Receiver Array Research Articles

Wideband Array Signal Processing with Real-Time Adaptive Interference Mitigation.

Wideband beamforming and interference cancellation for phased array antennas requires advances in signal processing algorithms, software, and specialized hardware platforms. A high-throughput array receiver has been developed that enables communication in radio frequency interference-rich environments with field programmable gate array (FPGA)-based frequency channelization and packetization. In this study, a real-time interference mitigation algorithm was implemented on graphics processing units (GPUs) contained in the data pipeline. The key contribution is a hardware and software pipeline for subchannelized wideband array signal processing with 150 MHz instantaneous bandwidth and interference cancellation with a heterogeneous, distributed, and scaleable digital signal processing (DSP) architecture that achieves 30 dB interferer cancellation null depth in real time with a moving interference source.

Three-dimensional location system based on an L-shaped array of Rydberg atomic receivers.

The Rydberg atomic receiver, sensing microwave electric field with high sensitivity and broad bandwidth, possesses the potential to be the staple for precise navigation and remote sensing. In this Letter, a Ku-band three-dimensional location system using an L-shaped array of Rydberg atomic receivers is theoretically proposed and experimentally demonstrated, and the proof of principle results show excellent consistency between the location-derived and the setting coordinates. The novel L-shaped array, together with the triangulation method, gives both phase difference and angle of arrival, achieving location of the horn for a signal microwave field in three-dimensional space. The concluded validity of this location system in the testing scene remains at approximately 90% with a theoretical maximum location tolerance of 5.7 mm. Furthermore, the estimation of two different spatiotemporal coordinates for the moving target confirms the velocity measurement capability of the system with errors less than 0.5 mm/s. The proposed location system using a Rydberg atomic receiver array is a verification for the most basic element and can be extended through repetition or nesting to a multi-input-multi-output system as well as multi-channel information processing.

Subspace-based higher-order compressive sensing algorithm for raypath separation in a shallow-water waveguide

In underwater acoustics, compressive sensing was applied to the separation of multiple raypaths based on direction of arrival (DOA) estimation. While it is impossible to separate raypaths directly without eliminating the interference between raypaths. This paper proposes a subspace-based higher-order compressive sensing algorithm, which enables separating raypaths interrupted by colored noise. In the algorithm, a trispectrum matrix is first calculated from the signal received on the reception array. To improve the robustness against noise, the trispectrum matrix is decomposed into signal and noise subspaces using an eigenvalue decomposition. Then, a subspace-based higher-order convex optimization problem is designed based on the signal subspace. The separation of raypaths is cast as the optimization problem solved in a greedy strategy approximation. The results obtained in both simulations and experiments show that the present method not only achieves the more precise separation of raypaths, but it also provides better suppression of noise as compared to the other algorithms.

Blind Adaptive Beamforming for a Global Navigation Satellite System Array Receiver Based on Direction Lock Loop

The adaptive beamforming algorithm can realize interference suppression and navigation signal enhancement, and has been widely used. However, achieving high-precision real-time estimation of the direction of arrival (DOA) parameters of navigation signals in strong-interference scenarios with low complexity is still a challenge. In this paper, a blind adaptive beamforming algorithm for a Global Navigation Satellite System (GNSS) array receiver based on direction lock loop is proposed without using the prior information of the DOA parameter. The direction lock loop is used for DOA tracking and estimation after interference suppression, which uses the spatial correlation of the array beam pattern to construct a closed direction-tracking loop. The DOA estimation value is adjusted in real time based on the loop errors. A blind beamformer is constructed using the DOA estimation results to provide gain by forming a beam in the satellite direction. This method improves the accuracy and dynamic adaptability of DOA estimation while significantly reducing the computational complexity. The theoretical analysis and simulation results verify the effectiveness of the proposed algorithm.

