Next-generation applications in communications require a low-cost mobile fronthaul (MFH) network architecture. We propose two quantization noise suppression schemes for low-order sigma-delta modulation (SDM) over fiber, subtracting either (1) one-bit sigma-delta modulation or, (2) analog noise modulation, of the in-band noise from the SDM signal. The resulting signals, unequal PAM-4 or quasi-one-bit respectively, allow the original signal to be recovered using only a simple bandpass filter, significantly reducing the overall system design and cost. The noise component is small relative to the desired signal such that intensity-modulation/direct-detection (IM-DD) can be used for low-cost distributed massive multiple-input multiple-output (M-MIMO) applications. Experimental results show EVM performance improvements of 256-QAM OFDM by 4.6 dB and 6.9 dB respectively, along with minimum optical dynamic ranges of 5 dB and 7 dB.

This work demonstrates a real-time full-stack 5G radio access network (RAN) integrating optical wireless communication (OWC) links as fronthaul and backhaul.

Radio Frequency Identification (RFID) is frequently deployed in high tag density environments, where tag read rate can become a limiting factor. Current Class 1 Gen 2 (C1G2) RFID systems are limited in read rate by the Framed Slotted Aloha (FSA) scheduling algorithm and physical layer modulation parameters. We propose a multi-user MIMO (MU-MIMO) RFID system compatible with C1G2 which enables simultaneous communication with multiple tags, achieving greater read rates. Multiple monostatic reader antennas are exploited to recover collided tag data and perform channel estimation. These channel estimates are then used to precode the reader’s ACK signals across multiple transmit antennas into spatial channels such that the tags will receive separated acknowledgements. To evaluate potential performance gains, we calculate theoretical throughput improvements and empirically measure the signal-to-interference ratio (SIR) required for commercial passive tags to respond to collided acknowledgements. Furthermore, we perform simulations to determine the effect of increasing number of tag responses on channel estimation accuracy, and hence the received SIR at tags. An experiment is carried out using two monostatic transceivers with two emulated tags, showing successful channel recoveries and uncollided reader acknowledgments commands at the tags, and hence compatability with C1G2 protocol provided a reader can be developed meeting the timing requirements.

This paper introduces novel sensing applications leveraging tag-to-tag communication. Building on a prior method for inter-tag channel estimation, we explore various proof-of-concept sensing modalities enabled by this technique and compare these to conventional reader to tag measurements. We demonstrate that tag displacement information, including both 1D and 2D localization, can be accurately estimated. Specifically, our approach achieves better than 2.5 cm error in over 90% of the test locations with only a single reader antenna. Furthermore, we investigate the inter-tag channel dependence on angular misalignment of the tags, and show that the inter-tag channel phase is independent of rotation and hence our method is robust to tag angular misalignment. Finally we demonstrate liquid level sensing of a container in the inter-tag channel, showing that the fill level of a bottle can be estimated, independent of its position.

A novel VCSEL structure capable of electronic beam steering is proposed. By etching the anode contact to form two independently biased electrodes, 1D 4°-6° far-field beam switching is demonstrated.

The increasing demands for data throughput and efficiency in next-generation Radio Access Networks (RAN) necessitate innovative solutions for the optical fronthaul. This work presents an AI-driven equalisation framework integrated with digital automatic gain control (DAGC) for compressive optical fronthaul systems. The proposed system uniquely performs joint phase and timing recovery while mitigating channel impairments, noise, and compression-induced signal loss. Leveraging a Convolutional Neural Network (CNN) architecture optimised through iterative pruning and quantisation, the model achieves high sparsity and reduced computational complexity. Experimental results demonstrate significant enhancements in Error Vector Magnitude (EVM) over the conventional technique, enabling efficient support for high-order modulation schemes. By addressing key challenges in lossy compression and signal distortion, this approach ensures robust performance, scalability, and low latency in practical 5G and beyond fronthaul scenarios, making it particularly suited for Open RAN architectures.

We demonstrate a simple laser linearization method, applied for the first time to a 405 nm laser-SiPM VLC link. Paired with low-complexity DFE, it achieves 5 Gb/s OOK at an irradiance of 4.1 W/m(2), offering 1.2x data rate and 6.4 dB sensitivity improvement over DFE-only. (c) 2025 The Author(s)

We demonstrate a simple laser linearization method, applied for the first time to a 405 nm laser-SiPM VLC link. Paired with low-complexity DFE, it achieves $5 \text{Gb} / \mathrm{s}$ OOK at an irradiance of 4.1 $\mathrm{W} / \mathrm{m}^{2}$, offering 1.2x data rate and 6.4 dB sensitivity improvement over DFE-only. ©2025 The Author(s)

