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Advanced Mobile Communication Networks 1
Integrated Communication Systems Group
Mobile Network Evolution – Part 2
From UMTS to LTE or
How to Further Increase Network Capacity and QoS
Andreas Mitschele-Thiel
Advanced Mobile Communication Networks 2
Integrated Communication Systems Group
Outline
• Evolution from Circuit Switching to Packet Switching – Architecture – Packet handling – Resource management and QoS
• LTE – Features and requirements – Architecture – Packet handling and resource management
• References
Advanced Mobile Communication Networks 3
Integrated Communication Systems Group
Review: From GSM to UMTS
GPRS Core (Packet Switched)
SGSN
GGSN
Internet
GSM RAN
Base station Base station controller
Base station
Base station
UTRAN
Radio network controller
node B node B
node B
MSC
PSTN
GSM Core (Circuit switched)
HLR AuC EIR
GMSC
IMS
+HSPA
+EDGE
Advanced Mobile Communication Networks 4
Integrated Communication Systems Group
Circuit vs. Packet Switched Communication
Connection (e.g. voice, CS data) => principle for GSM & UTRAN design • clearly defined start and end times • no burstiness => dedicated channels
minutes connection
setup connection
release
Packet session => supported by GPRS core, IMS, SAE, HSPA, LTE • packet arrival times are typically unknown to the system • traffic is highly bursty => shared channels & packet scheduling
hours
seconds
Advanced Mobile Communication Networks 5
Integrated Communication Systems Group
resource consumption
latency
• radio resources • channel codes • HW resources
• setup delay
• transient resource usage
cell_DCH
…
…
idle
T1
T2
T3
Resource Management in UMTS (radio link) When to free resources? After short or long breaks?
Advanced Mobile Communication Networks 6
Integrated Communication Systems Group
End-to-End Resource Management in UMTS (contr. plane) A sophisticated QoS architecture
Transl. Transl.
Adm.Contr
RAB Manager
UMTS BS Manager
UMTS BS Manager
UMTS BS Manager
Subscr. Control
Adm./Cap. Control
MT Gateway CN EDGE UTRAN
Ext. Service Control
Local Service Control
Iu BS Manager
Radio BS Manager
Iu NS Manager
UTRA ph. BS M
Radio BS Manager
UTRA ph. BS M
Local BS Manager
Adm./Cap. Control
Adm./Cap. Control
Adm./Cap. Control
Iu BS Manager
Iu NS Manager
CN BS Manager
Ext. BS Manager
CN BS Manager
service primitive interface protocol interface
BB NS Manager
BB NS Manager
TE Ext. Netw.
For details see 3GPP TS 23.207
Advanced Mobile Communication Networks 7
Integrated Communication Systems Group
End-to-End Resource Management in UMTS (user plane)
ResourceManager
Mapper
Classif
Cond.
ResourceManager
ResourceManager
Mapper
ResourceManager
Mapper
ResourceManager
ResourceManager
Cond.
Classif
Cond.
MT GatewayCN EDGEUTRAN
BB network serviceIu network serviceUTRA phys. BS
data flow with indication of direction
TE Ext.Netw.