Design and simulation of acoustic vortex wave arrays for long-range underwater communication

The formation and propagation of acoustic vortex waves have been of increasing interest for multiple applications, namely, underwater acoustic communications. Several methods have been presented to form these vortices in underwater environments; however, their performance and propagation over long distances is largely unstudied. Understanding the long-distance propagation of these waves is vital to enhancing their usefulness as an added degree of freedom in underwater acoustic communications systems. In this work, the ray tracing algorithm of bellhop is used to investigate the design parameters of vortex wave transducer and receiver arrays consisting of multiple rings of independently controlled transducers and simulate their performance.

P-526 Modified Applebaum uterine scoring system to predict uterine receptivity in frozen embryo transfer(FET) cycles

Abstract Study question To evaluate modified Applebaum uterine scoring system in predicting the uterine receptivity and clinical pregnancy rate? Summary answer The modified version of Applebaum uterine scoring system has sensitivity of 0.9411 and specificity of 0.5869 in predicting the uterine receptivity in embryo transfer cycle. What is known already The endometrial receptivity have been accepted to be major limiting factors in the establishment of pregnancy. Different techniques have been developed to evaluate endometrial receptivity, such as endometrial receptivity array or histological dating. The advantage of Ultrasound is it’s non-invasiveness, repeatability, real time monitoring and predictability. Study design, size, duration It is a prospective observational study. Study group comprises of 200 female with primary infertility over a period of 6 month. Participants/materials, setting, methods Exclusion criteria was patients associated with male sub-fertility or having uterine anomalies. The study was conducted at D.Y.Patil fertility centre, unit of Bloom IVF. All the patients were given uterine scoring before FET based on Endometrial thickness, morphology, vascularisation, myometrial echogenicity, uterine artery PI and EDF, myometrial blood flow. Main results and the role of chance The overall pregnancy rate was 54%. A perfect score of 20 was associated with 97.4% pregnancy rate. Scores of 17 to 19 was associated with the pregnancy rate of 85.4% and scores of 14 to 16 was associated with the pregnancy rate of 28.6%. Score less than 13 is not associated with any pregnancy. The Modified Applebaum scoring system showed the sensitivity of 0.9411 and specificity of 0.5869 in predicting the outcome of the cycle. On an individual basis, endometrial morphology, end diastolic blood flow(EDF) and Pulsatility index(PI) of uterine artery and myometrial blood flow were found to be significant for a pregnancy on the basis of Z score and p value of < 0.01 Limitations, reasons for caution As there were no case of secondary infertility, Grade III/IV endometriosis, endocrine disorder and uterine anomalies. The scoring system might not replicate the same results. Wider implications of the findings As the sensitivity and specificity of this uterine scoring system is quite good. It could be a good tool in assessing endometrium before embryo transfer. Trial registration number Not applicable

P-533 Comparison of Endometrial Receptivity Array (ERA) with Preimplantation genetic testing (PGT) versus ERA alone in improving outcomes in Recurrent implantation failure.

