Of On-off Keying Research Articles

Joint WDM and OAM Mode Group Multiplexed Transmission Over Conventional Multimode Fiber

To exploit the advantages of multimode fiber (MMF)-based transmission and to improve the overall capacity, transmission of OAM modes over a single wavelength needs to be replaced by multichannel transmission with the proper experimental demonstration in terms of achievable bit error rates (BER), cross-talk(x-talk), etc. over the entire transmission band. In this paper, we have experimentally shown the successful transmission of two OAM mode groups multiplexed signals jointly with three channels using wavelength division multiplexing (WDM) over a 1 km conventional MMF, namely OM3. In this experimental study, each OAM mode over each WDM channel uses 10 Gbps of on-off keying (OOK) modulation format. At the receiver end, the achieved bit error rate (BER) is found well below the required pre-FEC BER of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3.8\times 10^{-3}$</tex-math></inline-formula> without using any MIMO-DSP. To establish the efficacy of the signal transmission, the time evolutions of OAM mode x-talk and BER over wavelengths spanning the entire C-band have been experimentally measured. Under the influence of different x-talks, the BER performances of all three 50 GHz-spaced WDM channels for both OAM modes are measured. With proper adjustment of polarization at the receiver end, a BER value below the pre-FEC threshold is achieved over 900 seconds. The experimental results also revealed that the power penalty contribution of WDM x-talk is negligible compared to OAM mode x-talk.

Cooperative VLC system using OOK modulation with imperfect CSI

Visible light communication (VLC) is one of the aspirant tools for high data rate communication. VLC system employed in a large room requires cooperative transmission for reliable end-to-end communication. Cooperative communication (CC) utilizes several relay approaches to forward the message from transmitter to envisioned destination, and thus, attains high spatial diversity gain, reduced power consumption, improved transmission reliability, increased coverage area, and potentially enhanced system capacity. This paper investigates the error performance of on-off keying (OOK) modulated VLC system in a cooperative environment, where the relay adopts decode-and-forward (DF) protocol. In particular, two cases of cooperative VLC system are considered; (1) Case I, in which the destination node is in direct link with the previous node while in blockage or outside the field of view (FoV) for all the other nodes, (2) Case II, in which the destination node is in direct link with all upstream nodes. For the practical suitability of the system, the imperfect channel state information (CSI) is considered for performance analysis. The mathematical expressions for bit-error-rate (BER) of the considered systems are derived in the presence of perfect and imperfect CSI. The error performance of the considered systems is investigated for the various system parameters such as signal-to-noise ratio (SNR), channel estimation error and receiver locations. The result shows that for the case of blockage, i.e., Case I, the end-to-end communication for two-hop network can be established with the BER of 2 × 10−4 at 128 dB SNR and channel estimation error of 10−12. Further, in the case of non-blockage, i.e., Case II, the result shows that for two-hop communication, the BER in cooperative transmission improved to 5 × 10−5 in compare to 5 × 10−2 in direct communication, at 128 dB SNR and 10−12 channel estimation error. The extensive simulations are carried out to verify the analytical findings.

Underwater quasi-omnidirectional wireless optical communication based on perovskite quantum dots.

In this paper, a quasi-omnidirectional transmitter is proposed and demonstrated for underwater wireless optical communication (UWOC) using the photoluminescence of perovskite quantum dots (QDs). The proposed transmitter, without complex driving circuits, is compact and reliable thanks to the lens-free design. The system performance is tested in a 50-m swimming pool with a water attenuation coefficient of 0.38 dB/m. The maximum data rates of on-off-keying (OOK) signals over 10-m and 20-m transmission distances can reach 60 Mbps and 40 Mbps, respectively. When four clients are adopted in a code division multiple access (CDMA) based UWOC network, the maximum data rates of each client can reach 10 Mbps and 7.5 Mbps over 10-m and 20-m underwater channels, respectively. The system can meet the requirements of the last meter end-user access in the Internet of underwater things (IoUT) and underwater optical cellular network systems.

