- 标题
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- 实验方案
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Performance Evaluation of Hybrid FSO-SACOCDMA System under Different Weather Conditions
摘要： Spectral amplitude coding optical code division multiple access (SACOCDMA) is a multiplexing technique, which provides faster speed, efficiency, security and unlimited bandwidth. It is widely preferred because of its ability to eliminate multiple access interference (MAI). Free space optics (FSO) provides a wireless link to transmit data securely at higher rates for last mile access. In this work, a 100 Gb/s hybrid FSO-SACOCDMA is designed using direct detection. The performance of FSO using SACOCDMA utilizing NZCC (New Zero Cross Correlation) code is evaluated under different weather conditions (clear weather, haze and fog) for ten users where each user carries 10 Gb/s. The results indicate that in clear weather FSO distance can be extended up to 13 km. Moreover, after using pre-amplifier in clear weather, FSO enhances the maximum distance to 35 km with acceptable signal to noise ratio and bit error rate. Using an amplifier in the link not only makes the quality of the signal better but it also increases the communication range.
关键词： spectral amplitude coding optical code division multiple access (SACOCDMA),free space optics (FSO),direct detection (DD),new zero cross correlation (NZCC)
更新于2025-09-23 15:23:52
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Precise Performance Analysis of Dual-Hop Mixed RF/Unified-FSO DF Relaying with Heterodyne Detection and Two IM-DD Channel Models
摘要： This paper provides precise performance analysis of the dual-hop mixed radio frequency (RF)/unified free space optical (FSO) decode-and-forward (DF) relaying system, in which the heterodyne detection (HD) and the intensity modulation-direct detection (IM-DD) are taken into account for FSO detection. To this end, we derive closed-form expressions for the outage probability, average bit error rate (BER), and the ergodic channel capacity of this system. In this analysis, we utilize, for the first time as per our knowledge, a precise channel capacity result for the IM-DD channel. Moreover, this is the first time that not only the (IM-DD input-independent) but also the (IM-DD cost-dependent) AWGN channel is considered in such system analyses. Additionally in this study, we assume that the first hop (RF link) follows Nakagami-m fading, and the second hop (FSO link) follows Málaga (M) turbulence with pointing errors. These fading and turbulence models contain other models (such as Rayleigh and Gamma-Gamma) as special cases, thus our analyses can be seen as a generalized one from the RF and FSO fading models point of view. Also, in BER derivation, we assume that the modulation schemes in the two hops can be different, since not all modulation schemes are suitable for IM-DD FSO links. In addition, the system performance is investigated asymptotically at high signal to noise ratios (SNRs). This investigation leads to new non-reported coding gain and diversity order analyses of such system. Interestingly, we find that in the FSO hop, at high transmitted powers, all the considered FSO detectors result in the same diversity order. Furthermore, we provide simulation results that verify the accuracy of the obtained analytical and asymptotic expressions.
关键词： Nakagami-m fading,Málaga (M) fading,HD,DF,heterodyne detection,Mixed RF/FSO relay network,IM-DD,decode-and-forward,intensity modulation-direct detection
更新于2025-09-23 15:22:29
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On the Complexity Reduction of the 2nd-order Volterra Nonlinear Equalizer for IM/DD systems
摘要： To cope with the various nonlinear signal distortions in IM/DD transmission systems, a theoretical analysis on the Volterra nonlinear equalizer (VNLE) is provided, focusing on computational complexity aspects. The analysis yields a simple reduced-complexity scheme for the 2nd-order VNLE (R2-VNLE) based on a performance-complexity trade-off. An experimental verification is performed with single-sideband 28-GBaud PAM-4 electro-absorption modulated signals, generated by a distributed-feedback laser, over transmission distances of up to 80-km of standard single-mode fiber in the C-band. A comparison of the results for different equalization schemes, including a signal-signal beat interference mitigation technique, shows superior performance for the R2-VNLE.