Abstract Study question Whether addition of Preimplantation Genetic Testing for aneuploidy (PGT-A) to Endometrial Receptivity Array (ERA) helps in improving success rates in Recurrent Implantation Failure (RIF) patients. Summary answer Addition of PGT-A intervention to ERA in RIF patients did not improve outcomes. What is known already RIF causes great emotional stress and financial burden for the infertile couple. Successful implantation requires a synchronous interaction between a competent blastocyst and a receptive endometrium. Though ERA, as a measure to assess window of implantation (WOI), is around a decade old, its role in improving success rates in patients with RIF is still controversial. PGT-A, as a tool for selecting euploid embryos, though has shown to be beneficial in women with advanced maternal age, its role in improving success rates in RIF needs further evaluation. Study design, size, duration This is a multicenter retrospective cohort study carried out from September 2015 till September 2022. 285 patients with RIF with previous failed transfers with ≥ 3 good quality embryos were included. Participants/materials, setting, methods 285 patients with RIF were divided into 2 groups. Group 1 underwent PGT-A and Personalised Embryo Transfer (pET) guided by ERA and Group 2 underwent only ERA followed by pET. In Group 1 patients, embryo biopsy was done on day 5 and day 6 blastocyst before cryopreservation and NGS platform was used to detect euploid embryos. Both groups then underwent ERA followed by pET in the next cycle. Main results and the role of chance In total of 285 RIF patients studied, 59.2% patients showed displaced WOI. 91.7% ERA reports were pre-receptive. Group 1 included 137 patients and Group 2 had 148 patients & baseline characteristics were similar in both the groups. Group 1 had more self transfer cycles, i.e. 76.7% self and 17.2% donor oocytes, as compared to Group 2 with 40.2% self and 30.7% donor oocyte cycles. The implantation rate (IR), live birth rate (LBR), miscarriage rate and cumulative LBR were similar in both the groups. Higher Pregnancy rate (PR) in Group 2 (70.9% vs 57.83%) could be attributed to higher donor cycles in this group. Multiple gestation rate was also higher in Group 2 (31.49% vs 11.21%) as 2 blastocysts were transferred in most cycles in group 2 compared to Single embryo transfer(SET) in most cycles in Group 1. As PR was higher in ERA group, subgroup analysis of self gamete transfers and donor oocyte transfers was also done, which showed similar PR, IR and LBR in both the groups. Hence, PGT failed to show any value in improving pregnancy outcomes in RIF. Limitations, reasons for caution Retrospective study design. Wider implications of the findings The role of PGT in improving clinical outcomes in RIF patients needs to be studied in larger prospective studies. In our study, ERA as an intervention improved outcomes in RIF. Trial registration number not applicable

Using geometric mode decomposition for the background noise suppression on microseismic data

AbstractMicroseismic datasets typically have relatively low signal‐to‐noise ratio waveforms. To that end, several noise suppression techniques are often applied to improve the signal‐to‐noise ratio of the recorded waveforms. We apply a linear geometric mode decomposition approach to microseismic datasets for background noise suppression. The geometric mode decomposition method optimizes linear patterns within amplitude–frequency modulated modes and can efficiently distinguish microseismic events (signal) from the background noise. This method can also split linear and non‐linear dispersive seismic events into linear modes. The segmented events in different modes can then be added carefully to reconstruct the denoised signal. The application of geometric mode decomposition is well suited for microseismic acquisitions with smaller receiver spacing, where the signal may exhibit either (nearly) linear or non‐linear recording patterns, depending on the source location relative to the receiver array. Using synthetic and real microseismic data examples from limited‐aperture downhole recordings only, we show that geometric mode decomposition is robust in suppressing the background noise from the recorded waveforms. We also compare the filtering results from geometric mode decomposition with those obtained from FX‐Decon and one‐dimensional variational mode decomposition methods. For the examples used, geometric mode decomposition outperforms both FX‐Decon and one‐dimensional variational mode decomposition in background noise suppression.

Evaluating imaging uncertainty associated with the near surface and added value of vertical arrays using Bayesian seismic refraction tomography

AbstractTraditional tomographic methods do not consider the uncertainties associated with near-surface velocities and static corrections and provide a deterministic solution to the estimation problem. However, these uncertainties significantly affect structural mapping and interpretation of seismic imaging results. On the other hand, Bayesian first-arrival tomography provides multiple near-surface models that fit observed traveltimes equally well and enable the study of potential solution distributions. We demonstrate this approach on a complex synthetic near-surface model, representative of arid environments, to quantify associated velocity and statics uncertainties. We evaluate two different parameterizations for subsurface velocities in the context of near-surface Bayesian tomography: Voronoi tessellation with natural neighbor interpolation and the more conventional Delaunay triangulation with linear interpolation. Our analysis shows that the Voronoi cell parameterization with natural neighbor interpolation is more appropriate for this problem. Finally, the new approach is applied to compare two alternative acquisition geometries comprising conventional surface receivers and surface receivers augmented with vertical receiver arrays. The results demonstrate that adding vertical receiver arrays to conventional surface receivers can significantly reduce the near-surface velocity uncertainty and thus increases the accuracy of the seismic imaging results. Furthermore, the study shows that Bayesian tomography can be used as a tool for evaluating different source and receiver geometries during the acquisition design stage.