Serial-parallel combined all optical sequence matching system using highly nonlinear fibers for photonic firewall

Photonic firewall which can directly conduct intrusion detection and security protection in optical layer is an important network security device. The core part of photonic firewall is all optical sequence matching system. It is responsible for recognizing the target sequence in the input data sequence. In a real environment, the length of the target sequence is not fixed and may be dynamic changing. However, most of existing optical sequence matching systems can only handle the target sequence with a fixed maximum matching length. When the length of a target sequence exceeds the given maximum length, the performance of the system will deteriorate and even the system stops working. How to utilize the existing all optical sequence matching system with a fixed maximum matching length to handle the target sequence with a longer length becomes an important research focus. Moreover, the existing all optical sequence matching systems using all optical logic gates can only handle the optical signal with the modulation format of on-off keying (OOK). In this paper, we design a serial-parallel combined all optical sequence matching system using highly nonlinear fibers (HNLF). It can recognize the target sequence with the length of k times more than the existing all optical sequence matching system. Moreover, this system supports handling the optical signal with the modulation format of binary phase shift keying (BPSK). The simulation platform is constructed by the software of VPItransmissionMaker. Simulation results show that the serial-parallel combined all optical sequence matching can recognize target sequences with the length of 8bits and the modulation format of BPSK at 100 Gbps and 200 Gbps.

Mismatched Filters for Incoherent Pulse Compression in Laser Radar

A pulsed laser system is considered for long-range target detection. Single-pulse power received from a target may be low compared to the noise and background clutter power. Due to long-range and short laser wavelength, multi-pulse coherent processing is not possible, so incoherent detection is employed. Incoherent pulse compression sums received power from numerous pulses to increase SNR while maintaining single pulse range resolution. Following Levanon, aperiodic burst waveforms of on-off Keying (OOK) modulated transmitted pulses are derived from binary codes with optimal auto-correlation minimum integrated sidelobe level and minimum peak sidelobe level codes. Pulse compression uses real, continuous mismatched filters of lengths equal to or greater than the OOK code length. Filter values minimize a weighted sum of ISL and filter output power, the latter to increase SNR gain relative to that of a single pulse. Weighting can be adjusted to lower ISL for multiple target discrimination or to increase SNR gain for dim targets. A simple evolutionary modulation of the initial OOK code exchanges pairs of dissimilar samples to keep the number of on samples from decreasing and improves ISL performance. A very fast filter calculation is employed that permits an exploration of a wide variation in parameters.

Deep Learning for Improving Performance of OOK Modulation Over FSO Turbulent Channels

Free space optical (FSO) communication technology has become increasingly advanced with capabilities of high speed, high capacity, and low power consumption. However, despite the great potential of FSO, its performance is limited in a turbulent atmosphere. Atmospheric turbulence causes scintillation in the FSO propagated signals, leading to an increase in the bit error rate (BER) performance of the recovered signals at the receiver. In this paper, we demonstrate that the use of deep learning (DL) detection methods could overcome these limitations. We present a new detection method of on-off keying (OOK) modulated signals by using different models of DL over different strength FSO turbulent channels, without the need for prior knowledge of the parameters of the channel. The demonstrated DL decoders improve the performance of the FSO turbulent channel and decrease the power consumption. Moreover, the demonstrated DL models also work faster than maximum likelihood (ML) methods with perfect channel estimation decoders, with even slightly better performance because of the turbulence, thus enabling realization of FSO over turbulent atmospheric channels.

