M-ary Pulse Position Modulation Research Articles

A Power-Domain MST Scheme With BPPM in NLOS Ultraviolet Communications

Due to the high path loss of non-line-of-sight (NLOS) ultraviolet communications (UVC) channel, pulse modulation schemes, such as on-off keying (OOK) and M-ary pulse-position modulation (PPM), and photon-counting receivers are commonly adopted. Although M-ary PPM can be demodulated and decoded without the channel state information, its spectral efficiency is lower than OOK's. To improve the spectral efficiency of M-ary PPM in NLOS UVC, a power-domain multilayer-superposed transmission (MST) scheme with binary PPM (BPPM) is proposed in this work. Based on this scheme, the signal in each layer can be directly decoded without successive interference cancellation, which is necessary for other MST schemes in the power domain. Hence, a low complexity receiver in the NLOS UVC system can be realized. Additionally, the bit-error rate (BER) and achievable data rate (ADR) expressions of the proposed MST scheme are derived. Monte-Carlo simulations are performed to verify the analytical BER expression. The NLOS UVC system performance employing the proposed MST scheme is further demonstrated and compared with pure BPPM. The results indicate that with the optimal power allocation factor for each layer, the overall ADR of the NLOS UVC system with the proposed power-domain MST scheme can surpass that with pure BPPM.

Performance evaluation of the high-speed deep-space optical communication system assisted by preamplified thresholded pulse-position modulation

Deep-space free-space optical (FSO) communication utilized the light wave as carriers for information transfer which has the major benefit of small size, lightweight, and low consumption compared with microwave communication loaded with the same data rate. The M-ary pulse-position modulation (M-PPM) format is a favorable choice for deep-space FSO communication by means of its high sensitivity. The preamplified thresholded M-PPM technique has been confirmed, and a corresponding demonstration has been accomplished with data rates of 1.25 Gbps and 2.00 Gbps separately. The receiving sensitivities (BER@1 × 10−3) of 1.25 Gbps and 2.00 Gbps 16-PPM have been detected as -57.51 dBm (11.04 photons/bit) and -55.03 dBm (12.25 photons/bit), respectively. Simultaneously, the high extinction ratio of M-PPM has been achieved, for example, the extinction ratio of 16-PPM has been detected as 39.51 and 38.27 dB for 1.25 Gbps and 2.00 Gbps, which are 17.60 and 17.44 dB higher than that of on–off keying (OOK) modulation, respectively. The results imply that our communication scheme possessed high sensitivity and eliminated the requirements of single-photon detectors (SPDs) and high-speed analog-to-digital converters (ADCs) which finds an alternative solution for deep-space FSO communication.

Average symbol error probability and channel capacity of the underwater wireless optical communication systems over oceanic turbulence with pointing error impairments.

The influence of oceanic turbulence and pointing error impairments on the underwater wireless optical communication (UWOC) systems is considered in this study. We propose a generalized fading model, which comprises the path loss due to the absorption and scattering, the oceanic turbulence (modeled by Málaga distribution), and the pointing error impairments resulting from ocean movements. Thereafter, closed-form expressions of the average symbol error probability (SEP) and average channel capacity are proposed for optical waves propagate in oceanic turbulence with the M-ary pulse position modulation (PPM) and under the constraints of the limited average-power and peak-power. The Monte Carlo simulations are conducted to validate the analytical results and demonstrate that the fading parameters, including the mean-squared temperature, the salinity-temperature contribution factor, jitters, and water conditions, significantly affect the system performance. Moreover, the thermal noise and quantum noise in ocean environment have more serious impact than the background noise. Finally, we prove that the UWOC systems with the pure peak-power constraint performs better than that limited by average-power and peak-power.

