Mobile Communications/General Information on the LTE Mobile Communications Standard

1. Mobile Communications
2. LTE – Long Term Evolution
3. General Information on the LTE Mobile Communications Standard

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# OVERVIEW OF THE FOURTH MAIN CHAPTER #

This chapter provides an overview of  Long Term Evolution  (LTE). From today's perspective (2011), LTE is a new mobile communications standard that should replace UMTS and will probably continue to shape the next few years of mobile voice and data transmission.

In the following, a rough overview of the motivation, functionality and characteristics of LTE is given first. This is followed by a more detailed system description of the technical processes involved in LTE. This chapter will deal with this in detail:

• The motivation for LTE and the frequency band allocation,
• The development of mobile communications standards towards LTE,
• some technical details about voice and data transmission,
• the transmission method SC–FDMA used in the uplink and its differences to OFDMA,
• The description and function of the different channels in the bit transmission layer,
• an outlook on the successor system LTE–Advanced.

Addendum:   The LTE chapter was written in 2011, i.e. at the time when LTE had just been introduced. During the last editorial revision in autumn 2017, some earlier statements were revised which no longer corresponded to the facts after six years of intensive use by many customers. However, most of the chapter remained unchanged compared to 2011, as the LTE principle has not changed in the meantime.

Development of mobile users until 2010

Absolute and relative number of mobile devices in the years 2004 - 2010

Since the turn of the millennium, the number of mobile connections has increased dramatically.

• The graph shows for the years 2004 to 2010 an increase from 1.8 to approx. 5 billion mobile devices worldwide in absolute numbers (red bars, left scale).
• The blue bars (left scale) show the development of the world population in the same period.

• The (percentage) number of cell phones (green curve, right scale) in relation to the world population increased from just under 30% to over 70% between 2004 and 2010.
• The statistics include users with more than one cell phone. 2010 possessed thus by no means 70% of the world population a mobile telephone.
  

• the use of mobile data services has sharply increased, especially since the introduction of flatrate tariffs.

The following statements refer to the year 2010:

• Global mobile data traffic grew by 159 percent in 2010, a much stronger increase than expected. Since then, mobile data transmission has caused more network load than voice transmission in the mobile network.
  

• Mobile data traffic alone was thus three times as large in 2010 as the entire traffic volume in 2000 (at that time mainly voice traffic).
  

• Although smartphones accounted for only 13 percent of all mobile devices in 2010, they were responsible for 78 percent of data– and voice transmission.
  

• To this development also 94 million laptop–users contributed, who used the Internet on the way over UMTS–modems.
• Such a laptop–user causes thereby on the average 22–times the data quantity of an average Smartphone–user.

Essential properties of LTE

The abbreviation  LTE  stands for Long Term Evolution and refers to the mobile communications standard that follows UMTS. The new conceptual development of LTE was intended to satisfy the ever-increasing demand for bandwidth and higher speeds over the long term ("Long Term").

The LTE–standard was first defined in 2008 as UMTS–Release 8 by the  3GGP  (Third Generation Partnership Project), a conglomerate of various international telecommunications associations, and has since been continuously developed further by so-called "Releases". The commitment of the world's largest mobile communications providers has made LTE the first (largely) uniform standard for mobile communications technology.

According to UMTS–Release 8, LTE is also called "3.9G" because it initially did not fully meet the conditions specified by the ITU  (International Telecommunication Union)  for fourth generation (4G) mobile communications.

In contrast, the subsequent Release 10 (dated July 2011) complies with the 4G–standard. The chapter  LTE–Advanced  lists the features of this LTE enhancement. This technology is also referred to as "LTE–A".

Here is a summary of the important system features of LTE, based on this page  ITWissen :

• LTE is based on the multiple access methods OFDMA (Orthogonal Frequency Division Multiple Access) in the downlink and SC–FDMA (Single Carrier Frequency Division Multiple Access) in the uplink. The detailed description of OFDMA and especially its differences to  checkLink:_Buch_5 ⇒ OFDM  can be found in chapter  "the application of OFDMA and SC–FDMA in LTE".

• The use of this modulation method enables orthogonality between individual users, resulting in increased network capacity  [HT09]. In conjunction with Multiple Input Multiple Output (MIMO), this technology currently (2011) enables peak data rates of 100 Mbit/s in the downlink.

• In addition to the significantly higher data rate compared to the 3G system UMTS, LTE technology makes more efficient use of the available bandwidth. By combining the latest state-of-the-art technology with the existing experience of GSM and UMTS, the new standard is thus not only much faster, but also simpler and more flexible  [Mey10].

Motivation and goals of LTE

In 2010, the American telecommunications company Cisco Systems published a  White Paper  which assumes that in 2015

graphic from the Ericsson Mobility Report 2015

• the use of mobile data will be twenty-six times higher than in 2010,
  
• this usage is increasing by a further 92% per year, and *br>
• the gigantic amount of 6.3 exabyte (6.3 · 10¹⁸ byte) per month is reached.
  
