On-off Keying Research Articles

NOMA cooperative VLC systems: design and performance analysis with OOK and L-PPM modulation.

Visible light communication (VLC) allows white LEDs to communicate while lighting, which improves resource consumption. Multiple relay approaches can be employed in conjunction with cooperative communications to achieve large gains in spatial diversity, expand the coverage, and possibly boost system capacity. In this paper, the nonorthogonal multiple access (NOMA) cooperative techniques for VLC systems using on-off keying (OOK) and L-pulse-position modulation (L-PPM) are proposed. The maximum ratio combining (MRC) schemes is adopted at the receiving node to combine the signals received from cooperative transmissions. Further, the decode-and-forward relaying protocol is considered for cooperation. The proposed system is analyzed for a multiuser scenario that is followed by a two- and three-user scenario for detailed analysis. This study calculates the bit error probability (BEP) of an OOK/L-PPM modulated NOMA cooperative VLC system under perfect and imperfect successive interference cancellation. Simulation results are presented to validate the produced analytical BEP results.

Study of all-optical mode regeneration based on few-mode Mach–Zehnder interferometer

Mode division multiplexing (MDM) technology is a promising approach to improve the spectral efficiency of optical fibers. In MDM systems, all-optical mode regenerators can suppress the amplified spontaneous emission (ASE) noise and crosstalk of few-mode signals directly in the optical domain. In this paper, we focus on the mode regenerator based on few-mode Mach–Zehnder interferometer (FM-MZI) with a highly-nonlinear fiber, and propose an optimization method for the working points (WPs) of mode regeneration. An FM-MZI regenerator capable of supporting LP01, LP11, and LP21 modes is optimally designed for on/off keying (OOK) signals and the simulation results is in agreement with the theoretical analysis. Our simulation shows that, (1) when the input optical signal-to-noise ratios (OSNRs) of the three modes are 25 dB, 27 dB, and 27.5 dB, the FM-MZI regenerator has the maximum OSNR improvement by 1.7 dB, 1.5 dB, and 1.51 dB, respectively; (2) the introduction of the mode regenerator can reduce the bit error ratio (BER) of the 10 Gbit/s OOK system from 10−9 to 10−11, equivalent to the OSNR improvement by 1.87 dB, 2 dB, and 1.76 dB at BER = 10−9 for the three modes, respectively. In addition, we discuss the influence of optimization precision for the optical coupler, Q-factor improvement at different data rates, and Phase-preserving regeneration characteristics.

High-speed chaos-based secure optical communications over 130-km multi-core fiber.

Chaotic optical communication is of great significance for secure data transmission. Despite rapid development over the decades, high-speed (>100 Gbps) and long-distance (>100 km) chaotic optical communication in a single fiber is still full of challenges. Here, we propose and experimentally demonstrate high-speed and long-distance chaos-based secure optical communications using mutual injection of semiconductor lasers and space-division multiplexing (SDM) techniques. The encrypted signals are transmitted through all seven core channels of the multi-core fiber (MCF), which effectively expands the aggregate transmission capacity of a single fiber. A pair of source and synchronization devices based on mutual injection of semiconductor lasers are employed to effectively encrypt and decrypt signals. Chaos-based secure optical communications with 70-Gbps on-off keying (OOK) and 140-Gbps quadrature phase-shift keying (QPSK) signals over a 130-km MCF are successfully demonstrated in the experiment with favorable performance. The demonstration may pave the way for future ultrahigh capacity and ultra-long distance chaotic optical communications by fully exploiting multi-dimensional resources of light waves, including the spatial dimension.

