Multi-pulse Pulse Position Modulation Research Articles

Performance enhancement of RIS-assisted MRR-UOWC systems using the spectral-power-efficient [formula omitted]QAM-MPPM

Reconfigurable Intelligent Surfaces (RISs), proposed as innovative units, possess the potential to establish reliable connections in Underwater Optical Wireless Communication (UOWC) systems, where direct transmission (DT) experiences significant weakening due to dynamic channel conditions. In this paper, we examine the performance of a UOWC system consisting of an RIS and a modulating retroreflector (MRR), referred to as the RIS-assisted MRR-UOWC system. The channel is affected by a combination of path loss, gamma–gamma (G–G) turbulence, and pointing error (PE). The considered system employs the spectral-power-efficient L-ary Quadrature Amplitude Modulation Multi-Pulse Pulse-Position Modulation (LQAM-MPPM) technique. For our system performance measures, we present upper-bound (UB) and approximate UB expressions for the average bit-error rate (BER) of LQAM-MPPM signals. These expressions are used to analyze the system’s performance. Performance metrics are established by deriving the Probability Density Function (PDF), Cumulative Distribution Function (CDF), and Moment-Generating Function (MGF) for the end-to-end signal-to-noise ratio (SNR), resulting from the sum of products of independent but not identically distributed (i.ni.d) channel coefficients. The results of our study indicate that the LQAM-MPPM scheme surpasses traditional schemes.

Spectrum analysis of multi-pulse position modulation in optical communication

In this paper, the authors aim to compare the performance of space optical communication and wireless optical communication by analyzing the transmission mechanism, transmission method, and transmission rate of MPPM (Multi-Pulse Pulse Position Modulation). MPPM is a widely used modulation technique in optical communication systems, which has the advantage of reducing the effect of noise and improving the system's error rate. To achieve the objective, the authors will employ mathematical models to compare the performance of space optical communication and wireless optical communication. They will analyze the transmission mechanism, transmission method, and transmission rate of MPPM in both communication systems and draw conclusions based on their findings. The authors hope that the results of this study will positively promote the development of MPPM in the future. By comparing the performance of space optical communication and wireless optical communication, this study will provide insights into the strengths and weaknesses of both systems, which can help in the development of more efficient and reliable optical communication systems.

Performance of Multipulse Pulse-Position Modulation in NLOS Ultraviolet Communications

The performance of multipulse pulse-position modulation (MPPM) in non-line-of-sight (NLOS) ultraviolet communications (UVC) with output signals of detectors following Poisson distribution and Poisson-triggered Gaussian (PTG) distribution has been investigated. Specifically, the probabilities of a given number of incorrectly identified pulsed or empty slots in an MPPM symbol have been derived with output signals Poisson and PTG distributed. Based on those probabilities, the expressions of symbol-error rate and achievable data rate of MPPM in the NLOS UVC systems have been further obtained. Finally, Monte-Carlo simulations are presented to verify the theoretical results.

Performance analysis of MPPM FSO transmission over Gamma–Chi-square strong atmospheric turbulence

In this paper, performance analysis of free space optical (FSO) system operating in conditions of strong atmospheric turbulence over Gamma–Chi-square turbulence model, has been carried out. We have observed reception over multi-pulse pulse-position (MPPM) modulation format for the case of strong atmospheric turbulence conditions modeled with Gamma–Chi-square turbulence model and have compared it with turbulence modeling distributions such are: Gamma–Gamma distribution, K-distribution, negative exponential distribution, log–normal distribution. First, we have provided closed-form analytical expressions for average bit error rate (ABER) at the reception for each observed case and then based on them, we have obtained numerical and Monte Carlo simulation results in order to observe turbulence level impact on system performance.

Efficient and Low-Complexity Rate and Dimming Control of VLC for Industrial IoT Applications

Visible light communication (VLC) has emerged as a promising complementary technology to millimeter-wave communications for short-range communications to meet the increasing industrial Internet of Things (IIoT) capacity demands. Efficient illumination and data transmission face specific challenges, such as controlling dimming without compromising transmission capacity. In this article, we revisit multipulse pulse-position modulation (MPPM) for joint rate–dimming control in VLC. MPPM is widely considered a highly efficient modulation for optical communications. However, the computational complexity of current MPPM coding methods grows exponentially as the code rate is increased. To overcome this limitation, we propose novel encoding and soft-decision decoding strategies that allow fine-tuning dimming control and increase the data rate. Performance results show higher data rates with lower energy demands as compared to current standards. Moreover, the proposed encoding and decoding methods exhibit linear time complexity, which makes them suitable for implementation in low-cost VLC devices for massive IIoT deployments.

