Mobile Network Evolution

(1)

Mobile Network Evolution Andreas Mitschele-Thiel 1

-

From GSM to LTE

(2)

Outline

•  Evolution from GSM to UMTS

–  Architecture

–  Packet handling

–  Resource management

–  Comparison with 802.11

•  LTE + SAE = EPS

–  Features and requirements

–  Architecture

–  Protocols

–  Packet handling and resource management

–  Mobility management and HO

–  Self-organization

•  Conclusions

(3)

From GSM to UMTS: 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 IMS +HSPA +EDGE

(4)

From Circuit Switched to Packet Switched Communication

Connection (e.g. voice, CS data) => principle for GSM & UMTS RAN

•  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

(5)

UMTS RAN Resource Management

When to free resources? After short or long breaks?

hours seconds cell_DCH URA_PCH cell_FACH idle

(6)

resource

consumption

latency

•  radio resources •  channel codes •  setup delay •  transient resource usage cell_DCH URA_PCH cell_FACH idle T₁ T₂ T₃

UMTS RAN Resource Management

(7)

slow release

fast release

_{+ reduced fixed cost}

– increase of transitive cost cell_DCH URA_PCH cell_FACH idle T₁ T₂ T₃ – increase of fixed cost + decrease of transitive cost + decrease of mean call setup times

UMTS RAN Resource Management

(8)

UMTS Resource Management (control plane)

A sophisticated QoS architecture

Transl. Transl. Adm. Contr . Adm. Contr . Adm. Contr . Adm. Contr . Adm. Contr . RAB Manager UMTS BS Manager UMTS BS Manager UMTS BS Manager Subscr. Control Adm./Cap. Control

MT UTRAN CN EDGE Gateway

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 Manager Ext. BS CN BS

Manager

service primitive interface protocol interface BB NS Manager BB NS Manager TE Ext. Netw.

(9)

UMTS Resource Management (user plane)

Resource Manager Mapper Class if. Cond. Resource Manager Resource Manager Mapper Resource Manager Mapper Resource Manager Resource Manager Cond. Class if. Cond.

MT UTRAN CN EDGE Gateway

BB network service Iu network service

UTRA phys. BS

data flow with indication of direction

TE Ext.

Netw.

(10)

Compare to 802.11 Resource Management

t busy bo_e station₁ station₂ station₃ station₄ station₅ DIFS bo_e bo_e bo_e busy

elapsed backoff time busy medium not idle (frame, ack etc.)

bo_r bo_r DIFS bo_e bo_e bo_e bo_r DIFS busy busy DIFS bo_e busy bo_e bo_e bo_r bo_r

(11)

Compare to 802.11e Resource Management (EDCA)

•  Enhancement of access during Contention Period (CP)

•  Multiple backoff instances for data streams => different priorities

•  Priority over legacy stations (ensured for CW_min[TC]<15)

•  Parameters per Traffic Category (TC): •  AFIS Arbitration Inter Frame Space

•  CW Contention Window (min & max values)

(12)

Compare to 802.11e Resource Management (EDCA)

(13)

UMTS vs. 802.11 system operation

UMTS:

–  pros:

•  full control of radio spectrum

•  wide-area coverage

•  full fledged and individual QoS control (similar to IntServ)

–  cons: high initial overhead to set up business

•  high equipment cost

•  licence cost and spectrum availability

•  limited bandwidth

•  high administrative overhead to establish as a operator

•  acquisition of antenna locations

802.11:

–  pros: small cost to set up a business (in very dense areas)

•  no license needed

•  ample spectrum

•  widely available handsets (though not very mobile)

•  simple authentication and accounting (credit cards)

•  no long-term contracting with users

–  cons:

•  no control of radio spectrum (risk of investments in public areas)

•  limited coverage

•  limited QoS support (similar to DiffServ)

•  high installation cost (backhaul) in case of small traffic per area (use of mesh

networks to minimize backhaul cost)

(14)

From GSM to LTE/SAE: Protocols and Channels

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 for GSM systems

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

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

(15)

