Showing papers on "Pulse-position modulation published in 2021"

An exact BER analysis of NOMA-VLC system with imperfect SIC and CSI

Abstract: Visible Light Communication (VLC) has emerged as a promising technology for 5G and beyond networks by offering a wide license free spectrum. In order to develop a high data-rate and error-free network, in this paper, non-orthogonal multiple access (NOMA) technique is combined with VLC technology. In particular, a two user downlink NOMA based VLC system is considered in which the transmitter uses on–off keying (OOK) and L-ary pulse position modulation (L-PPM). The closed form mathematical expressions for bit-error-rate (BER) of OOK and L-PPM modulated NOMA-VLC system is derived in the presence of perfect and imperfect channel state information (CSI). Moreover, imperfect successive interference cancellation (SIC), which is a more practical scenario, is considered for this analysis. The analysis shows that the error performance of L-PPM modulated NOMA-VLC system is superior to OOK modulated NOMA-VLC system for (L > 2). Further, with the far user power allocation coefficient greater than 0.5, the far user completely outperforms the near user. Furthermore, the channel estimation error has an adverse effect on BER performance of the system under consideration. The performance of the considered system is investigated for the parameters of interest, i.e., location of the far user, field of view (FOV) and channel estimation error. The derived analytical BER expressions are verified with the simulation results.

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

Abstract: 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.

Dimming-Based Modulation Schemes for Visible Light Communication: Spectral Analysis and ISI Mitigation

Abstract: Visible light communication (VLC) is being envisioned as an enabling technology to provide the much-needed spectral relief for the ever-increasing demand for Internet connectivity and data consumption. Since VLC uses illumination sources for lighting as well as communication, it is required to provide dimming control for proper lighting and enhanced error performance for reliable data communication. In this paper, we address both these issues holistically. We formulate and study the power spectral densities of dimming-based modulation schemes, namely variable on-off keying (VOOK) and variable pulse position modulation (VPPM), and hence, derive their bandwidth requirements and spectral efficiencies. Moreover, the capacity of VLC systems is severely limited by the inter-symbol interference (ISI) occurring as a result of the multipath propagation of light signals in VLC. We propose to ameliorate the error performance of VLC systems by using channel equalization for ISI mitigation, thereby enhancing the system capacity. We develop the analytical model of a dimmable VLC system employing channel equalization and use this model to study the effect of dimming and data rate on the error performance of VOOK and VPPM schemes. We present simulation and analytical results to show that the performance of dimming-based modulation schemes is significantly improved using channel equalization.

A High-Speed and High-Sensitivity Photon-Counting Communication System Based on Multichannel SPAD Detection

Abstract: In order to achieve high-speed, high-sensitivity optical communication over long distances and high attenuation channels, we propose a photon-counting communication system based on the detection of multichannel single-photon avalanche diodes (SPADs). First, the ideal pulse position modulation (PPM) bit error rate (BER) expression for a multichannel detection system is derived, and then the effect of the detector's dead time is taken into account. The BER of the multichannel detection system was analyzed by means of a Monte Carlo simulation, after which we set up a four-channel receiving experimental verification system with a 1 × 4 fiber splitter and four single-photon counting modules (SPCMs). The simulation and experimental results demonstrated that the BER of the multichannel detection system could be greatly reduced and the communication speed substantially improved. Finally, a reliable photon-counting communication system with a rate of 50 Mbps and sensitivity of 4 photons/bit was developed using serially-concatenated pulse position modulation (SCPPM) technology.

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

Abstract: 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.

