lte mac rrc

국내 LTE 상용화 및 관련 MAC, RLC, PDCP, RRC 내용

November 2012

Bong Youl (Brian) Cho, 조 봉 열

[email protected]

mailto:[email protected]

TTA LTE/MIMO Standards/Technology Training

2 © Nokia Siemens Networks

Contents

• Field KPI

• Multi-Carrier operation and CA

• VoLTE and other GBR services

• How to cope with traffic growth?



LTE Field KPI



High level of expectation in Korea

• The quality of mobile service in Korea is the best in the world

Call setup success rate

Call drop rate Call completion rate

Grade

Korea (avg) 99.00% 0.10% 98.50% S

Word Top 7 cities 96.07% 1.95% 93.40% B



System Selection/Registration

* Qualcomm

Information on USIM

HPLMN on RAT basis

CSG Identities list

Forbidden PLMN list

RPLMN

etc…

Information written to USIM

Registered PLMN

Forbidden PLMN list

Information on ME

UE Category, RAT support

Frequency band

Forbidden PLMNs/TAs/Las

MRU Acquisition information

Barred Cells/Barred Frequencies

etc…



Overall UE Camping Procedure

NAS

AS

(1) PLMN selection

Read USIM

Read stored info on ME

Select Band, PLMN, etc

(3) Acquisition

Scan Band/Freq

(2) Trigger System Acquisition

(4) Schedule Broadcast Control Channel read

(5) Read MIB/SIB1

Using SI-RNTI

(6) Process SIB1

Check PLMN

Is Cell reserved?

Is CSG Id valid?

Cell belong to Forbidden TA?

Cell barred?

If fail, go back to (3).

If ok, go to (7).

(7) SIB2 and other SIBs

(8) All SIBs obtained

(9) Cell is selected and UE camps

(10) Service Obtained (Camped)

RRC

PHY



Cells and Services

Categories of Cell • Acceptable*: May “camp” to obtain Limited service

• Suitable*: Can “camp” to obtain Normal service

• Reserved: UEs with AC 11 & 15 are allowed to “camp” in HPLMN

• Barred: Not available for “camping”

• CSG: Only UE of Closed Subscriber Group can “camp”

Requirements for cell selection on a “Suitable Cell” • Part of Selected, Registered, or Equivalent PLMN

• Not barred

• Park of Tracking Area that is not Forbidden

• CSG ID mush be from the allowed CSG list

• Must satisfy the cell selection criteria

Types of Services • Normal: Receive Paging and can transition to Connected state

• Limited**: Emergency calls and ETWS

• Operator: For operators only on reserved cell

* Cell that is “Acceptable” to one UE can be a “Suitable” for another UE and vice versa.

** UE in “Limited Service” periodically scans system to obtain “Normal Service”



Cell Selection Criteria

Srxlev > 0 AND Squal > 0

where: Srxlev = Qrxlevmeas – (Qrxlevmin + Qrxlevminoffset) – Pcompensation

Squal = Qqualmeas – (Qqualmin + Qqualminoffset)

Srxlev Cell selection RX level value (dB)

Squal Cell selection quality value (dB)

Qrxlevmeas Measured cell RX level value (RSRP)

Qqualmeas Measured cell quality value (RSRQ)

Qrxlevmin Minimum required RX level in the cell (dBm), obtained in SIB1

Qqualmin Minimum required quality level in the cell (dB), obtained in SIB1

Qrxlevminoffset Offset to the signalled Qrxlevmin taken into account in the Srxlev evaluation as a

result of a periodic search for a higher priority PLMN while camped normally in

a VPLMN, obtained in SIB1

Qqualminoffset Offset to the signalled Qqualmin taken into account in the Squal evaluation as a

result of a periodic search for a higher priority PLMN while camped normally in

a VPLMN, obtained in SIB1

Pcompensation max(PEMAX_H –PPowerClass, 0) (dB)

PEMAX_H Maximum TX power level an UE may use when transmitting on the uplink in

the cell (dBm) defined as PEMAX_H in [TS 36.101], obtained in SIB1

PPowerClass Maximum RF output power of the UE (dBm) according to the UE power class

as defined in [TS 36.101]



EMM state model

• EPS mobility management state model

– The UE enters the EMM-REGISTERED state by a successful registration procedure

which is either an Attach procedure or a Tracking Area Update procedure



ECM state model

• EPS connection management state model

– For a UE in ECM-CONNECTED state, a signaling connection exists between the UE

and the MME. This signaling connection consists of two parts:

RRC connection (in UE)

UE-associated signaling connection across the S1_MME called UE-associated logical S1-

connection (in MME)



RRC Connection

RRC-Idle • A UE specific DRX may be configured by upper layers.

