LTE-Advanced - a Further Development of LTE

1. Mobile Communications
2. LTE – Long Term Evolution
3. LTE-Advanced - a Further Development of LTE

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How fast is LTE really?

Consumers are accustomed to being able to use (at least to a large extent) the speed offered by established cable-based services such as  $\rm DSL$  ("Digital Subscriber Line").

• But what is the situation with LTE?
  

• What data rates can the individual LTE user actually reach?

It is much more difficult for the providers of mobile radio systems to provide concrete data rate information, since many influences that are difficult to predict have to be taken into account for a radio connection.

As already described in chapter  "Technical Innovations of LTE"  according to the planning for 2011, data rates of up to 326 Mbit/s are possible in LTE downlink and approx. 86 Mbit/s in uplink.  These figures are only maximum achievable values.  In reality, however, the speed is determined by a variety of factors.  In the following we refer to the downlink, see  [Gut10]:

• Since LTE is a so-called  "Shared Medium" , all users of a cell have to share the entire data rate.  Note that voice transmission or normal use of the Internet generates less traffic than, for example,  "File Sharing"  or similar.
  

• The faster a user moves, the lower the available data rate will be.  An elementary component of the LTE specification is that for mobility up to 15 km/h the highest data rates are guaranteed and up to 300 km/h at least still "good functionality".
  

• The highest data rate is achieved in close proximity to the base station.  The further away a user is from the base station, the lower the data rate assigned to him, which can be explained by switching from "64–QAM" or "16–QAM" to "4–QAM" (QPSK), among other things.

• Shielding by walls and buildings or sources of interference of any kind limit the achievable data rate enormously.  Optimal would be a "Line of Sight" connection between receiver and base station, a scenario that is rather unusual.
  
  

The reality in summer 2011 was as follows:  LTE is already available in some countries  (at least for testing purposes).  In addition to LTE pioneer Sweden, these include the USA and Germany.  In various tests, download speeds of between 5 and 12 Mbit/s were achieved, and in very good conditions up to 40 Mbit/s.  Details can be found in the Internet article  [Gol11].

Moreover, the 2011 LTE network did not seem ready to replace the established wired Internet connections due to excessive delay times and the resulting occasional connection interruptions.  However, the development in this area progressed with giant strides, so that this information from summer 2011 was not relevant for very long.

Some system improvements through LTE-Advanced

While the first LTE systems corresponding to Release 8 of December 2008 slowly came onto the market in summer 2011, the successor was already on the doorstep.  The Release 10 of the  "3GPP"  completed in June 2011 is  "Long Term Evolution–Advanced", or in short  $\rm LTE-A$.  It is the first technology to meet the requirements of the ITU ("International Telecommunication Union") for a 4G standard.  A summary of these requirements, also called "IMT–Advanced", can be found in great detail in an $\text{ITU article  (PDF)}$.

Without claiming to be exhaustive, some of the features of LTE–Advanced are mentioned here:

• The data rate should be up to 1 Gbit/s with little movement of the user and up to 100 Mbit/s with fast movement.  In order to achieve these high data rates, some new technical specifications have been made, which will be briefly discussed here.
  

• LTE–Advanced supports bandwidths up to 100 MHz maximum, while the LTE specification  (after Release 8)  provides only 20 MHz.  The FDD spectra no longer have to be divided symmetrically between uplink and downlink.  For example, a higher channel bandwidth can be used for the downlink than for the uplink, which corresponds to the normal use of the mobile Internet with a smartphone.
  

• In the uplink of LTE–Advanced   $\text{SC–FDMA}$  is also used.  Since the 3GPP consortium was not satisfied with the SC–FDMA transmission in LTE, some essential improvements in the process were developed.
  

• Another interesting novelty is the introduction of so-called  "Relay Nodes".  Such a Relay Node  $\rm (RN)$  is placed at the edge of a cell to provide better transmission quality at the boundaries of a cell and thus increase the range of the cell.
  
  

Functionality of Relay Nodes

A relay node looks like a normal base station for a LTE terminal device  ("eNodeB").  However, it only has to supply a relatively small area of operation and therefore does not need to be connected to the backbone in a complicated way.  In most cases a relay node is connected to the next base station via directional radio.

In this way, high data rates and good transmission quality without interruptions are guaranteed without great effort.  By increasing the physical proximity to the base stations, the reception quality in buildings is also improved.

Another feature added to LTE–A is known as  "Coordinated Multiple Point Transmission and Reception"  $\rm (CoMP)$.  This is an attempt to reduce the disturbing influence of intercell interference.  With intelligent scheduling across several base stations, it is even possible to make intercell interference usable.  The information for a terminal device is available at two adjacent base stations and can be transmitted simultaneously.  Details on CoMP–technology can be found, for example, in the internet article  [Wan13]  from 3gpp.

$\text{Intermediate status of 2011:}$ 

• Thanks to the above measures in combination with many other improvements, primarily the introduction of  "4×4"  MIMO for the uplink and  "8×8"  MIMO in the downlink, it is possible to significantly increase the spectral efficiency  (i.e. the transferable flow of information in one Hertz bandwidth within one second)  of LTE–A compared to LTE, namely in the downlink from 15 bit/s/Hz  to  $\text{30 bit/s/Hz}$  and in the uplink from 3. 75 bit/s/Hz to  $\text{15 bit/s/Hz}$.
  

• Of course, backwards compatibility with the previous LTE standard and previous mobile phone systems must also be guaranteed.  Also with a UMTS cell phone one should be able to dial into a LTE network, even if one cannot use the LTE specific features.
  