Design and Optimization of Protograph LDPC-Coded Multipulse PPM Systems Over Poisson Channels

Combining powerful error-correction codes (ECCs) with multipulse pulse-position modulation (MPPM) has great potential to realize high-throughput and high-reliability transmissions in free-space optical (FSO) communication systems. This paper conducts an insightful investigation on protograph low-density parity-check (PLDPC)-coded MPPM systems over Poisson channels. To be specific, we first put forward a novel type of constellations, referred to as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">irregular pulse-distribution (IPD) constellations</i> , for MPPM. We also conceive a bit-level rate-adaptive (RA) scheme, which can exploit the structural property of the IPD constellations to significantly improve the convergence performance at the price of transmission-rate loss. Furthermore, with the aid of a modified protograph extrinsic information transfer (PEXIT) algorithm, we construct three enhanced PLDPC codes with code rates <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1/2, 2/3$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3/4$</tex-math></inline-formula> that exhibit excellent decoding thresholds over Poisson channels. The proposed PLDPC-coded MPPM systems with the use of the IPD constellations, RA scheme, and enhanced PLDPC codes are superior to the state-of-the-art counterparts.

Proposal of a Power Efficient $N$-Level Multipulse PPM-$L$QAM Technique

A new power efficient technique, that combines N-level multipulse pulse-position modulation with L-level quadrature-amplitude modulation, denoted by NMPPM-LQAM, is proposed. Its constrained power efficiency is derived and characterized. It is shown that the proposed combination provides a superior technique that is both power and spectral efficient simultaneously. The constrained power efficiencies of variations to this technique are considered and characterized as well. These include combining multilevel pulse-amplitude modulation with LQAM (NPAM-LQAM). The obtained constrained power efficiencies are compared numerically to that of traditional LQAM and MPPM-LQAM techniques. Our results disclose that proposed NMPPM-LQAM is the most power/spectral efficient technique. For example, at spectral efficiency constraints of 2.5 and 4.2 bs <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> /Hz/pol, the corresponding constrained power efficiencies of proposed NMPPM-LQAM technique are higher by about 4.87 and 3.62 dB, respectively, than that of traditional LQAM. In addition, the results reveal that NPAM-LQAM scheme has increased power and spectral efficiencies compared to that of traditional NPAM, but its power efficiency is less than that of traditional LQAM.

Performance Analysis of QAM-MPPM in Turbulence-Free FSO Channels: Accurate Derivations and Practical Approximations

Following the trends of index modulated (IM) techniques applied to optical communications, several new waveform proposals have been made, aiming at conveying a higher density of information by driving different signal properties. One of these proposals mixes multipulse pulse-position modulation (MPPM) and quadrature amplitude modulation (QAM). We present here a new way to demodulate it, and, for the nonturbulent free space optical (FSO) channel, we provide accurate analytical expressions for its error probabilities, both in the case of the traditional and the new detector. We also provide simplified expressions for the estimation of the error probabilities. We show that the new detector offers a gain of some tenths of dB in signal-to-noise ratio (SNR) with respect to the previously defined one, and that our error probability estimations are more accurate than previously published results. To the best of our knowledge, this work is the first to provide simulation results validating the study of the error probability performance of QAM-MPPM.

On the performance of adaptive hybrid MQAM-MPPM scheme over Nakagami and log-normal dynamic visible light communication channels.