  

It has also been predicted that five billion people will be connected to the Internet by 2015 [HT09]. In addition, other wireless transmission technologies are being developed at the same time, which promise equally high data transmission rates. All these factors called for further development of the 3GPP–mobile communications standard "UMTS".
.

The  Ericsson Mobility Report  of 2015 now shows that the 2010 forecast has been exceeded. In 2014 there were already 7.1 billion mobile users with Internet access, in 2020 there should be 9.2 billion.

The 3GPP–consortium started early to define the LTE–targets to keep up with the rapid development of line-based connections. The exact targets were then set out in the "LTE Release 6" compared to HSPA–technology (High Speed Packet Access) at the end of 2004.

The main goals were mentioned:

• A purely packet-oriented transmission and a high degree of mobility and security,
  
• reduced complexity, cost reduction and optimized battery life of the end devices,
  
• Bandwidth flexibility between 1.5 MHz and 20 MHz,
  
• a spectral efficiency as high as possible (data rate per one Hertz bandwidth),
  
• maximum possible data rates of 100 Mbit/s in downlink and 50 Mbit/s in uplink,
  
• Signal processing times less than 10 milliseconds.
  
  

Compared to HSPA, this means an increase in spectral efficiency by a factor of between two and four, a reduction in latency by half and a tenfold increase in the maximum data rate. The individual points, which represent a large part of the LTE–specific technical characteristics, are dealt with in more detail in the chapter  Mobile Communications/Technical innovations of LTE .

Development of the UMTS mobile phone standards towards LTE

The development of third-generation mobile communications standards was already discussed in detail in the third chapter of this book. For this reason, only the more recent developments are discussed in detail here.

First of all, a brief overview of UMTS releases before LTE from[Hin08]:

• Release 6 (March 2005):   Professorship of Communications Engineering, TU Munich, 2008:

• Release 99 (December 1999):   UMTS 3G FDD and TDD; 3.84 Mchip/s; CDMA–air interface.
  

• Release 4 (July 2001):   Lower chip rate (1.28 Mchip/s) for TDD; some fixes and minor improvements.
  

• Release 5 (March 2002):   IP Multimedia Subsystem (IMS); High-Speed Downlink Packet Access  (HSDPA).
  

• Release 6 (March 2005):   High-Speed Uplink Packet Access  (HSUPA); Multimedia Broadcast&Multicast Services (MBMS); Cooperation with Wireless LAN; Push–to–Talk; Generic Access Network (GAN).
  

• Release 7 (December 2007):   reduced latency; improved Quality of Service (QoS); real-time applications (for example VoIP, EDGE Evolution); MIMO for UMTS; TDD–Option 7.68 Mchip/s.
  
  

The Release 8 of December 2008 was synonymous with the introduction of Long Term Evolution (LTE) and the basis for the first generation of LTE–capable terminals. The main innovations and characteristics of Release 8, summarized by  3gpp  (Third Generation Partnership Project), were:

• High spectral efficiency and very short latency,
  

• the support of different bandwidths,
  

• a simple protocol– and system architecture,
  

• Backwards compatibility and compatibility to other systems like  cdma2000,
  

• FDD (Frequency Division Duplex) and TDD (Time Division Duplex) optionally usable,
  

• Self-organizing networks (SON) support.
  
  

These features (and some others more) are discussed in detail in the section  Mobile Communications/Technical innovations of LTE . The Release 9, on the other hand, contains only minor improvements and will not be discussed in detail here. The Release 10 from July 2011 describes the further development of LTE; LTE–Advanced  (LTE–A).

LTE–Frequenzbandaufteilung

LTE-Frequenzen um 800 MHz und 2.6 GHz

Für LTE wurden neue Frequenzen benötigt. In Deutschland gab es 2010 eine Versteigerung zweier Frequenzbereiche, an der sich alle deutschen Mobilfunkbetreiber beteiligten.

Die Grafik veranschaulicht die Ergebnisse dieser Versteigerung der Frequenzen im

• Bereich um 800 MHz (791 ... 862 MHz):
  Hier wurden nur gepaarte Spektren für FDD vergeben:   je zweimal 10 MHz für die Telekom, O2 und Vodafone;
  

• Bereich um 2.6 GHz (2.5 ... 2.69 GHz):
  Hier wurden neben gepaarten Spektren für FDD (insgesamt 140 MHz) auch ungepaarte Spektren für TDD (50 MHz) vergeben.

Mehr über den Unterschied zwischen FDD und TDD findet man im Abschnitt  Motivation für xDSL  im Buch „Beispiele von Nachrichtensystemen”.
Die beiden versteigerten Frequenzbereiche haben unterschiedliche Systemeigenschaften, die sie jeweils interessant für verschiedene Anwendungsbereiche machen.

