Radio Over Fiber System Research Articles

A High Spectral Efficiency Coherent RoF System Based on OSSB Modulation With Low-Cost Free-Running Laser Sources for UDWDM-PONs

A coherent radio over fiber (RoF) system based on optical single-sideband modulation with no optical carrier (OSSB) for ultradense wavelength division multiplexing passive optical networks (UDWDM-PONs) is proposed and experimentally demonstrated. For one channel of the UDWDM-PONs, at the transmitter, the OSSB RoF signal is generated using a dual parallel Mach–Zehnder modulator (DP-MZM) with a real-valued precoded microwave vector signal which is applied to the DP-MZM via the two electrodes with one having a 90° phase shift. Then, the OSSB RoF signal is sent to a coherent receiver over a single-mode fiber (SMF). The coherent receiver with a free-running laser source as a local oscillator (LO) is used to perform the coherent detection. To recover the standard microwave vector signals from the real-valued precoded microwave vector signal that is embedded in a strong phase noise introduced by both the transmitter laser source and the LO laser source, a digital signal processing algorithm is developed to perform phase noise cancellation. An experiment is performed. The transmission of a 1.25-Gbps quadrature phase shift keying, a 1.875-Gbps eight-phase shift keying (8-PSK), and a 2.5-Gbps 16 quadrature amplitude modulation (16-QAM) microwave vector signals with a channel spacing as narrow as 3 GHz over a 25-km SMF is experimentally demonstrated. For the transmission of the 2.5-Gbps 16-QAM microwave vector signal, the received optical sensitivity at forward error correction level over a 25-km SMF link is −24.8 dBm, while for the 1.875-Gbps 8-PSK microwave vector signal, it can reach −29.8 dBm which leaves an enough margin to accommodate the splitting losses in the optical distribution networks.

Performance optimization of RoF systems using 120° hybrid coupler for OSSB signal against third order intermodulation

The performance of radio over fiber (RoF) system with dual drive Mach Zehender modulator has been optimized against third order intermodulation distortion by using 120° hybrid coupler in transmission system. Signal to Noise Distortion ratio (SNDR) has been evaluated and a performance comparison is also drawn for the systems based on 90° and 120° hybrid coupler in both noise and intermodulation distortion dominant environment. The SNDR is efficiently improved by employing 120° hybrid coupler in noise dominant and intermodulation distortion dominant environment. An improvement of 4.86dB is obtained in the maximum SNDR with 120° hybrid coupler is obtained over at 20km optical fiber length compared with a 90° hybrid coupler based system. A significant reduction of third order intermodulation power at receiver has also been observed with 120° hybrid coupler.

Special cascade LMS equalization scheme suitable for 60-GHz RoF transmission system.

We design a specific cascade least mean square (LMS) equalizer and to the best of our knowledge, it is the first time this kind of equalizer has been employed for 60-GHz millimeter-wave (mm-wave) radio over fiber (RoF) system. The proposed cascade LMS equalizer consists of two sub-equalizers which are designated for optical and wireless channel compensations, respectively. We control the linear and nonlinear factors originated from optical link and wireless link separately. The cascade equalization scheme can keep the nonlinear distortions of the RoF system in a low degree. We theoretically and experimentally investigate the parameters of the two sub-equalizers to reach their best performances. The experiment results show that the cascade equalization scheme has a faster convergence speed. It needs a training sequence with a length of 10000 to reach its stable status, which is only half as long as the traditional LMS equalizer needs. With the utility of a proposed equalizer, the 60-GHz RoF system can successfully transmit 5-Gbps BPSK signal over 10-km fiber and 1.2-m wireless link under forward error correction (FEC) limit 10-3. An improvement of 4dBm and 1dBm in power sensitivity at BER 10-3 over traditional LMS equalizer can be observed when the signals are transmitted through Back-to-Back (BTB) and 10-km fiber 1.2-m wireless links, respectively.

