Radio-over-fiber Research Articles

Design of a RoF fronthaul link based on optical generation of mm-waves for 5G C-RANs

In this paper, a cloud-radio access networks based (C-RANs) radio-over-fiber (RoF) system have been reported with the optical generation of 28 GHz and 57 GHz millimeter-wave using phase modulation and stimulated Brillouin scattering effect in optical fibers. As a result, a cost-effective system with improved performance is achieved by the proposed method. Based on the proposed scheme, a 28 GHz (licensed band) and 57 GHz (Un-licensed band) optical millimeter-waves are generated by simulation only using 14 GHz and 16 GHz radio frequency (RF) respectively. Because the performance of any optical transmission system is limited by the Q factor and the bit error rate (BER) and any input power of the laser into the fiber needs to be less than the Brillouin threshold in order to avoid the sharp degradation of the Q factor. Also, the Brillouin threshold for this study setup is determined which is around 6 dBm in the case of licensed band and 2 dBm in the case of unlicensed band. The simulation results show that the proposed scheme can provide 100 km single-mode fiber for 28 GHz and 25 km for 57 GHz with transmission rates of 10 Gbps for both of them. In addition, a stable millimeter-wave RoF link, high quality carriers, and a reduction in nonlinearity effects are achieved with the proposed scheme.

4Gbaud PS-16QAM D-Band Fiber-Wireless Transmission over 4.6 km by Using Balance Complex-Valued NN Equalizer with Random Oversampling.

D-band (110-170 GHz) is a promising direction for the future of 6th generation mobile networks (6G) for high-speed mobile communication since it has a large available bandwidth, and it can provide a peak rate of hundreds of Gbit/s. Compared with the traditional electrical approach, photonics millimeter wave (mm-wave) generation in D-band is more practical and effectively overcomes the bottleneck of electrical devices. However, long-distance D-band wireless transmission is still limited by some key factors such as large absorption loss and nonlinear noises. Deep neural network algorithms are regarded as an important technique to model the nonlinear wireless behavior, among which the study on complex-value equalization is critical, especially in coherent detection systems. Moreover, probabilistic shaping is useful to improve the transmission capacity but also causes an imbalanced machine learning issue. In this paper, we propose a novel complex-valued neural network equalizer coupled with balanced random oversampling (ROS). Thanks to the adaptive deep learning method for probabilistic shaping-quadrature amplitude modulation (PS-QAM), we successfully realize a 135 GHz 4Gbaud PS-16QAM with a shaping entropy of 3.56 bit/symbol wireless transmission over 4.6 km. The bit error ratio (BER) of 4Gbaud PS-16QAM can be decreased to a soft-decision forward error correction (SD-FEC) with a 25% overhead of 2 × 10-2. Therefore, we can achieve a net rate of an 11.4 Gbit/s D-band radio-over-fiber (ROF) delivery over 4.6 km air free wireless distance.

Optical duobinary transmitter based OQPSK line coding phase offset for the prediction of OWC channel systems performance efficiency

Abstract This work demonstrates the optical duobinary transmitter based optical quadature phase shift keying line coding phase offset for the prediction of optical fiber wireless channel systems performance efficiency. The max signal light power variations with the spectral wavelength variations for different degree phase offsets based optical quadrature phase shift keying (OQPSK) transmitter are clarified. The max signal light power variations with the time variations for various degrees phase offset based OQPSK transmitter are demonstrated. The total power lighted after OWC channel for various degree phase offset based OQPSK transmitter are indicated. The max electrical power signal amplitude variations with the time variations for various degree phase offset based OQPSK transmitter are observed. Total electrical power signal after optical receiver for various degree phase offset based OQPSK transmitter is clarified. Total optical power variations after OWC channel for various degrees phase offset based OQPSK transmitter is studied.