A 5 x 5 VCSEL array-based optical wireless communication multi-beam transmitter is designed and simulated. Each element of the array addresses a separate spatial attocell. A microlens-array based homogenizer achieves uniform coverage at the receiver plane from each multi-mode VCSEL output. 1 m(2) total coverage is achieved with each attocell covering an area of 400 cm(2) at a range of 3 m. For a proof-of-concept demonstration a 1 x 3 channel VCSEL array-based transmitter prototype is experimentally tested. The performance is verified by demonstrating three channels achieving similar to 0.12 mW/m(2) uniform power with negligible optical interference to adjacent attocells (<-14 dB). With a simple receiver design using low cost, off-the-shelf components, each channel of the transmitter achieves similar to 10 Gb/s throughput using OFDM within 7 cm lateral range and >4 Gb/s within 12 cm lateral range at 3 m. The transmitter meets eye-safety restrictions and could be scaled to 250 Gb/s aggregate data rate by employing all 25 VCSELs with independent OFDM modulation.

In this paper, we put forward a proof of concept for sixth generation (6G) Terabit infrared (IR) laser-based indoor optical wireless networks. We propose a novel double-tier access point (AP) architecture based on an array of arrays of vertical cavity surface emitting lasers (VCSELs) to provide a seamless grid-of-beam coverage with multi-Gb/s per beam. We present systematic design and thorough analytical modeling of the AP architecture, which are then applied to downlink system modeling using non-imaging angle diversity receivers (ADRs). We propose static beam clustering with coordinated multi-beam joint transmission (CoMB-JT) for network interference management and devise various clustering strategies to address inter-beam interference (IBI) and inter-cluster interference (ICI). Non-orthogonal multiple access (NOMA) and orthogonal frequency division multiple access (OFDMA) schemes are also adopted to handle intra-cluster interference, and the resulting signal-to-interference-plus-noise ratio (SINR) and achievable data rate are derived. The network performance is studied in terms of spatial distributions and statistics of the downlink SINR and data rate through extensive computer simulations. The results demonstrate that data rates up to 15 Gb/s are achieved within the coverage area and a properly devised clustering strikes a balance between the sum rate and fairness depending on the number of users.

The demand for high-speed optical wireless communication (OWC) has surged due to the growing number of high bandwidth applications. Directly modulated lasers (DMLs) are a necessary alternative to light-emitting diodes (LEDs) for achieving higher speeds. However, at high data rates, the intrinsic non-linearity of DMLs degrades signal quality, limiting achievable data rates. We demonstrate the application of the ABCD linearization technique to a 2.5 GHz blue laser employing non-return-to-zero (NRZ) and carrierless amplitude/ phase (CAP) modulation. Using a 3.5 GHz PIN photodetector and feed-forward equalizer (FFE), this method improves the achievable data rate by similar to 1.8 times for NRZ, from 3.8 Gb/s to 7 Gb/s, and by 2.3x for CAP-16, achieving 9 Gb/s. These results validate the ABCD approximation method as a simple yet effective solution for mitigating laser non-linearity and enhancing data rates in high-speed OWC systems.

Optical wireless communication (OWC) is a strong candidate in the sixth generation (6G) of wireless communications as it can support data transmission at high communication speeds, low power consumption, high security, and high reliability. Near-infrared lasers, specifically vertical cavity surface emitting lasers (VCSELs), exhibit larger modulation bandwidth compared to light-emitting diodes (LEDs), and can provide aggregate data rates ranging up to Terabit per second (Tbps). This chapter proposes innovative optical transmitter and receiver designs for indoor laser-based wireless communications, aiming to provide seamless coverage in high-speed multi-user scenarios. The proposed optical transmitter is based on a 5 × 5 VCSEL array where each VCSEL can provide 10 Gigabit per second (Gbps) in a uniform coverage area of 20 cm x 20 cm, achieving a total of 250 Gbps in an area of 1 m2 at 3 m transmission distance. Moreover, two wide-FOV receiver designs that employ photodetector (PD) arrays in along with imaging or non-imaging optics are introduced to support such an ultra-high-speed optical link. The new design of OWC requires potential techniques to address various networking challenges, including cell formation, interference management, resource allocation, and backhauling. To this end, potential solutions for these challenges are discussed to help establish an end-to-end OWC infrastructure for practical deployment.

We demonstrate a new backscatter sensing modality that exploits the measurement of the channel between two backscatter tags. This channel is independent of the channel between the reader and each tag. A theoretical basis of the sensor modality for dipole tags in the near field is derived. A proof-of-concept distance sensor, using commercial RFID tags, exhibits conformity to theory and demonstrates separation measurement with sub-centimetre accuracy.