Selective delivery of broadband wireless and wired services in an integrated ROF-PON system using dual-sideband optical carrier suppression

Selective delivery of gigabit-per-second wireless and wired services is demonstrated in an integrated fiber-wireless access network using the millimeter-wave (mm-wave) radio-over-fiber (RoF) system employing the dual-sideband optical carrier suppression technique. A dual-electrode Mach-Zehnder modulator is used in this technique to generate 40 GHz carrier to distribute 1.25 Gbps data via direct modulation (DM) over a 20 km RoF system. The results show that selective signal delivery can be achieved using a low-cost DM laser diode drive current of 20 mA. The advantage of the proposed system is that it provides versatility to control the gigabit-per-second (Gbps) signal delivery in an integrated ROF-PON system with a common high frequency oscillator shared for the whole system. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1768–1773, 2016

Impact of Relative Intensity Noise on 60-GHz Radio-Over-Fiber Wireless Transmission Systems

This paper investigates a 60-GHz radio-over-fiber (RoF) communication system employing two different techniques to generate millimeter-wave (mm-wave) signals. The relative intensity noise (RIN) transferred during optical heterodyning of mm-wave signal is theoretically studied and experimentally investigated. Laser RIN induces noise at resultant electrical mm-wave signal and is directly generated from initial RIN at low frequency. Therefore, RIN impairs the performance of the mm-wave RoF system. The model of RIN is also presented and is in very close agreement with the experiment results. Furthermore, wireless transmission experiments to demonstrate the intensity noise effect are carried out and are compliant with the communication standards at mm-wave. Wireless transmission up to 3 m can be achieved using a transmit power of +4.5 dBm.

Performance Comparison of Analog and Digitized RoF Systems With Nonlinear Channel Condition

We have compared the performance of analog and digitized radio-over-fiber (RoF) systems with a nonlinear channel condition to investigate which one is more suitable for in-building wireless backhauling. For the comparison, we demonstrated optical multicasting of Wi-Fi compatible signals over both RoF links with nonlinear wavelength conversion, and measured error vector magnitude (EVM) performance of the transmitted wireless signals. In the demonstration, the digitized RoF system showed constant performance with EVM (3.75%), while the performance of analog counterpart is highly dependent on optical link conditions.

A Q-band radio-over-fiber system for distribution of uncompressed high-definition video signals

A Q-band radio-over-fiber (RoF) system for the distribution of uncompressed high-definition (HD) video signal is proposed and demonstrated. To eliminate the fiber dispersion induced RF power fading, which is a serious problem for the Q-band RoF system, a polarization modulator (PolM) based transmitter is applied, by which the peak of the frequency response of the fiber link can be shifted to any desired frequency. Besides, an injection-locked Q-band optoelectronic oscillator (OEO) is constructed in the receiver to perform the carrier extraction and frequency downconversion. A 40-GHz RoF system is established, which delivers a 720P uncompressed HD video signal to a targeted displayer through a 20-km fiber link and a ∼1-m wireless link.

Palm-shaped spectrum generation for dual-band millimeter wave and baseband signals over fiber

In order to offer abundant available bandwidth for radio access networks satisfying future 5G requirements on capacity, this paper proposes a simple and cost-effective palm-shaped spectrum generation scheme that can be used for high capacity radio over fiber (RoF) system. The proposed scheme can simultaneously generate an optical carrier used for upstream and two bands of millimeter wave (MMW) that are capable of carrying different downstream data. The experiment results show that the proposed palm-shaped spectrum generation scheme outperforms optical frequency comb (OFC) based multi-band MMW generation in terms of upstream transmission performance. Furthermore, simulation is carried out with different dual-band MMW configurations to verify the feasibility of using the proposed spectrum generation scheme in the RoF system.

