5_ LTE Tutorial - Higher Layers Part II

7/27/2019 5_ LTE Tutorial - Higher Layers Part II

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Mobility Functions: Network Architecture

Anchor with

Operators IP

services (e.g. IMS)

HSS

S1U

Mobility AnchorLTE and other3GPP techs.

Buffers DL datawhile paging.

non

. e a e o y an ng. Paging initiation.

Cellreselection

X2

Inter eNB HO Forwarding +

Buffering

ecisions. Mobility

measurements. Tracking Area

updates.

3 de 34

NAS

Mobility Control: ProtocolsUE

eNBNAS

EMM

ESM

MMEEMM

ESM

AS

PDCP

RLC

MACPHY

SCTP

IP

L2PHY

SCTP

IP

L2PHY

trol

Pla

ne

S1MME

AS

PDCP

RLC

MACPHY

LTEUu

Co eNB

X2AP

SCTP

IP

L2

PHY

eNBX2AP

SCTP

IP

L2

PHY

X2 4 de 34

HSPA in RNC.

PDCP only present

in PS user domain.'


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Mobility Control: Protocols.

eNB

UE

eNBNAS

36.331

lane

UE

AS

PDCP

RLC

MAC

PHY

AS

PDCP

RLC

MAC

PHY

LTEUu

Control

P RRC is the main controlling function in the AS.

Responsible for:

Establishing the radio bearers Configuring lower layers using RRC signaling.

Two possible states: RRC_CONNECTED and RRC_IDLE5 de 34

RRC States: RRC_CONNECTED

RRC_CONNECTED Network controlled mobility: Handover

IntraLTE: Intra Interfre uenc .

InterRAT.

UE has an RRC connection. UE has context in EUTRAN.

Network can TX/RX data to/from UE.

UE Monitors PDCCH (it has CRNTI)

Network can instruct DRX Reduced

power consumptionRRC_IDLE

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4/18

RRC States: RRC_IDLE

RRC_CONNECTED

UE controlled mobility: Cell(re)selection, update of tracking areas.

UE monitors paging messages.

UE performs radio channel quality

measurements (own cell + neighb.)

No RRC connection is established.(No signaling radio bearer SRB)RRC_IDLE

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Simplified RRC as compared to UMTS

After readin web a e

CS + PS domains ++ RRC overhead and complexity.

Recovering fast states takes undesired delays.

CELL_DCH

CELL_FACH

rConsum

ption

Click on link 23 s

delay/Continuous

Packet

Connectivity

_

URA_PCH

TX delay

Pow

IDLE_MODE

Battery Killer/Inactivity timeouts

state change.


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RRC States in LTE: Simpler and Faster

RRC_CONNECTED DRX UE only listens at certain

intervals

~ 100 ms

DRX resume transfer even quicker DRX reduced signalling

DRX also present in HSDPA Rel7 CPC(

RRC_IDLE

r nter ace structure.

RRC in eNB (not RNC)

Simpler RRC

Single inquiry by eNB to MME to getUE profile and authentication info.

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RRC Transitions UMTS LTE

CELL_DCH RRC _CONNECTEDHandover

CELL_FACH

CELL_PCH

URA_PCH

It is supposed to be a short

state so no transition with

LTE is supported

IDLE_MODE RRC _IDLECellreselection

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6/18

Mobility in RRC_CONNECTED: Handover

HSS

Flat structure. All network side

radio protocols at eNB

eNB controls HO making extensive

NAS

NAS

AS

AS

use o t e nter ace. X2 interface might not exist 2

types of HO: S1 and X2 HO.

Hard HO.

IntraeNB = IntereNB HO.

Proce ure contro e y RN n UMT s ower(

Quality based: UE reports neighbour cell with better channel.

Coverage based: handover to another RAT.

Loadbased: to avoid congestion in particular cells.11 de 34

X2 Handover: Basic Description

Before HO

X HO erformed between eNBs uick re aration

HO preparation

X

HO Execution HO Completion

Z

It is possible to forward data in a per bearer basis.

Y Multiple Preparation faster recovery if HO failure.

Z Late path switch MME only informed at the end.

Release of resources triggered by target eNB12 de 34


7/18

Measurement Control

UL allocation

Normal data transfer Normal data transfer

X2 Handover: Detailed DescriptionSource eNB Target eNB

L3 signaling

L1/2 sign.

