Electromagnetics for High-Speed Analog and Digital Communication Circuits: Distributed circuits

Due to the proliferation of underwater vehicles and sensors, underwater wireless optical communication (UWOC) is a key enabler for ocean exploration with a strong reliance on short-range bandwidth-intensive communications. A stable optical link is of primary importance for UWOC. A compact, low-power, and low-cost acquisition, pointing, and tracking (APT) system is proposed and experimentally demonstrated to realign the optical link within 0.04 s, even when the UWOC transmitter and receiver are in relative motion. The system successfully achieves rapid auto-alignment through a 4 m tap water channel with a relatively large number of bubbles. Furthermore, the required minimum illumination value is measured to be as low as 7.1 lx, implying that the proposed APT scheme is robust to dim underwater environments. Meanwhile, mobility experiments are performed to verify the performance of the APT system. The proposed system can rapidly and automatically align moving targets in complex and unstable underwater environments, which can potentially boost the practical applications of UWOC.

/pdf/machine-vision-based-acquisition-pointing-and-tracking-1tf8gi59v7.pdf

Machine-vision-based acquisition, pointing, and tracking system for underwater wireless optical communications

Electromagnetics for High-Speed Analog and Digital Communication Circuits: Microwave circuits

A free-space optical (FSO) receiver with high optical alignment robustness configured by a single optical lens is presented, in addition to a newly developed 2-D photodetector array (2D-PDA). A 6 × 6 square-shaped aligned arrangement matrix structure in the 2D-PDA provides a large active area for photodetection. In a 1.5-m FSO demonstration, the optical alignment tolerance on the receiver's lens is evaluated to be as large as 12 mm. The multiple-output signals from the 2D-PDA are used for the maximum ratio combining method in space diversity. The system design and alignment tolerance without a mechanical beam-tracking system are presented and the bit error rate contributed by space diversity is discussed.

/pdf/fso-receiver-with-high-optical-alignment-robustness-using-51w2s8qe1s.pdf

FSO Receiver With High Optical Alignment Robustness Using High-Speed 2D-PDA and Space Diversity Technique

The article deals with a computer-supported design of optimal and robust proportional-integral-derivative controllers with two degrees of freedom (2DoF PID) for a double integrator plus dead-time (DIPDT) process model. The particular design steps are discussed in terms of intelligent use of all available information extracted from a database of control tracking and disturbance rejection step responses, assessed by means of speed and shape-related performance measures of the process input and output signals, and denoted as a performance portrait (PP). In the first step, the performance portrait method (PPM) is used as a verifier, for whether the pilot analytical design of the parallel 2DoF PID controller did not omit practically interesting settings and shows that the optimality analysis can easily be extended to the series 2DoF PID controller. This is important as an explicit observer of equivalent input disturbances based on steady-state input values of ultra-local DIPDT models, while the parallel PID controller, allowing faster transient responses, needs an additional low-pass filter when reconstructed equivalent disturbances are required. Next, the design efficiency and conciseness in analyzing the effects of different loop parameters on changing the optimal processes are illustrated by an iterative use of PPM, enabled by the visualization of the dependence between the closed-loop performance and the shapes of the control signals. The main contributions of the paper are the introduction of PPM as an intelligent method for controller tuning that mimics an expert with sufficient experience to select the most appropriate solution based on a database of known solutions. In doing so, the analysis in this paper reveals new, previously undiscovered dimensions of PID control design.

/pdf/performance-portrait-method-an-intelligent-pid-controller-1c9rbpa1.pdf

Performance Portrait Method: An Intelligent PID Controller Design Based on a Database of Relevant Systems Behaviors

In the actual industrial production process, the method of adaptively tuning proportional–integral–derivative (PID) parameters online by neural network can adapt to different characteristics of different controlled objects better than the controller with PID. However, the commonly used microcontroller unit (MCU) cannot meet the application scenarios of real time and high reliability. Therefore, in this paper, a closed-loop motion control system based on BP neural network (BPNN) PID controller by using a Xilinx field programmable gate array (FPGA) solution is proposed. In the design of the controller, it is divided into several sub-modules according to the modular design idea. The forward propagation module is used to complete the forward propagation operation from the input layer to the output layer. The PID module implements the mapping of PID arithmetic to register transfer level (RTL) and is responsible for completing the output of control amount. The main state machine module generates enable signals that control the sequential execution of each sub-module. The error backpropagation and weight update module completes the update of the weights of each layer of the network. The peripheral modules of the control system are divided into two main parts. The speed measurement module completes the acquisition of the output pulse signal of the encoder and the measurement of the motor speed. The pulse width modulation (PWM) signal generation module generates PWM waves with different duty cycles to control the rotation speed of the motor. A co-simulation of Modelsim and Simulink is used to simulate and verify the system, and a test analysis is also performed on the development platform. The results show that the proposed system can realize the self-tuning of PID control parameters, and also has the characteristics of reliable performance, high real-time performance, and strong anti-interference. Compared with MCU, the convergence speed is far more than three orders of magnitude, which proves its superiority.

