School of

Engineering

References

[1] E. Dahlman, St. Parkvall, J. Sköld, «4G LTE / LTE Advanced for

Mobile Broadband», Elsevier, 2011.

[2] Rohde&Schwarz, «White Paper: LTE Technology Introduction», https://www.rohde-schwarz.com/us/solutions/wireless-communications/lte/in-focus/lte-technology-introduction_109234.html

[3] 3GPP (Magdalena Nohrborg, short, recommended to read):

http://www.3gpp.org/technologies/keywords-acronyms/98-lte

[4] detailed LTE handbook:

http://www.sharetechnote.com/html/Handbook_LTE.html

[5] LTE Release-Versionen und Gerätekategorien

http://www.lte-anbieter.info/technik/kategorien-und-3gpp-release.php

Introduction into 4G LTE WireCOM, MC, 1

Kontakt:

ZHAW Zürcher Hochschule für angewandte Wissenschaften

Prof. Dr. M. Rupf

ZSN Zentrum für Signalverarbeitung und Nachrichtentechnik

Technikumstrasse 9, TB425

CH-8401 Winterthur

Tel: ++41 (0)58 934 7129

Mail: marcel.rupf@zhaw.ch

Web: http://www.zsn.zhaw.ch

School of

Engineering Network Solutions from GSM to LTE WireCOM, MC, 2 Source [3]

(purely IP based!)

School of

Engineering Some Terms WireCOM, MC, 3

3GPP Third Generation Partnership Project

EDGE Enhanced Data rates for GSM Evolution

EPS/EPC Evolved Packet System / Core

GERAN GSM/EDGE Radio Access Network

GPRS General Packet Radio Services

HS(D)PA High-Speed Downlink Packet Access

IMT-2000 International Mobile Telecommunications 2000 / Advanced

IMT-Advanced (ITU’s name for the family of 3G / 4G standards)

LTE Long Term Evolution

UE User Equipment, the 3GPP name for the mobile terminal

UMTS Universal Mobile Telecommunications System

UTRAN Universal Terrestrial Radio Access Network

School of

Engineering

WireCOM, MC, 4

1991 2G GSM from CEPT/ETSI, TDMA, low bandwidth

mainly voice, data rates ≤ 9.6 kbps, SMS

1996 2.5G packet data in GSM time-slots, GMSK - 8PSK,

new core elements

1998 3G UMTS, wideband CDMA, voice and data

2006 3.5G HSDPA, high-rate extension of UMTS

2008 3.9G LTE Rel. 8 (E-UTRAN) from 3GPP/ITU-R, OFDM, IP-based

2011 4G LTE Rel. 10 (LTE-Advanced, IMT-Advanced-compatible)

2014 4.5G LTE Rel. 12 (LTE-Advanced Pro)

2017/18 Release 15 will be the first release of 5G specifications

From GSM to LTE

School of

Engineering

Source [5]

peak

WireCOM, MC, 5

From 2G GSM to 4G LTE

Impressive increase of (peak) data rate

School of

Engineering Cellular Module Overview

6

Example u-blox cellular technology selection https://www.u-blox.com/sites/default/files/CEL-module-selector_Overview_%28UBX-14001802%29.pdf

SARA G310 GSM/GPRS

quad-band 850/900/1800/1900 MHz

(worldwide cellular bands are diverse)

16.8 x 26.8 x 3.2 mm

(without SIM-card-holder)

price < 30$

WireCOM, MC, 6

LPWAN

School of

Engineering GSM

GSM-TDMA-Rahmenstruktur

FDMA

(optional

slow FH)

SDMA (in Form vieler Zellen)

FDD

(frame)

(time slot TS)

Normal Burst

(156.25 Bit [Tbit = 3.7 us], 270 kb/s)

klein (30.5 µs) dank time advance

4∙TS-Verschiebung zwischen UL und DL

(meiste MS sind nicht vollduplex-fähig)

für Kanalschätzung

(Egalisation Mehrweg bis 4∙Tbit)