3. HO decision

easuremen epor s

5. Admission Control

HO Request

HO Request ACK

HO Command

DL allocation

Detach from

old cell. SYNC

Deliver buffered

and in transit data

User data

o new ce o arge e

PDCP Status Transfer

Data Forwarding

Buffer packets

from source eNBRandom Access

UL Allocation + Timing Advance

HO Confirm 13 de 34

X2 Handover: Detailed Description

Source eNB Target eNB

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8/18

S1 Handover

Classical centralized HO.

Source eNB asks MME for HO.

MME sends HO command to target eNB.

eNB status is transferred via MME.

GTP Tunnel can be established between eNBs

only to forward data.

From the UE perspective both HO are

identical.

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PDCP and Handover

UE

NAS

RLC: ARQ but it also

considers Unackowledged

AS

RRC

PDCP

RLCMAC

PHY

AS

RRC

PDCP

RLCMAC

PHY

LTEUu

o e su a e or non

delay tolerant services.

Seamless HO.

PDCP not only for ROHC and ciphering, it is

also responsible for insequence delivery and

reordering of PDUs.

.

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PDCP and Seamless Handover

Seamless handover:

OBJETIVE: Interruption Time Minimization.

Used with Radio Bearers carrying control planedata and data bearers mapped on RLCUnacknowledged Mode (e.g. voice service).

eNB forwards only nontransmitted SDUs via X2 totarget eNB.

successfully received packets are lost.

Minimum complexity because context is not

transferred between eNB via X2. ROHC context is reset.

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PDCP and Lossless Handover

Lossless Handover:

OBJECTIVE: insequence delivery without losses.

Possible because PDCP adds a sequence number to

packets

Applied for radio bearers that are mapped on RLC

Acknowledged Mode (e.g. services that can

degrade because of TCP reaction to loss of packets)

Unacknowledged packets are forwarded via X2 an

retransmitted they may be received twice.

ROHC context is reset.

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10/18

Lossless Handover. UL Example

SDUs are delivered to

the GW in sequence

3

4

52

1

1

2

3

ACK 1

ACK 2

6

3

4

5

Source eNB transfers

via X2, outof

sequence SDUs

4

This message contains

STATUS TRANSFER

5

1 2 3 4 5 6

HandoverUnacknowledged

SDUs are reTX

duplicity of P43 4 5 6

6

Frame Numbers

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Lossless Handover: DL Example

5

4

3

7

End Marker is

forwarded. Target

eNB knows when it

End Marker

4

3

2

1

6

5

4

can s ar s

from SGW

ACK 1

5 4 3 2

STATUS TRANSFER

2

1

Handover

3

2 SDUs are delivered to

the UE in sequence

1 2 420 de 34


11/18

Automatic Neighbour Relation Function

O&MExample of SON

process in LTE

X2

X Configuration,

SW download,

connections.

Y Set up indicated X2s

.

Z X2 missin

^ Update Neighbour

Cell List and obtain IP

_ Set up new X2

] Reports Global CI

[ Global CI Request \ Identifies Global CI

YMEASUREMENT REPORT (PHY CI) X Identifies PHY CI

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ANRF: Some Details

` ANRF allows self optimizing the neighbour list:

Include cells with frequent HO requests.

m na e ce s w very ew a emps.

Eliminate cells with frequent HO failures.

The list should contain the exact set of necessary cells.

` ANRF must consider restrictions from O&M:

Blacklists: cells to which the eNB shall neither establish

nor keep a neighbour relation (test cells, Home eNBs...)

Whitelists.

Avoid certain X2 interfaces, while still allowing S1 HO.

LTE supports Closed Subscriber Groups (CSG)22 de 34


12/18

Example of ANR Architecture

R3080988 R3080731 R3080958 R3080933

O&M

Relation

Id

Local

Cell Id

Target

Cell Id

No

RemoveNo HO No X2

ANR epor

1 LCI#1 TCI#1 X

2 LCI#1 TCI#2 X

3 LCI#1 TCI#3 X

S1HO

Exchangeinfo (load,

interference)23 de 34

ANR: Collateral Implications

` X2 setup procedure allows automatic exchange of APPlayer configuration data, e.g. PHY CI, tracking area,frequency band

` This would enable another SON process: automaticcoordination of PHY CI among neighbours.

Proposes PHY CI coordination:R3080376

Confusion free: neigbours of neighbours.

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Automated Coordination of PHY CIs implybenefits beyond the mobility ones

` PHY CI coordination allows using different RS sequences

and with different frequency shifts.

` More on SON:32.500

pow

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Measurement Reporting for Mobility

RRC_CONNECTION_RECONFIGURATION

1Measurement ob ects e. . fre uenc blacklists.

