Introduction

Long Term Evolution (LTE) is commonly marketed as fourth generation (4G). LTE and LTE Advanced have been recognized by International Telecommunications Union – Radiocommunications (ITU-R) and International Telecommunications Union – Telecommunications (ITU-T) as the principal solution for the future mobile communication networks standards. Thus, they are the framework of what marketing calls 4G and maybe also fifth generation (5G). They have registered logos:

Figure I.1. LTE and LTE Advanced logo

It seems interesting to look at the evolution of mobile communication systems from their appearance upto LTE. This move has obviously been driven by commercial motivations as well as by the extraordinary improvement of microelectronics, especially from the 1960s to the present day. Functionalities, computing power and miniaturization have drastically progressed, while cost has constantly decreased.

I.1. Mobile communication systems: 0G, 1G, 2G, 3G, 4G and 5G

In this short introduction, many mobile communication systems will be omitted:

It does not mean that LTE will not have specific adaptations in order to fit the special requirements of such systems, especially for its radio interface, avoiding expensive developments being invested for a limited population of users.

Only public land mobile network (PLMN) will be considered: the so-called “4G” belongs to this category as long as LTE is used for public communication.

Also, the impressive list of various systems, which did not reach a high level of success, especially outside their country of origin, has been avoided.

The classification of mobile systems into generations is not strictly related to any given metrics or parameters. It corresponds to marketing considerations. Therefore, it is commonly agreed upon, both by industry and by academia, and hence conceived to be an unwritten standard.

I.1.1. Rationale

Mobile communications have always been a wish for most of the people. Of course, at the beginning, the mobile networks have been invested for precise applications, such as military communications or professional management. The introduction of PLMN came later. But the requirements for mobile services are most common for public systems and more specific networks.

For a network addressing all citizens, the investment is very high, especially in research and development – millions of coded instructions have to be written and validated. Also, the precise areas where the service will be necessary have to be determined. Therefore, it is necessary to analyze what the customers are ready to pay for to avoid vain efforts and investments. Excluding applications that are just using the mobile network as a support, mobile services can be classified into three categories:

For these services, the mobile network can provide two kinds of access:

The paradigm of mobile communications is simple to summarize:

Going into detail shows a lot of issues:

I.1.2. Short history of mobile communications, milestones

I.I.2.I. 0G

The systems that allow customers to communicate on the move depend on electronics and microelectronics technology. Therefore, before the mass production of semiconductors, only experimental services have been deployed. The first network appeared in the United States in 1940, with mobiles using electronic tubes for car mounted terminals. Connection to the called party was made by human operators, in a way similar to that ensured for maritime communications.

Between 1960 and 1980, quite a few mobile communication systems were designed and deployed for either telephony or paging. Most of the advanced countries installed a home-made network. These systems offered automatic dialing with a good communication quality, obtained with a frequency/phase modulation radio access network. The radio path consisted of narrow frequency channels – 30 kHz in Northern America and 25 kHz everywhere else in the world. With the advent of transistors, a few handheld mobiles were available, especially for paging.

Of course, the service was only operated by incumbent fixed telecommunication operators, which found a new service for wealthy customers.

These systems will be called 0G.

1.1.2.2. 1G

During the 70s, some important innovations have brought a kind of revolution in the mobile communication world:

All these innovations were applied to new designs including some important breakthroughs:

With all these new developments, the cost of R&D skyrocketed and only a few systems could be studied and deployed with a worldwide impact. Among them two standards will dominate the market:

In Europe and Japan, it was a modified version with a 25 kHz channel spacing, called Total Access Communication System (TACS), Europe TACS (ETACS) and Japan TACS (JTACS)). Due to some specific US political process aiming at introducing competition, AMPS and TACS massive deployment was delayed to 1985.

Nevertheless, due to its transnational origin, NMT introduced a very interesting feature: automatic international roaming.

Another cellular system of the first generation was designed and deployed in Germany (C-Netz) and France (Radiocom, 2000) and counted a few hundred thousand subscribers. There was also a Japanese home-made “cellular” system.

These systems and their unlucky competitors are considered to be 1G.