Power Efficient Communications Employing Phase Sensitive Pre-Amplified Receiver

The receiver sensitivity is a very important metric in optical communication links operating at low received signal powers. Phase sensitive optical amplifiers (PSAs) can amplify optical signals without excess noise, thus providing a fundamental sensitivity improvement of 3 dB when employed as a pre-amplifier compared to conventional erbium doped fiber amplifiers (EDFA). In this letter, we investigate, both theoretically and experimentally, the sensitivities achieved using power efficient multi-dimensional modulation formats such as M-ary pulse position modulation format (M-PPM) and M-PPM combined with quadrature phase shift keying (QPSK) along with a near-noiseless PSA pre-amplified coherent intradyne receiver. We find that at high signal to noise ratios (SNRs) corresponding to low bit-error-rates (BER), M-PPM+QPSK results in the best sensitivity, which is improved with the order M, while at low SNRs corresponding to high BER (~14% where 100% overhead forward error correction codes (FEC) would be needed to recover the data), QPSK is the most sensitive format, while at the same time providing the best spectral efficiency. We report experimental sensitivities of 2.1 photons per information bit (PPB) at a pre-FEC BER = 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> using 64-PPM+QPSK and assuming 7% FEC, and 0.8 PPB at a pre-FEC BER = 0.14 using QPSK and assuming 100% FEC.

Hybrid MPPM-BB84 Quantum Key Distribution Over FSO Channel Considering Atmospheric Turbulence and Pointing Errors

Nowadays, a high level of security is required for the transmission of critical information. Quantum Key Distribution (QKD) systems are considered the best option to protect such information. Many studies have shown the efficiency of the QKD optical fiber inspired by M-ary pulse position modulation (MPPM). Free-Space Optical (FSO) links provide an efficient and effective data transmission system. However, cumulative effects of laser beam divergence, misalignment, and turbulence-induced fading on the received irradiance in the FSO link might allow an external eavesdropper located near the authorized receiver to break the transmission under certain conditions. This paper introduces the development of an FSO system based on the MPPM and the BB84 protocol (MPPM-BB84) over the Gamma-Gamma (GG) turbulence channel with pointing errors. Time Binning is implemented using MPPM to increase system security and reduce the quantum bit error rate (QBER). The system security is investigated under photon number splitting attack and excess noise. Closed-form expressions for asymptotic expressions of the average symbol error probability (SER), raw key rate (RKR), and secret key rate (SKR) are introduced. Moreover, the Monte-Carlo simulations are then used to prove the validity of the analytical results. The optimal values for the average photon number per pulse (to achieve the maximum RKR and SKR) for each symbol length can guarantee the stability of the FSO system under different weather conditions. Smaller symbol lengths are more tolerant of detector loss. The proposed system supports linking distances from 1 km to 3 km while keeping the SKR almost constant.

Effects of adaptive optics on bit error rate of M-ary PPM oceanic optical wireless communication systems with aperture averaging in strong turbulence

Scintillation is the result of oceanic turbulence reducing the bit error rate (BER) performance of oceanic optical wireless communication (OWC) systems. The scintillation, also known as intensity fluctuations, occurs due to the turbulence-induced wavefront deformations. The correction of deformations by adaptive optics (AO) reduces the scintillation effect of turbulence and results in improved BER performance. In this paper, an oceanic OWC (OOWC) system that has a Gaussian laser beam at the transmitter, finite-sized circular aperture at the receiver, employing M-ary pulse position modulation (PPM) and operating in strong oceanic turbulence, is considered. Improvement in the BER performance of the OOWC system is examined with the implementation of AO correction. Comparison of BER performances between the AO and non-adaptive optics OOWC systems is shown by calculating the metric defined. BER of M-ary PPM OOWC links is evaluated over gamma–gamma fading channels. The modified Rytov theory together with the Zernike filter functions is used to find the AO corrected aperture averaged scintillation index where extended Huygens–Fresnel technique is used to obtain the average received signal power.