/pdf/a-design-of-fpga-based-neural-network-pid-controller-for-39s1m3hw.pdf

A Design of FPGA-Based Neural Network PID Controller for Motion Control System

In recent years, extensive investigations have been made on high-speed visible light communication (VLC) for indoor applications including data centres. For high-speed VLC systems, precise alignment between the VLC transceivers is usually required to establish an optical link with less optical loss. In this paper, an effective scheme of auto-alignment and tracking of transceivers is proposed for practical VLC systems with a high-speed camera for location of the target light source and a two-axis gimbal for initial auto-alignment between transceivers. To explore the feasibility of the proposed scheme, real-time dynamic 200 Mb/s carrierless amplitude-phase (CAP)-VLC transmission is experimentally demonstrated in ≥ 3 m VLC links with red light emitting diodes (LEDs) at an angular accuracy of ≤ 0.02º (0.35 mrad), a tracking speed of ≤ 27º/s and a latency of ≤ 21 ms. The proposed scheme can also be applied for coarse alignment in highspeed laser-based free space optical communication (FSO) systems with visible beacons. 10 Gb/s on-off keying (OOK) transmission is successfully demonstrated over a 1.8 m FSO link with the coarse alignment and the spatial light modulator (SLM)-based fine alignment. Experimental results indicate good flexibility and effectiveness of the proposed scheme for an FSO system with high spatial efficiency and low cabling complexity in data centres.

Effective auto-alignment and tracking of transceivers for visible-light communication in data centres

Mobility is one of important issues for line-of-sight visible light communication (VLC). For a high-speed VLC system, the field of view (FOV) of the transceivers is very narrow for high optical gain at the receiver so that precise alignment between the transceivers is required. To enhance the mobility performance, in this paper, a simple and effective scheme of tracking light source is designed and experimentally demonstrated for practical VLC systems. To detect the target light source, a beacon light encoded with a low-frequency label signal is used along with the information light at the transmitter, whilst a high-speed camera with wide FOV is used for location detection by differentiating received images at the receiver. The detected signal of the light source location is then digitally processed to control a two-axis gimbal for auto-alignment between two transceivers. To mitigate the effects of ambient and interference lights, adaptive threshold and dynamic search window are used. A field-programmable gate array (FPGA)-based on-off keying (OOK) transceiver with the adaptive tracking function is developed for evaluation of the tracking performance. Experimental results show that with the proposed scheme 25 Mbps OOK transmission is successfully demonstrated at a bit error rate of 18°/s. The angular accuracy and latency of tracking the LED transmitter are < 0.02° and < 21 ms, respectively.

A simple and effective tracking scheme for visible light communication systems

Owing to variations in the optical propagation distance and direction in dynamic visible light communication systems, an automatic gain control (AGC) amplifier is experimentally investigated to mitigate fluctuations in bit error rate (BER).

Experimental Investigation of Dynamic Visible Light Communication System with Automatic Gain Control

This paper proposes an optimal resource allocation method. The method is to maximize the Energy Efficiency (EE) for an Energy Harvesting (EH) enabled underlay Cognitive Radio (CR) network. First, we assumed the Secondary Users (SUs) can harvest energy from the surrounding Radio Frequency (RF) signals. Then, we modelled the EE maximisation problem as a joint time and power optimization model. Next, the optimal EH time allocation factor can be calculated. After that the optimal power allocation strategy can be obtain by the fractional programming and Lagrange multiplier method. Finally simulation results show that the proposed iterative method can be better performance advantages compared with the exhaustive method and genetic algorithm. And the EE of this system model is significantly improved compared to the EE model without considering EH.

Weibin Jiang

Papers

A Design of FPGA-Based Neural Network PID Controller for Motion Control System

Effective auto-alignment and tracking of transceivers for visible-light communication in data centres

A simple and effective tracking scheme for visible light communication systems

Experimental Investigation of Dynamic Visible Light Communication System with Automatic Gain Control

Optimal resource allocation method for energy harvesting based underlay Cognitive Radio networks