RoF System Research Articles

2-dB SNR Gain from Nonlinear Radio Signal Shaping in a Digital-Analog Hybrid RoF System

2-dB SNR Gain from Nonlinear Radio Signal Shaping in a Digital-Analog Hybrid RoF System

A Grouped-ANN Equalizer for the Rotated PS 64QAM OFDM in W-Band ROF System

A Grouped-ANN Equalizer for the Rotated PS 64QAM OFDM in W-Band ROF System

A secure scheme based on polar-coded and 3D mixed domain scrambling in W-band MMW-RoF system

With the development of 6G network, the issue of physical layer security in optical fiber communication is becoming more and more significant. In this paper, a polar-coded encryption and 3D mixed domain scrambling secure scheme in W-band millimeter-wave radio-over-fiber (MMW-RoF) system is proposed. The keys are divided into the shared key and the dynamic key, and the shared key is used for constellation-level encryption and 3D mixed domain scrambling with 3D cat mapping, the dynamic key is used for polar code encryption. After RoF system transmission, the scheme can achieve a large key space of 10453, which is powerful enough to resist brute-force. Because the key is randomly selected in the codebook, this encryption scheme has the effect of resisting chosen-plaintext attacks. In terms of reliability, compared to traditional polar-OFDM and 3D QAM polar-OFDM, this scheme can achieve ∼0.4 dB and ∼0.45 dB gains in receiver sensitivity, respectively. So, the proposed scheme has good security performance and reliability performance, which has a significant potential for application in future optical networks.

MZM–SOA based RoF system for 30-tuple millimeter-wave generation

Abstract In this paper, we have reported radio over fiber system with 30-tuple millimeter-wave generation using dual parallel Mach–Zehnder modulator and semiconductor optical amplifier. The optimum choice of Mach–Zehnder modulator parameters has resulted into generation of signal lightwave and pump signal with frequency separation of 10f RF. Four wave mixing effect in semiconductor optical amplifier results into 30-tuple millimeter-wave signal. The proposed scheme is applicable to radio over fiber system with multiple base stations. The multiple number of frequencies such as 50 GHZ, 100 GHz, and 150 GHz have been generated using 5 GHz radio frequency only. NRZ data at 2.5 Gbps was modulated and successfully transmitted via optical fiber. The impact of injection current on the sideband ratio and BER is investigated. The proposed scheme confirms quality reception of demodulated signal at a transmission distance of 20 km.

Secure transmission in a W-band RoF system based on delta-sigma modulation.

In this Letter, a delta-sigma modulation (DSM) encryption technique in a W-band RoF system is proposed. By performing DSM with different over-sample ratios (OSRs) on the OFDM signal based on the controlled keys generated by the chaotic system at the transmitter and performing constellation masking to disturb the transmitting signal for encryption, a high-order QAM-OFDM-DSM encrypted signal is achieved. In order to further improve the security of the system, bit bidirectional diffusion scrambling is used to resist chosen-plaintext attacks. After experimental verification, under the same transmission power, the encrypted DSM signal can achieve better security than single OSR of DSM signals through a 50-km standard single-mode fiber (SSMF) and a 3-m wireless channel, with the gain of sensitivity increased by ∼1 dBm. From the reliability of the system, the encrypted signal of the proposed scheme can be recovered, which meets a hard decision-forward error correction (HD-FEC) threshold of 3.8 × 10-3.

A Multipath Approach to Self-Interference Cancellation in MIMO Rayleigh Fading Channels

An optically enabled multipath self-interference (MSI) cancellation technique for in-band full duplex (IBFD) multiple input multiple output (MIMO) Radio over Fiber RoF systems under Rayleigh fading channels is proposed. A digitally assisted Rayleigh fading channel model generates the MSI signal. An optically tunable multipath delay lines (OTMDL) module is designed using optical delay lines and an optical attenuator for coarse and fine-tuning of time delays and amplitude matching between the locally generated reference (LR) signal and the MSI signal. The OTMDL module adjusts the LR signal to cancel the effect of MSI on the signal received through the fading channel. The concept is validated using a remote sensor node of a 3 × 3 IBFD MIMO RoF system with a Rayleigh fading channel. The system's performance is evaluated by determining the MSI cancellation depths using the OTMDL section for various cancellation channels and by computing the MSI cancellation for both single band and wideband signals across different cancellation channels. An average value of MSI cancellation depth of 20.38 dB is obtained for a single-tone radio frequency signal in the range 15–25 GHz. Thus, the proposed system for MSI cancellation can be utilized in wireless communication systems in multiple ways.

