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

TD-SCDMA 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 1.1‑1 Development and evolution of wireless communication technologies

1.1.2 Comparison Among WCDMA, TD-SCDMA, and CDMA2000

Table 1.1‑1 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 1.1‑2 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 1.1‑3 TD-SCDMA evolution

1.1.5 CDMA200 Evolution

CDMA One is a collection of all IS-95-based CDMA products. More specifically, IS-95 is used as a standard for key technologies of all CDMA One-based products.

When CDMA2000 1x employs 1.25 MHz bandwidth, the highest rate of single-carriers reaches 307.2 kbit/s, the peak rate of 1xEV-DO Rev.0 reaches 2.4 Mbit/s in the downlink, and the peak rate of Rev.A reaches 3.1 Mbit/s in the downlink.

Figure 1.1‑4 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 1.2‑1 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 2.1‑1 LTE indexes and requirements

2.2 Frequency Band Division

Table 2.2‑1 lists the E-UTRA frequency bands.

Table 2.2‑1 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

F_{UL_low} – F_{UL_high}

F_{DL_low} – F_{DL_high}

1920 MHz

–

1980 MHz

2110 MHz

–

2170 MHz

FDD

1850 MHz

–

1910 MHz

1930 MHz

–

1990 MHz

FDD

1710 MHz

–

1785 MHz

1805 MHz

–

1880 MHz

FDD

1710 MHz

–

1755 MHz

2110 MHz

–

2155 MHz

FDD

824 MHz

–

849 MHz

869 MHz

–

894MHz

FDD

830 MHz

–

840 MHz

875 MHz

–

885 MHz

FDD

2500 MHz

–

2570 MHz

2620 MHz

–

2690 MHz

FDD

880 MHz

–

915 MHz

925 MHz

–

960 MHz

FDD

1749.9 MHz

–

1784.9 MHz

1844.9 MHz

–

1879.9 MHz

FDD

1710 MHz

–

1770 MHz

2110 MHz

–

2170 MHz

FDD

1427.9 MHz

–

1452.9 MHz

1475.9 MHz

–

1500.9 MHz

FDD

698 MHz

–

716 MHz

728 MHz

–

746 MHz

FDD

777 MHz

–

787 MHz

746 MHz

–

756 MHz

FDD

788 MHz

–

798 MHz

758 MHz

–

768 MHz

FDD

…

704 MHz

–

716 MHz

734 MHz

–

746 MHz

FDD

...

1900 MHz

–

1920 MHz

1900 MHz

–

1920 MHz

TDD

2010 MHz

–

2025 MHz

2010 MHz

–

2025 MHz

TDD

1850 MHz

–

1910 MHz

1850 MHz

–

1910 MHz

TDD

1930 MHz

–

1990 MHz

1930 MHz

–

1990 MHz

TDD

1910 MHz

–

1930 MHz

1910 MHz

–

1930 MHz

TDD

2570 MHz

–

2620 MHz

2570 MHz

–

2620 MHz

TDD

1880 MHz

–

1920 MHz

1880 MHz

–

1920 MHz

TDD

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).

Widebands, MIMOs, and advanced modulation technologies are the key to increasing peak data rates.

2.4 Control Plane Delay

From residence to activation, similarly, from the idle mode to CELL_DCH state of Release 6, the transmission delay time of the control plane is shorter than 100 ms and does not include paging delay time or NAS delay time.

From sleep to activation, similarly, from the CELL_PCH state to CELL_DCH state of Release 6, the transmission delay time of the control plane is shorter than 50 ms and does not include the DRX interval.

Additionally, if the control plane operates at 5 MHz spectrum band, each cell is expected to support 200 activated users. In the case of higher spectrum bands, each cell is expected to support 400 activated users.

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.

In the case of "zero loads" (a single user and a single data flow) and "small IP packets" (only one IP header and no effective load), the user plane delay is expected to be no longer than 5 ms.

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.

R6 HSUPA uses 1T2R, and so does LTE.

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.

Uplink: On a network with effective load, the target LTE spectrum efficiency (measured by the bit quantity per site, per Hz, and per second) is two to three times more efficient than R6 HSUPA. R6 HSUPA uses 1T2R, and so does LTE.

2.8 Mobility

E-UTRAN can provide optimum network performance for mobile users at the speed of 0–15 km/h, high performance services at the speed of 15–120 km/h, and cell network services at the speed of 120–350 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.

In a special case where the moving speed exceeds 250 km/h (in a high-speed train), the physical layer parameters of E-UTRAN must be set to be capable of protecting the connections between users and networks at the highest speed of 350 km/h (the speed even reaches 500 km/h at specified bands).

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.

3. Maximum coverage radius: 100 km.

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.

On the other hand, the spectrum flexibility allows consolidation of spectrum bands.

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.

7. Paging information of only one of the GERAN, UTRA, or E-UTRA systems needs to be monitored for multi-mode terminals in non-active state (similar to R6 Idle mode or Cell_PCH state).

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 3.1‑1 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.

Measure the mobility and scheduling information and perform measurement reporting configuration.

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

The reachability of an UE in the idle state (including the control and implementation of paging signal re-transmission)

Tracking area list management

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

As the anchor point at local eNodeB handover, S-GW implements the following functions: data transfer between the eNodeB and the public data gateway, downlink packet buffer, and user-based billing.

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)

As the designated anchor point of the data bearer, the Public Data Network Gateway (P-GW) has the following functions: Packet forwarding, packet resolving, lawful interception, service-based billing, QoS control, and interconnection with non-3GPP networks.