A Scalable 26 GHz RoF Relay System Using Optoelectronic Extender

This letter presents data transmission over a 26 GHz millimeter-wave (mmW) radio signal and its coverage extension in an indoor environment using the radio-over-fiber (RoF) technology. The proposed system consists of two RoF seamless wireless links to emulate a mobile fronthaul using a transparent RoF relay link to overcome higher attenuation of the mmW signal. The system is experimentally evaluated for up to 64-quadrature amplitude modulation (QAM), showing the possibility of signal transmission over up to 20 km of optical fiber in the first Section transmission scheme without the usage of an optical amplifier. For the system with 20 km and 30 m long RoF links as well as 4 m and 1 m long relays with no optical amplification, the minimal experimentally measured error vector magnitude is as low as 5% for 64-QAM. Further, a self-developed integrable optoelectronic extender is used for the relay RoF system to simplify the antenna site and keep its footprint small. Moreover, the proposed setup is extended using an optical amplifier toward a scalable scheme with up to 75 km of optical fiber and 5 m long free space optical link.

Beyond 300-Gbps/λ photonics-aided THz-over-fiber transmission employing MIMO single-carrier frequency-domain equalizer.

We experimentally realized a 320-GHz 320-Gbps/λ terahertz (THz) radio-over-fiber (RoF) system based on a photonics-aided scheme with the help of polarization-division multiplexing (PDM) technology and multiple-input, multiple-output (MIMO) transmission. In this system, the low-complexity MIMO single-carrier frequency-domain equalizer (SCFDE) is implemented to compensate for the polarization-related impairments of the PDM signal, and the demultiplexing performances between SCFDE and the commonly used constant modulus algorithm (CMA) are also compared in this proposed system. After 20-km standard single-mode fiber (SSMF) and 3-m 2 × 2 MIMO wireless link transmission, the bit error rate (BER) of the received 46-GBaud PDM 16-ary quadrature amplitude modulation (16QAM) signal satisfies the soft-decision forward error correction (SD-FEC) threshold with 15% overhead, which corresponds to a record-breaking net bit rate of 320 Gbit/s.

Machine Learning-Based Digital Pre-Distortion Scheme for RoF Systems and Experimental 5G mm-waves Fiber-Wireless Implementation

The advent of the 5th generation of mobile networks brought a large number of new use case and applications to be supported by the physical layer (PHY), which must be more flexible than all previous radio access networks (RAN). The concept of the centralized RAN (C-RAN) allows all the baseband processing to be performed in the central office, simplifying the network deployment and also allowing the operators to dynamically control the PHY according with the applications requirements. The radio-frequency (RF) signal generated by the C-RAN can be transported to the remote radio unit (RRU) by using a radio over fiber (RoF) system. In this paper, we propose two RoF approaches for composing the transport and access networks of the next-generation systems. The first investigation relies on the implementation of a machine learning-based digital pre-distortion (DPD), designed for RoF systems. In the second approach, we implement an RoF system and characterize the optical and electrical power levels aiming to reduce the RoF non-linear distortions. The overall link performance is evaluated by measuring the error vector magnitude (EVMRMS) and 590 Mbit/s is achieved with EVMRMS as low as 4.4% in a 10 m reach cell.

Performance analysis of a heterogeneous network employing DAPSK based OFDMA-PON

Recent mobile broadband networks require heterogeneous networks supporting high capacity on demand. A hybrid Fiber-Wireless (Fi-Wi) access network integrating Differential Amplitude and Phase Shift Keying (DAPSK) based — Orthogonal Frequency Division Multiple Access (OFDMA) Passive Optical Network (PON) and 4G wireless network using Radio over Fiber (RoF) technique is proposed. The proposed heterogeneous network is simulated, and the performance is analyzed in terms of Bit Error Rate (BER), Error Vector Magnitude (EVM), Capacity, and Spectral efficiency. The proposed network is simulated considering a higher data rate of 10 and 25 Gbps, and the effect of system parameters like Laser Power, Fiber Length, and Number of users is analyzed. The results show that a higher network capacity of 720 Gbps with an average capacity of about 45 Gbps and a higher spectral efficiency of 4.85 bps/Hz is achieved for the multi-user heterogeneous network link with sixteen users. The minimum value of optical power sufficient to achieve the desired BER is found to be −6 dBm. The suitability of the proposed integrated architecture in supporting multiple services is analyzed by considering different services at each UE. The spectral efficiency of the multi-service link varies from 3 to 4 bps/Hz.

