evolution of the evolved packet system (eps) · pdf fileevolution of the evolved packet system...

Document Number: EADSxxx

EAF version affiliation: EAF version 5.1

Review Date: June 2014

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Version 1.0

Evolution of the Evolved Packet System

(EPS)

Author: Prasan de Silva

22nd November 2013

Total Slides: 20

2

© Copyright Telecom Corporation of New Zealand 2013. All rights reserved.

Contents

1. Scene Setting

• The road ahead for mobile

• Tackling MBB growth

• The HetNet Landscape

2. Radio Access Network Topics

• eICIC and Cell Range Extension

• New Carrier Type

• Cooperative Communications

• Multi-Flow Aggregation

3. Core Network Topics

• IP Flow Mobility – adding WLAN

• Software Defined Networks in Mobile

• Distributed Mobility Management

4. Long Term View of EPS

3


Scene Setting

4


The Road Ahead For Mobile.

• LTE Release 8 networks are widely deployed and operationally stable.

• Most operators seem to be adopting 2 band CA in targeted areas as the next evolutionary step.

• We all acknowledge that it will be a challenge to continue adding capacity to meet the projected exponential growth of traffic.

1 2

3

[Ref: Svensson, 2013]

• Some operators are actively deploying the “small cell” layer –

entering the era of HetNets.

• But what effective and field proven tools do we have to combat intercell interference?

• If we deploy small cells in volume can we retrospectively add cooperative techniques?

• If we add small cells how can we offload the macro in controlled and deterministic manner?

• At present pace, if we keep building out LTE capacity with no cooperative techniques we will be left with the situation depicted in figure 1.

• The consequences of figure 1 mean that we are not maximising our bang for buck in terms of potential capacity.

• Which will lead to more (non-optimal) investment – but figures 2 and 3 highlight a smarter way through cooperative techniques…

5


A 3-Prong Approach to Address MBB Growth

• The long range view for meeting future demand necessitates further innovation in a 3-pronged approach.

• Capacity growth must be addressed across 3 dimensions:

1. Technology improvements (LTE-A,B, -> 5G) 2. Network densification (small cells, cooperative techniques, offloading, WiFi etc) 3. New bands (with larger carrier bandwidths ->WRC15)

Source: T.Nakamura, NTT DoCoMo

Required Performance

Spectrum Extension

Network

Densifi

cation

Sp

ec

tru

m E

ffic

ien

cy

Femto/WiFi

Micro, Pico

cells

Traffic

Offloading

Current

Capacity

MU-MIMO

Massive MIMO/

3D Beamforming

Very Wide Super Wide

Existing Cellular bands

Freq.

New spectrum bands

>100MHz wide40MHz700/850/900/1800/2100/2600

Femto

Layer

Pico

Layer

Micro

Layer

Macro

Layer

Cooperative techniques

Co

op

era

tiv

e t

ec

hn

iqu

es

6


Layers within the Hierarchy

Macrocell

(~40W @700/850MHz)

Microcell

(~2W @1800MHz)

Picocell, Femtocell,

WiFi AP (~200mW

@>2.6GHz))

Device 2

Device

(~10mW)

Non-cellular

access (e.g WiFi)

Cellular access

(e.g GSM, UMTS,

LTE)

Inc

rea

sin

g C

ov

era

ge

Fo

otp

rin

t o

f C

ell

Co

ve

rag

e L

ay

er

Ca

pa

cit

y L

ay

er

• The future mobile landscape will be Multi-Tiered in the RAN, commonly referred to as Heterogeneous

Network (or HetNet)

• The HetNet paradigm will extend beyond a macro and a single small cell layer, encompassing both licensed,

and unlicensed band technologies as shown below.

• Behind the scene of this landscape will be effective cooperative and mobility robustness mechanisms to

enhance system capacity and offloading capability.

7


Radio Access Network Topics

8


HetNet Enabler: eICIC and CRE

• eICIC uses a concept called “Almost Blank Subframe” - a time domain technique that reduces cell edge interference between a macro and pico node in co-channel deployments.

•Cell Range Extension allows the pcio to reach into the macro cell’s “exclusion zone”.

•Research suggests best offload performance occurs when ABS and CRE are used together.