WireCOM, MC, 7

School of

Engineering

typisch

(Latenz im Bereich s)

class 10 Geräte

(max 2 slots Tx, max 4 slots Rx

max. 5 slots TRx)

no FEC

GPRS / EDGE

GPRS

neue Netzelemente erforderlich, Vorteil: Paket-orientiert

EDGE-Erweiterung

3π/8-offset 8PSK statt GMSK

48 kb/s statt 9.6 kb/s pro Zeitschlitz

=> max. 384 kb/s pro 200 kHz Kanal

WireCOM, MC, 8

School of

Engineering UMTS

GSM1800

UL

1710 1785

75 MHz

1805 1880 1900 1920 1980 2010 2025 2110 2170

75 MHz 20 MHz 60 MHz 15 MHz 60 MHz

DECT

(TDD)

GSM1800

DL

UMTS

TDD

UMTS

FDD

UMTS

TDD

UMTS

FDD

Spektrum Allokation im 2 GHz Band in Europa

5 MHz breite Bänder

R ≤ 384 kb/s (circuit switched), 2 Mb/s (packet switched)

ohne High Speed Packet Access (HSPA) - Erweiterung

Frequenzwiederholabstand = 1, GSM: 1-18

Chip-Rate = 3.84 MChip/s

BPSK/QPSK-Modulation

Wurzel-Raised-Cosine-Puls mit rolloff-Faktor r = 0.22

kohärente Demodulation in DL+UL, R=1/2 (1/3) Faltungs-/Turbocodes

=> Eb/N0 = 5 dB für Sprache, GSM: C/I = 9-12 dB

Power Control Frequenz = 1500 Hz, GSM: 2 Hz oder kleiner

WireCOM, MC, 9

School of

Engineering

Data Rate Peak data rates target 100 Mbps (downlink) and 50 Mbps (uplink) for 20 MHz

spectrum allocation, assuming 2 Rx antennas and 1 Tx antenna at the terminal

Throughput downlink average user throughput per MHz 3-4 times better than 3GPP R6

(uplink 2-3 times better) => higher spectrum efficiency required

Latency one-way transit time for a packet from IP layer to IP layer shall be <30 ms

Bandwidth support of a subset of bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz.

Interworking Interworking with existing UTRAN/GERAN

Mobility optimized for low mobile speed (0-15 km/h), but higher mobile speeds

be supported as well including high speed trains etc.

Spectrum operation in paired (Frequency Division Duplex / FDD mode)

allocation and unpaired spectrum (Time Division Duplex / TDD mode)

Co-existence Co-existence in the same geographical area and co-location with

GERAN/UTRAN shall be ensured. Also, co-existence between operators

in adjacent bands as well as cross-border co-existence is a requirement.

Quality End-to-end Quality of Service (QoS) shall be supported. VoIP should be

of Service supported with at least as good radio and backhaul efficiency and latency

as voice traffic over the UMTS circuit switched networks.

May 2017: Voice over LTE (VoLTE) is also used for VoIP

Some Design Goals for UMTS LTE (R8) [2], chap 2 WireCOM, MC, 10

School of

Engineering LTE and its Evolution [7], chap 7 WireCOM, MC, 11

Inter-Cell Interference Coordination

increasing peak data rate!

School of

Engineering Spectrum Flexibility [1], chap 7.1.6 WireCOM, MC, 12

A high degree of spectrum flexibility is one of the main characteristics of

the LTE radio-access technology, to allow LTE radio access

• in different frequency bands (see next slide)

• with different sizes of available spectrum (1.4, 3, 5, 10, 15, 20 MHz per carrier)

• including different duplex arrangements

(duplex filter required!)

School of

Engineering Frequency Bands for LTE [1], chap 17.1.2 WireCOM, MC, 13

Frequency bands for FDD

(frequency division multiplexing)

Frequency bands for TDD

(time division multiplexing)

Worldwide cellular bands are extremely

diverse, in particular for 4G technology!

