Enhancing reliability and spectral efficiency in future wireless networks via intelligent omni-surface enhanced MU-MIMO cooperative hybrid NOMA

Bringing Better Wireless to Every Corner

As our world fills with connected devices, from smartphones to self-driving cars and remote sensors, today’s wireless networks are struggling to keep up. The next generation of networks, often called beyond-5G or 6G, must deliver huge data rates, ultra-reliable links, and coverage even in hard-to-reach places. This paper explores a new way to shape and reuse radio waves in the air so that more users can be served at once, with higher efficiency and lower energy cost, without simply cranking up transmit power or building forests of antennas.

A Smart Wall That Bends Signals

At the heart of the study is a technology known as an intelligent omni-surface, or IOS: a thin, engineered panel made of many tiny elements that can reflect signals back and also bend them through to the opposite side. Unlike traditional smart surfaces, which only work on one side, an IOS can cover all directions around it. The authors place this smart surface between a base station with multiple antennas and a crowd of user devices. By carefully adjusting the tiny elements on the surface, incoming radio waves are redirected toward users on both sides, strengthening weak links and expanding coverage into areas that would otherwise be dead zones.

Sharing the Air Without Getting in the Way

To squeeze more users into limited radio spectrum, the system builds on a scheme called hybrid non-orthogonal multiple access, or hybrid NOMA. Instead of giving each user its own separate slice of frequency or time, certain users are paired and share the same resources, mainly separated by how much power they receive and how well their channels behave. A stronger user with a good link is paired with a weaker user at the edge of coverage. The strong device first decodes the weak device’s data and then its own, and it also acts as a helper: in a second step, it relays a cleaned-up copy of the weak user’s data, again through the IOS. This two-phase cooperation, combined with multi-antenna beamforming at the base station and signal shaping at the surface, greatly boosts the chance that the weak user receives a reliable message.

Designing for the Real World, Not a Perfect One

Most earlier studies assume flawless hardware and perfect interference cancellation, which is unrealistic in practice. Here, the authors build detailed mathematical models that explicitly account for leftover interference after cancellation and for imperfections in radio components, such as phase noise and amplifier distortions. They derive closed-form expressions that predict how often users will lose their connection (outage probability), how much useful data can be delivered (throughput), and how effectively the spectrum is used overall (sum spectral efficiency). Simulations confirm that these formulas closely match what happens in realistic conditions, providing a reliable toolkit for engineers designing future networks.

Smarter Pairing and Power, Not Just More Hardware

A key finding is that how users are paired and how power is split between them matters as much as the raw hardware. Among several pairing strategies, the so-called strong-weak strong-weak pattern—where users are sorted by channel quality and grouped to balance strengths and weaknesses—delivers the best results. Compared with other pairing methods, this strategy gives both strong and weak users noticeable gains in signal-to-noise ratio and extra bits per second per hertz of throughput. The authors also introduce a low-complexity rule for choosing power levels in the first transmission phase. This rule reaches nearly the best possible sum spectral efficiency while still meeting each user’s minimum data rate, and it does so without heavy iterative optimization.

More Benefit from Passive Tiles Than from Extra Antennas

Perhaps the most striking outcome is an energy-efficiency lesson. When the authors compare adding more active antennas at the base station with simply enlarging the IOS by adding more passive tiles, they find that the passive approach wins. Doubling the number of IOS elements yields roughly double to triple the performance gains compared with doubling the number of antennas, yet those tiles consume far less power and are cheaper to deploy. Even when the surface can only use a few discrete phase settings, or when it operates in a “blind” mode without detailed channel knowledge, performance remains close to the ideal. Overall, the study suggests that smart, passive surfaces combined with cooperative user behavior can deliver the reliability, coverage, and efficiency that future 6G networks demand, without an unsustainable explosion in active hardware.

Citation: Kennedy, H.S.J., Kumaravelu, V.B., Selvaprabhu, P. et al. Enhancing reliability and spectral efficiency in future wireless networks via intelligent omni-surface enhanced MU-MIMO cooperative hybrid NOMA. Sci Rep 16, 10407 (2026). https://doi.org/10.1038/s41598-026-39361-2

Keywords: intelligent omni-surface, hybrid NOMA, 6G wireless, massive MIMO, spectral efficiency