Pico UE

Macro UE

X2_LOAD_INFORMATION [ABS PATTERN]

Exclusion zone inside the macro coverage region

RE

regionPico coverage

with 0dB bias

Power

[dBm]

46

30

Subframe (ms)

Subframe (ms)

CRS interference

ABS Muting

(X dBm)

Protected subframe

that pico schedules UE

in RE region

Protected subframe

that pico schedules

UE in RE region

4 8 12

4 8 12

0 0 0 1 1 1 1 0 0 0

Subframe bit

0=Not ABS

1= ABS

20 bit pattern corresponding to 2 radio frames over 20msSubframe

No.1 2 3 4 5 6 7 8 9 10

Macro cell

Pico cell

Ref: IEEE Wireless Comms, Feb 2013, “Multicell Cooperation for LTE-A HetNet Network Scenario’s”, B.Soret et al

9


HetNet Enabler: New Carrier Type (NCT)

Phantom Cell

Users control signalling is

sent over the macro cell.

Mobility is achieved thru

anchoring on macrocell

User data is sent over

Phantom cell

Macro

eNodeB

• NCT for the Downlink is a new concept being discussed in 3GPP Rel12.

• NCT is a stripped down (or lean) version of current cells with minimum common control channel overhead.

• Therefore it is not detectable to a device – i.e. UE must be directed by the macro cell.

• The key advantage in this scheme is related to the reduction in interference that would otherwise be generated through Reference Signal and other common channel transmissions (co-channel deployments)

• The macro layer is used as an anchor for vital control and mobility procedures and hence the UE is dual connected.

• Results show that use of NCT can boost 5th-percentile rates upto 70% over Rel8 Legacy Carrier Type operation under low loads and 20% under high loads*

* IEEE Comms Magazine, Feb 2013, “A Lean carrier for LTE”, Hoymann et al

10


HetNet Enabler: Cooperative Communications

• As we saw in the introduction, simply building out LTE capacity with conventional interference mitigation

approaches (eg. Down tilting, power control etc) will lead to sub-optimal system capacity and over

investment in CAPEX.

• Cell edge, where the bulk of users lie, needs to be the focus of cooperative techniques to lift SINR and

hence capacity.

• Many cooperative schemes have been developed. These schemes allow multiple base stations to

formulate a cooperative cluster, and either coordinate to avoid interference or coordinate to

constructively exploit interference.

• In 3GPP Release 10 and 11 these have been referred to as CoMP, categorised into three types:

1. Coordinated Scheduling (e.g. (e)ICIC) – a cooperating cluster agree which resources

experience the most interference and hence derive partial reuse on such resources. This can

be achieved with preconfigured fractional (or soft) reuse schemes or determined on a dynamic

basis through exchanging interference reports over the X2 link.

2. Coordinated Beamforming – the cooperating cluster shares CSI info for cell edge users such

that each eNodeB can determine precoding matrices that will ensure beams concentrate

energy only to the desired UE. The CSI exchange is done via the X2 link.

3. Joint Processing – the cooperating cluster acts as a virtual antenna array, whereby multiple

sites transmit to the UE simultaneously. Constructively using transmissions which would

otherwise be considered as interference. This scheme requires CSI and user data to be

present at every member of the cluster. X2 is used to facilitate this info exchange.

11


HetNet Enabler: Cooperative Communications

• The largest gains come from the JP category of CoMP schemes. In Foschini’s paper, gains of upto 300%

(using ER-ZF-CCT for 4x4MIMO) where shown for the MU-MIMO based JP scheme.

• However in practice, 3GPP simulations show only modest gains of 20~30%.

X2

eNodeB

Region of

reuse=1

Region of

reuse=1/3

X2

eNodeB

X2

eNodeB

(a) Coordinated Scheduling

(b) Coordinated Beamforming

(c) Joint Processing

UE

Ref: IEEE Comms Magazine, Aug2013, Biermann et al, and Wireless Comms, G.J Foschini, “Coordinating multiple antenna cellular networks to achieve enormous spectral efficiency”

ER-ZF-CCT: Effective Rate, Zero-Forcing, Coherently Coordinate Transmission

• The major sources that contribute to the

loss in gains are backhaul performance

(<0.5ms RTT), accurate CSI and

quantization errors of CSI (4 bit

encoding), and reference signal collisions.

