What is 4G and how does it actually work? Internet is filled with quality scholarly articles, and you can find numerous books explaining the various intricacies of LTE (Long Term Evolution) in detail. My personal favorite is the classic: "LTE: The UMTS Evolution - From Theory to Practice" published by Wiley. However, sometimes the complexity and terminologies get too much over our head in establishing a bare minimum idea, particularly to those who are not from technical background. This series is a humble attempt in trying to remove all the complexities associated with technology. Using power of analogy with a sprinkle of humor, readers can get a better understanding of the otherwise vast 4G technology, filled with complexity and constant developments! Objective of this article is to give readers a bird's eye view of LTE: origin from 3GPP, the underlying electronics, and the architecture components.
A bit of history first!
Everything that your mobile does, the kitten videos you watch on YouTube, the calls you place, the call drops that happen, or those awesome selfies that you share on #instagram, everything is governed by a set of rules or protocols (some say, even life). These set of rules (analogous to code) decide how to process the selfie, when you press on the upload button. It includes the complete conversion of data into digital format, travelling over the air through towers, going through some complex processing and then eventually finding itself on the internet. These rules of processing are governed by 3GPP: 3rd Generation Partnership Project, which is essentially an association of major telecommunication giants who work tirelessly in researching ways and means to create faster mobile internet speed! The 3GPP organizational partner releases a set of rules/protocols after meetings conducted with almost all major telecommunication players. These protocols and the associated architecture are considered as worldwide standard, which is followed by all LTE stakeholders across the globe. Why do we need 3GPP? Well, if it had not been for them, than Airtel 4G Sims would work only on selected mobile such as the ones created by Apple only! In short, SIM cards would have had become Apple (end to end control anyone?).
Cup of Tea...
"Behind every communication technology is a radio wave". This holds true for LTE, which is nothing but means to make the radio waves transfer faster and more efficient. The claimed speed of LTE is approx. 300 Mbps downlink, and 75 Mbps uplink based on certain antenna conditions (actual speed and coverage differs country to country). It also promises to reduce latency (or delay in data transfer) up to five ms. In order to uphold the promises; significant overhaul in the underlying radio transfer technology was done to enable the high-speed transfer.
While the entire listing of changes is beyond the scope of this article, one major change factors in a lot. It is called OFDM or Orthogonal Frequency Division Multiplexing
Let us start with the basics of signal communications, i.e. Modulation. It simply means that a radio wave is modified with another radio wave carrying information which than together, can be transferred over long distances. The combined radio wave is called "carrier" signal, which transmits the original signal over long distances using process of Modulation. What if we want to transmit different information, e.g. black + white, in the same "carrier" signal? We create "sub carriers", which are nothing but parts of the main carrier signal, carrying different levels of additional information.
How to transmit these information on the limited bandwidth (or frequency channels) available? The traditional method (since 1870!) is by using Multiplexing, where multiple signals are clubbed together (or multiplexed) over a frequency channel. This is called Frequency Division Multiplexing (FDM). However, to make the traditional approach even faster, OFDM came into picture. In typical FDM, the total bandwidth is divided into several non-overlapping frequency bands, each of which is used to carry signal (see diagram below). Simplest application of this is in Radio, where we tune into different frequencies being broadcast at the same time. The extra O or "Orthogonality" is an advanced geometrical concept incorporated with FDM, which overlaps the different sub carriers "orthogonal" to each other, hence saving bandwidth and increasing transmission capacity. In Layman terms, OFDM helps various sub carriers, carrying different data, transmit in cost effective manner, saving bandwidth (by providing orthogonality) and enabling faster transmission which is required for LTE.
Orthogonality transmission of sub carriers saving bandwidth.
Now, to transmit so many of these sub carriers (analogy of tuning into different radio stations simultaneously), it would require several receiving and transmitting stations, one for each sub carrier. To eliminate this, Inverse Fast Fourier Transformation comes into rescue, which essentially transforms different sub carrier signals of varying frequency and strength into one combined time varying signal! In Layman terms, take one signal, divide it into different sub carriers carrying different information, and combine it into one signal to eliminate usage of different antennas, than reverse the steps on the receiving side! A more pictorial representation is given below:
This is the very basics of LTE as far as electronics aspect is concerned. Please do note that there are many additional concepts related to digital signal processing of LTE. There is cyclic prefix, which is essentially sending out redundant information to prevent signal distortion in the forms of Inter Signal and Inter Carrier interference. There is Single Carrier FDMA (SC-FDMA), which uses an additional technology of Discrete Fourier Transform to eliminate Peak to Average Power Ratio (PAPR) (nonlinear distortion of radio waves combined because some waves have much higher magnitude). It is used extensively in uplink transmission, as vast number of cell phones generate generates their own independent radio waves, summation of which results in a distorted radio wave signal. To save us from further electronics, let us move onto the Information Systems part of LTE!
