4G Introduction

4G
A historical and practical guide

Prologue 
Evolution To Mobile Operator
10 MHz
Set up a podcast to provide your family
weekend entertainment, kind of like a 1G provider

Prologue 
1 MHz
now neighbors want to join
You use FDMA to provide 10 neighbors

Prologue 
1 MHz
more neighbors want to join
You use TDMA on each 1MHz carrier 
because not everyone is using 
it the same time anyway

Prologue 
Far far away friends want to join
Mobility, security, policy control, planning…
Congratulations! You are now a mobile operator!

A Little History: 1G
• 1980
• Lack of roaming: various local systems
• Bad security
• Poor battery
https://img1.etsystatic.com/005/0/6011536/il_340x270.400991407_ig0s.jpg

• 1990, it’s all about voice, good voice and roaming voice
• GSM: Global System for Mobile Communications, the
success of mobile
• FDD/TDMA-FDMA
• SMS
• 10^2 kbit/s
http://upload.wikimedia.org/wikipedia/commons/thumb/d/d1/Gsm_structures.svg/350px-Gsm_structures.svg.png

Problem of 2G
• 2G focus on voice, results in an air interface
very inefﬁcient for data packet
• Various advances in MAC layer technology,
notably CDMA
Voice Data
Bit Rate small CBR
Variable BR 
Can be large
Band Width 64 Kbit/s 2Mbit/s
Packet small large
Delay small depends

CDMA
• Better auto correlation
• Low cross correlation
between different spread
code’s output signal
• Frequency reuse factor of
1 (as oppose to 4 in GSM)
• Improved security
• Hard to be jammed
Input Signal
Spreading Code
Output Signal

The Vision
The Martini Vision:
Anyone, Anywhere, Any Medium

IMT 2000 family Common term
mode of
operation
中華
電信
IMT-DS 
Direct Sequence
CDMA
W-CDMA FDD v
IMT-MC 
Multi Carrier
CDMA
Cdma2000 FDD v
IMT-TD 
Time Devision
CDMA
TD-CDMA TD-SCDMA TDD
IMT-SC 
Single Carrier
EDGE FDD
IMT-FT 
Frequency Time
DECT TDD
In Reality

3G: UMTSUniversal Mobile Telecommunications System
UE NodeB SGSN GGSN
Internet
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
Packet Data Network 
(packet Switch Stream,
IP Multimedia System)
UTRAN Core Network
UE NodeB
UE NodeB
RNC
RNC
Public
Phone
Network
Signaling
Network
Mobile Switching
Center
Gateway MSC
Home Location Register
Radio
Network
Controller

UE NodeB SGSN GGSN
Internet
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
UTRAN Core Network
RNC
Public
Phone
Network
Signaling
Network
Mobile Switching
Center
Gateway MSC
• You bought a phone right outside
NTHU, turn it on
• Your subscription is based on a 15
digits number in your SIM.
• After the phone found network,
the number is sent to HLR.
• Your phone and HLR now share
the same key for communication.
Radio
Network
Controller

UE NodeB SGSN GGSN
Internet
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
UTRAN Core Network
RNC
Radio
Network
Controller
Public
Phone
Network
Signaling
Network
Mobile Switching
Center
Gateway MSC
• First you make a call to inform your dad  
付清節快樂 (happy father’s paying day)
• Your UE requests MSC about a particular
number.
• MSC checks with HLR to see if you are permitted
to call.
• MSC set up resources required in RAN (radio
access network) and CN (core network).
• When the call ends, MSC and GMSC are
involved in producing call detail record.

UE NodeB SGSN GGSN
Internet
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
UTRAN Core Network
RNC
Radio
Network
Controller
Public
Phone
Network
Signaling
Network
Mobile Switching
Center
Gateway MSC
• Now you are riding your scooter back to
NCTU.
• After a while idle, your phone moves from
Mobility Management (MM) connect to
MM-IDLE. To avoid excessive location
update, few NodeB’s are grouped into a
location area. Location update happens
only when you enter new location area.
• So your phone happily sits idle and listen
if it receives call or location update.