• UE controlled mobility; (Cell selection/reselection, TA update)

• The UE:

– Monitors a Paging channel to detect incoming calls, system information change, for ETWS capable UEs, ETWS notification, and for CMAS capable UEs, CMAS notification;

– Performs neighbouring cell measurements and cell (re-)selection;

– Acquires system information.

RRC-Connected • Transfer of unicast data to/from UE.

• At lower layers, the UE may be configured with a UE specific DRX.

• Network controlled mobility, i.e. handover;

• The UE:

– Monitors a Paging channel and/ or System Information Block Type 1 contents to detect system information change, for ETWS capable UEs, ETWS notification, and for CMAS capable UEs, CMAS notification;

– Monitors control channels associated with the shared data channel to determine if data is scheduled for it;

– Provides channel quality and feedback information;

– Performs neighbouring cell measurements and measurement reporting;

– Acquires system information.

RRC-Idle RRC-connected

RRC Connection established

RRC Connection released



Connection Establish and Release Procedure



Random Access

• Objectives of random access – Get unique UE identity (C-RNTI)

– Timing correction information for uplink

• 5 Events invoking RA procedure – Initial access from RRC_IDLE

– RRC Connection Re-establishment procedure

– Handover requiring RA procedure

– DL data arrival during RRC_CONNECTED requiring RA procedure when UL synchronization status is “non-synchronised”

– UL data arrival during RRC_CONNECTED requiring RA procedure when UL synchronization status is “non-synchronised” or there is no PUCCH resources for SR

• Random Access channel characteristics – Contention-based transmission & Non-contention-based transmission (e.g. handover)

– Signal structure to support full coverage

– Small preamble to lower overhead (as in WCDMA)

– RA attempts are done in pre-defined time/frequency resources.

PRACH orthogonal to PUSCH/PUCCH (different from WCDMA PRACH)



Access “Preamble” Transmission



PRACH

• PRACH는 RA 과정에서 단말이 기지국으로 전송하는 preamble이다

• 6RB를 차지하며 부반송파 간격은 1.25kHz (format #4는 7.5kHz)

• 64 preamble sequences for each cell 64 random access opportunities per PRACH resource

• Sequence부분은 길이 839의 Z-C sequence로 구성 (format #4는 길이 139)

– Phase modulation: Due to the ideal auto-correlation property, there is no intra-cell interference from multiple random access attempt using preambles derived from the same Z-C root sequence.

• Five types of preamble formats to accommodate a wide range of scenarios

– Higher layers control the preamble format

일반적 환경 (~15km)

넓은 반경의 셀 환경과 같이 시간 지연이 긴 경우 (~100km)

SINR이 낮은 상황을 고려하여 sequence repetition (~30km)

SINR이 낮은 상황을 고려하여 sequence repetition (~100km)

TDD 모드용



Different Preamble Formats



PRACH Location

• One PRACH resource of 6 RBs per subframe (for FDD)

• Multiple UEs can access same PRACH resource by using different preambles

• PRACH may or may not present in every subframe and every frame

PRACH-Configuration-Index parameter indicates frame number and subframe

numbers where the PRACH resource is available.

• Starting frequency is specified by the network ( )

• No frequency hopping for PRACH



Random Access Types

• Non-contention-based (Contention-free) Random Access

– PDCCH or RRC indicates a RA preamble and PRACH resource (PRB) for UE

to send signaling or data on PUSCH

• Contention-based Random Access

– UE selects a RA preamble and PRACH resource to send signaling or data

on PUSCH

– There is probability that multiple UEs in the cell could pick the same

preamble signature and the eNB would assign the same PRB to both UEs

for UL transmission of message/data

– Contention resolution is needed



Non-contention-based Random Access

UE eNB

RA Preamble assignment0

Random Access Preamble 1

Random Access Response2

PRACH

PDSCH

PDSCH



Non-contention-based Random Access

0) Random Access Preamble assignment (and PRACH resource (PRB)) via dedicated signalling in DL:

Signalled via:

- HO command generated by target eNB and sent via source eNB for handover;

- PDCCH in case of DL data arrival.

