Friday, September 21, 2018

LTE Overview



Course Objectives:
·Understand the development of mobile communications, and Long Term Evolution (LTE) position and network architecture.
·Understand the protocol architecture and basic technologies of E-UTRAN.
·Understand key LTE technologies.





1 Overview
& Knowledge points
Mobile communications development
WCDMA evolution
CDMA2000 evolution

1.1 Background

1.1.1 Mobile Communications Evolution

The development history from 2G and 3G to 3.9 G is the development history from low-speed voice services to high-speed multimedia services of mobile communications.
3GPP has been progressively perfecting LTE R8 standard:
1.    LTE R8 RAN1 was frozen in December 2008.
2.    LTE R8 RAN2, RAN3, and RAN4 were frozen in December 2008..
3.    LTE R8 standard was complete by March 2009, implementing basic LTE functions at the first commercial use of LTE systems.
Figure 1.1‑1 shows the development and evolution of wireless communication technologies.
Figure 1.11  Development and evolution of wireless communication technologies

1.1.2 Comparison Among WCDMA, TD-SCDMA, and CDMA2000

Table 1.11 Comparison among WCDMA, TD-SCDMA, and CDMA2000
Standard
WCDMA
CDMA2000
TD-SCDMA
Inheritance basis
GSM
Narrowband CDMA
GSM
Synchronous mode
Asynchronous
Synchronous
Synchronous
Chip rate
3.84 Mcps
1.2288 Mcps
1.28 Mcps
System bandwidth
5 MHz
1.25 MHz
1.6 MHz
Core network
GSM MAP
ANSI-41
GSM MAP
Voice coding mode
AMR
QCELP, EVRC, and VMR-WB
AMR

1.1.3 WCDMA Evolution

Figure 1.1‑2 shows the WCDMA technology roadmap.
Figure 1.12  WCDMA technology roadmap

1.1.4 TD-SCDMA Evolution

ZTE wireless network equipment supports smooth evolution of recent TD evolution software.
TD evolution can be divided into two stages: standard stage of CDMA technologies and that of OFDMA technologies.
The standard stage of CDMA technologies can smoothly evolve to HSPA+ with spectrum efficiency close to that of LTE.
Figure 1.13  TD-SCDMA evolution

1.1.5 CDMA200 Evolution

Figure 1.14  CDMA200 evolution

1.2 LTE Overview and Standards Development

3GPP working groups started LTE standardization in December 2004. LTE focuses on the enhancement of UTRAN and UTRA.
The establishment of 3GPP standards can be divided into four stages including requirements proposal, architecture establishment, detailed specifications, and testing and verification.
3GPP works in workgroup mode and RAN1/2/3/4/5 workgroups are directly related to LTE.
Figure 1.21  Organization and establishment stages of 3GPP standards


2 LTE Indexes and Requirements

2.1 Overview

& Knowledge points
Spectrum division
LTE system requirements
Others
Physical channels and mapping relationship
Figure 2.1‑1 shows the LTE indexes and requirements prescribed by 3GPP.
Figure 2.11  LTE indexes and requirements

2.2 Frequency Band Division

Table 2.2‑1 lists the E-UTRA frequency bands.
Table 2.21  E-UTRA frequency bands
E‑UTRA Operating Band
Uplink (UL) operating band BS receive UE transmit
Downlink (DL) operating band BS transmit UE receive
Duplex Mode


FUL_low – FUL_high                            
FDL_low – FDL_high



1
1920 MHz
1980 MHz
2110 MHz
2170 MHz
FDD

2
1850 MHz
1910 MHz
1930 MHz
1990 MHz
FDD

3
1710 MHz
1785 MHz
1805 MHz
1880 MHz
FDD

4
1710 MHz
1755 MHz
2110 MHz
2155 MHz
FDD

5
824 MHz
849 MHz
869 MHz
894MHz
FDD

6
830 MHz
840 MHz
875 MHz
885 MHz
FDD

7
2500 MHz
2570 MHz
2620 MHz
2690 MHz
FDD

8
880 MHz
915 MHz
925 MHz
960 MHz
FDD

9
1749.9 MHz
1784.9 MHz
1844.9 MHz
1879.9 MHz
FDD

10
1710 MHz
1770 MHz
2110 MHz
2170 MHz
FDD

11
1427.9 MHz
1452.9 MHz
1475.9 MHz
1500.9 MHz
FDD

12
698 MHz
716 MHz
728 MHz
746 MHz
FDD

13
777 MHz
787 MHz
746 MHz
756 MHz
FDD

14
788 MHz
798 MHz
758 MHz
768 MHz
FDD









17
704 MHz
716 MHz
734 MHz
746 MHz
FDD

...








