Orthogonal Frequency Division Multiplexing Radio Over Fiber Research Articles

Analyzing the BER and optical fiber length performances in OFDM RoF links

Radio over fiber (RoF) can be assessed as a system of most convenient combination of optical fiber and radio signals. The technique of orthogonal frequency division multiplexing (OFDM) considers as a data distribution over a huge number of carriers having spaced from each other with specific frequencies at overlap bands. Hence incorporates OFDM with the optical fiber, OFDM-RoF system can be increased the modulation RF access capacity besides high-speed data transmission, it considers a broadband communication trend of the current and future applications specifically for 5G mobile. The optical network scenarios of various RF can be model with optisystem software, and OFDM in addition to use a section of the orthogonal multiplex frequency of 16-quadrature amplitude modulation (QAM) RF modulating signal. In the optical domain, Mach-Zehnder modulator (MZM) optical modulators are used to carry out different results with different fiber lengths. An OFDM-RoF wireless communication system considers as advanced data rate transmission achievement by minimum delays. The essential goal of this paper is for identifying the minimum bit error rate (BER) for the 16-QAM modulation with varying fiber length. The OFDM-RoF system can be able for realizing a fiber length 100 km with a restricted decreasing in the received power so that the constellation noise is became greater despite of applying electrical amplification and optical amplification.

Probabilistic shaping based constellation encryption for physical layer security in OFDM RoF system.

The physical layer security of radio-over-fiber (RoF) system is a very important problem for future communication. In this paper, a novel probabilistic shaping (PS) based constellation encryption scheme is proposed in which two bit-level encryption operations are firstly performed according to chaotic sequences and hash values. The chaotic sequences are generated by hyperchaotic system and hash values are obtained by SHA-512. Then PS is applied to enhance transmission performance. After PS-16-quadrature amplitude modulation (QAM), constellation encryption is implemented aiming at maintaining overall shaping distribution unchanged and improving security. An encrypted PS-16-QAM orthogonal frequency division multiplexing (OFDM) signal is successfully transmitted over 50 km standard single-mode fiber (SSMF) and 5 m wireless channel in our experiment. The results demonstrate that the key space of 10121 is achieved to defend malicious attacks. Moreover, the proposed PS-based encryption scheme can obtain approximately 2.4 dB gain at a BER of 10-3 compared with traditional OFDM signal. Thus, the proposed scheme has a good application prospect in the future OFDM-RoF system due to the dominant BER and security performance.

Linearization of multiband OFDM RoF system employing frequency-separated model based digital pre-distortion

To mitigate the nonlinear distortion of a multiband orthogonal frequency division multiplexing (OFDM) radio over fiber (RoF) system, a frequency-separated model-based digital pre-distortion (DPD) technique is proposed and experimentally demonstrated herein. Frequency-separated model DPD, when used as a pre-equalizer, mitigates nonlinearity in a transmitter. The nonlinear characteristic of an RoF system depends on the frequency band. Therefore, the proposed equalizer separates the input by frequency band and mitigates nonlinearities. A least mean square algorithm is used to estimate the variables of the proposed equalizer. Using the proposed DPD technique, performance enhancement was verified experimentally relative to the adjacent carrier leakage ratio (ACLR). The proposed technique obtained ACLR values of 27 to 30 dB. The results demonstrate that signal performance improved in terms of error vector magnitude from 6.3% to 3.5% at an optical modulation index value of 63%.

Doppler-free coherent detection using period-one nonlinear dynamics of semiconductor lasers for OFDM-RoF links.

This study investigates coherent detection that is free from the Doppler frequency shift effect for orthogonal frequency division multiplexing radio-over-fiber (OFDM-RoF) links using period-one (P1) nonlinear dynamics of semiconductor lasers. Even under a dynamically time-varying Doppler frequency shift of up to 100kHz, corresponding to a relative motion between a transmitter and a receiver with a velocity of more than 3850km/h at 28GHz, the microwave carrier of a received OFDM-RoF signal can be successfully regenerated instantaneously and uninterruptedly with its phase highly preserved through the P1 dynamics. No carrier frequency offset (CFO) due to the Doppler frequency shift effect happens if the regenerated microwave carrier is used as a microwave local oscillator for coherent detection of the received OFDM-RoF signal. As a result, a bit-error ratio of around 10-9 is achieved for coherent detection of a 28GHz OFDM-RoF signal carrying 4Gb/s 16-quadrature amplitude modulation data. Thus, no digital signal processing, either photonic or electronic, is required to compensate for such a CFO. This all-optical system is capable of operation up to at least 100GHz.