UE NodeB SGSN GGSN
Internet
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
UTRAN Core Network
RNC
Radio
Network
Controller
Public
Phone
Network
Signaling
Network
Mobile Switching
Center
Gateway MSC
• When your dad tries to call you (he
decides he don’t won’t to pay for this cell
phone), GMSC looks up HLR to see which
MSC is serving you. All NodeB’s of that
location area broadcast to wake up your
cellphone.
• During call, you are constantly moving, so
hand over is required. In CDMA, you are
often connected to multiple cell towers at
once, this facilitates soft handover.

UE NodeB SGSN GGSN
Internet
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
UTRAN Core Network
RNC
Radio
Network
Controller
Public
Phone
Network
Signaling
Network
Mobile Switching
Center
Gateway MSC
• Now you are wondering what is RNC, so you
open your browser.
• To send or receive packets, a PDP (packet
data protocol) context need to be
established.
• PDP context signals SGSN and GGSN to set
up context for packet data session. Context
include a subscriber IP and a QoS request.
• After done browsing, you deactivates the PDP
context.

UE NodeB SGSN GGSN
Internet
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
UTRAN Core Network
RNC
Radio
Network
Controller
Public
Phone
Network
Signaling
Network
Mobile Switching
Center
Gateway MSC
• QoS request is
simply ignored by
most (all) operators.

UE NodeB SGSN GGSN
Internet
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
UTRAN Core Network
RNC
Radio
Network
Controller
Public
Phone
Network
Signaling
Network
Mobile Switching
Center
Gateway MSC
• Now mobile operator is sending you a
SMS message to inform about the
data usage volume.
• GGSN checks HLR to obtain your
routing area, but also obtains that you
have no PDP context active. A paging
message is broadcast requesting
your phone to set up PDP context so
that the message can be sent.

Key notes on 2G/3G
2G 3G
Data Rate 10 kbit/s 10 kbits/s
MAC Scheme
TDMA 
FDMA
CDMA
Available
Bandwidth
2x5 MHz 
with TDMA
2x15 MHz
Cost and
Market
see next few slides
2 4

Bandwidth: 2G vs 3G
type bandwidth
winning bid
(in billion)
winner
A W-CDMA
2 x 15MHz+
5MHz
10.2 遠致
B W-CDMA
2 x 10MHz+
5MHz
7.7 聯邦
C W-CDMA
2 x 15MHz+
5MHz
10.3 台灣
D W-CDMA
2 x 15MHz+
5MHz
10.2 中華
E CDMA2000 2 x 20MHz 10.6 亞太
2G
1. About to be
“recycled”
2. At the time CHT
got its 2G license.
It is still
government run.
3G: around 49 billion NTD

3G growth
• Question: Why is it growing like this? Slow, exponential, ﬁnally slow.

Problem with 3G
• Why has it been slow to take off? 
Small coverage, lack of cheap and power friendly terminal, lack of
killer app
• W-CDMA cell breathing 
frequency reuse factor of 1 
-> all senders and receivers interfere with each other 
-> number of UE affects edge data rate 
-> making cell tower planning more difﬁcult
• Packet network scalability 
GGSN is a huge gateway that last for a long time (it is not just a
bottle neck, it is a static battle neck…)

LTE
• It is not 4G 
ITU made it clear… LTE is part of IMT-2000 3G family. We call LTE
3.9G, because despite its enormous improvement on bandwidth
(around 50 Mbit/s), it did not meet 4G standard (100 Mbit/s).
• It is designed to expect an all-packet-switching
network. 
3G was designed for both, but is in fact very inefﬁcient on IP.
• TLA 
Congratulations, you are ready for more TLA’s (three letter
acronym).