School of

Engineering Frequency Bands for LTE [1], chap 17.1.2 WireCOM, MC, 14

School of

Engineering Frequency Bands for LTE [1], chap 17.1.2 WireCOM, MC, 15

GSM!

Implementation of different Radio-Access Technologies at

the same sites (often sharing antennas and other parts of

the installation), or sharing even base-station equipment

(Multi-Standard Radio Base Stations).

“digital dividend”

School of

Engineering

Quelle

Frequency Bands for LTE WireCOM, MC, 16

Mobilfunkfrequenzen in der Schweiz

https://de.wikipedia.org/wiki/Mobilfunkfrequenzen_in_der_Schweiz, abgerufen am 2.6.2017 (Bänder um 2600 MHz fehlen).

School of

Engineering

≤20

15 kHz subcarrier spacing

Subcarriers are independently

QPSK, 16QAM or 64QAM modulated.

*** guard interval to combat inter-symbol-interference (ISI) due to channels delay spread

***

LTE Downlink Transmission Scheme [2], chap. 3.1 WireCOM, MC, 17

Downlink transmission for E-UTRA FDD and TDD modes is based on

conventional OFDM

• robustness against channel frequency selectivity without complex equalizers

School of

Engineering

OFDMA allows the access of multiple users on the available bandwidth.

Each user is assigned a specific time-frequency

resource.

OFDMA-Parametrization

In FDD mode, the 10 ms radio frame is divided into 20 equally sized

slots of 0.5 ms.

LTE Downlink Transmission Scheme [2], chap. 3.1 & 3.2 WireCOM, MC, 18

subcarrier spacing ∆f = 15 kHz, FFT-size 2048, sampling frequency fs = 30.72 MHz

(fs = 15 kHz * 2048 = 30.72 MHz = 1/Ts)

School of

Engineering LTE Downlink Transmission Scheme [2], chap. 3.2 WireCOM, MC, 19

Downlink ressource grid

12 subcarriers form one Resource Block

(RB), occupying a bandwidth of 180 kHz.

1 UE (user equipment) can be allocated

integer multiples of 1 resource block in the

frequency domain.

normal cyclic prefix = 4.7µs

extended cyclic prefix = 16.7µs (larger cells,

but only 6 OFDM symbols per slot)

School of

Engineering LTE Downlink Transmission Scheme [2], chap. 17.4 WireCOM, MC, 20

School of

Engineering

WireCOM, MC, 21

LTE Downlink Transmission Scheme [2], chap. 3.3

School of

Engineering

Data is allocated to a device (User Equipment, UE) in terms of resource

blocks (RB)

• 1 UE can be allocated integer multiples of 1 RB in the frequency domain.

• RBs do not have to be adjacent to each other.

• scheduling decision can be modified every transmission time interval

(TTI) of 1 ms

• all scheduling decisions for downlink and uplink are done in the base

station (enhanced NodeB, eNodeB or eNB).

The scheduling algorithm is vendor specific and has to take into account

• the radio link quality situation of different users

• the overall interference situation

• Quality of Service requirements

• service priorities

WireCOM, MC, 22

LTE Downlink Transmission Scheme [2], chap. 3.3

School of

Engineering

Channel-Dependent Scheduling and Rate Adaptation

WireCOM, MC, 23

LTE Downlink Transmission Scheme [1], chap. 7.1.2

rate adaptation can be seen as a

part of the scheduling functionality.

The scheduler is a key element

and to a large extent determines

the overall system performance.

School of

Engineering

WireCOM, MC, 24

LTE Downlink Channel Mapping [1], chap. 8.2.2

"MAC"

"PHY"

Example of a control channel (CCH)

• Broadcast Control Channel (BCCH)

transmission of system information from the network to all terminals in a cell.