Photonic microwave carrier recovery using period-one nonlinear dynamics of semiconductor lasers for OFDM-RoF coherent detection.

This study investigates an all-optical scheme based on period-one (P1) nonlinear dynamics of semiconductor lasers, which regenerates the microwave carrier of an orthogonal frequency division multiplexing radio-over-fiber (OFDM-RoF) signal and uses it as a microwave local oscillator for coherent detection. Through the injection locking established between the OFDM-RoF signal and the P1 dynamics, frequency synchronization with highly preserved phase quality is inherently achieved between the recovered microwave carrier and the microwave carrier of the OFDM-RoF signal. A bit-error ratio down to 1.9×10^-9 is achieved accordingly using the proposed scheme for coherent detection of a 32-GHz OFDM-RoF signal carrying 4 Gb/s 16-quadrature amplitude modulation data. No electronic microwave generators or electronic phase-locked loops are thus required. The proposed system can be operated up to at least 100GHz and can be self-adapted to certain changes in the operating microwave frequency.

Distortion Mitigation in Multiband OFDM RoF Transmission Employing Blind Post Equalizer

We propose and experimentally demonstrate a blind adaptive equalizer for a multiband (MB) orthogonal frequency-division multiplexing (OFDM) radio-over-fiber (RoF) system. The proposed equalizer adaptively decreases nonlinear and linear distortion, which might lead to serious signal degradation in MB OFDM transmission, without the use of a training signal. Instead of a training signal, error vector magnitude (EVM) and the power difference between the signal and the third-order intermodulation distortion components were observed in the equalizer. Therefore, the performance enhancement of MB OFDM transmission was experimentally verified in terms of EVM from 5.52% to 2.75% by mitigation of distortion. Consequently, the dynamic range of radio frequency input power was improved when the proposed equalizer was employed in an MB OFDM RoF system without increasing system overhead.

Simple and reconfigured single-sideband OFDM RoF system.

We propose a simple and reconfigured dispersion-tolerant single sideband (SSB) orthogonal frequency division multiplexing (OFDM) radio over fiber (RoF) system enabled by digital signal processing (DSP), one in-phase/quadrature (I/Q) modulator and direct-detection. The generated radio frequency (RF) is based on DSP and the frequency can be flexibly adjusted, which can be employed in the future software-defined radio access network (RAN). Based on our proposed system, we have experimentally demonstrated 16-ary quadrature amplitude modulation (16QAM) 21.87-Gb/s 21-GHz and 38-GHz SSB-OFDM RoF signal generation and transmission over 80-km single-mode fiber (SMF), respectively.

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.

2 <formula formulatype="inline"><tex Notation="TeX">$\times$</tex></formula> 2 MIMO OFDM-RoF System Employing LMS-Based Equalizer With I/Q Imbalance Compensation at 60 GHz

Multiple-input–multiple-output (MIMO) technology is a promising method to increase spectral efficiency in wireless communications. In this paper, a 60-GHz orthogonal frequency-division multiplexing radio over fiber (OFDM-RoF) system employing 2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\times$</tex></formula> 2 MIMO wireless technology is demonstrated. With the proposed equalizer employing least mean squares (LMS) algorithm, MIMO channel mixing and I/Q-mismatch can be compensated simultaneously. 16-QAM and 32-QAM OFDM signal transmissions under forward error correction (FEC) threshold ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$1\times 10^{-3}$</tex></formula> ) are demonstrated. A data rate of 76.3 Gb/s can be achieved with a bit-loading algorithm over 25-km fiber transmission and 3.5-m wireless transmission.

High spectral efficient W-band OFDM-RoF system with direct-detection by two cascaded single-drive MZMs

W-band wireless transmission has attracted a lot of interest due to its wider available bandwidth (i.e. 75-110 GHz). In this article, we propose a direct-detection orthogonal frequency division multiplexing radio over fiber (OFDM-RoF) system via two cascaded single-drive MZMs at center frequency of 103 GHz. We discuss maximum bandwidth of different modulation formats under forward error correction (FEC) threshold (3.8 x 10(-3)). Up to 40-Gbps 16-QAM OFDM signals is achieved over 25-km fiber and 2-m wireless transmission. To overcome the penalty from uneven frequency response, bit-loading algorithm is applied to discuss data rate and spectral efficiency with signal bandwidth from 5 to 10 GHz. With 10-GHz bandwidth, 46.4-Gb/s data rate and 4.64-bit/s/Hz spectral efficiency was achieved. To achieve 40-Gbps data rate, the required bandwidth of OFDM signal with bit-loading is 2 GHz less than that without bit-loading.