33
1900 MHz
1920 MHz
1900 MHz
1920 MHz
TDD

34
2010 MHz
2025 MHz
2010 MHz
2025 MHz
TDD

35
1850 MHz
1910 MHz
1850 MHz
1910 MHz
TDD

36
1930 MHz
1990 MHz
1930 MHz
1990 MHz
TDD

37
1910 MHz
1930 MHz
1910 MHz
1930 MHz
TDD

38
2570 MHz
2620 MHz
2570 MHz
2620 MHz
TDD

39
1880 MHz
1920 MHz
1880 MHz
1920 MHz
TDD

40
2300 MHz
2400 MHz
2300 MHz
2400 MHz
TDD

2.3 Peak Data Rate

The instantaneous downlink peak rate reaches 100 Mbit/s (5 bit/s/Hz) at 20 MHz downlink spectrum band (two transmit antennas on the network side and two receive antennas on the UE side).
The instantaneous uplink peak rate reaches 50 Mbit/s (2.5 bit/s/Hz) at 20 MHz uplink spectrum band (one receive antenna on the UE side).

2.4 Control Plane Delay

2.5 User Plane Delay

User plane delay is the unidirectional transmission time that a packet is transmitted from the IP layer of a UE/RAN edge node to the IP layer of a RAN edge node/UE. The RAN edge node indicates the interface nodes of the RAN and core network.

2.6 User Throughput

Downlink:
1.    The user throughput per MHz at the 5% Cumulative Distribution Function (CDF) must reach two to three times the throughput of R6 HSDPA.
2.    The average user throughput per MHz must reach three to four times the throughput of R6 HSDPA.
R6 HSDPA uses one transmitter one receiver (1T1R) while LTE uses two transmitter/two receiver (2T2R).
Uplink:
1.    The user throughput per MHz at the 5% CDF must reach two to three times the throughput of R6 HSUPA.
2.    The user throughput per MHz must reach two to three times the throughput of R6 HSUPA.

2.7 Spectrum Efficiency

Downlink: On a network with effective load, the target LTE spectrum efficiency (measured by the bit quantity per site, per Hz, and per second) is three to four times more efficient than R6 HSUPA. R6 HSDPA uses 1T1R while LTE uses 2T2R.

2.8 Mobility

E-UTRAN can provide optimum network performance for mobile users at the speed of 015 km/h, high performance services at the speed of 15120 km/h, and cell network services at the speed of 120350 km/h (the speed even reaches 500 km/h at specified bands).
Voice services and other realtime services provided in the R6 CS domain are supported by PS domain on the E-UTRAN and all these services can reach or exceed the quality of UTRAN services. The interrupt time caused by handovers within the E-UTRA system must be shorter than or equal to the handover time of the GERAN CS domain.

2.9 Coverage

The E-UTRA system must flexibly support all coverage scenarios on the basis of reusing the current UTRAN sites and frequencies to meet the preceding performance indexes such as the user throughput, spectrum efficiency, and mobility.
The performance requirements of the E-UTRA system within different coverage scope are listed as follows:
1.    Coverage radius within 5 km: The preceding performance indexes such as the user throughput, spectrum efficiency, and mobility must be fully satisfied.
2.    Coverage radius within 30 km: The throughput and spectrum efficiency are allowed to slightly drop but within an acceptable range, and the mobility index must be fully satisfied.

2.10 Spectrum Flexibility

On the one hand, the spectrum flexibility allows deployment of E-UTRA at varied bands including 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. The E-UTRA supports paired and unpaired spectrums.

2.11 Coexistence and Interoperability with Existing 3GPP Systems

Interoperability requirements of the E-UTRA and 3GPP systems include but not limited to:
1.    E-UTRAN and UTRAN/GERAN multi-mode terminals support UTRAN/GERAN measurement and handover between E-UTRAN systems and UTRAN/GERAN systems.
2.    The E-UTRAN system supports inter-system measurement.
3.    The handover interrupt time between R-UTRAN and UTRAN must be shorter than 300 ms for realtime services.
4.    The handover interrupt time between E-UTRAN and UTRAN must be shorter than 500 ms for non-realtime services.
5.    The handover interrupt time between E-UTRAN and GERAN must be shorter than 300 ms for realtime services.
6.    The handover interrupt time between E-UTRAN and GERAN must be shorter than 500 ms for non-realtime services.

2.12 Reducing CAPEX and OPEX

The flattening of the system architecture and the decrease in intermediate nodes dramatically reduces the equipment costs and maintenance costs.


