Quadrature Amplitude Modulation Orthogonal Frequency Division Multiplexing Research Articles

Utilization of Optical OFDM Modulation on Blue LED VLC Datacom Without Equalization for 4 m Wireless Link.

To achieve higher visible light communication (VLC) traffic capacity, using the wide bandwidth light-emitting diode (LED) and spectral efficiency modulation signal, is currently the most commonly used method. In this demonstration, we apply the orthogonal frequency division multiplexing quadrature amplitude modulation (OFDM-QAM) with bit- and power-loading algorithm on single blue LED to achieve >1 Gbit/s VLC capacity, when a 400 MHz bandwidth avalanche photodiode (APD)-based receiver (Rx) is exploited for decoding. Here, the higher sensitivity APD can be applied to compensate for the wireless VLC link length in the proposed LED VLC system, and due to the lower LED illumination (255 to 40 lux), is used for the indoor access network after passing the wireless link length of 1 to 4 m. As a result, using single blue LED can achieve 0.962 to 1.057 Gbit/s OFDM rate with available 400 MHz bandwidth APD in poorly illuminated condition indoors without applying analogy equalization.

Investigating orthogonal frequency division multiplexing using high‐power LED for visible light communication

AbstractSpectrally efficient 16 quadrature amplitude modulation‐orthogonal frequency division multiplexing (QAM‐OFDM) system using specifications of commercially available high‐power phosphorous coated LED (PLED) is proposed in this study. To address the challenges of signal attenuation and limited bandwidth, systems integrated with a band pass filter (BPF) after the photodetector and optical preamplifier. The effect of BPF bandwidth and preamplifier gain on the performance of 16 QAM‐OFDM system have been investigated. Results demonstrated that 375 MHz bandwidth evaluated from 1.5 × symbol rate, offered an optimum performance achieving minimum bit‐error‐rate of 3.05 × 10−4. For preamplifier gain of 20 dB, we achieved a maximum distance of 3 m which is limited to 1.5 m for lower gain values. With BPF‐optimized bandwidth and a preamplifier gain of 20 dB, we have achieved a data rate of 5 Gbps for maximum distance up to 2 m while considering the super‐forward‐error‐correction limit of 1.863 × 10−2. With data rate of 6 and 7 Gbps, the distance lower down to 1.8 and 1.5 m, respectively.

Study and Analysis of Modulation Schemes for Underwater Optical Wireless Communication

Communication technology is poised to play a crucial role in advancing the study of climate change, facilitating the monitoring of shifts in biological, biogeochemical, evolutionary, and ecological aspects within marine and oceanic environments. Additionally, it is imperative to ensure the efficient operation of underwater sensor networks, unmanned underwater vehicles (UUVs), submarines, ships, buoys, and divers. However, existing underwater acoustic communication technology falls short of delivering the high data rates required for comprehensive investigation and surveillance in these environments and facilities. In response to this challenge, optical wireless communication has emerged as a promising alternative. This study focuses on the design and examination of an underwater optical communication link capable of communication over a horizontal distance of up to 130 meters at a depth of 40 meters. The proposed system is rigorously assessed under clear ocean conditions, considering a bit rate of 15 Gbps and employing both Differential Quadrature Phase Shift Keying (DQPSK) technique and Orthogonal Frequency Division Multiplexing-Quadrature Amplitude Modulation (OFDM-QAM) technique. Received: 5 December 2023 | Revised: 7 April 2024 | Accepted: 27 May 2024 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data available on request from the corresponding author upon reasonable request. Author Contribution Statement Prasant Kumar Sahu: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Writing – original draft, Writing – review & editing, Visualization, Supervision. Debalina Ghosh: Conceptualization, Methodology, Software, Validation, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Project administration.