I.1.2.3. 2G

In the 1980s, with the spectacular increase of the computing power of integrated circuits, technology continued to progress with many breakthroughs:

In the meantime, continental European countries have been conscious of their technological backwardness compared with AMPS. In 1982 the “GSM” was created (at the beginning it was a “special mobile group” led by German FTZ and French Centre national d’études des télécommunications (CNET)), which was commissioned to study a revolutionary mobile system based on a fully digital radio access subsystem, since it was considered difficult to surpass AMPS as an analog system. This new system, also called GSM, passed through a lot of studies until 1991. Code division multiple access (CDMA), which was in the 1980s a spread spectrum technique in use for military purposes, was experienced in 1985. At that time, CDMA showed need for too much computing power, far over the performance of the available chips, thus a simpler process, time division multiple access (TDMA), was chosen.

In 1987, all countries of the European Union signed a Memorandum of Understanding (MoU), which was accepted afterward by all GSM operators, always labeled as MoU. In this MoU, these countries decided:

GSM takes up the C-Netz innovation of selling the mobile terminal and the operator subscription separately, the latter being materialized by a SIM card, which is inserted into the mobile set. The chip of the SIM card controls all the telecommunication functions of the mobile and masters the encryption of the radio path for the calls.

GSM introduces a kind of paging with the “SMS”, which became a very important part of the communications.

As a response to the introduction of GSM, the AMPS industry designed the D-AMPS (IS-136 standard), where AMPS channels are used in TDMA mode in order to increase the overall network capacity.

Beside the TDMA systems, the American society Qualcomm introduced its proprietary design based on a CDMA encoding, later called CDMA 2000, which was standardized as IS-95 by ANSI. This standard was adopted by South Korea, which had to solve a lot of difficulties.

And again, Japanese NTT developed and rolled out a TDMA system, called PDC. They also rolled out a simpler system called PHS, which is probably the first implementation of a multiple input multiple output (MIMO) antenna system.

All these systems can be considered to be the 2G mobile standards.

I.1.2.4. 3G, the need for fast data transmission

Of course, as time passed, the technology of chips continued to improve drastically. During the 1990s it finally delivered processors having a sufficient computing power to cope with the Qualcomm CDMA mobile system.

In the 1990s, while GSM was being implemented all over the world including Northen America, the operators of fixed communications introduced the Internet services. At the beginning the available bitrate was limited to 50 kbps. Later it was increased to 10 Mbps downlink particularly with an Asymmetric Digital Subscriber Line (ADSL), provided the customer’s home is located a few hundred meters from the central office. The industry of mobile communications decided to adopt the internet service in their strategy, even when the response from the subscribers’ base surveys showed very little interest in telephony and SMS. GSM developed a “wart”, called General Packet Radio Service (GPRS), supporting data transmission upto 50 kbps. In response, CDMA 2000 introduced data transmission upto 144 kbps. As an answer, GSM standardized Enhanced Data Rates for GSM Evolution (EDGE), providing upto 240 kbps, which was rolled out massively by ATT Wireless in the USA, where it was facing the competition of Verizon Wireless, the CDMA 2000 champion.

The way Qualcomm system manages data transmission makes it easy to reach good performances since the data flow and the telephony are transmitted by different networks, at least in the Evolution Data Optimized (EVDO) version. This conception answers the difficult challenge of mobility:

Considering that in a town like Paris the mobile terminals process an average of four handovers for a 2 min call, the network operator has to make a critical choice concerning the parameters of its network:

Of course, most of the GSM operators chose to favor telephone calls.

To examine what could be the future of mobile communications after the worldwide success of GSM, the European Union launched a consultation on the possible technologies which could be developed. Scandinavia pushed a variant of Qualcomm CDMA technology called wide band CDMA (WCDMA) very hard, which won the competition. This WCDMA technology immediately faced the issue of patents, since CEO of Qualcomm, who was a highly respected former professor of signal theory at MIT, had patented all possible implementation of CDMA. It also faced plenty of issues with the management of power, with the mobile needing too much energy, far more than GSM.

Nevertheless, the industry worked very hard and some 10 years later, beginning of the 2000s, the WCDMA, renamed High Speed Packet Access (HSPA) and HSPA+, could service data users correctly.

In the meantime, ATT had pushed in the 3rd Generation Partnership Project (3GPP) standard body, a variant of GSM, called EDGE, which had been rolled out by all GSM operators. The advantage of EDGE for the network operator is to keep the base stations of GSM for coverage and reuse the same backhaul infrastructure instead of deploying a new network. EDGE, described above, is a modification of GPRS (changing the modulation on the radio path) and provides 200 kbps and more.

