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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



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



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



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



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?



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



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



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



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



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



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



LTE: Requirements and Performance Targets



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



Multi-antenna Solutions



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



Interference Coordination



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)



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.



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 – …



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



Load Balancing

Overloaded Cells



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



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



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


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


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



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

http://www.3gpp.org/Highlights/LTE/LTE.htm

ftp://ftp.3gpp.org/Inbox/2008_web_files/LTA_Paper.pdf

http://www.lightreading.com/document.asp?doc_id=158441

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