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LTE fundamentals and system architect
Ahmad TalaatNSN Saudi - NPO
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Contents
• LTE Drivers
• LTE Main Requirements
• Network Architecture Evolution
• Key Features and Basics
• LTE Network Architecture• Highlight on some Important NSN Features
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The way to the Long-Term Evolution (LTE): a 3GPP driveninitiative
•LTE is 3GPP system for the years 2010 to 2020 &beyond.
•It shall especially compete with WiMAX 802.16e/m
•It must keep the support for high & highest
mobility users like in GSM/UMTS networks
•The architectural changes are big compared toUMTS
•LTE commercial launch has started early 2010.
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LTE Drivers
Wireline Evolution: pushes higher data
rates
Wireless Dataextensively used:
Pushes more capacity
Flat Rate pricing:
pushes cost efficiency
Other Wirelesstechnologies:
Competition pushes newcapabilities
Driving to clearLTE Targets
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What are the LTE challenges?
• Best price, transparent flat rate• Full Internet
• Click-bang responsiveness
• reduce cost per bit• provide high data rate
• provide low latency
The Users’ expectation… ..leads to the operator’s challenges
Price per Mbyte has to be reducedto remain profitable
User experience will have animpact on ARPU
LTE: lower cost per bit and improved end user experience
UMTS HSPA I-HSPA LTE
Cost per MByte
HSPA LTE HSPA LTE
Throughput Latency
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Reduction of network cost is necessary to remainprofitable
Source: Light Reading (adapted)
Traffic
Revenue
Revenues and Trafficdecoupled
T r a f f i c v o l u m e
€ / b
i t
Time
Profitability
Network
cost
Voicedominated
Datadominated
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Contents
• LTE Drivers
• LTE Main Requirements
• Network Architecture Evolution
• Key Features and Basics
• LTE Network Architecture• Highlight on some Important NSN Features
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LTE = Long Term Evolution
• Peak data rates of 303Mbps / 75 Mbps
• Low latency 10-20 ms
Enhanced consumer experience
• Scalable bandwidth of1.4 – 20 MHz
Easy to introduce on anyfrequency band
• OFDM technology
• Flat, scalable IP basedarchitecture
Decreased cost / GB
• Next step for
GSM/WCDMA/HSPAand CDMA A true global roaming technology
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Schedule for 3GPP releases
• Next step for
GSM/WCDMA/HSPAand cdma2000 A true global roaming technology
year
3GPP Rel. 99/4 Rel. 5 Rel. 6 Rel. 7
2007200520032000 2008
HSDPA
IMS
HSUPA
MBMS
WLAN IW
HSPA+
LTE Studies
Specification
2009
• LTE have been developed by the same standardization organization. The target has beensimple multimode implementation and backwards compatibility.
• HSPA and LTE have in common: – Sampling rate using the same clocking frequency
– Same kind of Turbo coding
• The harmonization of these parameters is important as sampling and Turbo decoding aretypically done on hardware due to high processing requirements.
• WiMAX and LTE do not have such harmonization.
