Subcarrier Intensity Modulation Research Articles

Anisotropy effect on performance of subcarrier intensity modulated binary phase shift keying optical wireless communication links in weakly turbulent underwater channel

ABSTRACTThe effect of the anisotropy on the bit-error-rate (BER) performance of subcarrier intensity modulated (SIM) binary phase shift keying (BPSK) optical wireless communication (OWC) links operating in weakly turbulent underwater channels is examined. BER variations versus the anisotropic factor are examined when the bandwidth, photodetector responsivity, load resistor and the underwater turbulence parameters are varied. As anisotropy in the underwater channel becomes larger, SIM BPSK OWC links have better BER performance at any link and turbulence parameter.

Performance Improvement for Mixed RF–FSO Communication System by Adopting Hybrid Subcarrier Intensity Modulation

The improvement for hybrid radio frequency–free space optical (RF–FSO) communication system in wireless optical communications has acquired growing interests in recent years, but rarely improvement is based on hybrid modulation. Therefore, we conduct a research on end-to-end mixed RF–FSO system with the hybrid pulse position modulation–binary phase shift keying–subcarrier intensity modulation (PPM–BPSK–SIM) scheme. The RF link obeys Rayleigh distribution and the FSO link experiences Gamma–Gamma distribution. The average bit error rate (BER) for various PPM–BPSK–SIM schemes has been derived with consideration of atmospheric turbulence influence and pointing error condition. The outage probability and the average channel capacity of the system are discussed as well. Simulation results indicate that the pointing error aggravates the influence of atmospheric turbulence on the channel capacity, and the RF–FSO systematic performance is improved obviously while adopting PPM–BPSK–SIM under strong turbulence and severe pointing error conditions, especially, when the system average symbol length is greater than eight.

Görünür Işık Haberleşmesi için Çift Dördün Uzaysal Yoğunluk Modülasyonu

In this paper, a new spectrally efficient space modulation technique, which is called double quadrature spatial intensity modulation (DQSIM), is proposed for multiple-input multiple-output (MIMO) visible light communication (VLC) systems. Sub-carrier intensity modulation (SIM), which ensures the use of in-phase/quadrature (I/Q) signals in intensity modulation direct detection (IM/DD) systems, is used as a digital modulation scheme. In RF, quadrature spatial modulation (QSM) transmits the I/Q signals through single or multiple antennas selected independently from each other. Furthermore, the orthogonality between I and Q components is provided for the half period of sinusoids. DQSIM utilizes these two features and transmits four fold more bits than spatial modulation (SM) via spatial constellation. SIM uses two-fold bandwidth compared to on-off keying (OOK), while DQSIM uses three fold. DQSIM outperforms benchmark modulation schemes, which are SIM-SM and PAM-SM, at the BER value of 10 -4 . Furthermore, DQSIM performance has increased with increasing number of LEDs.

BER and channel capacity of a deep space FSO communication system using L-PPM-MSK-SIM scheme during superior solar conjunction.

Although free space optical (FSO) communication is a promising technique for deep space communication and it can help in the rapid development of space exploration missions, it encounters coronal turbulence during superior solar conjunction. To improve the bit error rate (BER) performance of FSO communication system under the influence of coronal turbulence, a hybrid modulation scheme, L-PPM-MSK-SIM-which is a combination of pulse position modulation (PPM), minimum shift keying (MSK), and sub-carrier intensity modulation (SIM) techniques-is proposed in this study. Considering various noise sources, both the BER and channel capacity of the communication system are evaluated under the lognormal (LN) turbulence channel. Our simulation results demonstrate that the BER performance with the L-PPM-MSK-SIM scheme is superior to that with L-PPM and BPSK-SIM schemes. In addition, the parameters of the coronal turbulence and FSO communication system have a tremendous influence on the link BER and channel capacity. Moreover, our results also revel that thermal noise is more predominant than the short noise and background noise for the BER performance of deep space FSO communication.