Ultra-Compact Ultra-Broadband Two-Mode Transverse-Electric Based SWG Multiplexer Demonstrated at 64 Gbps

We designed and experimentally demonstrated an ultra-compact and ultra-broadband two-mode de-multiplexer based on a subwavelength grating (SWG) asymmetrical coupler (ADC) on a silicon-on-insulator (SOI) platform. The device consists of a cascaded strip waveguide tapered to a multimode segment and a SWG-based single-mode waveguide. Tapering the strip waveguide in multi-segments guarantees a high fabrication tolerance with a wider wavelength range of operation. The parameters of the periodic structure are chosen to meet the Bragg condition and phase-match the TE1 mode of the strip waveguide. These features produce a faster mode evolution with a shorter coupling length of only 8.5 µm and an entire mode division multiplexing (MDM) link (Mux and Demux) of only 55 µm. The MDM link operates over a wide wavelength range, covering the entire S-, C-, and L-bands. The insertion loss (IL) and crosstalk (CT) achieved at 1550 nm are better than 1 dB and -18 dB, respectively. The device also has low fabrication sensitivity to deviations in the waveguide's parameters. Additionally, the transmission performance of the link is demonstrated at 1550 nm wavelength using non-return-to-zero (NRZ) on-off keying (OOK) modulation, where clear eye diagrams are obtained at 64 Gbps.

Application of FWM-Based OFC for DWDM Optical Communication System with Embedded FBG Sensor Network

Abstract Four-wave mixing optical frequency comb fibre-based setups (FWM-OFCs) have the potential to improve the combined dense wavelength division multiplexed passive optical network (DWDM-PON) and fibre Bragg grating (FBG) temperature sensors network providing easier application, broader technological opportunities for network development, and energy efficiency by substituting a power-demanding laser array. In this research, OFCs are generated for the purpose of combined network application of DWDM-PON and FBG optical sensors. The paper also investigates compatibility scenarios with OFCs in such systems. The mathematical simulation model has been developed and the performance of FWM-OFC based 8-channel 50 GHz spaced non-return-to-zero on-off keying (NRZ-OOK) modulated DWDM-PON transmission system, operating at 50 km single-mode fibre (SMF) with a bit rate of at least 10 Gbps embedded with 7 FBG optical temperature sensors, has been studied. As it is shown, FWM application results in OFC source that has fluctuations of the individual comb tones of less than 3 dB in power, and with an extinction ratio of about 33 dB for operation range of 192.9–193.25 THz, acting as a unified light source for all the data transmission channels. Embedded FBG optical sensors network causes negligible 0.3 dB power penalty.

Dynamical behaviors of vertical-cavity surface-emitting lasers with an embedded saturable absorber subjected to an on-off keying (OOK) current modulation

Abstract We numerically study the dynamics of VCSEL-SA when modulated by an analog on-off keying (OOK) current. It is found that the laser gives a pulse-like response when operated below the threshold current. After the threshold current, which is in the excitable phase, the laser generates single spikes (phasic spiking) and a series of spikes (tonic spiking) wherein the amplitude of the spikes varies as the form of the current. Complex dynamics such as bursting oscillations and chaotic dynamics are successfully generated at low frequencies (few MHz). After this excitable phase, the laser copies the OOK current with underdamped oscillations generated during the OFF phase of the OOK current.

A capacitively coupled digital isolator with CMTI of 160 kV/μs and data rate of 230 Mbps

—This paper presents a capacitively coupled digital isolator with superior Common Mode Transient Immunity (CMTI) and high performances. This work adopts the On-Off Keying (OOK) architecture to cancel the influence of Common Mode Transient (CMT) and increase the speed performances. In addition, it adopts a fast-transient-response architecture for the Schmitt trigger to further improving the speed performances. Besides, this work proposes a gate-cross-coupled common-gate pre-amplifier with an active zero load, amplifying the signal after the isolation capacitance. By applying the proposed technique, the high-frequency gain retains to high value, while the low-frequency gain is greatly attenuated. It employs an envelope-comparator, an integrator and a filter as demodulator to reduce the propagation delay and speed up the data rate. Fabricated in a 0.18 μm CMOS process, the chip achieves 160 kV/μs CMTI, 230 Mbps data rate, 6 ns propagation delay, 1.5 mA dynamic current and 14 kV isolation breakdown voltage with the area of the isolation capacitance of 2 × 104 μm2.