Rel. 8
LTE & EPC
Rel. 9
LTE-A
studies
LTE-A: LTE-Advanced
Rel. 10
LTE-AUMTS/
WCDMA
2011
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Comparison of Throughput and Latency (1/2)
HSPA R6
Max. peak data rate
M b p s
Evolved HSPA(Rel. 7/8, 2x2MIMO)
LTE 2x20 MHz(2x2 MIMO)
LTE 2x20MHz (4x4MIMO)
Downlink
Uplink
350
300
250
200
150
100
50
0
HSPAevo
(Rel8)
LTE
* Server near RAN
Latency (Rountrip delay)*
DSL (~20-50 ms, depending on operator)
0 20 40 60 80 100 120 140 160 180 200
GSM/EDGE
HSPARel6
min max
ms
Enhanced consumer experience:- drives subscriber uptake
- allow for new applications
- provide additional revenue streams
• Peak data rates of303 Mbps / 75 Mbps
• Low latency 10-20ms
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Scalable bandwidth
• Scalable bandwidthof 1.4 – 20 MHz
Easy to introduce on anyfrequency band: FrequencyRefarming
(Cost efficient deployment on lowerfrequency bands supported)
Scalable Bandwidth
Urban
2006 2008 2010 2012 2014 2016 2018 2020
Rural
2006 2008 2010 2012 2014 2016 2018 2020
or
2.6 GHz
2.1 GHz
2.6 GHz
2.1 GHz
LTE
UMTS
UMTS
LTE
900 MHz
900 MHz GSM
or
GSM UMTS
LTE
LTE
LTE
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0.0
0.2
0.40.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
HSPA R6 HSPA R6 +
UE
equalizer
HSPA R7 WiMAX LTE R8
b p s / H z / c e l l
DownlinkUplink
Increased Spectral Efficiency
• All cases assume 2-antenna terminal reception
• HSPA R7, WiMAX and LTE assume 2-antenna BTS transmission (2x2 MIMO)
ITU contribution from
WiMAX Forum shows
DL 1.3 & UL 0.8 bps/Hz/cell
Reference:
- HSPA R6 and LTE R8 from 3GPP R1-071960
- HSPA R6 equalizer from 3GPP R1-063335
- HSPA R7 and WiMAX from NSN/Nokia
simulations
• OFDMA technologyincreases Spectral
efficiency
LTE efficiency is 3 x HSPA R6 indownlinkHSPA R7 and WiMAX have Similar
Spectral Efficiency
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Reduced Network Complexity
• Flat, scalable IP basedarchitecture Flat Architecture: 2 nodes architectureIP based Interfaces
Access Core Control
Evolved Node B Gateway
IMS HLR/HSS
Flat, IP based architecture
Internet
MME
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LTE/SAE Requirements Summary
1. Simplify the RAN:
- Reduce the number of different types of RAN nodes, and their complexity.
- Minimize the number of RAN interface types.2. Increase throughput: Peak data rates of UL/DL 50/100 Mbps
3. Reduce latency (prerequisite for CS replacement).
4. Improve spectrum efficiency: Capacity 2-4 x higher than with Release 6 HSPA
5. Frequency flexibility & bandwidth scalability: Frequency Refarming
6. Migrate to a PS only domain in the core network: CSFB for initial phase
7. Provide efficient support for a variety of different services. Traditional CS services
will be supported via VoIP, etc: EPS bearers for IMS based Voice
8. Minimise the presence of single points of failure in the network above the eNBs S1-
Flex interface
9. Support for inter-working with existing 3G system & non-3GPP specified systems.
10. Operation in FDD & TDD modes
11. Improved terminal power efficiency
A more detailed list of the requirements and objectives for LTE can be found in TR 25.913.
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Contents
• LTE Drivers
• LTE Main Requirements
• Network Architecture Evolution
• Key Features and Basics
• LTE Network Architecture
• Highlight on some Important NSN Features
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NSN Network Architecture Evolution (1/4)
Node B RNC SGSN GGSNInternet
3GPP Rel 6 / HSPA
User plane
Control Plane
• Original 3G architecture.• 2 nodes in the RAN.
• 2 nodes in the PS Core Network.
• Every Node introduces additional delay.
• Common path for User plane and Control plane data.• Air interface based on WCDMA.
• RAN interfaces based on ATM.
• Option for Iu-PS interface to be based on IP.
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NSN Network Architecture Evolution (2/4)
Direct tunnel
3GPP Rel 7 / HSPA
Internet
Node B RNC
SGSN
GGSN
User plane
Control Plane
• Separated path for Control Plane and User Plane data in the PSCore Network.
• Direct GTP tunnel from the GGSN to the RNC for User plane data:simplifies the Core Network and reduces Signalling.
• First step towards a flat network Architecture.
• 30% core network OPEX and CAPEX savings with Direct Tunnel.
• The SGSN still controls traffic plane handling, performs session andmobility management, and manages paging.
• Still 2 nodes in the RAN.
