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Future LTE Designed by SK Telecom: (1) 4.5G Evolution Roadmap - 5-CA Commercialization and 4x4 MIMO Deployment
June 13, 2017 | By Dr. Michelle M. Do @ Netmanias
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With the recent launch of Samsung Galaxy S8, new technologies from the local telcos are flooding the South Korean market. Probably to avoid the criticism that they in a mere contest of speed, all telcos in the nation are now playing up the importance of customer satisfaction and quality assurance. 


On April 12th, KT announced that it had begun deployment of C-DRX (Connected mode Discontinuous Reception) in its nationwide LTE network on April 1st, significantly reducing smartphone battery consumption by up to 45% in the tests followed.


SK Telecom on April 20th held a press conference, presenting a plan for commercialization of 5-CA (Carrier Aggregation) and 4x4 MIMO, and a roadmap for 4.5G evolution. The telco stressed the importance of AI-enabled network quality management as well. 


Why quality management matters?


• Traffic growth

Video is known to account for 94% of the total mobile traffic as of December 2016 (source: The Ministry of Science, ICT and Future Planning). This killer application in LTE has been driving a surge in LTE traffic. In December 2016, LTE traffic per subscriber and total LTE traffic recorded 5.9 GB and 250 PB, up by 34% and 46% from the previous year, respectively. In 2016, the total annual LTE traffic was 2.5 EB (Exabyte), including 1.1 EB generated by SK Telecom whose market share is approaching almost 50% in the market. This clearly opened a new era of Exa traffic. Analyzed based on Cisco VNI (Virtual Networking Index), mobile data traffic was expected to grow five-fold over the five years to come (2016 ~ 2021), with monthly traffic per subscriber reaching 30 GB and monthly total reaching 1.25 EB in 2021.


• Mobile network quality

Peak data rates of a mobile device (or capacity of a cell) can be achieved when the device has access to all cell resources available, in the best radio conditions. For example, the peak data rate of a device would be 150 Mbps when 20 MHz, 2x2 MIMO and 64 QAM are used. However, in real settings where the radio conditions can vary, it drops down by 50% or so depending on how well the quality of the network is managed. Because cell capacities have to be shared by users who concurrently access the cell, the more users access the cell, the lower the data rate gets.


For instance, a cell with 80 Mbps of average capacity which can easily support 20 users streaming a video clip of 4 Mbps will have difficulty in offering the same quality if the number of concurrent users increases. More users and traffic mean poorer service quality. So, the mobile network capacity must be expanded to keep the same service quality level. This is why the importance of enhanced capacity and quality management in mobile networks, rather than mere peak rates, is highlighted in the Exa traffic era.


The capacities of a mobile network can be improved in many ways. For instance, you can add more frequencies, apply more efficient modulation schemes, or adopt more antennas and smaller cells.


At the press conference by SK Telecom in April, presentation and Q&A sessions were held discussing the following three topics:

  • 4.5G evolution roadmap

  • Application of C-DRX

  • AI-enabled mobile network quality management


During the sessions, in the era of Exa traffic, SK Telecom shared its strategies for improving capacities and managing quality in mobile networks. Below, we will briefly discuss what was covered.



1. 4.5G Evolution Roadmap - 5-CA Commercialization and 4x4 MIMO Deployment


3GPP LTE Evolution


SK Telecom has just finished shaping up a 4.5G evolution roadmap that includes 5-CA commercialization. Before we explore the roadmap, we will review 3GPP’s LTE evolution made so far.


3GPP standards are managed as Releases. LTE series, classified as LTE, LTE-Advanced (LTE-A) and LTE-Advanced Pro (LTE-A Pro), are defined in Release 8 through Release 14, and 5G standard starts from Release 15.


LTE series: 

        - Release 8 - 9: LTE

- Release 10 - 12: LTE-A

- Release 13 - 14: LTE-A Pro


LTE-A Pro, also known as 4.5G, is the most evolved phase of all LTE series. it supports data rates of over 500 Mbps and even over 1Gbps, and is called ‘gigabit LTE’ as it offers gigabit speeds as in a wired network. These recent LTE evolution technologies like 4.5G will continue to expand even after the arrival of 5G.


LTE evolution phases by 3GPP


Specifications by 3GPP merely define features of each LTE solution while the actual LTE evolution is made by each telco in light of their own network conditions such as traffic volume, amount of spectrum, UE categories, and processing power of devices. For example, the following table shows the LTE evolutions of SK Telecom:


<Example: LTE Evolutions by SK Telecom>



4.5G Evolution Roadmap of SK Telecom


Now we will look into SK Telecom’s 4.5G roadmap (DL-centric).


4.5G evolution roadmap by SK Telecom (Source: SK Telecom)



Key technologies of 4.5G

The key technologies that underlie SK Telecom’s 4.5G evolution roadmap are Carrier Aggregation (CA), 256 QAM and 4x4 MIMO, the combination of which makes 4.5G evolution possible.