EVDO, WCDMA and EDGE could be considered as the 3G mobile systems.

I.1.2.5. 4G

As seen above, the work on Universal Mobile Telecommunications Service (UMTS) finally produced a competitive system, called HSPA, then HSPA+, that reached upto 7.2 Mbps, and even 14.4 Mbps per cell.

In the 3GPP studies, besides promoting EDGE, ATT called for a completely new system, strictly dedicated to mobile data transmission. Their concept at the beginning was to design something completely new with no backward compatibility with previous systems. The new system would be completely based on IP and would adopt a simple architecture. This project was called “LTE” and was the answer to ITU request of a future mobile system (called FPLMNTS in the 1990s, denomination replaced by IMT2000, then IMT Advanced).

The LTE standard was finalized only in 2008 with the release 8 of 3GPP.

When definitively designed in a viable release, LTE was immediately adopted by Qualcomm CDMA followers, especially Verizon, which will abandon CDMA 2000 progressively. So, de facto, LTE became the only standard of mobile communications for the future. The system is now widely deployed, mainly in Northern America with over 100 million subscribers there, and represents a very strong industry.

Having been badly fleeced with intellectual property rights (IPR) in the UMTS case by Qualcomm, and less seriously by Motorola for GSM, 3GPP’s “individual members” exert a certain control on the ETSI IPR database. In 2012, 50 companies had declared holding essential patents covering some parts of the LTE standards. Nevertheless, these declarations are left to the goodwill of the companies, even if at each TSG meeting participants are invited to declare their patents with a certain solemnity.

The 4G mobile system follows the LTE standard.

1.1.2.6. 5G

What about the “5G” on which many publications have already been edited? LTE radio access subsystem is based on different avatars of Orthogonal frequency-division multiplexing (OFDM), technology described in 1982 by the CCETT laboratory of Rennes (France). OFDM is now recognized as the best technique for transmitting high bitrate flows of data on wideband radio channels. It has been adopted for the last versions of Wi-Fi (IEEE 802.11n and further), by WiMAX (IEEE 802.16, beyond “e”), Communications over Power Lines (CPL, in UK power line communications (PLC),) and television broadcasters with the DVB-S2 and DVB-T2.

5G is probably what is considered as IMT-Advanced with the following requirements:

Table I.1. Mobile broadband explosion

(Source: mobile broadband explosion: the 3GPP wireless evolution, Rysavy Research/4G Americas, August 2012)

Assuming that the “5G” will be allocated a large amount of spectrum (e.g. more than 20 MHz, or upto 100 MHz if such a quantity of spectrum can be found), the radio transmission scheme could be improved or upgraded as has been the case for the change from Digital Video Broadcasting Terrestre (DVB-T) to DVB-T2 and from Digital Video Broadcasting Satellite (DVB-S) to DVB-S2. From the measured performance of DVB-T2 an overall bitrate of 100 Mbps available for the individual subscriber could be expected with a reasonable spectrum allowance.

1 Gbps would probably need a big part of spectrum, which could not be foreseen some 10–20 years ago, except if the system adopts frequencies above 3 GHz and restricts mobility.

The difficulty to make a valuable forecast comes from 2 sides:

LTE Advanced has been accepted as IMT-Advanced relevant solution in November 2010. LTE_advanced must be both backward and forward compatible with existing LTE. Devices must operate on both kinds of networks.

A few operators and manufacturers claim that their research and development laboratories have already tested IMT-Advanced solutions with:

Figure I.2 shows the evolution flow:

Figure I.2. The LTE project: milestones. Short history of the birth of a worldwide standard

What is now called LTE had been proposed in 1998 as a successor to GSM, but was not chosen and 3G has been based on WCDMA mainly.

LTE has been developed by 3GPP.

Figure I.3. 3GGP logo

After a long and difficult process in the 3GPP, ATT engineers succeeded to introduce LTE as a work item (3GPP, http://www.3gpp.org/specifications). Their concept was to describe a “green field” system, which would have replaced all existing techniques and would provide, at last, a worldwide accepted technology. The emergence of LTE has been delayed by European actors, both mobile operators and industrial manufacturers, which had spent a huge amount of money for WCDMA, the 3G system called UMTS. Operators had to pay enormous fees for UMTS licenses; industrial companies had to pay high patent dues to Qualcomm for the use of a patented technology, even if UMTS is quite different from the Qualcomm’s CDMA2000.

