Link Gain Research Articles

Millimeter Wave Reflection Pattern Codebook Design for RIS-Assisted V2V Communications

We consider a reflection pattern (RP) designfor reconfigurable intelligent surface (RIS)-assisted vehicle-to-vehicle (V2V) communication systems. Fast-moving-vehicle environments necessitate developing more intuitive RP alignment technique that aligns a predefined codeword to the dominant channel directions. To support a fast RP alignment in RIS-assisted V2V systems, we provide a design guideline of the RP codebook by considering passive reflecting elements at the RIS. We analyze distributions of the incident and reflection channels by taking the street geometry in V2V networks into consideration. By using the statistical information on the difference in spatial frequencies between the incident and reflection channels, we define a set of ideal RPs that are likely to maximize a reflection beamforming gain. The RP codebook is constructed by designing a set of reflecting codewords that can generate actual RPs close to predefined ideal RPs. Numerical results verify that the proposed RP codebook provides a higher link gain than previously reported codebooks.

Fully integrated hybrid microwave photonic receiver

Microwave photonic receivers are a promising candidate in breaking the bandwidth limitation of traditional radio-frequency (RF) receivers. To further balance the performance superiority with the requirements regarding size, weight, and power consumption (SWaP), the implementation of integrated microwave photonic microsystems has been considered an upgrade path. However, up to now, to the best of our knowledge, chip-scale fully integrated microwave photonic receivers have not been reported due to the limitation of material platforms. In this paper, we report a fully integrated hybrid microwave photonic receiver (FIH-MWPR) obtained by comprising the indium phosphide (InP) laser chip and the monolithic silicon-on-insulator (SOI) photonic circuit into the same substrate based on the low-coupling-loss micro-optics method. Benefiting from the integration of all optoelectronic components, the packaged FIH-MWPR exhibits a compact volume of 6 cm 3 and low power consumption of 1.2 W. The FIH-MWPR supports a wide operation bandwidth from 2 to 18 GHz. Furthermore, its RF-link performance to down-convert the RF signals to the intermediate frequency is experimentally characterized by measuring the link gain, the noise figure, and the spurious-free dynamic range metrics across the whole operation frequency band. Moreover, we have utilized it as a de-chirp receiver to process the broadband linear frequency-modulated (LFM) radar echo signals at different frequency bands (S-, C-, X-, and Ku-bands) and successfully demonstrated its high-resolution-ranging capability. To the best of our knowledge, this is the first realization of a chip-scale broadband fully integrated microwave photonic receiver, which is expected to be an important step in demonstrating the feasibility of all-integrated microwave photonic microsystems oriented to miniaturized application scenarios.

A reconfigurable wireless superheterodyne receiver for multi-standard communication systems

ABSTRACT The rapid growth of the communication frequency band leads to the diversity of receiving frequency bands of smart devices. This paper proposes a reconfigurable wireless superheterodyne receiver for multi-standard communication systems. The receiver is designed through architecture design, chip selection, layout drawing, and physical measurement. The designed receiver consists of receiving module, local oscillator module, and control module. Unlike previous receivers, the proposed receiver selects the frequency channel, local oscillator frequency, and link gain through the control module in the current scene. The control module consists of a single-chip microcomputer and computer. The receiver can work in application scenarios including 2.4–2.5 GHz, 3.3–3.6 GHz, and 4.8–6.0 GHz. This paper discusses the design process of the proposed reconfigurable receiver in detail. Compared with the traditional receiver, the proposed receiver can change its working mode by software and has the characteristics of flexible reconfiguration. In addition, it has the advantages of a large link gain range and good demodulation performance. Moreover, the receiver is low in design cost and easy to manufacture. Therefore, it can be widely used in receiving modules of WLAN and 5G communication systems.

The Self-Organization of Marine Microbial Networks under Evolutionary and Ecological Processes: Observations and Modeling.

