lte mac rrc

국내 LTE 상용화 및
관련 MAC, RLC, PDCP, RRC 내용
November 2012
Bong Youl (Brian) Cho, 조 봉 열
brian.cho@nsn.com

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 ㎒)
8
1
9
8
2
4
8
3
9
8
4
9
8
6
4
8
6
9
8
8
4
8
9
4
9
0
5
9
1
5
9
5
0
9
6
0
LG U+
UL
(10㎒)
SKT
UL
(10 ㎒)
KT
UL
(10㎒)
1
7
4
5
1
7
5
5
1
7
6
5
1
7
7
0
LG U+
DL
(10㎒)
SKT
DL
(10 ㎒)
KT
DL
(10㎒)
1
8
4
0
1
8
5
0
1
8
6
0
1
7
8
0
1
8
7
0
SKT
DL
(15㎒)
LG U+
DL
(10㎒)
KT
DL
(5 ㎒)
frequency sharing
b/w comm &
military/public (35㎒)
1
8
0
5
frequency sharing
b/w comm &
military/public (35㎒)
1
7
1
0
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㎒)
1
9
2
0
1
9
3
0
1
9
6
0
1
9
8
0
2
1
1
0
2
1
2
0
2
1
5
0
2
1
7
0
IMT-satellite
(30㎒)
KT
UL
(20㎒)
LG U+
UL
(10 ㎒)
SKT
UL
(30㎒)
IMT-satellite
(30㎒)
2
2
0
0
2
0
1
0

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_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: 12UE 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
MMES-GW RNCMSC

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
Availablenon-GBRcapacityper
cell“after”servingVoLTEusers

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
brian.cho@nsn.com
Mobile 010-4309-4129

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