The success story of LTE

Looking at the developments of LTE over the last years, and the planned developments for the future, could LTE be called a success?

That this is not such a straightforward question, with an easy, correct answer can be seen from uncountable disputes, blogs and opinions floating around the Internet. Trying to find an answer, one could try and compare the standard with competitors in the field. A little bit of research shows that LTE and WiMAX (Worldwide Interoperability for Microwave Access) are operating in the same area.

WiMAX is an IEEE standard for broadband wireless networks, and officially belongs to the 3G family according to the ITU (International Telecommunication Union). Updates are planned to increase data rates and be able to meet the ITU requirements for 4G systems.

‘Winning’

Comparing LTE to WiMAX seems to be a battle without an ending. For years now, the ‘fight’ has been going on, with its ups and downs for the WiMAX party. This might get spectators thinking that LTE is on the winning hand. The problem here is actually, when has one of the parties won? If winning is total extinction of the opponent, than it is not likely to happen in quite some years. LTE might have a huge fan-base, but there are not much examples of working LTE networks yet. More and more operators are starting to roll out LTE networks, and mobiles with LTE functionality are starting to be released, so it is looking good there. WiMAX however is already operational in some parts of the world for some years already, and has got a growing number of supporters too. Truth is, some parts of the (developed) world will not see a functional LTE network in the next five years, and other parts (might be more) will not have to option to use WiMAX services.

Economic value

Trying to answer the success-question, it may not be a good idea to focus on the debate of which technique will be the winner. Looking at economic values of the standard is another way of evaluation the question.

LTE does have the advantage of an economy of scale. The potential (and perhaps already established) size of the network is huge. It looks like whole countries or even continents are willing to use the standard as their main (stepping-stone-to) future generation mobile network. Network externalities is another factor that greatly favours LTE. When the network is established, I have the option to reach all other subscribers using the same services. Every new mobile connected to LTE will increase the size of the network. A side question here could be whether the users have a choice in this. As noted before, it is highly unlikely that LTE will have to compete with for instance WiMAX everywhere it is used. It might look a bit like local monopolies where the user can be connected to next generation mobile Internet services like LTE or WiMAX, but cannot choose which one, simply because there is only one network available at the users location.

This last effect might get people thinking about possible lock-in effects due to high switching cost if there would be an option to choose which network to use. Suppose you have a mobile with LTE functionality, but would like to change to the WiMAX standard, which is not compatible with your current hardware. In my opinion, this will not have any impact on the standard. The choice for the network is namely not really made by the user, but by the operator. That operator will most likely not make a huge capital investment in rolling out multiple networks to perform the same function. Choosing an operator brings a certain network and vice versa. Since the networks will all be connected to the Internet, it will be no problem calling or mailing an LTE mobile with a WiMAX one.

Conclusion

The fact that there is a global demand for LTE networks and the incredible amount of discussion about which one will be or is better (do a google on ‘LTE vs WiMAX’ and count the hits), does point out that LTE is a great success in my opinion. If a standard is able to grow this big, and is known by this many (future) users, the question whether it is the best is not important.

A success it is.

3GPP – The organisation behind the standard

LTE is defined as a standard through 3GPP, the 3^rd Generation Partnership Project.

This is a cooperation of telecommunications standardisation organisations. Large standardisation bodies from all over the world are united in 3GPP as ‘Organisational Partners’ (OPs). Originally 3GPP was established in 1998 to produce a set of technical specifications for a 3^rd Generation mobile system based on the GSM core network. Over the years, extra tasks were requested so that after making standards for the 3G system, the united organisations cooperation in 3GPP remained.

3GPP is structured in Project Coordination Groups (PCGs), which have the responsibility for the running of 3GPP. The PCG is the highest decision making body in 3GPP. The PCGs meet twice each year to adopt new work items submitted by the specification groups and to keep track of the overall time frame. The real specification work is done by Technical Specification Groups (TSGs) which can organise their work in Working Groups (WGs). The TSGs are divided in four groups with each their own responsibilities and WGs, they report to the PCGs.