Examples of a traffic channels (TCH)

• Dedicated Traffic Channel (DTCH) transmission of user data to/from a terminal

• Multicast Traffic Channel (MTCH), used for downlink transmission of Multimedia

Broadcast Multicast Services

(Downlink Shared Channel)

(Physical

Downlink Shared Channel)

School of

Engineering

WireCOM, MC, 25

LTE Uplink Transmission Scheme [2], chap. 4.1

LTE uplink transmission scheme for FDD and TDD mode is based on

SC-FDMA (Single Carrier Frequency Division Multiple Access).

SCFDMA signals have better PAPR (peak-to-average power ratio)

properties compared to an OFDMA signal.

The PAPR characteristics are important for cost-effective design of UE

power amplifiers.

There are different possibilities how to generate an SC-FDMA signal.

DFT-spread-OFDM (DFT-s-OFDM) has been selected for E-UTRA,

see next slide.

SC-FDMA signal processing has some similarities with OFDMA signal

processing, so parameterization of downlink and uplink is harmonized.

Scheduling of uplink resources is done by eNodeB. In uplink, data is

allocated in multiples of 1 resource block (12 subcarriers). The scheduling

decisions may be based on QoS parameters, UE buffer status, uplink

channel quality measurements, UE capabilities, UE measurement gaps, etc.

School of

Engineering

WireCOM, MC, 26

LTE Uplink Transmission Scheme [2], chap. 4.1

*** QPSK, 16QAM and 64QAM (Release 8 optional)

***

SC-FDMA: each subcarrier contains

information of all transmitted modulation

symbols (input data stream spread by

DFT transform over available subcarriers)

=> lowers the PAPR

School of

Engineering

DFT-s-OFDM supports orthogonal separation of uplink transmissions

also in the frequency domain.

WireCOM, MC, 27

LTE Uplink Transmission Scheme [3]

School of

Engineering

Uplink Shared Channel (UL-SCH) is the uplink counterpart to DL-SCH.

Random-Access Channel (RACH) is used for random access,

(to connect to the network).

WireCOM, MC, 28

LTE Uplink Channel Mapping [1], chap. 8.2.2

School of

Engineering

LTE bandwidths of Release 8:

Higher data rates with Carrier Aggregation (LTE Release 10):

• Up to 5 component carriers, possibly each of different bandwidth, can

be aggregated, allowing for transmission bandwidths up to 100 MHz.

• Each component carrier has release 8 structure providing backwards

compatibility

• In general, a different number of component carriers can be

aggregated for the downlink and uplink.

• Component carriers do not have to be contiguous in frequency,

which enables exploitation of fragmented spectrum

WireCOM, MC, 29

Carrier Aggregation [1], chap. 7.3.1

source [2]

School of

Engineering

WireCOM, MC, 30

Carrier Aggregation [1], chap. 7.3.1

From a baseband perspective, there is no difference between

the cases below and they are all supported by LTE release 10.

However, the RF-implementation complexity is vastly different

with the first case being the least complex.

School of

Engineering

WireCOM, MC, 31

LTE Protocol Architecture [1], chap. 8.2

Radio Link Control

Packet Data

Convergence Protocol

School of

Engineering

Fast hybrid ARQ with soft combining allows to rapidly request

retransmissions of erroneously received transport blocks.

Retransmissions can be rapidly requested after each packet

transmission.

Incremental redundancy is used as the soft combining strategy and

the receiver buffers the soft bits to be able to perform soft combining

between transmission attempts.

=> see Hybrid ARQ on the last slide and the connection to decoding

WireCOM, MC, 32

Fast hybrid ARQ with soft combining [1], chap. 7.1.4

School of

Engineering

WireCOM, MC, 33

LTE R8 MIMO Concepts [2], chap. 5

Multiple Input Multiple Output (MIMO) systems form an essential part of

LTE to achieve the requirements for throughput and spectral efficiency.

For the LTE downlink, a 2x2 configuration for MIMO is assumed as baseline

configuration, i.e. 2 Tx antennas at the base station and 2 Rx antennas at

the terminal side.

