Experimental and Analytical Investigations of an Optically Pre-Amplified FSO-MIMO System With Repetition Coding Over Non-Identically Distributed Correlated Channels

This paper presents theoretical and experimental bit error rate (BER) results for a freespace optical (FSO) multiple-input-multiple-output system over an arbitrarily correlated turbulence channel. We employ an erbium-doped fiber amplifier at the receiver (Rx), which results in an improved Rx’s sensitivity at the cost of an additional non-Gaussian amplified spontaneous emission noise. Repetition coding is used to combat turbulence and to improve the BER performance of the FSO links. A mathematical framework is provided for the considered FSO system over a correlated non-identically distributed Gamma-Gamma channel; and analytical BER results are derived with and without the pre-amplifier for a comparative study. Moreover, novel closed-form expressions for the asymptotic BER are derived; a comprehensive discussion about the diversity order and coding gain is presented by performing asymptotic analysis at high signal-tonoise ratio (SNR). To verify the analytical results, an experimental set-up of a 2 × 1 FSO-multiple-inputsingle-output (MISO) system with pre-amplifier at the Rx is developed. It is shown analytically that, both correlation and pre-amplification do not affect the diversity order of the system, however, both factors have contrasting behaviour with respect to coding gain. Further, to achieve the target forward error correction BER limit of 3.8 × 10−3 , a 2 × 1 FSO-MISO system with a pre-amplifier requires 6.5 dB lower SNR compared with the system with no pre-amplifier. Moreover, an SNR penalty of 2.5 dB is incurred at a higher correlation level for the developed 2×1 experimental FSO set-up, which is in agreement with the analytical findings

Impact of Channel Correlation on Different Performance Metrics of OSSK-Based FSO System

In this paper, we study the impact of correlation on the bit error rate (BER) and the channel capacity of a free-space optical (FSO) multiple-input-multiple-output (MIMO) system employing optical space shift keying (OSSK) over a fading channel. In order to study a practical correlated channel, we consider the effect of channel correlation due to both small-and large-scale eddies and show that the use of OSSK over correlated FSO channel can lead to an improved system performance with increasing correlation level of upto 0.9. In this work, we first develop an analytical framework for different performance metrics of the OSSK multiple-input single-output system with correlation and then extend our investigation by proposing an asymptotically accurate mathematical framework for MIMO. We also validate all the analytical results using MATLAB simulations. Finally, we develop an experimental setup of FSO with two correlated links to study the throughput and latency of the links at different turbulence levels

Optical CS-DSB Schemes for 5G mmW Fronthaul Seamless Transmission

[EN] This paper describes the experimental demonstration of the hybrid optical/millimeter wave signal generation and transmission over combined optical fiber and free space optics fronthaul network with a seamless antenna link. An electrical bandpass filter is used to filter out the spectrum after photodetection in order to realize the seamless antenna transmission. The successful transmission of 64/256-quadrature amplitude modulation (QAM) 5G signal with up to 200 MHz bandwidth is presented by using two different setups: one is based on two Mach-Zehnder modulators (MZM) and the other employs a directly modulated laser (DML) to provide more cost efficient fronthaul solution. The DML based approach reveals mildly better performance in comparison to the MZMs in terms of higher achieved signal-to-noise ratio and lower error vector magnitude (EVM). More specifically, the best signal-to-noise ratio and EVM achieved with the DML based setup has been 31.5 dB and 3. 3%, respectively, compared to 30.3 dB and 3.8% with the MZMs based setup while transmitting 256-QAM signal with 100 MHz bandwidth. However, both setups kept the EVM well below the given 9% and 4.5% limit for 64- and 256-QAM, respectively.This work was supported in part by the Ministry of Industry and Trade in Czech Republic under Grant FV40089, in part by EU COST Action NEWFOCUS under Grant CA19111, and in part by the Ministerio de Ciencia, Innovacion y Universidades under Grant FOCAL RTI2018-101658-B-I00.Bohata, J.; Vallejo-Castro, L.; Ortega Tamarit, B.; Zvanovec, S. (2022). Optical CS-DSB Schemes for 5G mmW Fronthaul Seamless Transmission. IEEE Photonics Journal. 14(2):1-7. https://doi.org/10.1109/JPHOT.2022.31610871714