1) Random Access Preamble on RACH in uplink:

UE transmits the assigned non-contention Random Access Preamble.

‘Power Ramp (with time backoff)’ can be applied until preamble is received.

- The amount of power increase is defined in specification

2) eNB sends a transmission on PDCCH identified using RA-RNTI

Actual RAR (Random Access Response) is on PDSCH pointed by PDCCH w/ RA-RNTI

- No HARQ

- RAR includes RA preamble ID

If UE finds the same RA preamble ID in RAR, UE consider RA was successful.



Contention-based Random Access

UE eNB

Random Access Preamble1

Random Access Response 2

Scheduled Transmission3

Contention Resolution 4

PRACH

PDSCH

PUSCH

PDSCH



Random Access Procedures

Step 1: Random-access preamble transmission

• The network broadcasts info to all UEs in which time-frequency resources random-

access preamble transmission is allowed (i.e., PRACH resources in SIB 2)

• In each cell, there are 64 preamble sequences available

– Two subsets (Preamble set #0 and set #1) as well as ‘preambles for contention-free access’

• A UE randomly selects one sequence in one of the subsets.

• Transmission of random-access preamble for eNB to estimate the UE transmission

timing.

• Only the first step uses physical-layer processing specifically designed for RA

• If UE has been requested to perform a contention-free random access (e.g. handover

to a new cell), the preamble to use is explicitly indicated from eNB

• For FDD, there is at most one random-access region per subframe

• ‘Power Ramp (with time backoff)’ can be applied until preamble is received



Random Access Procedures

Step 2: Random-access response

• After eNB detects the preamble, it sends a transmission on PDCCH identified using RA-

RNTI.

• Actual RAR is on PDSCH pointed by PDCCH w/ RA-RNTI

• Message contains:

– Index of the random-access preamble sequences detected at the network

– The timing correction calculated at the network

– A scheduling grant for Step 3

– A temporary identity, TC-RNTI, used for the following steps

• Collision when multiple UEs using the same preamble at the same time at Step 1.

In this case, multiple UEs will react upon the same downlink response message and

collision occurs.



Random Access Procedures – cont’d

Step 3: Terminal identification

• UE adjusts timing per timing correction info provided at Step 2.

• UE starts a contention resolution timer.

• Each UE will transmit its unique UL CCCH SDU on UL-SCH

• Transmitting the uplink message in the same manner as scheduled uplink data.

– Flexibility on grant size and modulation scheme

– It allows to use HARQ to enhance the receiving performance

Step 4: Contention resolution

• eNB will only receive UL-SCH from UE whose time adjustment was suitable

• Then, eNB sends a PDCCH with a TC-RNTI originally included in RAR and then the

Contention Resolution message on PDSCH where a Contention Resolution ID which

matches the CCCH SDU of only one of the UEs is included

• Each UE receiving the downlink message will compare the Contention Resolution ID

• Only one UE which observes a match b/w the ID received in Step 4 and the ID (CCCH

SDU) used in Step 3 will declare the random-access procedure successful.

• The timer will expire for the other UEs for them to restart the RA process



Timing Advance



LTE Handover

• LTE uses hard handover

• LTE uses UE-assisted network controlled handover – UE reports measurements;

network decides when handover and to which Cell

– For search and measurement of inter-frequency neighboring cells only carrier frequency need to be indicated

• X2 interface used for HO preparation and forwarding of user data – Target eNB prepares handover by sending required information to UE transparently

through source eNB as part of the Handover Request ACK message

– Buffered and new data is transferred from source to target eNB until path switch

preventing data loss

– UE uses contention-free random access to accelerate handover



Mobility Measurement Metrics

• Metrics within Events tell UE what to measure

• E-UTRA metrics

– Reference signal received power (RSRP)

– Reference signal received quality (RSRQ)

• UTRA metrics

– UTRA FDD CPICH RSCP

– UTRA FDD carrier RSSI

– UTRA FDD CPICH Ec/No

• GSM metrics

– GSM carrier RSSI

• CDMA2000 metrics

– CDMA2000 1xRTT pilot strength

– CDMA2000 HRPD pilot strength



Mobility Measurement Reporting

Event Reporting

Periodical Reporting • Report strong cells periodically regardless, if configured by network

Event Purpose

A1 Serving becomes better than threshold

A2 Serving becomes worse than threshold

A3 Neighbor becomes offset better than serving cell + extra margin

A4 Neighbor becomes better than threshold

A5 Serving becomes worse than threshold1 AND neighbor becomes better than threshold2

B1 Inter RAT neighbor becomes better than threshold

B2 Serving becomes worse than threshold1 AND inter RAT neighbor becomes better than threshold2



Inter-eNB Handover



Inter-eNB Handover (X2-based)

1. The source eNodeB makes the decision to handover the UE to the target eNodeB based on

the MEASUREMENT REPORT of the UE and RRM information.

