05 Introduction to LTE Feature 2.0

HUAWEI TECHNOLOGIES CO., LTD.

www.huawei.com

Huawei Confidential

Security Level:

Introduction to LTE Feature 2.0

ISSMS 4.0

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

1. LTE Random Access Algorithm

2. LTE Handover Algorithm

3. LTE Power Control Algorithm

4. LTE ICIC Algorithm

5. LTE Scheduling Algorithm


Access in LTE

Definition

In LTE system, access refers to the process of establishing a connection from UE

to eNodeB and MME.

Access Procedure Overview

When a UE needs to establish a connection with the network for any purpose (for

example, service request, location update, or paging), the access procedure is

performed. The generic procedure is as follows:

1. The UE performs random access.

2. Signaling connections between the UE and the MME are established. The connections are an

RRC connection and a dedicated S1 connection.

3. If the connection is for the purpose of a service request, the MME will then instruct the

eNodeB to establish an E-RAB. The MME establishes, modifies and releases the bearer

through radio bearer management.


Access Procedure (Paging) Major Functions

The UE requests to access： the system allocates a random access channel. The result is uplink synchronization and dedicated resources allocated.

Signaling connections contains RRC connection and dedicated S1 connection. RRC connection is established upon the request from the UE. Then, the eNodeB establishes dedicated S1 connection between eNodeB and MME. Once the dedicated S1 connection is established, there is a complete signaling pathway from the UE to the MME.

The E-RAB establishment creates radio bearers. Key connections are SRB2 (NAS signaling) and DRBs (user plane data).

Releasing signaling connections involves releasing both the RRC connection and the dedicated S1 connection. RRC connection release indicates release of the RRC connection and all radio bearers. Release may be triggered by either the eNodeB or the MME.


Random Access Scenarios

Random access is performed in the following 5 scenarios:


Random Access Types

Depending on whether contention is introduced, the random access procedure can be categorized into contention based random access and non-contention-based random access:


Random Access Procedure

UE eNB

RA Preamble assignment0

Random Access Preamble 1

Random Access Response2

contention-based and non-contention-based. 1) Non-contention 2) Contention

UE eNB

Random Access Preamble1

Random Access Response 2

Scheduled Transmission3

Contention Resolution 4

Major differences between contention and non-contention RA procedures: In contention-based RA, preambles are generated by UEs. Preambles from different UEs may

conflict, and the eNodeB performs contention resolution for UE access. Initial connection uses the contention-based RA procedure.

In non-contention-based RA, the eNodeB allocates preambles to UEs, so there is no conflict between UEs.


Access – Radio Bearers

Radio bearers are classified

into SRBs and DRBs.

Three SRBs SRB0 carries RRC messages before RRC

connections established. It is transmitted

on CCCH and uses TM at the RLC layer.

SRB1 carries RRC messages and also

carries NAS messages before SRB2 is

established. It is transmitted on DCCH

and uses AM at the RLC layer.

SRB2 carries NAS messages, is

transmitted on DCCH and uses AM on the

RLC layer.


Complete Access Procedure


Handover in LTE

Objectives The eNodeB sends the measurement configuration to a UE, and the UE

performs measurements and completes the handover procedure under the

control of the eNodeB to maintain seamless service.

Triggers for Handover in LTE

Coverage: Coverage-based handover connects a moving UE to the cell with

the best signal quality at any given moment, to guarantee that calls are not

dropped during mobility. (Huawei eRAN2.0 currently supports coverage-

based handover only.) Load: Load-based handover transfers UEs from a heavily loaded or

congested cell to a less loaded cell, to maximize use of system resources.

(Not supported at present) Type of service: Cells which support high speed data services transfer UEs

with only voice services to other RATs. (Not supported at present)


Types of Handover in LTE

Intra-frequency Handover Handover between two LTE cells on the same frequency. Intra-frequency handovers are triggered by UE measurements. As a UE moves from its serving

cell to a neighboring cell on the same frequency, it detects that signal quality is higher in the

neighboring cell, and this triggers a coverage-based handover.