3 LTE Architecture

& Knowledge points
Radio protocol structure
S1 interface
X2 interface

3.1 System Architecture

LTE adopts an OFDM-based air interface technology which is different from those of 2G and 3G. LTE adopts a flat network architecture within which E-UTRAN contains only eNodeBs instead of RNC, so as to optimize the traditional 3G network architecture. LTE supports functions of PDCP/RLC/MAC/physical layer protocols on the E-UTRA user plane and functions of the RRC protocol on the control plane. Figure 3.1‑1 shows the E-UTRAN system architecture.
Figure 3.11  E-UTRAN architecture
eNodeBs are connected over an x2 interface and every eNodeB is connected to the Evolved Packet Core (EPC) network over an S1 interface. The user plane of S1 interfaces terminates on the Serving-Gateway (S-GW) and the control plane of S1 interfaces terminates on the Mobile Management Entity (MME). The other end of the control plane and user plane terminates on the eNodeB. Functions of all NEs in the preceding figure are listed as follows:
·   eNodeB
       Besides the original eNodeB functions, eNodeB of LTE undertakes most of original RNC functions such as physical layer, MAC (including HARQ), RLC layer (including ARQ functions), PDCP, RRC, scheduling, radio access control, access mobility management, and radio resource management among different cells.
       LTE eNodeBs have the following functions:
       Manage radio resources: Radio bearer control, radio access control, connection mobility control, and dynamic resource assignment of uplink and downlink (scheduling).
       Compress IP headers and encrypt user data streams.
       Choose the UE-attached MME when the MME routing information cannot be known from the information provided for the UE.
       Transmit routing data of user planes to the S-GW.
       Schedule and transmit the paging information initiated by the MME.
       Schedule and transmit the broadcast information initiated by the MME or O&M.
       Schedule and transmit the Earthquake and Tsunami Warning System (ETWS) information initiated by the MME.
·   MME
       As the control core of the SAE, MME implements such functions as user access control, service bearer control, paging, and handover control.
       The function of the MME is separated from that of the gateway. The control plane/user plane separated structure facilitates network deployment, single technology evolution, and flexible capacity expansion.
       NAS signaling
       NAS signaling security
       AS security control
       Mobile signaling among 3GPP radio networks
       P-GW or S-GW selection
       MME selection at the time of handover
       SGSN selection at handover to 2G or 3GPP network
       Roaming
       Authentication
       Bearer management, including dedicated bearer establishment
       ETWS signal transmission
·   S-GW
       Local mobile anchor points at eNodeB handover
       Mobile anchor points among 3GPP systems.
       Downlink packet buffering and initialization of network-triggered service request procedure in the E-UTRAN idle mode
       Lawful interception
       Packet routing and forwarding
       Transport-layer packet marking (uplink/downlink)
       Accounting on user and QCI granularity for inter-operator charging.
       Uplink/downlink charging per UE, PDN, or QCI
·   PDN gateway (P-GW)
       Per-user packet filtering (for example, utilize deep packet inspection)
       Lawful interception
       IP address assignment of the UE
       Transport-layer packet marking (downlink)
       Aggregate Maximum Bit Rate (AMBR)-based downlink rate control
As shown in the preceding figure, the original lu interface, lub interface, and lur interface are replaced with the S1 interface and X2 interface in the new LTE architecture.
Figure 3.1‑2 shows the functional split between E-UTRAN and EPC. Yellow boxes depict the logical nodes, white boxes the functional entities of the control plane, and blue boxes the radio protocol layers.
Figure 3.12  Functional split between E-UTRAN and EPC

3.2 Radio Protocol Architecture

3.2.1 Control Plane Protocol Architecture

Figure 3.2‑1 shows the control plane protocol architecture.
Figure 3.21  Control plane protocol stack
The PDCP terminates at eNodeB and implements functions such as control plane encryption and integrity protection.
The RLC and MAC terminate at eNodeB on the network side and implement identical functions of the user plane and control plane.
The RRC terminates at eNodeB and implements such functions as broadcast, paging, RRC connection management, RB control, mobility, and UE measurement reporting and control.

3.2.2 User Plane Protocol Architecture

Figure 3.2‑2 shows the user plane protocol architecture.
Figure 3.22  User plane protocol stack