Simple SummaryThe properties and structure of ecological networks in marine microbial communities determine ecosystem functions and stability; however, the principles of microbial network assemblages are poorly understood. In this study, we revealed the influences of species phylogeny and niches on the self-organization of marine microbial co-occurrence networks and provided a mathematical framework to simulate microbial network assemblages. Our results provide deep insights into network stability from the perspective of network assembly principles and not just network properties, such as complexity and modularity.Evolutionary and ecological processes are primary drivers of ecological network constrictions. However, the ways that these processes underpin self-organization and modularity in networks are poorly understood. Here, we performed network analyses to explore the evolutionary and ecological effects on global marine microbial co-occurrence networks across multiple network levels, including those of nodes, motifs, modules and whole networks. We found that both direct and indirect species interactions were evolutionarily and ecologically constrained across at least four network levels. Compared to ecological processes, evolutionary processes generally showed stronger long-lasting effects on indirect interactions and dominated the network assembly of particle-associated communities in spatially homogeneous environments. Regarding the large network path distance, the contributions of either processes to species interactions generally decrease and almost disappear when network path distance is larger than six. Accordingly, we developed a novel mathematical model based on scale-free networks by considering the joint effects of evolutionary and ecological processes. We simulated the self-organization of microbial co-occurrence networks and found that long-lasting effects increased network stability via decreasing link gain or loss. Overall, these results revealed that evolutionary and ecological processes played key roles in the self-organization and modularization of microbial co-occurrence networks.

Feasibility Analysis of Distributed Power Control System for Cognitive Radio Networks

The need for an efficient transmit power is affected by the condition of user and power control methods used. User conditions that categorized in cognitive femtocell networks included in the category as distributed user, so it required a distributed power control (DPC). To be implemented in cognitive radio network (CRN) communication, the system must be feasible. The problem raised in this research regarding the feasibility of implementing the DPC system on the CR network To meet the feasible requirements, it is necessary to test the system's feasibility through testing the eigenvalues of the link gain matrix obtained and testing the non-negative power vector conditions. In this study, experiments were carried out on 2 schemes of the number of users, namely the scheme of 5 users and 10 users, to determine the power requirements of each user according to the channel distribution. The results obtained for both schemes show that the total eigenvalue of the link gain matrix for all channels is less than 1 and all users meet the non-negative power vector requirements. So it can be concluded that those two schemes are feasible to implement a distributed power control system. Furthermore, as more users use the channel and the closer the distance between users, the more power is consumed due to high interference, necessitating high power compensation in order to maintain the target of signal to interference and noise ratio (SINR).

High-performance dual-band radio-over-fiber link for future 5G radio access applications

For the fronthaul between the baseband unit and the remote radio unit (RRU), radio over fiber (RoF) is promising to replace the Common Public Radio Interface in beyond fifth-generation and the sixth-generation wireless communication systems. The weight, size, and power consumption of the RRU can be greatly reduced, along with easy support for the millimeter-wave band. In this paper, a dual-band RoF link is proposed, where flexible switching between high-frequency (28 GHz) and low-frequency (3.5 GHz) RF channels is realized through polarization control. Single-sideband modulation is performed on 28 GHz signals to avoid periodic power fading during long-distance fiber transmission. By adjusting the DC bias, the third-order intermodulation distortion component in the 3.5 GHz signal is suppressed, and the spur-free dynamic range (SFDR) is improved. Experimental results show a channel isolation of above 43 dB. The link gain of the 28 GHz signal channel is flat, and the SFDR of the 3.5 GHz signal channel can reach 118.6 d B ⋅ H z 4 / 5 . In the case of RF vector signal transmission, the adjacent channel power ratio of the 3.5 GHz signal channel is optimally up to 48 dB, and the error vector magnitude is 2.9%.