Reduction of Intercarrier Interference Based on Window Shaping in OFDM RoF Systems

In this letter, we theoretically investigate the intercarrier interference (ICI) that is induced by carrier frequency offset (CFO) and sampling frequency offset (SFO) for orthogonal frequency division multiplexing (OFDM) radio-over-fiber (RoF) system. A window shaping technique in the time domain at the OFDM receiver is presented, which can improve the tolerance to the frequency offset and reduce ICI. Compared with the conventional demodulation scheme, the simulation shows that the utilization of the window shaping method can increase the resistance to residual CFO to about eight times at power penalty of 2 dB. It can also improve the tolerance to SFO. A 4.65 Gb/s 4QAM OFDM RoF system over 40 km fiber link and 60 GHz wireless link is demonstrated experimentally. The bit error rate (BER) performance of the scheme is measured, with and without the proposed window shaping method, respectively. About 0.9 dB improvement of the required receiver power at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> shows the feasibility of the window shaping method for ICI reduction in OFDM RoF system.

A novel transform domain processing based channel estimation method for OFDM radio-over-fiber systems

In this paper, a transform domain processing (TDP) based channel estimation method for orthogonal frequency-division multiplexing (OFDM) Radio-over-Fiber (RoF) systems is proposed. Theoretically investigation shows that TDP can greatly reduce the number of required training symbols. An 8 x 4.65 Gb/s multi-user OFDM RoF system over 40 km fiber link and 60 GHz wireless link is experimentally demonstrated utilizing TDP scheme. Compared with conventional time domain averaging (TDA) scheme, the overhead can be reduced from several tens of training symbols to merely one symbol and the receiver sensitivity has been improved by 1.8 dB at BER of 3.8 x 10(-3). The calculated BER performance for 8 wireless users clearly validates the feasibility of this TDP-based channel estimation method.

Transmission of 100 GHz w‐band frequency MIMO‐OFDM signals with 90 Gbps downstream and 30 Gbps upstream using radio over fiber system

AbstractIn this article, we propose and demonstrate an orthogonal frequency division multiplexing‐radio over fiber (OFDM‐ROF) system based on three channels sextupling‐frequency scheme using an external modulation of a distributed feedback laser diode (DFB‐LD) and dual drive Mach–Zehnder modulator (DD‐MZM) for carrying 100 GHz W‐band frequency multiple‐input multiple‐output (MIMO)‐OFDM signals with 90 Gbps downstream. MIMO‐OFDM algorithms effectively compensate for impairments in the wireless link. Without using costly W‐band components, a transmission system with 50 km single mode fiber (SMF) and 4 m wireless transmission operation at 100 GHz is experimentally validated. The power penalties for MIMO‐OFDM signals of base stations are less than 3 dBm. For the upstream transmission, wavelength reuse with 30 Gbps 4QAM upstream signals is experimentally demonstrated. The minimum optical spectral gap between residue downstream OFDM band and upstream OFDM band that guarantees a tolerable amount of optical interference has been determined through experiment. The frequency of local oscillator is reduced due to frequency sextupling scheme. The cost of the proposed system is largely reduced. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:93–99, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27251

SSBI mitigation at 60GHz OFDM-ROF system based on optimization of training sequence

We have theoretically and experimentally investigated the effect of the interference between subcarrier-signal beat interference (SSBI) in 60 GHz orthogonal frequency division multiplexing - radio-over-fiber (OFDM-ROF) system. In order to reduce the influence of SSBI, we compared four kinds of OFDM frames with different training sequences as all-real, all-complex, complex-zero and real-zero training. The experimental results show the power penalty of all-real, all-complex, complex-zero and real-zero training is 2.5, 5.5, 4 and 1dB at BER of 1x10(-3) after 20 km standard single mode fiber (SMF) transmission, respectively. The real-zero training OFDM frame with interleave structure and lower modulation order signal suffered from the least SSBI shows the best performance.

Full‐duplex OFDM‐ROF architecture based on millimeter‐wave generated by optical phase modulator

AbstractWe proposed and experimentally demonstrate a bidirectional orthogonal frequency‐division multiplexing‐radio‐over‐fiber (OFDM‐ROF) system by using an optical phase modulator and a fiber Bragger gating (FBG) to generate millimeter‐wave.The downstream date is 2.5‐Gb/s OFDM signals and the downstream wavelength is reused without signal erasure. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1335–1337, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25175