermediate communication nodes require layers 1 through 3
Internal operation within each layer is independent of the internal operation in any other layer
Note: LTE covers Layers 1-3 of OSI Model

6. LTE protocol-control plane
NAS – Non Access Stratum
RRC – Radio Resource Control
PDCP – Packet Data Convergence Protocol
RLC – Radio Link Control
MAC – Medium Access Control
S1-AP – S1 Application
SCTP – Stream Control Transmission Prot.
IP – Internet Protocol
Note: LTE control plane is almost the same as WCDMA (PDCP did not exist in WCDMA control plane)

7. LTE protocol- user plane
PDCP – Packet Data Convergence Protocol
RLC – Radio Link Control
MAC – Medium Access Control
GTP-U - GPRS Tunneling Protocol
Note: LTE user plane is identical to UMTS PS side. There is no CS in LTE – user plane is simplified.

8. LTE protocol – X2
Connects all eNodeB’s that are supporting end user active mobility (handover)
Supports both user plane and control plane
Control plane – signaling required for handover execution
User plane – packet forwarding during handover
Control plane
GTP-U: GPRS tunneling protocol
STCP: Stream Transmission Control Protocol
User plane

9. Part 2
LTE Uu channelization

10. Channel structure Channels – defined on Uu Logical channels
Formed by RLC
Characterized by type of information
Transport channels
Formed by MAC
Characterized by how the data are organized
Physical channels
Formed by PHY
Consist of a group of assignable radio resource elements
Uu interface
Note: LTE defines same types of channels as WCDMA/HSPA

11. LTE - channel mapping

12. Channels: common, shared, dedicated
Channel – way of organizing information
Common channel
Received by all UEs
Decoded by all UEs
Information of interest to all UEs
Shared
Only portion of information of interest to a given UE
Dedicated
Decoded only if of interest to a given UE

13. Logical channels (“what channels”)
BCCH – Broadcast Control CH
System information sent to all UEs
PCCH – Paging Control CH
Paging information when addressing UE
CCCH – Common Control CH
Access information during call establishment
DCCH – Dedicated Control CH
User specific signaling and control
DTCH – Dedicated Traffic CH
User data
MCCH – Multicast Control CH
Signaling for multi-cast
MTCH – Multicast Traffic CH
Multicast data
Red – common, green – shared, blue - dedicated
LTE Channels

14. Transport channels(“how channels”)
BCH – Broadcast CH (DL)
Transport for BCCH
PCH – Paging CH (DL)
Transport for PCH
DL-SCH – Downlink Shared CH (DL)
Transport of user data and signaling. Used by many logical channels
UL-SCH – Uplink Shared CH (UL)
Transport for user data and signaling
RACH – Random Access CH (UL)
Used for UE’s accessing the network
MCH – Multicast channel
Used for multicast transmission
Red – common, green – shared
LTE Channels

15. PHY Channels LTE Channels Red – common, green – shared
PBCH – Physical Broadcast CH
Broadcast information necessary for accessing the network
PDSCH – Physical DL Shared CH
Uni-cast transmission and paging
PDCCH – Physical Downlink Control CH
Only PHY: Carries mainly scheduling information
PCIFIC – Physical Control Format Indicator
Only PHY: Information required by UE so that PDSCH can be demodulated (format of PDSCH)
PHICH – Physical Hybrid ARQ Indicator
Only PHY: Reports status of Hybrid ARQ
PUSCH – Physical Uplink Shared Channel
Uplink user data and signaling
PUCCH – Physical Uplink Control Channel
Only PHY: Reports Hybrid ARQ acknowledgements
PRACH – Physical Random Access Channel
Used for random access
PMCH – Physical Multicast Channel
Data and signaling for multicast
LTE Channels
Red – common, green – shared

16. Review Name major elements of E-UTRAN Name major elements of EPS
What is the interface between UE and eNodeB?
Name the interface between eNodeBs
Name the interface between eNodeB and MME
What are the properties of common channels?
Are there any common channels on the UL?
What is a shared channel?
Give an example of a shared channel?
What PHY channels are used for broadcast information?