QoS Analysis and Signal Characteristics for Short-Range Visible-Light Communications

Abstract: Visible-light communications (VLCs) are energy-efficient communication means and a popular alternative to the radio-frequency technology. VLCs are referred to as free-space optical communication systems which can be built upon the existing lighting infrastructure. Due to the cost-effectiveness concern, light emitting diodes (LEDs) are adopted as the visible-light sources. In this paper, we demonstrate a VLC prototype using white LEDs and pulse position modulation (PPM), which is aimed for short-range communications. Based on the acquired VLC signal waveforms, characteristics related to electronic components, LEDs, and photo diodes (PDs) are studied thoroughly. The non-square shape of received pulses is modeled by new template functions involving rising and setting time intervals. A new PPM demodulator is devised thereupon. Meanwhile, the probability density function of noise is derived using the Edgeworth expansion. As all of the aforementioned aspects are taken into account, the VLC quality-of-service (QoS) in terms of package error rate and throughput is studied in this work. Experiments are taken to justify the theoretical QoS metric and evaluate our proposed new PPM demodulator.

Energy-limited Joint Source--Channel Coding via Analog Pulse Position Modulation

Abstract: We study the problem of transmitting a source sample with minimum distortion over an infinite-bandwidth additive white Gaussian noise channel under an energy constraint. To that end, we construct a joint source--channel coding scheme using analog pulse position modulation (PPM) and bound its quadratic distortion. We show that this scheme outperforms existing techniques since its quadratic distortion attains both the exponential and polynomial decay orders of Burnashev's outer bound. We supplement our theoretical results with numerical simulations and comparisons to existing schemes.

A Simple Resonant Switched-Capacitor LED Driver Employed as a Fast Pulse-Based Transmitter for VLC Applications

Abstract: This article presents a resonant switched-capacitor (RSC) dc–dc converter for visible light communication (VLC) applications operating as both high-efficiency power converter and fast-response data transmitter. By operating under soft switching, the topology allows for higher switching frequency and higher slew rate so that the VLC functionality can be embedded into the power stage without an auxiliary switch. In the literature, this additional switch has been presented as a viable implementation of on–off-keying (OOK) and variable pulse position modulation (VPPM) for data transmission yet, at the same time, is a major efficiency bottleneck for higher transmission rates due to its inherent hard-switching operation. This justifies new efforts in enabling pulse-based transmission (PBT) without this additional switch. A 10-W prototype was built to demonstrate such feasibility, operating at a switching frequency of 500 kHz, resulting in nominal efficiency of 85% during data transmission under the VPPM scheme, achieving up to 100 kb/s for various brightness levels, over a distance up to 1m.

Analysis of multi-pulse position modulation free space optical communication system employing wavelength and time diversity over Malaga turbulence channel

Abstract: Free space optics (FSO) communication has proved to be a useful technology both in the scientific and commercial domains in response to exponential growth in demand for ultrahigh bandwidth for applications such as urban broadband services, cellular backhaul and earth to satellite links among others. However, atmospheric turbulence, prevailing adverse weather conditions and pointing errors between the transmitter and receiver affect significantly this technology. To mitigate these challenges, different approaches have been considered in literature such as error control coding, spatial diversity, the use of relays and so on alongside different modulation techniques. Therefore in this paper, we have considered the use of multipulse position modulation (MPPM) modulation technique first with wavelength diversity and then with time diversity techniques over the Malaga (M) distribution as a way of mitigating against turbulence fading and pointing error effects. Closed form expressions for the average bit error rate (BER) and outage probability have been derived and later on used to analyze the system performance. The effect of diversity order, normalized jitter and beam width has been scrutinized, all as functions of the transmitted power. Beside the fact that the increase in diversity order improves both the BER and outage probability, it has been noted that the system performance is highly degraded when the normalized jitter is increased beyond 4 for any given diversity order. The BER decreases while the receiver beam width, W z increases for all diversity orders, reaching to an optimum value of 0.5 m and 1.2 m for normalized jitter of 2 and 5 respectively. Ultimately, the conclusion drawn from the analytical results of this paper support the application of wavelength as well as time diversity as means of enhancing the FSO communication system performance