Performance Analysis of 5G New Radio LDPC over Different Multipath Fading Channel Models

The creation and developing of a wireless network communication that is fast, secure, dependable, and cost-effective enough to suit the needs of the modern world is a difficult undertaking. Channel coding schemes must be chosen carefully to ensure timely and error-free data transfer in a noisy and fading channel. To ensure that the data received matches the data transmitted, channel coding is an essential part of the communication system's architecture. NR LDPC (New Radio Low Density Parity Check) code has been recommended for the fifth-generation (5G) to achieve the need for more internet traffic capacity in mobile communications and to provide both high coding gain and low energy consumption. This research presents NR-LDPC for data transmission over two different multipath fading channel models, such as Nakagami-m and Rayleigh in AWGN. The BER performance of the NR-LDPC code using two kinds of rate-compatible base graphs has been examined for the QAM-OFDM (Quadrature Amplitude Modulation-Orthogonal Frequency Division Multiplexing) system and compared to the uncoded QAM-OFDM system. The BER performance obtained via Monte Carlo simulation demonstrates that the LDPC works efficiently with two different kinds of channel models: those that do not fade and those that fade and achieves significant BER improvements with high coding gain. It makes sense to use LDPC codes in 5G because they are more efficient for long data transmissions, and the key to a good code is an effective decoding algorithm. The results demonstrated a coding gain improvement of up to 15 dB at 10-3 BER.

Surface Photonic Crystal Engineering of a Multi-Mode VCSEL for a Bit-Loaded Broadband QAM-OFDM Data Link at 99 Gbit/s

Bit-loaded quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM) encoding and photonic-crystal-engineered multi-mode vertical-cavity surface-emitting lasers (MM-VCSELs) transmission performance are analyzed. Two different surface photonic-crystal designs are used to configure the core and cladding regions of MM-VCSELs, producing continuous-wave and digital-encoding outputs. These outputs are combined with the end-face-flattened OM5 multi-mode fiber (MMF) for 100 m short-reach transmission. The photonic-crystal (PhC) structure exhibits a spatial mode-filtering ability, supporting few or single-mode outputs from the MM-VCSEL. This helps reduce the modal dispersion during OM5-MMF transmission of the encoded data. Comparing the original MM-VCSEL with two different surface-photonic-crystal-configured MM-VCSELs, the allowable bit-loaded QAM-OFDM data rate can be increased from 60.7 (for the VCSEL without the PhC structure) to 85/65 Gbit/s (for the PhC VCSELs with 2-layer PhC structures in the cladding layer and the ones with a 1-layer PhC structure in the core layer and 2-layer PhC structures in the cladding layer, respectively) under back-to-back (BtB) encoding and enable the 100 m OM5-MMF transmission to increase from 58.5 (for the VCSEL without the PhC structure) to 81.2/64.6 Gbit/s (for the PhC VCSELs with 2-layer PhC structures in the cladding layer and the ones with a 1-layer PhC structure in the core layer and 2-layer PhC structures in the cladding layer), respectively. Furthermore, by comparing the 7°-titled and 0°-normalized vertical coupling conditions, it can be observed that the purely normalized vertical coupling can collect more output power, resulting in an improved signal-to-noise ratio. This significantly increases the allowable error-free data rate from 85 to 98.9 Gbit/s in the BtB case and from 81.2 Gbit/s to 95.3 Gbit/s in the 100 m OM5-MMF case.

Transmission of 4096-QAM OFDM at D-band.

We experimentally demonstrate the transmission of multi-order quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) millimeter wave signals at D-band. Meanwhile, the system nonlinearity analysis is also given, which is originated from the unsatisfactory optoelectronic devices, multi-order QAM and the high peak-to-average power ratio (PAPR) of OFDM signal. To alleviate the system nonlinearity, Volterra nonlinearity compensation (VNC) is adopted. Probabilistic shaping (PS) has been regarded as an effective approach to ensure the system robustness. By using the technologies of probabilistic shaping and Volterra nonlinearity compensation, 57.21-Gbit/s 4096-QAM OFDM signal at 117 GHz can be delivered over 13.42-m wireless distance in our experiment, achieving the normalized general mutual information (NGMI) threshold of 0.83 with 25% soft-decision forward-error correction (SD-FEC) overhead. In addition, we simulated the D-band millimeter wave simulation system in VPI software. The NGMI performance between conventional and discrete Fourier transform-spread (DFT-S) 16-QAM OFDM has been compared in simulation at the same optical signal-to-noise ratio (OSNR). The case of conventional 16-QAM OFDM has better performance. To the best of our knowledge, this is the first demonstration of transmission of multi-order QAM OFDM millimeter wave signal at D-band using PS and VNC methods.

