High-speed Communication Systems Research Articles

Improvements of Organic Photodetectors for VLC Using a New Active Layer, Focal Lens, and a Transimpedance Amplifier

Beyond 5G networks, and for short distance but high-speed communication systems, there is an incipient growing interest in visible light communications (VLC). Furthermore, it is an interesting alternative within the framework of the Internet of Things (IoT). However, there is a problem on the part of the receiver in these systems, motivated by the non-existence of photovoltaic elements used particularly for this purpose. Because of their simplicity and small investment, organic-type photodetectors have a high capacity for use in VLC systems. With a structure of polymers represented by an organic photodetector fabricated with poly (3-hexylthiophene) (P3HT) and a bulk heterojunction active layer of phenyl-C61-butyric acid methyl ester (PCBM) and commercial LEDs, we show our system in this paper. The main novelty of this work is in reception. With different upgrade using a new active layer or adding a focal lens or inserting a transimpedance amplifier, we have achieved improved performance results related to voltage and distance, with an increase of more than 40 %, and Bit Error Rate (BER) by modifying the active layer concentration with respect to results obtained in a former work. Also, we have tested the use of a transimpedance amplifier to obtain the best results in distances of 12 cm to 20 cm and a focal lens with the same objective of improving the BER in critical environments, where the Signal-to-Noise Ratio (SNR) is close to zero. To conclude, these modifications show that it is possible to increase the main parameters of our system to be useful in VLC systems.

Modulation of Multichannel Electronic Communication Signal Parameters Based on a Nonlinear Phase Principle

In order to solve the difficulty of the optical fiber communication system and network as the infrastructure of the global communication network, which is faced with the requirement of large capacity and high speed, the author proposes a method to modulate the parameters of multichannel electronic communication signals based on the nonlinear phase principle. The method includes multichannel electronic communication signal search, multichannel electronic communication signal parameter modulation, and multichannel electronic communication signal automatic acquisition algorithm realization. Experimental results show that under the conditions that the sampling frequency is set to f = 8.145 MHz, the length of the C/A code period is set to 1 ms, and the 1 ms data packet contains 8145 sampling points, under the same experimental conditions, the capture probability of this experiment reaches 100% and the traditional algorithm has a capture probability of up to 70%. Modulation of multichannel electronic communication signal parameters based on nonlinear phase principle has a positive guiding role in building a high-speed optical fiber communication system and network with long distance, large capacity, high elasticity, high reliability, and low delay.

Improvement of Overlap for 2x2 MZI Electro-Optic Switch Based on Lithium Tantalite (LiTaO3)

This research introduces a method of an electro-optic effect and electro-refractive effect that considers very imperative for high-speed optical communication systems. In this research, it presents way by a reduction the gap between the electrodes d, and this technique achieves to solve the problem of overlap for Mach-Zehnder interferometer MZI electro-optical switch base on lithium tantalite LiTaO3, also this technique suggests a model for analysis the effect parameters on the electro-optic overlap of the electro-optic switch as the ordinary positive changing of refractive index and a length of arm switch. This study achieves a better overlap by large positive changing refractive index with a suitable small length of arm about 8µm and low driving power at least 4V/µm. Also, for lithium tantalite LiTaO3, this research achieves a better performance for system using the near infrared wavelength.

Design of Low-Power High-Speed 8 Bit CMOS Current Steering DAC for AI Applications

This paper describes a current steering 8-bit DAC architecture for low power and high-speed assistance in AI networks. This design is most suitable for 5G and next-generation high-speed communication systems on chip (SoCs). This DAC keeps a constant load current and leads to faster operations in wideband portable device applications. The design is based on weighted current transmission through current mirrors wherein current reduces from MSB to LSB continuously. By choosing a low current for LSB, the power dissipation reduces. Power and area are also reduced by using a 2-bit binary to thermometer decoder. The DAC's integral nonlinearity (INL) and differential nonlinearity (DNL) are found to be within 0.4 and 0.9 LSB, respectively. The DAC's highest operating speed is 1GHz, with a power dissipation of around 24.2 mW with the supply voltage of 1.8v using 180nm CMOS technology.

Frequency Scanning Dual-Mode Asymmetric Dual-OAM-Wave Generation Base on Broadband PB Metasurface.