In this paper, we introduce the idea of using adaptive hybrid modulation techniques to overcome channel fading effects on visible light communication (VLC) systems. A hybrid $ M $M-ary quadrature-amplitude modulation ($ M{\rm QAM} $MQAM) and multipulse pulse-position modulation (MPPM) technique is considered due to its ability to make gradual changes in spectral efficiency to cope with channel effects. First, the Zemax optics studio simulator is used to simulate dynamic VLC channels. The results of Zemax show that Nakagami and log-normal distributions give the best fitting for simulation results. The performance of $ M{\rm QAM} $MQAM-MPPM is analytically investigated for both Nakagami and log-normal channels, where we obtain closed-form expressions for the average bit-error rate (BER). The optimization problem of evaluating the hybrid modulation technique settings that lead to the highest spectral efficiency under a specific channel status and constraint of outage probability is formulated and solved using an exhaustive search. Our results reveal that the adaptive hybrid scheme improves system spectral efficiency compared to ordinary QAM and MPPM schemes. Our results reveal that the adaptive hybrid scheme improves system spectral efficiency compared to ordinary QAM and MPPM schemes. Specifically, at low average transmitted power, $ - 32\;{\rm dBm} $-32dBm, the adaptive hybrid scheme shows 280% improvement in spectral efficiency compared to adaptive versions of ordinary schemes. At higher power, $ - 20\;{\rm dBm} $-20dBm, 6.5% and 725% improvement are obtained compared to ordinary QAM and ordinary MPPM, respectively. Also, the adaptive hybrid scheme shows great improvement in average BER and outage probability compared to ordinary schemes. The hybrid scheme shows 28%, 34%, and 38% improvement, respectively, for $ m = 1,2,3 $m=1,2,3 for Nakagami channels at $ {\rm BER}{ = 10^{ - 3}} $BER=10-3. Also, the outage probability of hybrid schemes of $ {\rm BER}{ = 10^{ - 3}} $BER=10-3 shows 30% and 14% better performance than ordinary $ M{\rm QAM} $MQAM and MPPM schemes, respectively.

Hybrid two-level MPPM-MDPSK modulation for high-speed optical communication networks.

A hybrid optical modulation approach is described, which layers a continuous wave $M$M-ary differential phase-shift keying ($M{\rm DPSK}$MDPSK) and a two-level ($2L$2L) multipulse pulse-position modulation (MPPM) intensity-modulated signal for improved spectral efficiency. These $2L$2L techniques are a generalization of earlier hybrid MPPM-$M{\rm DPSK}$MDPSK techniques and have the added advantage of reducing transmitter and detector complexities over previous hybrid modulation approaches. The spectral and power efficiencies for the proposed $2L$2L-MPPM-$M{\rm DPSK}$MDPSK modulation techniques are formulated and shown to have the highest spectral efficiency in comparison to other hybrid techniques with lower implementation complexity. The performance of the proposed $2L$2L hybrid techniques is quantified over free-space optical (FSO) networks as well as fiber networks and verified using Monte Carlo simulation. For FSO channels, the proposed $2L$2L-MPPM-$M{\rm DPSK}$MDPSK technique outperforms the traditional MPPM-$M{\rm DPSK}$MDPSK scheme by approximately 2 dB at a bit-error rate (BER) of ${10^{-4}}$10-4 and a spectral efficiency of 2.5 bit/s/Hz. Similarly, in optical fiber, the proposed scheme relaxes the impact of nonlinearity in comparison to traditional MPPM-$M{\rm DPSK}$MDPSK. Specifically, at a ${\rm BER}{=10^{-3}}$BER=10-3, the $2L$2L-MPPM-$M{\rm DPSK}$MDPSK technique outreaches the MPPM-$M{\rm DPSK}$MDPSK by 2000 km at a spectral efficiency of 2.5 bit/s/Hz and an average transmit power of $-{3}\,\,{\rm dBm}$-3dBm.

Chaotic Polarization-Assisted ${L}$ DPSK-MPPM Modulation for Free-Space Optical Communications

In this paper, we present a polarization-assisted $L$ -ary differential phase-shift keying multipulse pulse-position modulation (PA. $L$ DPSK-MPPM) technique that is secured in the physical layer by a discrete-chaos system. The all-optical PA. $L$ DPSK-MPPM scheme benefits from the polarization as an additional degree of freedom which greatly reduces the system complexity relative to prior implementations. The discrete-chaos scrambling is based on a message-seeded two-dimensional chaotic map tailored for independent perturbation of the occupied time-slot positions (MPPM information) and their relative phase shift ( $L$ DPSK information). Synchronized and non-synchronized implementations of the chaotic PA. $L$ DPSK-MPPM technique are proposed with expressions for the corresponding spectral efficiencies being determined and compared with prior $L$ DPSK-MPPM setups. The performance of PA. $L$ DPSK-MPPM under gamma-gamma (GG) free-space optical (FSO) fading channels is analytically verified to outperform the prior designs for different FSO channel states which is supplemented by Monte Carlo (MC) simulations. The system security is numerically examined against various types of attacks, including brute-force, differential, and statistical attacks.