• Der niederfrequentere Bereich (um 800 MHz) wird auch als Digitale Dividende bezeichnet, da er durch die Umstellung der (terrestrischen) TV–Übertragung von PAL auf DVB–T („Digitalisierung”) frei wurde.

• Laut Vereinbarung der Bundesregierung mit den (deutschen) Netzbetreibern muss dieser Bereich dazu genutzt werden, bisher schlecht versorgte Regionen zu „Schnellem Internet” zu verhelfen. Definiert wurden vier Stufen für den Versorgungsgrad einer Region mit Breitbandinternet. Erst wenn in ganz Deutschland 90% der jeweilig vorangegangenen Stufe abgedeckt sein werden, darf mit der nächsten Stufe begonnen werden.

• Die Wahl für dieses Projekt fiel auf den vergleichsweise niedrigen Frequenzbereich um 800 MHz mit besseren Ausbreitungseigenschaften als bei 2600 MHz, was für die kostengünstige Versorgung ländlicher Bereiche sinnvoll und auch notwendig ist. Eine LTE–800 Basisstation erreicht einen maximalen Senderadius von etwa 10 km. Das Verhältnis Nutzer pro Fläche ist aber geringer als bei LTE–2600. Daraus ergibt sich, dass LTE–800 eher für dünn besiedelte Regionen geeignet ist.
  

• Der Frequenzbereich von 821 MHz bis 832 MHz bleibt frei, um Interferenzen zwischen dem Uplink und dem Downlink zu vermeiden. Man spricht von der Duplexlücke. Darüber hinaus kann dieser Frequenzbereich für die Veranstaltungstechnik genutzt werden, da schon vor Einführung von LTE für Funkmikrofone der Frequenzbereich um 800 MHz üblich war. In solchen Gebieten, in denen LTE flächendeckend verfügbar ist, müssen zukünftig Funkmikrofone auf die Duplexlücke ausweichen können.
  

Die unterschiedliche Bedeutung der Frequenzbereiche aus Betreibersicht werden am Ergebnis der Frequenzversteigerung von 2010 deutlich:

• Die 60 MHz um 800 MHz erbrachten knapp 3.6 Milliarden Euro (60 €/Hz), die 190 MHz um 2.6 GHz nur 344 Millionen Euro (1,80 €/Hz).
• Zum Vergleich:   Die UMTS–Versteigerung im Jahr 2000 ergab die astronomische Summe von 50 Milliarden Euro für 60 MHz   ⇒   833 €/Hz.
  
  

3GPP – Third Generation Partnership Project

Auf den letzten Seiten wurde schon mehrfach das  Third Generation Partnership Project  (oder kurz 3GPP) erwähnt. Hier soll ein kurzer Überblick über das Selbstverständnis dieser Gruppe, seine Struktur und seine Aktivitäten gegeben werden. Die Informationen sind direkt der  3GPP–Website  entnommen.

3GPP ist eine Gruppe verschiedener internationaler Normierungsorganisationen, die sich zum Zweck der Vereinheitlichkeit von Mobilfunksystemen zusammengeschlossen haben. Es wurde am 4.12.1998 von fünf Partnern gegründet:

• ARIB   (Association of Radio Industries and Businesses, Japan)
  
• ETSI   (European Telecommunication Standards Institute)
  
• ATIS   (Alliance for Telecommunications Industry Solutions, USA)
  
• TTA   (Telecommunications Technology Association, Korea)
  
• TTC   (Telecommunications Technology Committee, Japan)
  
  

Das 3GPP entwickelt, akzeptiert und pflegt einen weltweit anwendbaren Standard im Mobilfunk. Die regelmäßig und häufig abgehaltenen Konferenzen sind die wichtigsten Instanzen bei der Fortschreibung der Standardisierung der technischen Spezifikationen von LTE.

• Änderungsanträge durchlaufen einen festgesetzten Standardisierungsprozess mit drei Stufen, der hohe Qualität und eine gute Strukturierung der Arbeit des 3GPP ermöglicht.
• Hat ein Release die letzte Stufe erreicht und ist fertiggestellt, wird er von den in den Partnerorganisationen vereinigten Telekommunikationsunternehmen an den Markt weitergegeben.
  

In  [Gut10]  findet man folgende Einschätzung:
„Ziel der 3GPP–Standardisierung ist die Erstellung von technischen Spezifikationen (TS), die alle technischen Details einer Mobilfunktechnologie detailliert beschreiben. Die Spezifikationen für LTE sind extrem umfangreich. Der Detailgrad ist so hoch gewählt, damit Mobilfunkgeräte unterschiedlicher Hersteller in allen Netzen problemlos funktionieren”.

Aufgabe zum Kapitel

A4.1:  Allgemeine Fragen zu LTE