Sunday, 5 April 2020

LTE - Types, Features and Working


WHAT IS IT?

Assuming this is a new term for you and you have no idea what this is, “what on earth does this mean” is the first thing you should ask. Let’s know the full form first. LTE stands for Long-Term Evolution.
Ok. But evolution of what? I don’t know either. According to sources, this naming conventions were a part of advertising the technology and appeal to the customer base. Alright, enough of the intro, let’s know it’s simple explanation borrowed from Wikipedia:
Long-Term Evolution (LTE) is a standard for wireless broadband communication for mobile devices and data terminals.
You still don’t get it, did you? Remember 2G and 3G technologies? This LTE is the next stone in that journey. So the architecture was purely ased on the 3G technology by UMTS. Much of the LTE standard addresses the upgrading of 3G UMTS to what will eventually be 4G.
What’s the major difference between LTE and the third generation (3G)? Well, a large amount of the work is aimed at simplifying the architecture of the system. But is it 4G? We’ll discuss this in the end of this blog. For now, let’s jump to its classification.

TYPES

There are basically 2 mobile data transmission technologies based on 2 major factors, viz:
How data is uploaded and downloaded
What frequency spectra the networks are deployed in
So, based on these two factors, we have two types of LTE.
1. Long-Term Evolution Time-Division Duplex (LTE-TDD)
2. Long-Term Evolution Frequency-Division Duplex (LTE-FDD)
Before proceeding with this, let’s know some basics of GSM and CDMA so that you know what these “divisions” are. Afterwards, you’ll be able to digest this easily.

GSM, CDMA and LTE

GSM and CDMA are two different ways to accomplish the two things. LTE is newer.
The way GSM solves (1) is by something called TDMA (time division multiple access). When you're in a phone call, you're phone is scheduled a bunch of time slots when your phone either sends or receives data. These exclusive to your phone and different from other phones in the cell so there's no interference. This way, multiple phones can talk to the cell tower (seemingly) at once (the bursts of time are super short so you don't notice them).
CDMA deals with (1) in a completely different way. It breaks up the channel into codes/signals (Code division random access). This is a little hard to explain without some math, but there's a notion called orthogonality. If two signals are orthogonal you can pull one signal out without getting interference from the other. Every user is assigned a different code/signal and these are (approximately) orthogonal to each other. This is a more advanced technique and generally thought of as advantageous since there isn't as much waste (TDMA needs little bits of extra time between users to make sure there's no overlap, for example).
The way (2) is accomplished is also very different. In fact there are many different ways it is done even within GSM or CDMA. The way data is sent along depends a lot on how good the quality of the radio signal and other factors. That's a whole other thing. But the options for GSM and CDMA differ.
3G and 4G are kind of marketing terms that come from "3rd generation" and "4th generation". They refer to families of standards, but not specific methods to accomplish (1) or (2).
Now you know the basics, let’s get back to types of LTE.

LTE-TDD and LTE-FDD

LTE-TDD Uses a single frequency, alternating between uploading and downloading data through time while LTE-FDD paired frequencies to upload and download data.
Despite the differences in how the two types of LTE handle data transmission., LTE-TDD and LTE-FDD share 90 percent of their core technology. This makes it possible for the same chipsets and networks to use both versions of LTE.
Several companies produce dual-mode chips or mobile devices, including Samsung and Qualcomm.

FEATURES


  • Peak download rates up to 299.6 Mbit/s and upload rates up to 75.4 Mbit/s
  • Cost effective
  • Low data transfer latencies
  • Lower latencies for handover and connection setup time 
  • Higher network throughput
  • Improved support for mobility, exemplified by support for terminals moving at up to 350 km/h
  • Orthogonal frequency-division multiple access for the downlink, Single-carrier FDMA for the uplink to conserve power
  • Support for inter-operation and co-existence with legacy standards (GSM/GPRS or W-CDMA-based UMTS )
  • Uplink and downlink Carrier aggregation.
  • Packet-switched radio interface
  • It’s because of these features that most carriers supporting GSM networks can be expected to upgrade their networks to LTE at some stage


MADE OF?

What is LET made of? That means it’s working backbone consists of these things, most of which we have already discussed above. For the concepts you might not find familiar, I’ve attached link to resources so that you can have an idea of what they are.
OFDM (Orthogonal Frequency Division Multiplexing) for Downlink
SC-FDMA (Single Carrier FDMA) for Uplink
MIMO (Multiple Input Multiple Output)
E-UTRAN (for Network)

VOICE CALLS IN LTE

One of the major problems they faced designing LTE was how to handle voice calls using it. LTE was primarily meant for (internet) data transfer, so the transfer of voice data to integrate with telecom operators was an issue.
With the adoption of LTE, carriers had to re-engineer their voice call network. The reason behind this was that the LTE standard supports only packet switching with its all-IP network. On the other hand, voice calls in GSM, UMTS and CDMA2000 are circuit switched.
3 different approaches sprang up to handle this:

1] Voice over LTE (VoLTE)

VoLTE networks support both voice and data at the same time, without hampering the other. Whereas, the traditional LTE networks may or may not support data and voice together, or may affect the quality of the voice call

2] Circuit-Switched Fallback (CSFB)

LTE just provides data services. When voice call is to be made, it will fall back to the circuit-switched domain.
Advantage: Operators can provide services quickly.
Disadvantage: Requires longer call setup delay.

3] Simultaneous Voice and LTE (SVLTE)

Handset works simultaneously in the LTE and circuit switched modes.
LTE mode providing data services and the circuit switched mode providing the voice service. This is a solution solely based on the handset, which does not have special requirements on the network.
Disadvantage: The phone can become expensive with high power consumption.

IS IT 4G?

Now the controversy (not a big one, I know… but still, it is there.)
Contrary to popular belief, LTE at the current stage was not always considered 4G. ITU (International Telecommunication Union) determines what can be considered 4G and they initially had defined all the standards which a technology had to meet. LTE couldn’t meet those requirements.
Therefore, LTE is popularly known as 3.95G.
LTE-Advanced did make the cut through. But the business and telecom operators had allegedly “influenced” the ITU to update their standards so that they can advertise their services as 4G to attract users.
As a result, there is a slight disagreement between the businesspeople and technophiles on definition of 4G. technophiles consider the original ITU guidelines as a standard for 4G.

CONCLUSION

To solve “How to get many people to share a piece of spectrum”, LTE uses OFDMA which increases throughput
Hope you get at least the gist of what’s been explained in this blog. If not, jump over to the pages linked in the article or post comment if you are reading this on ShakesVision.

SHAKEEB AHMAD
April 05, 2020

Shakeeb Ahmad Maharashtra, India

Shakeeb Ahmad is a blogger, poet, enthusiast programmer, student of comparative religion and psychology, public speaker, singer and Vedic Maths expert. He loves playing with the numbers and invented a shortcut method to square the numbers at the age of 16. In sports, football is root to his happiness. He lives it.

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