3GPP Evolution towards LTE/SAE – Background (1/3)

Discussion started in December 2004 State of the art then:

•  The HSPA extension for UMTS provides very efficient packet

data transmission capabilities, but UMTS should continue to be evolved to meet the ever increasing demand of new applications and user expectations

•  10 years have passed since the initiation of the 3G program and

it is time to initiate a new program to evolve 3G which will lead to a 4G technology

(16)

3GPP Evolution towards LTE/SAE – Background (2/3)

•  From the application/user perspectives,

the UMTS evolution should target at significantly higher data rates and throughput, lower network latency and support of always-on connectivity

•  From the operator perspectives,

an evolved UMTS will make business sense if it:

- _{provides significantly}_{improved power and bandwidth} efficiencies

- _{facilitates the}_{convergence with other networks/technologies} - _{reduces transport network cost}

(17)

3GPP Evolution towards LTE/SAE – Background (3/3)

•  Evolved-UTRA is a packet only network - there is no support for

circuit-switched services (no MSC)

•  Evolved-UTRA starts on a clean state - everything is up for

discussion including the system architecture and the split of functionality between RAN and CN

•  Led to 3GPP Study Item (Study Phase: 2005-4Q2006)

•  „3G Long-term Evolution (LTE)” for new Radio Access and

(18)

Economic Drivers for Network Evolution

Voice Data Traffic volume Time Profit Network cost (existing technologies) Network cost (LTE)

Decouple network cost from traffic volume!

(19)

(20)

Key Features of LTE to Meet Requirements

•  Selection of Orthogonal Frequency Division Multiplexing (OFDM) for

the air interface

–  Less receiver complexity

–  Robust to frequency selective fading and inter-symbol interference (ISI)

–  Access to both time and frequency domain allows additional flexibility in

scheduling (including interference coordination)

–  Scalable OFDM makes it straightforward to extend to different

transmission bandwidths

•  Integration of Multiple-Input Multiple-Output (MIMO) techniques

–  Pilot structure to support 1, 2, or 4 Tx antennas in the Downlink (DL) and

Multi-user MIMO (MU-MIMO) in the Uplink (UL)

•  Simplified network architecture

–  Reduction in number of logical nodes à flatter architecture

(21)

Transition to LTE/SAE: 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

(22)

Network Simplification: From 3GPP to 3GPP LTE

•  3GPP architecture

–  4 functional entities on the

control plane and user plane –  3 standardized user plane

and control plane interfaces

S-GW: Access Server Gateway

•  3GPP LTE architecture

–  2 functional entities on the user

plane: eNodeB and S-GW

–  SGSN control plane functions =>

S-GW & MME

–  Less interfaces, some functions

will disappear

•  4 layers into 2 layers

–  Evolve GGSN à integrated

S-GW

–  Moving SGSN functionalities to

S-GW

–  RNC evolutions to RRM on a IP

distributed network for enhancing mobility management

–  Part of RNC mobility function

being moved to S-GW & eNodeB

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odeB ASGW eNodeB MMF GGSN SGSN RNC NodeB

Control plane User plane

ASGW eNodeB MMF S-GW eNodeB MME

Control plane User plane

$7FOC%$'+<30Q%F2(')2P ""IC%"*U363(P%"202Q';'0(%I0(3(P

(23)

Evolved Packet System (EPS) Architecture

eNB eNB eNB MME/S-GW MME/S-GW X2 EPC E-U T R AN S1 S1 S1 S1 S1 S1 X2 X2

EPC = Evolved Packet Core

Key elements of network architecture

– No more RNC

– RNC layers/functionalities

moves in eNB

– X2 interface for seamless

mobility (i.e. data/context forwarding) and interference management

Note: Standard only defines logical structure!