关键词： PAM-4,Volterra filter,direct detection,Nonlinear equalization,optical interconnects,intensity modulation
更新于2025-09-23 15:22:29
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Millimeter-wave home area network prospect with cost-effective RoF links
摘要： The growth towards the millimeter-wave band in the home area networks (HAN) leads to high data rate transmission to satisfy the new user services. Unfortunately, the transmission coverage in this band is limited to short distances because of the strong air absorption and obstacles such as walls. The effort is then focused on the extension of the network coverage of the wireless link in this band. Solutions based on multiple connected access points to optical fibers are useful methods to ensure wireless connectivity to the entire home. For HAN applications, radio-over-fiber (RoF) using intensity modulation and direct detection technique is the mostly favorite technology for the transmission of a broadband wireless signal because dealing with a cost-effective solution. We investigate in this paper the performance of such RoF-wireless architecture with low-cost optoelectronic modules through the error vector magnitude (EVM) metric. The RoF links investigated are a directly modulated VCSEL with integrated photoreceiver module, an electroabsorption-modulated laser with PIN photodiode and a Mach–Zehnder Modulator with PIN photodiode. A simulation approach based on equivalent electrical circuit models of photonic components is developed in ADS (Advanced Design System) by using a co-simulation technique that combines both analog and digital signals. The downlink channel of the complete transmission system including wireless channel and frequency conversion circuits to millimeter-wave (mm-wave) band is studied by simulation. The obtained results of EVM show good performances of cost-effective links with QPSK and 16-QAM modulation over a dynamic range of 15 dB.
关键词： Radio over fiber,Intensity modulation–direct detection,Home area network,Wireless channel
更新于2025-09-23 15:22:29
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Study of Chromatic Dispersion Impacts on Kramers-Kronig and SSBI Iterative Cancellation Receiver
摘要： Field recovery of single sideband (SSB) signals with direct detection has recently been investigated for short-reach communications. One of the cruxes of such direct-detected transmission system is signal-signal beat interference (SSBI) mitigation without sacrificing spectral efficiency. Among various digital signal processing schemes, Kramers-Kronig (KK) algorithm has attracted considerable interest recently due to its effective mitigation of SSBI, and the phase of signals can be recovered using intensity information. As such, chromatic dispersion (CD) can be digitally compensated. Beside KK algorithm, SSBI can also be sufficiently mitigated iteratively. In this paper, we carry out an 80-Gb/s 160-km transmission experiment to investigate chromatic dispersion impacts on both KK and SSBI iterative cancellation (IC) receiver. It is shown that for KK receiver, optimal carrier-to-signal power ratio (CSPR) values increase with transmission distance. This is because that CD induced peak-to-average power ratio (PAPR) increase violates minimum phase condition, and thus the field cannot be reconstructed accurately, leading to degradation of transmission performance. Consequently, OSNR sensitivity for KK receiver is dependent on CD. In contrast, IC receiver has no limitation of minimum phase condition, and thus exhibits high robustness against CD regardless of CSPRs. Besides, experimental results show that after 160-km transmission at the BER threshold of 10-3, the required OSNR for IC receiver is 1.9 dB lower than that of KK receiver.
关键词： direct detection,Kramers-Kronig receiver,virtual single sideband signal,signal-signal beat interference,Chromatic dispersion
更新于2025-09-23 15:22:29
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Performance Analysis of Kramers-Kronig Receiver in the Presence of IQ Imbalance
摘要： We investigate the impact of IQ imbalance of the transmitter on the performance of the direct-detection system utilizing the Kramers-Kronig receiver. We show through theoretical analysis that the amplitude imbalance, timing misalignment, and IQ phase mismatch create double-sideband distortions, which, in turn, serve to violate the minimum phase condition and also lead to the dispersion-induced RF power fading after transmission. The theoretical analysis is verified by using numerical simulations. The results show that the amplitude imbalance and timing misalignment should be less than 2 dB and 2 ps, respectively, when the receiver sensitivity penalty is smaller than 1 dB for the transmission of 112-Gb/s 16-QAM OFDM signal.
关键词： direct detection,optical communication,optical modulation
更新于2025-09-23 15:21:21
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Significant improvement on electrical properties of BaSi <sub/>2</sub> due to atomic H passivation by radio-frequency plasma
摘要： We demonstrate for the ?rst time an intensity-modulated direct-detection link using four states of polarization. The four data-independent tributaries are each assigned distinct states of polarization to enable the receiver to separate the signals. Polarization rotation due to propagation over optical ?ber is tracked and compensated with simple digital signal processing in Stokes space. Transmission below the forward error correction limit is shown for maximum net bitrates of 100 Gb/s (4 × 27 GBd) and 120 Gb/s (4 × 32 GBd) over 2-km standard single-mode ?ber at a center wavelength of 1550 nm.
