OISMA: Optical Intelligent Surface Multiple Access

• OISMA is an optical multiple-access paradigm that integrates ORIS with FSO systems to create virtual LoS via beam steering and beam splitting.
• The framework employs downlink NOMA with dynamic power allocations to serve dual receivers without direct LoS, thereby enhancing spectral efficiency over OMA schemes.
• Analytical results incorporate atmospheric loss, turbulence, and 3D pointing errors, with Monte Carlo simulations validating its superior outage performance.

Searching arXiv for the OISMA paper and closely related context papers. OISMA, short for Optical Intelligent Surface Multiple Access, denotes an optical wireless multiple-access paradigm in which optical reconfigurable intelligent surfaces (ORISs) enable multi-user free-space optical (FSO) connectivity through beam steering and beam splitting. In the formulation introduced for downlink ORIS-enabled non-orthogonal multiple access (NOMA), a single optical transmitter serves two receivers through an ORIS, with no direct line-of-sight (LoS) between the transmitter and receivers. The framework is motivated by the use of ORISs to create virtual LoS paths, mitigate LoS constraints, and support simultaneous multi-user service with analytical performance characterization under atmospheric loss, turbulence, and 3D pointing errors (Chondrogiannis et al., 10 Feb 2025).

1. Conceptual definition

OISMA is presented as the integration of ORISs into FSO systems to realize optical multiple access. Its central premise is that an ORIS can do more than passively reflect an optical beam: it can reorient the incident beam toward selected users, split that beam into distinct optical branches, and thereby enable multi-user communication in scenarios where the transmitter does not have direct LoS to the receivers (Chondrogiannis et al., 10 Feb 2025).

Within this formulation, ORISs are identified as key enablers of next-generation FSO multiple-access systems because they address a structural limitation of FSO links: the dependence on LoS. By redirecting and splitting optical beams, an ORIS creates virtual LoS paths and supports multi-user connectivity. The paper places this functionality specifically in the context of downlink NOMA, where multiple users are served simultaneously using the same resources but with different power allocations and beam-splitting ratios, yielding higher spectral efficiency and user capacity than orthogonal multiple access (OMA) schemes (Chondrogiannis et al., 10 Feb 2025).

A useful distinction is that OISMA, in this formulation, is not merely a reflective relay architecture. The ORIS is an active configurational element in the system model, controlling beam direction and optical power partitioning. This suggests that the “multiple access” aspect of OISMA arises jointly from optical surface control and NOMA superposition rather than from multiplexing at the transmitter alone.

2. System model and signal structure

The canonical OISMA configuration consists of a single optical transmitter (Tx), an ORIS, and two receivers (Rxs). Communication is entirely mediated by the ORIS; the model assumes no direct LoS between the transmitter and receivers, while the ORIS maintains LoS with both the Tx and the two Rxs. The transmitter is a single optical source employing intensity modulation/direct detection (IM/DD) (Chondrogiannis et al., 10 Feb 2025).

In this system, the ORIS performs three stated functions:

• Beam steering toward desired directions
• Beam splitting into distinct beams toward each user
• Power control through splitting factors $B_1$ and $B_2$

Possible realizations mentioned for the ORIS include mirror arrays and, preferably because of fast response, optical metasurfaces (Chondrogiannis et al., 10 Feb 2025).

The receivers collect the reflected optical signal and operate under a NOMA decoding structure. The transmitted superposition signal is

$x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$

where $x_j$ is the data stream for receiver $j$, $P$ is the total transmit power, and $a_1 + a_2 = 1$. The received signal at receiver $j$ is

$y_j = B_j h_j x + n_j,$

with beam-splitting factor $B_j$, channel gain $B_2$0, and noise $B_2$1 (Chondrogiannis et al., 10 Feb 2025).

The receiver roles are asymmetric. Rx1 decodes its message directly while treating the other stream as interference. Rx2 applies successive interference cancellation (SIC): it first decodes and cancels Rx1’s message and then decodes its own message. This asymmetry is standard within the specific NOMA structure adopted in the model (Chondrogiannis et al., 10 Feb 2025).

3. Channel modeling and propagation impairments

A central contribution of the OISMA framework is the analytical characterization of the Tx–ORIS–Rx channel under realistic optical impairments. The end-to-end channel gain for receiver $B_2$2 is modeled as

$B_2$3

where $B_2$4 denotes deterministic path or atmospheric loss, $B_2$5 models atmospheric turbulence, and $B_2$6 captures 3D pointing error between the ORIS and receiver $B_2$7 (Chondrogiannis et al., 10 Feb 2025).