Polarization-insensitive composite gradient-index metasurface array for microwave power reception

A composite gradient-index metasurface (C-GM) array for microwave power reception (MPR) operating at 5.8 GHz center frequency was introduced. The array is insensitive to the polarization of incident plane waves and possesses cosine gradient modulation characteristics, which can convert the incident plane waves into surface waves focused at the center of the array. The focused surface wave energy is then collected by an omnidirectional antenna and fed back to a single rectifier for radio frequency (RF) to direct current (DC) conversion, resulting in DC output. Simulation results show that the array can fully excite surface waves under different polarized plane wave excitations, and the omnidirectional antenna has good matching characteristics with the array, achieving an energy collection efficiency of 66.52%. The array was fabricated and measured, achieving an energy reception efficiency of 59.91% and an RF-DC conversion efficiency of 34.83%, which is consistent with the simulation results. The proposed C-GM array can capture higher electromagnetic power by simply increasing its size, without the need for additional rectifiers or complex matching networks, making it a flexible and efficient MPR solution for different application scenarios.

Single Packet, Single Channel, Switched Antenna Array for RF Localization

Cost-effective and accurate means of localizing radio transmitters has the potential to enable a wide range of applications in the consumer electronics, IoT, and healthcare domains. However, existing multi-antenna localization methods require high-cost synchronized receivers, long integration times, and/or specialized packet structures. This paper proposes using a high-speed RF mux that sequentially connects antennas to a single 2MHz radio receiver and sub-packet switching to determine the Angle of Arrival of individual packets. Importantly, this approach does not need synchronization between the mux and the receiver, reducing cost and system complexity. Our signal processing pipeline recovers both switch timing and the antenna number from the received RF signal. The sub-packet waveforms are used to generate a synthetic reference packet, and our customized Multi-Resolution Beaming and MUSIC algorithms are used to determine the Angle of Arrival. Results show that our real-time system is highly accurate even when the target is moving, with a mean AoA accuracy of 3.4 degrees and a 2D localization accuracy of 36.4 cm. Furthermore, the system is capable of tracking multiple users carrying smartphones in either their hands or pockets. Ultimately this approach enables a single low-cost, low bandwidth commodity RF receiver to be used to create an N-element phased array receiver.

A Sparse Shared Aperture Design for Simultaneous Transmit and Receive Arrays with Beam Constraints

The utilization of efficient digital self-interference cancellation technology enables the simultaneous transmit and receive (STAR) phased array system to meet most application requirements through STAR capabilities. However, the development of application scenario requirements makes array configuration technology for STAR phased arrays increasingly important. Thus, this paper proposes a sparse shared aperture STAR reconfigurable phased array design based on beam constraints which are achieved by a genetic algorithm. Firstly, a design scheme for transmit and receive arrays with symmetrical shared apertures is adopted to improve the aperture efficiency of both transmit and receive arrays. Then, on the basis of shared aperture, sparse array design is introduced to further reduce system complexity and hardware costs. Finally, the shape of the transmit and receive arrays is determined by constraining the side lobe level (SLL), main lobe gain, and beam width. The simulated results indicate that the SLL of the transmit and receive patterns under beam-constrained design have been reduced by 4.1 dBi and 7.1 dBi, respectively. The cost of SLL improvement is a reduction in transmit gain, receive gain, and EII of 1.9 dBi, 2.1 dBi, and 3.9 dB, respectively. When the sparsity ratio is greater than 0.78, the SLL suppression effect is also significant, and the attenuation of EII, transmit, and receive gains do not exceed 3 dB and 2 dB, respectively. Overall, the results demonstrate the effectiveness of a sparse shared aperture design based on beam constraints in producing high gain, low SLL, and low-cost transmit and receive arrays.