A Novel Encoding Scheme for Improving the Bandwidth Efficiency of DPPM

Abstract: The differential pulse position modulation (DPPM) is one of the popular power-efficient schemes for supporting visible light communication in underwater environments and across the air-water interface. Despite such an advantage, DPPM does not efficiently utilize the available channel capacity. This paper aspires to tackle such shortcomings by striking a better balance between power and bandwidth efficiency. Particularly, L-DPPM is considered where a block of M input data bits is mapped into one of the L distinct waveforms containing only one ‘on’ chip. A novel encoding algorithm and frame structure are proposed in order to shorten the time between consecutive symbols and consequently improve the bit rate of L-DPPM. The idea is based on avoiding bit patterns that contribute the most to bandwidth inefficiency. The proposed algorithm explores a number of bit patterns remapping through simple complement and shifting operations. A detailed frame structure with all necessary control bits is provided. Overall, boosting the bandwidth efficacy comes at the expense of a slight increase in control bit count and transmission power. The simulation results demonstrate the effectiveness of the proposed encoding algorithm and provide guidelines for determining M for best performance.

Satellite Navigation and Communication Integration Based on Correlation Domain Indefinite Pulse Position Modulation Signal

Abstract: Ubiquitous signal coverage is a basic demand of Internet of Things (IoT) communications, which meets the feature of satellite communications. Infinite user number is a basic demand of IoT location-based services, which meets the feature of Global Navigation Satellite System (GNSS). Both of these demands make Satellite Navigation and Communication Integration (SNCI) an important supporting technology for IoT. Inherited from the satellite communications system, GNSS itself has a certain data transmission capacity. Thus, enhancing the communication function of the GNSS is a promising means of achieving SNCI. Considering that a unified signal system cannot currently realize high-precision positioning and high-speed data transmission simultaneously in SNCI, this project proposes a Correlation Domain Indefinite Pulse Position Modulation (CDIPPM). A pilot channel and a data channel are introduced in this technology, which are distinguished by Code Division Multiplexing (CDMA). The synchronization function is provided by the pilot channel, thereby freeing the data channel of this function. The phase of the pseudorandom code can then be used as the carrier of information. In order to transmit more information, the transmitter of the proposed technology superimposes on the data channel multiple sets of spread spectrum sequence, which are generated from one set of spread spectrum sequence by different cyclic shifting operations. The receiver will identify the number and location of the correlation function peaks by a detection algorithm and recover the message. It can be seen by theoretical analysis and simulation verification. The technology can significantly improve satellite data transmission rates and maintain the original positioning function while minimizing change in the original GNSS signal. Therefore, the SNCI system based on this technology has the following advantages: a unified signal system, high positioning accuracy, high data transmission rate, and a backward navigation function, and it is easy to promote.

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

Abstract: 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.

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

Abstract: 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.

Mono Camera-Based Optical Vehicular Communication for an Advanced Driver Assistance System

Abstract: This technical paper proposes a new waveform combining the low-rate and high-rate data streams to detect the region-of-interest signal in a high-mobility environment using optical camera communication. The proposed technique augments the bit rate of the low-rate stream; consequently, the link setup time is reduced and the requirement of low frame rate camera is eliminated. Additionally, both the low-rate and high-rate data streams in the proposed bi-level pulse position modulation are decoded with a unique adaptive thresholding mechanism with a high frame rate camera. We also propose a vehicle localization scheme to assist the drivers in maintaining a safe following distance that can significantly reduce the frequency of accidents. Moreover, two neural networks are proposed to detect the light-emitting diodes (LEDs) for localization and communication, and to estimate the road curvature from different rear LED shapes of the forwarding vehicle, respectively. The system is implemented, and its performance is analyzed in Python 3.7. The implementation results show that the proposed system is able to achieve 75% localization accuracy, a 150 bps low-rate stream, and a 600 bps high-rate stream over a range of 25 m with a commercial 30 fps camera.