The turbulence component is modeled using the Gamma-Gamma distribution, while the pointing-error component follows a 3D misalignment model associated with effects such as building sway. The framework therefore combines deterministic attenuation, stochastic turbulence, and geometric misalignment within a single end-to-end optical channel model. The authors derive analytical expressions for the corresponding PDF and CDF and report tractable series representations involving Meijer $B_2$8-functions to capture the convolution of turbulence and pointing effects (Chondrogiannis et al., 10 Feb 2025).

This modeling choice is significant because it places OISMA analysis beyond idealized beam-redirection assumptions. The framework explicitly treats the ORIS-assisted optical path as subject to the same classes of impairments that dominate practical FSO performance. A plausible implication is that OISMA design cannot be reduced to geometric beam routing; it is fundamentally constrained by the coupled statistics of turbulence and misalignment.

4. Outage analysis and high-SNR behavior

The performance metric developed most fully for OISMA is outage probability (OP). The paper derives exact analytical expressions for the outage probability of each receiver and supplements them with high-SNR asymptotic expressions (Chondrogiannis et al., 10 Feb 2025).

The instantaneous signal-to-interference-plus-noise ratios are given as follows. For Rx1, which does not use SIC,

$B_2$9

For Rx2, which performs SIC,

$x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$0

where

$x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$1

These expressions expose the joint dependence of receiver performance on NOMA power coefficients, ORIS beam-splitting factors, and the end-to-end optical channel (Chondrogiannis et al., 10 Feb 2025).

At high SNR, the analysis yields the diversity order

$x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$2

where $x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$3 and $x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$4 are turbulence parameters and $x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$5 is related to pointing-error statistics. The asymptotic analysis identifies the dominant limiting factor: when turbulence is weak, pointing errors dominate performance, whereas under strong turbulence, turbulence dominates. This separation is analytically useful because it indicates which physical impairment sets the outage slope in different operating regimes (Chondrogiannis et al., 10 Feb 2025).

5. Comparative performance and validation

The analytical framework is validated by Monte Carlo simulations, and the reported simulation and analytical results match perfectly. The numerical study examines transmit SNR, beam-splitting ratios, power allocation, atmospheric parameters, turbulence strength $x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$6, and user distances (Chondrogiannis et al., 10 Feb 2025).

The principal comparative result is that ORIS-enabled NOMA consistently outperforms traditional OMA in outage probability across the considered scenarios. The abstract states that simulations “showcase its superiority over its orthogonal-based counterpart,” while the detailed summary specifies that lower outage probability is observed especially as spectral-efficiency or user-density targets increase (Chondrogiannis et al., 10 Feb 2025).

The reported gains are tied to two mechanisms. First, ORIS functionality relaxes the direct-LoS requirement by redirecting and splitting the optical beam. Second, NOMA allows simultaneous service of multiple users with differentiated power allocation. In combination, these mechanisms make OISMA a multiple-access architecture rather than only an LoS-restoration technique.

The study also emphasizes parameter trade-offs. Power-allocation coefficients $x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$7 and beam-splitting factors $x = \sqrt{a_1 P} x_1 + \sqrt{a_2 P} x_2,$8 must be tuned for fairness and performance, and the authors identify optimal or fair allocation as a topic for future work. This indicates that OISMA performance is highly configuration-dependent even within the two-user downlink setting (Chondrogiannis et al., 10 Feb 2025).

6. Research significance, scope, and limitations

OISMA occupies a specific place within optical wireless communications research: it is formulated as an ORIS-assisted FSO multiple-access system rather than as a generic optical networking abstraction. Its significance lies in the combination of three elements that are usually treated separately in optical-link studies: LoS reconstruction, multi-user access, and rigorous outage analysis under realistic optical impairments (Chondrogiannis et al., 10 Feb 2025).

A common simplification would be to view the ORIS as only a passive reflector. In the OISMA formulation, that view is incomplete. The ORIS is modeled as supporting precision beam steering, beam splitting, and controllable power allocation, which are precisely the capabilities that make multiple-access operation possible. Likewise, the system is not presented as a direct replacement for orthogonal access in all optical settings; rather, its analyzed advantage is established within the stated two-receiver NOMA model and the considered outage criterion (Chondrogiannis et al., 10 Feb 2025).

The framework also has explicit scope conditions. The modeled system uses a single transmitter and two receivers, assumes communication entirely via the ORIS, and evaluates performance primarily through outage probability and high-SNR asymptotics. This suggests that broader OISMA generalizations—such as many-user scheduling, fairness-optimal control, or alternative receiver architectures—remain open problems rather than completed parts of the current analytical framework.

In that sense, OISMA can be understood as a foundational formulation for ORIS-enabled optical multiple access: it identifies the physical mechanisms, establishes the channel model, derives receiver-wise outage expressions, and demonstrates that ORIS-enabled NOMA outperforms its orthogonal counterpart under the modeled conditions (Chondrogiannis et al., 10 Feb 2025).