Signal Transmission Performance Research Articles

A Novel Low-Complexity High-Order DPSK System With Constellation Reconstruction for FSO Communication

Free Space Optical (FSO) communication has been widely studied because of its advantages such as rich spectrum resource, high transmission capacity, high security, low power consumption and flexible installation. However, FSO link is sensitive to weather conditions and atmospheric turbulence, which poses a great challenge on signal transmission quality. Differential Phase Shift Keying (DPSK) modulation is well recognized as a promising technique to deal with the inter-symbol interference due to channel fading. Nevertheless, the existing system structure for high-order DPSK modulation technology is too complex to be used in practice for FSO system. Therefore, this letter proposes a simplified DPSK modulation scheme. In order to alleviate signal transmission performance degradation caused by simplification, a constellation remapping method is employed in the proposed scheme to achieve flexible signal transmission and improve the Bit Error Rate (BER) performance. It is demonstrated that compared with the traditional DPSK system, the proposed scheme significantly reduces the system complexity and has better BER performance under low to moderate atmospheric turbulence.

Ring based hybrid FSO- fiber optic architecture utilizing same wavelengths for downstream and upstream transmission with FN/DN protection capability

This paper proposes a reliable hybrid 4 × 10 Gbps fiber optic-FSO based ring architecture. The proposed architecture aims to provide reliable and bandwidth-efficient transmission. The proposed architecture has a fault protection capability in presence of the link failure occurring at the feeder network (FN) and distribution network (DN) towards the central office (CO) and optical networking unit (ONU) respectively. To avail the benefits of free space optics (FSO), it is integrated with the optical fiber at the user end. The architecture transmits the data on the ring in only a clockwise direction for both downstream and upstream transmission and therefore enables the utilization of the same wavelengths without any interference. i.e. the proposed architecture improves the bandwidth utilization and needs only half of the spectrum. In the proposed architecture, four 10 Gbps signals are propagated through a 20 km single-mode fiber (SMF) and a 200 m length of free-space/optical fiber link for the downstream and upstream transmissions. We also compared the signal transmission performance of architecture in terms of bit error rate (BER) for different weather conditions of the FSO link at the user side. The architecture works well for the different weather conditions and can transmit data through the FSO link for upto 700 m and 200 m for clear and heavy rain weather conditions respectively. Protection against faults in the fiber links; improves the survivability and reliability of the network. The proposed architecture is useful in rural and urban hilly areas where signal transmission interrupts frequently due to various geographical challenges.

Single Wavelength Simultaneous Optical Intensity-Polarization-Phase Modulation for Multi-Dimensional Optical Transmission

We propose a novel multi-dimensional optical transmission system based on a direct detection system. In the proposed system, quadrature phase shift keying (QPSK), binary polarized intensity rotational frequency shift keying (PIRBFSK), and binary differential phase shift keying (DBPSK) signals modulated by optical intensity, polarization, and phase are simultaneously transmitted for optical multi-dimensional transmission. The signal transmission performance of the proposed modulation technique and the possible interference of each dimension modulation were numerically and experimentally analyzed. The performance of the proposed system was verified using the bit error rate (BER), eye diagram, and spectrum of the received multi-dimensional signal.

Performance Assessments of Joint Linear and Nonlinear Pre-Equalization Schemes in Next Generation IM/DD PON

Nonlinear distortions in passive optical network (PON) systems degrade signal transmission performance. Joint linear and nonlinear pre-equalizers based on the Volterra series, memory polynomials and artificial neural networks (ANNs) are utilized to mitigate linear and nonlinear impairments. Centralized pre-equalization at the transmitter side of the optical line terminal (OLT) keeps the receiver side digital signal processing (DSP) at the optical network unit (ONU) simple. In this study, performance assessments of these three different pre-equalization schemes in intensity modulation and direct detection (IM/DD)-based 25-GBaud PON systems were evaluated. The joint linear and nonlinear pre-equalization schemes were based on the weight coefficients and the model obtained by channel estimation on the receiver side. We studied and compared the performance of three pre-equalization methods under various implementation conditions, such as received optical power (ROP), number of equalizer taps, and semiconductor optical amplifier (SOA) current. Besides, we studied the equalization performance under different modulation orders, which were applied for data rate optimization to support different power budgets, being the potential solutions for future PON systems with various fiber-reach and split-ratio distributions. As a proof-of-concept, the equalization performance of the 25-Gbaud signals modulated with non-return-to-zero (NRZ), four-level pulse amplitude modulation (PAM-4) and PAM-8 formats, corresponding to 25-, 50-, and 75-Gbps data rates, respectively, were tested. Both numerical simulations and experimental demonstrations were conducted to assess the performance of different pre-equalization schemes. With ANN pre-equalization, more than 4dB improvement in power budget was achieved for 25-GBaud PAM4 and PAM8 signals after 20 km fiber transmission. ANN-based pre-equalizer performed better than ANN-based post-equalizer even when the received signals were in low SNR. The power budgets of the 25-Gbaud NRZ, PAM4 and PAM8 signals after 20 km fiber transmission were 36.2 dB, 29.5 dB and 18 dB, respectively.