• TSG GERAN (GSM EDGE Radio Access Network)
• TSG RAN (Radio Access Network)
• TSG SA (Service & Systems Aspects)
• TSG CT (Core Network & Terminals)

The PCGs have plenary meetings twice each year; the TSGs have these official meetings each quartile. The individual WGs also meet between these plenary meetings. To make sure the work done by the TSGs meets market requirements, Market Representation Partners (MPRs) are invited to 3GPP. The MPRs themselves are not standardisation bodies, but do have high competence in their field of work. They provide feedback and input on what features and functionality is needed in new specifications.

The specifications are grouped in ‘Releases’. Dates are set for new releases to be finished. The features which are ready to be implemented in the release by that date are ‘frozen’ into the release. Features which did not make the freeze date are postponed to a later release. When a release is frozen, it can be used to build mobile systems, as all specifications and standards are known and will not be changed.

A few releases, and a very simple description about their content.

Release 99 (2000)

Specifications of the UMTS network and the CDMA air interface

Release 5 (2002)

Introduction of High Speed Downlink Packet Access (HSDPA)

Release 6 (2004)

Integrate operation of Wireless LAN and introduction of HSUPA (Uplink)

Release 8 (2008)

First release of LTE, introducing All-IP network and OFDM

Release 10 (2011)

First official 4G compatible specifications: LTE-Advanced

Release 11 is currently being developed and planned to be released in 2012

The Technical Specifications developed by the TSGs are owned by the Organisational Partners. 3GPP does however, not make the formal contributions to the International Telecommunication Union (ITU). Submission to the ITU is done by the individual members following their own national/regional processes. Reason for this is that 3GPP is not established as a legal entity, and therefore the standardisation body is not a de jure organisation. The ITU itself is such a de jure standardisation organisation. The Technical Specifications, developed by 3GPP, submitted by the individual members, to the ITU, will therefore be effective as de jure standards, even though they are developed in a de facto standardisation body, 3GPP. 

References:

Partnership Project Description

Partnership Project Agreement

3GPP website

More LTE details

Since OFDM is an important feature of, but not the only one in LTE, this post will contain some more details about what makes LTE into the standard it needs to be.

LTE Bandwidth

As already mentioned briefly, LTE is designed to operate in frequency bands between 700 and 2600 MHz. Parts of the frequency within that range may be used for LTE. For those parts, regulations are made as to how the blocks of bandwidth must be used. The frequency can be used in blocks of 1.4, 3, 5, 10, 15 or 20 MHz bandwidth. The advantage of using such blocks is that it is possible to use a small block when the rest of the surrounding frequency is already used. When a big block of bandwidth can be allocated, the spectrum efficiency will increase. For larger bandwidth, the relative overhead of guard bands (to separate channels) and control channels is smaller. Fading is the process of attenuation of the signal when traveling through the ether. This can be because of obstruction of the signal, or interference from reflections. Should part of the spectrum fade, this will have more impact for smaller bandwidths. A large block of bandwidth is less likely to experience fading of the complete channel. Therefore, it is advisable to implement LTE on as large bandwidth as possible.

Error correction codes

Since it is only expected that not all bits of information sent at the transmitter will arrive at the receiver as intended, error correcting codes are implemented. Error correcting codes have the ability to somehow reconstruct the original data, in case some parts of it are gone (too noisy, never received, jammed) How that works exactly for the latest ‘Turbo coding’ techniques is a bit much technical detail for now, but a short example might help to see it is possible. Suppose the sender has got 1 bit (0 or 1) to send, a very simple and redundant code could be to just send the bit 3 times. If the communication channel is introduces some errors, the receiver might see 8 versions of the message.

Received data	Decoded as
000	0 (error free)
001	0
010	0
100	0
111	1 (error free)
110	1
101	1
011	1

So instead of taking 1 bit, and deciding what it is, the receiver takes 3 bits, and ‘averages’ them into 1. This is just an example of a very redundant error correction code example; it sends 3 times the data needed. More sophisticated codes use more ‘tricks’ to be able to correct more difficult errors. As long as there are not too many errors in a row (called a burst) they can mostly be corrected. This is the part where frequency jumps in again. Error correcting codes in LTE can distribute a stream of data over multiple subcarriers. This technique is called frequency interleaving. If a single subcarrier fades, it is possible for the correction mechanism to repair the bits that were lost, since is contains ‘random’ bits from the multiple data streams. The same technique is used for the time domain. The data stream is then ‘scrambled’ so that an error burst during transmission is not a burst anymore when the decoding places the bits in the right order again.