Channel

coefficients

MIMO can be also used to exploit diversity and increase the robustness

of data transmission. Transmit diversity is also part of LTE.

School of

Engineering

1

1/4

X’1

X’2

Y1

Y2

j

j/2

-0.99

-0.14

0.14·j

-0.99·j R2 = 0.53·X2

R1 = 1.43∙X1 X1

X2

-0.74

0.67·j

0.67

j·0.74

precoding receive shaping channel

«TM4» – Example: 2x2 MIMO (1 subchannel, no noise)

WireCOM, MC, 34

LTE R8 MIMO Concepts [2], chap. 5

School of

Engineering

The antenna ports transmit the same data symbols,

but with different coding and on different subcarriers.

(Space Frequency Block Coding)

WireCOM, MC, 35

Example to Transmit Diversity [2], chap. 5

School of

Engineering

WireCOM, MC, 36

System Architecture Evolution (SAE) [1], chap. 8

The LTE RAN (Radio Access Network) and the EPC (Evolved Packet

Core) build the EPS (Evolved Packet System)

The RAN is responsible for all radio-related functionality

of the overall network including, for example, scheduling,

radio-resource handling, retransmission protocols, coding

and various multiantenna schemes.

The EPC is responsible for

functions needed for providing

a complete mobile-broadband

network (including e.g.

authentication, charging,

setup of end-to-end

connections).

MME: Mobility Management Entity

HSS: Home Subscriber Server

P-GW: Packet-Data Network Gateway

S-GW: Serving Gateway

School of

Engineering

LTE-RAN uses flat architecture with a single type of node – eNodeB

eNodeB is a logical node and there are different physical implementations

(3-sector site, baseband processing unit with connected remote radio heads)

LTE is designed to operate with a 1-cell

frequency reuse!

X2 interface may be used for multi-cell

Radio Resource Management (RRM)

functions such as Inter-Cell Interference

Coordination (ICIC) in the scheduling

process

WireCOM, MC, 37

System Architecture Evolution (SAE) [1], chap. 8, and [3]

School of

Engineering

WireCOM, MC, 38

Depending on the data rate and MIMO capabilities,

different LTE UE categories are defined:

WireCOM, MC, 38

Terminal Capabilities [1], chap. 7.4

MIMO not

supported

UE power class defines a nominal maximum output power for QPSK modulation. It may be

different in different operating bands, but the main UE power class is today set at 23 dBm

(200 mW) for all bands.

School of

Engineering

«Heute unterstützen nahezu alle neueren LTE-Smartphones wenigsten LTE CAT6».

see [5] for UE categories of LTE Releases > 10.

WireCOM, MC, 39 WireCOM, MC, 39

Terminal Capabilities [5]

School of

Engineering

WireCOM, MC, 40 WireCOM, MC, 40

Narrowband IoT https://en.wikipedia.org/wiki/NarrowBand_IOT

NB-IoT is a narrowband radio technology designed for the Internet of Things (IoT),

and is one of a range of Mobile IoT (MIoT) technologies standardized by the 3GPP.

NB-IoT can be deployed “in-band” in LTE spectrum (using resource blocks within a normal

LTE carrier), or within a LTE carrier’s guard-band, or “standalone” (e.g. refarming GSM channels)

Actual status (May 2017): There are modules (e.g. from uBlox), but not R13 services yet.

≤ 6 RBs

single subcarrier

School of

Engineering

WireCOM, MC, 41 WireCOM, MC, 41

Performance [1], chap. 18.3

Performance Evaluation of LTE-Advanced (Rel. 10)

School of

Engineering

WireCOM, MC, 42 WireCOM, MC, 42

Performance [1], chap. 18.3

10 MHz DL + 10 MHz UL, 33.6 Mbps @ 10 MHz

The cell spectral efficiency is the aggregated throughput over all users, averaged

over all cells and divided by the channel bandwidth. It is a measure of the maximum

total “capacity” available in the system to be shared between users; it is

measured in bits/s/Hz/cell.