Inter-frequency Handover Handover between two LTE cells on different frequencies. Inter-frequency measurements are triggered by UE measurements. As a UE moves from its

serving cell to a neighboring cell on a different frequency, when signal quality in the serving cell

drops below a certain threshold, this triggers coverage-based inter-frequency measurements.

Inter-RAT Handover Handover from LTE cells to GSM/WCDMA/TD-SCDMA/CDMA2000 cells. Inter-RAT measurements are triggered by UE measurements. As a UE moves out of the area

covered by the LTE system, when signal quality in the serving cell drops below a certain

threshold, this triggers coverage-based inter-RAT measurements.


Event-Triggered Reporting in LTE Events

Event A1: Signal quality in the serving cell is above a threshold. When a UE reports that

the serving cell meets the triggering condition, the eNodeB stops inter-frequency or inter-

RAT measurements.

Event A2: Signal quality in the serving cell is below a threshold. When a UE reports that

the serving cell meets the triggering condition, the eNodeB starts inter-frequency or inter-

RAT measurements.

Event A3: Signal quality in intra-frequency neighboring cells is higher than that in the

serving cell. When a UE reports this event, the eNodeB sends an intra-frequency

handover request.

Event A4: Signal quality in inter-frequency neighboring cells is above a threshold. When

a UE reports this event, the eNodeB sends an inter-frequency handover request.

Event B1: Signal quality in inter-RAT neighboring cells is above a threshold. When a UE

reports this event, the eNodeB sends an inter-RAT handover request.

Reporting Event-triggered periodic reporting


Complete LTE Handover Process Three Phases of Handover

Handover measurement: UEs perform

measurements, which are triggered as

described in the previous slide. Handover decision: Based on

measurement reports from UEs, the

eNodeB decides whether to initiate

handovers. Handover execution: The handover

procedure is executed under the control

of the eNodeB.

Note This presentation uses the common type intra-

frequency handover for example.

Inter-frequency and inter-RAT handover

procedures are similar.


Coverage-Based Intra-Frequency Handover: Intra-Frequency Measurement

Entering/Leaving Conditions for Event A3 Entering condition:

Leaving condition:

Parameters Mn and Ms are the measurement results of the

neighboring and serving cells, respectively. Ofn and Ofs are the frequency specific offsets for

the neighboring and serving cells, respectively. Ocn and Ocs are the cell specific offsets for the

neighboring and serving cells, respectively. Hys is the hysteresis for event A3. Off is the offset for event A3.

Measurement Quantity

RSRP, RSRQ, or both

Measurement Reporting

Event-triggered periodic reporting


Coverage-Based Intra-Frequency Handover: Decision and Execution

Decision1. The eNodeB generates a list of candidate cells that meet the condition for event A3

based on UE measurement reports.

2. It then screens the list of candidate cells. Where measurement results are identical,

intra-eNodeB cells are prioritized over inter-eNodeB cells.

Execution The eNodeB triggers a handover to the target cell with the best signal quality.

There are four possible scenarios: Inter-eNodeB intra-MME handover in the presence of X2. Signaling messages and

packet data are transmitted over the X2 interface between the eNodeBs. Inter-eNodeB intra-MME handover in the absence of X2. Signaling messages and

packet data are transmitted over the S1 interface. Inter-eNodeB inter-MME handover in the presence of X2. Signaling messages are

transmitted over the S1 interface and EPC, and packet data is forwarded over the X2

interface. Inter-eNodeB inter-MME handover in the absence of X2. Signaling messages and

packet data are transmitted over the S1 interface and EPC.


Handover Procedure over X2 Interface


Handover Procedure over S1 Interface


Handover Procedure over S1 Interface (Cont’d)


Inter-Cell Intra-eNodeB Handover Procedure


Power Control: Function and Purpose

Function LTE power control is used to compensate for path loss on channels and shadow

fading, and reduces inter-cell interference.