3GPP
LTE
EPS
E-UTRAN
SAE
EPC
Release 8
Third Generation Partnership Project
Long Term Evolution System Architecture Evolution
Evolved Packet CoreEvolved UTRAN
Evolved Packet System

3GPP
LTE
EPS
E-UTRAN
SAE
EPC
Release 8
Term used
for marketing

3GPP
LTE
EPS
E-UTRAN
SAE
EPC
Release 8
Terms with
actual meaning
Terms with
actual meaning
Term should
have been used
for marketing

EPS Architecture
UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
User Equipment Evolved NodeB Serving Gateway PDN Gateway Packet Data Network 
E-UTRAN Core Network (EPC)
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Mobile Location Center
Gateway Mobile 
Location Center

EPS Architecture
UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
So called “cell phone” 
but could be
other devices
On a UE,  
UMSI: Unique Mobility Subscriber Id
identiﬁes a subscriber.
UMEI: Unique Mobility Equipment Id
identiﬁes equipment. 
UMEI can be obtained by typing *#06#
EPS Architecture

EPS Architecture
UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
So called “cell tower”
e-NodeB
• Provide radio access to UE’s (Uu interface).
• Interface: logical connection between
endpoint.
Uu
S1-MME
S1-U

EPS Architecture
UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Control Trafﬁc
Uu S1-U
S1-MME
Data
e-NodeB
• Separate control plan and data plan.
• Tunnels control trafﬁc between UE and MME
(S1-MME interface).
• Tunnels data between UE and services 
(S1-U interface).

EPS Architecture
UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Control Trafﬁc
Uu S1-U
S1-MME
Data
e-NodeB
• Concert with other eNodeB’s to handle
mobility (X-2 interface).
UE
User Equipment
Uu
e-NodeB
X-2
Control Trafﬁc
D
ata

EPS Architecture
UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
MME
• Keep track of UE’s.
• Setting up and tearing down sessions.
S11
S6a
S5 SGi

EPS Architecture
UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
MME
• Authentication and gate keeping.
S11
S6a
S5 SGi

EPS Architecture
UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
MME
• Selecting S-GW and P-GW.
• Primary responsibilities are divided into
EMM (Evolved Mobility Management) and
ESM (Evolved Session Management).
• A user is on al most one MME at all time.
S11
S6a
S5 SGi

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
HSS
• Database of subscriber information.
• Queried by MME.
• Holds security information of all SIM cards
of a mobile network.
• Keeps a “birds eye view” of what users are
located in what network (i.e. what SIM is
registered with which MME). Similar to HLR
in UMTS.
S11
S6a
S5 SGi
EPS Architecture

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
S-GW
• One or more S-GW’s can serve one or more
eNB’s.
• One UE can be served by only one S-GW.
• Receives instructions from MME to self up
and teardown UE sessions.
• Handle signaling between MME and P-GW.
• Handle IP packet between UE and P-GW.
S11
S6a
S5 SGi
EPS Architecture

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
S-GW
• One or more S-GW’s can serve one or more
eNB’s.
• One UE can be served by only one S-GW.
• Receives instructions from MME to self up
and teardown UE sessions.
S11
S6a
S5 SGi
EPS Architecture

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
S-GW
• Handle signaling between MME and P-GW.
S11
S6a
S5 SGi
EPS Architecture

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
S-GW
• Handle IP packet between UE and P-GW.
S11
S6a
S5 SGi
EPS Architecture

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
P-GW
• Provide access to external PDN
• One UE can be associated with multiple P-
GW if it connect to multiple PDN’s.
• Dictates the QoS and bandwidth parameter
for subscriber’s session.
S11
S6a
S5 SGi
EPS Architecture

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
PCRS
• The core function of a PCRF is to make
policy decisions for the network.That means
it needs inputs (eg: from a subscriber
database, from real-time network
information, from a billing system, from local
conﬁguration) and it needs to translate that
into a decision to direct the policy enforcer
(PCEF) to take appropriate actions.
S11
S6a
S5 SGi
EPS Architecture
PCRS
Gx