3.3 S1 Interface and X2 Interface

3.3.1 S1 Interface

The S1 interface is defined as the interface between the E-UTRAN and EPC. The S1 interface contains two parts: the control plane S1-MME interface and user plane S1-U interface. The S1-MME interface is defined as the interface between the eNodeB and MME; the S1-UE interface is defined as the interface between the eNodeB and S-GW. Figure 3.3‑1 and Figure 3.3‑2 respectively show the protocol stack architecture of the S1-MME interface and S1-U interface.
Figure 3.31  S1 interface control plane (eNodeB-MME)
Figure 3.32  S1 interface user plane (eNodeBS-GW)
The S1 interface has the following acknowledged functions:
·   E-RAB service management
       Establishment, modification, and release
·   UE mobility in the ECM-CONNECTED state
       Handover within the LTE system
       Handover between the LTE system and the 3GPP system
·   S1 paging
·   NAS signaling transmission
·   S1 interface management
       Reset
·   Network sharing
·   Roaming and area restriction
·   NAS node selection
·   Initial context establishment
·   UE context modification
·   MME load balance
·   Location report
·   ETWS message transmission
·   Overload
·   RAN information management
·   The S1 interface has the following acknowledged signaling procedures:
·   E-RAB signaling procedure
       E-RAB establishment
       E-RAB modification
       MME-initiated E-RAB release
       eNodeB-initiated E-RAB release
·   Handover signaling procedure
       Handover preparation
       Resource assignment
       Handover termination
       Handover cancellation
·   Paging
·   NAS transmission procedure
       Direct uplink transmission (initial UE message)
       Direct uplink transmission (uplink NAS transmission)
       Direct downlink transmission (downlink NAS transmission)
·   Error indication procedure
       eNodeB-initiated error indication
       MME-initiated error indication
·   Reset
       eNodeB-initiated reset
       MME-initiated reset
·   Initial context establishment
·   UE context modification
·   S1 establishment
·   eNodeB configuration update
·   MME configuration update
·   Location report
       Location report control
       Location report
       Location report failure indication
·   Overload startup
·   Overload stop
·   Directly transmitted information transfer
Figure 3.3‑3 shows the S1 interface signaling procedure.
Figure 3.33  Initial context establishment (blue parts) in Idle-to-Active procedure

3.3.2 X2 Interface

The X2 interface is defined as the interface between eNodeBs. The X2 interface contains two parts: the X2-CP and X2-U, where the X2-CP is the control plane interface between eNodeBs and the X2-U is the user plane interface between eNodeBs. Figure 3.3‑4 and Figure 3.3‑5 respectively show the protocol stack architecture of the X2-CP interface and X2-U interface.
Figure 3.34  X2 interface control plane
Figure 3.35  X2 interface user plane
The X2-CP has the following functions:
·   UE mobility in the ECM-CONNECTED state within the LTE system
       Context transfer from the source eNodeB to the target eNodeB
       User plane channel control between the source eNodeB and the target eNodeB
       Handover cancellation
·   Uplink load management
·   General X2 interface management and error processing
       Error indication
      
The X2-CP interface has the following acknowledged signaling procedures:
·   Handover preparation
·   Handover cancellation
·   UE context release
·   Error indication
·   Load management
The management of load among cells is implemented over the X2 interface.
Figure 3.3‑6 shows that the LOAD INDICATOR message is used for load state communication among eNodeBs.
Figure 3.36  X2 interface LOAD INDICATION message


4 Physical Layer

4.1 Frame Structure

The LTE system supports the following two radio frame structures:
·   Structure 1: Applicable to the FDD mode.
·   Structure 2: Applicable to the TDD mode.
Figure 4.1‑1 shows the frame structure 1. Every 10 ms radio frame is divided into ten sub-frames of fixed length. Each sub-frame contains two time slots each of which is 0.5 ms long.
Figure 4.11  Frame structure 1

4.2 Physical Resources

The minimum resource unit for uplink/downlink transmission in the LTE system is called the Resource Element (RE).
At the time of data transmission, the LTE system consolidates uplink and downlink time-frequency domain physical resources into Resource Blocks (RBs) for scheduling and allocation.
Several REs constitute an RB. There are 12 consecutive sub-carriers on the frequency domain and seven consecutive OFDM symbols (six marks with the Extended CP). That is, the frequency domain width is 180 kHz and the time length is 0.5 ms.
Figure 4.2‑1 and Figure 4.2‑2 respectively show the physical resource structures of downlink and uplink slots.
Figure 4.21  Physical resource structure of downlink slot
Figure 4.22  Physical resource structure of uplink slot

4.3 Physical Channels

The downlink physical channels contain the following channels:
1.    Physical Broadcast Channel (PBCH)
       The coded BCH transmission block maps to four sub-frames within an 40 ms interval.
       With excellent-enough channels, every sub-frame that the PBCH located can separately decode signals.
2.    Physical Control Format Indicator Channel (PCFICH)
       Notify the number of PDCCH-occupied OFDM mark to the UE.
       Transmit the information in every sub-frame.
3.    Physical Downlink Control Channel (PDCCH)
       Notify the resource assignment information of the PCH and DL-SCH and DL-SCH-related HARQ information to the UE.
       Carry the uplink scheduling information.
       Carry the HARQ ACK/NACKs for uplink data transfer.
5.    Physical Downlink Sharing Channel (PDSCH)
       Carry the DL-SCH and PCH information.
6.    Physical Multicast Channel (PMCH)
       Carry the MCH information.
The uplink physical channels contain the following channels:
1.    Physical Uplink Control Channel (PUCCH)
       Carry HARQ ACK/NACKs for downlink data transfer.
       Carry the scheduling request information.
       Carry the CQI report information.
2.    Physical Uplink Sharing Channel (PUSCH)
       Carry the UL-SCH information.
3.    Physical Random Access Channel (PRACH)