关键词： direct detection (DD),intensity modulation (IM),digital signal processing,Stokes space,100G,polarization
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Precursor reaction method with high Ga Cu(In,Ga)(S,Se) <sub/>2</sub> to achieve increased open-circuit voltage
摘要： Direct detection transceivers offer advantages, including low cost and complexity, in short- and medium-haul links. We carried out studies seeking to identify the signal formats which offer the highest information spectral densities and maximum transmission distances for direct detection links. The performance of two spectrally efficient optical signal formats, single-sideband (SSB) Nyquist pulse-shaped subcarrier modulation (SCM) and SSB orthogonal frequency-division multiplexing (OFDM), are compared by means of simulations. The comparison is performed for a range of wavelength-division multiplexing (WDM) net information spectral densities up to 2.0 b/s/Hz by varying the signal bandwidth, modulation cardinality, and WDM channel spacing. The signal formats’ tolerance to signal–signal beating interference, resulting from square-law detection, is investigated, and the Nyquist-SCM format is found to suffer lower penalties from this nonlinearity at high information spectral densities. In 7 × 28 Gb/s WDM transmission at 2.0 b/s/Hz (with electronic pre-distortion and EDFA-only amplification), Nyquist-SCM signals can be transmitted over distances of up to 720 km of standard SMF in comparison to a maximum of 320 km with the OFDM signal format.
关键词： Digital signal processing,direct detection,wavelength division multiplexing,subcarrier modulation,electronic pre-distortion,optical communication,Nyquist pulse shaping,signal–signal beating interference,orthogonal frequency division multiplexing
更新于2025-09-23 15:19:57
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Analytic and simulative comparison of turbulent FSO system with different modulation techniques
摘要： In this paper, we characterize the performance of Intensity Modulation/Direct Detection (IM/DD) and coherent detection modulation techniques in free-space optical (FSO) communication system in terms of bit error rate (BER). The system of interest includes M-ary Pulse Position Modulation (M-PPM) in correspondence to IM/DD and M-ary Phase Shift Keying (M-PSK) and M-ary Quadrature Amplitude Modulation (M-QAM) with respect to coherent detection. The system is subjected to weak turbulence regime of log-normal channel with scintillation index less than 0.75. Coherent techniques involve the amount of signal pulses transmitted in a particular time as the major component of their generation, except IM/DD which is a result of photon intensity, i.e. the number of photons forming a pulse. It is worth mentioning that in previous studies, the performance of IM/DD techniques had been evaluated in terms of photon-count fluctuation statistics and thus the impact of fading strength of channel on signal intensity was not discussed anywhere. In this work, an objective equivalence has been achieved between these two kinds of detection by deriving the BER expression of M-PPM in terms of probability density function of signal intensity, while considering fading strength, scintillation index, thermal noise and outage probability as system parameters for numerical analysis.
关键词： M-ary Pulse Position Modulation (MPPM),M-ary Phase Shift Keying (MPSK),M-ary Quadrature Amplitude Modulation (M-QAM),Intensity Modulation/Direct Detection (IM/DD),Scintillation index,Coherent detection
更新于2025-09-19 17:15:36
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Envelope Detection of 16QAM Single Carrier Signal for IM/DD RoF System at Q-band
摘要： In this paper, an envelope detection scheme of single carrier 16-ary Intensity-Modulation/Direct-Detection (IM/DD) radio-over-fiber (RoF) system is theoretically and experimentally investigated. Based on the proposed scheme, the mm-wave 16QAM signal is down-converted to the intermediate frequency (IF) 16QAM one by an envelope detector (ED) and there is no use of a mixer at the user side. We theoretically and experimentally study the performance of the signal under various conditions. In the system, 2GBaud 16QAM signal is delivered over 25km standard single mode fiber (SSMF) link and 2.9m wireless link under bit error rate (BER) of 3.8×10-3.
关键词： Radio-over-fiber (RoF),Intensity-Modulation/Direct-Detection (IM/DD),Envelope detection
更新于2025-09-19 17:15:36