(24)

(25)

EPS Architecture - Control Plane Layout over S1

eNB PHY UE PHY MAC RLC MAC MME RLC NAS NAS RRC RRC PDCP PDCP UE eNode-B MME RRC sub-layer performs: §  Broadcasting §  Paging §  Connection Mgt

§  Radio bearer control

§  Mobility functions

§  UE measurement reporting & control

PDCP sub-layer performs:

§  Integrity protection & ciphering

NAS sub-layer performs: §  Authentication

§  Security control

§  Idle mode mobility handling

(26)

EPS Architecture - User Plane Layout over S1

eNB PHY UE PHY MAC RLC MAC PDCP PDCP RLC S-Gateway RLC sub-layer performs:

§  Transferring upper layer PDUs

§  In-sequence delivery of PDUs

§  Error correction through ARQ

§  Duplicate detection §  Flow control §  Concatenation/Concatenation of SDUs PDCP sub-layer performs: §  Header compression §  Ciphering

MAC sub-layer performs: §  Scheduling

§  Error correction through HARQ

§  Priority handling across UEs & logical

channels

§ Multiplexing/de-multiplexing of RLC

radio bearers into/from PhCHs on TrCHs Physical sub-layer performs:

§  DL: OFDMA, UL: SC-FDMA

§  Forward Error Correction (FEC)

§  UL power control

(27)

LTE Key Features (Release 8)

•  Multiple access scheme

–  DL: OFDMA with Cyclic Prefix (CP)

–  UL: Single Carrier FDMA (SC-FDMA) with CP

•  Adaptive modulation and coding

–  DL modulations: QPSK, 16QAM, and 64QAM

–  UL modulations: QPSK and 16QAM (optional for UE)

–  Rel. 6 Turbo code: Coding rate of 1/3, two 8-state constituent encoders, and

a contention-free internal interleaver

•  ARQ within RLC sublayer and Hybrid ARQ within MAC sublayer

•  Advanced MIMO spatial multiplexing techniques –  (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

(28)

Integrated Communication Systems Group

Multi-antenna Solutions

ple-input multiple-output [MIMO], as well as multi-user MIMO) with up to four antennas, and beamforming. Which of the schemes (or which combination of the schemes) to use depends on the scenario (Fig. 5). In the uplink, both open-and closed-loop transmit-antenna selection are supported as optional features.

LTE transmit diversity is based on so-called space-frequency block coding (SFBC), comple-mented with frequency-switched transmit diversi-ty (FSTD) in the case of four transmit antennas [1]. Transmit diversity is primarily intended for common downlink channels to provide addition-al diversity for transmissions for which channel-dependent scheduling is not possible. However, transmit diversity also can be applied to user-data transmission, for example, to voice-over-IP (VoIP), where the relatively low user-data rates may not justify the additional overhead associat-ed with channel-dependent schassociat-eduling.

In case of spatial multiplexing, multiple anten-nas at both the transmitter (base station) and

the receiver (terminal) side are used to provide

simultaneous transmission of multiple, parallel

data streams, also known as layers, over a single radio link, thereby significantly increasing the peak data rates that can be provided over the radio link. As an example, with four base-station transmit antennas and a corresponding set of (at least) four receive antennas at the terminal side, up to four data streams can be transmitted in parallel over the same radio link, effectively increasing the data rate by a factor of four.

LTE multi-stream transmission is pre-coder

based. A number of transmission layers are mapped to up to four antennas by means of a precoder matrix of size N_A×N_L, where the num-ber of layers N_L, also known as the transmission rank, is less than or equal to the number of antennas N_A. The transmission rank, as well as the exact precoder matrix, can be selected by the network, based on channel-status measurements performed and reported by the terminal, also known as closed-loop spatial multiplexing.

In the case of spatial multiplexing, by select-ing rank-1 transmission, the precoder matrix, which then becomes an N_A×1 precoder vector, performs a (single-layer) beamforming function. More specifically, this type of beamforming can be referred to as codebook-based beamforming

as the beamforming can be done only according to a limited set of pre-defined beamforming (precoder) vectors.

In addition to the codebook-based beam-forming as a special case of the LTE spatial mul-tiplexing, LTE also supports more general

non-codebook-based beamforming. In contrast to

codebook-based beamforming, in the case of non-codebook-based beamforming, the terminal must make an estimate of the overall beam-formed channel. To enable this, LTE provides the possibility for the transmission of user equip-ment (UE)-specific reference symbols, transmit-ted using the same beamforming as the user data, and enabled for the terminal to estimate the overall beamformed channel.