  • Carrier Aggregation (CA) – Enhances data rates by expanding the total bandwidth via combining frequency bands. A n-fold increase in bandwidth improves data rates by n-fold.

  • 256 QAM – Data transmission efficiency increased by 33% compared to 64 QAM

  • 4x4 MIMO - Enhances data rates with additional antennas. Doubling the number of antennas from 2X2 to 4x4 can double the data rates.



UE categories

Gigabit devices must become available in the market first. 1 Gbps-compatible UE categories are defined in Release 12 (Cat. 16) and 1.2 Gbps-compatible (Cat. 18) and 1.6 Gbps-compatible (Cat. 19) UE categories are defined in Release 13.


<UE category>


■ 256 QAM


1) 3-CA & 256 QAM introduced in June 2016, achieving up to 500 Mbps

In last June, SK Telecom presented 4.5G, offering up to 500 Mbps by applying 256 QAM to its 3-band LTE-A service. 

- 3-CA - total BW: 50MHz (10 MHz@B5 + 20 MHz@B1 + 20 MHz@B3), Peak data rate: 375 Mbps

- 256 QAM - across all 3-CA-enabled carriers (33% ↑)

⇒ 500 Mbps




2) 5-CA introduced in June 2017, achieving up to 700 Mbps

On June 5, the telco launched a commercial 4.5G service, offering up to 700 Mbps using 5-CA and 256 QAM, but not 4x4 MIMO.

- 5-CA - total BW: 70 MHz (10 MHz@B5 + 10 MHz@B1 + 20 MHz@B3 + 20 MHz@B7 + 10 MHz@B7), Peak data rate: 525 Mbps

- 256 QAM - across all 5-CA-enabled carriers (33% ↑)

⇒ 700 Mbps


5-CA speed test


SK Telecom, with five LTE carriers, needs 5-CA in DL. 5-CA was made possible because Samsung Galaxy S8, a smartphone model debuted in April, came with a modem (Samsung's Exynos LTE modem 355) that supports 5-CA.


•  LTE frequencies in use by SK Telecom

SK Telecom has now secured five carriers, a total of 70 MHz bandwidth, across four LTE Bands - LTE Band 1 (2.1 GHz), Band 3 (1.8 GHz), Band 5 (850 MHz) and Band 7 (2.6 GHz). – as a result of acquisition of two more carriers (i.e. 20 MHz and 10 MHz) in 2.6 GHz in the auction in May 2016, and return of 10 MHz (out of 20 MHz in 2.1 GHz) at the end of 2016. To combine all the LTE carriers it had, the telco needed 5-CA.


LTE frequencies owned by Korean big 3 telcos (as of May 2017)


KT is using a total of 50 MHz in four carriers across three LTE Bands (Band 1, 3 and 8). LG U+ has a total of 50 MHz in three carriers across three LTE Bands (Band 1, 5 and 7). To be able to combine all LTE carriers they have, KT and LG U+ need 4-CA and 3-CA, respectively.


The speed enhancement (or capacity increase) through CA depends on the total bandwidths that can be combined through CA. Although 5-CA combines five carriers, 4-CA, if the total bandwidth aggregated is greater than 5-CA’s, can still perform better than 5-CA.  


• LTE Modem: Samsung Exynos vs. Qualcomm Snapdragon

Samsung Galaxy S8 comes with a mobile AP, either Exynos 9 (Exynos 8895) by Samsung, or Snapdragon 835 by Qualcomm. Exynos 9 and Snapdragon feature LTE modems, Shannon 355 and X16, respectively. Most Galaxy S8 released in South Korea come with Exynos.


Both Shannon 355 and X16 are compatible with UE category 16 (Cat. 16) in DL, offering up to 1 Gbps. For DL CA, Samsung 355 supports 5-CA while Qualcomm X16 supports 4-CA. For UL, they both support 2-CA and Cat. 13, offering up to 150 Mbps. SK Telecom does have a roadmap for UL CA, but is not very aggressive in introducing CA in UL as their UL traffic accounts for merely 10% of the total traffic.



<LTE modem: Samsung Shannon 355 vs. Qualcomm X16>


Reference: Samsung Exynos 8895 vs. Qualcomm Snapdragon 835


■ 4x4 MIMO 


Areas with high volume of concurrent users and traffic require increased capacities more than anywhere else. When utilizing all available frequencies does not help, adding more antennas is an option to facilitate data transmission.


4x4 MIMO requires four Tx antennas at base station and four Rx antennas on mobile device (UE), and can double the data rates (or capacities) compared to 2X2 MIMO.



To double the number of base station antennas, the telco will build 4Tx base stations near hotspots first and then expand the coverage and bands of 4X4 MIMO as traffic grows. Devices will also have to have four antennas like Galaxy S8, to be able to support 4X4 MIMO communication.