2 Type of reporting: periodic or event triggered.

3 Criteria (BB = becomes better than, BW = worse)

A1/A2: serving BB/BW thresholds (thrs).

A3: neighbour BB serving + offset.

A4: neighbour BB thr.

A5: servin BW thr. and nei hbour BB another thr.

InterRAT:

B1: neighbour BB thr.

B2: serving BW thr. and neighbour BB another thr.

4Measurement Gaps: Periodic 6 ms gaps to evaluate other

RATs. During this time LTE TX/RX activities are interrupted. 26 de 34


14/18

UMTS: UE updates Location & Routing Areas (CS & PS).

LTE: Only PS domain: UE updates Tracking Area.

UMTS: Specific PHY Channel for paging: PICH

Mobility in RRC_IDLE: Paging.

LTE: Short Duration of L1/L2 signaling Normal DL data.

Possibility to define a paging DRX cycle.

Paging can be also used to indicate change in system info: themessage contains a SystemInfoModification flag.

Decodes message, it contains id of paged UE(s). Own id not found

Discards message. UE sleeps again according to DRX cycle

PDCCH PDCCH PDSCHPDSCH

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Cell selection: UE searches strongest cell on all EUTRAN bands that

supportsmay use historical info into service as fast as

possible. Criteria: Ref Symb RX Power and Quality RSRP, RSRQ.

Mobility in RRC_IDLE: Cell (re)selection

Intrafrequency cell reselection: After camping on a cell, UE

continues searching better candidates. Criteria: RSRP with classical

hysteresis and timetotrigger.

Interfrequency and InterRAT cell reselection: In order to avoid

(UTRAN used same ranking for intra/interfrequency

.

UEs only consider lower priorities if current cell quality is below

ThreshHIGH

and target one is over ThreshLOW 28 de 34


15/18

From Idle to Connected

RRC_IDLE

36.300Paging or UE has

data to TX

RRC_CONNECTION_REQUEST (SRB0)

RRC_CONNECTION_SETUP (or REJECT)

RRC_CONNECTION_SETUP_COMPLETE

Admission

Control

Random Access and response with

initial UL resource assignment

RRC_CONNECTED

UE asks first UL grant on PUCCH.

Unless DRX, UE monitors CCEs in PDCCH

1000 times/s (DRX max = paging cycle).

Security Functions

Random Access Procedure

Preamble Transmission

Power setting according to DL estimation on RSRP.

Power ramping supported

RA Response (PDCCH tagged with RARNTI + PDSCH)

UL resource grant.

Temporary Cell Radio Network Id: TCRNTI

Backoff

Timing Advance 30 de 34


16/18

Random Access Procedure

First PUSCH TX Includes CRNTI

If UEs collided, they will collide now again.

eNB detects one CRNTI and uses it. Rest of UEs

understand there was a collision.

Timing Advance (TA) is required to align UL TXs.

First one based on the received delay measured on

.

Process = GSM but higher granularity: 0.52 s

Maximum TA = 0.67 ms (RTT 200 kmmaximum

LTE cell radius = 100 km)

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Admission Control

` AC basically evaluates whether the scheduler can

handle an incoming bearer with the required QoS:

New bearer QoS

Existent bearers QoSResource situation

Priority levels

AC

` QoS is given by

` Guaranteed Bit Rate or Aggregate Maximum Bit

Rate (depending on the service).

` QoS class identifier.32 de 34


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Admission Control

QCI # Priority

L2 packet

delayL2 packet

Example services

budget

1 (GBR) 2 100 ms 102 Conversational voice

2 (GBR) 4 150 ms 103 Conversational video

3 (GBR) 5 300 ms 106 Buffered streaming

4 (GBR) 3 50 ms 103 Realtime gaming

5 (nonGBR) 1 100 ms 106 IMS signaling

6 nonGBR 7 100 ms 10 Live streaming

7 (nonGBR) 6 300 ms 106

email, browsing, file

download, etc8 (nonGBR) 8 300 ms 106

9 (nonGBR) 9 300 ms 106

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More

InterRAT Mobility (interworking issues):

Towards GERAN/UMTS S1 HO without transferring.

Towards cdma2000 dedicated procedures:tunnelling cdma2000 signalling between UE andcdma2000 system over S1, without eNB interpretation

Towards other non3GPP technologies (WIMAX)

CircuitSwitched Fallback: temporary solution?until high quality VoIP is supported? Until VolgaForum solution? (www.volgaforum.com)

HO Security Issues 32.500

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Thank You.

Mario GarciaLozano

mario arcia tsc.u c.edu

5_ LTE Tutorial - Higher Layers Part II

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