Wide-field-of-view optical detectors for deep ultraviolet light communication using all-inorganic CsPbBr3 perovskite nanocrystals.

Optical wireless communication (OWC) links suffer from strict requirements of pointing, acquisition, and tracking (PAT) between the transmitter and receiver. Extending the narrow field-of-view (FoV) of conventional light-focusing elements at the receiver side can relax the PAT requirements. Herein, we use all-inorganic CsPbBr3 nanocrystals (NCs) to extend various optical concentrators' FOV to 60°, regardless of the original FOV values of the concentrators. Given the robustness of UV light against communication channel misalignment, the used CsPbBr3 NCs provide another advantage of converting transmitted UVC light into a green color that matches the peak absorption of the widely available Si-based detectors. We evaluated the feasibility of the reported wide FoV optical detectors by including them in deep UV OWC systems, deploying non-return-to-zero on-off keying (NRZ-OOK) and orthogonal-frequency division multiplexing (OFDM) modulation schemes. The NRZ-OOK and OFDM schemes exhibit stable communication over the 60° FoV, providing data transmission rates of 100 Mb/s and 71.6 Mb/s, respectively, a unique capability to the reported design.

Next generation PON architecture using PD-NOMA employing OAM and WDM multiplexing

In this paper, we propose and experimentally demonstrate the efficacy of a next-generation passive optical network (PON) architecture for free space optical link, which utilizes power domain (PD) non-orthogonal multiple access (NOMA) along with simultaneous orbital angular momentum (OAM) mode and wavelength-division multiplexing (WDM) techniques. In this proposed architecture, many optical network units (ONUs) are accommodated by clustering them based on their power budgets and their data streams are allocated with different powers accordingly. The clustered ONUs are served with multiple OAM modes over multiple wavelengths to maintain high capacity, low latency, and increased reliability. As a proof-of-principle experimental demonstration of the proposed architecture, we have experimentally emulated two ONU clusters having a power ratio of (near:far)−3.17dB for implementing the PD-NOMA system for downlink. Each ONU cluster uses three 50 GHz spaced WDM channels, where each WDM channel carries two multiplexed OAM modes having opposite topological charge (l=±1 and ±2) values. Each cluster’s six ONUs is delivered with a 10 Gbps On-Off Keying (OOK) signal. We have demonstrated that all users can achieve a pre-forward error correction (pre-FEC) bit error rate (BER) below the 7% overhead-FEC (OH-FEC) BER limit of 3.8×10−3. We have also measured the x-talk due to WDM and mode multiplexing, and it has been revealed that the main contribution to the power penalty (relative to the no cross-talk condition) comes from OAM mode cross-talk.

Design of remote temperature monitoring system tool using VHF waves based on VFC LM331

A remote temperature monitoring system has been designed and manufactured using VHF waves based on VFC LM331. This remote temperature monitoring system uses the IC LM35 temperature sensor. The technique used for sending data uses radio waves on VHF lines with an OOK (On-Off Keying) modulation system. So that the analogue voltage signal from the sensor can be modulated and transmitted by the transmitter, the voltage must be converted to frequency using a VFC LM331. From the results of measuring the accuracy of the design tool, it was found that the design tool worked well at a temperature of 0 oC up to 99% compared to a reference device. The range of the system that has been designed is much influenced by the frequency of the transmitter used, the more users on that frequency, the shorter the range. The farthest distance that can be reached is around 120 meters at a frequency of 80 MHz while at a frequency of 89 – 106.3 MHz it can only reach around 48 meters.