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NSN Network Architecture Evolution (3/4)
Direct tunnel
3GPP Rel 7 / Internet HSPA
Internet
Node B
SGSN
GGSN
Node B
(RNC Funct.)User plane
Control Plane
• I-HSPA introduces the first true flat architecture to WCDMA.• Standardized in 3GPP Release 7 as: “Direct Tunnel with collapsedRNC”.
• Most part of the RNC functionalities are moved to the Node B.
• Direct Tunnels runs now from the GGSN to the Node B.
• Solution for cost-efficient broadband wireless access.
• Improves the delay performance (less node in RAN).
• Deployable with existing NSN WCDMA base stations.
• Transmission savings
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NSN Network Architecture Evolution (4/4)
Direct tunnel
3GPP Rel 8 / LTE
Internet
Evolved Node B
MME
SAE GW
• LTE takes the same Flat architecture from Internet HSPA.• Air interface based on OFDMA.
• All-IP network.
• New spectrum allocation (i.e 2600 MHz band)
• Possibility to reuse spectrum (i.e. 900 MHZ)
User plane
Control Plane
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NSN Network Architecture Evolution - Summary
Node B RNC SGSN GGSN
Internet
3GPP Rel 6 / HSPA
Direct tunnel
3GPP Rel 7 / HSPA
Internet
Node BRNC
SGSN
GGSN
Direct tunnel
3GPP Rel 7 / Internet HSPA
Internet
Node B
SGSN
GGSN
Node B
(RNC Funct.)
Direct tunnel
3GPP Rel 8 / LTE
Internet
Evolved Node B
MME
SAE GW
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Contents
• LTE Drivers
• LTE Main Requirements
• Network Architecture Evolution
• Key Features and Basics
• LTE Network Architecture
• Highlight on some Important NSN Features
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Evolved Packet Core (EPC)LTE Radio
Access Network(EUTRAN)
MME
Serving
GWPDN
GW
PacketData
Network
SAE-GW
eNode-B
LTE Radio Interface Key Features
LTE Radio Interface Key Features
• Retransmission Handling (HARQ/ARQ)
• Spectrum Flexibility• FDD & TDD modes
• Multi-Antenna Transmission
• Frequency and time Domain scheduling
• Uplink (UL) Power Control
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Evolved Packet Core (EPC)LTE Radio
Access Network(EUTRAN)
MME
Serving
GWPDN
GW
PacketData
Network
SAE-GW
eNode-B
EUTRAN Key Features
EUTRAN Key Features:
• Evolved NodeB
• IP transport layer
• UL/DL resource scheduling
• QoS Awareness
• Self-configuration
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Evolved Packet Core (EPC)LTE Radio
Access Network(EUTRAN)
MME
Serving
GWPDN
GW
PacketData
Network
SAE-GW
eNode-B
EPC Key Features
EPC Key Features:
• IP transport layer
• QoS Awareness
• Packet Switched Domain only
• 3GPP (GTP) or IETF (MIPv6) option
• Prepare to connect to non-3GPP access networks
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TDMA
f
t
f
• Time Division
FDMA
f
f
t
• Frequency Division
CDMA
f
t
f
• Code Division
OFDMA
f
f
t
• Frequency Division
• Orthogonal subcarriers
Multiple Access Methods User 1 User 2 User 3 User ..
OFDM is the state-of-the-art and most efficient and robust air interface
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The Rectangular Pulse
Advantages:
+ Simple to implement: there is no complexfilter system required to detect such pulses
and to generate them.+ The pulse has a clearly defined duration.This is a major advantage in case of multi-path propagation environments as it simplifieshandling of inter-symbol interference.