POWER CONTROL AND

INTER-CELL INTERFERENCE COORDINATION LTE provides (intra-cell) orthogonality between users in both uplink and downlink, that is, at least in the ideal case, no interference between transmissions within the same cell but only inter-ference between cells. Hence, LTE performance in terms of spectrum efficiency and available data rates is, relatively speaking, more limited by interference from other cells (inter-cell interfer-ence) compared to WCDMA/HSPA, especially for users at the cell edge. Therefore, the means to reduce or control the inter-cell interference potentially can provide substantial benefits to LTE performance, especially in terms of the ser-vice (data rates, etc.) that can be provided to users at the cell edge.

Uplink power control is one of the mecha-nisms in LTE used for this purpose. It is used to control not only the received signal strength in the intended cell, but also to control the amount of interference in neighboring cells. LTE uplink-power control supports fractional path-loss

com-pensation, implying that users close to the cell

border use relatively less transmit power, and thus generate relatively less interference to neighbor cells. However, LTE provides more advanced interference-handling schemes as well.

Inter-cell interference coordination (ICIC) is in essence a scheduling strategy used to limit the inter-cell interference. A simple method to improve cell-edge data rates is to restrict the usage of parts of the bandwidth statically, for example, through a reuse larger than one. Such schemes improve the signal-to-interference ratios of the used frequencies. However, the loss due to reduced bandwidth availability is typically larger than the corresponding gain due to higher signal-to-interference ratio, leading to an overall loss of efficiency. Therefore, the LTE standard provides tools for dynamic inter-cell-interference coordina-tion of the scheduling in neighbor cells such that cell-edge users in different cells preferably are scheduled on complementary parts of the spec-trum when required. Note that a major difference from static reuse schemes is that LTE still allows for the total available spectrum to be used in all cells. Bandwidth restrictions are applied only when motivated by traffic and radio conditions.

Interference coordination can be applied to both uplink and downlink, although with some fundamental differences between the two links. In

!

! Figure 5. Multiple-antenna techniques in LTE.

Diversity for improved

system performance Beam-forming for improved coverage(less cells to cover a given area)

Spatial-division multiple access (”MU-MIMO”) for improved capacity

(more users per cell)

Multi-layer transmission

(”SU-MIMO”) for higher data rates in a given bandwidth

(29)

Interference Coordination

(30)

Downlink Peak Rates

(31)

Uplink Peak Rates

Assumptions: code rate =1, 2PRBs reserved for PUCCH (1 for 1.4MHz), no SRS, ignores subframes with PRACH, takes into account highest prime-factor restriction

(32)

Scheduling and Resource Allocation (1/2)

•  LTE uses a scheduled, shared channel on both the uplink

(UL-SCH) and the downlink (DL-(UL-SCH)

•  Normally, there is no concept of an autonomous transmission; all

transmissions in both uplink and downlink must be explicitly scheduled

(33)

Scheduling and Resource Allocation (2/2)

•  Basic unit of allocation is called a Resource Block (RB) –  12 subcarriers in frequency (= 180 kHz)

–  1 sub-frame in time (= 1 ms, = 14 OFDM symbols)

–  Multiple resource blocks can be allocated to a user in a given subframe

(34)

LTE Handover (1/2)

•  LTE uses UE-assisted network controlled handover

–  UE reports measurements; network decides when to handover and to which

cell

–  Relies on UE to detect neighbor cells à no need to maintain and broadcast

neighbor lists

-  Allows "plug-and-play" capability; saves BCH resources

–  For search and measurement of inter-frequency neighboring cells only carrier

frequency need to be indicated

•  X2 interface used for handover preparation and data forwarding

–  Target eNB prepares handover by sending required information to UE

transparently through source eNB as part of the Handover Request Acknowledge message

-  New configuration information needed from system broadcast

-  Accelerates handover as UE does not need to read BCH on target cell

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

switch à prevents data loss

(35)