A New Hybrid Prime Code for OCDMA Network Multimedia Applications

Abstract: This paper presents a new family of spreading code sequences called hybrid prime code (HPC), to be used as source code for the optical code division multiple access (OCDMA) network for large network capacity. The network capacity directly depends on the number of available code sequences provided and their correlation properties. Therefore, the proposed HPC is designed based on combining two or more different code words belonging to two or more different prime numbers. This increases the number of code sequences generated. The code construction method utilized allows the generation of different code sets, each with different code length and weight, according to the number of prime numbers used. In addition, the incoherent pulse position modulation (PPM) OCDMA system is proposed based on the HPC code. Furthermore, the bit error rate (BER) performance analysis is introduced versus the received optical power and the number of active users. Moreover, the error vector magnitude (EVM) is calculated versus the optical signal-to-noise ratio. This work proves that using two prime numbers simultaneously generates far more codes than using prime numbers separately. It also achieved an OCDMA system capacity higher than the system that uses the optical orthogonal codes (OOCs), modified prime codes (MPCs) families, and two code families with separate simultaneously prime numbers, at a BER below 10−9 which is the optimum level.

Design and implementation of VLC-based smart barrier gate systems

Abstract: In this paper, an innovative and smart Visible Light Communication (VLC)-based Intelligent Transportation System (ITS) is designed. The proposed system uses vehicle LED headlamps as a remote controller. Differential Pulse Position Modulation (DPPM) is utilized for the sake of its asynchronicity. The system features an innovative optical interference cancellation mechanism to address the unwanted variable DC component and AC line noise in the received signal. The feasibility of the proposed system is demonstrated experimentally in day and night conditions using an off-the-shelf LED headlights. The Bit Error Rate (BER) performance of the system in terms of angular position of the vehicle with respect to the VLC receiver at different link ranges is evaluated. The prototype successfully demonstrates the smart control over the barrier gate using the ATmega microcontrollers family for the outdoor environment. BER of lower than 10 - 3 is achieved for a maximum link range of 4.4 meters.

Target Localization and Tracking Using an Ultra-Wideband Chaotic Radar With Wireless Synchronization Command

Abstract: An ultra-wideband chaotic radar with wireless synchronization command is proposed and experimentally demonstrated for target localization and tracking. This radar uses the wideband chaotic pulse position modulation (CPPM) signal as the probe signal and the radar structure of single-transmitting-dual-receiving. The echo signal scattered from a target is collected by two receivers. The target is located and tracked accurately in two-dimensional space using the signal processing scheme. In particular, the radar receivers can directly generate the CPPM reference signals through a wireless synchronization command, so that the transceivers can be physically separated without cable or optical fiber connection. Experimental results demonstrate the proposed chaotic radar can locate and track the target accurately. A localization error of 11 cm and a detection resolution of 17 cm can be both achieved. Moreover, this radar possesses the excellent immune performance to the external electromagnetic interferences, which makes it suitable in the complex electromagnetic environment caused by the cooperative work of multiple radars.

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

Abstract: 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.

BER Performance Analysis of Non-Coherent Q-Ary Pulse Position Modulation Receivers on AWGN Channel

Abstract: This paper introduces the structure of a Q-ary pulse position modulation (PPM) signal and presents a noncoherent suboptimal receiver and a noncoherent optimal receiver. Aiming at addressing the lack of an accurate theoretical formula of the bit error rate (BER) of a Q-ary PPM receiver in the additive white Gaussian noise (AWGN) channel in the existing literature, the theoretical formulas of the BER of a noncoherent suboptimal receiver and noncoherent optimal receiver are derived, respectively. The simulation results verify the correctness of the theoretical formulas. The theoretical formulas can be applied to a Q-ary PPM system including binary PPM. In addition, the analysis shows that the larger the Q, the better the error performance of the receiver and that the error performance of the optimal receiver is about 2 dB better than that of the suboptimal receiver. The relationship between the threshold coefficient of the suboptimal receiver and the error performance is also given.