4.4 Transport Channels

The downlink transport channels contain the following channels:
1.    Broadcast Channel (BCH)
       Fixed predefined transport format
       Broadcast in the entire coverage area of the cell
2.    Downlink Sharing Channel (DL-SCH)
       Support HARQ.
       Implement dynamic link adaptation by varying the demodulation, coding mode, and transmit power.
       Support broadcast in the entire cell.
       Support beamforming.
       Support dynamic or semi-static resource allocation.
       Support the UE Discontinuous Reception (DRX) to enable UE power saving.
       Support the MBMS transmission.
3.    Paging Channel (PCH)
       Support the UE DRX to save power. (The network notifies the DRX period to the UE.)
       Broadcast in the entire coverage area of the cell
       Map to physical resources which can be used dynamically also for traffic or other control channels.
4.    Multicast Channel (MCH)
       Broadcast in the entire coverage area of the cell
       Support Multicast/Broadcast over Single Frequency Network (MBSFN) combing of MBMS transmission on multiple cells.
       Support semi-static resource allocation.
The uplink transport channels contain the following channels:
1.    Uplink Sharing Channel (UL-SCH)
       Support beamforming.
       Implement dynamic link adaptation by varying the transmit power, potential demodulation, and coding mode.
       Support HARQ.
       Support dynamic or semi-static resource allocation.
2.    Random Access Channel (RACH)
       Carry limited control information.
       Have collision risks.

4.5 Mapping Between Transport Channels and Physical Channels

Figure 4.5‑1 and Figure 4.5‑2 respectively show the mapping relationships between downlink/uplink transport channels and downlink/uplink physical channels.
Figure 4.51  Mapping between downlink transport channels and downlink physical channels
Figure 4.52  Mapping between uplink transport channels and uplink physical channels

4.6 Physical Signals

Physical signals correspond to several physical layer REs, but do not carry any information that comes from higher layers.
The downlink physical signals include the reference signal and the synchronization signal.
·   Reference signal
       The downlink reference signals include the following three types of reference signals:
       Cell-specific reference signals, associated with non-MBSFN transmission
       MBSFN reference signals, associated with MBSFN transmission
       UE-specific reference signals
·   Synchronization signals
       The synchronization signals include the following two types of signals:
       Primary synchronization signal
       Secondary synchronization signal
       For FDD, the primary synchronization signal maps to the last OFDM symbol of the time slot 0 and time slot 10. The secondary synchronization signal maps to the second last OFDM symbol of the time slot 0 and time slot 10.
       The uplink physical signals include the reference signals.
·   Reference signals
       The uplink reference signals include the following two types of signals:
       Demodulation reference signals, associated with PUSCH or PUCCH transmission
       Sounding reference signals, not associated with PUSCH or PUCCH transmission

4.7 Physical Layer Model

The following figures show the physical layer models of various types of channels. Node Bs in all of the following figures are called eNodeBs or eNodeB in LTE.
Figure 4.71  physical layer model for DL-SCH transmission
Figure 4.72  Physical layer model for BCH transmission

Figure 4.73  Physical layer model for PCH transmission
Figure 4.74  Physical layer model for MCH transmission
Figure 4.75  Physical layer model for UL-SCH transmission

4.8 Physical Layer Procedures

4.8.1 Synchronization Procedures

·   Cell search
·   Timing synchronization

4.8.2 Power Control

Power control determines the energy per resource element (EPRE). EPRE denotes the energy prior to CP insertion. EPRE also denotes the average energy taken over all constellation points for the modulation scheme applied. Uplink power control determines the average power of one DFT-SOFDM symbol on a physical channel.
·   Uplink power control
       Uplink power control procedure controls the transmit power of different uplink physical channels.
·   Downlink power allocation

4.8.3 Random Access Procedures

Prior to initiation of the non-synchronized physical random access procedure, physical layer shall receive the following information from the higher layers:
1.    Random access channel parameters (PRACH configuration, frequency position, and preamble format).
2.    Parameters for determining the root sequences and their cyclic shifts in the preamble sequence set for the cell (index to root sequence table, cyclic shift (Ncs), and set type (normal or high-speed set)).
From the physical layer perspective, the physical random access procedure encompasses the transmission of random access preamble and random access response. The remaining messages are scheduled for transmission by the higher layer on the shared data channel and are not considered part of the L1 random access procedure.
The following steps are required for the physical random access procedure:
1.    Physical layer procedure is triggered upon request of a preamble transmission by higher layers.
2.    A preamble index, preamble transmission power (PREAMBLE_TRANSMISSION_POWER), associated RA-RNTI, and PRACH resource are indicated by higher layers as part of the request.
3.    Determine preamble transmit power: PPRACH = min{Pmax, PREAMBLE_RECEIVED_TARGET_POWER + PL}; where, Pmax indicates the maximum allowed power configured at higher layers, and PL indicates UE-calculated downlink path loss.
4.    A preamble sequence is then selected from the preamble sequence set using the preamble index.
5.    A single preamble transmission then occurs using the selected preamble sequence with transmission power PREAMBLE_TRANSMISSION_POWER on the indicated PRACH resource.