17. Part 3
DL Phy channels

18. PHY channels/signals for DL TX
Service to MAC
Only at PHY
PBCH – used to broadcast static portion of the BCCH
PDSCH – carries user information and signaling from upper layers of protocol stack
SCH – allows mobile to synchronize to the DL TX during acquisition
PDCCH – channel used by MAC scheduler to configure L1/L2 and assign resources (DL scheduling and UL grants)
PCFICH – explains to the UE the format of the DL transmission
PHICH – support for HARQ on the uplink
PUCCH – support for HARQ on the downlink
Channels required for DL transmission

19. Time/Frequency location of PBCH and SS - FDD
PBCH = Physical Broadcast Channel
Used for BCH transport channel
SS = Synchronization Signal
P-SS = Primary Synchronization Signal
S-SS = Secondary Synchronization Signal
SS are used only on Layer 1 – for system acquisition and Layer 1 cell identity
Note: PBCH and SS use innermost part of the spectrum. This way the system acquisition is the same regardless of deployed bandwidth

20. Time/Frequency location of PBCH and SS - TDD
PBCH = Physical Broadcast Channel
Used for BCH transport channel
SS = Synchronization Signal
P-SS = Primary Synchronization Signal
S-SS = Secondary Synchronization Signal
SS are used only on Layer 1 – for system acquisition and Layer 1 cell identity
Note: The position of the P-SS is different in TDD and FDD. By acquiring P-SS, the UE already knows if the system is FDD or TDD.

21. LTE resource grid – detailed view (FDD)
Note: DC subcarrier 0 not represented.
See also:

22. Synchronization Channel (SCH)
SCH – first channel acquired by UE
Based on SCH, UE determines eNode B PHY cell identity (PCI)
504 possible PHY layer cell IDs (PCI = 0,.., 503)
168 groups with 3 identities per group
SCH consist of 2 signals
PSS (Primary Synchronization Signal)
SSS (Secondary Synchronization Signal)
3 possible PSS sequences: NID(2) = 0,1, 2
168 possible SSS sequences: NID(1) = 0,1, …, 167
Cell ID: NIDcell = 3* NID(1) + NID(2)
For FDD (frame type 1)
PSS is transmitted on OFDM symbol 7 in the first time slot of subframe 0 and 5
SSS is transmitted on OFDM symbol 6 in the first time slot of subframe 0 and 5
For TDD (frame type 2)
PSS is transmitted on OFDM symbol 3 in the first time slot of subframe 1 and 6

23. Mapping of the BCCH information
PBCH
PBCH = PHY Broadcast Channel
PBCH provides PHY channel for static part of Broadcast Control Channel (BCCH)
BCCH carriers RRC System Information (SI) messages
SI messages carry System Information Blocks (SIBs)
SI-M is a special SI that carrier Master Information Block (MIB)
In LTE BCCH is split into two parts
Primary broadcast: Carriers MIB and provides UE with fast access to vital system broadcast information. Primary broadcast is mapped to PBCH
Dynamic broadcast: Carries all SIBs that contain quasi-static information on system operating parameters. Dynamic broadcast is mapped to PDSCH
Mapping of the BCCH information
See also:

24. PCH PCH = Paging Channel
Transmitted over PDSCH (messages), PDCCH (paging indicator)
LTE support DRX (UE sleeps between paging occasions)
LTE defines DRX cycle
UE is assigned to P-RNTI (Paging – Radio Network Temporary Identifier)
P-RNTI is set on PDCCH
UE that finds set P-RNTI reads PCH on PDSCH to determine if it is being paged
DRX cycle compromise
Long cycle: good battery life, higher paging delay
Short cycle: faster paging response, shorter UE battery life
DRX and paging
Mapping of PCCH

25. Downlink L1/L2 signaling
Signaling that supports DL transmission
Originates at L1/L2 (no higher layer data or messaging)
Consists of
Scheduling assignments and associated information required for demodulation and decoding of DL-SCH
Uplink scheduling grants for UL-SCH
HARQ acknowledgements
Power control commands
L1/L2 signaling is transmitting in first 1-3 symbols of a subframe – control region
Size of control region may vary dynamically – always whole number of OFDM symbols (1,2,3)
Signaling – beginning of the subframe
Reduces delay for scheduled mobiles
Improves power consumption for non-scheduled mobiles
Three different PHY channel types
PCFIC (PHY Control Format Indicator Channel)
PHICH (PHY – Hybrid ARQ Channel)
PDCCH (PHY Downlink Control Channel)

