LTE Mobility. Top right corner for field-mark, customer or partner logotypes. See Best practice for...

LTE Mobility

Top right corner for field-mark, customer or partner logotypes. See Best practice for example.

Slide title 40 pt

Slide subtitle 24 pt

Text 24 pt

Bullets level 2-520 pt

Ericsson Internal LTE Mobility2

Content of presentation

Background, Requirements and Solutions for Intra-LTE mobility Inter-RAT mobility with GERAN/UTRAN Inter-RAT mobility with CDMA2000

Intra-LTE mobility


Slide title 40 pt


Text 24 pt



Service requirements on intra-LTE mobility

Not so strong compared to other requirements such as user plane latency (< 10 ms), capacity, …

– 3GPP TR 25.913 only states that the service interruption should be less or equal than GSM CS

Looking at possible services today it is difficult to find some services with strong requirements

– Voice works with < 200 ms– TCP should probably cope with 100 ms interruption as long

as there are not packet losses– Play out buffers for streaming would probably be much

larger than 200 ms Requirements for future services are unknown


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Text 24 pt



Radio requirements

The characteristics of the LTE radio system will lead to quite tough requirements on the intra-LTE mobility solution

– No soft handover– Reuse 1 (potential for strong interference at street corners

etc.)– Problems seen today when using hard handover in HSPA

This leads to a risk that UE is looses connection to serving cell before handover is completed (illustrated on next slide)

– UE experiences a radio link failure, leading to longer service interruption


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Cell 1

Cell 2

The serving cell (1) is no longer

best cell

Threshold (e.g. 3 dB)

Cell 2 is X dB better than Cell 1 (handover is initiated)

After this point the serving cell will no longer be able to

communicate with terminal

time

power

Mobility procedure need to finish in shorter time than this

Cell 3

Risk for radio link failure


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Text 24 pt



Handover Preparation Time in LTE

• The terminal performs continuous measurements on its own and neighboring cells and send measurement reports when required.

• Once the measurement report is sent the serving eNB can take a handover decision and start the handover preparation phase. When the terminal successfully receives the handover command no more communication is required in the source cell

• T1 is the time from when the handover should occur until it do occur

UE Source eNode B

Target eNode B

2. Handover Decision

3. Handover Request

4. Admission Control

5. Handover Request Ack.

7. Handover Command

6. Processing

1. Measurement Report

UE filtering (e.g. 100-200 ms)

T1


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Conclusion / Way forward

Although current service requirements are not so strong it is still probably important to have a mobility solution in the standard that allows for very short service interruption

– It is good to have a future proof solution since it might be difficult to add improvements at a later stage

– PS VoIP performance in LTE need to as good as existing CS networks

Fast handover execution is important– Flat architecture and faster signaling channels etc. could help a bit– We will also continue to study handover performance to

understand the issues– In case this turns out to be an issue we have introduced support

for handover failure recovery (see later slides) which can be further improved in the products if needed


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Intra-LTE mobility solutionBasic principles

eNB controls the handover (network controlled handover)

– Allows tuning, more predictable mobile behavior– Works well with network prepared resources (measurement

report triggers preparation)– Some companies have pushed UE controlled handover

(resources are setup when UE arrive)– Operators like network controlled handover probably for

interoperability and tuning reasons

Lossless handover is supported– Good for TCP and the UDP Streaming performance


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packet data

7. Handover Command (incl. pre-amble)

DL allocation

DL Data Forwarding

10. Handover Confirm

13. Release Resource

11. Handover Complete

UE Source eNB Target eNB Core Network

Deliver buffered and in transit packets to target eNB

Buffer packets from Source eNB

8. Synchronisation (on Random Access Channel using dedicated pre-amble)

9. UL allocation + TA for UE

Flush DL buffer, continue delivering in-

transit packets

Path Switching

12. Handover Complete Ack

Han

dove

r C

ompl

etio

nH

ando

ver

Exe

cutio

n

Legend

L3 signalling

L1/L2 signalling

User Data

UL/DL Data

~20 ms serviceinterruption


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Text 24 pt



Radio link failurePrevious hot topic in 3GPP

In case UE looses contact with source cell it will select a new cell and send a RRC recovery request message (incl. UE identity and “shared secret”)

In case the eNB who receives knows the UE it would be possible to recover the connection with low service interruption

– In case the serving eNB looses contact with the UE it can prepare neighbor eNBs about the potential arrival of the UE

LTE NodeBLTE NodeB

Inter-RAT mobility with GERAN / UTRA


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Text 24 pt



Requirements

3GPP TR 25.913 requires service interruption below 300 ms Most important is probably to support fall back from LTE (initial

spotty coverage) to GERAN/UTRAN (high coverage), mobility in opposite direction also supported

Strong requirements have also lately come for supporting fall back from LTE PS VoIP to GSM/WCDMA CS as well as other forms of CS inter-working

– So far multiple solutions are being studied. PS to CS fallback requires both radio and CN domain handover. Solutions for CS paging over LTE is studied.

