5G has two new frequency bands: sub-6 GHz (3.5 - 7 GHz) and mmWave (24 - 100 GHz). 5G sub-6 GHz, with a frequency relatively close to the 4G frequency range, is a popular choice because it finds a balance between providing excellent data throughput and being reasonably priced. According to IDTechEx's "5G Market 2023-2033: Technology, Trends, Forecasts, Players" report, 53% of 5G commercial/pre-commercial services as of 2022 are based on sub-6 GHz, with mmWave accounting only for less than 10% of the market. Despite the growing market of 5G, the fact that both 5G sub-6 GHz and mmWave bands have higher frequencies than the previous 4G makes the signal travel distance shorter, with mmWave suffering the most. Hence, new technological improvements are essential to allow 5G deployment to be deployed more cost-effectively.

Massive Multiple Input, Multiple Output (MIMO) technology has been developed and widely adopted in the 5G era. Massive MIMO technology is important because radio devices with such technology can have 32 or 64 TRX channels, with up to 512 or even more antenna elements, resulting in much better capacity gain than traditional equipment with only two, four, or at most eight TRX channels.

Massive MIMO's most essential characteristic is to improve coverage on new and higher 5G frequency bands through beamforming, allowing for the same coverage on 5G bands as on 4G utilizing the old site grid. In addition to this, other benefits of massive MIMO bring along include:

Allow users connected to the same base station to share time and frequency resources, which greatly increases network capacity without the need for more dense base stations or a wider bandwidth.

Provide more possible signal paths and better performance in terms of data rate and link reliability

Utilize beamforming technology, increasing spectrum efficiency

Massive MIMO provides far greater vertical flexibility compared to traditional MIMO

Reduce Total-cost-of-ownership (TCO) per capacity in high traffic load scenario

In summary, massive MIMO technology is the key in 5G to increase capacity, enhance network coverage, and thus improve user experience.

According to Ericsson's statement on their 5G sub-6 GHz deployment in China, the ratio of mMIMO radios in the areas they covered was approximately 80% Massive MIMO vs. 20% conventional RRU (remote radio unit) solutions for the 5G sub-6 GHz spectrum at 3.5 GHz. Though the ratio varies based on the deployment environment, it is higher in dense metropolitan areas and lower in suburban areas. For a given deployment scenario, the ratio of Massive MIMO to RRU is predicted to grow with time.

Despite being on the market for 2-3 years, large MIMO radios are still under continuous development since there are still some obstacles ahead. Key development trends of massive MIMO radios include (1) Weight and size reduction, (2) Power consumption reduction, (3) Effective isotropic radiated power (EIRP) improvement, and (4) Thermal management.

Si technology is one of the key components to continuously shrink massive MIMO radio size and weight and reduce power consumption. In telecom systems, 95% of the functionality on a radio base station receiver board is signal processing, which relies on one or several powerful Si pieces to execute. Hence, having a well-designed Si is critical for building lightweight, more power-efficient massive MIMO base stations. The "5G Market 2023-2033: Technology, Trends, Forecasts, Players" research from IDTechEx has a more in-depth discussion on power consumption management made possible by Si innovations from various companies. The selection of semiconductors for power amplifiers is another important factor essential to massive MIMO. It is estimated that the PA consumes more than 60% of the radio's electricity. As a result, having a high-efficiency power amplifier is crucial, and the current development trend for achieving the goals includes (1) integrating more discrete stepsa single package and (2) adopting new technology such as high-efficiency GaN. Last but not least, software development is as important to hardware advancement. Implement suitable software and/or use AI/ML in the system, for example, to optimize energy usage throughout the whole network infrastructure.