M-QAM transmission over hybrid microwave photonic links at the K-band

Two experimental configurations of a hybrid K-band (25 GHz) microwave photonic link (MPL) are investigated for seamless broadband wireless access networks. Experimental configurations consist of optical fiber, free-space optics (FSO) and radio frequency (RF) wireless channels. We analyze in detail the effects of channel impairments, namely fiber chromatic dispersion, atmospheric turbulence and multipath-induced fading on the transmission performance. In the first configuration, transmission of the 64-quadrature amplitude modulation (QAM) signal with 5, 20 and 50 MHz bandwidths over 5 km standard single-mode fiber (SSMF), 2 m turbulent FSO and 3 m RF wireless channels is investigated. We show that, for QAM with a high bandwidth, the link performance is being affected more by atmospheric turbulence. In the second configuration, the 20 MHz 4/16/64-QAM signals over a 50 km SSMF and 40 m FSO/RF wireless links are successfully transmitted with the measured error vector magnitude (EVM) values of 12, 9 and 7.9%, respectively. It is shown that, for all transmitted microwave vector signals, the bit error rate is lower than the hard-decision forward-error-correction limit of 3.8×10−3. Moreover, an extended FSO link span of 500 m for 25 GHz hybrid MPL with 16-QAM at 10 Gb/s under the weak and strong turbulence regimes is evaluated via simulation analysis to mimic a practical outdoor system

M-QAM signal transmission at the photonically generated K-band over thermal-induced turbulent FSO links with different turbulence distributions