5 Layer 2

Layer 2 consists of three sublayers PDCP, RLC, and MAC. Figure 28 and Figure 29 respectively show Layer 2 downlink and uplink structures.
Figure 4.81  Layer 2 downlink structure
Figure 4.82  Layer 2 uplink structure
The connection points among sublayers are known as the Service Access Points (SAP). The service provided by PDCP is referred to as the radio bearer. The PDCP provides the Robust Header Compression (ROHC) and security protection. The SAP between physical layer and MAC layer provides transport channels and that between MAC layer and RLC layer provides logical channels.
The MAC layer provides multiplexing and mapping of logical channels (radio bearer) to transport channels (transport block).

5.1 MAC Sublayer

5.1.1 MAC Functions

The MAC sublayer provides the following functions:
·   Mapping between logical channels and transport channels.
·   MAC Service Data Unit (SDU) multiplexing/demultiplexing.
·   Scheduling information report.
·   Error correction through HARQ
·   Logical channel prioritization of the same UE.
·   UE prioritization through dynamic scheduling.
·   Selection of transmission formats.

5.1.2 Logical Channels

MAC provides different types of data transmission services. The type of each logical channel is defined based on the type of transmitted data.
Logical channels are categorized into:
·   Control channels: used to transfer data on the control plane.
·   Traffic channels: used to transfer data on the user plane.
Control channels include:
·   Broadcast Control Channel (BCCH).
       The BCCH is a downlink channel used to broadcast system control messages.
·   Paging Control Channel (PCCH).
       The PCCH is a downlink channel used to transfer paging messages and system information change notifications. The PCCH is used to page a UE when the UE cell location is unknown to the network.
·   Common Control Channel (CCCH).
       The CCCH is used to transfer control messages between UEs and network when there is no RRC connection between them.
·   Multicast Control Channel (MCCH).
       A point-to-multipoint downlink channel used for transmitting MBMS control information from the network to the UE, for one or several MTCHs. This channel is only used to UEs that receive MBMS.
·   Dedicated Control Channel (DCCH).
       A point-to-point bi-directional channel that transmits dedicated control information between a UE and the network. This channel is used by UEs having an RRC connection.
Traffic channels include:
·   Dedicated Traffic Channel (DTCH).
       The DTCH is a point-to-point channel, dedicated to one UE, for the transfer of user information.
·   Multicast Traffic Channel (MTCH).

5.1.3 Mapping Between Logical Channels and Transport Channels

Figure 5.1‑1 and Figure 5.1‑2 respectively show the mapping between downlink and uplink logical channels and transport channels.
Figure 5.11  Mapping between downlink logical channels and transport channels
Figure 5.12  Mapping between uplink logical channels and transport channels

5.2 RLC Sublayer

5.2.1 RLC Functions

The RLC sublayer provides the following functions:
·   Transfer of upper layer PDUs.
·   Error Correction through ARQ (only for AM data transfer).
·   Concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM data transfer).
·   Re-segmentation of RLC data PDUs (only for AM data transfer).
·   In sequence delivery of upper layer PDUs (only for UM and AM data transfer).
·   Duplicate detection (only for UM and AM data transfer).
·   Protocol error detection and recovery.
·   RLC SDU discard (only for UM and AM data transfer).
·   RLC re-establishment.

5.2.2 PDU Structure

Figure 5.2‑1 shows the RLC PDU structure.
·   The PDU sequence number carried by the RLC header is independent of the SDU sequence number (that is, the PDCP sequence number).
·   The red dotted lines in Figure 32 indicate segmentation positions.
Figure 5.21  RLC PDU structure

5.3 PDCP Sublayer

5.3.1 PDCP Functions

The main services and functions of the PDCP sublayer for the user plane include:
·   Header compression and decompression: ROHC only.
·   Transfer of user data.
·   In-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLC AM.
·   Duplicate detection of lower layer SDUs at PDCP re-establishment procedure for RLC AM.
·   Retransmission of PDCP SDUs at handover for RLC AM.
·   Ciphering and deciphering.
·   Timer-based SDU discard in uplink.
·   The main services and functions of the PDCP sublayer for the control plane include:
·   Ciphering and Integrity Protection.
·   Transfer of control plane data.