Increasing information capacity is significant for high-speed communication systems in a congested radio frequency sequence. Vortex waves carrying mode orthogonal orbital angular momentum (OAM) have gained considerable attention in recent years, owing to their multiplexing quality. In this study, a broadband Pancharatnam–Berry (PB) metasurface element with a simple structure is proposed, which exhibits an efficient reflection of the co-polarized component and a full 2π phase variation in 10.5–21.5 GHz under circularly polarized wave incidence. By convolution and addition operations, the elaborate phase distribution is arranged and the corresponding metasurface-reflecting dual-mode asymmetric dual-OAM waves is constructed. Under continuous control of the working frequency, the OAM vortex beams with the topological charges 1 and −1 are steered to scan within the angle range of 11.9°–24.9° and 17.9°–39.1° at φ = 315° and 135° planes, respectively. The simulation and measurement results verified the feasibility of generating frequency-controlled asymmetric dual beams and the validity of dual-mode OAM characteristics, both in the near and far fields. This design approach has considerable potential in OAM wave multiplexing and wireless communication system transmission.

Parallel micro-LED arrays with a high modulation bandwidth for a visible light communication.

Over the past few decades, GaN-based LEDs have been widely used in solid-state lighting (SSL) due to their energy-saving and long-lifetime characteristics. However, the limited modulation bandwidth of conventional commercial LED chips limits their application in a high-speed visible light communication (VLC) system. Herein, this work designs vertical parallel micro-LED arrays with different array numbers to develop LED sources for communication and lighting. The as-prepared micro-LEDs in a 2 × 2 array reveal a high modulation bandwidth of ∼785 MHz at 6.67 kA/cm2. Meanwhile, the light output power is over 7 mW, which is more suitable for VLC in free space.

Photonics based frequency hopping spread spectrum system for secure terahertz communications.

Terahertz (THz) spectrum (100 GHz-10 THz) is considered the next frontier in the design of high-speed wireless communication systems. While the high-power THz sources have commercially become available, it increases the possibility of developing THz jammers to disrupt the THz communication link. Therefore, the development of novel anti-jamming solutions is the need of the hour. In this work, we present the photonics-based THz communication system and demonstrate the frequency hopping spread spectrum (FHSS) technique which acts against the single/multi-tone jamming attack in the frequency window of 110 GHz-170 GHz. By tuning the output wavelength of the distributed feedback lasers, the THz carrier frequencies are swept back and forth within the scanning window. The frequency tuning range was measured for different scanning rates of the laser which decreases rapidly with the increase in the scanning rate. Next, we demonstrate the THz FHSS technique in a real-time communication system by transmitting a 6 Gbps NRZ signal in both wireless and THz-fiber-based links within the link distance of 1.75 m. We experimentally found that the measured bit error rate in the THz FHSS system is the time average of the measured BER for individual carrier frequencies within the hopping frequency window. By combining with the forward error correction codes and by using the tunable filter in the receiver, we believe that the proposed technique will offer a novel and compact solution against the single/multi-tone jammer for high-bit rate THz communications.

MTM-Inspired Graphene-Based THz MIMO Antenna Configurations Using Characteristic Mode Analysis for 6G/IoT Applications

6G wireless communications will be immersed in the future with different applications. It is expected to support all IoT services and satellite communications, and it is expected to support artificial intelligence (AI) and machine learning (ML). The THz frequency band has a vital role in 6G communication. In this study, a new graphene plasmonic two-port Terahertz (THz) MIMO antenna is analyzed by the characteristic mode theory (CMA), which gives a better insight into the physical behavior of the MIMO configurations. The proposed MIMO antenna is compact and designed on a Teflon substrate of 130 × 85 µm2. The antenna provides a wide impedance bandwidth of 0.6 THz (3.2–3.8 THz). The CMA is applied to clarify the position at which the mutual coupling gives a maximum concentrated current distribution. It is mainly used to reveal the preferable MIMO antenna configuration by the usage of the model significant and model current distribution property. To reduce the mutual coupling between the radiating elements, a complementary dumbbell-structure Metamaterial (MTM) unit cell is etched in the ground plane to block the coupling mode without any affection on the dominant mode. The preferred MIMO configuration gives high isolation of −55 dB between the radiating patches. The fundamental characteristics have been discussed in detail. The proposed MIMO design offers several attractive features such as large bandwidth of 0.6 THz, low envelope correlation coefficient (ECC) of 0.000168, compact size, stable radiation, high gain of 7.23 dB, and low channel capacity loss (CCL) of 0.006. The proposed MIMO design is suitable for different applications in the THz band according to the high-performance parameters such as biomedical applications, security scanning, sensing, IoT, and 6G high-speed wireless communication systems.