Blind Signal Detection Under Synchronization Errors for FSO Links With High Mobility

We consider the use of free-space optical communication for fast moving platforms such as high-speed trains, where the sampling clock offset is randomly changing, in addition, the receiver does not have any information on the instantaneous channel fading coefficient. By employing multiple samplers at the receiver, we propose a class of sequence detection methods for the case of On-Off keying (OOK) signaling without using any training sequence. First, we study maximum likelihood-based detection, which has a relatively high-computational complexity. Second, by employing generalized likelihood ratio test, we propose a more practical blind sequence detection method of reduced complexity. To further reduce the computational complexity, third, we propose a novel scheme that uses two wavelengths at the transmitter and differential blind detection at the receiver. Fourth, to benefit from diversity gain with this differential scheme, we consider the use of sufficiently different wavelengths along with sufficient spatial separation between the transmitters and/or the receivers, where we propose an efficient blind detection method. The pros and cons of the proposed detection methods are contrasted through numerical results and their processing loads are compared.

Receiver Design for OOK Modulation Over Turbulence Channels Using Source Transformation

For coherent detection of ON-OFF keying (OOK) symbols in free-space optical (FSO) communications, the receiver requires the instantaneous channel fading coefficients. To accurately detect OOK symbols over FSO channels without requiring transmission of pilot symbols, in the first part of this letter, we propose an expectation-maximization (EM)-based sequence detection (SD) method with low implementation complexity which is shown to be particularly suitable for fast FSO communication systems. In the second part of this letter, to remove the error floor and to improve the accuracy of the proposed detector, by utilizing a source information transformation we propose an EM-based SD for this state which significantly outperforms than classical EM-based method.

VCSEL-based differential modulation technique for high-speed gigabit passive optical networks

ABSTRACTWith the convergence towards 5G, optical networks need to be upgraded to support the emerging data tsunami. This work experimentally demonstrates the first real-time transmission of 20 Gbps over a class 10G 1550 nm vertical cavity surface emitting laser (VCSEL) in the context of on-off-keying (OOK) modulation format, by employing VCSEL differential drive mode technique, for adoption in high-speed gigabit passive optical networks (GPONs). Two OOK data streams each with 10 Gbps are differentially modulated onto a single VCSEL, therefore generating an aggregated data rate of 20 Gbps OOK signal. A receiver sensitivity of -13.36 dBm is experimentally achieved. Through extinction ratio optimization, an error free transmission over 24.7 km single mode fibre is attained, with a transmission penalty of 1.91 dB. Our proposed technique alleviates band-limitation of the VCSEL carrier, and doubles the channel data rate without replacing the transmitter optics.

Binary signaling design for visible light communication: a deep learning framework.

This paper develops a deep learning framework for the design of on-off keying (OOK) based binary signaling transceiver in dimmable visible light communication (VLC) systems. The dimming support for the OOK optical signal is achieved by adjusting the number of ones in a binary codeword, which boils down to a combinatorial design problem for the codebook of a constant weight code (CWC) over signal-dependent noise channels. To tackle this challenge, we employ an autoencoder (AE) approach to learn a neural network of the encoder-decoder pair that reconstructs the output identical to an input. In addition, optical channel layers and binarization techniques are introduced to reflect the physical and discrete nature of the OOK-based VLC systems. The VLC transceiver is designed and optimized via the end-to-end training procedure for the AE. Numerical results verify that the proposed transceiver performs better than baseline CWC schemes.

Transmission Performance of 112 Gb/s POLMUX QPSK Signal in OOK/DPSK WDM System

AbstractIn this article, the impact of cross-phase modulation (XPM) and cross-polarization modulation (XpolM) on transmission of 112 Gb/s polarization multiplexed quadrature phase shift keying (POLMUX QPSK) signal in a wavelength division multiplexing (WDM) system has been investigated. This WDM system comprises of on-off keying (OOK) or differential phase shift keying (DPSK) channels. It is observed that the effects of XPM and XpolM are greatly reduced in a hybrid system of co-propagating OOK and DPSK channels. This is due to the dominance of phase modulation of DPSK signals rather than the intensity modulated OOK signals. The error vector magnitude (EVM) of the received optical signal is evaluated for the increase in number of neighbouring OOK and DPSK channels respectively within a bandwidth of 350 GHz. Also, the effect of increase in bit rate for two neighbouring OOK and DPSK channels has been observed individually on the 112 Gb/s POLMUX QPSK signal. It is concluded that DPSK signals display an improvement of −9.44 dB in EVM over OOK signals when there are eight neighbouring channels in the transmission system.