[EN] We present a theoretical and experimental study on the impact of different thermal-induced free-space turbulence distributions on the M-quadrature amplitude modulation (M-QAM) signal transmission in radio frequency K-band over hybrid optical links of standard single mode fiber (SSMF) and free-space optics (FSO). Frequency multiplication using an external intensity modulator biased at the null transmission point has been employed to photonically generate radio signals at a frequency of 25 GHz, included for the frequency bands for fifth-generation (5G) mobile networks. Moreover, extensive simulations have been performed for 10 Gb/s with 4-, 16-, and 64-QAM over 5 km of SSMF and 500 m long FSO channels under scenarios with different turbulence levels and distributions. Proof-of-concept experiments have been conducted for 20 MHz with 4- and 64-QAM over 5 km of SSMF and 2 m long FSO channels under turbulence conditions. Both theoretical and experimental systems have been analyzed in terms of error vector magnitude (EVM) performance showing feasible transmission over the hybrid links in the received optical power range. Non-uniform turbulence distributions are shown to have a different impact on M-QAM modulation formats, i.e., turbulence distributions with higher strength in the middle of the FSO link reveal a 1.9 dB penalty when using 64-QAM signals compared to a 1.3 dB penalty using 4-QAM signals, whereas higher penalties have been measured when 4-QAM format is transmitted over turbulence distributions with larger magnitude in the second half of the FSO link. The results have been validated by theoretical predictions and lead to practical consequences on future networks' deployment.Generalitat Valenciana (PROMETEO 2017/103); Ministerio de Ciencia, Innovacion y Universidades (FOCAL RTI2018-101658-B-I00); Ministerstvo Prumyslu a Obchodu (FV30427) and within European Cooperation in Science andTechnology (CA16220).Vallejo-Castro, L.; Nguyen, D.; Bohata, J.; Ortega Tamarit, B.; Zvanovec, S. (2020). M-QAM signal transmission at the photonically generated K-band over thermal-induced turbulent FSO links with different turbulence distributions. Applied Optics. 59(16):4997-5005. https://doi.org/10.1364/AO.390103S499750055916Zhang, R., Lu, F., Xu, M., Liu, S., Peng, P.-C., Shen, S., … Chang, G.-K. (2018). An Ultra-Reliable MMW/FSO A-RoF System Based on Coordinated Mapping and Combining Technique for 5G and Beyond Mobile Fronthaul. Journal of Lightwave Technology, 36(20), 4952-4959. doi:10.1109/jlt.2018.2866767Lee, C. H. (Ed.). (2017). 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A Novel Radio-Over-Fiber System Based on Carrier Suppressed Frequency Eightfold Millimeter Wave Generation. IEEE Photonics Journal, 9(5), 1-6. doi:10.1109/jphot.2017.2731620Khalighi, M. A., & Uysal, M. (2014). Survey on Free Space Optical Communication: A Communication Theory Perspective. IEEE Communications Surveys & Tutorials, 16(4), 2231-2258. doi:10.1109/comst.2014.2329501Bloom, S., Korevaar, E., Schuster, J., & Willebrand, H. (2003). Understanding the performance of free-space optics [Invited]. Journal of Optical Networking, 2(6), 178. doi:10.1364/jon.2.000178Anderson, H. R. (2003). Fixed Broadband Wireless System Design. doi:10.1002/0470861290Ghassemlooy, Z., Popoola, W., & Rajbhandari, S. (2019). Optical Wireless Communications. doi:10.1201/9781315151724Borah, D. K., & Voelz, D. G. (2009). Pointing Error Effects on Free-Space Optical Communication Links in the Presence of Atmospheric Turbulence. Journal of Lightwave Technology, 27(18), 3965-3973. doi:10.1109/jlt.2009.2022771Esmail, M. A., Ragheb, A., Fathallah, H., & Alouini, M.-S. (2017). Investigation and Demonstration of High Speed Full-Optical Hybrid FSO/Fiber Communication System Under Light Sand Storm Condition. IEEE Photonics Journal, 9(1), 1-12. doi:10.1109/jphot.2016.2641741Libich, J., & Zvanovec, S. (2011). Influences of turbulences in near vicinity of buildings on free-space optical links. IET Microwaves, Antennas & Propagation, 5(9), 1039. doi:10.1049/iet-map.2010.0630Niachou, K., Livada, I., & Santamouris, M. (2008). Experimental study of temperature and airflow distribution inside an urban street canyon during hot summer weather conditions. Part II: Airflow analysis. Building and Environment, 43(8), 1393-1403. doi:10.1016/j.buildenv.2007.01.040Nguyen, D.-N., Bohata, J., Spacil, J., Dousek, D., Komanec, M., Zvanovec, S., … Ortega, B. (2019). M-QAM transmission over hybrid microwave photonic links at the K-band. Optics Express, 27(23), 33745. doi:10.1364/oe.27.033745Nguyen, D.-N., Bohata, J., Komanec, M., Zvanovec, S., Ortega, B., & Ghassemlooy, Z. (2019). Seamless 25 GHz Transmission of LTE 4/16/64-QAM Signals Over Hybrid SMF/FSO and Wireless Link. Journal of Lightwave Technology, 37(24), 6040-6047. doi:10.1109/jlt.2019.2945588Vallejo, L., Komanec, M., Ortega, B., Bohata, J., Nguyen, D.-N., Zvanovec, S., & Almenar, V. (2020). Impact of Thermal-Induced Turbulent Distribution Along FSO Link on Transmission of Photonically Generated mmW Signals in the Frequency Range 26–40 GHz. IEEE Photonics Journal, 12(1), 1-9. doi:10.1109/jphot.2019.2959227Qi, G., Yao, J., Seregelyi, J., Paquet, S., Belisle, C., Zhang, X., … Kashyap, R. (2006). Phase-Noise Analysis of Optically Generated Millimeter-Wave Signals With External Optical Modulation Techniques. Journal of Lightwave Technology, 24(12), 4861-4875. doi:10.1109/jlt.2006.884990Ma, J., Yu, J., Yu, C., Xin, X., Zeng, J., & Chen, L. (2007). 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Usability of a 5G fronthaul based on a DML and external modulation for M-QAM transmission over photonically generated 40 GHz

[EN] In this paper, we numerically and experimentally present the bandwidth constraints of a cost-effective 5G mobile fronthaul based on a directly-modulated laser for data modulation and a Mach-Zehnder modulator-based optical double sideband with carrier suppression scheme for optical millimeter wave (mmW) signal generation. The effect of chirp, fiber dispersion and a combination of both on different bandwidth M-Quadrature Amplitude Modulation (M-QAM) signals, i.e. M = 4, 16 and 64, at 40 GHz has also been investigated. Simulation results are firrst carried out to evaluate the impact of higher chirp of the directly-modulated laser on the link performance as a function of modulation format and signal bandwidth. We then experimentally demonstrate the same scheme transmitting M-QAM signals with bandwidths ranging from 50 to 1000 MHz over a 10 km long single mode fiber. Both experimental and simulation results show that larger signal bandwidths lead to higher optical power penalties due to the combined effect with the error vector magnitudes (EVMs), however still satisfying the required limits of 3GPP standard for allQAMsignals. Experimental measurements also showthe feasibility of including free space optics links in the optical distribution network with no further signi cant penalties. Finally, a multiband signal (three-band) transmission is demonstrated leading to an increase of the total bitrate with the measured EVMs are well below the EVM requirement.This work was supported in part by the Generalitat Valenciana under Grant PROMETEO 2017/103, in part by the Ministerio de Ciencia, Innovacion y Universidades under Grant FOCAL RTI2018-101658-B-I00, in part by the Ministerstvo Prumyslu a Obchodu under Grant FV40089, and in part by the European Cooperation in Science and Technology under Grant CA16220.Vallejo-Castro, L.; Ortega Tamarit, B.; Nguyen, D.; Bohata, J.; Almenar Terre, V.; Zvanovec, S. (2020). Usability of a 5G fronthaul based on a DML and external modulation for M-QAM transmission over photonically generated 40 GHz. IEEE Access. 8:223730-223742. https://doi.org/10.1109/ACCESS.2020.3042756S223730223742