Simultaneous Terahertz Imaging With Information and Power Transfer (STIIPT)

Terahertz (THz) band transmission has the potential to revolutionize future-generation wireless networks by jointly meeting communication and non-communication demands of their connected devices. Recent advances in THz semiconductor technologies and antenna design are closing the THz band gap in millimeter-scale devices which are often battery-limited. The localization of these mobile devices in future wireless networks is of paramount significance for beamforming to overcome THz propagation loss. Consequently, prospective signal processing techniques with co-design architectures are emerging either for joint communication and sensing or for simultaneous information and power transfer. In this paper, we present a novel approach toward Simultaneous Terahertz Imaging with Information and Power Transfer (STIIPT) from a base station transceiver to an Integrated Receiver (IntRx). Leveraging the proposed non-linear rectenna model for energy harvesting, a customized On-Off Keying (cOOK) modulation scheme is proposed for simultaneous communication through a non-linear THz channel while generating a radar-like image to localize the IntRx acting as a target. The proposed theoretical models are corroborated with simulations using a THz band GaAs Schottky diode to demonstrate STIIPT performances which also emphasize the significance of ranging information to optimize rate–energy transfer tradeoff under the cOOK modulation scheme.

Image transmission performance analysis through free space optical communication link using coherent QPSK modulation under various environmental conditions

AbstractFree space optics (FSO) technology has been used recently in many applications due to its various advantages such as high bandwidth, easy deployment, high security, free installation license and immunity to electromagnetic interference. However, this type of communication is vulnerable to meteorological conditions such as rain, haze and fog which significantly degrade the system's efficiency. To enhance the effectiveness of the FSO systems, Quadrature Phase Shift Keying (QPSK) modulation based on coherent detection constitutes a promising technique for achieving high spectral efficiency and long‐distance FSO links with the characteristics of low‐cost implementation and simple design. This work aims to investigate the performance of FSO communication links on image transmission under the presence of atmospheric attenuations. A comparative study has been made using QPSK modulation scheme and on–off‐keying (OOK) modulation scheme to estimate the maximum range that was used to recover an RGB transmitted image over an FSO link under different meteorological weathers. The obtained results clearly show that the quality of the received image has degraded significantly during transmission through free space yielding to limit the propagation range. Moreover, the proposed FSO communication system performs well when using QPSK modulation rather than OOK modulation in different environmental conditions. Thus, to improve the quality of the received image under adverse fog weather condition, high power and small beam divergence angle have been suggested to increase system's performance. The proposed solution increases the communication range of the FSO link by 230 m and 100 m for moderate and heavy fog, respectively.

Self-Pilot Tone Based Adaptive Threshold RZ-OOK Decision for Free-Space Optical Communications

This paper studies a novel self-pilot tone based adaptive threshold return-to-zero on-off keying (RZ-OOK) decision for free-space optical (FSO) communications. RZ-OOK has the characteristics of impulse series in the spectrum. Therefore, these impulses can be utilized as the pilot tones of the transmitted signal to convey the channel state information (CSI) of FSO links. Then, the CSI signal is extracted using a local oscillator (LO) with the frequencies of the impulse series and low pass filter. Finally, the adaptive threshold decision (ATD) is realized by assigning optimized weight factors into the extracted CSI signal. The proposed adaptive threshold RZ-OOK decision was studied in simulation under various pulse durations of RZ-OOK signal and frequencies of LO. Simulation results demonstrated that RZ-OOK with the proposed impulse tone-extracted CSI signal under optimized weight factor performs close to the conventional ATD under precise CSI knowledge.

Semiconductor Optical Amplifier (SOA)-Driven Reservoir Computing for Dense Wavelength-Division Multiplexing (DWDM) Signal Compensation