Power control is implemented on both the eNodeB and the UE. There are uplink

and downlink power control.

Purposes Maintaining service quality

Reducing interference

Reducing energy consumption

Improving coverage and increasing capacity


Downlink Power Control

Signals and ChannelsCell-specific reference signal

Synchronization signal

Physical Broadcast Channel (PBCH)

Physical Control Format Indicator Channel (PCFICH)

Physical Downlink Control Channel (PDCCH)

Physical Downlink Shared Channel (PDSCH)

Physical HARQ Indication Channel (PHICH)

Downlink Power Control Policies Fixed power assignment: Users set a fixed power level for reference signal (RS),

synchronization signal, PBCH, and PCFICH, as well as PDCCH and PDSCH,

which carry common cell information. Dynamic power control: Dynamic power control helps meet QoS requirements,

reduce interference, improve cell coverage, and increase cell capacity. It is

applicable to PHICH, as well as PDCCH and PDSCH, which carry UE dedicated

information.


Downlink PDSCH Power Control The PDSCH uses AMC and HARQ, so there is no strict requirement about PDSCH power control

in protocol. PDSCH power control is classified into power control for dynamic scheduling and for semi-

persistent scheduling. For non-VoIP and hybrid services, with dynamic scheduling, there is

(uniform/non-uniform) power control, or two power levels can be set (with ICIC). VoIP services, with

semi-persistent scheduling, use closed-loop power control.


Uplink Power Control

Power Control of Uplink Signals and Channels

Sounding reference signal

Physical Random Access Channel (PRACH)

Physical Uplink Shared Channel (PUSCH)

Physical Uplink Control Channel (PUCCH)


is the PUSCH transmit power expected by the eNodeB during normal PUSCH demodulation.

Uplink PUSCH Power Control

: the ith uplink subframe

: maximum transmit power of the UE

: number of resource blocks (RBs) allocated to PUSCH, namely PUSCH bandwidth on the ith subframe

: target signal power expected by the eNodeB in the reference transport format (TF) of PUSCH

: power compensation factor

: downlink path loss estimated by the UE, calculated using the measured RSRP and cell-specific RS

: power offset between each MCS and the reference MCS

: adjustment to the PUSCH power at the UE, calculated based on the TPC information in PDCCH

)}()()()())((log10,min{)( TFO_PUSCHPUSCH10CMAXPUSCH ifiPLjjPiMPiP

CMAXP

)(PUSCH iM

i

)(O_PUSCH jP

)( j

PL

)(TF i

)(if

)(PUSCH O_NOMINAL_ jP)(O_UE_PUSCH jP

)(PUSCH O_NOMINAL_ jP

is the power offset of the UE relative to , reflecting the impact of UE

category, service type and channel quality on the PUSCH transmit power at the UE.


PUSCH Power Control eNB updates Po_nominal according to the IN_own( interference level of

current cell ) and OI(overload information) in open loop power control.


Uplink PUCCH Power Control

: the ith uplink subframe


: signal power expected by the eNodeB

: downlink path loss estimated by the UE, calculated using the measured RSRP and cell-

specific RS

: determined by the PUCCH format. nCQI is the number of information bits in CQI; nHARQ the

number in HARQ. It reflects the effect of CQI and HARQ bit counts on power.

: effect of the PUCCH transport format on the transmit power.

: adjustment to the PUCCH power at the UE, calculated based on TPC information on

PDCCH

CMAXP

i

PL

is the target signal power expected by the eNodeB for the reference transport format.

igFnnhPLPPiP HARQCQI F_PUCCH0_PUCCHCMAXPUCCH ,,min

O_PUCCHP

HARQCQI nnh ,

F_PUCCH ( )F

)(ig

O_UE_PUCCHP

PUCCH O_NOMINAL_P

is the power offset of the UE relative to the cell-level , reflecting the impact of

UE category, service type and channel quality on the PUCCH transmit power at the UE.