Amplify-and-forward multihop non-line-of-sight ultraviolet communication in the gamma–gamma fading channel

In this paper, we propose amplify-and-forward-based multihop non-line-of-sight (NLOS) ultraviolet (UV) communication with subcarrier intensity modulation to mitigate turbulence-induced fading. Atmospheric turbulence is one of the main impairments in the performance of UV links, as it causes random fluctuation of the received signal. An aggregated UV channel model of both path loss and turbulence-induced gamma–gamma fading is considered. We derive the probability density function (PDF) of the end-to-end received signal-to-noise ratio (SNR). With this PDF and the random coding error exponent, an exact solution to the optimal number of hops in the proposed multihop UV system is presented. Over the turbulence-induced gamma–gamma fading channel, a closed-form expression for the moment-generating function (MGF) of the inverse of the instantaneous received SNR is also derived. Based on the derived MGF, two closed-form analytical expressions of average bit error rate and outage probability are further derived, together with an upper bound of the ergodic capacity of the proposed system. From the analytical expressions derived, the proposed multihop NLOS UV system is analyzed. Simulation results show that the proposed UV system can effectively mitigate the turbulence-induced fading, thus resulting in an increased coverage distance of the UV system without sacrificing important performance criteria such as the outage probability and the average bit error rate. It is also found that the optimal number of hops decreases with an increasing data rate.

Amplify-And-Forward Based Cascaded RF-UWOC System

A cascaded radio frequency-underwater wireless optical communication (RF-UWOC) system using an amplify-and-forward relay is considered. UWOC supports high speed communication for underwater surveillance, monitoring of climate change, and different deep-sea mining activities making it a s suitable substitute to underwater acoustic communication. The proposed fixed-gain AF based cascaded radio-optical system can connect underwater with land. The system comprises of Nakagami-m faded radio link and mixture Exponential-Generalized Gamma (EGG) faded UWOC link. Salinity, air bubbles, and thermal fluctuations in water causes underwater optical turbulence (UOT). Optical signals are modulated by subcarrier intensity modulation technique at the relay and heterodyne or direct detection is performed at destination. For this proposed communication system, outage and error analyses are carried out. It is observed that the performance of the considered system deteriorates more because of the underwater optical turbulence (UOT) due to thermal fluctuations and air bubbles as compared to UOT introduced by salinity.

Effect of wind pressure and modulation schemes on rain interrupted optical wireless links under tropical climates

Tropical and subtropical regions experience heavy rain intensities often accompanied with medium to strong winds. In this work, the effect of perpendicular wind flow and various modulation formats on a rain interrupted optical wireless link is investigated experimentally under controlled laboratory conditions. Attenuation as a function of rain rate is observed at different wind pressure. It is found that rain induced scattering dominates the rain specific attenuation however significant attenuation is expected at much higher wind pressure which normally increases with altitudes. A comparative performance of modulation formats like direct intensity modulation (D-IM), pulse width modulation (PWM) and various subcarrier intensity modulated (SIM) signals under heavy rain conditions is reported. It is found that SIM-FSK and SIM-AM offer better signal to noise performance (approximately two times) followed by subcarrier phase (SIM-PM) and frequency (SIM-FM) respectively. Also, SIM-FSK and PWM are least attenuated in heavy precipitation.

Effect of strong atmospheric non-Kolmogorov turbulence on the M-ary PSK subcarrier intensity modulated free space optical communications system performance.

Atmospheric turbulence is one of the significant phenomena that degrades the free space optical (FSO) communications system performance, and thus designers need to define the requirements related to turbulence and optimize the system design to ensure optimum performance. The subcarrier intensity modulation (SIM) shows superiority in terms of bandwidth usage over the other modulation techniques. Performance of FSO communication systems exercising M-ary phase-shift-keying (PSK) SIM with the PIN photodiode receiver is evaluated in non-Kolmogorov strong atmospheric turbulence when a Gaussian beam is used as the excitation. Bit-error-rate (BER) of PSK SIM FSO communication systems is examined, and the results are presented versus the non-Kolmogorov atmospheric turbulence and positive-intrinsic-negative (PIN) photodetector parameters such as PIN photodetector responsivity, equivalent load resistor, modulation order, noise factor, bandwidth, propagation distance, and beam source size.

Error performance of deep space optical communication with M-ary pulse position modulation over coronal turbulence channels.

Free space optical (FSO) communication is a promising technology for future deep space exploration, but it encounters coronal turbulence during superior solar conjunction. In this paper, the bit-error rate (BER) performance of deep space FSO communication systems is evaluated for optical waves propagating in the non-Kolmogorov coronal turbulence. By virtue of its high energy efficiency, the pulse position modulation (PPM) technique is adopted to mitigate the influence of turbulence under lognormal distribution channels. The effects of the parameters of the coronal turbulence and of the FSO system, such as the turbulence outer scale, spectral index, symbol number, data bit rate, equivalent load resistor, and average gain, on the BER are investigated and discussed in this paper. In addition, the performance improvement from M-ary PPM and binary phase-shift keying subcarrier intensity modulation is studied. The results of a numerical evaluation illustrate that a deep space FSO communication system with PPM scheme can well be used to mitigate the impact of coronal turbulence.