Disadvantage:
- it allocates a quite huge spectrum. Howeverthe spectral power density has null pointsexactly at multiples of the frequency fs = 1/Ts.This will be important in OFDM.
time
a m p l i t u d e
Ts f s 1
T s
Time Domain
frequency f/f s
s p e c t r a l p o w e r d e n s i t y
Frequency Domain
f s
Fourier
Transform
InverseFourier
Transform
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Air Interface - OFDM Basics
• Data is sent in parallel across the set of subcarriers, each subcarrier only
transports a part of the whole transmission• The throughput is the sum of the data rates of each individual (or used)
subcarriers while the power is distributed to all used subcarriers
• FFT ( Fast Fourier Transform) is used to create the orthogonal subcarriers. Thenumber of subcarriers is determined by the FFT size ( by the bandwidth)
Power
frequency
bandwidth
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The OFDM Signal
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OFDMA Parameters in LTE
• Channel bandwidth: DL bandwidths ranging from 1.4 MHz to 20 MHz
• Data subcarriers: the number of data subcarriers varies with thebandwidth
– 72 for 1.4 MHz to 1200 for 20 MHz
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Resource Block and Resource Element
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
Subcarrier 1
Subcarrier 12
1 8 0 K H z
1 slot 1 slot
1 ms subframe
ResourceElement
• Physical Resource Block PBR or Resource Block RB:
– 12 subcarriers in frequency domain x 1 slot period in time domain
– Capacity allocation based on Resource Blocks
Resource Element RE: – 1 subcarrier x 1 symbol period
– theoretical min. capacity allocation unit
– 1 RE is the equivalent of 1 modulationsymbol on a subcarrier, i.e. 2 bits(QPSK), 4 bits (16QAM), 6 bits (64QAM).
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Physical Resource Blocks
....
12 subcarriers
Time
Frequency
0.5 ms slot
1 ms subframe
or TTI
Resource
block
During each TTI,
resource blocks for
different UEs arescheduled in the
eNodeB
• In both the DL & UL direction, data isallocated to users in terms of
resource blocks (RBs).
• a RB consists of 12 consecutivesubcarriers in the frequency domain,
reserved for the duration of 0.5 ms
slot.• The smallest resource unit a
scheduler can assign to a user is a
scheduling block which consists of
two consecutive resource blocks
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LTE Channel Options
Bandwidth options: 1.4, 1.6, 3, 3.2, 5, 10, 15 and 20 MHz
Subcarriers in frequency domain (15 kHz or 7.5 kHz subcarrier spacing)
Channel bandwidth
(MHz)
Number of
subcarriers
Number of resource
blocks
1.4
72
6
3
180
15
5
300
25
10
600
50
15
900
75
20
1200
100
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LTE RRM: Scheduling
• Motivation
– Bad channel condition avoidance
OFDMA
The part of total available
channel experiencing badchannel condition (fading)
can be avoided during
allocation procedure.
CDMA
Single Carrier transmission
does not allow to allocate
only particular frequency
parts. Every fading gap
effects the data.
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Contents
• LTE Drivers
• LTE Main Requirements• Network Architecture Evolution
• Key Features and Basics
• LTE Network Architecture
• Highlight on some Important NSN Features
N k A hi E l i
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Network Architecture Evolution
SAE GWGGSN
SGSN
RNC
Node B
(NB)
Direct tunnel
GGSN
SGSN
I-HSPA
MME/SGSN
HSPA R7 HSPA R7 LTE R8
Node B +
RNC
Functionality
Evolved
Node B
(eNB)
GGSN
SGSN
RNC
Node B
(NB)
HSPA
HSPA R6
LTE
User plane
Control Plane
• Flat architecture: single network element in userplane in radio network and core network
E l d P k t S t (EPS) A hit t S b t
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Evolved Packet System (EPS) Architecture - Subsystems
• The EPS architecture goal is to optimize the system for packet data transfer.
• There are no circuit switched components. The EPS architecture is made up of: – EPC: Evolved Packet Core, also referred as SAE
– eUTRAN: Radio Access Network, also referred as LTE
LTE or eUTRAN SAE or EPC
EPS Architecture
• EPC provides access toexternal packet IP networks and
performs a number of CN
related functions (e.g. QoS,
security, mobility and terminal
context management) for idle
and active terminals
• eUTRAN performs all radiointerface related functions
LTE/SAE Network Elements
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LTE/SAE Network Elements
Main references to architecture in 3GPP specs.: TS23.401,TS23.402,TS36.300
LTE-UE
Evolved UTRAN (E-UTRAN)
MME S10
S6a
Serving
Gateway
S1-U
S11
PDN
Gateway
PDN
Evolved Packet Core (EPC)
PCRF
S7 Rx+
SGiS5/S8
Evolved Node B
(eNB)
X2
LTE-Uu
HSS
Mobility
Management
Entity Policy &
Charging Rule
Function
SAE
Gateway
eNB
C t t
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Contents
• LTE Drivers
• LTE Main Requirements• Network Architecture Evolution
• Key Features and Basics
• LTE Network Architecture
• Highlight on some Important NSN Features
UL Ph i l R Bl k DRS & SRS
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UL Physical Resource Block: DRS & SRS
....