Development of hybrid envelop memory polynomial based predistorter for RoF system

Radio over Fiber (RoF), an empowering innovation for dissemination of wireless broadband service signals through simple optical connections experiences non-linear distortion. We have designed and implemented a novel predistorter model to reduce nonlinear distortion using hybrid envelop memory polynomial (HEMPM) for the RoF system. The link gives satisfactory performance in the range of GHz signal. The designed algorithm is superior to popular approaches like memory polynomial model (MPM) and envelop memory polynomial model (EMPM) in terms of order of the memory and degree of nonlinearity. As per author's the best knowledge, this is exclusively first time result obtained for HEMPM technique for RoF link and also, for MPM, EMPM based predistorter for RoF link using MATLAB – OptiSystem co-simulation. The results shows that adjacent channel power (ACP) is suppressed by ∼0.45dBm, ∼28.4dBm and ∼7.65dBm of MPM & EMPM and HEMPM model for K=5 &Q=2 whereas for K=7 &Q=3 the value of suppressed power is ∼36.3dBm, ∼47.7dB and ∼05.8dBm, respectively as compared to input signal. NMSEs for (K=7) and memory length (Q=3) reduced by ∼−5.003dBm for HEMPM model and increased by ∼−4.13dBm for MPM model. The EVM is increased from ∼1.56% to ∼1.96% for HEMPM model and increased from ∼4.38% to ∼14.73% for MPM model for K=7 &Q=3.

Simulation and Analysis of Radio over Fiber (RoF) Systems using Frequency Up-Conversion Technique

Radio-over-Fiber (RoF) technology is an integration of microwave and optical networks [1]. RoF technology uses optical fiber as a backend technology due to the enormous advantages offered by it. SCM-WDM RoF systems (Subcarrier based Wavelength division multiplexing RoF system) improves spectral efficiency with high dispersion tolerance [7]. The data to be transmitted is electrically modulated with an IF (Intermediate frequency)or a RF (Radio frequency) carrier and electrically multiplexed using a multiplexer these signals are further optically modulated using an optical modulator and multiplexed using WDM to exploit the high bandwidth offered by the optical fiber. A comparison between IF over fiber and RF over has been analyzed in terms of quality factor and BER (Bit error rate) in a RoF system. In which the IF over fiber shows better performance than RF over fiber in terms of BER and Quality factor. IF signals are up-converted using HBT (Hetero-junction bipolar transistor) electronic mixer in the remote antenna units to the RF frequencies with the help of LO (local oscillator) and transmitted wirelessly [27]. General Terms Wireless communication systems, Optical fiber communication, Subcarrier multiplexing, Wavelength division multiplexing, Radio-over fiber systems.

Full-Duplex Transmission of LTE-A Carrier Aggregation Signal Over a Bidirectional Seamless Fiber-Millimeter-Wave System

We propose a flexible and high-performance fronthaul system for future mobile networks using a seamless combination of fiber-optic and millimeter-wave (MMW) systems. The proposed system employs a high-quality optical MMW signal generation at the transmitter and a stable and high-performance MMW self-homodyne detection at the receiver. In the downlink direction, successful transmission of intraband and interband carrier aggregation (CA) long-term evolution-advanced (LTE-A) signals over the system is experimentally confirmed. We also confirm satisfactory performance for the transmission over a fiber–wireless bridge using a cascade of the seamless system and a conventional radio-over-fiber (RoF) link. In the uplink direction, we successfully demonstrate the transmission of an intraband CA LTE-A signal over a cascade of a radio-on-radio and a RoF system. In addition, we confirm that the full-duplex transmission of LTE-A signals over the proposed bidirectional system does not experience performance degradation compared to the case with half-duplex transmission. The proposed system is a potential solution for mobile-signal transmission in future networks.

Study on 4PAM Radio over Fiber System Using Self-Mixing Technique

In this paper, a simplified optical millimeter-wave generated by two optical sidebands beating together in a 60 GHz radio over fiber (RoF) system with 10 Gbit/s 4-pulse amplitude modulation (4 PAM) transmission signal is proposed and simulated. 10 Gbit/s electrical 4 PAM signals modulated are conveyed over the length of 40 km standard single mode fiber (SMF) and recovered via the self-mixing technique after detecting directly at the receiver. Graphs of time-domain wave, frequency-domain and optical spectrum are measured out in different period, and the comparison of error vector magnitude curves of NRZ and 4 PAM signals under the different length of fiber is accomplished. The capacity of 4 PAM modulation is higher, though NRZ performs better than 4 PAM selected in RoF system within 80 km of fiber length as shown in the simulation results.