An overview of recent studies on the limitations of semiconductor lasers under direct modulation for use in analog RoF systems

An overview of recent studies on the limitations of semiconductor lasers under direct modulation for use in analog RoF systems

Demonstration of LDPC-coded PS-64QAM OFDM employing novel bit-class distribution matching in a W-band RoF system

Demonstration of LDPC-coded PS-64QAM OFDM employing novel bit-class distribution matching in a W-band RoF system

Secure RoF system based on key nested polar code and feedback neural network.

With the development of 6 G network, the issue of information security is becoming more and more significant. In this paper, a secure RoF system based on key nested polar code and feedback neural network (FNN) is proposed. For the nested polar code, the original key is randomly selected from the constructed codebook and the index of key is encoded by inner polar code which is placed at the location with better channel quality bit of the frozen bit of outer polar code, for the other part of outer polar code, information bits are encrypted by chaotic sequence generated by 4-D cellular neural network. The polar coded sequence is mapped to the 16-QAM symbol for orthogonal frequency division multiplexing (OFDM) and then the OFDM signal is modulated to the optical pulse, which is delivered to users through 50 km standard single-mode fiber and 5 m wireless channel. In the receiver, successive cancellation list (SCL) decoder is used for decoding outer polar code and FNN is used for decoding inner polar code to reduce the latency. The experimental results show that, compared with the existing scheme, when the bit err rate is 10-3, the received optical power (ROP) gain of the proposed scheme with SCL2 decoder and SCL4 decoder is ∼1.2 dB and ∼1.6 dB, respectively. And compared with the traditional OFDM signal with polar code, when the bit err rate is 10-3, the ROP gain of the proposed scheme with SCL4 decoder is ∼1 dB. What's more, the randomness of the chaotic key sequence, the ability to resist brute-force attacks and the ability to resist chosen-plaintext attacks are elaborated. Therefore, the proposed scheme can greatly improve the security of the system while ensuring the correct transmission of information.

Beam Control Method for Analog RoF Systems Based on Pre-Beamforming with a Few Antenna Elements

Beam Control Method for Analog RoF Systems Based on Pre-Beamforming with a Few Antenna Elements

RETRACTED ARTICLE: Improving the performance of cost-effective millimeter wave-based front-haul RoF system for up to 140 km link length using predistortion device and FBG technique

RETRACTED ARTICLE: Improving the performance of cost-effective millimeter wave-based front-haul RoF system for up to 140 km link length using predistortion device and FBG technique

Evaluation of Three-Level Code Division Multiplexing for High-Quality Radio over Fiber Communication

Radio over Fiber system (RoF) technology facilitates the transmission of wireless signals over optical fibers, which provides many benefits, including low signal loss, and immunity to electromagnetic interference. Despite these benefits, conventional RoF systems grapple with signal impairments and limited user capacity, as each user must be allocated a specific frequency. To address these limitations, this paper explores the implementation of the Three-Level Division Multiplexing (3LCDM) technique with RoF, a superior multiplexing strategy that allows two users to share a single channel, thereby doubling capacity. This innovative combination was evaluated for various cases using 2.4 GHz, 5 GHz, and the combination of 2.4 GHz and 5 GHz carrier frequencies, and its performance was compared with traditional RoF systems. Simulations were carried out using OptiSystem in cooperation with the MATLAB simulator. The findings of this study reveal that the 3LCDM-RoF system can accommodate twice the number of users as the conventional RoF system without the need for amplifiers. Furthermore, it supports higher bit rates and longer transmission distances. Specifically, the 3LCDM-RoF system achieved maximum data rates at maximum fiber length of 2 x 1.1 Gbps at 60 km, (2.4 GHz), 2 x 2 Gbps at 40 km (5 GHz), and 2 x 0.5 Gbps per channel at 43 km (combined 2.4 GHz and 5 GHz) respectively. Meanwhile, the conventional RoF with 2.4 GHz, 5GHz and the combination of 2.4 GHz and 5 GHz can only achieve maximum data rate at a maximum fiber length of 1.1 Gbps at 45 km, 1.6 Gbps at 35 km, and 0.4 Gbps at 35 km respectively