Silicon Photomultipliers (SiPMs) can provide optical wireless communication (OWC) receivers with better sensitivities than PIN photodiodes, thanks to their photon counting capabilities. The commercial availability of SiPM with fast output pulse width allows high-speed data transmission at low irradiance levels. This paper investigates the use of a commercially available SiPM with an active area of 1 mm 2 and fast output pulse width of 0.6 ns in a Near-infrared (NIR) OWC link and compares the performance of a 3 mm x 3 mm SiPM with a fast output pulse width of 1.4 ns. Although both SiPMs have maximum detection efficiency at 450 nm, a wavelength of 850 nm is used owing to the availability of high-speed VCSELs, higher eye safety limit and ability to filter ambient light when using this wavelength. The OWC link is designed and tested at a 35 cm transmission distance using On-Off-Keying (OOK) and Decision Feedback Equalization (DFE), and a maximum data rate of 8.2 Gbps at a BER of 3.8x10 -3 was obtained with 15.34 W/m 2 irradiance at the SiPM. These results are achieved in the dark and under 500 lux of White Light Emitting Diode (WLED) ambient light. A long pass colour glass filter is used to reject light up to 700 nm wavelength, thus rejecting most of the interference from WLEDs, resulting in data rates similar to dark environments. This is the highest data rate achieved using SiPMs in an NIR link.

A novel hybrid analog-digital free space optical fronthaul is proposed. Wideband spectral nulls in the digitized fronthaul allow analog RF insertion, enabling cost-effective simultaneous transmission.

To achieve multi-Gb/s data rates in 6G optical wireless access networks based on narrow infrared (IR) laser beams, a high-speed receiver with two key specifications is needed: a sufficiently large aperture to collect the required optical power and a wide field of view (FOV) to avoid strict alignment issues. This paper puts forward the systematic design and optimisation of multi-tier non-imaging angle diversity receivers (ADRs) composed of compound parabolic concentrators (CPCs) coupled with photodiode (PD) arrays for laser-based optical wireless communication (OWC) links. Design tradeoffs include the gain-FOV tradeoff for each receiver element and the area-bandwidth tradeoff for each PD array. The rate maximisation is formulated as a non-convex optimisation problem under the constraints on the minimum required FOV and the overall ADR dimensions to find optimum configuration of the receiver bandwidth and FOV, and a low-complexity optimal solution is proposed. The ADR performance is studied using computer simulations and insightful design guidelines are provided through various numerical examples. An efficient technique is also proposed to reduce the ADR dimensions based on CPC length truncation. It is shown that a compact ADR with a height of $\leq0.5$ cm and an effective area of $\leq0.5$ cm$^2$ reaches a data rate of $12$ Gb/s with a half-angle FOV of $30^\circ$ over a $3$ m link distance.

Radio Frequency Identification (RFID) is often used in high tag density scenarios where tag read rate becomes a limiting factor. Current Class 1 Gen 2 (C1G2) RFID systems are limited in read rate by the Framed Slotted Aloha (FSA) scheduling algorithm and physical layer modulation parameters. We propose a multi-user MIMO (MU-MIMO) RFID system compatible with C1G2 which is capable of communicating with more than one tag simultaneously allowing greater read rates. Multiple reader receiver antennas are exploited to recover collided tag data and perform channel estimation. The channel estimates are used to precode the reader ACK signals from multiple transmit antennas into spatial channels such that the tags will receive fully separated acknowledgements. An experiment is carried out using two monostatic transceivers with two emulated tags, showing successful channel recoveries and uncollided reader acknowledgments commands at the tags.

An optical wireless receiver at 850 nm is realized, providing 8.6 Gbps maximum data rate and > 7 Gbps data rate across a 9.5 cm lateral coverage at 3 m range with a BER of < 2 × 10 −3 .

The growing demand for traffic shaping and manipulation for efficient last-mile coverage has driven extensive research using emerging artificial intelligence to overcome the capacity hurdle in next-generation wireless systems. In the radio access network (RAN), modulation format can be critical information to determine the channel condition and implement resource allocation and data compression so as to improve the quality of service and spectral efficiency of data transmission. This paper proposes a novel deep learning-based automatic modulation classification algorithm that trains neural networks as classifiers to determine the modulation format of signals transmitted in the RAN. To conquer the problem of limited training data with the received dataset, the proposed algorithm exploits a signal generation method that generates massive simulated data for training instead of relying on the received signal stream. To eliminate the issue of inconsistent data distribution between the training and inferring stages, data augmentation is applied to increase the diversity of training data and enrich the training dataset. The experiment results demonstrate that the proposed algorithm accurately identifies the modulation formats of signals received from the RAN.

This article introduces the general concepts of light fidelity (LiFi) 2.0 for sixth generation (6G) of wireless networks that will be based on indoor laser-based wireless networks capable of achieving aggregate data-rates of terabits per second as widely accepted as a 6G key performance indicator. The main focus of this article is on the technologies supporting the near infrared region of the optical spectrum. The main challenges in the design of the transmitter and receiver systems and communication/networking schemes are identified and new insights are provided. This article also covers the previous and recent standards as well as industrial applications for optical wireless communications (OWC) and LiFi.