2. The source eNodeB issues a HANDOVER REQUEST message via the X2 interface to the

target eNodeB which passes necessary information to prepare the handover at the target

side.

This message includes signalling references, transport layer addresses and tunnel endpoint

identifiers to enable the target eNodeB to communicate with the source eNodeB and the EPC

nodes, as well as QoS information for the UE's bearers and RRM information.

3. Admission Control is performed by the target eNodeB dependent on the received radio

bearer QoS information and S1 connectivity to increase the likelihood of a successful

handover.

If the resources can be granted by the target eNodeB, it configures the required resources

according to the received UE context information, and reserves a C-RNTI (cell radio network

temporary identifier) and a dedicated preamble for the UE.

4. The target eNodeB prepares the handover regarding layer 1 and layer 2 and sends a

HANDOVER REQUEST ACKNOWLEDGE message via X2 to the source eNodeB.

The HANDOVER REQUEST ACKNOWLEDGE message includes a transparent container to

be sent to the UE later as part of the CONNECTION RECONFIGURATION message. The

container includes the new C-RNTI and the value of the dedicated preamble to be used by

the UE to synchronise with the target cell as well as other parameters required by the UE.




5. The source eNodeB sends a CONNECTION RECONFIGURATION message towards the

UE, which includes the transparent container (of the previous step) received from the target

eNodeB.

6. The SN STATUS TRANSFER message is sent from the source to the target eNodeB.

Thereby PDCP layer information is transferred to ensure uplink and downlink PDCP SN

continuity for every bearer that requires PDCP status preservation.

7. Some time after sending the CONNECTION RECONFIGURATION message to the UE (and

possibly before sending the SN STATUS TRANSFER message to the target eNodeB), the

source eNodeB begins forwarding user data in the form of PDCP SDUs using the resources

set up previously and continues as long as packets are received at the source eNB from the

EPC.

8. When the UE receives the CONNECTION RECONFIGURATION message with the

necessary parameters (i.e. new C-RNTI, dedicated preamble, target cell ID etc.) it is

commanded by the source eNodeB to perform the handover immediately to the target cell.

The UE then performs the non-contention based random access procedure.

9. The random access response conveys timing alignment information and initial uplink grant

for handover.

10. When the UE has successfully accessed the target cell, it sends the CONNECTION

RECONFIGURATION COMPLETE message (containing its new C-RNTI) to the target

eNodeB to indicate that the handover procedure is completed for the UE.




11. If a new “Measurement Configuration” is to be sent to the UE, it is sent in a separate

CONNECTION RECONFIGURATION message.

12. The target eNodeB sends a PATH SWITCH REQUEST message to the MME to inform it

that the UE has been handed over to another eNodeB.

13. The MME sends a USER PLANE UPDATE REQUEST message to the S-GW, which

includes the target eNodeB's TEID(s) received before to enable the user data path to be

switched from the source to the target eNodeB.

14. The S-GW switches the downlink data path to the target eNodeB.

Before the S-GW can release any U-plane/TNL resources towards the source eNodeB, it

sends one or more “end marker” packet(s) to the source eNodeB as an indication that the

downlink data path has been switched.

15. The S-GW sends a USER PLANE UPDATE RESPONSE message to the MME to confirm

that it has switched the downlink data path.

16. The MME confirms the PATH SWITCH REQUEST message with the PATH SWITCH

REQUEST ACK message.

17. By sending a UE CONTEXT RELEASE message, the target eNodeB informs the source

eNodeB of the success of the handover and triggers the release of resources.

The target eNodeB does not release its data forwarding tunnels from the source eNodeB

until it has received an “end marker” packet.