Two-Dimensional Intensity Distribution and Adaptive Power Allocation for Ultraviolet Ad-Hoc Network

We consider a directional antenna array in an ultraviolet (UV) scattering communication ad-hoc network. To efficiently characterize the link gain coverage of a single antenna, we propose an algorithm based on one-dimensional (1D) numerical integration and an off-line data library. We also investigate the two-dimensional (2D) scattering intensity distribution, which shows that the link gain profile can be well fitted by elliptic models. In addition, assuming that the node distribution of an ad-hoc network obeys Poisson point process (PPP), we investigate the network connectivity probability and the minimum power that the network remains connected under different antenna parameters, and compare the performance of directional antenna array with that of omnidirectional antenna array. Numerical results show that employing directional antenna arrays can effectively reduce the power required for network connectivity. Moreover, we consider a two-layer network using directional antenna array, and design adaptive node assignment and power allocation to increase the minimum rate. Numerical results show that the proposed algorithm can improve the minimum node rate by more than 10%. Moreover, similar performance gain can be observed even considering the overhead of a media-access control (MAC) layer protocol.

Investigation of a balanced microwave photonic link utilizing a single few-mode fiber.

A balanced microwave photonic link, which utilizes mode-division multiplexing in order to combine both of its optical paths into and out of a single six-mode few-mode fiber, is demonstrated for the first time, to the best of our knowledge. Due to non-negligible modal crosstalk, the link exhibited excess radio-frequency gain fluctuations when compared to an equivalent conventional balanced link. The LP02+LP01 mode pair was the most stable with 2σ (two standard deviations) fluctuations of 0.4 dB about the average link gain, compared to the conventional link's 2σ of 0.16 dB. The excess crosstalk-induced fluctuations may render the link impractical to use outside of the laboratory.

Improved Resource Allocation Model for Reducing Interference Among Secondary Users in TV White Space for Broadband Services

In recent years, the Television White Space has attracted the interest of many researchers due to its propagation characteristics obtainable between 470MHz and 790MHz spectrum bands. However, aggregate interference increase when secondary users in the wireless network increase. The aggregate interference on the side of Primary Users has been extensively scrutinized. Therefore, resource allocation (power and spectrum) is crucial when designing the Television White Space network to avoid interferences from Secondary Users to Primary Users and among Secondary Users themselves. This paper proposes a resource allocation model that uses joint power and spectrum hybrid Particle Swarm Optimization, Firefly, and Genetic algorithm for reducing the aggregate interference among Secondary Users. The algorithm is integrated with the admission control algorithm so that; there is a possibility to remove some of the Secondary Users in the network whenever the Signal to Noise Interference Ratio threshold for Secondary and Primary Users is not met. We considered the infeasible system whereby all Secondary and Primary Users may not be supported simultaneously. Metrics such as Primary User Signal-to-noise ratio, sum throughput, and secondary user signal-to-noise ratio less than the threshold used to compare the performance of the proposed algorithm and the results show that the PSOFAGA with effective link gain ratio admission control has the best performance compared to particle swarm optimization, genetic algorithm, firefly algorithm, and PSOFAGA algorithm.

Enhanced Coverage in the Shadow Region Using Dipole Scatterers at the Corner

Coverage in mobile communications systems requires an acceptable link gain over a maximum service area, with areas of low link gain being problematic. A standard approach to maximize link gain is to deploy multiple-input–multiple-output (MIMO) antennas that adapt to the changing multipath. There is also recent interest in using active surfaces for adaptive reflections within the multipath environments, and this calls for new ideas at the system and component levels. A critical mechanism in urban propagation is corner diffraction, which illuminates shadow areas but with low link gain. We present a simple add-on system for corners, comprising a simple scattering dipole or scattering array, which can significantly improve link gain in the shadow region over a wide bandwidth. The concept is demonstrated through analysis, simulation, and physical measurement. Only shadowed areas are boosted, and the line-of-sight coverage is not significantly affected. Our demonstration is for a passive, fixed configuration, which is suitable for retrofitting to existing systems.