• At the beginning of June 2011 the first tests of LTE–Advanced were conducted.  Sweden, which has already set up the first commercial LTE network, once again took the lead.  Ericsson demonstrated for the first time a test system with practical, commercially available terminals and began commercial use of LTE–Advanced in 2013.
• In a YouTube video, an LTE test can be seen in a moving minibus, in which data rates of over 900 Mbit/s in the downlink and 300 Mbit/s in the uplink were achieved.

Standards in competition with LTE or LTE-Advanced

In addition to the LTE specified by the 3GPP consortium, there are other standards that are intended to serve the purpose of fast mobile data transmission.  The two most important ones are briefly discussed here:

$\rm cdma2000$  (or "IS–2000")  and its further development $\rm UMB$  ("Ultra Mobile Broadband"):

This is a third-generation mobile communications standard that was specified and further developed by  $\text{3GPP2}$  ("Third Generation Partnership Project 2").  Further information on cdma2000 can be found in the section  $\text{IMT–2000 standard}$.

Far less is known about the further development of this standard than about LTE.  It is worth mentioning that for cdma2000 and UMB there is a sub–standard specified exclusively for data transmission.  The Cologne telecommunications provider  "NetCologne" has been offering mobile Internet in the 450 MHz range on this basis since 2011.  Furthermore, cdma2000 is insignificant in Germany.

Note:   The "3GPP2" was founded almost at the same time as the almost identically named  $\text{3GPP}$  in December 1998, obviously due to ideological differences.

$\rm WiMAX$  (Worldwide Interoperability for Microwave Access):

This term refers to a wireless transmission technology based on the IEEE standard 802.16.  It belongs to the family of the 802 standards like WLAN (802.11) and Ethernet (802.3).  There are two different sub–specifications to WiMAX, namely

• one for operating a static connection that does not allow handover, and
  

• one for the mobile operation, which is to compete with UMTS and LTE.
  
  

The potential of the static WiMAX connections lies mainly in the long range with nevertheless comparatively high data rate.  For this reason, static WiMAX was initially traded as DSL alternative for thinly populated areas.  For example, with a Line of Sight (LoS) connection between transmitter and receiver over 15 kilometers, about 4.5 Mbit/s are possible.  In urban areas without line of sight, WiMAX still has a range of about 600 meters, a much better value than the 100 meters typically offered by WLAN.

At the moment  (2011)  it also worked on a further development called  "WiMAX2".  According to the initiators,  WiMAX2 in the mobile version is a 4G standard which, just like LTE–Advanced, can achieve data rates of up to 1 Gbit/s.  WiMAX2 was implemented in practice by the end of 2011.

In Germany, WiMAX does not play a major role (in 2011), since both the German government in its broadband offensive and all major mobile phone operators have declared  "Long Term Evolution"  (LTE or LTE–A)  to be the future of mobile data transmission.

Milestones in the development of LTE and LTE-Advanced

Finally, a brief overview of some milestones in the development towards LTE from the perspective of 2011:

• 2004    The Japanese telecommunications company  $\text{NTT DoCoMo}$  proposes LTE as the new international mobile communications standard.
  

• 09/2006    Nokia Siemens Networks (NSN) presents together with  $\text{Nomor Research}$  for the first time an emulator of an LTE network. 
  For demonstration purposes, a HD–video is transmitted and two users play an interactive online game.
  

• 02/2007    At the  "3GSM World Congress", the world's largest mobile phone trade fair, the Swedish company  $\text{Ericsson}$  demonstrates an LTE system with 144 Mbit/s.
  

• 04/2008    $\text{DoCoMo}$  demonstrates an LTE data rate of 250 Mbit/s. 
  Almost simultaneously   $\text{Nortel Networks Corp.}$  (Canada) achieves a data rate in vehicle speed of 100 km/h of at least 50 Mbit/s.
  

• 10/2008    Test of the first working LTE modem by Ericsson in Stockholm.  This date is the starting point for the commercial use of LTE.
  

• 12/2008    Completion of Release 8 of 3GPP, synonymous with LTE.  The company  $\text{LG Electronics}$  develops the first LTE chip for cell phones.
  

• 03/2009    At the CeBIT in Hanover, Germany,  $\text{T–Mobile}$  shows Video conferencing and online games from a moving car.
  

• 12/2009    The world's first commercial LTE network starts in downtown Stockholm, only 14 months after the start of the test phase.
  

• 04/2010    3GPP begins with the specification of Release 10, synonymous with LTE–A.
  

• 05/2010    The LTE frequency auction in Germany ends.  At 4.4 billion euros, the proceeds are significantly lower than experts had expected and politicians had hoped for.
  

• 08/2010    T-Mobile is building Germany's first commercially usable LTE base station in Kyritz.  For a functioning operation, suitable terminals are still missing.
  

• 12/2010    In Germany, the first major pilot tests are running on the networks of Telekom,  $\text{O2}$  and  $\text{Vodafone}$.  In the meantime, corresponding LTE routers are available.

• 02/2011    In South Korea the first successful tests with the successor LTE–Advanced are being conducted.
  

• 03/2011    The 3GPP Release 10 is completed.
  

• 06/2011    Launch of the first German LTE network in Cologne. 
  By middle 2012, Deutsche Telekom will ensure that LTE network is rolled out across a wide area in 100 additional cities.
  

Exercise for the chapter

Exercise 4.5: LTE vs LTE-Advanced