Per-user packet filtering (for example, utilize deep packet inspection)

Lawful interception

IP address assignment of the UE

Transport-layer packet marking (downlink)

Uplink/downlink service level charging, gating, and rate enforcement

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 3.1‑2 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 3.2‑1 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.

The NAS terminates at MME and implements such functions as EPS bearer management, authentication, idle-mode EPS Connection Management (ECM), idle-mode ECM paging, and security control.

3.2.2 User Plane Protocol Architecture

Figure 3.2‑2 shows the user plane protocol architecture.

Figure 3.2‑2 User plane protocol stack

The user plane PDCP, RLC, and MAC terminate at eNodeB and implements such functions as header compression, encryption, scheduling, ARQ, and HARQ.

3.3 S1 Interface and X2 Interface

Different from those in 2G and 3G systems, S1 interface and X2 interface are newly added in the LTE system.

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 3.3‑1 S1 interface control plane (eNodeB-MME)

Figure 3.3‑2 S1 interface user plane (eNodeB–S-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

Error indication

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

· Write replacement alarm

· Directly transmitted information transfer

Figure 3.3‑3 shows the S1 interface signaling procedure.

Figure 3.3‑3 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 3.3‑4 X2 interface control plane

Figure 3.3‑5 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 3.3‑6 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 4.1‑1 Frame structure 1

For FDD, at every 10 ms, ten sub-frames can be used for downlink transmission and another ten sub-frames can be used for uplink transmission. The uplink transmission and downlink transmission are separated on the frequency domain.

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 4.2‑1 Physical resource structure of downlink slot

Figure 4.2‑2 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.

The 40 ms timing is obtained by blind tests, namely, no specified signaling indicates the 40 ms timing.

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.

4. Physical HARQ Indicator Channel (PHICH)

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)

Carry the random access preamble.

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 4.5‑1 Mapping between downlink transport channels and downlink physical channels

Figure 4.5‑2 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

The demodulation reference signals and the sounding reference signals use the same base sequence set.

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 4.7‑1 physical layer model for DL-SCH transmission

Figure 4.7‑2 Physical layer model for BCH transmission

Figure 4.7‑3 Physical layer model for PCH transmission

Figure 4.7‑4 Physical layer model for MCH transmission

Figure 4.7‑5 Physical layer model for UL-SCH transmission

4.8 Physical Layer Procedures

4.8.1 Synchronization Procedures

· Cell search

Cell search is the procedure by which a UE acquires time and frequency synchronization with a cell and detects that cell’s physical layer cell ID. E-UTRA cell search is based on various signals transmitted in the downlink such as primary and secondary synchronization signals, and downlink reference signals.

· Timing synchronization

Timing synchronization procedures include radio link monitoring, inter-cell synchronization, and transmission timing adjustments.

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

eNodeB determines the downlink transmit energy per resource element.

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: P_PRACH = min{P_max, PREAMBLE_RECEIVED_TARGET_POWER + PL}; where, P_max 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.

6. The associated PDCCH with RA-RNTI is detected in the random access response window controlled by higher layers. If an associated PDCCH with RA-RNTI is detected then the corresponding PDSCH transport block is passed to the higher layers. Higher layers resolve the transport block and indicate the 20-bit UL-SCH grant to the physical layer.

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 4.8‑1 Layer 2 downlink structure

Figure 4.8‑2 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).

Only one transport block is generated at each TTI (1 ms) in the uplink or downlink in the case of non-MIMO.

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.

· Padding.

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).

A point-to-multipoint downlink channel for transmitting traffic data from the network to the UE. This channel is only used to UEs that receive MBMS.

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 5.1‑1 Mapping between downlink logical channels and transport channels

Figure 5.1‑2 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 5.2‑1 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 5.3‑1 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

UE location: Known to the network at cell level.

6.4 RRC Procedure

RRC procedure includes the System Information, Connection Control, mobility procedure, measurements, and direct transfer.

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.

· The MIB maps to the BCCH and BCH. The SI maps to the BCCH and DL-SCH, and is identifies through the System Information RNTI (SI-RNTI). The MIB uses a fixed dispatch cycle of 40 ms. The System Information Block Type 1 uses a fixed dispatch cycle of 80 ms. The other SI dispatch cycle is not fixed and indicated by the System Information Block Type 1.

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 7.2‑1 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 7.2‑2 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 7.3‑1 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:

The baseline antenna configuration for uplink MIMO is either SIMO 1X2 antenna configuration or MU-MIMO. To allow for MU-MIMO reception at the Node B, allocation of the same time and frequency resource to several UEs, each of which transmitting on a single antenna, is supported.

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:

Include three link adaptation techniques: 1) adaptive transmit bandwidth, 2) transmit power control, and 3) adaptive modulation and channel code rate.

7.5 HARQ and ARQ

E-UTRAN provides ARQ and HARQ functionalities.

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.

· Measurement gaps are of a higher priority than HARQ retransmissions: Whenever an H-ARQ retransmission collides with a measurement gap, the H-ARQ retransmission does not take place.

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.

· The RLC must poll RLC status reports.

· Status reports can be triggered by upper layers.

7.5.3 HARQ/ARQ Interactions

If the HARQ transmitter detects a failed delivery of a TB — for example, maximum retransmission limit is reached — the relevant transmitting ARQ entities are notified and potential retransmissions and re-segmentation can be initiated.

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

Friday, September 21, 2018

LTE Overview

2.12 Reducing CAPEX and OPEX

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