Digital Pulse Position Modulation Research Articles

High anti-interference 3D imaging LIDAR system based on digital chaotic pulse position modulation

High anti-interference 3D imaging LIDAR system based on digital chaotic pulse position modulation

FSO-CDMA system performance enhancement based on new hybrid code and M-ary digital pulse position modulation technique

FSO-CDMA system performance enhancement based on new hybrid code and M-ary digital pulse position modulation technique

Performance enhancement of hybrid fiber wavelength division multiplexing passive optical network FSO systems using M-ary DPPM techniques under interchannel crosstalk and atmospheric turbulence

The performance of moment generating function approaches, specifically Chernoff bound (CB) and modified Chernoff bound (MCB), is examined and improved in this study. We evaluates and enhances the performance of a wavelength division multiplexing (WDM) technique for free-space optical (FSO) fibre communications based on passive optical network (PON) using the M-ary digital pulse-position modulation (M-ary DPPM) schemes under amplified spontaneous emission (ASE) noise effects, interchannel crosstalk (ICC), and atmospheric turbulence (AT). We use a data rate of 2.5 Gbps for eight channels over a PON/DWDM-FSO optical fibre system in the C-band with 100 GHz channel spacing start from 1550 nm. The results achieve 20 Gbit/s transmissions (2.5 Gbps $$\times $$ 8 channels). This is a technology that can have extended leverage, higher data rates, power-efficient, and is considered an ideal option for the provision of bandwidth for potential access networks. When compared to the CB at a low gain (G = 8), the MCB outperforms the Gaussian approximation at high gain (G = 30). Because of its superior performance at a high gain (G = 30), the MCB offers the tightest limit on the bit error rate (BER). In comparison to an equivalent on–off keying (OOK) non-return-to-zero (NRZ), the M-ary DPPM scheme with a coding level (M) of 2 improves average power about by 2.9 dB at a data rate of 2.5 Gbps on the 1550 nm wavelength and BER of $${10}^{-{9}}$$ . The sensitivity of the M-ary DPPM modulation scheme remains improved over OOK in the presence of ICC. The lower power penalty is predicted to be approximately 0.2–3.0 dB in the DWDM-FSO systems for low coding level M $$=$$ 2. We achieve a lower power penalty at 0.2–3.0 dB for the hybrid fiber DWDM/PON-FSO optical communication system at a BER of $${10}^{-{9}}$$ . At a target BER of $${10}^{-{12}}$$ , the hybrid OOK-NRZ/M-ary DPPM offers about 4–8 dB of optical signal-to-noise-ratio improvements over the M-DPPM of the WDM-PON/FSO link for strong turbulence. The results demonstrated that the M-ary DPPM and the optical relaying amplification technique are powerful treatments for mitigating the impacts of ASE noise, AT, and ICC.

Performance Enhancement of DWDM-FSO Optical Fiber Communication Systems Based on Hybrid Modulation Techniques under Atmospheric Turbulence Channel

In this paper, we enhance the performance efficiency of the free-space optical (FSO) communication link using the hybrid on-off keying (OOK) modulation, M-ary digital pulse position modulation (M-ary DPPM), and M-pulse amplitude and position modulation (M-PAPM). This work analyzes and enhances the bit error rate (BER) performance of the moment generating function, modified Chernoff bound, and Gaussian approximation techniques. In the existence of both an amplified spontaneous emission (ASE) noise, atmospheric turbulence (AT) channels, and interchannel crosstalk (ICC), we propose a system model of the passive optical network (PON) wavelength division multiplexing (WDM) technique for a dense WDM (DWDM) based on the hybrid fiber FSO (HFFSO) link. We use eight wavelength channels that have been transmitted at a data rate of 2.5 Gbps over a turbulent HFFSO-DWDM system and PON-FSO optical fiber start from 1550 nm channel spacing in the C-band of 100 GHz. The results demonstrate (2.5 Gbps × 8 channels) 20 Gbit/s-4000 m transmission with favorable performance. In this design, M-ary DPPM-M-PAPM modulation is used to provide extra information bits to increase performance. We also propose to incorporate adaptive optics to mitigate the AT effect and improve the modulation efficiency. We investigate the impact of the turbulence effect on the proposed system performance based on OOK-M-ary PAPM-DPPM modulation as a function of M-ary DPPM-PAPM and other atmospheric parameters. The proposed M-ary hybrid DPPM-M-PAPM solution increases the receiver sensitivity compared to OOK, improves the reliability and achieves a lower power penalty of 0.2–3.0 dB at low coding level (M) 2 in the WDM-FSO systems for the weak turbulence. The OOK/M-ary hybrid DPPM-M-PAPM provides an optical signal-to-noise ratio of about 4–8 dB of the DWDM-HFFSO link for the strong turbulence at a target BER of 10−12. The numerical results indicate that the proposed design can be enhanced with the hybrid OOK/M-DPPM and M-PAPM for DWDM-HFFSO systems. The calculation results show that PAPM-DPPM has increased about 10–11 dB at BER of 10−12 more than the OOK-NRZ approach. The simulation results show that the proposed hybrid optical modulation technique can be used in the DWDM-FSO hybrid links for optical-wireless and fiber-optic communication systems, significantly increasing their efficiency. Finally, the use of the hybrid OOK/M-ary DPPM-M-PAPM modulation schemes is a new technique to reduce the AT, ICC, ASE noise for the DWDM-FSO optical fiber communication systems.