Secure Cognitive Radio-Enabled Vehicular Communications under Spectrum-Sharing Constraints.

Vehicular communication has been envisioned to support a myriad of essential fifth-generation and beyond use-cases. However, the increasing proliferation of smart and intelligent vehicles has generated a lot of design and infrastructure challenges. Of particular interest are the problems of spectrum scarcity and communication security. Consequently, we considered a cognitive radio-enabled vehicular network framework for accessing additional radio spectrum and exploit physical layer security for secure communications. In particular, we investigated the secrecy performance of a cognitive radio vehicular network, where all the nodes in the network are moving vehicles and the channels between them are modeled as double-Rayleigh fading. Furthermore, adopting an underlay approach, the communication between secondary nodes can be performed by employing two interference constraint strategies at the primary receiver; (1) Strategy I: the secondary transmitter power is constrained by the interference threshold of the primary receiver, and (2) Strategy II: the secondary transmitter power is constrained by both the interference threshold of the primary receiver and the maximum transmit power of the secondary network. Under the considered strategies, we derive the exact secrecy outage probability (SOP) and ergodic secrecy capacity (ESC) expressions over double-Rayleigh fading. Moreover, by analyzing the asymptotic SOP behavior, we show that a full secrecy diversity of 1 can be achieved, when the average channel gain of the main link goes to infinity with a fixed average wiretap channel gain. From the ESC analysis, it is revealed that the ESC follows a scaling law of for large and , where and are the average channel gains of the main link and wiretap link. The numerical and simulation results verify our analytical findings.

Photodetector optic power optimization to increase the gain on sub-octave microwave photonic link / Optimização da potência óptica do fotodetector para aumentar o ganho na ligação fotónica de microondas sub-octave

An investigation of the optic spectral components beating at the photodetector to recover the RF signal at the output of a sub-octave microwave photonic link is presented, by a theoretical and experimental approach. It is demonstrated the best efficiency is achieved when the carrier to sideband ratio (CSR) is 0 dB at a low bias voltage condition on Mach-Zehnder (MZM) intensity modulator. A RF power link gain improvement of 9.7 dB is demonstrated for a same photodetector incident optic power, compared with a link operating at quadrature bias voltage condition on the MZM.

True Time Delay Optical Beamforming Network Based on Hybrid Inp-Silicon Nitride Integration

We demonstrate a broadband and continuously tunable 1×4 optical beamforming network (OBFN), based on the hybrid integration of indium phosphide (InP) components in the silicon nitride (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) platform. The photonic integrated circuit (PIC) comprises a hybrid InP-Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> external cavity laser, a pair of InP phase modulators, a Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> optical single-sideband full carrier (SSBFC) filter followed by four tunable optical true time delay lines (OTTDLs), and four InP photodetectors. Each OTTDL consists of eight cascaded thermo-optical micro-ring resonators (MRRs) that impose tunable true time delay on the propagating optical signals. The OBFN-PIC is designed to facilitate the steering of a microwave signal with carrier frequency up to 40 GHz over a continuous set of beam angles. We evaluate the performance of the OBFN-PIC to handle and process microwave signals, measuring the link gain, the noise figure (NF), and the spurious-free dynamic range (SFDR) parameters. Moreover, we assess its beamforming capabilities assuming that the OBFN-PIC is part of a wireless system operating in the downlink direction and feeds a multi-element antenna array. Using microwave signals at 5 and 10 GHz with quadrature amplitude modulation (QAM) formats at 500 Mbaud, we evaluate the performance of the OBFN-PIC under various configurations. We show that error-free performance can be achieved at both operating frequencies and for all the investigated beam angles ranging from 45° to 135°, thus validating its potential for high-quality beamforming performance.