The Europeans insisted that LTE would be (and now is) quite compatible with GSM and its successors (WCDMA or TD-SCDMA, even when this second development seems strictly applicable to China).

LTE is by many sides a revolutionary technology.

Parallel to the 3GPP work, ITU-T set a work item for the future mobile communication system, first called FPLMNTS then renamed IMT to finish with IMT2000, followed by IMT Advanced.

LTE release 8 is the first standard describing a working technology. Issued in 2008, this release 8 showed a system, which had no telephony service and was fully dedicated to Internet communications, and therefore had to fall back to GSM or WCDMA for telephony if not leaving the task to OTT applications. LTE was and is a pure Internet-based system deliberately designed for packet data communications. Packet communications are no longer a kind of wart added to a telephony system, like GPRS or EDGE for GSM, but the principal objective of a full “Internet multimedia system”.

LTE had to wait for release 11 (at the end of 2012) to be able to provide a telephony service. Nevertheless, it has been recognized as the practical incarnation of IMT Advanced in 2010. This recognition has been eased by the renunciation of Qualcomm’s 3GPP2, the experts of which could not follow the breakthroughs obtained by the hundreds (maybe thousands) of engineers working on LTE. Moreover, the champion of CDMA2000, the American operator Verizon Wireless, was among the first in the world to roll out LTE.

Some features will only be available in release 12 (at end of 2014) and probably later. It is expected that the “change requests” on LTE standards will continue to flourish until 2020.

But now, the only competing standard is WIMAX, the IEEE 802.16 standard, which has evolved recently to somehow adopt the same technological choices as LTE on the radio path, especially OFDMA. Also, Wi-Fi, 802.11, in its last avatar has also switched to OFDMA. Wi-Fi is more in a position to compete since it has not at all the same business model, offering mainly free communications carried by unlicensed frequencies. The advantage of LTE on all competitors is that it is the only system which has a fully described and standardized core network, based on IMS.

LTE has been the substrate of the frequency battle in ITU-R world radio conference 2007 with the American pushing for allocating the 700 MHz band to mobile communications (i.e. LTE) and the European deciding to offer to LTE high frequencies such as 2.6 GHz, 3.8 GHz and even higher. These frequencies may only be suitable for “Wi-Fi like” communications because at these high frequencies tens of thousands of base stations are needed with little chance to cover each more than one stretch of a street. They are obviously inadequate for the coverage of wide spaces, like a full country. Of course, on the opposite, the 700 MHz is excellent for the coverage of wide areas, e.g. the Middle West area. In urban areas, frequencies under 1 GHz are also much more efficient, as they better penetrate the buildings or the underground.

The consequence of these choices is that LTE/4G is, in 2014, mainly rolled out in the United States and Canada using 700 MHz and 1800 MHz base stations. The market of many tens of millions of subscribers is a strong incentive to provide cheap and excellent smartphones following the American choices. The customers’ base in Northern America is already far over 100 million subscribers and increasing sharply.

Not surprisingly, at the 2012 world radio conference (WRC 2012), African and Middle East countries pushed a motion requiring that, in Region 1, the 700 MHz band be allocated to mobile services, i.e. LTE, like in the USA. European delegations were not aware of this initiative and had to follow the movement.

In Europe, at last the 800 MHz band has been freed for LTE, and the take off of LTE may be expected for the next five years. With around 20 million subscribers, LTE is far behind GSM and UMTS, considering the relative penetration rate. It will probably wait for 2015 when the next WRC 2015 will definitively allow the 700 MHz worldwide to LTE/4G. Already now, LTE is offered in the main European countries, such as the United Kingdom, Germany, France, Italy, Spain Belgium and Switzerland.

In Europe, frequencies for LTE in the 800 MHz band are not optimal: while LTE allows us to engineer LTE with bandwidths from 1.4 MHz to 20 MHz, the allocations are limited to 5 MHz or 10 MHz. Of course, two allocations of 10 MHz, not adjacent, will carry less than one of 20 MHz and the ongoing proposals for the 700 MHz band do not seem to provide large bandwidths.