Performance of DSSS Signal Transmission with SCM over Low-Frequency MMF Passbands

The transmission of a high data rate signal over low-frequency passbands of multimode fibers is studied in this paper. The subcarrier multiplexing (SCM) technique is applied to mitigate the frequency-selective nature of the passbands, at which many nulls can degrade the signal transmission. The subcarrier frequencies must be chosen appropriately, especially for some low-frequency passbands; otherwise, poorly received subcarrier signals will be obtained, affecting the entire transmission. Rather than transmitting many subcarrier signals over these passbands, the direct sequence spread spectrum (DSSS) technique can be adopted. In this work, a high data rate signal is transmitted over 1 km of multimode fiber using the 3-dB modal band and six other low-frequency passbands. The signal is separated into four sub-signals transmitted over four different channels: the 3-dB modal band, two low-frequency passbands, and one passband (containing four low-frequency passbands). In the last passband, the sub-signal is transmitted using the DSSS, while the other sub-signals are transmitted through amplitude shift keying (ASK) modulation. The performance of the system is determined using the bit error rate (BER). The findings reveal that by applying the DSSS to some low-frequency passbands, robustness is obtained in the subcarrier frequency for use in the DSSS passband. A BER lower than 10-9 with a total data rate of 600 Mbps is achieved. This data rate is three times higher than the data rate obtained by the 3-dB modal band. This performance is achieved without applying any error-correction code.

Investigation into the Reliability and Encryption Performance of Wireless Signal Transmission by Network Coding Combined with Blockchain in Natural Disaster Scenarios

To enhance the reliability and encryption of unmanned aerial vehicle (UAV) wireless signals in natural disaster scenarios, firstly, the present work analyzes the current wireless signal transmission mode of UAV. In addition, it discusses the efficient network coding of wireless signal transmission model and blockchain with strong encryption ability. Secondly, the signal transmission model of network coding is explored. Finally, the network coding wireless signal transmission model is combined with the blockchain wireless signal transmission model to realize efficient and encrypted data transmission. The research results show that the network coding wireless signal transmission model combined with blockchain technology realizes the maximum difference of network coding wireless signal transmission rate of 1.5 Mb/s. The model also encrypts the data in the simulation scenario of natural disasters through blockchain technology. After encryption, the data protection effect of the transmission model is significantly improved and meets the requirements of standard data transmission. Meanwhile, the wireless signal transmission model can reduce the resource occupation rate in the process of data transmission and improve the success rate and universality of data transmission in natural disaster scenarios. The probability of data being successfully protected in disaster is more than 90%. The results provide technical support for the stable transmission of wireless signals in natural disaster scenarios and provide a reference for improving the reliability and encryption of wireless signal transmission.

Evaluation of Cost-Effective Flexible High-Speed Data Exchange Links for Heterogeneously Integrated Multi-Chip Modules and Boards

With increasing complexity and heterogeneity, miniaturized integrated system on both multi-chip module and printed circuit board levels relies more and more on high-speed point-to-point serial signal transmission links as the backbone of inter-chip data signal exchange network, which are inevitably accompanied by signal integrity problems such as loss, reflection, and crosstalk. The difficulties in the physical design phase of interconnect routing for high-speed link on densely occupied package interposers or printed circuit boards and the associated planar area overhead (keep-out zone for the crosstalk prevention and impedance matching, etc.), as well as the relevant cost in manufacturing, performance analysis and actual measurement or evaluation, are also sharply increasing; furthermore, the interconnects implemented on interposer or printed circuit board substrate are physically inflexible, and the corresponding microsystems are not suitable for emerging applications that generally demand good deformability and good conformality to 3-dimensionally shaped mounting surface. How to simultaneously elevate the cost-effectiveness, signal transmission performance and physical flexibility of the high-speed link, while keeping low profile of the whole module, has become one of the major challenges in the evolution of micro/nano system technology. Accordingly, this paper proposes a cable-based point-to-point link method, which adopts physically flexible and widely available off-the-shell cables that can be assembled onto the surface of the interposers or boards as a potential cost-effective solution to the challenge mentioned above. Universal Serial Bus, micro-coaxial cables, and Twinax cables are explored as candidates. The full links for each cable, from one of the paired connectors to another, are physically modeled and validated by an electromagnetic full-wave structural simulation tool, with key components of each type of link taken into considerations. The simulated results and the measured results from vector network analyzers are compared, which verifies the effectiveness of our proposal.