Local BS External BS
Advanced Mobile Communication Networks 8
Integrated Communication Systems Group
Evolution from GSM to UMTS and LTE GSM: voice-dominated, dedicated channels, heavy states GPRS: add support for packet data on shared channels; add IP-based core
network EDGE: increased packet data capacity of GSM system UMTS: separate voice and packet data support; focus on dedicated channels
and heavy states, complicated RAN architecture and protocols due to macro diversity and QoS requirements
HSPA: improved support for packet data; emphasis on shared channels and fast radio resource management
IMS: support for IP-based services, e.g. voice (VoIP) LTE: strong packet data support (latency, throughput, control overhead),
limited state; simplified protocols; PS only, i.e. no CS core network
Transition ⇒ from circuit switching to packet switching ⇒ from slow, explicit setup and release of resources to fast channel-
condition- and demand-specific resource management
Advanced Mobile Communication Networks 9
Integrated Communication Systems Group
Evolution towards LTE – Architecture
• LTE radio system is a packet-only network - there is no support for circuit-switched services (no MSC)
• LTE starts on a clean state - everything is up for discussion including the system architecture and the split of functionality between Radio Access Network (RAN) and Core Network (CN)
• 3GPP (3rd Generation Partnership Program) study items • „3G Long-term Evolution” (LTE) for new Radio Access and • “System Architecture Evolution” (SAE) for Evolved Network
Advanced Mobile Communication Networks 10
Integrated Communication Systems Group
Evolution towards LTE – Architecture
GPRS Core (Packet Switched)
SGSN
GGSN
Internet
GSM RAN
Base station Base station controller
Base station
Base station
UTRAN
Radio network controller
node B node B
node B
MSC
PSTN
GSM Core (Circuit switched)
HLR AuC EIR
GMSC
E- e-
e- e- S-GW
P-GW
IMS
EPC
Advanced Mobile Communication Networks 11
Integrated Communication Systems Group
LTE: Evolved Packet System (EPS) Architecture
eNB
eNB
eNB
MME/S-GW MME/S-GW
X2
EPC E
-UTR
AN
S1
S1
S1 S1
S1 S1
X2
X2
EPC = Evolved Packet Core
2 instead of 4 user plane entities Key changes
– eNB: merging of base station and RNC functionality
– s-GW: merger of SGSN and GGSN functionality
Advanced Mobile Communication Networks 12
Integrated Communication Systems Group
LTE: Requirements and Performance Targets
Advanced Mobile Communication Networks 13
Integrated Communication Systems Group
LTE Key Features (Release 8)
• Support for both FDD and TDD
• Adaptive modulation and coding – DL modulations: QPSK, 16QAM, and 64QAM – UL modulations: QPSK and 16QAM
• Hybrid ARQ in addition to ARQ
• Multi-antenna solutions
– (2 or 4) x (2 or 4) downlink and uplink supported – Multi-layer transmission with up to four streams – Multi-user MIMO also supported
• Implicit support for interference coordination
Advanced Mobile Communication Networks 14
Integrated Communication Systems Group
Multi-antenna Solutions
Advanced Mobile Communication Networks 15
Integrated Communication Systems Group
Scheduling and Resource Allocation
• Fast scheduling • Scheduled, shared channel on both uplink and downlink
⇒ all transmissions in UL and DL must be explicitly scheduled
• Support for "semi-persistent" (periodical) allocation of resources, e.g. for VoIP
Advanced Mobile Communication Networks 16
Integrated Communication Systems Group
Interference Coordination
Advanced Mobile Communication Networks 17
Integrated Communication Systems Group
Self-Organization in LTE
Goal: minimize OPEX by automation of planning, optimization and repair Use Cases • Physical cell-ID automatic configuration (PCI) • Automatic Neighbor Relation (ANR) • Coverage and capacity optimization (CCO) • Inter-cell interference coordination (ICIC) • Random Access Channel (RACH) optimization • Mobility load balancing optimization (MLB) • Mobility robust optimization (MRO) • Energy saving (power on/off)
Advanced Mobile Communication Networks 18
Integrated Communication Systems Group
Example: RACH Optimization
• Delay to access to RACH depends on current network parameters – Transmission power, handover threshold, etc. changing networks parameters requires optimizing the RACH
• Approach
– eNB measures derived • random access delay, • random access success rate, • random access load, etc.
– RACH parameters are optimized based on measurements • RACH physical resources, • RACH persistence level and backoff control, • RACH transmission power control, etc.
Advanced Mobile Communication Networks 19
Integrated Communication Systems Group
Mobility Robustness Optimization (MRO)
Hys
Filtered RSRP [dB]
• Optimize HO performance amidst mobility – Hence Mobility Robustness
Optimization
• Goal: minimize – link failures due to early HO – link failures due to late HO – HO to wrong cell – ping-pong handovers
• Parameters
– Hysteresis (Hys) – Time to Trigger (TTT)
• Optimal settings depend on
– user mobility – other cell paramaters – …
Advanced Mobile Communication Networks 20
Integrated Communication Systems Group
MRO
– Late HOs: UE leaves coverage cell before HO is complete
– Early HOs: island coverage of cell B inside cell A’s coverage or UE handed over before cell B is steadily better than cell A
– HO to wrong cell: improper settings between
cells A and B → UE handed to cell C when should have been handed to cell B
• E.g. due to PCI confusion
HO Triggering RLF
RLF
HO Triggering RLF
Advanced Mobile Communication Networks 21
Integrated Communication Systems Group
Load Balancing
Overloaded Cells
Advanced Mobile Communication Networks 22
Integrated Communication Systems Group
Mobility Load Balancing
RSRP: Reference Signal Received Power Hys: Hysteresis CIO: Cell Individual Offset TTT: Time to Trigger P: Preparation time
CIOS
CIOt
(RSRPt+CIOt) – (RSRPs+CIOs) > Hys
Source Cell s
Target Cell t
Hys
HO Command
HO Decision
Start of TTT
P
RSRP
Time
Advanced Mobile Communication Networks 23
Integrated Communication Systems Group
SON Coordination Problem
• Use Cases (UCs) conflict within and across cells
CELL 1A
MRO
CCO
MLB
ICIC
….