Comparing the Dual-Mode VCSEL in OM4-MMF and GI-SMF Links for NRZ-OOK and 16-QAM-OFDM Transmissions

A dual-mode (DM) vertical-cavity surface-emitting laser (VCSEL) is investigated for carrying high-speed data transmission with either the non-return-zero on-off keying (NRZ-OOK) or the quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM) format. In both the back-to-back (BtB) and the 100-m transmission cases with using either the OM4 multimode fiber (OM4-MMF) or the graded-index single-mode fiber (GI-SMF), the mismatch between the core diameter of the lensed MMF pick-up head and the mode field of the DM-VCSEL output controls the coupled transverse mode number and decrease the modal dispersion effect. Using pre-emphasized NRZ-OOK data can compensate the SNR degradation to improve the BER to 5.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−12</sup> under BtB and 6.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−10</sup> after 100-m GI-SMF for the DM-VCSEL delivered NRZ-OOK data at 53 Gbit/s. For 16-QAM OFDM transmission, the pre-leveling algorithm shows better data compensation than the pre-emphasis algorithm in both BtB and the 100-m GI-SMF cases. With the pre-leveling compensation of the 16-QAM OFDM data encoded to the DM-VCSEL with a 0.4-dB/GHz slope, the DM-VCSEL allows 136 Gbit/s for BtB, 112 Gbit/s for 100-m OM4-MMF, and 92 Gbit/s for 100-m GI-SMF transmissions. The pre-emphasis NRZ-OOK and the pre-leveling 16-QAM OFDM data carried by the DM-VCSEL can be used in ultrahigh-speed intra-data-center links in the future.

All-inorganic halide-perovskite polymer-fiber-photodetector for high-speed optical wireless communication.

The use of optical carrier frequencies will enable seamless data connection for future terrestrial and underwater internet uses and will resolve the technological gap faced by other communication modalities. However, several issues must be solved to propel this technological shift, which include the limitations in designing optical receivers with large detection areas, omnidirectionality, and high modulation bandwidth, mimicking antennas operating in the radio-frequency spectrum. To address this technological gap, herein, we demonstrate halide-perovskite-polymer-based scintillating fibers as a near-omnidirectional detection platform for several tens-to-hundreds of Mbit/s optical communication in both free space and underwater links. The incorporation of all-inorganic CsPbBr3 nanocrystals by engineering the nanocrystal concentration in an ultraviolet-curable polymer matrix ensures a high photoluminescence quantum yield, Mega-Hertz modulation bandwidth and Mbit/s data rate suitable to be used as a high-speed fibers-based receiver. The resultant perovskite polymer-based scintillating fibers offer flexibility in terms of shape and near-omnidirectional detection features. Such fiber properties also introduce a scalable detection area which can resolve the resistance-capacitance and angle-of-acceptance limits in planar-based detectors, which conventionally impose a trade-off between the modulation bandwidth, detection area, and angle of view. A high bit rate of 23 Mbit/s and 152.5 Mbit/s was achieved using an intensity-modulated laser for non-return-to-zero on-off-keying (NRZ-OOK) modulation scheme in free-space and quadrature amplitude modulation orthogonal frequency-division multiplexing (QAM-OFDM) modulation scheme in an underwater environment, respectively. Our near-omnidirectional optical-based antenna based on perovskite-polymer-based scintillating fibers sheds light on the immense possibilities of incorporating functional nanomaterials for empowering light-based terrestrial- and underwater-internet systems.

4-QAM OFDM Data Switching via Free Carrier Absorption in Si-Rich SiC Waveguide

The all-optical cross-wavelength quadrature amplitude modulation orthogonal frequency-division multiplexing (QAM-OFDM) data switching in the silicon rich silicon carbide (Si-rich SiC) micro-ring (μ-ring) waveguide is demonstrated for the first time by using the two-photon absorption (TPA) induced free carrier absorption (FCA) process. With enlarging the allowable 4-QAM OFDM data bandwidth to 1.16 GHz, the all-optical 4-QAM OFDM pump-to-probe switching with allowable bandwidth of 1.16 GHz can achieve a raw data rate up to 2.32 Gbit/s with forward error correction (FEC) qualified error vector magnitude (EVM), signal-to-noise ratio (SNR), and bit-err-ratio (BER) of 31.9%, 9.92 dB, and 8.7 × 10−4, respectively. With upgrading the bandwidth of electrical pre-amplifier to 1.5 GHz, the wavelength-converted probe data can successfully pass the FEC criterion with qualified SNR of 9.49 dB, BER of 1.4 × 10−3 and EVM of 33.5%, to demonstrate the all-optical switching data rate approaching 3 Gbit/s.