12 subcarriers
Time
0.5 ms slot
1 ms subframe
or TTI
Frequency
Sounding Reference
Signal on last OFDM
symbol of 1 subframe;
Periodic or aperiodic
transmission
Demodulation
Reference Signal in
subframes that carry
PUSCH
• The Demodulation ReferenceSignal is transmitted in the third
SC-FDMA symbol (counting from
zero) in all resource blocks
allocated to the PUSCH carryingthe user data.
• This signal is needed for channelestimation, which in turn is
essential for coherent
demodulation of the UL signal in
the eNodeB.
• The Sounding Reference SignalSRS provides UL channel quality
information as a basis for
scheduling decisions in the base
station. This signal is distributed inthe last SC-FDMA symbol of
subframes that carry neither
PUSCH nor PUCCH data. [SRS is
always disabled in FDD RL30 and
before.]PUCCH: Physical UL Control Channel
RL30U li k S h d l
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• Flexi eNodeB takes into account the noise and interference measurements together withthe UE Tx power density (= UE TX power per PRB) when allocating PRBs in thefrequency domain
• Cell edge users are assigned to frequency sub-bands with low measured inter-cellinterference
• Up to 10% gain for cell edge users in low and medium loaded networks
• Easier to implement than channel aware scheduling (no sounding reference signal used)
Improvement in UL coverage by optimizing the cell edge performance
eNode Bmeasuredinterference
subband with lowinterference
subband with highinterference
subband with mediuminterference
PRBs
Feature ID(s): LTE619
RL30Uplink SchedulerIAS: Interference Aware Scheduler UL
High Tx power density indicates
cell edge users / strong interferers
LTE46 UL Ch l A S h d li
RL40
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LTE46, UL Channel Aware Scheduling
• Channel Unaware Scheduling (CUS)
– random allocation of PRBs => averaging of inter-cell interference
– simple and robust, no UL channel sounding required
– no FDPS gain
• Interference Aware Scheduling (IAS, LTE619)
– rudimentary interference reduction via coarse segmentation
– scheduling criterion based on Tx power density =>Tx power per PRB
– no UL channel sounding required
– lower FDPS gain than CAS, LTE46
• Channel Aware Scheduling (CAS, LTE46)
– very similar implementation in RL15 and RL40
– sophisticated SRS- and PUSCH-based PRB allocation according to UEspecific channel state information (CSI)
– UL channel sounding required
– FDPS gain (low for a high # of PRBs allocated to a specific UE )
RL40
LTE RRM: Connection Mobility Control
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LTE RRM: Connection Mobility ControlHandover Types
• Intra-RAT handover
– Intra eNodeB and Inter eNodeB handover – Above handovers can also be Inter-frequency handovers (RL20) i.e. to support different
frequency bands and deployments within one frequency band but with different center
frequencies
– Data forwarding over X2 for inter eNodeB HO
– HO via S1 interface (RL20): HO in case of no X2 interface configured between servingeNB and target eNB
• Inter-RAT handover
– LTE to WCDMA: RL30
– WCDMA to LTE: RL40
– LTE to CDMA2000: RL40 (CDMA2000 to LTE not assigned)
– LTE GSM and GSM LTE: not assigned
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Intra frequency handover via X2
• Basic Mobility Feature
• Event triggered handover basedon DL measurements (ref.
