[Editor's Note] The history of communication is the history of human's ceaseless efforts to connect. Since prehistoric times, the function of communication has served as a means of communication and promise for humans, who are social animals. In Korea, telecommunications was first introduced in 1888 during the Joseon Dynasty, and the information age began in the 1980s after liberation with the rapid development of communication businesses and technology. Now, as we enter the 5G and 6G eras, we are looking at satellite communication and quantum communication, which are considered the next-generation communication. With the development of cutting-edge technologies such as artificial intelligence (AI), robots, cloud, and UAM, communication is becoming increasingly important and is expected to continue to develop endlessly. Communication is the most basic and core technology that spans almost all fields. Through this series, our magazine will cover various aspects related to communication, from the history of communication to minor events, technologies, and trends.

■ 4G, the era of 10 million subscribers has begun

As we enter the full-fledged multimedia era, various terminals of different sizes and names, such as flip phones and slide phones, have been released. Terminal manufacturers quickly adopted the trend and released models with small and slim designs. Popular cell phones such as the Chocolate Phone, Lollipop Phone, and Blackberry Phone were created.

This design began to be simplified in the 2010s as touchscreens were introduced to smartphones, and has remained so to this day. The Galaxy A, which was equipped with Android 2.1 and sold for 900,000 won, was overshadowed by the success of the Galaxy S. LG Electronics' Optimus series and Motorola also gained popularity during that time. In particular, Apple officially released the iPhone 4 on SKT in 2011.

In 2006, KT commercialized WiBro in response to the demand for high-quality mobile communications. The mobile Internet, WiBro (WiBro, Wireless Broadband Internet), is a technology developed by manufacturers and telecommunications companies such as ETRI, Samsung Electronics, KT, KTF, SKT, and Hanaro Telecom from 2003 to 2005. It opened the door to technology that allows high-speed Internet services while on the move, including in vehicles.

WiBro was adopted as an international standard for 3rd generation mobile communications by the ITU in the second half of 2007, and the 2.3GHz band, which is the frequency band of WiBro, was selected as a global common frequency band for 4th generation mobile communications, and was also evaluated as a 3.5G technology that increased the possibility of 4G (fourth generation) mobile communications technology. It also adopted multiple antenna technology (MIMO).

However, WiBro did not receive much attention for a long time because most telecommunications companies focused on developing LTE, despite expectations. In the 2010s, the speed of the telecommunications network increased like a rocket gaining momentum.

SKT and LG U+ commercialized the first 4G (LTE) service in Korea in July 2011. Although KT was late in launching its LTE service, it attracted subscribers by enabling 3G rate plans to be opened on LTE terminals acquired from manufacturers in advance.

LTE is an abbreviation for 'Long Term Evolution', and it is known that it was adopted to mean an evolved version of existing generation technologies such as WCDMA. Initially, LTE was classified as 3.9G, which was regulated and developed by 3GPP, but was later called 4G. It has the advantage of greatly increased transmission speed and efficiency, improved performance, and minimized transmission delay.

The data transmission speed of LTE is measured to have achieved a maximum speed of 75 Mbps based on a 20 MHz bandwidth. The theoretical maximum speed reached 1 Gbps. Based on this speed, LTE has enabled an increase in data traffic capacity for the proliferation of mobile devices such as smartphones and IoT, and has provided revenue generation opportunities for new application services.

Meanwhile, the LTE service area spread from the metropolitan area to the entire country, and the number of domestic LTE users exceeded one million at the end of 2011. It increased rapidly, and after mid-2012, the number of LTE service subscribers exceeded 10 million.

■ Broadband LTE-A Appears... Fierce Frequency Competition Begins




The bandwidth of the frequency is proportional to the communication speed. In other words, the more bandwidth, the faster the speed. With the introduction of LTE, the frequency allocation and auctions of domestic telecommunications companies have become fierce. The initial frequency of the LTE service was 850MHz (5 bands) for SKT and LG U+, and 1.8GHz (3 bands) for KT, with each being allocated a bandwidth of 10MHz.

In August 2013, an additional frequency auction was held, after which SKT was allocated 850MHz and 1.8GHz, KT was allocated 1.8GHz (3 bands) and 900MHz, and LG U+ was allocated 20MHz of 850MHz and 2.6GHz (7 bands).

At this time, the three telecommunication companies began to compete by introducing marketing terms such as LTE-A and broadband LTE. The LTE-A serviced by SKT and LG U+ was the most competitive when it added a 20MHz bandwidth auxiliary frequency to provide a speed of 150Mbps, which was twice as fast. At this time, the telecommunication companies utilized a technology that combined two different frequencies to increase the speed, which was called 'carrier aggregation.'

'Carrier aggregation' is a method of combining two frequencies of each telecommunications company to use the maximum speed. It is explained that applying CA technology to multiple 10MHz bandwidth frequencies to overcome the limitations of frequency bandwidth has the same effect as a frequency with a 20MHz bandwidth. For example, you can increase the speed by increasing the number of cylinders in a car engine from 4 to 8. This is similar to 'Wi-Fi dual band', which is like using two antennas to capture two Wi-Fi frequency bandwidths.

However, this method had the problem of being expensive because it required installing base stations across the country. Accordingly, the telecommunications company introduced the concept of 'broadband LTE-A', which does not require additional base station installation by broadening the existing frequency band.

In September 2013, SKT and KT began providing broadband LTE-A services in Seoul based on the 1.8GHz (3 bands) band, which was called the golden frequency at the time. However, strictly speaking, the service was provided only for the download band, and the upload band was separated by 10MHz and 5MHz, so spectrum aggregation (CA) technology was still required.

Since then, the three mobile carriers have launched broadband LTE-A services, 3-band combined services, etc. In 2016, in the third frequency auction, LG U+ was allocated 2.1GHz band, SKT 40MHz and 20MHz of 2.6GHz (7th band), and KT 200MHz of 1.8GHz (3rd band), and they began providing broadband upload services.

Since the commercialization of LTE, traffic has been used more than 20 times that of 3G, reaching capacity limits, and the advent of 5G is beginning to be anticipated.