PUCCH O_NOMINAL_P


Uplink PRACH Power Control


: target power expected by the eNodeB when the PRACH preamble format is 0 and the requirements for

the preamble detection performance are met.

: downlink path loss estimated by the UE, calculated using the measured RSRP and cell-specific RS

: power offset for the current preamble format relative to preamble format 0

: total number of preambles sent by UE during RA process. It cannot exceed the maximum number.

: preamble power ramping step

CMAXP

PL

Process Outline

The eNodeB sets the expected receive power for the initial preamble. The UE calculates path loss

based on RS power. The eNodeB sends and to the UE through system information.

The UE calculates the correct RA preamble power. If an RA attempt receives no response, the UE

increases PRACH power by one step for the next attempt.

steppreNPLPPP )1(,min preamble0_preCMAXPRACH

O_preP

preamble

preN

step

PL

O_preP step


Inter-Cell Interference Coordination (ICIC) Interference in LTE

Within a single cell, the RBs used by all UEs are orthogonal, so intra-cell interference is negligible.

All cells can use the entire system bandwidth, so inter-cell interference is obvious. In particular,

cell edge users (CEUs) are affected by severe interference from neighboring cells.

Two Solutions to Reduce Inter-Cell Interference IRC: combines receiving antennas to combat strong colored inter-cell interference. It operates at

the physical layer. For details, see the MIMO Feature Parameter Description. ICIC: reduces inter-cell interference by collaborating with scheduling and power control. It

operates at the MAC layer. The principle is that the eNodeB limits the time-frequency and power

resources it can allocate to cell center users (CCUs) and CEUs. CEUs experiencing significant

interference from a neighboring cell are allocated resources orthogonal to that cell, or CEUs are

scheduled at staggered times. In this way, inter-cell interference is minimized, throughput is

increased for CEUs, and coverage is improved.

Types of ICIC Dynamic ICIC and static ICIC: The classification depends on the need for dynamic adjustments of

resources on edge bands. Uplink ICIC and downlink ICIC: are both implemented by the eNodeB.


Downlink Initial Band Division and Adjustment

Initial Band Division in Downlink Static ICIC A hexagon represents one cell. White is central area. One of three possible ICIC band division schemes is set by

the parameter CELLBANDDIV. Three neighboring cells will

each use a different scheme.

When the cell edge load is high, more edge bandwidth is assigned.

When increasing edge bandwidth, the eNodeB evaluates interference from neighboring

cells and performs interference coordination on the neighboring cells causing greatest

interference.

When the cell edge load is low, the edge bandwidth is reduced.

When reducing edge bandwidth, the eNodeB removes most recently added bandwidth

first.


UE Type Determination

When UEs access a cell initially, they are CCUs as default. When UEs

access a cell by handover, they are CEUs.

When entering A3 event, that is, the eNodeB receives a measurement report

of RSRP contains both the serving and neighboring cells from this UE, the

UE is treated as a CEU.

When leaving A3 event , that is, the eNodeB receives a measurement report

of RSRP only with the serving cell from this UE, the UE is treated as a

CCU .


ICIC Concept


Static Downlink ICIC Procedure

During network planning, the operating band in each cell is divided into an edge

band and a center band. Edge bands in neighboring cells are orthogonal.

Downlink ICIC evaluates cell load and determines whether to block RBs. If some

RBs on the center band are blocked, interference on neighboring cells is reduced.

Based on cell load and RSRP reported by UEs, the eNodeB adjusts UE types.

When UEs access a cell initially , they are CCUs as default. When UEs access a

cell by handover, they are CEUs.