LTE Handover (2/2)

Characteristics •  No soft handover •  Handover latency (2. –11.) ~ 55 msec •  Handover Interruption (7. –11.) ~ 35 msec •  Synchronization (9.) on RACH

(36)

Tracking Area

Tracking Area Identifier (TAI) sent over Broadcast Channel BCH Tracking Areas can be shared by multiple MMEs

(37)

(38)

LTE RRC States

•  No RRC connection, no

context in eNodeB (but EPS bearers are retained)

•  UE controls mobility through

cell selection

•  UE-specific paging DRX

cycle controlled by upper layers

•  UE acquires system

information from BCH

•  UE monitors paging channel

to detect incoming calls

•  RRC connection and context in

eNodeB

•  Network controlled mobility

•  Transfer of unicast and

broadcast data to and from UE •  UE monitors control channels

associated with the shared data channels

•  UE provides channel quality

and feedback information

(39)

EPS Connection Management States

•  No signaling connection

between UE and core

network (no S1-U/ S1-MME) •  No RRC connection (i.e.

RRC_IDLE)

•  UE performs cell selection

and tracking area updates

•  Signaling connection

established between UE and MME, consists of two

components

–  RRC connection

–  S1-MME connection

•  UE location is known to

(40)

EPS Mobility Management States

•  EMM context holds no valid

location or routing information for UE

•  UE is not reachable by MME

as UE location is not known

•  UE successfully registers with

MME with Attach procedure or Tracking Area Update

•  UE location known within

tracking area

•  MME can page to UE

•  UE always has at least one

(41)

(42)

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

•  Bearer mapping PCRF •  Local mobility •  Session setup •  Bearer mapping AAA _HA

(43)

Mobile Network Evolution Andreas Mitschele-Thiel 44 C

S

₃ C

S

₅ C

S

₁ C

S

₄ C

S

₂ Local interactions (environment, neighborhood) Local system control Simple local behavior C

S

₆

(44)

Property Description

No central control

No global control system No global information

Subsystems perform completely autonomous

Emerging structures Global behavior or functioning of the system _{emerges in form of observable pattern or structures}

Resulting complexity

Even if the individual subsystems can be simple as well as their basic rules, the resulting overall system becomes complex and often unpredictable

High scalability

No performance degradation if more subsystems are added to the system

System performs as requested regardless of the number of subsystems

(45)

Self-organization in LTE

Motivation and drivers

•  Multitude of re-configurable parameters, e.g. transmit powers,

control channel powers, handover parameters etc.

•  Huge number of eNBs expected with the introduction of Home

eNB concept •  Home eNB

–  Small Coverage Area

–  Small number of users per cell

–  May be switched off by user

–  Not physically accessible for operators

•  Self-organization (SO) is driven by operators to reduce

Operational Expenses (OPEX)

•  Main push of Self-Optimizing Networks (SON) by NGMN alliance

(46)

SO Functionality in LTE (1/5)

SO functionality includes

•

Self-configuration

•

Self-optimization

(47)

SO Functionality in LTE (2/5)

Self-Configuration

•  Objective is to have plug-n-play enabled nodes

•  Works in pre-operational state, which starts when the node is

powered up and has backbone connectivity until the RF transmitter is switched on

•  Automatic installation procedures for newly deployed nodes

•  Automatic creation of the logical associations (interfaces) with the

network and establishment of the necessary security contexts •  Download of configuration files from a configuration server

•  Performing a self-test to determine if everything is working as

intended

(48)

SO Functionality in LTE (3/5)

Self-optimization

•  Uses UE & eNB measurements and performance statistics to

auto-tune the network

•  Works in operational state, which starts when the RF interface is

(49)

SO Functionality in LTE (4/5)

Self-optimization process includes •  Neighbor list optimization

–  Reconfigures the neighbor list to have the minimum set of cells

necessary for handover

•  Coverage and capacity optimization

–  Maximizes the system capacity while ensuring an appropriate

overlapping area between the adjacent cells

•  Mobility robustness optimization

–  Adjusts the handover thresholds to avoid unnecessary handovers

•  Mobility load balancing optimization

–  Automatically handover some UEs at the edge of a congested cell to

neighboring less congested cells

•  Energy Saving

–  Autonomously switching off some of the resources or the complete

(50)