SIMO subcarrier PSK FSO links with phase noise and non‐zero boresight pointing errors over turbulence channels

Terrestrial free-space optical (FSO) communication systems with subcarrier intensity modulation have experienced a particular research attention in the recent past. However, their performance strongly degrades in the presence of atmospheric turbulence, pointing errors, and phase noise impairments. In order to overcome these limitations, the authors consider a receiver diversity scheme of a typical subcarrier phase-shift keying (PSK) system and investigate the performance by means of the average symbol error probability (ASEP). They assume a wide range of turbulence conditions, non-zero boresight pointing errors, and phase noise strengths described through the gamma-gamma, Beckmann, and Tikhonov distributions, respectively. Novel approximate ASEP expressions are derived for single-input single-output and single-input multiple-output (SIMO) configurations. Appropriate numerical results are depicted and validated by Monte Carlo simulations.

Error performance enhancement of satellite to earth FSO downlink employing hybrid subcarrier intensity modulation scheme with aperture averaging technique

In this work, we have evaluated the bit error rate (BER) of free space optical downlink using hybrid-subcarrier-intensity-modulation (hybrid-SIM) scheme. Also, we have employed the aperture averaging technique for the improvement of its error performance. The required BER analysis has been performed over the gamma–gamma channel model with the scintillation effects. The BER analysis is simplified using Meijer-G function and it is simulated in MATLAB. The simulation results show that the improvement in error performance is observed by hybrid-SIM technique compared to other modulation schemes like PPM and BPSK-SIM and also the BER improves significantly with the increase of aperture size due to the aperture averaging effect.

Performance enhancement of BPSK-SIM- and DPSK-SIM-based FSO downlink over atmospheric turbulence using aperture averaging and receiver diversity

In this paper, we evaluate the bit error rate (BER) performance of a free-space optical satellite downlink by considering the atmospheric turbulence effects using binary shift keying subcarrier intensity modulation and differential phase shift keying subcarrier intensity modulation (DPSK-SIM). The performance of the link is enhanced using aperture averaging and receiver diversity. The closed form mathematical expressions of BER for BPSK-SIM and DPSK-SIM schemes are derived and analyzed. It is observed that on varying the turbulence level, the performance of the link degrades when the turbulence level increases. The improved BER of 10−12 and 10−10 at signal-to-noise ratio of 30 dB of the link for both BPSK-SIM and DPSK-SIM is obtained by using aperture averaging (aperture diameter, D = 10 cm) and receiver diversity with optimal combining.

Performance of multiple-input multiple-output free space optics using hybrid subcarrier intensity modulation with avalanche photodiode receiver

In order to improve the performance of a free space optical (FSO) communication system, hybrid pulse position modulation-binary phase shift keying-subcarrier intensity modulation (PPM-BPSK-SIM) technique is proposed. The system performance is further improved by using multiple-input multiple-output (MIMO) configuration and avalanche photodiode (APD) receiver. The use of multiple lasers and photo detectors in MIMO FSO system reduces the scintillation effect in the atmosphere. In this study, the impact of different parameters like irradiance, link distance, and turbulence level have been considered for the bit error rate (BER) analysis. The relevant mathematical model is also presented. The simulation results show that the hybrid PPM-BPSK-SIM scheme performs better compared to PPM and BPSK-SIM schemes. Also, APD receiver shows a noticeable BER improvement than p-type intrinsic n-type (PIN) receiver in our proposed scheme.

Performance of multiple-input multiple-output free space optics using hybrid subcarrier intensity modulation with avalanche photodiode receiver

In order to improve the performance of a free space optical (FSO) communication system, hybrid pulse position modulation-binary phase shift keying-subcarrier intensity modulation (PPM-BPSK-SIM) tec...