Dual Polarization DQPSK ROF System with Duo Binary Precoding and Hybrid Amplification for Effective Hybrid SMF FSO Transmission Medium

This article demonstrates the utilization of a hybrid amplification technique on the transmission part of the proposed hybrid medium transmission system which includes both using Single Mode Fiber (SMF) with 60 km and Free Space Optic (FSO) with a range between 5 km and 25 km. It has included four weather situations with an investigation of the FSO medium-based system performance. The system uses 64 channels based on Dual Polarization-Differential Quadratic Phase Shift Keying (DP-DQPSK) Dense Wavelength Division Multiplexing (DWDM) for the Radio over Fiber (RoF) system using the Duo Binary coding scheme to improve the system efficiency in general and the cross-talk in particular. The investigations will include using the hybrid amplifiers of Erbium Doped Fiber Amplifier (EDFA) and Optical Amplifier (OA) for transmission. The analysis results show that using the hybrid amplification could improve the transmission to reach 25 km for light air case, meanwhile, for light haze, it could reach up to 20 km. Moderate haze could improve transmission efficiency for a distance of 7 km. Finally, for moderate rain situations, the transmission could be further improved to cover a distance of up to 5 km.

TL-ANN Based Nonlinear Equalization for Multi-Users Radio Over Fiber System

To mitigate nonlinear distortions in multi-user analog radio over fiber (A-RoF) system, a nonlinear equalizer (NLE) which combines transfer learning (TL) and waveform regression-based artificial neural network (ANN) is proposed and validated experimentally in this research. Unlike traditional ANNs, waveform regression ANNs can be regarded as waveform training ANNs and avoid complex-value training. In this paper, we first analyze the modulation distortions that appear in multi-user RoF systems and then propose a waveform regression ANN-based nonlinear equalizer (ANN-NLE). Subsequently, we use TL to reduce training costs and increase the compatibility of the ANN-NLE. Finally, an A-RoF system with multicore fiber is adopted to verify the proposed approach. According to the simulation and experimental results, the bit error ratio (BER) of a multi-user signal is decreased to the threshold of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> , and the improved optical receiver sensitivity is greater than 1.5 dB. This proposed method could realize nonlinear equalization and display good compatibility with different systems.

A survey on machine learning schemes for fiber nonlinearity mitigation in radio over fiber system

Abstract The fifth generation is the most recent generation of communication needed for high data rates. High spectrum availability, low jitter, high reliability, minimal latency, and increased capacity are just a few benefits of 5th generation. Optical fiber supports the 5G network’s backhaul to meet the enhanced capacity and big data rate requirements. When the fiber is used as a propagation medium, a significant number of nonlinearities manifest. These nonlinearity effects in optical fiber communication are among the most detrimental to modern communication systems because it results in various modulator distortions like phase, harmonic, and intermodulation, distortion, adjoining channel noise, and many more undesirable consequences. The primary fiber nonlinear effects in the radio over fiber communication systems are the Kerr nonlinearity and scattering effects, which are caused by alterations in refractive index as a result of the signal. To overcome these limits, several strategies have been put forth. In particular, the nonlinearity during signal modulation, transmission, and detection has attracted a lot of study attention due to the complex physical layer restrictions in RoF systems. One such fascinating potential is machine learning (ML) methods. In this article, we look at recent advances in ML methods for RoF systems, notably those that use ML models to reduce various types of impairments and improve system performance.