signals)
• Network evaluated HO decision• Operator configurable
thresholds for
• coverage based &• best cell based handover
• Data forwarding via X2• Radio Admission Control (RAC)gives priority to HO related
access over other scenarios S1
S1 X2
MMES-GW
P-GW
Feature ID(s): LTE53
A reliable and lossless mobility
RL20
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Intra LTE Handover via S1
Extended mobility option to X2 handover
• Handover in case of
• no X2 interface between eNodeBs, e.g. multi-vendor scenarios
• eNodeBs connected to different CN elements
• Operator configurable thresholds for
• coverage based (A5) and• best cell based (A3) handover
• DL Data forwarding via S1
Feature ID(s): LTE54
RL20
• Admission Control gives priority to HO
related access over other scenarios• Blacklists
RL20
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Inter Frequency Handover
Multi-band mobility
• Network controlled
• Event triggered based on DLmeasurement RSRP and RSRQ
• Inter frequency measurementstriggered by events A1/A2
• Operator configurable thresholds for
coverage based (A5),
best cell based (A3) handover
• Service continuity for LTE deployment
in different frequency bands as wellas for LTE deployments within onefrequency band but with differentcenter frequencies
• Blacklists
Feature ID(s): LTE55
RL20
RL30
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Inter RAT Handover to WCDMA
• Coverage based inter-RAT PS handover• Only for multimode devices supporting
LTE and WCDMA
• Event triggered handover based on DLmeasurement RSRP (reference signalreceived power)
• Operator configurable RSRP threshold
• Network evaluated HO decision
• Target cells are operator configurable
• An ANR functionality may be applied
optionally
Feature ID(s): LTE56
• Blacklisting
• eNB initiates handover via EPC
RL30
CC GSRL30
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47 © Nokia Siemens Networks
eNACC to GSMNetwork Assisted Cell Change to GSM
Service continuity to GSM
• Network change from LTE to GSM inRRC Connected Mode when LTE
coverage (RSRP) is ending
• Prior to actual reselection process the
measurements of 2G network aretriggered
• Only applicable for NACC capabledevices
• Inter RAT measurements triggered byevents A1/A2
• Operator configurable handoverthreshold (event B2)
• Target cells for IRAT measurements canbe configured by the operator
• Blacklisting of target cells is supportedFeature ID(s): LTE442
RL30
LTE735: RRC Connection Reestablishment RL30
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LTE735: RRC Connection Reestablishment
• eNode B takes UE back to RRCCONNECTED
• UE initiated procedure
• Typical scenarios:
• Radio link failures (e.g. T310expires)
• Handover failure (e.g. T304expires)
• RRC connection reconfigurationfailure
Advanced failure handling
MMES-GW
UE reverts back to
source cell due to
handover failure
RL30
Automated Neighbor Relation (ANR) Configuration
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Automated Neighbor Relation (ANR) Configuration
• Neighbour relations are important as wrong neighbour definitions cause HOfailures and dropped calls
• Self configuration of relations avoids manual planning & maintenance
ANR covers 4 steps:
1) Neighbour cell discovery
2) Neighbour Site’s X2 transport configuration discovery (i.e. Neighbour Site IP@)
3) X2 Connection Set-up with neighbour cell configuration update
4) ANR Optimization
• The scope within ANR is to establish an X2 connection between source andtarget nodes and for that it is necessary that source eNB knows the target eNBIP@
• How the source eNB gets the IP@ differentiates the ANR features: – Central ANR (RL10)
– ANR (RL20)
– ANR- Fully UE based (RL30)
3GPP ANR Configuration Principle
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MME
3GPP ANR Configuration Principle
Site
eNB - A
Neighbor
Site
eNB - B
New cell
discovered
New cell
identified
by ECGI
CM
X2 Setup : IPsec, SCTP, X2-AP [site & cell info]
UE
connected
S1 : Request X2 Transport Configuration (ECGI)
S1: Request X2 Transport Configuration
relays
request
S1: Respond X2 Transport Configuration (IP@)
S1 : Respond X2 Transport Configuration (IP@)
CM
relays
response
Add Site & Cell
parameter of
eNB-A CM CM
Add Site & Cell
Parameter of
eNB-B
Neighbor Cell Tables in both eNB updated
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Thank You