Adaptive optics compensation of M-ary pulse position modulated communication systems in anisotropic non-Kolmogorov turbulent atmosphere

Adaptive optics compensation effect on the performance of an optical wireless communication system (OWC) employing M-ary pulse position modulation (PPM) scheme in anisotropic non-Kolmogorov turbulent atmosphere is investigated. Avalanche photodetector (APD) is used at the receiver side and log-normal channel that models the weak turbulence conditions is utilized. Anisotropy, generally resulting in better performance in OWC systems operating in the turbulent medium, combined with the adaptive optics applications will enhance the bit-error-rate (BER) of the OWC systems significantly. Results are obtained depending on various parameters for both the turbulent atmosphere and the receiver. Our work gives OWC system designers a perspective to optimize their design.

A Splitting-Detection Joint-Decision Receiver for Ultrasonic Intra-Body Communications

Ultrasonic intra-body communication (IBC) is a promising enabling technology for future healthcare applications, due to low attenuation and medical safety of ultrasonic waves for the human body. A splitting receiver, referred to as the splitting-detection separate-decision (SDSD) receiver, is introduced for ultrasonic pulse-based IBCs, and SDSD can significantly improve bit-error rate (BER) performance over the traditional coherent-detection (CD) and energy detection (ED) receivers. To overcome the high complexity and improve the BER performance of SDSD, a splitting-detection joint-decision (SDJD) receiver is proposed. The core idea of SDJD is to split the received signal into two streams that can be separately processed by CD and ED, and then summed up as joint decision variables to achieve diversity combining. The theoretical channel capacity and BER of the SDSD and SDJD are derived for M-ary pulse position modulation ( M-PPM) and PPM with spreading codes. The derivation takes into account the channel noise, intra-body channel fading, and channel estimation error. Simulation results verify the theoretical analysis and show that both SDSD and SDJD can achieve higher channel capacity and lower BER than the CD and ED receivers with perfect channel estimation, while SDJD can achieve the lowest BER with imperfect channel estimation.

Performance of M-ary pulse position modulated optical wireless communications systems in the marine atmosphere.

The marine atmosphere exhibits different turbulence spectrum characteristics when compared to the turbulence spectra of the land atmosphere and underwater medium. The performance of M-ary pulse position modulated (PPM) optical wireless communications (OWC) systems operating in the marine atmosphere, as measured by the bit error rate (BER), is studied here. In our investigation, the scintillation index and the average intensity in marine atmospheric turbulence are used. The variations of BER performance are reported against the marine atmospheric turbulence parameters for various values of the average current gain of the avalanche photodetector (APD), data bit rate of the OWC link, and M value of the M-ary PPM.

Assessment of the FSO communication system using adaptive and MIMO MPPM with pointing errors and an atmospheric turbulence channel.

The terrestrial free space optical (FSO) communication system is attracting increased attention among the scientific and commercial research community due to its ultra-high data rate capability, licensed free large bandwidth, cost efficiency, fast and easy deployment, and secure wireless data transmission. However, the FSO system is severely affected by atmospheric conditions such as local weather conditions and fading due to turbulence. Moreover, system performance is significantly affected by pointing errors, which are caused by the misalignment between transmitter-receiver sections. Many statistical models have been proposed in the literature in order to address this significant impairment of the FSO system. In this paper, M-ary pulse position modulation (MPPM)-based FSO signal transmission over a Gamma-Gamma (G-G) fading channel is analyzed in the presence of weak to strong atmospheric turbulence and pointing errors. A multiple-input-multiple-output (MIMO) system with an equal gain combining (EGC) diversity scheme is proposed to enhance the performance of the system. The analytical closed-form expressions are obtained in terms of MeijerG-function to approximate the average bit error rate (BER) and outage probability. Furthermore, the adaptive transmission modulation (ATM) scheme is proposed to enhance the bandwidth efficiency of the FSO system link. The analytical results exhibit that the effect of turbulence and misalignment on the performance metrics (BER, outage probability) and the proposed MIMO-FSO communication link with the EGC scheme appreciably improves the system performance, and Monte Carlo simulation confirms the validation of the analytical expressions. It can also observe that bandwidth efficiency significantly improved with the proposed ATM scheme over non-adaptive counterparts.