Performance improvement of FSO system using multi‐pulse pulse position modulation and SIMO under atmospheric turbulence conditions and with pointing errors

Free space optics (FSO) communication links are impaired by the fading due to turbulence and misalignment. In this paper, we theoretically analyze the pointing error effects on performance of FSO systems using multi-pulse pulse position modulation (MP-PPM) over the Gamma-Gamma turbulence channel. We consider the moderate and strong atmospheric turbulence regimes with the combined effect of the pointing errors (PEs), and study the link average symbol error rate (ASER) and the outage probability. The numerical results are presented to show the impact of the pointing error on the ASER and the system outage. However, to overcome the channel degradation resulting from the turbulence effects and the PE, the single-input multiple-output (SIMO) system with maximal ratio combining (MRC) diversity is used. Exact close-form expressions for ASER and outage probability are derived and verified by using Monte Carlo simulation. We concluded that the optimal values of the system parameters are, the transmitted power is 20 dBm, jitter variance should be less than 0.5 m and laser beam width equals 0.2 cm. These values are significantly reduced the impacts of misalignment and fading whereas outage probability is less than at maximum jitter variance.

Proposal and performance analysis on the PDM microwave photonic link for the mm-wave signal with hybrid QAM-MPPM-RZ modulation

A polarization division multiplexed (PDM) microwave photonic link for the millimeter (MM)-wave signal with hybrid modulation scheme is proposed in this paper, which is based on the combination of quadrature amplitude modulation, multi-pulse pulse-position modulation and return to zero modulation (QAM-MPPM-RZ). In this scheme, the two orthogonal polarization states enable simultaneous transmission of four data flows, which can provide different services for users according to the data rate requirement. To generate hybrid QAM-MPPM-RZ mm-wave signal, the QAM mm-wave signal is directly modulated by MPPM-RZ signal without using digital signal processing (DSP) devices, which reduces the overhead of the encoding process. Then, the generated QAM-MPPM-RZ mm-wave signal is transmitted in PDM microwave photonic link based on SSB modulation. The sparsity characteristic of QAM-MPPM-RZ not only improves the power efficiency, but also decreases the degradation caused by the fiber chromatic dispersion. The simulation results show that, under the constraint of the same transmitted data rate, the PDM microwave photonic link with 50 GHz QAM-MPPM-RZ mm-wave signal achieves much lower levels of bit-error rate than ordinary 32-QAM. In addition, the increase of laser linewidth brings no additional impact to the proposed scheme.

Noise stability of signal reception algorithms with multipulse pulse-position modulation

An algorithm for estimating time positions and amplitudes of a periodic pulse sequence from a small number of samples was proposed. The number of these samples was determined only by the number of pulses. The performance of this algorithm was considered on the assumption that the spectrum of the original signal is limited with an ideal low-pass filter or the Nyquist filter, and conditions for the conversion from one filter to the other were determined. The efficiency of the proposed algorithm was investigated through analyzing in which way the dispersion of estimates of time positions and amplitudes depends on the signal-to-noise ratio and on the number of pulses in the sequence. It was shown that, from this point of view, the efficiency of the algorithm decreases with increasing number of sequence pulses. Besides, the efficiency of the proposed algorithm decreases with decreasing signal-to-noise ratio. It was found that, unlike the classical maximum likelihood algorithm, the proposed algorithm does not require a search for the maximum of a multivariable function, meanwhile characteristics of the estimates are practically the same for both these methods. Also, it was shown that the estimation accuracy of the proposed algorithm can be increased by an insignificant increase in the number of signal samples. The results obtained may be used in the practical design of laser communication systems, in which the multipulse pulse-position modulation is used for message transmission.

Ergodic channel capacity of spatial correlated multiple-input multiple-output free space optical links using multipulse pulse-position modulation

Ergodic channel capacity of spatial correlated multiple-input multiple-output free space optical links using multipulse pulse-position modulation

Performance Analysis of a Hybrid QAM-MPPM Technique Over Turbulence-Free and Gamma–Gamma Free-Space Optical Channels