QAM–OFDM transmission in underwater wireless optical communication system with limited resolution DAC

Underwater wireless optical communication (UWOC) can realize high speed, low delay and flexible information transmission. We experimentally demonstrate a 3-m UWOC system using blue laser diode and avalanche photodiode with quadrature amplitude modulation (QAM) and orthogonal frequency division multiplexing (OFDM) transmission. We achieve net bit rates of 6.23 Gb/s at a bit error rate (BER) of 1.55 × 10−3, by using 128-QAM OFDM signals. High-order QAM signals require higher bit resolution of digital-to-analog converter (DAC). Therefore, the effect of quantization noise on transmission performance is further investigated. In order to meet the requirement that the BER is lower than 3.8 × 10−3, the bit resolution of DAC is required to be at least 5, 6 and 7 bit for 32-QAM, 64-QAM and 128-QAM signals, respectively.

Incoherent Laser Heterodyned Long-Reach 60-GHz MMWoF Link With Volterra Filtered 16-QAM OFDM Beyond 13 Gbps

By remotely heterodyning two independent laser carriers, the long-reach 60-GHz millimeter-wave-over-fiber (MMWoF) link is demonstrated for the Volterra series filtered quadrature amplitude modulation orthogonal frequency division multiplexing (QAM-OFDM) transmission with nonlinear noise suppression, which enables 13-Gbps data delivery through 50-km single-mode fiber (SMF) and 3-m free-space links. A wavelength tunable colorless laser diode transmits the Volterra filter equalized QAM-OFDM data to remotely couple with a localized single-mode laser carrier at the optical receiving end of the MMWoF system. Such an incoherently coupled dual-mode carrier facilitates the optical single-carrier modulation to suppress chromatic dispersion induced power fading effect of the SMF transmitted QAM-OFDM data. The 2nd+3rd-order nonlinear noise induced by direct modulation, heterodyne conversion, and phase fluctuation of the incoherently coupled dual-mode carrier is corrected with the Volterra filter equalization to upgrade the decoded signal-to-noise ratio (SNR) by >2 dB. After remotely heterodyning the downstream and the localized carriers with mutual incoherence in between, the 16-QAM OFDM transmission at a data rate up to 13.2 Gbps is successfully delivered over 3-m wireless link, which reveals the FEC certificated error vector magnitude of 14.1%, SNR of 17 dB, and bit error rate of 1.7 × 10−3.

Average bit error rate performance analysis of a low-density parity-check-coded orthogonal frequency-division multiplexing FSO system under Málaga distribution considering atmospheric attenuation and pointing errors.

The average bit error rate (ABER) performance of low-density parity-check (LDPC)-coded orthogonal frequency-division multiplexing (OFDM) free-space optical communication system with K-ary quadrature amplitude modulation (QAM) and phase shift keying (PSK) modulation schemes is investigated over the composite Málaga fading channel with atmospheric attenuation and pointing errors considered. The probability density function and cumulative distribution function regarding the aggregated channel model are derived with the help of the generalized Gauss-Laguerre quadrature rule, the analytical ABER expressions for both QAM and PSK OFDM systems are then obtained. On the basis of them, the ABER performance is analyzed with different turbulence strengths, weather conditions, normalized beam width, normalized jitter, and specifically, different values of Málaga distribution parameter ρ. Monte Carlo simulation is offered to confirm the correctness of the proposed ABER models. Moreover, LDPC codes are added into the simulation to enhance system performance. The result shows that, for the same turbulence, weather, and pointing error conditions, whether the LDPC codes are taken into account or not, the ABER performance of 16-QAM OFDM system is better than that of 16-PSK OFDM system over the Málaga fading channel, and the ABER result decreases with higher ρ for both modulation schemes. Furthermore, the LDPC coding can significantly improve the system performance over this aggregated fading channel for these two modulation schemes, and a lower LDPC code rate can obtain a better ABER performance. This work is beneficial for free-space optical system design.