Ultra-Wideband and Adaptive Photonic Signal Processing of Microwave Signals

Microwave photonic techniques are attractive for processing high bandwidth signals, overcoming inherent electronic limitations. These processors provide new capabilities for realizing adaptive processing over extremely wide microwave frequency ranges, ultra-wideband operation, and electromagnetic interference immunity. In-fiber signal processors are inherently compatible with fiber-wireless systems, and can provide connectivity with in-built signal conditioning. Recent new methods in wideband microwave photonic processing are presented, including ultra-wideband phase shifters and true time delays for phased array beamforming, widely tunable single passband filters, switchable microwave photonic filters, wideband photonic mixers, high-resolution multiple frequency microwave photonic measurement systems, and photonic RF memory structures.

Photonic methods of millimeter-wave generation based on Brillouin fiber laser

In optical communication link, generation and delivering millimeter-wave (mm-waves) in radio over fiber (RoF) systems has limitation due to fiber non-linearity effects. To solve this problem, photonic methods of mm-wave generation based on characterizations of Brillouin fiber laser are proposed in this work for the first time. Three novel photonic approaches for mm-wave generation methods based on Brillouin fiber laser and phase modulator are proposed and demonstrated by simulation. According to our theoretical analysis and simulation, mm-waves with frequency up to 80GHz and good signal to noise ratio (SNR) up to 90dB are generated by new and cost effective methods of generation that make them suitable for applications of the fifth generation (5G) networks. The proposed configurations increase the stability and the quality of the mm-wave generation system by using a single laser source as a pump wave and the fiber non-linearity effects are reduced. A key advantage of this research is that proposed a number of very simple generation methods and cost effective which only use standard components of optical telecommunications. Stimulated Brillouin Scattering (SBS) effect that exists in the optical fiber is studied with the characterization of phase modulator. An all optically stable mm-wave carriers are achieved successfully in the three different methods with different frequencies from 20GHz up to 80GHz. Simulation results show that all these carriers have low phase noise, good SNR ranging between 60 and 90dB and tuning capability in comparison with previous methods reported. This makes them suitable for mm-wave transmission in RoF systems to transmit data in the next generation networks.

Spectral Shape Impact of Nonlinear Compensator Signal in LTE RoF System

In this letter, a large scale investigation is carried out, utilizing several spectral shapes as the source for direct modulation based frequency dithering (DMFD). DMFD mitigates the nonlinear effect of long term evolution (LTE) radio-over-fiber (RoF) systems. The dithering signal shapes are; sine, square, saw, sinc and Gaussian with different spectral width characteristics. We show that by varying the dithering signal with increasing spectral width, no additional distortion is introduced in the linear and optimum optical launch power regions, which are dominated by the frequency chirp and chromatic dispersion (CD). Additionally, it is revealed herein that introducing dithering signals with varying spectral widths does not change the nonlinear compensator characteristic towards suppression of nonlinearity. The reason for this is that as long as the optical source linewidth is larger than stimulated Brillouin scattering (SBS) linewidth, the proposed method completely suppresses SBS. Finally, the degree of freedom for the dithering signal is infinite, with an optical power budget improvement of up to 8 dB at an optical launch power of 10 dBm, which can in turn be used towards connecting multiple relay nodes (RNs).

Nonlinearity Detection and Compensation in Radio over Fiber Systems Using a Monitoring Channel

A radio over fiber (RoF) system is a kind of analog optical transmission system and considered as a strong candidate for the next-generation fronthaul link in the future mobile network. In RoF systems, nonlinearity compensation is essential to increase the link capacity. In this paper, we propose a nonlinearity detection and compensation scheme using a monitoring channel in RoF systems. A monitoring channel is added at the transmitter site and used for transmitting a reference signal in an RoF transmission. The nonlinearity in the RoF transmission is detected by comparing the received monitoring signal and the original reference signal at the receiver site. Finally, the nonlinearity is compensated at the receiver by giving the reverse function of the detected nonlinearity. Our results show that the proposed scheme can almost remove the error vector magnitude degradation induced by the nonlinearity in the RoF system.