Performance enhancement of hybrid diversity for M-ary modified pulse-position modulation and spatial modulation of MIMO-FSO systems under the atmospheric turbulence effects with geometric spreading

In this paper, we propose a novel model for hybrid spatial diversity of M-ary pulse position modulation (M-ary PPM) and spatial modulation (SM) with a multiple-input multiple-output (MIMO) links (i.e., optical receiver diversity) in a free-space optical (FSO) communication system under the atmospheric turbulence (AT) effects with geometric spreading (GS). In the proposed design, the spatial index modulator (SIM) and modified pulse position modulation (MPPM) schemes are combined to improve the system efficiency of the spatial diversity for the M-ary PPM modulated MIMO–FSO communication. In this work, we investigate and enhance the performance of the MIMO-FSO link using a digital pulse position modulation (DPPM) and on–off keying non-return-to-zero (OOK–NRZ). We propose a MIMO-based FSO link using spatial diversity and M-ary PPM modulation technique to compensate for the performance degradation due to geometric losses and atmospheric attenuation. Here, we have combined the N-SM with L-MPPM (N-SM/L-MPPM) and (M × N MIMO) to improve the system performance and provide high bandwidth and a higher throughput under the impact of the AT and GS. We analyze the GS impact on the performance of MIMO–FSO systems using SM over the Gamma–Gamma (GG) model. The performance is achieved by using the PPM technique, so the AT influences and fading are mitigated hence the ability to combat AT and the FSO link systems are enhanced sufficiently. Also, we improve the performance of the proposed link using a novel hybrid of SM/PPM and DPPM over GG to maximize the range and enhance the receiver sensitivity. Simulation results obtained for the bit-error-rate (BER) and average transmitted optical power for the DPPM and OOK modulation against various AT conditions are compared with the spatial diversity techniques and proved that both of the FSO systems based MIMO–SM/MPPM offers better performance in the receiver sensitivity and channel capacity. The obtained results show that the conjunction of the receiver diversity and SM/M-ary MPPM is a magnificent solution for mitigating the strong turbulence (ST) and GS effects. The proposed design provides an excellent optical signal-to-noise ratio (SNR) and high-sensitivity for the SIM/PPM-MIMO in the ST regime and GS. The numerical results report that the DPPM sensitivity improves about 10–11 dB at a distance of 2.5 km and the BER of 10−12 more than an equivalent OOK–NRZ modulation. The SIM/PPM-MIMO offers about 4 dB, 2 dB optical SNR improvements over without SIM/PPM-MIMO for the no turbulence and ST with GS for the FSO link, respectively. This work could be beneficial to the practical implementation of the hybrid spatial diversity for the SM/M-ary MPPM based MIMO-FSO links under the AT effects with GS.

Average bit error rate performance of free-space optical systems over double generalized gamma fading channels based on avalanche photodiode detector

The performance of free-space optical (FSO) communication systems based on avalanche photodiodes (APDs) is investigated over the aggregated double generalized gamma (double GG) fading channels. The approximate average bit error rate (ABER) expression is theoretically derived in terms of the double GG distributions under moderate and strong turbulent atmospheric conditions considering thermal noise and shot noise. The union bound and Hermite polynomials are then used to estimate the ABER performance of M-ary pulse-position modulation (PPM)-based systems and orthogonal frequency division multiplexing scheme (OFDM)-based systems. The ABER performance is studied with different receiver noise temperatures, modulation orders, turbulence strengths, and average photon counts assuming plane wave and spherical wave propagations. The results show that adopting an optimal average APD gain affected by the receiver temperature minimizes the ABER value for both wave propagations. In addition, the present APD-based system offers better ABER performance than that of a PIN-based FSO system over the double GG fading channels at two receiver noise temperatures of 200 and 400 K for both the PPM and OFDM schemes. We provide a reference for FSO system design.