Numerical Investigation on the Temperature dependent Impedance Characteristics of Far-Infrared Quantum Cascade Lasers

Quantum Cascade Lasers (QCLs) as Terahertz (THz) frequency sources offer a potentially viable solution for new applications in mid and far-infrared frequency bands. This research work exhaustively investigates the temperature dependence on the impedance of temperature dependent Quantum Cascade Lasers (QCLs) operating at 116μm, for the first time. In the 90-stage QCL considered for the work, the cold finger temperature is varied from 15K to 45K. When the device is biased at 0.6A current along with a cold finger temperature of 45K, the magnitude of intrinsic impedance was found to be 23.91mΩ, at a frequency of 4GHz. As the cold finger temperature is increased from 15K to 45K, the impedance response of the device becomes flat and stays constant. At 45K with an injected current of 1.5A, maximum impedance of 3.1mΩ is obtained. The resonant frequency characteristics of the device increase with increase in injected current and cold finger temperature. Also, it is observed that the magnitude of intrinsic impedance decreases with increase in injected current. The impact of cold finger temperature on the intrinsic impedance characteristics are detailed for prospective Radio over Fiber (RoF) applications.

A novel method to generate and transmit 40-tupling frequency millimeter wave over fiber based on remodulation of MZMs

An novel method to generate 40-tupling frequency millimeter (MMW) based on the remodulation of MZMs and a novel radio over fiber (ROF) system to transmit the generated MMW are proposed. At the central station (CS), the ±4th order sidebands generated by two Mach-Zehnder modulators (MZMs) in parallel are used as the optical carriers for the remodulation. The radio frequency (RF) signal for the remodulation can be generated by injecting the ±4th order sidebands in the photodetector (PD). The main components in the signal after remodulation are ±4th, ±12th and ±20th order sidebands, among them, the +20th sideband is filtered out by a fiber Bragg grating (FBG). After the +20th order sideband is modulated with the downlink data, the ±20th order sidebands are combined again and transmitted to the base station (BS) by optical fiber. At the BS, a part of −20th order sideband is filtered out with a FBG, and with which the uplink data is modulated on it and sent back to the CS for carrier wave reuse. The 40-tupling frequency MMW signal with downlink data is generated by beating the output signal from FBG in the PD. In the case of data rate is 2.5G/bps and the bit error rate is less than 10−9, the transmission distance can exceed 90 km, the power penalty of the uplink and downlink is less than 1 dB and 0.29 dB, respectively. Our scheme has simple structure, high frequency multiplier factor, it has important application prospects in MMW technology.

A Power-Efficient 20–35-GHz MZM Driver With Programmable Linearizer for Analog Photonic Links in 28-nm CMOS

Analog photonic links require linear drive of electrooptic modulators at high frequency to support emerging millimeter wave (mm-wave) communication standards. However, this is challenging due to the nonlinear distortion of commonly used Mach–Zehnder modulators (MZMs). This article presents the first CMOS MZM driver capable of operating over a wide 20–35-GHz frequency range with a programmable linearizer. A broadband design is achieved with a magnetically coupled resonator (MCR) technique that provides wideband impedance matching for the interstage and output-stage matching networks. Linearization is achieved with a topology consisting of inverter-based amplifier segments that provide programmable predistortion gains over the input signal regions. Fabricated in 28-nm CMOS, the driver delivers 2.5-Vpp swing to an external MZM. Operating the majority of the circuitry at 0.9 V, except for the 1.6-V output stage, allows for a power consumption of only 180 mW. The proposed programmable linearizer is able to compensate the amplitude-to-amplitude modulation (AM–AM) compression of the amplifier stages and the external MZM, extending output power 1-dB compression point ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {OP}_{1~\text {dB}}$ </tex-math></inline-formula> ) of the whole radio-over-fiber (RoF) link by 3 dB and achieving 4.8-dBm third-order input intercept point (IIP3) at 25 GHz.