Effect of different weather conditions on BER performance of single-channel free space optical links

This paper studies and compares the performance of on-off keying (OOK), pulse position modulation (PPM), digital pulse interval modulation (DPIM) and dual-header pulse interval modulation (DH-PIM) schemes in FSO channels in the presence of different weather conditions. The bit error rate (BER) curves for these modulations are simulated. Moreover, a performance comparison between these modulation techniques is provided. Generally, in the absence of turbulence OOK-NRZ (non-return-to-zero) and PPM is found to achieve a better BER performance as compared to DPIM and DHPIM. In the presence of fog, OOK-NRZ and PPM is better than DPIM and DH-PIM by approximately 1dB at BER 1e-3. While, in case of rain, OOK-NRZ and PPM is better than DPIM and DH-PIM by approximately 1.5dB at BER 1e-3. Moreover, in case of snow, OOK-NRZ and PPM is better than DPIM and DH-PIM by approximately 1.7dB at BER 1e-3. Additionally, in the presence of turbulence, in case of weak turbulence, OOK-NRZ and PPM is better than DPIM and DH-PIM by approximately 8dB and 10dB, respectively at BER 1e-3. Furthermore, in case of moderate turbulence, OOK-NRZ and PPM is better than DPIM and DH-PIM by approximately 6dB and 8dB, respectively at BER 1e-3. Finally, in case of strong turbulence, OOK-NRZ and PPM is better than DPIM and DH-PIM by approximately 3dB and 4dB, respectively at BER 1e-3.

Low-cost coherent UDWDM-PON by hybrid DBPSK/ASK-2 modulation

The coherent ultra-dense wavelength division multiplexed passive optical network (UDWDM-PON) has been widely studied recently, in which the envelop detection based coherent reception of on-off keying (OOK) signal has been shown to possess both high receiver sensitivity and tolerance against laser linewidth/chirp. In order to increase the spectral efficiency (SE) to 2bit/s/Hz, researchers formulated a hybrid DBPSK/ASK-2 modulation using the silicon Mach–Zehnder modulator (MZM), where both amplitude and phase modulation are employed. The experimental result shows that the proposed DBPSK/ASK-2 modulation is of better performance than PAM-4 at the same SE of 2bit/s/Hz. When the low-cost silicon MZM and DFB laser of 4-MHz linewidth are employed, the receiver sensitivity of DBPSK/ASK-2 exceeds that of the PAM-4 by about 5.7dB. This work can achieve about −46dBm receiver sensitivity at 2.5GBaud after transmission over 80-km standard single mode fiber (SSMF). The proposed DBPSK/ASK-2 modulation using low-cost silicon MZM and DFB laser is considered as a practical and reliable method for the future UDWDM-PON at the SE of 2bit/s/Hz.

Incoherent on-off keying with classical and non-classical light

We analyze the performance of on-off keying (OOK) and its restricted version pulse position modulation (PPM) over a lossy narrowband optical channel under the constraint of a low average photon number, when direct detection is used at the output. An analytical approximation for the maximum PPM transmission rate is derived, quantifying the effects of photon statistics on the communication efficiency in terms of the g((2)) second-order intensity correlation function of the light source. Enhancement attainable through the use of sub-Poissonian light is discussed.

Is blue optical filter necessary in high speed phosphor-based white light LED visible light communications?