BER performance of M-ary pulse position modulated communication systems in anisotropic non-Kolmogorov turbulent atmosphere

We investigated the effect of anisotropic non-Kolmogorov atmospheric turbulence on the performance of the optical wireless systems when M-ary Pulse Position Modulation (PPM) is applied to a Gaussian beam. The performance of the optical wireless systems that use avalanche photodetector at the receiver is evaluated in terms of the bit error rate (BER). The effects of the parameters, such as the anisotropy factors in x–y directions, modulation order, data bit rate, equivalent load resistor, photodetector quantum efficiency, non-Kolmogorov turbulence power law exponent, beam source size, link length, photodetector gain and structure constant on BER of the M-ary PPM Gaussian beam propagating in anisotropic non-Kolmogorov atmospheric turbulence, are examined.

Performance enhancement of M-ary pulse-position modulation for a wavelength division multiplexing free-space optical systems impaired by interchannel crosstalk, pointing error, and ASE noise

The performance evaluations and enhancements of wavelength-division-multiplexing (WDM) for the free-space optical (FSO) communication systems using a digital pulse-position modulation (DPPM), M-ary pulse-position modulation (M-ary PPM), and on–offkeying (OOK) are investigated in this paper. In the WDM/DPPM-FSO communication systems, WDM channels suffer from the inter-channel crosstalk (ICC) while FSO channels can be severely affected by the atmospheric turbulence (AT). These impairments and the accumulation of an amplified spontaneous emission (ASE) noise cause reducing of the link efficiency and system performance. To deal with this problem, the use of the M-ary PPM to mitigate the effects of AT and improve the receiver sensitivity. The impact of AT, ICC, scintillation, pointing error, and ASE noise has been taken into account. Here, we have combined the N-hybrid diversity of the spatial modulation (N-SM) with M-ary PPM to improve the BER performance and system efficiency of SM/M-ary PPM-based FSO systems. To reduce the turbulence-induced scintillation and optical power penalty, the use of an aperture averaging has been proposed in this work. Such a system, which could provide a power-efficient, a low cost, excessive flexibility, and reliable or considered a massive solution in the bandwidth provision for future access networks, and together for higher data rate. The SM/PPM offers about 14 dB and 3.0 dB sensitivity improvements more than the OOK non-return-to-zero (NRZ) and PPM approaches for the WDM/FSO link in the absence of AT, respectively. Also, an improvement of the receiver sensitivity at a BER of 10−12 about 8.0–9.0 dB for a coding level of 5 and FSO link length of 2500 m can be potentially achieved using the SM/PPM technique over OOK−NRZ approach when impaired by the weak turbulence. The proposed system shows a considerable improvement in the receiver sensitivity and power penalty using the SM/PPM technique over the OOK−NRZ approach.

Performance of free space optical communication system based on M-ary PPM modulation over double generalized gamma channel

In this paper, we provide analytical results on average Symbol Error Probability (SEP) of a Free Space Optics (FSO) link employing M-ary Pulse Position Modulation (PPM), subjected to turbulent atmosphere modeled with Double Generalized Gamma (DGG) distribution. FSO link is generally impaired by turbulent atmosphere and pointing errors. As far as we know, results are presented in previous works by considering the atmosphere turbulence modeled with a Gamma-Gamma distribution. In our work, we also give asymptotic results on average SEP in order to approximate its evolution at high Signal-to-Noise-Ratio (SNR). Numerical results showed that FSO link performance is enhanced when PPM-modulation index is increased, for both strong and moderate turbulence regimes, and for both strong and weak pointing error jitter. Monte-Carlo simulations were presented to corroborate our analytical expressions.