A modified GADIA-based upper-bound to the capacity of Gaussian general N-relay networks

In this paper, we present a general Gaussian N-relay network by allowing relays to communicate to each other and allowing a direct channel between source and destination as compared to the standard diamond network in Nazaroğlu et al. (IEEE Trans Inf Theory 60:6329–6341, 2014) at the cost of extra channel uses. Our main focus is to examine the min-cut bound capacities of the relay network. Very recently, the results in Uykan (IEEE Trans Neural Netw Learn Syst 31:3294–3304, 2020) imply that the GADIA in Babadi and Tarokh (IEEE Trans Inf Theory 56:6228–6252, 2010), a pioneering algorithm in the interference avoidance literature, actually performs max-cut of a given power-domain (nonnegative) link gain matrix in the 2-channel case. Using the results of the diamond network in Nazaroğlu et al. (2014) and the results in Uykan (2020), in this paper, we (i) turn the mutual information maximization problem in the Gaussian N-relay network into an upper bound minimization problem, (ii) propose a modified GADIA-based algorithm to find the min-cut capacity bound and (iii) present an upper and a lower bound to its min-cut capacity bound using the modified GADIA as applied to the defined “squared channel gain matrix/graph”. Some advantages of the proposed modified GADIA-based simple algorithm are as follows: (1) The Gaussian N-relay network can determine the relay clusters in a distributed fashion and (2) the presented upper bound gives an insight into whether allowing the relays to communicate to each other pays off the extra channel uses or not as far as the min-cut capacity bound is concerned. The simulation results confirm the findings. Furthermore, the min-cut upper bound found by the proposed modified-GADIA is verified by the cut-set bounds found by the spectral clustering based solutions as well.

Preliminary Characterization of Coverage for Water-to-Air Visible Light Communication Through Wavy Water Surface

In this paper, we establish a water-to-air (W2A) visible light communication (VLC) link using green light emitting diode (LED), and investigate the coverage characteristics of the designed W2A-VLC link under calm and wavy water conditions. By transmitting a high-frequency sinusoid signal, we extract the variation of link gain. Based on the received signals of an experimental W2A-VLC system, we obtain the real link gains at different receiver points and analyze the channel temporal properties in good link conditions (called link “on” state). It is seen that the mean channel gain under wavy water surface condition can be larger than that under calm water surface condition, especially when the transmitter and receiver are not perfectly aligned, due to the random spatial modulation effect of wavy water surface. Moreover, the “on” state duration and interval can be well fitted by a shifted exponential distribution and a shifted lognormal distribution, respectively. Bit error rate (BER) results reveal the effect of expanded link gain variation under wavy water surface condition. This work provides significant guidance for future works on the communication protocol design and related performance analysis.

Microwave photonic notch filter with integrated phase-to-intensity modulation transformation and optical carrier suppression.

We demonstrate for the first time, to the best of our knowledge, an on-chip microwave photonic (MWP) notch filter with high stopband rejection and integrated optical carrier suppression in a phase modulator-based system. The notch filter was achieved through phase modulation to intensity modulation (PM-to-IM) transformation and dual-sideband-processing using a network of three ring resonators (RRs) in a low-loss silicon nitride (Si3N4) platform. We show simultaneous PM-to-IM conversion and optical carrier processing for enhancing the filter performance using a single RR. We achieve filtering with a high stopband rejection of >55dB, an optical carrier suppression up to 3 dB, a radio frequency link gain of 3 dB, a noise figure of 31 dB, and a spurious-free dynamic range of 100dB⋅Hz2/3. These experiments point to the importance of vectorial spectral shaping of an MWP spectrum for advanced functionalities.