FPGA-Based Dual-Pulse Anti-Interference Lidar System Using Digital Chaotic Pulse Position Modulation

We investigated an FPGA-based dual-pulse anti-interference light detection and ranging (LiDAR) system with digital chaotic pulse position modulation (DCPPM). The dual-pulse signal is a periodic pulse pair, in which the first pulse is a periodic pulse, and the second pulse based on DCPPM is a pulse with a random time interval from the first pulse in each period. The real-time generation and detection of the position-modulated dual-pulse are realized by a field-programmable gate array (FPGA). The DCPPM-based dual-pulse lidar system integrates the characteristics of anti-interference, high pulse peak power, and fast measurement. In this letter, the repetition frequency of the dual-pulse signal is 100kHz. There is an initial time interval of 128ns between dual pulses, the step number of random time interval between dual pulses is 0~255, and the step accuracy is 6.4ns. Under a 1.25GSa/s sampling rate of the analog to digital converter (ADC), an accuracy within ±6cm has been obtained. Finally, under 100kHz periodic pulse interference and 100kHz DCPPM-based dual-pulse interference, the probability of correct detection has been counted every 250 measurements (up to 2000 times). The two correct detection probabilities with average values above 99% have been obtained, which are respectively 99.29% and 99.68%. The good anti-interference performance of the proposed lidar system has been verified.

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.

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 enhancement of the power penalty in DWDM FSO communication using DPPM and OOK modulation

This paper presents the design and performance enhancement of the power penalty (PP) in a dense wavelength division multiplexing based on free space optical communication (FSOC) link using digital pulse position modulation (DPPM) and on–off keying (OOK) modulation. Such a system has a high performance, low cost, robust and power efficient, reliable, excessive flexibility, and higher data rate for access networks. The system performance is evaluated for an 8-channel wavelength-division-multiplexing for hybrid fiber FSOC system at 2.5 Gbps on widely accepted modulation schemes under various atmospheric turbulence (AT) regimes conditions. The performance of system is introduced in terms of PP, bit-error rate (BER), transmission distance and the average received optical power. The numerical results shows that the improvement of the PP using DPPM modulation of 0.2–3.0 dB for weak turbulence (WT) regimes for BER of 10−6 and above 20, 25 dB for strong turbulence (ST) regimes are reported for BER of 10−6 and 10−9, as respectively (depending on the AT level). Further, we develop of improvement the PP caused by multiple-access interference about 6.686 dB which is predicted for target BER of 10−9 in WT and 1 dB at target BER of 10−6 in ST when the 8 user are active on the system of optical network units. Additionally, the optical power budget and margin losses of a system are calculated with different link length. The proposed approach of DPPM merges superiority with higher enhancement of PP about 0.8 dB for BER equal 10−9 at FSO link length lfso = 2000 m compared to OOK at 1 dB for WT. An improvement of 2 dB is observed using the DPPM scheme over an OOK due to capability of detect pulses under background noise conditions with increased receiver sensitivity.

Simulation and Analysis of Power Spectral Density for Digital Pulse Interval Modulation

In free space optical communication the signal power is changing with the bandwidth therefore PSD curves are very important in the link design. The power spectral density(PSD) of intensity modulation scheme i.e. Digital Pulse Interval Modulation (DPIM) has been presented. Results which are generated by simulations of an experimental system are presented. Which shows that DPIM has higher transmission capacity compared with digital pulse position modulation (DPPM) and is less complex to implement

Performance evaluation of turbulence‐accentuated interchannel crosstalk for hybrid fibre and free‐space optical wavelength‐division‐multiplexing systems using digital pulse‐position modulation

A hybrid fibre and free-space optical communication link using digital pulse-position modulation (DPPM) in a wavelength-division-multiplexing system is proposed. Such a system, which could provide a power efficient, robust and flexible solution to high-speed access networks, is a contender for a passive optical network solution and could readily be deployed in areas with restrictions in optical fibre installation, or alternatively as a disaster recovery network. Interchannel crosstalk and atmospheric turbulence are major impairments in such a system and could combine in some cases to degrade the system. Both impairments are investigated here and the results are presented in the form of bit error probability, required optical transmission power and power penalties. Depending on the position of the interferer relative to the desired user, power penalties of about 0.2–3.0 dB for weak turbulence and above 20 dB for strong turbulence regimes are reported for bit error rate of 10−6. DPPM scheme with a coding level of 2 show about 2 dB improvements over on–off-keying scheme.