18. Upon reception of the UE CONTEXT RELEASE message, the source eNodeB may forward

any remaining PDCP SDUs



RRC Timers Timer Start Stop At expiry

T300

Transmission of RRCConnectionRequest Reception of RRCConnectionSetup or RRCConnectionReject

message, cell re-selection and upon abortion of connection

establishment by upper layers

Perform the actions as specified in 5.3.3.6

T301 Transmission of

RRCConnectionReestabilshmentRequest

Reception of RRCConnectionReestablishment or

RRCConnectionReestablishmentReject message as well as

when the selected cell becomes unsuitable

Go to RRC_IDLE

T302 Reception of RRCConnectionReject while

performing RRC connection establishment

Upon entering RRC_CONNECTED and upon cell re-selection Inform upper layers about barring alleviation as

specified in 5.3.3.7

T303 Access barred while performing RRC

connection establishment for mobile

originating calls



T304 Reception of RRCConnectionReconfiguration

message including the MobilityControl Info or

reception of MobilityFromEUTRACommand

message including CellChangeOrder

Criterion for successful completion of handover to EUTRA or

cell change order is met (the criterion is specified in the target

RAT in case of inter-RAT)

In case of cell change order from E-UTRA or intra E-

UTRA handover, initiate the RRC connection re-

establishment procedure; In case of handover to E-

UTRA, perform the actions defined in the

specifications applicable for the source RAT.



originating signalling





originating CS fallback.



T310 Upon detecting physical layer problems i.e.

upon receiving N310 consecutive out-of-sync

indications from lower layers

Upon receiving N311 consecutive in-sync indications from lower

layers, upon triggering the handover procedure and upon

initiating the connection re-establishment procedure

If security is not activated: go to RRC_IDLE else:

initiate the connection re-establishment procedure

T311 Upon initiating the RRC connection re-

establishment procedure

Selection of a suitable E-UTRA cell or a cell using another RAT. Enter RRC_IDLE

T320 Upon receiving t320 or upon cell (re)selection

to E-UTRA from another RAT with validity

time configured for dedicated priorities (in

which case the remaining validity time is

applied).

Upon entering RRC_CONNECTED, when PLMN selection is

performed on request by NAS, or upon cell (re)selection to

another RAT (in which case the timer is carried on to the other

RAT).

Discard the cell reselection priority rmation provided

by dedicated signalling.

T321 Upon receiving measConfig including a

reportConfig with the purpose set to

reportCGI

Upon acquiring the rmation needed to set all fields of

cellGlobalId for the requested cell, upon receiving measConfig

that includes removal of the reportConfig with the purpose set to

reportCGI

Initiate the measurement reporting procedure, stop

performing the related measurements and remove the

corresponding measId

T330 Upon receiving

LoggedMeasurementConfiguration message

Upon log volume exceeding the suitable UE memory, upon

initiating the release of LoggedMeasurementConfiguration

procedure

Perform the actions specified in 5.6.6.4

Constant Usage

N310 Maximum number of consecutive "out-of-sync" indications received from lower layers

N311 Maximum number of consecutive "in-sync" indications received from lower layers



Multi-Carrier operation and CA



Spectral Efficiency of HSPA and LTE*

* Harri Holma and Antti Toskala, LTE for UMTS: OFDMA and SC-FDMA Based Radio Access, Wiley, 2009



LTE DL Spectral Efficiency Benefit over R6 HSDPA in Macro Cells*

LTE Benefit Gain Explanation

OFDM with freq.

domain EQ

Up to +70%

depending on

the multi-path

profile

HSDPA suffers from intra-cell interference fro

the Rake receiver. Rake receiver is assumed

in R6. However, most HSDPA terminals have

an EQ that removes most intra-cell

interference.

Freq. domain packet

scheduling (using

OFDMA)

+40%

Frequency domain scheduling is possible in

OFDM system, but not in single carrier

HSDPA. The dual carrier HSDPA can get part

of the frequency domain scheduling gain.

MIMO +15%

No MIMO defined in HSDPA R6. The gain is

relative to single antenna BS transmission.

HSDPA R7 includes MIMO.

Inter-cell interference

rejection combining +10%

The interference rejection combining works

better in OFDM system with long symbols.