Bidirectional high-speed chaotic communication system based on an all-optical time-delay feedback loop

A bidirectional high-speed chaotic optical communication scheme with physical layer encryption is proposed and studied theoretically. The external cavity optical feedback method is analyzed. An erbium-doped fiber amplifier is used to represent the all-optical delay feedback loop of the traditional external cavity; it can overcome the shortcomings of the traditional method such as lower precision and high equipment volume requirements. The bidirectional communication scheme is discussed; it sets the encryption device at the transmitter, uses the correlation between the two encryption signals to decrypt, and cancels the decryption device at the receiver, which not only simplifies the experimental equipment but also solves the problem that the receiver cannot decrypt synchronously due to the channel damage in remote communication. Further, it is easily applied in production and life. Finally, the simulation results show that the bit error rate is <10 − 5, and the bidirectional transmission of 10-Gb / s information over an 85-km single-mode fiber is successfully realized.

Automatic detection of code-modulated visual evoked potentials using novel covariance estimators and short-time EEG signals

Background and Objective:Over the last years, code-modulated visual evoked potentials (cVEP)-based brain–computer interfaces (BCIs) have been developed as robust and non-invasive tools to construct high-speed communication systems. Recently, beamforming-based algorithms have extensively been used in cVEP-based BCI systems because of the need for short-time stimulation and less training data. One of the main drawbacks of the beamforming-based approaches is that their performance highly depends on estimating data covariance matrix and calculating activation patterns. Methods:In the present study, two novel covariance estimators (i.e., the modified convex combination (MCC) and the maximum likelihood (ML) techniques) are proposed to estimate a robust and more reliable covariance matrix. In the ML method, a new sparsity constraint is considered to express the specific eigendecomposition of the covariance matrix as a sparse matrix transform (SMT). Then, the SMT is calculated using the product of pairwise coordinate rotations. These rotations can be constructed by a cross-validation method. Two stimulation presentation rates of 60 and 120 Hz are used for the coding sequence. Results:Both of the suggested approaches (i.e., the MCC and SMT-based techniques) can efficiently improve the performance of the conventional spatiotemporal beamforming-based methods by providing a robust estimate of the covariance matrix in short stimulation times. Based on the experimental results, it can be concluded that the proposed SMT and MCC methods achieve the best results for the 60 and 120 Hz stimulus presentation rates, respectively. However, for both stimulus presentation rates, the proposed SMT and MCC-based methods remarkably outperform other state-of-the-art methods in cVEP-based BCI, such as conventional spatiotemporal beamforming and optimized support vector machines (SVM). Also, the results showed that the 120 Hz stimulus presentation rate provided faster communication. This procedure is performed by obtaining a maximal Information Transfer Rate (ITR) of 187.38 bits/minute. Conclusion:Finally, the present study suggested that the proposed MCC and SMT-based techniques could automatically detect the gazed targets. Also, these methods could be used as non-invasive alternatives over conventional methods.

A 3D MIMO Channel Model for a High-Speed Train Millimeter Wave Communication System under Cutting and Viaduct Environments

Incorporating MIMO technology with 3D geometry-based stochastic models (GBSM) is a promising channel modeling technique for 5G and beyond. These models could be extended to high-speed train (HST) environments at mmWave bands. In this paper, the proposed 3D MIMO model is composed of the line of sight component (LOS), the non-line of sight component (NLOS) from one sphere, and multiple stochastic confocal elliptic cylinders. The model is applied in the viaduct and cutting environments with a time-varying Rician K-factor. The local channel statistical properties such as the auto correlation function, stationarity distance, and the level crossing rate (LCR) are derived and thoroughly investigated at the 41GHz frequency. These properties are compared with the corresponding measured results at the same wave frequency for an HST wireless channel. There is a strong correlation between the results from the derived model and the measured results. Therefore, this model can be extended to be used for viaduct and cutting channel modeling at the mmWave band.

Patterns Quantization With Noise Using Gaussian Features and Bayesian Learning in VLC Systems

Nonlinear impairments seriously affect the transmission performance of high-speed visible light communication (VLC) systems, which have become the bottleneck of VLC systems in practical applications. To compensate for the nonlinear impairments of VLC systems, we propose a Pattern quantization method (PQM) based on Gaussian feature inputs and Bayesian learning in the time-domain. First, we investigate the signal distribution of VLC systems in the presence of additive white Gaussian noise (AWGN) and nonlinear impairments. Second, probability statistics are used to quantify the noise. Finally, a nonlinear compensator for PAM-8 VLC systems is realized using the Bayesian machine learning principle. In the experiment, a PAM-8 VLC system with a maximum transmission data rate of 1 Gb/s and bit error rate (BER) below the threshold of hard decision forward error correction (HD-FEC) is successfully demonstrated. The results indicate that the PQM compensator can significantly reduce nonlinear impairment and improve BER performance while requiring little computational effort. The Q-Factor is improved by 2.1 dB, the transmission distance is increased by 1/3, and the BER is reduced by 90.05% when compared with conventional nonlinear Volterra equalizers. As far as we know, our study is the first to investigate the input features and quantify the white noise in VLC systems, thereby providing a novel approach to machine learning input data processing.