5.3.2 PDU Structure

Figure 5.3‑1 shows the PDCP PDU structure.
·   PDCP PDU and PDCP header are octet-aligned.
·   PDCP header can be either 1 or 2 bytes long.
Figure 5.31  PDCP PDU structure


6 RRC

6.1 RRC Functions

Main Functions of RRC include:
·   Broadcast of system information related to the NASs
·   Broadcast of system information related to the ASs
·   Paging
·   Establishment, retention, and release of RRC connection between UEs and E-UTRANs, including:
       Allocation of temporary identifiers between UEs and E-UTRANs
       Configuration of the Signaling Radio Bearers (SRBs) for RRC connection
       Low priority and high priority SRBs
·   Security management including key management
·   Establishment, configuration, retention, and release point-to-point RBs
·   Mobility management, including:
       Measurement report and reporting control of the mobile UEs between cells and between RATs.
       Handover
       UE cell selection and reselection; cell selection and reselection control
       Context forwarding during handover
·   MBMS notification
·   Establishment, configuration, retention, and release of RBs for the MBMS
·   QoS management
·   UE measurement report and reporting control
·   NAS direct transfer

6.2 RRC State

RRC state includes RRC_IDLE and RRC_CONNECTED
·   RRC idle state (RRC_IDLE)
       PLMN selection
       DRX configured by NAS
       System information broadcast
       Paging
       Cell reselection mobility
       A unique identifier allocated to a UE within a Tracking Area (TA)
       No RRC contexts stored in eNodeBs
·   Connection state (RRC_CONNECTED)
       The UE has an E-UTRAN-RRC connection.
       The UE has a context in E-UTRAN.
       The E-UTRAN knows the cell which the UE belongs to.
       The network can transmit and receive data to/from the UEs.
       Network controlled mobility (handover).
       Neighbor cell measurements.
       The PDCP/RLC/MAC features of the RRC_CONNECTED
       The UE can transmit and receive data to/from the networks.
       The UE intercepts controlled signaling channels related to the shared data channels to view that whether the UE is allocated any data on the shared data channel.
       The UE also reports channel quality information and feeds back information to eNodeB.
       The DRX cycle can be conformed according to the UE mobility level to save UE power and enhance resource efficiency. This function is controlled by eNodeB.

6.3 NAS State and the Relationship With the RRC state

The NAS state model can be described by the two-dimensional state model of the EPS Mobility Management state (EMM) and the EPS Connection Management state.
·   EMM state:
       EMM-DEREGISTERED state
       EMM-REGISTERED state
·   ECM state:
       ECM-IDLE state
       ECM-CONNECTED state
Note: The EMM state and the ECM state are mutually independent.
The relationship between the NAS state and the RRC state is as follows:
·   EMM-DEREGISTERED state + ECM-IDLE state Þ RRC_IDLE state
       Mobility feature: PLMN selection
       UE location: Unknown to the network.
·   EMM-REGISTERED state + ECM-IDLE state Þ RRC_IDLE state
       Mobility feature: Cell selection
       UE location: Known to the network at TA level.
·   EMM-REGISTERED state + ECM-CONNECTED state + RB Established Þ RRC_CONNECTED state
       Mobility feature: Handover

6.4 RRC Procedure

6.4.1 System Information

System information includes the Master Information Block (MIB) and a series of System Information Blocks (SIBs).
·   Master Information Block: defines the most important physical information of the cells and is used to receive a further system information.
·   System Information Block Type 1: assesses the related information of whether the UE is allowed to access to a cell and defines the dispatch of other system information blocks.
·   System Information Block Type 2: includes common and shared channel information.
·   System Information Block Type 3: includes cell reselection information; mainly related to the service cells.
·   System Information Block Type 4: includes cell reselection related service frequency points and intra-frequency neighboring cell information.
·   System Information Block Type 5: includes cell reselection related other E-UTRA frequency points and inter-frequency neighboring cell information.
·   System Information Block Type 6: includes cell reselection related UTRA frequency points and UTRA neighboring cell information.
·   System Information Block Type 7: includes cell reselection related GERAN frequency points information.
·   System Information Block Type 8: includes cell reselection related CDMA2000 frequency points and CDMA2000 neighboring cell information.
·   System Information Block Type 9: includes home eNodeB identifiers (HNBID).
·   System Information Block Type 10: includes ETWS primary notification.
·   System Information Block Type 11: includes ETWS secondary notification.

6.4.2 Connection Control

RRC connection control includes:
·   Paging
·   RRC connection establishment
·   Initial security activation
·   RRC connection reconfiguration
·   Counter check
·   RRC connection re-establishment
·   RRC connection release
·   Radio resource configuration
       SRB addition/ modification
       DRB release
       SRB addition/ modification
       MAC main reconfiguration
       Semi-persistent scheduling reconfiguration
       Physical channel reconfiguration
·   Radio link failure related actions


7 Core LTE Technologies

7.1 Duplex Mode

In addition to FDD and TDD duplex modes, the LTE system is expected to further support the half-duplex FDD.