Analysis of different sub-carrier allocation of M-ary QAM-OFDM downlink in RoF system

In this paper, the performance of a 60 GHz radio over fiber (RoF) system with 4/16/64 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) downstream signals is studied. Delivery of 10 Gbit/s M-ary QAM (MQAM) OFDM signals through the 20-km-long single-mode fiber (SMF) is complicated in terms of intensity modulation and direct detection (IM/DD). Using self-homodyne method, the beating of two independent light waves generating the millimeter-wave at the photodetector can be down-converted to baseband in the electrical domain. Meanwhile, three kinds of sub-carrier arrangement schemes are compared and discussed, and the simulation results show that lower peak-to-average power ratio (PAPR) can be obtained adopting the adjacent scheme. At bit error rate (BER) of 10-3, the receiver sensitivity using 4QAM-OFDM sub-carrier signal is almost enhanced by 4 dB and 9 dB compared with those of 16QAM-OFDM signal and 64QAM-OFDM signal.

A Novel Chaos-Based Encryption Approach for Future-Generation Passive Optical Networks Using SHA-2

A physical layer enhanced secure future generation passive optical network (PON) based on chaotic signal scrambling and the secure hash algorithm (SHA) is proposed and demonstrated. In this paper, the architecture of a wavelength-division multiplexed orthogonal frequency division multiplexing (OFDM) PON system based on a centralized light source using direct detection is analyzed. A logistic chaos map is employed here for the scrambling of OFDM symbols in the frequency and time domains. Before transmitting the signal over optical fiber, a message- digest of scrambled and descrambled OFDM signals is computed and compared at the optical line terminal and optical network unit, respectively, to verify the actual data recovered. For the downstream channel, a 10 Gbps 32 quadrature amplitude modulation OFDM signal is successfully transmitted over a distance of 50 km single-mode fiber within the limits of the peak-to-average-power value. The results show that the proposed scheme can protect the system from bad actors and eavesdroppers, while chaos encryption with SHA-2 provides a robust and promising secure strategy for future-generation PON systems.

Using a Single VCSEL Source Employing OFDM Downstream Signal and Remodulated OOK Upstream Signal for Bi-directional Visible Light Communications

In this work, we propose and demonstrate for the first time up to our knowledge, using a 682 nm visible vertical-cavity surface-emitting laser (VCSEL) applied in a bi-directional wavelength remodulated VLC system with a free space transmission distance of 3 m. To achieve a high VLC downstream traffic, spectral efficient orthogonal-frequency-division-multiplexing quadrature-amplitude-modulation (OFDM-QAM) with bit and power loading algorithms are applied on the VCSEL in the central office (CO). The OFDM downstream wavelength is remodulated by an acousto-optic modulator (AOM) with OOK modulation to produce the upstream traffic in the client side. Hence, only a single VCSEL laser is needed for the proposed bi-directional VLC system, achieving 10.6 Gbit/s OFDM downstream and 2 Mbit/s remodulated OOK upstream simultaneously. For the proposed system, as a single laser source with wavelength remodulation is used, the laser wavelength and temperature managements at the client side are not needed; and the whole system could be cost effective and energy efficient.

Destructively Interfered Beating Dual-Mode VCSEL for Carrierless MMW Fiber-Wireless Access Link With Suppressed RF Fading

Long-reach fiber-wireless access link using a dual-mode vertical-cavity surface-emitting laser (DM-VCSEL) is established for carrierless millimeter-wave (MMW) transmission with suppressed RF fading. By destructively interfered beating the orthogonally polarized dual carrier from the DM-VCSEL, the remotely beat MMW central carrier suppresses its central peak power up to 33 dB, which ensure more gain for the carried quadrature-amplitude modulation orthogonal frequency-division multiplexing (QAM-OFDM) data during electrical amplification to lengthen the distance of wireless link. With suppressing the MMW central carrier and mitigating the RF fading by destructively interfered beating and optical single-carrier modulation of the DM-VCSEL, the received optical signal-to-noise ratio as high as 18.1 dB is determined after fiber transmission. Such a long-reach 38-GHz carrierless MMW over fiber system enables 12-Gb/s 16-QAM OFDM data transmission over 50 km in single-mode fiber and 4 m in free space. After the proposed fiber-wireless access, the single-carrier modulated QAM-OFDM data certifies to pass the forward error correction criterion with an error vector magnitude of 17.2% and a bit error rate of 3.6 × 10–3.

TO-56-can packaged colorless WRC-FPLD for QAM OFDM transmission at 42 Gbit/s over 25-km SMF.

The weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) with colorless and channelized mode features is a new-class optical transmitter fulfilling the need of next-generation communications. By packaging the colorless WRC-FPLD transmitter with a 10-GHz transistor-outline-56-can (TO-56-can), the premier demonstration on directly modulated 42-Gbit/s/channel quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) transmission is demonstrated via wavelength injection-locking. Enlarging the injection level effectively up-shifts the relaxation oscillation peak and suppresses the relative intensity noise, which facilitates the TO-56-can packaged WRC-FPLD to improve its modulation throughput bandwidth to 9 GHz and enhance its signal-to-noise ratio to 22 dB. By pre-amplifying the directly modulated QAM-OFDM data with a total raw bit rate of 42 Gbit/s, the receiving bit-error-rate (BER) under back-to-back transmission can be reduced below the forward-error-correction (FEC) limited BER of 3.8 × 10(-3). Such a colorless WRC-FPLD enables the QAM-OFDM transmission over a 25-km long single-mode-fiber based metropolitan access network with its BER matching the FEC criterion at a receiving power of -2 dBm.

Performance Comparison of DFT-Spread and Pre-Equalization for 8 × 244.2-Gb/s PDM-16QAM-OFDM

In this paper, we experimentally compared the performance of discrete-Fourier-transform spread (DFT-spread) and pre-equalization in a 244.2-Gb/s polarization-division-multiplexed 16-ary quadrature amplitude-modulation orthogonal frequency-division multiplexing (PDM-16QAM-OFDM) transmission system. The pre-equalization is effective to overcome the high-frequency power attenuation in the channel. However, the acquisition of static channel response for pre-equalization is really complicated and the peak-to-average power ratio (PAPR) of the signal after pre-equalization even becomes a little higher. The DFT-spread can be applied to simultaneously resist high-frequency power attenuation and reduce the PAPR of OFDM signal. The experimental results also show that one band DFT-spread demonstrates the best narrow optical filtering tolerance. The transmission distance for 8 × 244.2-Gb/s wavelength-division-multiplexing (WDM) PDM-16QAM-OFDM at the soft-decision forward-error correction threshold of 2.4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> is 2× 420 km based on pre-equalization, while extended to over 3×420 km based on one band DFT-spread, which well illustrates one band DFT-spread is more efficient for high-bandwidth coherent WDM-OFDM system.

Experimental demonstration of a full-duplex high-speed visible light communication access network architecture based on frequency division multiplexing

We propose and experimentally demonstrate a full-duplex high-speed visible light communication (VLC) access network based on star topology architecture to offer high-speed optical wireless access for a large number of users. Optical fiber is used as the backbone of the VLC network and directly connected to the light-emitting diode lamps. Frequency division multiplexing (FDM) is utilized for both the downlink and uplink. The bidirectional transmission of 32 quadrature amplitude modulation orthogonal FDM signals at an overall throughput of 4 Gb/s is successfully achieved to support four users access, and each user is offered 500 Mb/s downstream and 500 Mb/s upstream. The measured bit error rates of the downlink and uplink for all four users are <7% pre-forward error correction limit of 3.8×10−3 after a 25 km standard single-mode fiber and 65 cm free space, which clearly validates the promising potential of the proposed VLC network architecture to offer more than 10 Gb/s wireless access.

BER estimation for multi-hop RoFSO QAM or PSK OFDM communication systems over gamma gamma or exponentially modeled turbulence channels

Abstract The optical wireless and in particular the radio-on-free-space-optical (RoFSO) communication systems are gaining popularity due to their high date rates, license free spectrum and adequate reliability at installation and operational costs which are much lower than comparable technologies. One significant disadvantage of these systems concerns the randomly time varying characteristics of the propagation path mainly caused by the atmospheric turbulence. In this work, we study the BER performance of a multi-hop RoFSO system which is using an orthogonal frequency division multiplexing (OFDM) scheme, with either quadrature amplitude modulation (QAM) or phase shift keying format (PSK), over atmospheric turbulence channels modeled with the gamma gamma or the negative exponential distribution. The individual RoFSO parts of the whole optical link are connected to each other by using regenerators relay nodes. The dominant impairments which are the most significant and have been taken into account are the atmospheric turbulence, the path losses, the nonlinear responsivity of the laser diode and the inter-modulation distortion effect. For this setup, we derive closed form mathematical expressions for the estimation of the BER performance for each individual OFDM RoFSO link and for the whole relayed optical communication system, as well. Finally, the corresponding numerical results, for common link׳s parameters, are presented.