Dynamic Downlink ICIC Procedure

The serving cell adjusts its edge band based on the

following information and informs the scheduler of

the band information: Band division scheme, as in the network plan

Private ICIC messages from neighboring cells

Target cells for ICIC, determined based on cell information

and interference evaluation. The neighboring cell list is

managed based on private messages and RSRP reported

by UEs.

Results of load evaluations Based on load evaluations, DL ICIC determines

whether or not to block RBs. If some RBs on the

center band are blocked, interference effects on

neighboring cells are reduced. Based on the RSRP and evaluated cell load reported

by UEs, the eNodeB adjusts UE types, and

scheduling changes in turn.


Static Uplink ICIC Procedure

During network planning, the uplink operating band in each cell is divided into an edge

band and a center band. Edge bands in neighboring cells are orthogonal. Based on RSRP measurement reports from UEs, the eNodeB divides UEs into CEUs

and CCUs, and informs the scheduler. Neighboring cells continually check themselves for interference. When interference

exceeds the OI threshold, a cell sends an OI message to all neighboring cells. When a

serving cell receives an OI message, it checks its validity and executes the necessary

adjustments.


Dynamic Uplink ICIC Procedure

Based on RSRP measurement reports from UEs, the eNodeB divides UEs into CEUs and

CCUs, and informs the scheduler. The eNodeB maps band division information into HII messages and sends them to

neighboring cells (HII target cells). The eNodeB of the serving cell (HII source cell) then

continually adjusts its edge-band bandwidth according to edge-band load and its

neighboring cell list. Then, the eNodeB informs the scheduler. Neighboring cells continually check themselves for interference. When interference

exceeds the OI threshold, a cell sends an OI message to all neighboring cells. When a

serving cell receives an OI message, it checks its validity and executes the necessary

adjustments.


Intra-eNodeB Time-Domain Uplink ICIC Procedure

For interference coordination between

different cells on a single eNodeB When frequency coordination fails to

resolve high interference Not for TDD mode or handover users

Procedure:

Based on RSRP measurement reports from UEs, the eNodeB divides UEs into CEUs and CCUs,

and informs the scheduler.

Neighboring cell list is managed based on RSRP and HII messages. Intra-eNodeB coordination

covers intra-eNodeB cells on the cell-level neighboring cell list.

Neighboring cells continually check themselves for interference. When interference exceeds the OI

threshold, a cell sends an OI message to all neighboring cells. When a serving cell receives an OI

message, it checks its validity and executes the necessary adjustments.

UE types and neighboring cell information are inputs to the scheduler. The scheduler determines

which neighboring cell is causing the interference, and then decides for each CEU to use either odd

or even sub-frames only.


What Is Scheduling?

Overview When LTE is using shared channels, time-frequency resources are

dynamically shared. How does the eNodeB allocate resources? Through

scheduling. Scheduling is the process of allocating time-frequency

resources to UEs based on service type, data volume, and channel

quality. Scheduling for both uplink and downlink is completed at the MAC layer.

Objectives The objectives of scheduling are to transmit as much data as possible

over good quality connections and maximize capacity, while also meeting

QoS requirements.


Concepts about Scheduling

Channel Quality Channel Quality Indicator (CQI). CQI is a downlink quality indicator. CQI is reported by the UEs under

control the of eNodeB. Reports can be periodic, event-triggered, or both.

Signal to Interference plus Noise Ratio (SINR). In downlink scheduling, uplink SINR is the channel quality

indicator. SINR is measured at the physical layer. To make the IBLER for each UE approach the target

IBLER, the eNodeB adjusts SINR based on uplink data ACK/NACK.

QoS


Scheduling Modes and Policies

Scheduling Modes Dynamic scheduling. The eNodeB makes a scheduling decision every TTI and informs all

UEs to be scheduled. One TTI is 1 ms.

Semi-persistent scheduling. Within a preset semi-persistent scheduling period (20 ms for the

Huawei eNodeB), a single user will use the same time-frequency resources until they are

released. Semi-persistent scheduling is usually used for services with fixed bit rates, periodic

data arrival and small delays, such as VoIP. This type of scheduling can reduces signaling

overhead.