Analyses of Dual Polarization WDM and SCM Radio over Fiber and Radio over FSO for C-RAN Architecture

En este trabajo se simulan y verifican experimentalmente los esquemas de transmisión para una Arquitectura de Red de Acceso Radio Centralizada (C-RAN) basados en la combinación de dos tecnologías: Radio sobre Fibra (RoF) y Radio sobre FSO (RoFSO). Las configuraciones propuestas se optimizan para la evolución a largo plazo (LTE) con un ancho de banda de 20 MHz utilizando una modulación de amplitud en cuadratura de 64-QAM en términos de magnitud de vector de error (EVM). En primer lugar, se comparan las mediciones de la multiplexación por división de polarización mediante la combinación de RoF y RoFSO (PDM-RoF/FSO) con los modelos de simulación. Esto se amplía con la combinación de PDM-Multiplexación por División por Longitud de Onda (WDM)-RoF/FSO y PDM-Multiplexación por Subportadora (SCM)-RoF/FSO, respectivamente. Los resultados indican un mejor rendimiento de PDM-SCM-RoF/FSO que de WDM RoF/RoFSO en términos de potencia de lanzamiento para alcanzar el límite EVM.JCI-2012-14805SGS14/190/OHK3/3T/13In this paper, the transmission schemes for Centralized Radio Access Network Architecture (C-RAN) based on combination of two technologies - Radio over Fiber (RoF) and Radio over FSO (RoFSO) are simulated and experimentally verified. The proposed setups are optimized for Long Term Evolution (LTE) with 20 MHz bandwidth using 64 Quadrature amplitude modulation in terms of Error Vector Magnitude (EVM). At the first, the measurements of Polarization Division Multiplexing using combination of RoF a RoFSO (PDM-RoF/FSO) is compared with simulation models. This is further extended by combination of PDM-Wavelength Division Multiplexing (WDM)-RoF/FSO and PDM-Subcarrier Multiplexing (SCM)-RoF/FSO, respectively. Results indicate better performance of PDM-SCM-RoF/FSO than WDM RoF/RoFSO in terms of launch power to reach EVM limit

Characterization of dual-polarization analogue radio over fiber fronthaul for LTE C-RAN architecture

En este artículo se presentan los resultados de la medición ampliada de la radio analógica de doble polarización (DP) sobre fibra (RoF) en una arquitectura de red de acceso radio en la nube (C-RAN) de evolución a largo plazo (LTE). Esta técnica se propone para las conexiones de fibra entre las oficinas centrales y las estaciones base remotas. Se investigan varias longitudes de fibra óptica para determinar el mejor rendimiento del sistema en términos de magnitud de vector de error (EVM) y tasa de error de bit. La distancia máxima alcanzada para el caso de un ancho de banda LTE de 20 MHz es de 50 km, mostrando un valor de EVM admisible del 8,5% a la frecuencia de radio de 2,6 GHz cuando se utiliza el esquema de modulación 64 QAM.JCI-2012-14805SGS14/190/OHK3/3T/13COST Action IC1101 OPTICWISEIn this paper the results from extended measurement of dual-polarization (DP) analogue radio over fiber (RoF) in a long term evolution (LTE) cloud radio access network (C-RAN) architecture are presented. This technique is proposed for fiber connections between central offices and remote base stations. Investigation of various optical fiber length is carried out to determine the best system performance in terms of error vector magnitude (EVM) and bit error rate. Maximal achieved distance for the case of LTE bandwidth of 20 MHz is 50 km displaying permissible EVM value of 8.5 % at the radio frequency of 2.6 GHz when using 64 QAM modulation scheme