Let us recall that “LTE Advanced” is supposed to receive 2 × 100 MHz in order to reach 1 Gbps downlink.

I.2. High speed broadband mobile services: what the customers are waiting for

I.2.1. Customers’ expectancies

Demands for wireless data services are showing rapid growth due to evolved networks for high-speed connectivity, wide-scale deployment, flat-rate pricing plans and Internet-friendly devices (smartphones). Consumers rely heavily, and often exclusively, on mobile devices for their communications needs. Therefore, the normal trend is to require, from the mobile system, the same performances as the one offered by fixed networks with ADSL. Very high bit-rate DSL (VDSL), fiber optics or coaxial cable. This comparison raises the level of the bitrate upto 10 Mbps in the first step, and increases upto 30 Mbps. Officially, the target stands at 100 Mbps, the requirement assigned by ITU-T IMT Advanced, but as observed on the fixed networks, very few customers can make a proper use of such a bitrate.

Applications are developed to follow the technical improvement of the systems. They offer a whole range of services, which subsequently increases the request for more bandwidth and more capacity. Basically, they are composed of:

Whichever are the services, wireless operators must also provide a high-quality cellular coverage anywhere customers want to communicate. This requirement is not related to broadband mobile services, it is the principal need for any mobile subscriber and for any service to be provided.

Due to the high costs of backhaul, alternative means to improve cellular coverage in locations, which are difficult to reach, as well as to off-load traffic from the wireless networks. A way to fit to the subscribers’ wishes is to install femtocells, taking advantage of the home Internet high-speed link. It is a way to better support residential and small/home office applications. Vodafone UK was the first operator to launch a commercial femtocell service in Europe (July 2009). AT&T (2H 2009) and Verizon (early 2010) also launched commercial femtocell offerings.

From a competitive perspective, femtocells can help mobile operators seize residential minutes from fixed providers, increase market share and respond to emerging Voice over Internet Protocol (VoIP) and Wi-Fi offerings. This of course implies a sharing agreement to be negotiated with the Internet service provider.

From a QoS perspective, femtocells will improve the user experience in the home. This is essential for reducing churn and providing new revenues. Just recall that with the advent of smartphones, mobile communications are heavily using the Internet and high bitrates.

A rapid increase of mobile data usage and the emergence of new applications such as Multimedia Online Gaming (MMOG), mobile TV, web 2.0, streaming contents have motivated the 3GPP to work on the LTE on the way toward 4G mobile.

1.2.2. Advantages of LTE for fulfilling these expectancies

The main goal of LTE is to provide a high data rate, low latency and packet optimized radio access technology supporting flexible bandwidth deployments. At the same time its network architecture has been designed with the goal to support packet-switched traffic with seamless mobility and great QoS.

LTE provides:

1.2.3. How the advent of smartphones impacts customers’ expectations

In recent years, the revolutionary event has been the introduction of the iPhone on the mobile market. Earlier, the mobile industry was under the constraints of operators, due to the common practice of operators buying millions of mobiles and including their delivery to the subscriber within the monthly subscription bill, especially in Europe. By these means, they have been able to banish many of the services, which the customer was very keen to obtain. Such applications were relatively easy to include in high-end mobiles, technically speaking.

With the iPhone, Steve Jobs introduced a different paradigm. This paradigm has been the same as the one underlying the phenomenal success of “Minitel” in France. Developers are free to post applications into a common store – such as the “Applestore”, managed by Apple. Apple collects the fees from the customers and pays back a certain percentage to the author. In that value chain, the operator is limited to provision of the telecommunication duct and receives little money for the use of its network.

Of course, operators adapted themselves to the new framework. They are now selling iPhones the same way as the other mobile terminals.

Following the path opened by Apple, Google introduced Android, mainly based on Linux software, opened to any manufacturer without fee. As a result, Android is now the dominant standard for smartphones. Microsoftand Blackberry show little success in their smartphones at present. The Android world offers nearly the same applications as the Apple world.

Among thousands of applications, it seems that location services and location based services are the key services. For this purpose, the smartphones include a GPS receiver and the necessary processor of the satellite signals, combined with precise maps of different areas of interest.

However, smartphones include a Wi-Fi access, which is generally put as a priority choice. When Wi-Fi is present, the smartphone will automatically try to connect via the Wi-Fi, instead of the mobile network.

Other successful applications are all kinds of games.