An electroactive hybrid biointerface for enhancing neuronal differentiation and axonal outgrowth on bio-subretinal chip.

Retinal prostheses offer viable vision restoration therapy for patients with blindness. However, a critical requirement for maintaining the stable performance of electrical stimulation and signal transmission is the biocompatibility of the electrode interface. Here, we demonstrated a functionalized electrode-neuron biointerface composed of an annealed graphene oxide-collagen (aGO-COL) composite and neuronal cells. The aGO-COL exhibited an electroactive 3D crumpled surface structure and enhanced the differentiation efficiency of PC-12 ​cells. It is integrated into a photovoltaic self-powered retinal chip to develop a biohybrid retinal implant that facilitates biocompatibility and tissue regeneration. Moreover, aGO-COL micropatterns fabricated via 3D bioprinting can be used to create neuronal cell microarrays, which supports the possibility of retaining the high spatial resolution achieved through electrical stimulation of the retinal chip. This study paves the way for the next generation of biohybrid retinal implants based on biointerfaces.

Effects of bounded noise and time delay on signal transmission in excitable neural networks

The influence of bounded noise and time delay on the sub–threshold signal transmission in FitzHugh–Nagumo neuronal networks is studied in this paper. It is found that the signal transmission performance can be enhanced by moderate noise levels in neuronal systems. There is an optimal cross–correlation time where the noise enhances signal transmission best. Moreover, the positively correlated bounded noise–induced stochastic anti–resonance phenomenon monotonically enhances with the increasing cross–correlated intensity. Interestingly, the stochastic anti–resonance phenomenon disappears when the noise is negatively correlated. With the fine–tuning of the time delay, the resonance peaks occur at each half–integer multiples of the signal period, implying delay–induced multiple stochastic resonances. The sub–harmonic stochastic resonance and stochastic anti–resonance alternatively appear at the appropriate coupling strength. These results may provide a novel perspective on sub–threshold signal transmission in the nervous system.

Wireless Control Combining Myoelectric Signal and Human Body Communication for Wearable Robots.

In this study, a communication module based on human body communication was developed to wirelessly control a wearable robot hand based on myoelectric signals. The communication module adopts 10–60 MHz band and an impulse radio multi-pulse position modulation method to achieve low transmission loss and high data rate. A technique to reduce the module size was developed by sharing the myoelectric signal detection electrode and transmitting electrode, and three receiving electrode structures were investigated to improve signal transmission performance. As a result, the developed communication module provides a packet detection rate of 100% and a bit error rate of less than 10 up to at least 110 cm along the arm, and a wearable robot hand was demonstrated to be properly controlled based on a human subject’s myoelectric signals.

Multi‐path separation and parameter estimation by single DMA in fading channel

The propagation of electromagnetic waves will produce multi-path fading of wireless channel, which degrades communication performance substantially. If multi-path can be separated, better signal transmission and reception strategies can be designed to weaken or eliminate fading and improve signal transmission performance. However, it is challenging for communication nodes with limited number of antennas. A general multi-path separation and measurement framework based on single dynamic metasurface antenna is established which rapidly changes patterns within a single pilot symbol period so that equivalent multi-dimensional received signals can be obtained. Based on the framework, a multi-path channel estimation scheme is proposed. Specifically, the parameter estimation problem is formulated and present the algorithm based on atomic norm minimisation to estimate parameters including angle of arrival and complex gain of each propagation path. Simulation results illustrate that single dynamic metasurface antenna can approach the capability of a conventional multi-antenna array, and even using single dynamic metasurface antenna with 1-bit coding can estimate angle of arrivals and complex gains of multi-path components accurately.

Improved Design of Flange Mount Coaxial Connector With Low Passive Intermodulation Distortion

Imperfect electrical connections cause multiple problems in radio-frequency (RF) measurements, with passive intermodulation (PIM) being the most common one. This article proposes a new design approach to reduce the PIM distortion caused by the imperfect electrical connection in flange mount coaxial connectors. The proposed approach employs a flexible ring embedded in the outer conductor of the flange mount coaxial connector to improve the reliability of the metal electrical connection. A simulation model is further developed to analyze the effects of the embedded ring on the signal transmission performance. The effectiveness of the proposed approach is verified by experiments, demonstrating that the improved design can not only decrease the PIM level by up to 9 dB, but also show a good reliability and stability in the conditions requiring repeated connection and disconnection, and thus, this method has the potential for the application of all flange mount devices.