Low frequency 3D transmission ultrasound tomography: technical details and clinical implications

A novel 3D ultrasound tomographic (3D UT) method (called volography) that creates a speed of sound (SOS) map and a reflection modality that is co-registered are reviewed and shown to be artifact free even in the presence of high contrast and thus shown to be applicable for breast, orthopedic and pediatric clinical use cases. The 3D UT images are almost isotropic with mm resolution and the reflection image is compounded over 360 degrees to create sub-mm resolution in plane. MethodsThe physics of ultrasound scattering requires 3D modeling and the concomitant high computational cost is ameliorated with a bespoke algorithm (paraxial approximation – discussed here) and Nvidia GPUs. The resulting reconstruction times are tabulated for clinical relevance. The resulting SOS map is used to create a refraction corrected reflection image at ∼3.6 MHz center frequency. The transmission data are highly redundant, collected over 360 degrees and at 2 mm levels by true matrix receiver arrays yielding 3D data.The high resolution SOS and attenuation maps and reflection images are used in a segmentation algorithm that optimally utilizes this information to segment out glandular, ductal, connective tissue, fat and skin. These volumes are used to estimate breast density, an important correlate to cancer. ResultsMultiple SOS images of breast, knee and segmentations of breast glandular and ductal tissue are shown. Spearman rho is calculated between our volumetric breast density estimates and Volpara™ from mammograms, as 0.9332. Multiple timing results are shown and indicate the variability of the reconstruction times with breast size and type but are ∼30 minutes for average size breast. The timing results with the 3D algorithm indicate ∼60 minute reconstruction times for pediatrics with two Nvidia GPUs. Characteristic variations of the glandular and ductal volumes over time are shown. The SOS from QT images are compared with literature values.The results of a multi-reader multi-case (MRMC) study are shown that compares the 3D UT with full field digital mammography and resulted in an average increase in ROC AUC of 10%. Orthopedic (knee) 3D UT images compared with MRI indicate regions of zero signal in the MRI are clearly displayed in the QT image.Explicit representation of the acoustic field is shown, indicating its 3D nature. An image of in vivo breast with the chest muscle is shown and speed of sound agreement with literature values are tabulated. Reference is made to a recently published paper validating pediatric imaging. ConclusionsThe high Spearman rho indicates a monotonic (not necessarily linear) relation between our method and industry gold standard Volpara™ density. The acoustic field verifies the need for 3D modeling. The MRMC study, the orthopedic images, breast density study, and references, all indicate the clinical utility of the SOS and reflection images. The QT image of the knee shows its ability to monitor tissue the MRI cannot. The included references and images herein indicate the proof of concept for 3D UT as a viable and valuable clinical adjunct in pediatric and orthopedic situations in addition to the breast imaging.

Regional Mapping of Small‐Scale Equatorial Ionospheric Irregularities Using Swarm Echo Satellite Measurements

AbstractWe propose a novel approach to produce regional maps of small‐scale scintillation‐causing irregularities using a single satellite. To construct the maps, we employ several ionospheric GPS indices, including total electron content, high‐resolution ROTI, and S4, calculated from the Swarm Echo GPS Attitude, Positioning, and Profiling Experiment Occultation (GAP‐O) receiver with its antenna pointed upward. GAP‐O's high‐sample‐rate observations enable irregularities as small as 320 m to be resolved. We present two case studies in which we compare the maps with in situ measurements of irregularities and simultaneous vertical TEC maps obtained from the ground. In situ measurements of net current onto the external surface of the Imaging and Rapid‐scanning Ion Mass Spectrometer sensor on board Swarm Echo were utilized to quantify plasma density fluctuations. Then, we apply the method to synthetic data to illustrate the efficacy of the method. Modeling results show that the irregularity maps can determine the horizontal geo‐locations of small‐scale irregularities, though with significant uncertainties in the cross‐track direction (east‐west). As Swarm Echo traverses different altitudes, these maps provide additional information on the altitudinal distribution of plasma fluctuations. This technique facilitates a better understanding of the morphology of scintillation‐causing irregularities, which are challenging to map from ground‐based receiver arrays alone.

