The reasons for the stagnation of mmWave deployment in Japan can be summarized as follows

• Narrow coverage: Due to the strong straightness and the influence of shielding, coverage is very narrow (even without shielding, 100-200 meters is a realistic distance). Indoors, it is difficult to cover multiple floors with a single base station, and it is difficult to cover multiple rooms on a single floor except for the room near the base station.
• Complex and expensive: Unlike Sub 6 SA, 28 GHz NSA requires 4G as an anchor band. Therefore, the system configuration is more complex than Sub 6 SA, and the cost of 4G equipment is added in addition to the local 5G equipment. The 4G frequency used as the anchor band is an autonomous BWA frequency, which is the same band as local BWA frequencies in Japan, so it is difficult to use outdoors, especially in cities, due to interference issues. 
• Few devices and high cost: Local 5G devices (industrial routers, etc.) that support millimeters are few and expensive. As a result, they are mostly used as repeaters that convert to Wi-Fi, which in some cases obviates the need for local 5G. 
• Vendors focus development on Sub 6 equipment: Since Sub 6 was opened in December 2020, vendors have focused on Sub 6 products because of their wide coverage, simple configuration, and relative ease of development.
• Focus on developing local 5G Sub 6 use cases: Use case designs are being made within the scope of the Sub 6 specification rather than use cases that take advantage of the ultra-wide bandwidth of mmWave.

On the other hand, Sub 6 SA networks are the opposite of the shortcomings of mmWave networks in each of the above items. Currently, the local 5G network in Japan is dominated by Sub 6 SA.

3. Industry trends related to local 5G in Japan and the future of local 5G (=5G SA NR-DC)

♦ Currently, operators providing local 5G network construction and operation services for enterprises, such as NTT East, NTT com, and NSSOL, are mainly building local 5G networks with 4.7 GHz 5G SA. However, we do not see any cases of networks being built with 28GHz SA, or NR-DC (New Radio-Dual Connectivity) SA.​

♦ For example, NTT East launched a local 5G network deployment service called Gigiraku 5G (a 4.7 GHz SA service) in 2022, and as of February 2023, it has more than 50 deployments, of which six are 5G NSA network deployments using 28 GHz, and all six are at the level of test lab environment, and three of them are Ministry of Internal Affairs and Communications demonstration projects. There are also no 28GHz SA or NR-DC SA services, which are more advanced network architectures than 28GHz NSA.

♦ The Japanese industry is proposing the parallel use of mmWave and Sub 6 as the next version of local 5G, which is currently a Sub 6 SA network architecture. In Japan's public 5G network, NR-DC services using a combination of Sub 6 and mmWave have already been commercialized for smartphones, with NTT DoCoMo launching NR-DC services in August 2022 in areas with large crowds, such as train stations and event venues (using DoCoMo's public 5G network frequencies Sub 6 (3.7 GHz band/4.5 GHz band) and mmWave frequencies in the 28 GHz band: maximum network speeds of 1.1 Gbps uplink and 4.9 Gbps downlink). 

♦ Starcat Cable opened its local 5G NR-DC lab in March 2023 to provide a free NR-DC demonstration environment for Sub 6 (local 5G: 4.6 to 4.9 GHz) and mmWave (local 5G: 28.2 to 29.1 GHz). NR-DC uses 4.7 GHz and 28 GHz simultaneously to increase communication reliability and enable local 5G to provide ultra-high capacity uplinks and downlinks. It is also an SA configuration that uses only 5G NR, which enables full utilization of SA features such as ultra-low latency, multi-connectivity, and network slicing. It is expected to be utilized for demonstration trials of high-speed, high-capacity applications such as 8K camera high-definition video transmission.

<StarCat's NAGOYA LOCAL5G LAB configuration diagram: NR-DC 5G network equipment Samsung/5G terminals Kyocera>

♦ In April 2023, NTT Com established a local 5G NR-DC lab and confirmed communication speeds of 337.3 Mbps on average uplink and 3.1 Gbps on average downlink. NTT Com cites the delivery of ultra-high-resolution MRI/CT data in tele-cooperative surgery (downlink) and the simultaneous delivery of videos from multiple viewpoints, such as surgeons and nurses, to remote specialists (uplink) as anticipated use cases. It will also be used in cases requiring high-speed transmission and reception capacity (uplink), such as simultaneous delivery of multiple high-definition images or remote control of multiple devices.

♦ In the announcement of the 5G Business Working Group of the Ministry of Internal Affairs and Communications in 2023, NEC presented the issue of the current main local 5G network, Sub 6, and the parallel operation of Sub 6 and mmWaves as a solution. NEC cites the following situation as an example where this parallel operation is necessary. In a place where many construction equipments are densely packed, real-time transmission of multiple camera videos per equipment to the remote operation room (requires large-capacity uplink). It is reported that in applications requiring large-capacity uplinks within the workplace, the Sub 6 network has limitations and mmWaves must be additionally introduced.

<Utilizing mmWave in dense construction equipment areas to increase uplink capacity and build low-latency networks with low signal transmission latency>

♦ For the time being, local 5G adoption is expected to be centered on Sub 6, but as the number of local 5G terminals in the workplace increases and applications become high-capacity (especially uplinks), mmWave will be utilized again by adding 28 GHz base stations to the existing Sub 6 network (NR-DC) that can provide high-capacity uplinks at a time when the uplink of the Sub 6 local 5G network becomes a communication bottleneck.

<Network Architecture Evolution of Local 5G from the Japanese Industry's Perspective>

The three-year demonstration project of the Ministry of Internal Affairs and Communications described above is mostly an application where on-site situations captured by high-definition cameras are transmitted to AI servers or control rooms through the local 5G network. In other words, the downlink capacity of the Sub 6 local 5G network is larger than the uplink, and the actual traffic generated is mostly uplink traffic, unlike the public network. 

For example, in the case of real-time monitoring with 4K cameras, one camera generates about 20~25Mbps of data, and if 10 cameras are operated, the Sub 6 100MHz bandwidth (64QAM, 2x2 MIMO, synchronous operation) will use up all the uplink capacity, making it difficult to use other 5G devices. 

On the other hand, the 400 MHz bandwidth of mmWave (64 QAM, 2x2 MIMO, synchronous operation) can provide up to 800 Mbps of communication capacity on the uplink, leaving plenty of room for additional 4K cameras and other 5G devices. Ultimately, it's the need for high-capacity uplinks that is driving the adoption of mmWave in local 5G networks.