Optical signal processing (OSP) technology is a crucial part of the optical switching node in the modern optical-fiber communication system, especially when advanced modulation formats, e.g., quadrature amplitude modulation (QAM), are applied. However, the conventional on–off keying (OOK) signal is still widely used in access or metro transmission systems, which leads to the compatibility requirement of OSP for incoherent and coherent signals. In this paper, we propose a reservoir computing (RC)-OSP scheme based on nonlinear mapping behavior through a semiconductor optical amplifier (SOA) to deal with the non-return-to-zero (NRZ) signals and the differential quadrature phase-shift keying (DQPSK) signals in the nonlinear dense wavelength-division multiplexing (DWDM) channel. We optimized the key parameters of SOA-based RC to improve compensation performance. Based on the simulation investigation, we observed a significant improvement in signal quality over 10 dB compared to the distorted signals on each DWDM channel for both the NRZ and DQPSK transmission cases. The compatible OSP achieved by the proposed SOA-based RC could be a potential application of the optical switching node in the complex optical fiber communication system, where incoherent and coherent signals meet.

Improving the data rate for long distance visible light communication using h-BN/CdZnSeS@ZnSeS quantum dot composite.

Quantum dots (QDs) are exploited in visible light communication (VLC) due to their unique optical properties. However, it is still a challenge to conquer heating generation and photobleaching under prolonged illumination. In this paper, we proposed to utilize hexagonal boron nitride (h-BN) nanoplates to improve the thermal stability and photo stability of QDs and long-distance VLC data rate. After heating to 373 K and cooling to the initial temperature, photoluminescence (PL) emission intensity recovers to 62% of the original intensity and after 33 hours of illumination, PL emission intensity still maintains 80% of the initial intensity, while that of the bare QDs is only 34% and 53%, respectively. The QDs/h-BN composites perform a maximum achievable data rate of 98 Mbit/s by applying on-off keying (OOK) modulation, while the bare QDs are only 78 Mbps. In the process of extending the transmission distance from 0.3 m to 5 m, the QDs/h-BN composites exhibit superior luminosity corresponding to higher transmission data rates than bare QDs. Particularly, when the transmission distance reaches 5 m, the QDs/h-BN composites still show a clear eye diagram at a transmission rate of 50 Mbps while the eye diagram of bare QDs is indistinguishable at 25 Mbps. During 50 hours of continuous illumination, the QDs/h-BN composites keep a relatively stable bit error rate (BER) at 80 Mbps while that of QDs continuously increase, and the -3 dB bandwidth of QDs/h-BN composites keep around10 MHz while the bare QDs decrease from 12.6 MHz to 8.5 MHz. After illumination, the QDs/h-BN composites still indicate a clear eye diagram at a data rate of 50 Mbps while that of pure QDs is indistinguishable. Our results provide a feasible solution for realizing an enhanced transmission performance of QDs in longer-distance VLC.

Long-range underwater optical wireless communication systems in turbulent conditions.

In this paper, single-photon avalanche diode (SPAD) photodetectors are leveraged across long-range underwater optical wireless communication (UOWC) systems for non-turbid waters, i.e., pure sea and clear ocean, in weak turbulent conditions. We derive the bit error probability of the system using on-off keying (OOK) along with two types of SPADs: ideal, i.e., with zero dead time, and practical, i.e., with non-zero dead time. In our investigations for OOK systems, we study the effect of using both the optimum threshold (OTH) and constant threshold (CTH) at the receiver. Furthermore, we analyze the performance of systems using binary pulse position modulation (B-PPM) and compare them with the ones using OOK. Our results are presented for practical SPADs and both active and passive quenching circuits. We demonstrate that OOK systems with OTH perform slightly better than B-PPM. However, our investigations reveal that in turbulent conditions where using OTH may be challenging, employing B-PPM can be preferable to OOK.