Ultrafast dynamic switching of optical response based on nonlinear hyperbolic metamaterial platform

The pursuit of high-speed and on-chip optical communication systems has promoted extensive exploration of all-optical control of light-matter interactions via nonlinear optical processes. Here, we have numerically investigated the ultrafast dynamic switching of optical response using tunable hyperbolic metamaterial (HMM) which consists of five pairs of alternating layers of indium tin oxide (ITO) and SiO2. The nonlinearity of the HMM is analyzed by the ultrafast dynamics of the hot electrons in the epsilon-near-zero (ENZ) ITO. Our approach allows large and broad all-optical modulation of the effective permittivity and topology of the HMM on the femtosecond time-scale. Based on the proposed HMM platform, we have shown considerable tunability in the extinction ratio and Purcell enhancement under various pump fluence. In addition, we have achieved all-optical control of the coupling strength through depositing plasmonic resonators on the HMM platform. A significant tuning of the coupled resonance is observed by changing pump fluence, which leads to a switching time within 213 fs at a specific wavelength with a relative modulation depth more than 15 dB.

Wireless Propagation in a Metallic Pipe for the Transmission of Sensory Oil and Gas Well Data

The feasibility of a wireless system is examined for propagation inside an oil and gas well pipeline. The well bore environment is modeled as a circular aluminium pipe and treated as a metallic microwave waveguide. The experimentation test bed was based on the nominal diameters of commercially available oil and gas well pipelines. At the transceivers, half-wave dipole antennas operating at 2.5 GHz were employed. Due to the excitation frequency and the enclosed pipe environment, parameters such as the propagating mode, the directivity, and the realized effective gain of the antennas also needed to be investigated for this scenario. Additionally, a numerical transmission path loss model was developed and verified using full-wave simulations and measurements. The communications link facilitated the continuous monitoring of sensory data with real-time temperature and pressure levels transmitted using N210 universal software radio peripheral modems by National Instruments and symbol coding using orthogonal frequency division multiplexing. This study and experimental work can be a basis for the implementation of a high-speed wireless communications system for deployment inside oil and gas well pipelines for real-time data transmission at microwave frequencies.

Vulnerability Analysis of LTE-R Train-to-Ground Communication Time Synchronization

The time synchronization of LTE-R train-to-ground communication systems plays an important role in ensuring the safety of high-speed railways. In the LTE-R time synchronization process, existing problems, such as the time synchronization message broadcast address and LTE-R all-IP architecture, are vulnerable to attack. In order to analyze the impact of these problems, we propose a new vulnerability analysis method of LTE-R time synchronization based on stochastic Petri nets. Firstly, we construct a stochastic Petri net model of an LTE-R time synchronization process under attack. Secondly, steady-state probability expressions are obtained using the model isomorphism Markov chain. Finally, bychanging the firing rate of several key vulnerable nodes, the relationship curve between the firing rate and the steady-state probability of the clock node is obtained. Simulations show that the vulnerability of LTE-R time synchronization is most affected by the attack on eNodeB of the LTE-R base station. The results can provide a certain theoretical basis for the evolution of high-speed railway GSM-R communication systems to LTE-R.

Coherent chaotic optical communication of 30 Gb/s over 340-km fiber transmission via deep learning.

Chaotic optical communication has attracted much attention as a hardware encryption method in the physical layer. Limited by the requirements of chaotic hardware synchronization, fiber transmission impairments are restrictedly compensated in the optical domain. There has been little experimental demonstration of high-speed and long-distance chaotic optical communication systems. Here, we propose a method to overcome such limitations. Using a deep-learning model to realize chaotic synchronization in the digital domain, fiber transmission impairments can be compensated by digital-signal processing (DSP) algorithms with coherent detection. A successful transmission of 30 Gb/s quadrature phase-shift keying messages hidden in a 15 GHz wideband chaotic optical carrier was experimentally demonstrated over a 340-km fiber link. Meanwhile, the chaotic receiver can be significantly simplified without compromising security. The proposed method is a possible way to promote the practical application of chaotic optical communications.