M-ary pulse position modulation performance with adaptive optics corrections in atmospheric turbulence

ABSTRACTThe performance of M-ary pulse position modulated (PPM) optical wireless communication (OWC) systems in atmospheric weak turbulence medium is evaluated by using adaptive optics corrections. Piston, tilt, defocus and coma components of adaptive optics corrections are applied to the avalanche photodetector (APD) type of receiver and the results are obtained depending on various turbulence and receiver parameters. The lognormal channel distribution is used to model the weak atmospheric turbulence conditions. Adaptive optics correction increases the bit-error-rate (BER) performance of an OWC system operating in atmospheric turbulence conditions. Piston component yields the highest BER performance, followed by the tilt, defocus and coma adaptive optics correction components respectively.

Performance of M-ary pulse position modulation for aeronautical uplink communications in an atmospheric turbulent medium.

This paper discusses the bit-error-rate (BER) performance of an aeronautical uplink optical wireless communication system (OWCS) when a Gaussian beam is employed and the M-ary pulse position modulation technique is used in an atmospheric turbulent medium. Weak turbulence conditions and log-normal distribution are utilized. The Gaussian beam is assumed to propagate on a slant path, the transmitter being ground-based, and the airborne receiver is on-axis positioned. Variations of BER are obtained against the variations in the link length, Gaussian beam source size, zenith angle, wind speed, wavelength, modulation order, data bit rate, equivalent load resistor, avalanche photodetector gain, and detector quantum efficiency. It is observed that the performance of the aeronautical uplink OWCS is affected from atmospheric turbulence significantly.

Towards 5G wireless systems: A modified Rake receiver for UWB indoor multipath channels

This paper presents a modified receiver based on the conventional Rake receiver for Ultra-Wide Band (UWB) indoor channels of femtocell systems and aims to propose a new solution to mitigate the multipath phenomenon. Furthermore, this work proposes an upgrade for the conventional Rake receiver to fulfill the needs of 5G wireless systems through a new concept named “hybrid femtocell” that joins UWB with millimeter wave (mmWave) signals. The modified receiver is considered to be a part of the UWB/mmWave hybrid femtocell system, where it is developed for confronting the indoor multipath channels and to ensure a flexible transmission based on an Intelligent Controlling System (ICS). Hence, we seek to exploit the circumstances when the channel is less complex to switch the transmission to a higher data rate through higher M-ary Pulse Position Modulation (PPM). Furthermore, an ICS algorithm is proposed and an analytical model is developed followed by performance studies through simulation results. The results show that using the UWB technology through the modified receiver in femtocells could aid in mitigating the multipath effects and ensuring high throughputs. Thus, the UWB based system promotes Internet of Things (IoT) devices in indoor multipath channels of future 5G.

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.

Bit-error rate investigation of satellite-to-ground downlink optical communication employing spatial diversity and modulation techniques

In this paper, the error performance of multiple apertures receiver system under different modulation schemes is evaluated for satellite-to-ground downlink optical communications. Gamma–Gamma channel model is used for the consideration of moderate to strong atmospheric turbulence. Error rate expression equations of maximum ratio combining (MRC), equal gain combining (EGC), and selection combining (SC) techniques are derived for M-ary pulse position modulation (M-PPM) and M-ary differential PPM (M-DPPM) modulation schemes. Bit-error rate (BER) performances of M-PPM and M-DPPM modulated MRC, EGC, and SC direct detection receiver systems are compared with a single monolithic aperture receiver system. Performances of downlink direct detection multiple apertures receiver system are also compared among on–off keying (OOK), M-PPM, and M-DPPM modulation schemes. Numerical calculations and Monte Carlo (MC) simulations are used to exam the results of our analysis. It is found that, for M-PPM and M-DPPM, the effect of atmospheric turbulence can be reduced by MRC and EGC receiver system, and SC receiver system can show its advantages compared to a single aperture receiver system in the case of large zenith angles. The downlink BER performances of OOK, 8-PPM, and 8-DPPM multiple apertures receiver system are decreased according to the order of 8-PPM, 8-DPPM, and OOK.