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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: [email protected]
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.