Two Rapid Power Iterative DOA Estimators for UAV Emitter Using Massive/Ultra-Massive Receive Array

To provide rapid direction finding (DF) for unmanned aerial vehicle (UAV) emitters in future wireless networks, a low-complexity direction of arrival (DOA) estimation architecture for massive multiple-input multiple-output (MIMO) receiver arrays is constructed. In this paper, we propose two strategies to address the extremely high complexity caused by eigenvalue decomposition of the received signal covariance matrix. Firstly, a rapid power iterative rotational invariance (RPI-RI) method is proposed, which adopts the signal subspace generated by power iteration to obtain the final direction estimation through rotational invariance between subarrays. RPI-RI causes a significant complexity reduction at the cost of a substantial performance loss. In order to further reduce the complexity and provide good directional measurement results, the rapid power iterative polynomial rooting (RPI-PR) method is proposed, which utilizes the noise subspace combined with the polynomial solution method to obtain the optimal direction estimation. In addition, the influence of initial vector selection on convergence in the power iteration is analyzed, especially when the initial vector is orthogonal to the incident wave. Simulation results show that the two proposed methods outperform the conventional DOA estimation methods in terms of computational complexity. In particular, the RPI-PR method achieves more than two orders of magnitude lower complexity than conventional methods and achieves performance close to the Cramér–Rao Lower Bound (CRLB). Moreover, it is verified that the initial vector and the relative error have a significant impact on the performance with respect to the computational complexity.

Probability of Atlantic Salmon Post-Smolts Encountering a Tidal Turbine Installation in Minas Passage, Bay of Fundy

Tidal stream energy is a renewable energy resource that might be developed to offset carbon emissions. A tidal energy demonstration (TED) area has been designated in Minas Passage, Bay of Fundy, for testing and installing marine hydrokinetic (MHK) turbines. Regulations require quantification of the potential for MHK turbine installations to harm local populations of marine animals. Here, we use acoustic telemetry to quantify the probability that post-smolt inner Bay of Fundy salmon encounter a turbine installation at the TED area. Previous work has quantified the detection efficiency of Innovasea HR acoustic tags as a function of the current speed and range from a moored HR2 receiver and also demonstrated that drifters carrying HR tags will be effectively detected when the drifter track crosses the array of HR2 receivers in Minas Passage. Salmon smolts were tagged and released in Gaspereau and Stewiacke Rivers, Nova Scotia, in order that the HR2 receiver array could monitor seaward migration of the post-smolts through Minas Passage and particularly through the TED area. Presently, we formulate and apply a method by which tag signals detected by the HR2 array can be used to estimate the expected number of times that a post-smolt would encounter a single near-surface MHK turbine installation during its seaward migration.

Double-source frequency–wavenumber transform for accurate extraction of 2-D media dispersion

SUMMARY Extracting the dispersion energy image is one of the key steps of surface wave analysis, which is considered an effective and important way to obtain the vertical velocity structure. The quality of the dispersion energy image directly affects the accuracy of selected dispersion curves and the subsequent inversion. However, if we can theoretically obtain an accurate 2-D dispersion energy diagram, we will skip the step of extracting the dispersion curves. Here, we present the double-source frequency–wavenumber (DSFK) transform to extract theoretical 2-D dispersion energy images from multichannel data. Unlike 1-D dispersion energy images, which are based on the assumption of a horizontally layered medium structure, 2-D dispersion energy images also reflect information about the irregular interfaces of media. We adopt a geometry in which two reciprocal sources are on both ends of a receiver array. Then, the multichannel data obtained by this geometry are transformed into the frequency domain, and a 2-D dispersion energy image that corresponds to the 2-D structure is obtained by the DSFK transform. By producing a variety of synthetic data and processing active source data from the Salton Seismic Imaging Project, we confirm the accuracy and applicability of the DSFK transform. As demonstrated by the results, the DSFK transform can obtain the theoretical 2-D dispersion energy distribution and shows significant potential in the field of seismic tomography.