Amplified radio-over-fiber system linearization using recurrent neural networks

Ubiquitous communication is an emergent feature of the future sixth generation of mobile communication (6G) networks. One of the main challenges of this upcoming mobile network is providing broadband communication wherever connectivity is necessary, including rural areas. Up to now, all previous generations of mobile networks have not satisfactorily accomplished this task, and the high cost of deploying and maintaining complex communication infrastructure in remote areas is one of the main reasons. The centralized radio access network might play an important role in overcoming it, since it enables all baseband centralization in a central office (CO), simplifying network deployment and reducing operating/maintenance costs. Additionally, in this scenario, the radio over fiber (RoF) system might be used for transporting analog signals from the CO to a simplified remote base station, composed only of an optical detector and radio-frequency front-end. However, the Mach–Zehnder modulator and power amplifier, commonly employed in RoF systems, introduce undesired nonlinear effects that can severely degrade overall system performance and prohibitively increase the out-of-band emission. We investigate the use of machine learning (ML) algorithms applied to the linearization of an electrical-amplified RoF system. Particularly, a memory recurrent neural network (RNN) linearization is proposed and compared with a memoryless multilayer perceptron linearization. The root mean square error vector magnitude, normalized mean square error, and adjacent channel leakage ratio metrics have been calculated to evaluate the performance of our ML-based approach. Numerical results demonstrate promising linearization performance when the RNN memory depth is equal to or higher than the amplified-RoF system memory depth.

Verification of Applicability of 90 GHz Band Millimeter‐Wave for Obstacle Detection to Railway

AbstractObstacles on railway tracks are a factor hindering safe and stable operation. For this reason, obstacle detection systems have been introduced at level crossings, slopes and under platforms. However, they have been introduced only in limited sections for limited applications. Therefore, the authors considered to introduce an obstacle monitoring system that combines 90 GHz band millimeter‐wave and Radio over Fiber (RoF) technology, as an obstacle monitoring system over tracks to monitor the entire line. Since the millimeter‐wave band has a wide bandwidth, high precision detection is possible when they are used in radar. In addition, since radar control units can be grouped in one place by introducing the RoF technology, we can build a system at a low cost. In order to study the feasibility of introducing a new obstacles monitoring system combining 90 GHz band millimeter‐wave and RoF technology in railway environment, a field test using prototype equipment was conducted on a railway track. As a result, it was confirmed that the prototype radar system could detect humans and non‐metallic objects entering a track at a distance of about 200 m from the location of the prototype system. These results shows that the proposed system has the potential to be introduced as a new railway obstacle monitoring system using 90 GHz band millimeter‐waves and RoF technology. © 2023 The Authors. IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Millimeter-Wave Channel Measurements and Path Loss Characterization in a Typical Indoor Office Environment

In this paper, a path loss characterization at millimeter-wave (mmWave) frequencies is performed in a typical indoor office environment. Path loss results were derived from propagation channel measurements collected in the 25–40 GHz frequency band, in both line-of-sight (LOS) and obstructed-LOS (OLOS) propagation conditions. The channel measurements were performed using a frequency-domain channel sounder, which integrates an amplified radio over fiber (RoF) link to avoid the high losses at mmWave. The path loss was analyzed in the 26 GHz, 28 GHz, 33 GHz and 38 GHz frequency bands through the close-in free space reference distance (CI) and the floating-intercept (FI) models. These models take into account the distance dependence of the path loss for a single frequency. Nevertheless, to jointly study the distance and frequency dependence of the path loss, multi-frequency models were considered. The parameters of the ABG (A-alpha, B-beta and G-gamma) and the close-in free space reference distance with frequency path loss exponent (CIF) models were derived from the channel measurements in the whole 25–40 GHz band under the minimum mean square error (MMSE) approach. The results show that, in general, there is some relationship between the model parameters and the frequency. Path loss exponent (PLE) values smaller than the theoretical free space propagation were obtained, showing that there are a waveguide effect and a constructive interference of multipath components (MPCs). Since the measurements were obtained in the same environment and with the same configuration and measurement setup, it is possible to establish realistic comparisons between the model parameters and the propagation behavior at the different frequencies considered. The results provided here allow us to have a better knowledge of the propagation at mmWave frequencies and may be of interest to other researchers in the simulation and performance evaluation of future wireless communication systems in indoor hotspot environments.

