[Report] First Time on the Subway... Telecom 5G 28GHz Experiment

Division of Roles Among Three Companies... Application of Samsung Equipment
First Challenge for Moving Objects at 60~70km/h
Wi-Fi Download Speed 600~800Mbps
More Than 8 Times Faster Than Regular Subway
Intermittent Disconnections... Need for Improvement

Cho Kyung-sik, Vice Minister of Science and ICT, is listening to an explanation before boarding the subway at the '5G 28GHz-based Subway Wi-Fi Performance Improvement Demonstration Launch Event' held on the platform of Sindap Station on Seoul Subway Line 2 on the afternoon of the 28th. Photo by Cha Min-young

[Asia Economy Reporter Cha Min-young] 'Average 600~800 Mbps (megabits per second, a speed capable of transmitting one million bits per second)'

This is the Wi-Fi download speed measured on the Seongsu-bound Line 2 subway departing from Sindap Station in Seoul around 3:30 PM on the 28th. It is more than eight times faster than the usual Wi-Fi speed of 71.05 Mbps in a typical subway car.

The on-site demonstration was conducted in the presence of officials from the Ministry of Science and ICT, the three mobile carriers (SK Telecom, KT, LG Uplus), Samsung Electronics, and the Electronics and Telecommunications Research Institute (ETRI), who form the '5G 28 GHz Deployment Activation Task Force.' This result was achieved after six months of work since the task force was formed in March. Due to the nature of the space?a four-car Line 2 subway used by ordinary citizens?there were challenges during the deployment process.

Vice Minister Jo Kyung-sik is observing the demonstration process of measuring the Wi-Fi download speed value based on 5G 28 GHz on a Line 2 train car. Photo by Ministry of Science and ICT

The highest Wi-Fi download speed based on 5G 28 GHz recorded that day was 1.2 Gbps (gigabits per second, a speed capable of transmitting one gigabit per second). While stable sections maintained speeds around 800~900 Mbps, there were intermittent dropouts. This speed was more than three times faster than the simultaneously measured LTE-based Wi-Fi speeds of 100~300 Mbps.

5G 28 GHz is known for its high transmission speed but has the drawback of a short reach distance. In subway tunnels, where natural phenomena like rain or snow and other interferences are minimal, it is possible to secure a longer reach distance, making it a suitable alternative technology for improving subway Wi-Fi quality.

The technical principle is as follows. The 5G 28 GHz signal is sent through a base station, received by a Customer Premises Equipment (CPE), and then transmitted again via optical fiber using a handover method (a technology that enables seamless service between base stations). Newer trains are equipped with optical fiber as a standard, enabling the establishment of a demonstration network. The need for optical fiber and the impossibility of a fully wireless connection remain points of consideration.

The section between Sinseol-dong Station and Seongsu Station was chosen as the pilot site due to its geographical advantages. Park Tae-wan, Director of Frequency Policy at the Radio Policy Bureau of the Ministry of Science and ICT, explained, "Seoul Metro frequently uses this area as a pilot space. There are three aboveground and two underground stations, allowing tests in both aboveground and underground environments."

5G 28㎓ Wi-Fi Installation in Subway. Wi-Fi wireless access point (AP) device installed on one side of the luggage compartment wall inside the train car. Photo by Cha Min-young

Along the Seongsu branch line, 26 integrated antenna-type 5G 28 GHz base stations were installed. The three telecom companies shared various roles, including optical fiber installation, electrical wiring work, and base station equipment installation. The equipment is from Samsung Electronics. Communication facilities such as 10 CPEs and 20 Wi-Fi 6E routers were installed in the train driver's cabin. Notably, the CPE routers are products of the domestic SME Hucom Wireless, recognized for their technology over foreign CPEs. Vice Minister Cho Kyung-sik stated, "The CPE routers are domestically produced equipment. Samsung terminals are also necessary, and this can serve as a reference and opportunity for the domestic equipment ecosystem."

I searched for the Wi-Fi network directly on the reporter's smartphone inside a Line 2 train car equipped with 5G 28㎓-based Wi-Fi. Currently, Wi-Fi connection is blocked due to security issues. Photo by Cha Min-young

The three mobile carriers plan to conduct about a month more of testing. During the demonstration period, they will continue to improve subway Wi-Fi speeds while simultaneously conducting technical verification. In addition to improvements on the router modem side, enhancements within the subway cars themselves are also necessary.

The public release is expected within this year. Vice Minister Cho Kyung-sik said, "By around November, we expect to announce plans on how to implement 28 GHz in other subways in consultation with the Seoul Metropolitan Government. We will continue research and discussions with relevant agencies to make an announcement within the year." It is also anticipated that plans for expanding application to everyday life will be included.

Meanwhile, prior to the demonstration kickoff meeting, Vice Minister Cho Kyung-sik held a roundtable with the three telecom companies, Seoul Metro, Samsung Electronics, and others to discuss future demonstration plans and activation measures for 5G 28 GHz.