Superhydrophobic ZIF-8/PEN films with ultralow dielectric constant and outstanding mechanical properties

Polymer dielectrics with stable ultralow dielectric constant (k) and outstanding flexibility are expected to be used in the field of high-speed communications system. Herein, in order to reduce dielectric constant, enhance hydrophobic properties and increase flexibility of dielectric material, ZIF-8/polyarylene ether nitrile (PEN) films are reasonably designed and successfully fabricated via delayed phase inversion approach. It is intriguingly found that with the increase of the amount of ZIF-8, the honeycomb microporous structure, dielectric properties, water resistance and mechanical properties of ZIF-8/PEN films can be finely tuned. The results show that ZIF-8 grows uniformly on the honeycomb pore walls of ZIF-8/PEN films, and the size of honeycomb pores increases from 1.6 μm to 5.8 μm with the increase in the amount of ZIF-8. The dielectric constant of ZIF-8/PEN films is significantly reduced from 1.83 to 1.41. The ZIF-8/PEN films can maintain k values under 1.5 when exposing to a relative humidity of 80% for 7 days. More laudably, the ZIF-8/PEN films reveal superior elongation at break higher than 112% and outstanding flexibility which can be folded repeatedly without rupture. The approach of regulating the pore size by generating ZIF-8 in situ to adjust the dielectric and mechanical properties of composites opens up a novel way for the design of flexible ultra-low dielectric materials.

220 GHz Multi Circuit Integrated Front End Based on Solid‐State Circuits for High Speed Communication System

This paper presents the research on a 220 GHz multi circuit inte-grated front end based on solid-state circuits. This integrated front end integrates a 220 GHz subharmonic mixer, a 110 GHz tripler, a 110 GHz 8 dB hybrid coupler and a 220 GHz waveguide bandpass filter (BPF) in one single block. Compared to the traditional transceivers which usually use cascade connection of the independent mixers and multipliers, the size of the proposed multi circuit integrated front-end block is 25 mm × 20 mm × 20 mm, ten times smaller than the cascading transceiver. In order to check the tripler’s output power, a modified compact 110 GHz 8 dB hybrid coupler is set between mixer and tripler. Due to the characteristics of the hybrid coupler, the deterioration of cascading transceiver’s performance caused by mismatch has also been improved. In addition, to achieve single sideband (SSB) communication, a 220 GHz BPF with high selectivity is integrated in the circuit. The measured conversion loss of the fabricated multi circuit integrated front end is less than 11 dB, where the LO and RF frequency are 37 and 210−220 GHz. Based on this front-end, a 220 GHz high speed communication system has been setup and it can achieve 10 Gbps data transmission using 16QAM modulation.

A Compact 60GHz Power Amplifier in 65nm CMOS Technology

A compact 60GHz power amplifier chip in 65nm CMOS technology of three-stage common source structure is presented. The first two amplifiers offer sufficient gain to pre-amplify the small input power. The third stage amplifier uses two sets of differential pairs to achieve power synthesis. On-chip transformer coupling is adopted to realize inter-stage impedance matching as well as input and output matching. The compact structure of on-chip transformer can reduce the chip size and improve the integration degree. The measured small signal gain at 60GHz of 22.3dB, the saturation power of 20.2dBm, the output P-1dB of 17.3dBm, the PAE of 14%, and the core area is 0.19mm2. The power amplifier can be used in high-speed short-range wireless communication system to enhance communication data transmission capacity.

Time jitter generation and injection algorithms for high-speed applications.

Time jitter is an important means for evaluating the performance of high-speed communication systems. Current high-speed digital designs require faster edge speeds and smaller effective data windows. Therefore, analysis of the root cause of jitter has become the key factor in determining the success or failure of a design. To analyze the jitter source of the whole link, the jitter is usually extracted and analyzed by software or hardware at the receivers. To verify the accuracy of jitter extraction at the receivers, many instrument manufacturing companies have developed oscilloscope software to inject jitter at the transmitters, but the core algorithms for jitter generation are commercially sensitive and the software cannot inject all types of jitter, particularly bounded uncorrelated jitter, into the pure signals. This paper proposes a software jitter modeling and injection algorithm that can be implemented in MATLAB and includes transmitter test signal modeling, jitter generation, and the injection of various types of jitter. Unlike other research and commercial software, the proposed algorithm enables the injection of various types of jitter, notably bounded uncorrelated jitter, into test signals. This algorithm is suitable for integration into real-time oscilloscopes for jitter generation and injection.