Error performance of optical wireless communication systems exercising BPSK subcarrier intensity modulation in non-Kolmogorov turbulent atmosphere

Abstract Subcarrier intensity modulation (SIM) scheme is preferred due to efficient bandwidth usage superiority over other modulation techniques such as on–off keying (OOK), pulse position modulation (PPM). In this paper, we investigate the bit error rate (BER) performance of optical wireless communication (OWC) system using binary phase shift keying (BPSK) SIM in non-Kolmogorov turbulent atmosphere. We pay attention to the weak turbulence conditions by using Rytov approximation and considering that the receiver is a PIN photodetector. Propagating beam type is Gaussian. It is seen that BER performance of the BPSK SIM OWC is significantly affected from non-Kolmogorov power law exponent, load resistor, responsivity of the PIN photodetector, bandwidth, beam source size, turbulence strength and noise factor.

BER analysis and capacity evaluation of FSO system using hybrid subcarrier intensity modulation with receiver spatial diversity over log-normal and gamma–gamma channel model

In this work, the performance of free space optical system is evaluated in terms of bit error rate (BER) and capacity using PPM–BPSK–SIM (hybrid-SIM) modulation scheme. Addition to that, we have applied spatial diversity technique for the proposed system. We have calculated the BER and the capacity at various atmospheric turbulence levels over the log-normal and gamma–gamma channel models. The analysis has been carried out at different signal-to-noise-ratio (SNR) values and link distances. The simulation results show that hybrid-SIM modulation scheme achieves better BER performance than BPSK–SIM scheme in both the channel models; furthermore, the BER performance gets improved significantly by spatial diversity technique.

紫外光通信中副载波强度调制的低密度奇偶校验码研究

紫外光通信中副载波强度调制的低密度奇偶校验码研究

Performance analysis of non-identically distributed FSO systems with dual- and triple-branch based on MRC over Gamma-Gamma fading channels

In this work, the performance of free-space optical (FSO) communication system based on maximal ratio combining using binary phase shift keying subcarrier intensity modulation over Gamma-Gamma fading channels has been studied systematically. Under identically or non-identically distributed branches, the analytical expressions for the bit error rate function of signal-to-noise are derived by expressing the modified Bessel function of second kind with Meijer G-function for dual- and triple-branch systems, respectively. In terms of H-fox function, the new expressions have more general forms and are more efficient for computation. It is found that the dual- and triple-branch systems significantly outperform the direct link system under weak, moderate and strong turbulence conditions. Monte Carlo simulation is also provided to confirm the accuracy of the proposed model.

Design and Security Analysis of Quantum Key Distribution Protocol Over Free-Space Optics Using Dual-Threshold Direct-Detection Receiver

This paper proposes a novel design and analyzes security performance of quantum key distribution (QKD) protocol over free-space optics (FSO). Unlike conventional QKD protocols based on physical characteristics of quantum mechanics, the proposed QKD protocol can be implemented on standard FSO systems using subcarrier intensity modulation binary phase shift keying and direct detection with a dual-threshold receiver. Under security constraints, the design criteria for FSO transmitter and receiver, in particular, the modulation depth and the selection of dual-threshold detection, respectively, is analytically investigated. For the security analysis, quantum bit error rate, ergodic secret-key rate, and final key-creation rate are concisely derived in novel closed-form expressions in terms of finite power series, taking into account the channel loss, atmospheric turbulence-induced fading, and receiver noises. Furthermore, Monte-Carlo simulations are performed to verify analytical results and the feasibility of the proposed QKD protocol.

Subcarrier intensity modulation for MIMO visible light communications

In this paper, subcarrier intensity modulation (SIM) is investigated for multiple-input multiple-output (MIMO) visible light communication (VLC) systems. A new modulation scheme called DC-aid SIM (DCA-SIM) is proposed for the spatial modulation (SM) transmission plan. Then, DCA-SIM is extended for multiple subcarrier case which is called DC-aid Multiple Subcarrier Modulation (DCA-MSM). Bit error rate (BER) performances of the considered system are analyzed for different MIMO schemes. The power efficiencies of DCA-SIM and DCA-MSM are shown in correlated MIMO VLC channels. The upper bound BER performances of the proposed models are obtained analytically for PSK and QAM modulation types in order to validate the simulation results. Additionally, the effect of power imbalance method on the performance of SIM is studied and remarkable power gains are obtained compared to the non-power imbalanced cases. In this work, Pulse amplitude modulation (PAM) and MSM-Index are used as benchmarks for single carrier and multiple carrier cases, respectively. And the results show that the proposed schemes outperform PAM and MSM-Index for considered single carrier and multiple carrier communication scenarios.