SO Functionality in LTE (5/5)

Self-healing and self-repair

•  Detects equipment faults, identifies the root causes and takes

recovery actions such as

–  Reducing transmit power in case of temperature alarm

–  Fallback to the previous software version

–  Switching to backup units

•  If the fault can not be resolved locally by the above measures, the

affected cell and the neighboring cells take cooperative actions to minimize QoS degradation

•  Results in a reduced failure recovery time and a more efficient

(51)

SON Architecture (1/4)

•  Based on the location of SO functionality three architectural

approaches are possible –  Centralized

–  Distributed

(52)

SON Architecture (2/4)

Centralized Architecture

•  SO functionality resides in the

OAM system at higher level of network architecture

•  Easy to deploy due to fewer

number of installation sites •  OAM is vendor specific, so no

support for multi-vendor optimization

•  Existing interface N (Itf-N)

between Network Manager (NM) and Element Manager (EM) or Network Element (NE) needs to be extended

(53)

SON Architecture (3/4)

Distributed Architecture

•  SO functionality resides in the

eNB at the lower level of network architecture

•  Difficult to deploy because of

large number of installation sites

•  Difficult to perform complex

optimizations involving large number of eNBs

•  Better performance for less

complex optimizations involving a small number of eNBs

•  X2 interface between the eNBs

(54)

SON Architecture (4/4)

Hybrid Architecture

•  SO functionality resides both at

the OAM and eNB level

•  Difficult to deploy because of

large number of installation sites involved

•  Optimization problems can be

categorized depending upon their complexity level and can be performed either locally at eNB or at OAM center

•  Requires multiple interfaces

(55)

Conclusions

•  LTE is a new air interface with no backward compatibility to WCDMA –  Combination of OFDM, MIMO and Higher-Order Modulation

•  SAE/EPS realizes a flatter IP-based network architecture with less

complexity

–  eNodeB, S-GW, P-GW

•  Some procedures/protocols are being reused from UMTS –  Protocol stack

–  Concept of Logical, Transport and Physical Channels

•  Complexity is significantly reduced –  Reduced UE state space

–  Most transmission uses shared channels

•  LTE standard (Rel. 8) is stable

–  Enhancements are discussed for Rel. 10 under LTE+

-  Support of wider spectrum bandwidth (up to 100 MHz)

-  Spatial multiplexing in UL and DL

-  Beamforming and Higher-order MIMO in DL

-  Coordinated multipoint transmission and reception

(56)

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

(57)

Abbreviations

CP Cyclic Prefix

DFT Discrete Fourier Transformation DRX Discontinuous Reception

ECM EPS Connection Management EMM EPS Mobility Management eNodeB Evolved NodeB

eNB Evolved NodeB EPC Evolved Packet Core EPS volved Packet System E-UTRAN Evolved UTRAN

FDD Frequency-Division Duplex FDM Frequency-Division Multiplexing FFT Fast Fourier Transformation HD-FDD Half-Duplex FDD

HO Handover

HOM Higher Order Modulation IFFT Inverse FFT

ISI Inter-Symbol Interference LTE Long Term Evolution

MIMO Multiple-Input Multiple-Output MME Mobility Management Entity

OAM Operation, Administration and Management

OFDM Orthogonal Frequency-Division Multiplexing

OFDMA Orthogonal Frequency-Division Access

PDN Packet Data Network P-GW PDN Gateway

RA Random Access

RB Resource Block

RRC Radio Resource Control SAE System Architecture Evolution SCH Shared Channel

S-GW Serving Gateway SC-FDMA Single Carrier FDMA TDD Time-Division Duplex

TA Timing Advance/ Tracking Area TAI Tracking Area Indicator

TAU Tracking Area Update UE User Equipment

Mobile Network Evolution - From GSM to LTE