26. PCFICH PCFICH – PHY Channel Format Indicator Channel
Indicates to UE the size of the control region (1,2 or 3 OFDM symbols)
PCFICH value may be 1, 2 or 3 (0 is reserved for future use)
Decoding of PCFICH is essential for UE operation
Encoded with 1/16 repetition code
Uses QPSK modulation
Mapped to the first symbol of each subframe
16 resource elements in 4 groups of 4 (RE Groups)
Location of the resource elements depends on cell identity
Processing of PCFICH
Note: REGs of the PCFICH are spread in frequency domain to achieve frequency diversity

27. PHICH Processing of PHICH PHICH = PHY Hybrid-ARQ Indicator Channel
HARQ acknowledgements for UL-SCH transmission
As many PHICH channels as the number of UEs in the cell
A set of PHICH channels is multiplexed on the same resource elements (8 normal CP, 4 extended CP)
Transmitted in the first OFDM symbol of the subframe
Occupies 3 resource element groups (REGs) = 12 resource elements (RE)
PHICH response comes 4 sub-frames after PU-SCH
Processing of PHICH

28. PDCCH PDCCH = Physical Downlink Control Channel Used for
DL scheduling assignments
UL scheduling grants
Power control commands
PDCCH message occupies 1,2,4 or 8 Control Channel Elements (CCEs)
CCE = 9 Resource Element groups (REGs) = 36 Resource Elements (REs)
One PDCCH carrier one message with a specific Downlink Control Information (DCI)
Multiple UE-s scheduled simultaneously -> Multiple PDCCH transmissions in a subframe

29. PDCCH DCIs DCI formats of PDCCH
PDCCH carrier Downlink Control Information (DCI)
Multiple DCI formats are defined based on type of information
DCI formats of PDCCH
Format
Purpose
Content
# of bits (FDD)
UL PUSCH grant
RB assignment, MCS, hopping flag, NDI, cyclic shift of DM-RS, CQI, … 44 1
DL PDSCH grant for single code word
Resource allocation header, RB allocation, MCS, HARQ, HARQ PID, … 55 1A
Compact DL PDSCH grant of single code word
Similar to format 1, but with smaller flexibility
RACH initiated by PDCCH order
Localized/distributed VRB assignment flag, preamble index, PRACH message mask index 1B
Compact DL PDSCH grant with pre-coding information
Similar to 1, but with distributed VRB flag, reduced RB allocation flexibility, transmit PMI and pre-coding 49 1C
Very compact DL PDSCH grant
Reduced payload for improved coverage, always uses QPSK on associated PDSCH, restricted RB assignment, No HARQ, … 31 1D
Compact DL PDSCH grant with pre-coding information and power offset
Same as 1, but with reduced RB allocation flexibility and addition of distributed VRB transmission flag. Transmit PMI information for pre-coding, DL power offset 2
MIMO DL grant
Same as 1, but for MIMO transmission 76 2A
Compact MIMO DL grant
Same as 1A, but for MIMO transmission 68 3
2-bit UL power control
TPC for 14 UEs plus 16 bit CRC 3A
1-bit UL power control
TPC for 28 UEs plus 16 bit CRC

30. PDSCH DL-SCH = DL Shared channel
Used for user data coming from upper layers (both signaling and payload)
Optimized for low latency and high data rate
Individual steps in the processing chain operate on data blocks – enables parallel processing
Many different adaptation modes
Modulation
Coding
Transport block size
Antenna mapping (TX diversity, beam forming, spatial multiplexing)

31. Summary of PHY DL channels
L1/L2 signaling
L1/L2 Control
Coding scheme
PHY Channel
Modulation
CFI (Channel format Indicator)
Block code R=1/16
PCFICH
QPSK
HI (HARQ information)
Repetition 1/3
PHICH
BPSK
DCI (Downlink control Information)
Convolutional 1/3 with rate matching
PDCCH
Services to upper layers
Transport channel
Coding scheme
PHY Channel
Modulation
DL-SCH
Turbo 1/3
PDSCH
QPSK, 16-QAM, 64-QAM
BCH
Convolutional 1/3
PBCH
QPSK
PCH
MCH
PMCH

32. Section review
What are two PHY channels providing service to MAC layer?
What are the two signals used in SCH?
What is PCI?
How many PCIs are defined in LTE?
Explain discontinuous reception (DRX)
What is L1/L2 signaling?
Which LTE OFDM symbols are used for L1/L2 signaling?
What is the use of PDCCH?
What is the use of PCFICH?
What type of error control coding is implemented on PDSCH?
Use website to explore different formats of the LTE DL resource grid.