Research on RF Voltage Measurement Method of Chip Pins

As the core device of electronic equipment, integrated circuit (IC) usually produces large high-frequency electromagnetic interference. In order to study the generation mechanism and suppression methods of such noise, accurate noise measurement and extraction must be carried out. At present, the measurement standard of chip level electromagnetic compatibility is not perfect, and the high-frequency characteristics of pin noise are difficult to be measured accurately. In order to achieve accurate chip pin RF voltage measurement, this paper designs a chip pin RF voltage measurement method, establishes the 3D model of the chip pin RF voltage measurement module, studies the effects of its wiring, via, substrate dielectric constant and other parameters on its high-frequency signal transmission performance, and then optimizes the module. Simulation and experimental results show that the optimization method effectively improves its high-frequency signal transmission characteristics. Finally, the RF voltage of the output pin of the active crystal oscillator is extracted by using the detection system designed in this paper.

The hydroxyapatite microtubes enhanced GelMA hydrogel scaffold with inner “pipeline framework” structure for bone tissue regeneration

The critical bone defect is a ubiquitous problem and attracts extensive research attentions. The artificial material GelMA hydrogels (GH) with high biocompatibility, biodegradability and light curing property is promising for treating bone defect, but hindered by its weak mechanical property and low interconnection of the inner pores. While the normal inorganic materials including hydroxyapatite (HA), mainly in the morphologies of micro-/nanorods, wires and particles, have been composited with GH to enhance the mechanical properties, they can hardly improve porosity or their interconnections. In this study, a GH-based pipeline framework composite hydrogel scaffold was constructed by hybridizing hydroxyapatite microtube (HAMT) and GH. The tubular HAMT increases the mechanical properties of the scaffold, also interconnects the adjacent hole in the scaffold for the signal transmission performance and good breathability. Besides, the surface of the composite scaffold turns to much rougher with the addition of HAMT. Thus, this composite scaffold exhibits high adhesion performance, mechanical properties, breathability, and signal transmission function. Based on these properties, this pipeline framework composite scaffold displays excellent proliferation and differentiation ability of bone marrow mesenchymal stem cells (BMSCs) in vitro and bone repair capability in vivo. This research provides a new idea for multi-functional composite scaffold construction with a simple but practical strategy for bone defect repair.

Low profile and miniaturized dual‐band antenna based on graphene assembled film for wearable applications

Wearable electronic devices are the basic components of wireless human body local area network. Due to their close contact with the human body, it is necessary to improve the flexibility and isolation of the antenna to maintain high signal transmission performance. In this paper, a flexible wearable antenna based on highly conductive graphene assembled film (GAF) and polydimethylsiloxane dielectric material is proposed. The planar combination of the powerful novel materials and supple polymer maximizes the flexibility and chemical stability of the antenna. In addition, the coplanar waveguide feeding and artificial magnetic conductor (AMC) structure enhance the efficiency and isolation with an easier preparation process. In the wearing measurement, the GAF antenna operates at 3.5 GHz for 5G communication frequency band and 5.8 GHz for ISM (Industrial, Scientific, Medical) frequency band. The GAF antenna has a minimizes SAR level, which in accordance with IEEE C95.1 International standard, by taking up a small space with 50.5 × 48.5 × 2.08 mm3. Furthermore, the GAF antenna has good radiation performance both under several different bending conditions and human body conditions.

Effects of chaotic activity and time delay on signal transmission in FitzHugh-Nagumo neuronal system.

The influences of chaotic activity and time delay on the transmission of the sub-threshold signal (STS) in a single FitzHugh-Nagumo neuron and coupled neuronal networks are studied. It is found that a moderate chaotic activity level can enhance the system's detection and transmission of STS. This phenomenon is known as chaotic resonance (CR). In a single neuron, the large amplitude and small period of the STS have a positive effect on the CR phenomenon. In the coupled neuronal network, however, the signal transmission performance of chemical synapses is better than that of electrical synapses. The time delay can determine the trend of the system response, and the multiple chaotic resonances phenomenon is observed upon fine-tuning the time delay length. Both sub-harmonic chaotic resonance and chaotic anti-resonance appear when the STS period and time delay are locked. In chained networks, the signal transmission performance between electrical synapses attenuates continuously. Conversely, the performance between chemical synapses reaches a steady state.

Integrated Multiplex Sensing Bandage for In Situ Monitoring of Early Infected Wounds.