Operators also put requirement on more flexible terminal steering mechanism (e.g. subscription based) both for Camping and Active users


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Inter-RAT (GERAN/UTRAN) mobility (PS) Basic principles

similar to intra-LTE

Loss-less network controlled handover

The UE context is “converted” in the network during the handover preparation phase

S1 - UP

AGW - UP AGW - UP

Gi

Packet Data Networks

S4 - CP(Gn)

Node B Node B

RNC RNC

BTS BTS

BSC BSC

2G SGSN 2G SGSN

S4(Gn)

S3 (Gn)

Iu - CP

Iub

Gb Iu - UP / S4 - UP

S3(Gn)

LTE RAN UTRAN(incl. Ev. HSPA) GERAN

Control Interface User Data Interface

AGW - AGW -

eNode B eNode B

S1 - CP

S11

3G SGSN 3G SGSN

S1 - UP

AGW - UP P/S -GW

Gi


S4 - CP(Gn)

Node B Node B

RNC RNC

BTS BTS

BSC BSC

2G SGSN 2G SGSN

S4(Gn)

S3 (Gn)

Iu - CP

Iub


S3(Gn)


Control Interface User Data Interface Control Interface User Data Interface

AGW MME

eNode B eNode B

S1 - CP

3G SGSN 3G SGSN


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Text 24 pt



Terminal Steering

The basic concept is that the terminal is assigned a list with the priorities of the different RATs and frequency bands (based on “subscription” information)

Different UEs can get different lists A terminal in idle only searches for

higher priority accesses In active mode the eNB controls the

access selection (can also be based on “subscription” information)

1. LTE12. LTE23. WCDMA4. GSM

S1 - UP

AGW - UP AGW - UP

Gi


S4 - CP(Gn)

Node B Node B

RNC RNC

BTS BTS

BSC BSC

2G SGSN 2G SGSN

S4(Gn)

S3 (Gn)

Iu - CP

Iub


S3(Gn)


Control Interface User Data Interface

AGW - AGW -

eNode B eNode B

S1 - CP

S11

3G SGSN 3G SGSN

S1 - UP

AGW - UP P/S -GW

Gi


S4 - CP(Gn)

Node B Node B

RNC RNC

BTS BTS

BSC BSC

2G SGSN 2G SGSN

S4(Gn)

S3 (Gn)

Iu - CP

Iub


S3(Gn)


Control Interface User Data Interface Control Interface User Data Interface

AGW MME

eNode B eNode B

S1 - CP

3G SGSN 3G SGSN

Access Selection

Inter-RAT mobility with CDMA2000


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Text 24 pt



Requirements

Work item was created at RAN plenary in December and Stage 2 CR was agreed (the solution is stable)

Requirements are the same as for inter-RAT handover with GERAN/UTRAN

– Driven mainly by Verizon Wireless, but also KDDI, US Cellular, Alltel

– Goal is to support smooth migration from 3GPP2 systems to LTE

Focus is on handover for “single radio” terminals from LTE to CDMA2000 EV-DO (HRPD) and also CS fallback for LTE VoIP (PS) to CDMA2000 1xRTT (CS)

– CS fallback is already supported between EV-DO (PS) and 1xRTT (CS)


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Principles for CDMA2000 mobility

Although the radio principles for CDMA2000 EV-DO is in many ways similar to HSPA the higher layer protocols stacks are very different from 3GPP accesses

– Different security, UE context, addressing, identities, mobility concepts etc.

It was concluded it would not be possible to “convert” the UE context in the network without involving the UE

Instead a solution was adopted where the UE communicates with the target RAT in a tunnel over the source RAT

– This minimizes the dependencies with between the different access (LTE doesn’t need to know so much about CDMA2000)


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Text 24 pt



LTE to EV-DO handover

PDN GW

S1-MME

S10

MME

S11

UE

E-UTRAN

S7

SGi S1-U

PCRF

Operator's IP services

Rx+

S2a

S101

RNC/PCF PDSN

CDMA2K EV-DO

Serving GW

S5

Han

dove

rco

mm

and

Acc

ess

Similar solution is used for CS fallback


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Text 24 pt



LTE to EV-DO handoverComments

The service interruption of the proposes solution should be similar to the service interruption experienced for handover to GERAN/UTRAN

The preparation time will however likely be longer since UE need to be involved in the preparation signaling

Solution is to separate the preparation into two phases– “pre-registration” which takes longer time and is performed

in advance– “handover execution” which is faster and is performed at

the handover instance


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Text 24 pt



Conclusions on LTE Mobility

The LTE standard have good support for intra and inter-RAT mobility

– Service interruption will be around 20 ms for intra-LTE handover and probably below 200 ms for inter-RAT handover

– It is likely that the handover triggering will be faster in LTE compared to existing 3G networks

Fast handover execution is important in order to minimize the risk for radio link failure

CS fallback is important for operators, in order to be able to deploy VoIP on LTE


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Text 24 pt



Date post:	14-Jan-2016
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