• Does this mean that we can only

implement CoMP types (a) and (b) in

practical systems? Will that be worth

the investment?

• How can we future proof current

deployments for such cooperative

schemes?

12


HetNet Enabler: Multi-Flow Aggregation

• NCT and Carrier Aggregation give rise to the concept of “dual connectivity” – i.e being actively attached to 2 or more cells

concurrently.

• This concept is being extended above the PHY and MAC layers (where NCT and CA operate) in capability referred to as

Multi-Flow, which facilitates both capacity and mobility robustness.

• This work is being discussed in 3GPP Rel12. The concept is illustrated below.

Ref: 3GPP TR36.842, “Study on Small Cell Enhancements – Higher Layer Aspects”

MME SGW

PGW

S11

S5

HSS

S6a

Aggregation

Router

X2 VRF

S1 VRF

S1-US1-C

Macro eNodeB

(PCell)

Pico eNodeB 1

(SCell)

f1

f2 f2X2

X2X2

GTP-U

UDP

IP

ETH

Payload:

IP datagram

PDCP

RLC

MAC

PHY

PDSCHPDSCH

PDCCH

UE

Pico eNodeB 2

(SCell)

RLC

MAC

PHY

RLC

MAC

PHY

MME SGW

PGW

S11

S5

HSS

S6a

Aggregation

Router

X2 VRF

S1 VRF

S1-US1-C

Macro eNodeB

(PCell)

Pico eNodeB 1

(SCell)

f1

f2 f2X2

X2X2

GTP-U

UDP

IP

ETH

Payload:

IP datagram

PDCP

RLC

MAC

PHY

UE

Pico eNodeB 2

(SCell)

PDSCH

RLC

MAC

PHY

RLC

MAC

PHY

UE moves out

of PeNB1 and

into PeNB2

PDSCH

PDCCH

13


Core Network Topics

14


HetNet Enabler: IP Flow Mobility (IFOM)

• Through the adoption of Mobile IP based

protocols, 3GPP paved the way for non-

cellular access networks like WiFi, WiMAX

etc to be integrated to the EPC.

• The integration of WiFi to the EPC, allows

the addition of WiFi Access Points as

members of the small cell layer.

LTE WiFi

LTE WLAN Access

Network

VoLTE FTP

Flow 2: Traffic

steered via WLAN

LTE Access

Network

Smartphone with

DSMIPv6 support

Evolved Packet

Core

Flow 1: Traffic

steered via LTE

• IP Flow Mobility (IFOM) was standardised in 3GPP Release 10 (TS23.261) .

• IFOM allows the network to steer traffic across LTE and WiFi access based on traffic policies

which can be pushed to the device.

• The device is then able to maintain concurrent flows, move flows between the access types,

or combine flows into a single flow.

• The capability is based on Dual Stack Mobile IPv6 (or DSMIPv6).

15


A Closer Look at Flow Mobility

• Below we see a UE with WiFi and LTE operate concurrent sessions across the WLAN and LTE networks.

• In the example, a user is enjoying the benefits of the high data rate WLAN for their FTP download while

receiving a quality assured connection for their VoIP call over LTE.

• The DSMIPv6 protocol allows traffic flow selectors to be installed at UE and PGW to filter and steer the

relevant applications over the respective access network connections.

• Using Flow Mobility, when the user moves out of WiFi coverage, it is possible to move the FTP session to

the LTE access network connection through a DSMIPv6 signaling message from UE to PGW (i.e. via a

Binding Update).

MME

WLAN Access

Network

SGW PGW

WLAN LTE

TCP

APPLICATION

AP

eNodeB

IP[a]IP[b]

TFS

IP (DSMIPv6)

IP[h] IP[a] A 1 SIP/RTP

IP[h] IP[b] A 2 FTP

HoA CoA BID FID TFS

PGW Binding

Cache Entry

IP[h]

VoLTE

FTP

Evolved

Packet Core

MME

WLAN Access

Network

SGW PGW

WLAN LTE

TCP

APLLICATION

AP

eNodeB

IP[a]

IP(DSMIPv6)

IP[h] IP[a] A 1 SIP/RTP

IP[h] IP[a] A 2 FTP

HoA CoA BID FID TFS

PGW Binding

Cache Entry

User moves

out of WLAN

coverage

IP[h]

VoLTE

FTP

TFS

Evolved

Packet Core

16


SDN in Mobile Networks – a New Functional Architecture

• When we apply SDN concepts to the mobile and transport domains we arrive at the functional architecture depicted below. Two new entities are shown, namely the Mobile Forwarding Entity (M-FE) and Mobile Controller (M-CE) Entity.

