Terminology » Massive MIMO vs Ultra Massive MIMO : Key differences

Massive MIMO vs Ultra Massive MIMO : Key differences

wireless 6g massive mimo ultra massive mimo um-mimo mimo

Introduction : With the rapid growth of wireless communication technologies, the demand for higher data rates, improved spectral efficiency and reliable connectivity has led to the development of advanced antenna systems such as MIMO, massive MIMO and UM-MIMO.

Massive MIMO : Massive Multiple Input Multiple Output is a key technology in 5G networks that uses a large number of antennas at the base station to serve multiple users simultaneously.

Massive MIMO is central to current 5G networks, offering high spectral efficiency and robust multi-user communication.

UM-MIMO : As networks evolve toward 6G, the concept has been further extended to Ultra Massive MIMO (UM-MIMO), which employs an even larger scale of antenna arrays, often reaching thousands of elements. This advancement enables terahertz communication, enhanced beamforming precision and unprecedented data throughput.

Ultra Massive MIMO is envisioned for 6G and beyond, leverages extremely large antenna arrays operating at millimeter wave and terahertz frequencies to achieve ultra high data rates, precise beamforming and energy efficient communication.

Key differences

Feature	Massive MIMO (in 5G)	Ultra-Massive MIMO (for 6G)
Generational Context	A foundational technology for the 5G New Radio (NR) standard.	A key enabling technology envisioned for the future 6G standard.
Scale of Antenna Array	Employs a “large” number of antenna elements, typically in the tens to a few hundred (e.g., 64, 128, 256).	Employs an “extremely large” or “Giga” number of antenna elements, scaling into the thousands or more.
Primary Operating Frequency	Operates in sub-6 GHz and millimeter wave (mmWave) frequency bands (e.g., 28 GHz, 39 GHz).	Designed to operate in much higher sub-Terahertz (sub-THz) and Terahertz (THz) frequency bands (e.g., above 100 GHz).
Antenna Density & Size	The shorter wavelengths of mmWave allow for a relatively compact and dense packing of antenna elements.	The extremely short wavelengths of THz allow for unprecedented density, packing thousands of minuscule antennas into a similar physical area.
Dominant Physics	Operates predominantly in the far-field, where radio waves can be modeled as flat “plane waves.”	Operates increasingly in the near field, where waves are curved “spherical waves,” requiring entirely new channel models and algorithms.
Beam Characteristics	Generates a large number of sharp, steerable beams to serve multiple users simultaneously.	Generates a vast number of ultra-narrow, “pencil-like” beams with extreme spatial precision and resolution.
Primary Application Goal	Primarily used to drastically increase spectral efficiency, network capacity, and link reliability.	Extends this goal to also be a core enabler for high-resolution Joint Communications and Sensing (JCAS), using the beams to “see” the environment
Core Technical Challenge	Managing channel estimation overhead, inter-user interference, and efficient beam management.	Overcoming the fundamental challenges of near-field physics and the immense signal processing complexity.
Hardware & Power Challenge	Managing the complexity and cost of hundreds of Radio Frequency (RF) chains.	Managing extreme power consumption and heat dissipation from thousands of active RF chains packed into a small space.
Underlying Antenna Tech	Utilizes conventional microstrip patch antenna array designs.	May require new and futuristic antenna technologies, such as the plasmonic antennas mentioned in the document, to be physically realized.

Summary : Both Massive MIMO and Ultra Massive MIMO aim to enhance wireless communication capacity and efficiency through the use of multiple antennas, but they differ significantly in scale, frequency range and performance potential. As research progresses, Ultra Massive MIMO is expected to overcome the physical and technical limitations of Massive MIMO, paving the way for the next generation of intelligent and immersive wireless networks.