The performance of a hybrid M-ary quadrature amplitude modulation multi-pulse pulse-position modulation (hybrid QAM-MPPM) technique is investigated in both turbulence-free and gamma-gamma freespace optical (FSO) channels. Both the spectral efficiency and asymptotic power efficiency of the hybrid QAM-MPPM are estimated and compared to traditional QAM and MPPM techniques. The bit error rate (BER) of intensity-modulation direct-detection (IM-DD) systems adopting the hybrid technique is investigated over turbulence-free FSO channels. Upper-bound expressions for the average BER and outage probability are derived for FSO systems by adopting a hybrid QAM-MPPM scheme over gamma-gamma turbulent channels. In addition, the performance of a Reed-Solomon coded hybrid QAM-MPPM is considered. The obtained expressions are used to numerically investigate the performance of the hybrid technique. Our results reveal that, under the conditions of comparable data rates, the same bandwidth, and the same energy per bit, FSO systems adopting the hybrid technique outperform those adopting traditional MPPM, QAM, and on-off keying (OOK) techniques by 1.5, 0.4, and 3 dB, respectively, in the case of turbulence-free channels. Moreover, the new technique shows a better BER performance under different turbulence levels when compared with traditional MPPM and QAM techniques in turbulent FSO communication channels. Also, it shows an improvement in outage probability compared to MPPM, QAM, and OOK over gamma-gamma FSO channels.

Symbol error rate performance analysis of soft-decision decoded MPPM free space optical system over exponentiated Weibull fading channels

The symbol error rate (SER) performance of a multipulse pulse-position modulation (MPPM) free space optical (FSO) system under the combined effect of turbulence-induced fading modeled by exponentiated Weibull (EW) distribution and pointing errors with a soft-decision detector is investigated systematically. Particularly, the theoretical conditional SER (CSER) of soft-decision decoded MPPM is derived. The corresponding closed-form CSER is obtained via curve fitting with the Levenberg–Marquardt method. The analytical SER expression over the aggregated fading channels is then achieved in terms of Laguerre integration. Monte Carlo simulation results are also offered to corroborate the validity of the proposed SER model.

SER Analysis of MPPM-Coded MIMO-FSO System over Uncorrelated and Correlated Gamma-Gamma Atmospheric Turbulence Channels

The performance of multiple-input multiple-output free space optical (MIMO-FSO) communication systems, that adopt multipulse pulse position modulation (MPPM) techniques, is analyzed. Both exact and approximate symbol-error rates (SERs) are derived for both cases of uncorrelated and correlated channels. The effects of background noise, receiver shot-noise, and atmospheric turbulence are taken into consideration in our analysis. The random fluctuations of the received optical irradiance, produced by the atmospheric turbulence, is modeled by the widely used gamma-gamma statistical distribution. Uncorrelated MIMO channels are modeled by the α-μ distribution. A closed-form expression for the probability density function of the optical received irradiance is derived for the case of correlated MIMO channels. Using our analytical expressions, the degradation of the system performance with the increment of the correlation coefficients between MIMO channels is corroborated.

Maximum Achievable Constrained Power Efficiencies of MPPM-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$L$ &lt;/tex-math&gt;&lt;/inline-formula&gt;QAM Techniques

The maximum achievable power efficiency of a multipulse pulse-position modulation- $\boldsymbol L$ -ary quadrature-amplitude modulation (MPPM- $\boldsymbol L$ QAM) technique under a constraint on its spectral efficiency is obtained. Variations to this technique that include polarization multiplexing and switching are considered as well. A simple characterization to the maximum achievable power efficiency is derived under the above constraint. Our results are compared with that of traditional QAM techniques under same constraints. The results reveal that at spectral efficiency constraints of 1.5, 2.5, and 3.5 bit/sym/pol, the power efficiency of MPPM- $\boldsymbol L$ QAM technique is better than that of traditional QAM technique by $\sim \boldsymbol {3.9}$ , 2.2, and 1.4 dB, respectively.

A Power-Harvesting Pad-Less Millimeter-Sized Radio

A wireless-powered pad-less single-chip radio is implemented in 65 nm CMOS for applications in Internet of Things (IoT) and wireless tagging. This fully-self-sufficient mm-wave radio has no pads or external components (e.g., power supply), and the entire radio is a single chip with dimensions of 3.7 mm by 1.2 mm. To provide multi-access, and to mitigate interference, it uses two separate mm-wave bands for RX/TX and integrates both antennas to provide a measured communication range of 50 cm. The transmitter uses a modified Multipulse Pulse Position Modulation (MPPM) with 2 GHz of bandwidth on a 60 GHz carrier to communicate the data sequence as well as the local timing reference. The entire system operates with standby harvested power below 1.5 µW and achieves an aggregate data rate > 12 Mbps.