UE

S1-C

SDN Transport Domain

SDN Evolved Packet SystemControl Plane

User Plane

Legacy eNodeB

S1-U

Legacy MME

Legacy SGW

Legacy PGW

S3, S10,S11

S11, S5,S8,S4

S5, S8, S2, Gx, Gy

RF INTF Mobile FE

CONTROL INTF

CONTROL INTF

MME SGW PGW

PCRF GGSN CSCF

SGSN SaMOG HSS

MOCN ANDSFCoMP

CONTROL INTF

MPLS BGP L2TP

DPI GGSN CSCF

BNG etcAAA

Mobile FE

CONTROL INTF

Transport FE

CONTROL INTF

Transport FE

CONTROL INTF

E.g. OpenFlow

M-FE M-FE

M-CE

Ref: IEEE Comms Magazine, July 2013, “Mobile Flow: Toward SDN in Mobile Networks”, K.Pentikousis et al

17


SDN in Mobile Networks – Applied View #2 Local Breakout

UE

SDN Transport

Domain

SDN Evolved Packet System Control Plane

User Plane

RF INTF

CONTROL INTF

MPLS LDP BGP

E.g. OpenFlow

CONTROL INTF

MME SGW PGW

GTP-U

S1AP

GTP-U

GTP-C

GTP-U

eNodeB, SGW, PGW FE

Control Intf

S1-C

S1-U

S11, S5-C

S5-UUDP/

IP/Eth

LDP/PW

CW

MPLS/

Eth

Control Intf

CE Node

CDN Server

PDN

User plane

Packet

LDP/PW

CW

MPLS/

Eth

Control Intf

IP/EthIP/Eth

M-FE

M-CE

18


Distributed Mobility Management (DMM)

APN1:HoA_A

eNodeB

SGW/PGW

A

MME AAA HSS

LMA/MAG

A

AP

SGW/PGW

B

LMA/MAG

B

Internet

S11,S1-C,S5-C

HoA_A

CoA_A

HoA_B

CoA_B

MovementMovement

APN2:HoA_B

CN_2CN_1

New binding cache entry

added to PGW A after UE

moves to PGW B:

HoA_A -> HoA_B

LTE:

GTP Solution

WiFi:

PMIPv6 Solution

S6a

SWx

S1

Mobile SDN

Controller

New binding cache entry

added to LMA A after UE

moves to LMA B:

HoA_A -> HoA_B

GTP-U

TunnelIPv6-in-IPv6

Tunnel

UE

SWm

• In EPS, mobility management is based on either GTP or derivatives of MobileIP (DSMIPv6, PMIPv6, MIPv4 or v6). These are based on a centralised anchor point, which must remain the same for session continuity.

• DMM moves the control and user plane mobility anchor points closer to the edge and allows the UE to move between mobility anchors while still maintaining session continuity.

• DMM solutions are classified as either a) client-based b) network based (with full or partial distribution) or c) routing based.

Ref: IEEE Comms Magazine, March 2013, “Distributed Mobility Management: A Standards Landscape, J. Zuniga et al

19


The Long Term View of EPS

20


Long Term Multi-Tier Landscape

• Putting it all together….

Coverage Layer

(macro layer)

eNB

WiFi AP

Capacity Layer

(Indoors)

Capacity Layer

(Outdoors)eNodeB

eNB

WiFi AP

eNB

Control Intf

S1AP

CONTROL INTF

MME SaMOG S/PGW-C

Centralised Data Centre for

Control Plane

SDN

MC

Distributed

M-FE

Capacity Layer

(Indoors)

(e)ICIC

eICIC

(e)ICIC

UE

CA + IFOM +

Multi-Flow

User

Plane

PDN

CDN

Internet

application

SaMOG/

SGW/

PGW

Distributed

M-FE

S1

S1

X2 X2

X2

CoMP Beamforming

CoMP Beamfo

rming

Tn

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