CELL 2C
MRO
CCO
MLB
ICIC
….
CELL 1B
MRO
CCO
MLB
ICIC
….
Base Station 1
Base Station 2
MLB: Mobility Load balancing (MLB) MRO: Mobility Robustness (Handover) Optimization CCO: Coverage and Capacity Optimization ICIC: Inter Cell Interference Coordination
Possible Conflicts / dependencies Intra-cell Inter cell, intraBS - same UC Inter cell, intraBS - different UCs NB: Inter BS == inter cell
Advanced Mobile Communication Networks 24
Integrated Communication Systems Group
LTE vs. WiMax vs. 3GPP2
IMS
• Authenticator • Paging Controller • Page buffering
WiMAX
Access Point
CAP-C FA/Router
• Handover Control • Radio Resource
Management • ARQ/MAC/PHY • L2 Ciphering • Classification/
ROHC
E-Node B
MME Serv GW
HSS
IMS
• Authenticator • Paging Controller • Session setup
• Handover Control • Radio Resource
Management • ARQ/MAC/PHY • L2 Ciphering • ROHC
3GPP/LTE
PDN GW
• Local mobility • Page buffering
• Local mobility • Session setup • Bearer mapping
eBTS
SRNC Access GW
AAA
IMS
• Authenticator • Paging
Controller
• Handover Control • Radio Resource
Management • ARQ/MAC/PHY • L2 Ciphering • ROHC
3GPP2/UMB
HA
PCRF
IETF-centric architecture IETF-centric architecture IETF-friendly, but still
some flavor of UMTS/GPRS – GTP, etc
• Bearer mapping
PCRF
• Local mobility • Session setup • Bearer mapping
AAA HA
Advanced Mobile Communication Networks 25
Integrated Communication Systems Group
References
LTE/SAE • A. Toskala et al, “UTRAN Long-Term Evolution,” Chapter 16 in Holma/ Toskala: WCDMA for UMTS, Wiley
2007 • E. Dahlman et al, “3G Evolution, HSPA and LTE for Mobile Broadband,” Elsevier Journal, 2007 • Special Issue on LTE/ WIMAX, Nachrichtentechnische Zeitung, pp. 12–24, 1/2007 • 3rd Generation Partnership Project Long Term Evolution (LTE), official website:
http://www.3gpp.org/Highlights/LTE/LTE.htm • Technical Paper, “UTRA-UTRAN Long Term Evolution (LTE) and 3GPP System Architecture Evolution (SAE)”,
last update October 2006, available at: ftp://ftp.3gpp.org/Inbox/2008_web_files/LTA_Paper.pdf Standards • TS 36.xxx series, RAN Aspects • TS 36.300, “E-UTRAN; Overall description; Stage 2” • TR 25.912, “Feasibility study for evolved Universal Terrestrial Radio Access (UTRA) and Universal Terrestrial
Radio Access Network (UTRAN)” • TR 25.814, “Physical layer aspect for evolved UTRA” • TR 23.882, “3GPP System Architecture Evolution: Report on Technical Options and Conclusions”
Self-organizing networks and LTE • Self-organizing networks and LTE, http://www.lightreading.com/document.asp?doc_id=158441 • NGMN Recommendation on SON and O&M Requirements, Dec. 5, 2008, NGMN,
http://www.ngmn.org/uploads/media/NGMN_Recommendation_on_SON_and_O_M_Requirements.pdf