7.2 Multi-access Mode

OFDMA is employed as the multiplexing scheme in the LTE downlink systems.
Figure 7.21  Multiplexing scheme in LTE downlink systems
DFT-S-OFDM (also called SC-FDMA) is employed as the multiplexing scheme in the LTE uplink systems.
Figure 7.22  Multiplexing scheme in LTE uplink systems

7.3 Multi-antenna Technologies

Downlink multi-antenna transmission:
Multi-antenna transmission supports two or four antennas. The maximum number of code words is 2 and irrelevant of the number of antennas, but there is a fixed mapping relationship between core words and layers. Figure 35 shows the general relationship among code words, layers, and antenna ports.
Figure 7.31  Physical channel processing
Multi-antenna technologies include the SDM and transmit diversity. The SDM supports SU-MIMO and MU-MIMO. When a MIMO channel is solely assigned to a single UE, this is called SU-MIMO. When MIMO data streams are spatially assigned to different UEs, this is called MU-MIMO.
Uplink multi-antenna transmission:
Closed loop type adaptive antenna selection transmit diversity shall be supported for FDD (optional in UE).

7.4 Link Adaptation

Downlink adaptation:
Refer to the adaptive modulation and coding (AMC) that is applied with three modulation schemes (QPSK, 16QAM, and 64QAM) and variable code rates.
Uplink adaptation:

7.5 HARQ and ARQ

7.5.1 HARQ

The HARQ within the MAC sublayer has the following characteristics:
·   N-process Stop-And-Wait HARQ is used.
·   The HARQ transmits and retransmits TBs.
In the downlink:
·   Asynchronous adaptive HARQ
·   PUSCH or PUCCH used for ACK/NACKS for DL (re-)transmissions
·   PDCCH used to signal the HARQ process number and if re-transmission or transmission
·   Adaptive re-transmissions scheduled through PDCCH
In the uplink:
·   Synchronous HARQ
·   Maximum number of re-transmissions configured per UE (instead of per radio bearer)
·   PHICH used to transmit ACK/NACKs for non-adaptive UL (re-)transmissions
·   HARQ operation in uplink is governed by the following principles:
       Regardless of the content of the HARQ feedback (ACK or NACK), when a PDCCH for the UE is correctly received, the UE follows what the PDCCH asks the UE to do i.e. perform a transmission or a retransmission (referred to as adaptive retransmission).
       When no PDCCH addressed to the C-RNTI of the UE is detected, the HARQ feedback dictates how the UE performs retransmissions.
       NACK: The UE performs a non-adaptive retransmission.
       ACK: The UE does not perform any UL (re)transmission and keeps the data in the HARQ buffer.

7.5.2 ARQ

The ARQ within the RLC sublayer has the following characteristics:
·   The ARQ retransmits RLC SDUs or RLC PDUs (segments).
       ARQ retransmissions are based on either RLC status reports or HARQ/ARQ interactions.
·   Status reports can be triggered by upper layers.

7.5.3 HARQ/ARQ Interactions



Appendix A Abbreviations
Abbreviation
Full Name
3GPP
3rd Generation Partnership Project
BPSK
Binary Phase Shift Keying
CAPEX
Capital Expenditure
DFT
Discrete Fourier Transform
DRX
Discontinuous Reception
E-MBMS
Evolved Multimedia Broadcast and Multicast Service
eNodeB
Evolution Node B
E3G
evolved 3G
EPC
Evolved Packet Core
E-UTRA
Evolved Universal Terrestrial Radio Access
HCR
High Chip Rate
HeNB
Home eNodeB
IASA
Inter Access System Anchor
IFFT
Inverse Discrete Fourier transform
LCR
Low Chip Rate
LDPC
low-density parity-check
LTE
Long Term Evolution
MIMO
Multiple Input Multiple Output
MME
Mobile Management Entity
OFDM
Orthogonal Frequency Division Multiplex
OPEX
Operating Expenditure
PAPR
Peak to Average Power Ratio
QAM
QUADRATURE AMPLITUDE MODULATION
QoS
Quality of Service
QPSK
QUADRATURE PHASE SHIFT KEYING
RRC
Radio Resource Control
SAE
System Architecture Evolution
SC-FDMA
Single Carrier – Frequency Division Multiple Access
SDM
Spatial Division Multiple
S-GW
Serving Gateway
TTI
Transmission Time Interval


Appendix B References
SN
Name
1
25.912 Feasibility study for evolved Universal Terrestrial Radio Access (UTRA) and Universal Terrestrial Radio Access Network (UTRAN)
2
25.913 Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)
3
36.300 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Overall description
4
25.814 Physical layer aspects for evolved Universal Terrestrial Radio Access (UTRA)
5
36.211 Physical Channels and Modulation
6
36.212 Multiplexing and channel coding
7
36.213 Physical layer procedures
8
36.214 Physical layer – Measurements
9
36.302 Services provided by the physical layer
10
36.331 Radio Resource Control (RRC)
11
36.104 Base Station (BS) radio transmission and reception
12
36.321 Medium Access Control (MAC) protocol specification
13
23.401 General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access
14
23.203 Policy and charging control architecture


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