Integrated Direct Single Sideband Modulation Utilizing Sideband Amplification Injection Locking Effect Based on Multi-Section Mutual Injection DFB Laser

An integrated single sideband (SSB) modulation method benefitting from the sideband amplification injection locking (SAIL) effect for radio-over-fiber (ROF) link is proposed and experimentally demonstrated, which is based on an integrated multi-section mutual injection (IMSMI) DFB laser. The IMSMI-DFB laser, which overcomes the drawbacks of using discrete devices, simplifies the whole structure. The SAIL effect, which is regulated by the input RF power and bias current of IMSMI-DFB laser, promises a good pathway for adjusting and controlling the modulation frequency, optical carrier to sideband ratio (OCSR), and sideband suppression ratio (SSR), meanwhile, provides high gain in the link. The characteristics of SAIL effect are investigated. The OCSR can be optimized to 0 dB, the SSR is over 26 dB, and the transmission link gain improves over 20 dB from 16 GHz to 26 GHz. The ROF transmission experiments demonstrate that the power fading introduced by fiber dispersion is dramatically eliminated, and the error vector magnitudes (EVMs) of the received 20 MSymbol/s 32 QAM signals at frequencies from17 GHz to 22.3 GHz after 50 km fiber transmission are below 4.8%. This work provides an effective way to realize integrated direct SSB modulation with outstanding features for ROF link.

Secrecy performance of FSO communication systems with non‐zero boresight pointing errors

Free space optical (FSO) communication is a promising candidate for the next generation (5G and beyond) wireless communication systems, due to its merits (i.e. low latency, high data rate, and license-free band, among others). However, atmospheric turbulence (AT) as well as pointing error (PE) are two of the main challenges with FSO communication that affect its performance. Here, the exact closed-form expression of the average secrecy capacity and secrecy outage probability under the composite effect of AT and non-zero boresight PEs is evaluated. For all the regimes of the AT (weak to strong), a generalised Malaga distribution is used to model the channel fading gain of the FSO link. The expressions are generalised and valid for all turbulence, and are applicable for intensity modulation direct detection as well as heterodyne detection techniques.

High-Gain Ka-Band Analog Photonic Link Using High-Power Photodiode at 1064 nm

We report high-gain, low-noise-figure, and high linearity analog photonic links at 1064 nm using InP/InGaAs modified uni-traveling-carrier (MUTC) photodiodes. Balanced photodiodes reach output powers of 17.7 dBm, 19.8 dBm, 20.7 dBm, and 22 dBm at 38 GHz, 29 GHz, 27 GHz, and 24.5 GHz, respectively. High common-mode rejection ratio (CMRR) of 25 dB and good linearity with a third-order intercept point (OIP3) of up to 34 dBm were measured at 38 GHz for 10-μm-diameter balanced photodiodes. We demonstrate two analog photonic links with different noise reduction techniques without electronic amplification. In the first link, we use balanced detection with a quadrature-biased Mach–Zehnder modulator (MZM) for noise cancellation. Link gain of 6.8 dB, noise figure (NF) of 25.8 dB and spurious free dynamic range (SFDR3) of 114 dB·Hz2/3 at 38 GHz were achieved. The second link works at low bias modulation for improved signal-to-noise ratio with a single photodetector. Record-high gain (19.3 dB at 26 GHz and 17 dB at 38 GHz) and low noise figure (14.5 dB at 26 GHz and 17 dB at 38 GHz) were demonstrated.

Communicating With Large Intelligent Surfaces: Fundamental Limits and Models

This paper analyzes the optimal communication involving large intelligent surfaces (LIS) starting from electromagnetic arguments. Since the numerical solution of the corresponding eigenfunction problems is in general computationally prohibitive, simple but accurate analytical expressions for the link gain and available spatial degrees-of-freedom (DoF) are derived. It is shown that the achievable DoF and gain offered by the wireless link are determined only by geometric factors, and that the classical Friis’ formula is no longer valid in this scenario where the transmitter and receiver could operate in the near-field regime. Furthermore, results indicate that, contrarily to classical MIMO systems, when using LIS-based antennas DoF larger than 1 can be exploited even in strong line-of-sight (LOS) channel conditions, which corresponds to a significant increase in spatial capacity density, especially when working at millimeter waves.