Picture explaining how interleaving helps with burst errors. Source: Link

Architecture

Besides higher data rates, LTE has the goal of low latency and making an All IP Network (AIPN). These goals result in a simpler network with fewer elements. In the 2G and 3G network, most activity is done close to the core of the network. The access points (NodeB) together with the Radio Network Controllers (RNC) form the Radio Access Network. The NodeBs are implemented as relative simple elements in the network. The real intelligence is at the high capacity RNCs; they support resource and traffic management (for instance switching a call from one NodeB to another) and various other essential radio protocols. In LTE, the NodeB has evolved into the (not very originally named) evolved NodeB (eNodeB). This eNodeB is the only element in the evolved UMTS Terrestrial Radio Access Network (eUTRAN) for LTE, and connects directly to the core network (Evolved Packet Core – EPC). With more intelligence at the eNodeBs, they handle parts of traffic management themselves. Handovers (switching calls to other access points) can be done without bothering the core network, since eNodeBs communicate with each other and handle those handovers themselves. This is a good step forward to lower latency in the access network.

LTE Architecture. Source: Link

The LTE architecture also satisfies the goal of realizing an All IP Network. In UMTS, the air interface uses extra protocols, like GPRS Tunneling Protocol (GTP) to handle the voice data in combination with data packets on the same network. Historically, the telephone system uses a circuit switched network. For a call, a dedicated connection path is set up, that circuit is ‘ours’ to use for the duration of the phone call. The internet is a packet switched network, meaning that data packets are individually routed over the World Wide Web. All packets combined, they assemble the website or whatever you requested from the internet. Main difference is resource usage, the packet switched network is not being used when I have downloaded the website and I’m reading the text from my screen. The circuit switched network for phone calls is loaded with our call, whether we are talking or not. In GSM and GPRS, these services were combined; in LTE, the switch is made to a total packet switched network. To integrate with the rest of the internet, the Internet Protocol (IP) is used.

References:

Book: LTE for UMTS

Overview of 3GPP Release 8

LTE and OFDM

In this post I want to explain what the goal of LTE is, and how frequency utilisation helps to achieve that.

We as consumers want to be able to use our mobile phones as multimedia devices. Listening to music and watching videos on the go, using the mobile network. We ever want it better and faster, not having to wait for downloads. More and more people are getting used to high speed internet access at home, and expect the mobile network to deliver the same services. This means we need to improve the network to handle all that traffic at the speed we want.

One of the main goals of the LTE standard is increasing data throughput rates. LTE networks should bring the worlds of very high speed data access at home and that of high mobility cellular networks closer together.

To achieve this, spectrum will be utilised more efficiently. Key instrument is the modulation technique that is used:  Orthogonal Frequency Division Multiplexing (OFDM). In an attempt to explain what modulation is, I’ll describe it as a method for ‘putting information on the radio waves’. The radio waves can be sent and received using antennas, the modulation and demodulation steps make sure the information is put on the waves, and picked off again at the receiving end.

There are various ways to implement modulation, each with their advantages and disadvantages. Some pose high requirements at the transmitter or receiver, others are extremely difficult to intercept or decode if the interceptor does not have the required key.

Main advantages of OFDM are that it allows for relatively simple transmitters and receivers, and that it can handle bad channel conditions rather well. Interference in the radio spectrum and interference of the signal on itself are dealt with without having to use complex filters.

Disadvantage is that the system is sensitive to frequency synchronisation problems between transmitter and receiver. Doppler shift also raises problems, making OFDM perform worse when users are travelling at high speeds (by car or train for example).

At the end of this post a bit more on the frequency part. One thing that makes the OFDM method a very useful and efficient method is the ‘orthogonality’ part. The modulation puts the information on the radio wave. Orthogonality means that the various ‘waves’ used (real terminology is sub-carriers) will not affect each other. The sub-carriers are chosen in such a way that the frequency bands don’t cause cross-talk. Compare this with multiple persons in a room all talking at the same time; this cross-talk makes it more difficult to understand the one person you are talking with. If all the couples would talk in different languages, is would be easier for them to understand each other. This can be seen as a form of orthogonality, the conversations would not interfere. In ODM this is called ‘Inter-Carrier-Interference’ (ICI), and is at the same time one of the weaknesses of the system. Sub-carriers must be synchronised very accurate to keep this orthogonality principle working. When the frequencies change a bit, the communication channels start talking the same language and will influence each other, degrading performance of the system. 