Data transmission scheme based on the DC-QOSTBC in indoor MIMO-VLC systems.

Abstract: We propose a data transmission scheme based on the dimming coding and quasi-orthogonal space-time block coding (QOSTBC) to improve the performance of indoor multiple-input multiple-output visible-light communication (MIMO-VLC) systems. After channel coding, the dimming coding was first applied to encode the input information bits into dimming bits. Then these encoded dimming bits were mapped to different symbols by head pulse position modulation. Finally, the symbol matrix was constructed on the basis of QOSTBC; then the light-emitting diodes would be activated to transmit the optical signals carrying the information according to the symbol matrix. The Monte Carlo simulations demonstrated the superiority of the proposed scheme in channel capacity and bit error ratio (BER). The channel capacity was a good approximation to the actual one, even though the full diversity gain could not be completely achieved. The BER could achieve 0.4×10−6 when the number of photodetectors was two.

Comparing high order pulse position modulation to burst differential phase shift keying in intersatellite optical communications links

Abstract: Distributed satellite mesh networks utilizing low-cost small satellites require communications components that have low impact on the cost, size, weight and power (SWaP-c) while long range, high bandwidth communications can reduce the number of required satellites in the mesh network. Free space laser communications provide a potential for low-SWaP, long-range communications links by leveraging high aperture gains due to short wavelengths yielding narrow divergence. Additionally, wide band optical booster amplifiers frequently operate with an average power limit rather than a peak power limit enabling low-duty cycle formats to take advantage of high peak powers. Full realization of these benefits depends on the format being utilized. New-space laser communications terminals leverage much of the existing fiber optical telecommunication infrastructure to repurpose products for long range free space applications that currently only have a launch amplifier and, potentially, a preamplified receiver. While long haul fiber applications favor binary phase shift keying formats, low cost applications of optical fiber telecommunications links that require low-SWaP on the transmitter and receiver ends of the link frequently drive designs towards intensity modulated direct drive (IM-DD) links. We investigate extending the range of a free space optical link through use of three different variable data rate methods including, reducing receiver bandwidth, utilizing burst waveforms, and pulse position modulation formats (PPM). Our results indicate that although a higher SNR is required for PPM formats, orders higher than 64 can acquire links at comparable average power and data rate as differential phase shift keying formats under similar receiver conditions.

About Digital Communication Methods for Visible Light Communication

Abstract: The visible light communication (VLC) by LED is one of the important communication methods because LED can work as high speed and VLC sends the information by high flushing LED. We use the pulse wave modulation for the VLC with LED because LED can be controlled easily by the microcontroller, which has the digital output pins. At the pulse wave modulation, deciding the high and low voltage by the middle voltage when the receiving signal level is amplified is equal to deciding it by the threshold voltage without amplification. In this paper, we proposed two methods that adjust the threshold value using counting the slot number and measuring the signal level. The number of signal slots is constant per one symbol when we use Pulse Position Modulation (PPM). If the number of received signal slots per one symbol time is less than the theoretical value, that means the threshold value is higher than the optimal value. If it is more than the theoretical value, that means the threshold value is lower. So, we can adjust the threshold value using the number of received signal slots. At the second proposed method, the average received signal level is not equal to the signal level because there is a ratio between the number of high slots and low slots. So, we can calculate the threshold value from the average received signal level and the slot ratio. We show these performances as real experiments.

Universal Joint Source-Channel Coding Under an Input Energy Constraint.

Abstract: We consider the problem of transmitting a source over an infinite-bandwidth additive white Gaussian noise channel with unknown noise level under an input energy constraint. We construct a universal scheme that uses modulo-lattice modulation with multiple layers; for each layer we employ either analog linear modulation or analog pulse position modulation (PPM). We show that the designed scheme with linear layers requires less energy compared to existing solutions to achieve the same quadratically increasing distortion profile with the noise level; replacing the linear layers with PPM layers offers an additional improvement.