Spectral characterisation of offset pulse position modulation

Offset pulse position modulation (PPM) has been shown to be more attractive for use in optical fibre channels than on–off keying, digital PPM and in some respects multiple PPM in some applications. However the spectral analysis of this coding scheme has not yet been addressed. In this study the authors present, for the first time, the spectral characteristics of an offset PPM sequence. The results show strong frequency components at the frame rate and, if return-to-zero pulses are used, the slot rate.

Spectral analysis of intensity modulation schemes in free space optical communications

In this study, power spectral densities (PSDs) of intensity modulation schemes used in free space optical communications namely, on-off keying (OOK), pulse-position modulation (PPM), digital pulse interval modulation (DPIM), pulse amplitude and position modulation (PAPM) and differential amplitude pulse interval modulation (DAPIM) have been derived. The bandwidth requirements of these schemes are determined from the occurrence of the first null in the PSDs. For comparison we have considered OOK, 8-PPM, 8-DPIM, 2 × 4-PAPM and 2 × 4-DAPIM. Among all the schemes considered, the bandwidth requirement of 2 × 4-DAPIM is the least. Although 8-PPM has the least effect of baseline wander and the maximum detected optical power among all the schemes considered, the bandwidth requirement is very high. This may not be desirable in certain cases. The PSD curves are quite important in the link design as these will give information on how the signal power is changing with the bandwidth. If the noise PSD is also known then these curves can be used to determine the optimum bandwidth for maximum signal-to-noise ratio. The results are helpful in the selection of modulation scheme for free space optical links and to determine how the power content of the signals is affected by filters and other devices in the link.

Performance evaluation of digital pulse position modulation for wavelength division multiplexing FSO systems impaired by interchannel crosstalk

Wavelength division multiplexing (WDM) has been proposed for fibre, intersatellite, free space and indoor optical communication systems. Digital pulse position modulation (DPPM) is a more power efficient modulation format than on-off keying (OOK) and a strong contender for the modulation of free-space systems. Although DPPM obtains this advantage in exchange for a bandwidth expansion, WDM systems using it are still potentially attractive, particularly for moderate coding levels. However, WDM systems are susceptible to interchannel crosstalk and modelling this in a WDM DPPM system is necessary. Models of varying complexity, based on simplifying assumptions, are presented and evaluated for the case of a single crosstalk wavelength. For a single crosstalk, results can be straightforwardly obtained by artificially imposing the computationally convenient constraint that frames (and thus slots also) align. Multiple crosstalk effects are additionally investigated, for the most practically relevant cases of modest coding level, and using both simulation and analytical methods. In general, DPPM maintains its sensitivity advantage over OOK even in the presence of crosstalk while predicting lower power penalty at low coding level in WDM systems.

Duobinary pulse position modulation – a novel coding scheme for the dispersive optical channel

Pulse position modulation (PPM) coding schemes have been proposed and investigated widely as a technique of utilising the very high bandwidth available in optical fibres, achieving a significant improvement in sensitivity of 5-11 dB compared with an equivalent non-return-to-zero on-off keying scheme. However, this improvement has some tradeoffs. When using eight-level digital PPM, the final data rate can be as high as 32 times that of the original data, thus implementation becomes extremely difficult to the point where commercial viability becomes doubtful. In this study, the authors describe a novel coding scheme that combines the duobinary scheme with PPM to form DuoPPM. It is shown that DuoPPM gives a sensitivity greater than digital PPM while operating at two times the original data rate. Original results presented in this study predict that a high fibre bandwidth DuoPPM system can give a sensitivity of -42.2 dBm when operating with 1 Gbit/s on-off keying (OOK) data and a fibre bandwidth of 100 GHz. In addition, it is shown that DuoPPM outperforms optimised digital PPM at low fibre bandwidths (1 GHz) by 8.7 dB.