Infection, the most common complication of chronic wounds, has placed tremendous burden on patients and society. Existing care strategies could hardly reflect in situ wound status, resulting in overly aggressive or conservative therapeutic options. Multiplexed tracking of wound markers to obtain diagnostic information in a more accurate way is highly promising and in great demand for the emerging development of personalized medicine. Here, an integrated multiplex sensing bandage (MSB) system, including a multiplex sensor array (MSA), a corresponding flexible circuit, and a mobile application, was developed for real-time monitoring of sodium, potassium, calcium, pH, uric acid, and temperature indicators in the wound site to provide a quantitative diagnostic basis. The MSB was optimized for wound-oriented management applications, which exhibits a broad linear response, excellent selectivity, temporal stability, mechanical stability, reproducibility, and reliable signal transmission performance on the aforementioned physiological indicators. The results of in vivo experiments demonstrate that the MSA is capable of real-time monitoring of actual wounds as well as early prediction of infection. The results ultimately point to the potential clinical applicability of the MSB, which might benefit the quantifications of the complexity and diversity of the wound healing process. This work provides a unique strategy that holds promise for broad application in optimizing wound management and even coping with other diseases.

Quantification of Performance Variation and Crack Evolution of Bond-Wire Interconnects Under Harsh Temperature Environments by S-Parameter Analysis

Electrical interconnects play important roles in both the performance and reliability of integrated circuits. As the operating frequency has increased and products have been exposed to harsh environments such as temperature extremes and thermal cycling, it has become essential to quantify the thermal effects on the reliability of such circuits. In particular, the effects on the signal transmission performance of the interconnects and the evolution of cracks caused by thermo-mechanical stresses need to be investigated. This study proposes that both research goals can be accomplished by S-parameter analysis alone. First, the performance variation was experimentally quantified by in situ measurements of S21 (an indicator of signal transmission performance) on bond-wire test vehicles at static temperatures between -60 °C and 120 °C. An impedance model of the interconnect was developed focusing on thermal expansion effects and it predicted the performance variation of the interconnect successfully at the given temperatures. Second, the results of ex situ measurements of S11 (an indicator of return signal) obtained using a test vehicle under thermal cycling were compared with scanning electron microscopy images of crack propagation in the interconnect. In the crack initiation phase, a resonance peak occurred on the S-parameter pattern and the peak moved toward lower frequencies as the crack propagated until failure. SPICE simulations using a suggested impedance model of the cracked interconnect confirmed the experimental results. In addition, this study demonstrates that monitoring the resonant frequency in the S-parameter pattern as a prognostic factor can predict the initiation and evolution of cracks earlier and is more sensitive than the conventional dc resistance measurement method.

Ultrasonic Signal Transmission Performance in Bolted Connections of Wood Structures under Different Preloads

In industrial applications, bolt connections are simple and economical, contributing to their popularity for use in wood packing boxes. However, they can easily fail when subjected to a continuous vibrational load under usual working conditions such as transportation and hoisting. Based on an ultrasonic technique, nondestructive evaluation can be used to quickly detect large-scale structures, but the complex propagation properties in wood limit its application. To solve this problem, a time-reversal method was adopted to predict the residual preload on bolted connections by focusing on the signals collected by wood structures, which helps to assess the structures’ reliability. In this study, the residual preload of bolted connections in wood structures was predicted using the deep-learning method, LSTM, one-dimensional Resnet and Densenet, and tree classification models. It was confirmed that the use of the time-reversal method for ultrasonic detection focused on the signals transmitted in bolted connections of wood structures and deep-learning methods are a feasible way to predict an ultrasonic transmission model.

Modeling and Optimization Design of Signal Interconnect Channel Considering Signal Integrity in Three Dimensional Integrated Circuits

The signal integrity (SI) analysis of a high-speed signal interconnect channel composed of through silicon vias (TSVs) and horizontal re-distribution layers (RDL) is carried out, and the problems of SI, such as transmission loss, crosstalk and coupling effect in the transmission channel, are analyzed and studied. These signal integrity issues are considered in this paper, a signal interconnect channel model is proposed and the equivalent circuit model is deduced as well. Compared with the traditional one, this interconnect channel model has better performance in SI. Further sweep frequency analysis is carried out for different material parameters to achieve signal transmission performance optimization aimed at this model. Test samples of the proposed signal interconnect channel model are designed and fabricated according to the process index, and measured to verify the actual transmission performance. The design and optimization rule of high-speed signal interconnect channel are summarized which proved that the proposed structure has more advantages in signal transmission performance, and has important guiding significance for practical design.