FiWi network planning for WiFi enabled gram panchayats of India: A frame work using component placement optimization

Fiber Wireless (FiWi) access network consists of high speed passive optical network (PON) at back end and wireless mesh network at front end. It is emerging as the most prominent access network due to its inherent feature. It may provide fast Internet services at minimum possible cost. Many of the villages of the India are still not connected with high speed network hence the present paper provides FiWi network planning for creating the Wireless Fidelity (WiFi) enabled villages (Gram Panchayats) of India. The main aim of the paper is to deploy the cost effective FiWi network to provide the faster internet services at reasonable prices to the users of the gram panchayat (GP) in India. The area of the GP and the user’s location in particular GP is taken as input for network planning. The proposed planning provides the optimized position of wireless routers and Optical Network Units (ONUs) in terms of latitude and longitude. For optimizing position of wireless router and ONUs, we propose to use customized Slime Mould algorithm (SMA). We considered four gram panchayats of Indore region of India to make them WiFi enabled using FiWi access network. The customized SMA algorithm provides the best possible position and number of wireless routers and ONUs to connect all the users of gram panchayat. Beside, the total fiber length from the Optical Line Terminal (OLT) to all the ONUs and total cost estimation is also given to create the complete network.

Enhanced 4×4 MIMO RoF architecture for 5G mmWave indoor applications at 60 GHz unlicensed band

4×4 Multiple Input Multiple Output (MIMO) optical architecture based on Radio over Fiber (RoF) is proposed for 5G millimeter Wave (mmWave) indoor applications in the unlicensed 60 GHz band. First-order and second-order sidebands, generated by Dual-Drive Mach-Zehnder Modulator (DD-MZM), are exploited as optical subcarriers in order to reduce the number of Local Oscillators (LOs) implemented. Four MIMO-OFDM signals are multiplexed using Dual-Parallel Mach-Zehnder Modulator (DP-MZM) configured to perform Optical Carrier Suppression (OCS) modulation. 60 GHz spacing is ensured between each data signal and its corresponding subcarrier which allows simple heterodyne detection at Radio Access Point (RAP) level. In addition, we have proposed a 4×4 MIMO extension of Triple-S-and-Valenzuela (TSV) radio channel model based on geometrical approach. We demonstrate that the proposed RoF system with adequate configuration can meet the 5G New Radio (NR) requirement in terms of Error Vector Magnitude (EVM). Moreover, Bit Error Rate (BER) performance is evaluated with and without 5G NR channel coding, for transmission over 25 km of optical fiber followed by 3 m of radio channel, by exploiting the overall allocated band at 60 GHz which allows to achieve a very high data rate up to 122.5 Gb/s.

An 18-Tupled Photonic Millimeter-Wave Generation Using Cascaded Mach-Zehnder Modulators

ABSTRACT This article presents an optical generation scheme of mm-wave carriers by 18-tupling of radio frequency (RF) signal using three cascaded Mach-Zehnder modulators. The proper selection of modulation index, biasing points and phase shifts leads to generation of desired ninth-order sidebands. A thorough mathematical analysis has been performed to validate the mm-wave generation and the results obtained are also consistent with simulation findings. Moreover, the effect of variation of key system parameters from their ideal values is also investigated. The higher tupling factor and elimination of optical filtering in the proposed scheme make it promising for implementation in radio-over-fiber (RoF) transmissions.

Transformer-based High-fidelity Modeling Method for Radio over Fiber Link

High-fidelity modeling is of great importance for digital twin (DT) technology. A Transformer-based modeling method for radio over fiber (RoF) link is developed and experimentally demonstrated, in which the Transformer is a kind of deep learning network. The modeling performance of the constructed model by using the proposed method is evaluated, which is better than the ones based on fully connected neural network (FCNN), convolution neural network (CNN), and generative adversarial network (GAN). In addition, the modeling consistency with different laser launch power, fiber length, carrier frequency, and signal-to-noise ratio (SNR) is also investigated. Experimental results show that the fitting waveforms predicted by the proposed method agree well with the actual waveforms at the receiver end. The normalized mean square errors of the fitting waveforms are lower than the acceptable bound of 0.02.