Deep learning based BER improvement for NOMA-VLC systems with perfect and imperfect successive interference cancellation

This paper focuses in the improvement of the BER performance of multiple-input multiple-output (MIMO) systems is investigated utilizing non-orthogonal multiple access-visible light communication (NOMA-VLC). Applying multi-user downlink MIMO-NOMA-VLC system within equal gain combiner at the receiver is used with two types of modulation; On–Off Keying (OOK) and L-Pulse Position Modulation, with L = 4 and 8. The perfect and imperfect successive interference cancellation scenario is used in this system, and the scenario is considered for two and three users. Our proposed framework is divided into two stages. First, data is collected using the MATLAB software. Second, two deep learning models (DLMs); ResNet50V2 and InceptionResNetV2 which are trained and tested. Python software is then used to develop and train the DLMs. The obtained results assures the superiority of ResNet50V2 over InceptionResNetV2, in different cases and for all users. The BER performance is also studied versus α for two and three users OOK modulation single-input single-output (SISO), (2 × 2) and (3 × 2) MIMO-NOMA-VLC systems based on the two DL techniques; ResNet50V2 and InceptionResNetV2. Again, ResNet50V2 achieves better results than InceptionResNetV2. The obtained results are compared with the previously published ones, showing that the proposed system and techniques achieve better results.

Multi-Level Logarithmic Amplification-Based Fixed Threshold Circular Polarized On-Off Keying Detection for Free-Space Optical Communications

This study investigates a multi-level logarithmic amplification (MLA)-based fixed threshold circular polarized on-off keying (CP-OOK) detection for free-space optical (FSO) communication links. OOK signal is polarized into a single circular polarization state by a linear polarizer (LP) and a quarter-wave plate (QWP). In the receiver terminal, firstly, circular polarization is transformed into linear polarization utilizing QWP without polarization coordinates alignment between transmitter and receiver. Then, the background noises are decreased by polarization filtering using LP. Then, CP-OOK signal intensity variation is eliminated by nonlinear gains from MLAs in the low gain nonlinearity condition. Finally, fixed threshold decision (FTD) is realized by optimizing cascaded LAs to reduce the extinction ratio distortion of the CP-OOK signal. The proposed CP-OOK transmission is analyzed under various strengths of turbulence channel and different configurations of MLAs. Simulation results demonstrated that the proposed CP-OOK signal was effectively detected by FTD with optimized MLAs.

A Novel ML-Based Symbol Detection Pipeline for Molecular Communication

Molecular Communication (MC) is the process of sending information by the use of particles instead of electromagnetic (EM) waves. This change in paradigm allows the use of MC in areas where EM transmission is undesirable. These include underground, underwater and even intra-body communications. While this novel paradigm promises new areas for communication, one of the major setbacks is its relatively low throughput caused by the propagation speed. This can be improved by decreasing the symbol duration; however, this can be a detriment to the correct decoding of symbols. This paper proposes a novel symbol detection pipeline to increase the possible throughput without increasing the error rate of the communication. This is based on a machine-learning algorithm for classification tasks using an L-point discrete time moving average filter and a wide range of features. Extensive simulations with long sequences at different signal-to-noise ratio (SNR) values were performed to determine how well the proposed method detects symbols. The results show that our method can detect symbols received when On-Off Keying (OOK) modulations are used with a 10 dB gain, even when transmissions with untrained SNR values occur.

A Long-Distance Underwater Wireless Optical Link Enabled by a Solar Array With a Baseline Compensator

In this paper, a self-designed solar cell-based optical detector is proposed and demonstrated in a long-distance underwater wireless optical communication (UWOC) link. Benefitting from a large detection area, the detector could successfully capture optical signals with a received power density of 5.62 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . To resist the baseline drift caused by the low-frequency cut-off of the system, an envelope detector-based baseline compensator is proposed. Comparing with digital solutions, the proposed compensator could be established in analog domain with common electronic components. With the compensator, a frequency domain equalizer (FDE) and a maximum ratio combing (MRC) algorithm, an 18 Mbps non-return-to-zero (NRZ) on-off keying (OOK) modulated link over an 80 m underwater channel is finally achieved. The proposed baseline compensator could compensate the low-frequency components effectively with low cost. Moreover, under a strong ambient light of approximately 1200 lux, the performance of the link shows little degradation. Our work shows a potential solution of long-distance UWOC system with ambient light tolerance, which is compatible with practical environment.