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
PCRS
• What is the difference between PCRS and
PCEF in P-GW?
• In CSFB, is PCRS involved?
• Why can’t PCRS simply be a function of P-
GW?
S11
S6a
S5 SGi
EPS Architecture
PCRS
Gx

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Evolved Serving 
Gateway Mobile 
Location Center
Uu S1-U
S1-MME
AS vs NAS
• AS (access stratum): link to link
communication.
• NAS (non-access stratum): provide
communication between access network
and core network. NAS makes the direct
communication between MME and UE
possible.
S11
S6a
S5 SGi
EPS Architecture
PCRS
Gx

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
E-SMLC GMLC
Mobility 
Management
Entity
Home 
Subscriber 
Server
Uu
Evolved Serving 
Gateway Mobile 
Location Center
S1-U
S1-MME
Control plan - - - - - - - - - -
User plan - - - - - - - - - -
S11
S6a
S5 SGi
EPS Architecture

UE e-NodeB
MME
S-GW P-GW
PDN 
(PSS, IME)
HSS
Mobility 
Management
Entity
Home 
Subscriber 
Server
Uu S1-U
S1-MME
S11
S6a
S8 SGi
Roaming Scenario
Roaming
User Foo
Visited
Network (VPLMN,
visited PLMN)
Foo’s Subscribed 
Network (HPLMN, home public
land mobile network)

Architectural
Comparison
UE e-NodeB
MME
S-GW P-GW
HSS
User Equipment Evolved NodeB Serving Gateway PDN Gateway
Mobility 
Management
Entity
Home 
Subscriber 
Server
UE NodeB
SGSN GGSN
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
RNC
Radio
Network
Controller
Signaling
Network
Mobile Switching
Center
Gateway MSC
Control plan - - - - - - - - - -
User plan - - - - - - - - - -

Architectural
Comparison
UE e-NodeB
MME
S-GW P-GW
HSS
Mobility 
Management
Entity
Home 
Subscriber 
Server
UE NodeB
SGSN GGSN
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
RNC
Radio
Network
Controller
Signaling
Network
Mobile Switching
Center
Gateway MSC
With X-2 interface,
eNodeB’s can
communicate with
each other to handle
mobility, so RNC is
merged into eNodeB.

Architectural
Comparison
UE e-NodeB
MME
S-GW P-GW
HSS
Mobility 
Management
Entity
Home 
Subscriber 
Server
UE NodeB
SGSN GGSN
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
RNC
Radio
Network
Controller
Signaling
Network
Mobile Switching
Center
Gateway MSC
The forwarding
function of MSC and
SGSN is handled by
S-GW, while the
session management
function is handled by
MME.

Architectural
Comparison
UE e-NodeB
MME
S-GW P-GW
HSS
Mobility 
Management
Entity
Home 
Subscriber 
Server
UE NodeB
SGSN GGSN
HLR
MSC GMSC
User
Equipment
Serving GPRS 
Support Node
Gateway GPRS 
Support Node
RNC
Radio
Network
Controller
Signaling
Network
Mobile Switching
Center
Gateway MSC
GMSC and GGSN
correspond to P-GW
and HLR correspond
to HSS is pretty much
accurate.

2013年度綜合財報
2014 第三季股東說明會講稿

2015 ⼀一⽉月份營運報告（內含2014⽉月營運報告）

Reference
1. 中華電信財務報表：http://www.cht.com.tw/ir/upload/ﬁles/
CHT2013_AnnualReport_0528Chinese.PDF
2. Wisely, David. IP for 4G. John Wiley & Sons, 2009.
3. Kasera, Sumit, and Nishit Narang. 3G Mobile Networks: Architecture, Protocols and
Procedures Based on 3GPP Speciﬁcations for UMTS WCDMA Networks. McGraw-Hill
Professional Publishing, 2005.
4. Russell’s Youtube Channel: https://www.youtube.com/user/QuadraticSquared

4G Introduction

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