4 × 4 MIMO Fiber-Wireless System with RoF Transmission Capability

Transport networks, particularly fronthaul systems are facing substantial issues as a result of the expansion of radio access technologies (RATs) in 5G and beyond networks. Due to the difficulties and high expense of installing fiber links, a traditional fiber-optic based mobile transport system will not be adequate for delivering radio signals to new antenna sites. The ease and speed of installation make wireless transport systems an appealing alternative. In this work, a 4×4 MIMO fiber wireless system with wavelength division multiplexing (WDM) and polarisation division multiplexing (PDM) radio over fiber (RoF) transmission capacity is proposed and Simulated. Moreover, a Filter Bank Multicarrier modulation is employed to increase the system capacity. In order to improve the spectral efficiency of RoF and fiber-wireless systems, FBMC is an excellent choice for modulation. Also a 4×4 MIMO OQAM based FBMC signal is simulated and its performance is compared with 2 × 2 MIMO system. Satisfactory performance is confirmed with quality factor of 14.6040 and minimum BER of 1.22×10-45. 4 × 4 MIMO fiber wireless system achieved better quality factor compared to 2×2 MIMO system. Simulation of both systems are performed using Matlab integrated with Optisystem Software. It offers an affordable solution to enable massive amount of MIMO signal transmission and may be a potential approach for upcoming mobile access and radio transport networks in high frequency bands.

METHODS FOR MEASURING RELATIVE NOISE INTENSITY (RIN) OF LASER RADIATION

Over the past decades, in the field of ultra-wideband receiving and transmitting systems, there has been a process of replacing “electronic” systems with “photonic” ones. This transition is primarily due to the fact that the photon, by its nature, has no charge and mass, unlike electrons. As a result, photonic systems are not affected by electromagnetic fields and also have a wider signal bandwidth. In modern fiber optic technologies, the requirements for optical transmitters and lasers are constantly increasing, since they are one of the main components of the fiber optic communication system. The signal-to-noise ratio in optical communication lines depends significantly on the instability of laser radiation power. In this regard, it is necessary to know the features and characteristics of this instability. The results of a study of the relative noise intensity of laser radiation for an optical signal transmission system are presented. An analysis of typical methods for measuring RIN was carried out by conducting a series of measurements of the parameters of the radio over fiber (ROF) transceiver optical system. Based on a comparison of the results of various methods for measuring RIN, it is shown that the most effective measurement method in laboratory conditions is a method based on subtracting noise of different origins from the total value.

Fiber Wireless (FiWi) Access Network Planning &amp; Deployment using Reptile Search Algorithm

Aim: The aim of this study is the deployment of components in an efficient manner to make a cost-effective FiWi network. Background: Fiber Wireless access network is the boost to broadband access technology for providing network services to Internet users at a lower cost. Deployment of components in FiWi access network is very crucial since it affects the deployment cost and network performance. Objective: We investigate the planning process for efficient placement of components in FiWi access networks. For optimizing the position of components (wireless routers and ONUs) in the network, a novel nature inspired Reptile Search Algorithm (RSA) is proposed in the paper. Methods: Extensive simulation is carried out to implement proposed work. A simulation model and code is developed in MATLAB to get the optimized position of components for existing and proposed algorithms. Result: We compare the performance of proposed algorithm with existing algorithm. The obtained results show that the proposed algorithm has superior performance than the existing algorithm. Conclusion: The present work optimizes the position of components using RSA algorithm. RSA returns the lower number of required wireless routers/ONUs, lesser TCD, increased AONUC, fast convergence rate, lesser execution run time than WSSA algorithm. The outcome of the paper highlights the importance of the proposed work in network planning and component deployment in FiWi access network.