Total =3.0x 1.7 x 1.4 x 1.15 x 1.1

* Harri Holma and Antti Toskala, LTE for UMTS: OFDMA and SC-FDMA Based Radio Access, Wiley, 2009



한국 FDD Spectrum Map

850MHz B5/B26

1.8GHz B3

2.1GHz B1

SKT UL

(15㎒)

LG U+ UL

(10㎒)

KT UL

(10㎒)

KT DL

(10㎒)

KT UL

(5 ㎒)

819

824

839

849

864

869

884

894

905

915

950

960

LG U+ UL

(10㎒)

SKT UL

(10 ㎒)

KT UL

(10㎒)

1745

1755

1765

1770

LG U+ DL

(10㎒)

SKT DL

(10 ㎒)

KT DL

(10㎒)

1840

1850

1860

1780

1870

SKT DL

(15㎒)

LG U+ DL

(10㎒)

KT DL

(5 ㎒)

frequency sharing b/w comm &

military/public (35㎒)

1805

frequency sharing b/w comm &

military/public (35㎒)

1710

2G CDMA 3G WCDMA 4G LTE

Empty spectrum To be assigned (’12-’13)

900MHz B8

4G LTE planned (2nd carrier)

KT UL

(20㎒)

LG U+ UL

(10 ㎒)

SKT UL

(30㎒)

1920

1930

1960

1980

2110

2120

2150

2170

IMT-satellite (30㎒)

KT UL

(20㎒)

LG U+ UL

(10 ㎒)

SKT UL

(30㎒)

IMT-satellite (30㎒)

2200

2010



Multi-Carrier Operation

• Mobility

– Intra-frequency handover

– Inter-frequency handover

• Load balancing

– Idle mode cell selection priority

– Idle mode load balancing

– Connected mode load balancing

– Service aware(?)

UE

1st carrier

1st carrier

2nd carrier?

2nd carrier?



MC와 CA의 차이점

• MC (Multi Carrier) • 예: SKT가 현재 850MHz 2x10MHz와 1.8GHz의 2x10MHz에서 MC LTE를 운용 중

• 850MHz망만 운용하는 것에 비하여 시스템 용량은 2배 증가

• 한 단말기가 동시에 850MHz와 1.8GHz를 사용하지 않으므로, 단말 구현의 난이도는 높지 않음

• 한 단말기가 동시에 850MHz와 1.8GHz를 사용할 수는 없으므로, 사용자 PDR은 2배로 증가하지 않음 여전히 DL 75Mbps

• CA (Carrier Aggregation) • 한 단말기가 동시에 N개의 주파수를 동시에 사용할 수 있음.

• 이에 따라 위의 SKT의 예에서는 사용자 PDR이 2배로 증가 가능 최대 DL 150Mbps

• 실제 시스템 용량은 MC에 비하여 크게 증가하지 않음

• 단말기 구현의 난이도가 높음

• Intra-band contiguous CA (하)

• Intra-band non-contiguous CA

• Inter-band (non-contiguous) CA (상)



구현 난이도



3GPP Defined LTE CA Band Combinations

Release 10 • Band1 + Band5 LG U+

Release 11 Work Items • LTE_CA_B1_B7: LTE Advanced Carrier Aggregation of Band 1 and Band 7

• LTE_CA_B1_B18: LTE Advanced Carrier Aggregation of Band 1 and Band 18




• LTE_CA_B3_B5: LTE Advanced Carrier Aggregation of Band 3 and Band 5 SK Telecom

• LTE_CA_B3_B7: LTE-Advanced Carrier Aggregation of Band 3 and Band 7

• LTE_CA_B3_B8: LTE-Advanced Carrier Aggregation of Band 3 and Band 8 KT












• LTE_CA_B7: LTE Advanced Carrier Aggregation in Band 7

• LTE_CA_B25: LTE Advanced Carrier Aggregation Intra-Band, Non-Contiguous in Band 25



* CA Band Combination은 사업자의 요구에 따라 지속적으로 늘어남



VoLTE and other GBR services



Short Call Setup time & HD Voice

• Call setup time

– 3G voice: ~ 4-5 sec

– 4G (?) CSFB voice: ~ 4-5 sec + ~ 1-2 sec

– 4G (!) VoLTE: ~ 1 sec

• HD (High Definition) Voice with WB-AMR

Narrow Band: AMR-NB 12.2kbps

Wide Band: AMR-WB 12.65kbps

Wide Band: AMR-WB 23.85kbps

Male Female Music Music2



Possible worries on VoLTE

• Concerns on handover success rate due to LTE’s hard handover nature

• Requires ‘good LTE coverage’