Initially, 4X4 MIMO will be applied only in one carrier (2.6 GHz) and two carriers (2.6 GHz and 1.8 GHz) starting June, and then another carrier in 2018.


On June 5, in addition to 5-CA commercialization, two new levels of 4x4 MIMO-based 4.5G services were also launched: one that supports up to 800 Mbps with 4-CA and 1-4X4 MIMO (2.6 GHz) and the other that offers up to 900 Mbps with 3-CA and 2-4x4 MIMO (2.6 GHz and 1.8 GHz). Then, in the first half of 2018, 4-CA and 2-4x4 MIMO supporting 1 Gbps will be presented, followed by 5-CA and 3-4X4 MIMO supporting 1.2 Gbps. 


SK Telecom's 4x4 MIMO evolution


3) June 2017: Up to 800 Mbps (4-CA & 1-4x4 MIMO)

- 4-CA - total BW: 60 MHz (10 MHz@B5 + 10 MHz@B1 + 20 MHz@B3 + 20 MHz@B7), peak rates: 450 Mbps

- 256 QAM - across all 4-CA-enabled carriers (33% ↑)   

- 4x4 MIMO - applied in one band: 20 MHz@B7 (2x )


4) June 2017: Up to 900 Mbps (3-CA & 2-4x4 MIMO)

- 3-CA - total BW: 50 MHz (10 MHz@B1 + 20 MHz@B3 + 20 MHz@B7), Peak data rate: 375 Mbps

- 256 QAM - across all 3-CA-enabled carriers (33% ↑)

- 4x4 MIMO - applied in two bands: 20 MHz@B7, 20 MHz@B3 (2x )


5) 1H of 2018: Up to 1 Gbps (4-CA & 2-4x4 MIMO)

- 4-CA - total BW: 60 MHz (10 MHz@B5 + 10 MHz@B1 + 20 MHz@B3 + 20 MHz@B7), Peak data rate: 450 Mbps

- 256 QAM - across all 4-CA-enabled carriers (33% ↑)

- 4x4 MIMO - applied in two bands: 20 MHz@B7, 20 MHz@B3 (2x )


6) After 1H of 2018: Up to 1.2 Gbps (5-CA & 3-4x4 MIMO)

- 5-CA - total BW: 70 MHz (10 MHz@B5 + 10 MHz@B1 + 20 MHz@B3 + 20 MHz@B7 + 10 MHz@B7), Peak data rate: 525 Mbps

- 256 QAM - across all 5-CA-enabled carriers (33% ↑)

- 4x4 MIMO - applied in three bands (2x )


Aggregation of all five carriers and application of 256 QAM and 4x4 MIMO in all bands will certainly boost data rates up to 1.4 Gbps. However, 4.5G data rates will improve gradually depending on the processing performance of the commercial devices in use (e.g. the number of data streams that can be processed simultaneously). The newly released Galaxy S8 can support up to ten data streams and 900 Mbps. 4.5G, scheduled to be launched in and after 2018 to offer 1 Gbps or higher, will require new devices that are technically compatible with the new technology.


■ 4.5G Service Coverage   


SK Telecom plans to continue to expand the coverage of 4.5G according to the following timeframe, ultimately serving 51% of the entire population in South Korea by the end of the year:

  • 57 cities, including Seoul and other metropolitan cities, by June 5, 2017 
  • 85 major cities by the end of 1H in 2017
  • 85 major cities and some counties by the end of 2017


SK Telecom's plan for 4.5G coverage expansion





Future LTE Designed by SK Telecom 


(1) 4.5G Evolution Roadmap - 5-CA Commercialization and 4x4 MIMO Deployment

(2) Application of C-DRX

(3) AI-enabled Mobile Network Quality Management: TBD 

Blaine (EAF LLC) via LinkedIn 2017-06-21 12:30:54

Thank you for sharing this --very good article with lots of information.

Brad (RANlytics) via LinkedIn 2017-06-23 12:47:12

Little do people know that even with 3CA the radio chip needs 15Watts. That means 5CA will be 20W or more. On a phone that has a capacity of 12Whr. It's obviously driven by marketing and not engineers. 5CA is litterally just 5 radio's transmitting at once. It's not ground breaking at all, infact it's more of a hack to try make it look like improvements were made so vendors can sell more Basestations and everyone is falling for it

onlyashu19 2017-09-28 18:31:07

Hi Brad , Interesting info by you , so what you mean to say as bottom line ?

Kumaresan (Samsung) via LinkedIn 2017-06-23 18:11:13


Khaled (du) via LinkedIn 2017-06-24 18:15:40

Very nice article, IBS would be the next challenging part to deliver the same capacity and latency reading as physical infra doesn't have so far developed higher effective 4X4

James Peng 2017-07-26 18:53:39

Great article

Thank you for visiting Netmanias! Please leave your comment if you have a question or suggestion.

[HFR Private 5G: my5G]


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