Direct and External Intensity Modulation in OFDM RoF Links

Radio-over-fiber (RoF) systems comprise light modulation and transmission of millimeter-wave signals over fiber links. The aim of this study is to investigate the performance of external and direct intensity modulation in RoF links and to analyze the drawbacks induced by different components of the optical system. In external modulation, the Mach-Zehnder modulator (MZM) is used, whereas the vertical-cavity surface-emitting laser (VCSEL) is utilized in direct modulation. Both modulation schemes are tested for a vector modulation format, i.e., the quadrature amplitude modulation (QAM), where an orthogonal frequency-division multiplexing (OFDM) scheme is used to generate signal subcarriers. The simulations are carried out with the same values of common global parameters for both schemes of intensity modulation. Although VCSEL is a promising device for future RoF systems, the external modulation shows a more robust performance compared with that of VCSEL when implemented with the OFDM modulation technique.

Analysis of Dual Wavelength Linearization Technique for Radio-Over-Fiber Systems With Electro-Absorption Modulator

The dual wavelength linearization (DWL) technique using two lasers with different wavelengths is for the first time comprehensively studied theoretically and experimentally to improve output signal power and suppress second- and third-order nonlinearities in radio-over-fiber (RoF) systems using an electro-absorption modulator (EAM). Spurious-free dynamic ranges (SFDRs) are calculated and measured. Both the calculation and experiments show that not only the RF signal power is significantly increased, but also both the second- and third-, as well as fifth-order nonlinearities are suppressed. For our considered EAM, when the second-order nonlinearity is suppressed maximally, the SFDRs with respect to second-order harmonic distortion and second-order intermodulation distortion are improved by 11.5 and 8.5 dB, respectively. In the mean time, the SFDRs with respect to third-order harmonic distortion (HD3) and third-order intermodulation distortion (IMD3) are improved by 1.8 and 1.3 dB, respectively. When the third order is suppressed maximally, the SFDRs with respect to HD3 and IMD3 are improved by 8.1 and 20.4 dB, respectively. The fifth-order intermodulation distortion is also suppressed at the same time. The RoF transmissions for WiFi signals are also verified. As a result, 3.5 dB at 2.4-GHz improvement and 2.8 dB at 5-GHz improvement of error vector magnitude are obtained for an RoF system by using the DWL technique.

Simultaneous generation of 3G and millimeter-wave signals using a dual-electrode MZM in ROF systems

A novel radio-over-fiber (ROF) scheme to simultaneously generate and transmit the 3rd generation telecommunication (3G) and millimeter-wave (MMW) signals by using a single dual-electrode Mach-Zehnder modulator (MZM) is proposed. There is no apparent nonlinearity induced by the ROF system. By employing this analog ROF signal transmission technique, highly transparent fiber-wireless convergence networks can be realized, which are ideal for multi-standard wireless system operation.

Impact of Amplitude Noise in Millimeter-Wave Radio-Over-Fiber Systems

In this paper, a complete theoretical and experimental study of amplitude noise impact on performance of radio-over-fiber (RoF) communication system in millimeter-wave (MMW) frequency band is presented. A simulation method is also presented, using which one can determine the origin of the amplitude noise which has the most impact on error vector magnitude (EVM). This method is based on analyzing the trends of EVM versus received optical power. The impact of different optical and electrical noise such as relative intensity noise, shot noise and thermal noise on EVM is precisely studied employing experimental and theoretical analysis. In the proposed RoF system, two techniques are used to generate MMW signal, and the EVM results are compared from amplitude noise viewpoint. In the first technique, two independent distributed feedback lasers are used to generate MMW signal at the output of a photodetector, and the second technique is based on a passively mode-locked laser diode. Impact of optical sources phase noise on performance of the system is removed using a noncoherent down-conversion method based on envelope detector. Using this method, a very good matching between the experimental and the simulation results is observed.