OFDM sub-carriers do not interfere with eachother. Source: link

The picture above shows that the various carriers (A-E) are 'active' or 'talking' when the others are not, so they do not interfere with each other. Note, this picture is in the frequency domain. As long as the frequencies of the sub-carriers are chosen exactly right, they seem to be invisible to each other.

Given a good synchronised, orthogonal set of sub-carriers, this brings the advantage of multiple channels to send the information. Suppose you have 100 times as much channels to use, you could send each stream of information parallel, 100 times slower per stream, and still send the same amount of information. This then opens up the opportunity to simplify the receiver since working slower is easier.

References:

LTE Encyclopedia

A bit on LTE background

LTE is a standard developed by the 3rd Generation Partnership Project (3GPP). This is a group of telecommunications associations, who initially joined up to standardise the 3G mobile phone system. The following list shows the partners in the 3GPP.

• European Telecommunications Standards Institute (ETSI)
• Association of Radio Industries and Businesses/Telecommunication Technology Committee (ARIB/TTC)
• China Communications Standards Association
• Alliance for Telecommunications Industry Solutions
• Telecommunications Technology Association.

3GPP 'releases' standards with typical version names "Release X", where X is the version number. Release 99 is the first UMTS specification and was released in 2000. After that, version numbers started at 4, and release 11 is planned for 2012. Release 8 is the first LTE release, but does not comply with the 4G requirements. LTE actually is the little brother of the 4G family. LTE Advanced is the first standard that fulfills the real 4G requirements which set peak speed requirements at 100Mbit/s for high mobility users (in a car or train for instance) and at 1Gbit/s for low mobility users (walking or not moving at all).

LTE might be seen as a stepping stone from 3G (UMTS) techniques, to 4G technologies. LTE advanced is backwards compatible with LTE, it uses the same frequency bands. By treating frequency utilisation of LTE, I immediately do that for the 4th generation standards of the future.

Tip of the iceberg on frequency bands used in LTE.

LTE can be used on many different frequency bands. Worldwide the range of frequency bands include 700, 900, 1800, 1900 and 2600 MHz. Which bands will be used is part of local regulations. In Europe for instance, 900, 1800 and 2600 MHz are planned to be used, while North America will use 700 and 1900 MHz bands.

Within these bands, LTE takes up a certain amount of bandwidth: 1.4, 3, 5, 10, 15 and 20 MHz are specified in the standard. This can be compared to roads for your car, the 1.4 MHz band could be the little country road, where a bandwidth of 20MHz behaves like the multi-lane highway.

3... 2... 1... Takeoff!

This will be my first try at blogging, so bear with me please.

I've never had a topic I wanted to bother other people about on the internet, but now a course in my master has given me the chance. The course is about Regulations and Standards for wireless communications and it is part of the Broadband Telecommunications Technologies Master at the Eindhoven University of Technology.

It will be a blog about the wireless technique LTE (Long Term Evolution) and more specific, about how LTE handles frequency.

Let's start with some history. As noted, LTE stands for Long Term Evolution, and it is a technique for mobile communication. Everybody is familiar with mobile phones, and most probably also with the newer concept, smartphones. These wonders of technology communicate through wireless techniques. GSM and UMTS are examples of such techniques. GSM (Global System for Mobile communication) is a second generation standard for cellular networks. The successor, UMTS (Universal Mobile Telecommunications System) is a third generation technology. Currently under development is the fourth generation of cellular wireless standards, LTE-advanced.

The various generations differ at numerous ways, but main changes can be seen at modulation and frequency utilisation. Hereby I want to explain my interpretation of frequency utilisation with a little example.

When traveling by car, you use roads to go from one place to another. This can be on little country roads which take you home to the place you belong. Or on the highway where Bruce Springsteen is working on. All these roads have in common the rules which apply there. How people use the roads, the way they drive their car from place A to place B, is what I would call road utilisation.

This analogy can be projected on frequency utilisation. Then the roads become the frequency spectrum and the rules to use the roads become the standards in which is organised how the frequency spectrum must be used.

In short, I want to talk about the traffic rules of the new mobile communication network.