• Unspecified concerns on VoIP for primary voice service

• …



Near mandatory requirements

• QCI1 EPS bearer

• ROHC (Robust Header Compression)

– Robust Header Compression (RoHC) according to RFC3095 and RFC4995

– RTP/UDP/IP headers of 40 bytes (IPv4) / 60 bytes (IPv6) are compressed to typically 3 bytes

– Typical AMR-NB payload of 14 … 32 bytes (4.75 kbit/s … 12.2 kbit/s)

– Leads to > 50% reduction of data volume at the air interface

• Proper level of LTE network performance itself

– PDCCH, PDSCH, PUSCH capacity

– Coverage performance, particularly in cell edge

– RAN optimization (parameter/field optimization) becomes more critical in VoLTE era



EPS Bearer Service Architecture



EPS Bearer Terminology

• Quality of service

– GBR bearer: Guaranteed bit rate

– Non-GBR bearer: No guaranteed bit rate

• Establishment time

– Default bearer

Established when UE connects to PDN

Provides always-on connectivity

Always non-GBR

– Dedicated bearer established later

Can be GBR or non-GBR

• Every EPS bearer

– QoS class identifier (QCI): This is a number which describes the error rate and delay

that are associated with the service.

– Allocation and retention priority (ARP): This determines whether a bearer can be

dropped if the network gets congested, or whether it can cause other bearers to be

dropped. Emergency calls might be associated with a high ARP, for example.



QCI (QoS Class Identifier)



DRX in RRC connected

UE power saving

• Significant UE power reduction (> 90%)

• UE needs to read the PDCCH only at DRX active and can switch off parts of the receiver during DRX inactivity

• Operator configurable DRX profiles which can be assigned to different QCI profiles

• Example:

• QCI = 1 - DRX cycle: 20 ms (for VoLTE)

• QCI = 7 - DRX cycle: 80 ms

• QCI = 9 - DRX cycle: 2.5 s

• Uplink out-of-sync handling



Channel/Interference Aware Scheduler (CAS/IAS)

• Assignment of PRBs (physical resource blocks) in the frequency domain based on CSI (channel state indicator)

• UL example below

Optimize the air-link performance

0 1 0 1 2 3

0 1 3 1 1 0

3 1 2 1 0 0

‚CSI table‘

Channel

aware

Channel

unaware

Resulting

weight: 12 UE A

UE B

UE C

PRBs

Resulting

weight: 2



SRVCC to WCDMA

VoIP continuity to WCDMA

• Extension to WCDMA handover

• Only applied if EPS bearer with

QCI = 1 is established and MME

indicates that SRVCC is possible

MME S-GW RNC MSC



Hurdles to overcome…

• Call drop… shall be minimized

– GSMA IR.92 says “If the PDN connectivity is lost, then the UE must re-establish the PDN connection.”

– Connection RLF Re-establishment Fail? Call drop

– Network optimization is “THE” key.

• MOS (Mean opinion score)

– Packet loss (<2%, <5%)

– Delay (<50ms, <80ms)

– Codec (higher rate, better)

– Etc…

• Admission control for GBR

– 3GPP TS23.203 says “An operator would choose GBR QCIs for services where the preferred user experience is "service blocking over service dropping", i.e. rather block a service request than risk degraded performance of an already admitted service request.”

• How to win a game over OTT?



How to cope with traffic growth?



0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0% 13% 25% 38% 51% 63% 76% 88%

bps/Hz

Loading

Spectral Efficiency vs Load (Example)

3GPP Case 1 simulations with full buffer gives 1.74 bps/Hz/cell

Assumes nice hexagonal grid + uncorrelated antennas



Non-GBR capacity “after” serving VoLTE (Example)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 50 100 150 200 250 300 350 400

DL available non-GBR throughput

UL available non-GBR throughput

Number of VoLTE users per cell

Availa

ble

non

-GB

R c

apacity p

er

cell

“after”

serv

ing V

oLT

E u

sers



Thank you !

www.nokiasiemensnetworks.com

Nokia Siemens Networks

20F, Meritz Tower, 825-2

Yeoksam-Dong, Kangnam-Gu

Seoul 135-080, Korea

Bong Youl (Brian) Cho Lead Product Manager Korea, Ph.D.

LTE Business Line, MBB

[email protected]

Mobile 010-4309-4129

mailto:[email protected]