Frequency 24-tupling ROF System Based on Cascaded DMZM

Frequency 24-tupling ROF System Based on Cascaded DMZM

Effect of fiber properties and dispersion management on distortions associated with two subcarriers modulation of laser diode in radio over fiber systems

We present numerical modeling and simulation on the effects of standard single-mode fiber (SSMF) properties and different dispersion management approaches on the distortions of laser diode. These distortions are associated with the two-tone modulation of laser diode for use in radio over fiber systems. The fiber properties include attenuation and dispersion. The dispersion management approaches include the use of nonzero dispersion-shifted fiber (NZ-DSF), fiber Brag grating (FBG), and dispersion-compensating fiber (DCF). The laser is directly modulated with two analog frequencies of 25 and 25.1 GHz at different modulation depths (m). The modulated laser signals are then propagated through SSMF at different lengths (L). The investigated laser signal distortions include the 2nd harmonic distortion (HD2), and the 2nd and 3rd intermodulation distortions (IMD2 and IMD3, respectively). The results reveal that all laser distortions are exacerbated as the fiber length increases, which is mainly due to the chromatic dispersion, while fiber attenuation has no effect. The use of dispersion management approaches gives almost similar effects on the reduction of IMD3 when L = 1 km, regardless of the value of m. Up to m = 0.3, DCF is the most effective approach for reducing all distortions over the entire fiber length range, while NZ-DSF is the least. When L = 2 km, FBG is the most effective approach for reducing both IMD2 and HD2 when m ≥ 0.4, whereas when L is increased to 6 km, DCF is the most effective approach up to m = 0.5.Graphical abstractSimulation setup of RoF system for two-tone direct modulation of laser diode using different dispersion management approaches

Design and analysis of 160 GHz millimeter wave RoF system with dispersion tolerance

Design and analysis of 160 GHz millimeter wave RoF system with dispersion tolerance

Multiband RoF System with Good Transmission Performance Based on Additional SCS

A wavelength division multiplexing radio-over-fiber (WDM-RoF) system that can support multiband radio signals based on an additional subcentral station (SCS) is proposed and demonstrated in this paper. The dispersion characteristics of the multiband radio signals over fiber transmission are explored, and we exploit an improved transmission structure consisting of the central station (CS), the SCS, and base stations (BSs) to optimize the antidispersion performance of the proposed RoF system. At the SCS, a dual-drive Mach-Zehnder modulator (MZM) is employed to realize a cost-effective multiband radio signal generation of WDM signals with great spectral flatness, and an optical cross-connect unit is utilized to achieve a flexible distribution of different band radio signals for remote BSs. Based on the additional SCS, we establish a verification WDM-RoF system, which can support reliable transmission of multiband radio signals including 13 GHz, 26 GHz, 39 GHz, and 52 GHz. The WDM signals with each data rate at 2.5 Gbps are successfully transmitted over a 40 km standard single-mode fiber.

Digital mobile fronthaul based on delta-sigma modulation employing a simple self-coherent receiver

The coherent digital radio-over-fiber (DRoF) system is a promising candidate for future mobile fronthaul networks (MFNs) due to its high receiver sensitivity and excellent robustness against nonlinearities. However, conventional coherent receivers with complicated structure and heavy algorithms are too expensive and power-hungry for cost-sensitive MFN applications. In addition, currently deployed digital MFNs based on common public radio interface (CPRI) suffer from low spectral efficiency and high data rate. Towards these issues we propose a novel DRoF downlink scheme employing a simple self-coherent receiver. In baseband unit (BBU), the radio signal is converted to a digital bit stream by a band-pass delta-sigma modulator (BP-DSM), which can be simply recovered with the utilization of a band-pass filter at the receiver. In remote radio unit (RRU), an electro-absorption modulated laser (EML) acts as a low-cost coherent homodyne receiver in virtue of injection locking technique. In the experiment, the injection-locked operation of the DSM signal is successfully achieved, and two modified schemes are proposed for the DSM signal to increase the locking range with a tolerable sensitivity penalty. The experimental results demonstrate the superiority of our approach in two aspects: 1) the EML-based coherent receiver outperforms a PIN photodiode in terms of receiver sensitivity; 2) compared to the analog RoF system, a 5-dB improvement in loss budget is obtained when DSM is employed with the aid of a simple equalizer.