Scheduling Policies Huawei eNodeB supports three basic scheduling policies: Max C/I, Round Robin (RR), and

Proportional Fair (PF). It also supports one enhanced policy: Enhanced PF (EPF).

In the basic policies, all services use dynamic scheduling. In EPF, only VoIP uses semi-

persistent scheduling.

In actual network deployment, EPF is generally used.


Scheduling types Frequency-selective scheduling. In DL scheduling, frequency-selective

scheduling allocates continuous subcarriers or RBs to UEs. This technology

requires that the eNodeB have detailed channel quality information. Using sub-

band CQIs, the eNodeB finds good quality resources increasing system utilization

and peak speed of UEs. Non-frequency-selective scheduling. In DL scheduling, non-frequency-

selective scheduling allocates discrete subcarriers or RBs to UEs. For this mode,

the eNodeB only needs full band CQIs, so signaling overhead is lower. In UL

scheduling, non-frequency-selective scheduling searches within a band from high

to low for continuous usable RBs. When few UEs need to be scheduled in a cell,

frequency-selective scheduling generates many data fragments. Non-frequency-

selective scheduling is therefore prioritized.


Scheduling _Resource Allocation

Resource Allocation Type: Localized: is propitious to frequency-selective scheduling

Distributed: can bring frequency diversity gain.

PDSCH Resource Allocation Type Resource allocation type 0:Based on RBG, bitmap indicates resource allocation.

Resource allocation type 1:Based on RBG subset, bitmap in subset indicates resource allocation

Couldn’t allocate resource from different RBG subset.

Resource allocation type 2:Virtual RB map to Physical RB;

Including localized VRB and Distributed VRB.


Scheduling _Resource Allocation

TYPE 0 : RBG TYPE 1 : RBG Subset


Scheduling _Resource Allocation TYPE 2 based on RB.


Downlink Scheduling

Overview Downlink scheduling allocates time-frequency resources in PDSCH to system information or

data transmission.

The scheduler measures the remaining power and calculates resources that can be scheduled.

It then decides scheduling priorities and MCS based on the volume of data waiting in the RLC

layer, the QoS requirements for each bearer, and UE channel quality (CQIs reported by UEs).

Procedure Scheduling priorities in descending order: VoIP services, control plane data/IMS signaling

messages, data to be retransmitted, and other initially transmitted data services.

The scheduler uses semi-persistent scheduling for VoIP services and dynamic scheduling for

other data.

Control plane data is second in priority only to VoIP. It is dynamically scheduled. Control plane

data includes common control messages and UE level control messages. The scheduling of

IMS signaling messages is consistent with UE level control message processing (SRB1,

SRB2).


Uplink Scheduling Overview

Uplink scheduling is the allocation of suitable PUSCH resources to the right UE at the right time.

EPF scheduling is the default.

Uplink scheduling begins after a request by the UE. MCS is selected and a specific number of RBs

are allocated based on the current UE channel quality, volume of data to be scheduled, and power

headroom.

During uplink scheduling, UE channel quality is indicated by SINR measured at the physical layer by

the eNodeB; data volume is reported by the UE in its BSR; power headroom is reported by the UE in

its PHR.

Procedure Scheduling priorities in descending order: VoIP services, control plane data/IMS signaling

messages, data to be retransmitted, and other initially transmitted data services.

The scheduler uses semi-persistent scheduling for VoIP services and dynamic scheduling for other

data.

Control plane data is second in priority only to VoIP. It is dynamically scheduled. Control plane data

includes common control messages and UE level control messages. The scheduling of IMS

signaling messages is consistent with UE level control message processing (SRB1, SRB2).

Thank youwww.huawei.com

05 Introduction to LTE Feature 2.0

Documents

Transcript of 05 Introduction to LTE Feature 2.0