LTE architecture, components and interfaces
A bit of history first!
Everything that your mobile does, the kitten videos you watch on YouTube, the calls you place, the call drops that happen, or those awesome selfies that you share on #instagram, everything is governed by a set of rules or protocols (some say, even life). These set of rules (analogous to code) decide how to process the selfie, when you press on the upload button. It includes the complete conversion of data into digital format, travelling over the air through towers, going through some complex processing and then eventually finding itself on the internet. These rules of processing are governed by 3GPP: 3rd Generation Partnership Project, which is essentially an association of major telecommunication giants who work tirelessly in researching ways and means to create faster mobile internet speed! The 3GPP organizational partner releases a set of rules/protocols after meetings conducted with almost all major telecommunication players. These protocols and the associated architecture are considered as worldwide standard, which is followed by all LTE stakeholders across the globe. Why do we need 3GPP? Well, if it had not been for them, than Airtel 4G Sims would work only on selected mobile such as the ones created by Apple only! In short, SIM cards would have had become Apple (end to end control anyone?).
Cup of Tea...
"Behind every communication technology is a radio wave". This holds true for LTE, which is nothing but means to make the radio waves transfer faster and more efficient. The claimed speed of LTE is approx. 300 Mbps downlink, and 75 Mbps uplink based on certain antenna conditions (actual speed and coverage differs country to country). It also promises to reduce latency (or delay in data transfer) up to five ms. In order to uphold the promises; significant overhaul in the underlying radio transfer technology was done to enable the high-speed transfer.
While the entire listing of changes is beyond the scope of this article, one major change factors in a lot. It is called OFDM or Orthogonal Frequency Division Multiplexing
Let us start with the basics of signal communications, i.e. Modulation. It simply means that a radio wave is modified with another radio wave carrying information which than together, can be transferred over long distances. The combined radio wave is called "carrier" signal, which transmits the original signal over long distances using process of Modulation. What if we want to transmit different information, e.g. black + white, in the same "carrier" signal? We create "sub carriers", which are nothing but parts of the main carrier signal, carrying different levels of additional information.
How to transmit these information on the limited bandwidth (or frequency channels) available? The traditional method (since 1870!) is by using Multiplexing, where multiple signals are clubbed together (or multiplexed) over a frequency channel. This is called Frequency Division Multiplexing (FDM). However, to make the traditional approach even faster, OFDM came into picture. In typical FDM, the total bandwidth is divided into several non-overlapping frequency bands, each of which is used to carry signal (see diagram below). Simplest application of this is in Radio, where we tune into different frequencies being broadcast at the same time. The extra O or "Orthogonality" is an advanced geometrical concept incorporated with FDM, which overlaps the different sub carriers "orthogonal" to each other, hence saving bandwidth and increasing transmission capacity. In Layman terms, OFDM helps various sub carriers, carrying different data, transmit in cost effective manner, saving bandwidth (by providing orthogonality) and enabling faster transmission which is required for LTE.
Orthogonality transmission of sub carriers saving bandwidth.
Now, to transmit so many of these sub carriers (analogy of tuning into different radio stations simultaneously), it would require several receiving and transmitting stations, one for each sub carrier. To eliminate this, Inverse Fast Fourier Transformation comes into rescue, which essentially transforms different sub carrier signals of varying frequency and strength into one combined time varying signal! In Layman terms, take one signal, divide it into different sub carriers carrying different information, and combine it into one signal to eliminate usage of different antennas, than reverse the steps on the receiving side! A more pictorial representation is given below:
This is the very basics of LTE as far as electronics aspect is concerned. Please do note that there are many additional concepts related to digital signal processing of LTE. There is cyclic prefix, which is essentially sending out redundant information to prevent signal distortion in the forms of Inter Signal and Inter Carrier interference. There is Single Carrier FDMA (SC-FDMA), which uses an additional technology of Discrete Fourier Transform to eliminate Peak to Average Power Ratio (PAPR) (nonlinear distortion of radio waves combined because some waves have much higher magnitude). It is used extensively in uplink transmission, as vast number of cell phones generate generates their own independent radio waves, summation of which results in a distorted radio wave signal. To save us from further electronics, let us move onto the Information Systems part of LTE!
LTE architecture, components and interfaces
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