Marine reserve use by a migratory coastal shark, Carcharias taurus

Networks of small no-take marine protected areas (MPAs) are a popular approach to protect mobile marine species at key sites along their migration routes. Understanding how individuals vary in their use of these sites is needed to ensure MPA networks are optimised to offer maximum protection benefits. Using diver-led surveys, coded acoustic tags and a continental-scale collaborative network of acoustic receivers, we investigated variation in the use of three Australian MPAs by aggregating grey nurse sharks, Carcharias taurus. The Wolf Rock MPA was used year-round by C. taurus and as a gestation site, with females spending up to 254 d at the site with 2.2–3.7 year absences between residencies. In contrast, Flat Rock and Cherubs Cave-Henderson Rock MPAs were used as a transitory aggregation site with males and females occurring at the site for 30 min–59 d intervals between June–January, only. Migratory movements ranged up to 1500 km along the coastline, intersected 18 MPAs and/or recognised C. taurus aggregation sites, and connected temperate waters at Montague Island (36.25° S) with that of the southern Great Barrier Reef (23.40° S). Our study demonstrates how local receiver arrays and national collaborative acoustic telemetry networks are powerful tools to reveal use, fidelity and connectivity of MPA networks by marine migratory species. As the east Australian C. taurus population is critically endangered and at particular risk of anthropogenic threats, ongoing monitoring of the species' movement behaviour and complementary management outside protected area boundaries is warranted to assist its protection.

A 28 GHz Phased-Array Transceiver for 5G Applications in 22 nm FD-SOI CMOS.

This paper presents the design and implementation of a 28 GHz phased array transceiver for 5G applications using 22 nm FD-SOI CMOS technology. The transceiver consists of a four-channel phased array receiver and transmitter, which employs phase shifting based on coarse and fine controls. The transceiver employs a zero-IF architecture, which is suitable for small footprints and low power requirements. The receiver achieves a 3.5 dB NF with a 1 dB compression point of -21 dBm and a gain of 13 dB.

Highly Sensitive SPAD-Based Receiver for Dimming Control in LiFi Networks

Visible light communication (VLC) is an emerging mode of wireless communication that supports both illumination and communication. One essential function of VLC systems is the dimming control, which requires a sensitive receiver for low-light conditions. The use of an array of single-photon avalanche diodes (SPADs) is one promising approach to enhancing receivers’ sensitivity in a VLC system. However, because of the non-linear effects brought on by the SPAD dead time, an increase in the brightness of the light might degrade its performance. In this paper, an adaptive SPAD receiver is proposed for VLC systems to ensure reliable operation under various dimming levels. In the proposed receiver, a variable optical attenuator (VOA) is used to adaptively control the SPAD’s incident photon rate according to the instantaneous received optical power so that SPAD operates in its optimal conditions. The application of the proposed receiver in systems with various modulation schemes is investigated. When binary on–off keying (OOK) modulation is employed due to its good power efficiency, two dimming control methods of the IEEE 802.15.7 standard based on analogue and digital dimming are considered. We also investigate the application of the proposed receiver in the spectral efficient VLC systems with multi-carrier modulation schemes, i.e., direct current (DCO) and asymmetrically clipped optical (ACO) orthogonal frequency division multiplexing (OFDM). Through extensive numerical results, it is demonstrated that the suggested adaptive receiver outperforms the conventional PIN PD and SPAD array receivers in terms of bit error rate (BER) and achievable data rate.