Experimental Evaluation of Conditions for Short-distance Transmission of Event Timing Data

Specifics of event timing data transmission are experimentally investigated under conditions typical for multi-channel data acquisition from a large quantity of signal sources. The events, in the considered case, are analog input signal and sinusoidal reference function crossings. The sequences of the crossing time instants represent the respective analog input signals and these sequences have to be transmitted to the signal reconstruction subsystem. An experimental system for fast short-distance transmission has been built. It performs data encoding on the basis of digital pulse position modulation with 10 picoseconds resolution. The achievable data encoding resolution and other vital parameters characterizing data transmission systems of this type were evaluated on this basis. DOI: http://dx.doi.org/10.5755/j01.eee.19.4.4055

Performance Analysis of Offset Pulse-Position Modulation Over an Optical Channel

This paper presents an original performance analysis of an offset pulse-position modulation (PPM) scheme using graded index plastic optical fiber with a Gaussian impulse response. The main aim of this analysis is to predict how sensitivity, error, number of required photons, threshold voltage, and the effect of intersymbol interference will change with the change in the number of data bits encoded at a rate of 1 Gbit/s. An information theory analysis is presented in detail and the bandwidth-utilization efficiency is determined. Results are compared to equivalent digital PPM and multiple PPM schemes and it is also shown that offset PPM gives a 7.5 dB advantage over nonreturn-to-zero on-off keying.

Performance evaluation of optically preamplified digital pulse position modulation turbulent free-space optical communication systems

Optical preamplification introduces non-Gaussian electrical domain noises (beat noises) to digital pulse position modulation (DPPM) free-space optical (FSO) communication systems impaired by atmospheric turbulence, which do not appear for a simple PIN photodiode-based FSO receivers and thus necessitate a more sophisticated approach to bit error rate (BER) modelling. To explore this BER performance analyses, notably the Gaussian approximation, Chernoff bound and modified Chernoff bound (MCB), for such a system are presented and the MCB is seen to be an appropriate technique to use. Furthermore, the effectiveness of spatial diversity techniques, specifically aperture averaging, in mitigating the turbulence effect is investigated. The gamma-gamma distribution model is used to characterise the whole range of turbulence conditions. The results reveal the superiority of DPPM with improved receiver sensitivity (at a binary data rate 2.5-Gb/s and at typical FSO BER of 10 -9 ) of about 7-9-dB [for coding level of 5 and optical link length (for turbulent interaction) of 1500-m] more than an equivalent optically preamplified on-off keying non-return-to-zero approach, depending on the level of turbulence.

Analysis of offset pulse position modulation – a novel reduced bandwidth coding scheme

This study describes a novel version of digital pulse position modulation (PPM) called offset PPM, which operates at half the line rate of digital PPM and offers an increase in sensitivity. To demonstrate the effectiveness of the technique, theoretical results are presented for an offset PPM system coding 3 bits of pulse code modulation (PCM) data, at a rate of 1 Gbit/s. An optical channel with a Gaussian impulse response, such as that obtained from graded-index plastic optical fibre, was considered. The results are compared to those obtained for digital PPM, using a maximum likelihood sequence detector, and it is shown that offset PPM is more tolerant of pulse dispersion giving a 3.1 dB increase in sensitivity when operating with a channel bandwidth equal to half the PCM bit rate.

Pulse position modulation coding schemes for optical intersatellite links

The rapid and significant development of communications links between satellites has made it possible to use various applications such as relay voice, video, multimedia, etc. As a result, much research has been carried out in this field during recent years to reduce power consumption and increase transmission reliability. This reported work focuses on analysis of intersatellite links in free space, with optical links using laser sources being considered in particular. The use of several different coding schemes are discussed for use in such links: multiple pulse position modulation (MPPM); digital pulse position modulation (DPPM); Dicode pulse position modulation (Dicode PPM). Work has been carried out to compare these coding schemes in terms of error weightings and coding efficiency through showing how the PCM error rate is affected by false alarm and erasure errors for MPPM, DPPM and Dicode PPM coding 3 bits of PCM. Comparison between these coding schemes is drawn in terms of sensitivity and bandwidth efficiency.

Real-Time Noncrosstalk Sonar System by Short Optimized Pulse-Position Modulation Sequences

Ultrasonic crosstalk is one of the main causes of false distance measurements that reduce the work efficiency of sonar sensors in mobile robots. To enhance the real-time performance of sonar systems, short digital pulse-position modulation (PPM) sequences are used to trigger ultrasonic transducers. Due to their properties of sharp autocorrelation and flat cross correlation, chaotic and pseudorandom number series are used to modulate pulse positions. A genetic algorithm is adopted to optimize the range of duration between pulses. Real experiments using Polaroid 600 series instrument-grade electrostatic transducers validate the suitability of the proposed method.