Optical blue filter is usually regarded as a critical optical component for high speed phosphor-based white light emitting diode (LED) visible-light-communication (VLC). However, the optical blue filter plays different roles in VLC when using modulations of on-off keying (OOK) or discrete multi-tone (DMT). We show that in the DMT VLC system, the blue optical filter may be unnecessary, and even degrade the transmission performance (by reducing the optical signal-to-noise ratio (SNR)). Analyses and verifications by experiments are performed. To the best of our knowledge, this is the first time the function of blue filters in VLC is explicitly analyzed.

A new modulation scheme of visible light communication

In order to use white light emitting diode (LED) as a lighting source and communication part, a new modulation scheme called reverse dual header pulse interval modulation (RDH-PIM) is proposed for indoor visible light communications based on the analyses of the structures of on-off keying (OOK), pulse position modulation (PPM), digital pulse interval modulation (DPIM) and dual header pulse interval modulation (DH-PIM). After analyzing and comparing the symbol structure, bandwidth requirement and average transmission power of different modulation methods, the slot error rate is derived. Simulation results show that OOK has the minimum bandwidth, while RDH-PIM has the highest average transmission power and its bandwidth efficiency is obviously better than those of PPM and DPIM. Hence, RDH-PIM is superior in optical wireless communication systems.

Importance of noise models in FSO communications

Free-space optical (FSO) communication is an emerging technology which offers enormous bandwidth, license-free spectrum and highly secure link. Avalanche photodiodes (APD) are normally used for the detection of high-speed FSO signals, where the noise shows signal-dependent Gaussian noise (SDGN) distribution rather than the signal-independent Gaussian noise (SIGN) distribution. We investigate the use of on-off keying (OOK) and low density parity check (LDPC) code on the performance of a FSO communication system. We also provide a good comparison of FSO communication noise models considering a moderate atmospheric turbulence condition. We show that large gains are possible using an LDPC decoder (i.e. at a bit error rate of 10-3, there is a gain of about 6 dB considering the SDGN model in case of no turbulence condition at λ = 10 dB), when the channel state information (CSI) is known at the receiver. We develop an extrinsic information transfer (EXIT) chart to measure the decoder convergence with and without the effect of turbulence noise. It is also shown that the SDGN model should be considered for the optimum detection with significant gain of 2.5 dB at λ = 0 dB and about 1 dB at λ = 10 dB.

Packet error rate analysis of OOK, DPIM, and PPM modulation schemes for ground-to-satellite laser uplink communications

Performance of on-off keying (OOK), digital pulse interval modulation (DPIM), and pulse position modulation (PPM) schemes are researched for ground-to-satellite laser uplink communications. Packet error rates of these modulation systems are compared, with consideration of the combined effect of intensity fluctuation and beam wander. Based on the numerical results, performances of different modulation systems are discussed. Optimum divergence angle and transmitted beam radius of different modulation systems are indicated and the relations of the transmitted laser power to them are analyzed. This work can be helpful for modulation scheme selection and system design in ground-to-satellite laser uplink communications.

312.5 Mbit/s Visible Light Communication System Based on OOK Modulation

We report an indoor visible light communication (VLC) system by using of on-off-keying (OOK). Firstly, the magnitude of the channels frequency response was measured. Based on the measured data, we introduced the pre-equalization technology into the system. Finally, the system operated up to 312.5 Mbit/s with bit-error-ratios below 10-6. The results were achieved for illuminance levels recommended by lighting standards.

Receiver Architecture for Channel-Aided, OOK, APD-based FSO Communications Through Turbulent Atmosphere

The problem of optimum signal detection for the channel-aided free-space optics (FSO) communications is addressed. It is assumed that the avalanced-photo-detection (APD) is utilized for the direct-detection (DD) of on-off-keying (OOK) signals impaired by optical turbulence. The average primary photon count due to the background radiation is assumed to be large enough to allow for a Gaussian operation for the APD receiver. In the presence of large signal fluctuations, it is shown that the optimum structure, motivated by the maximum a-posteriori (MAP) rule, is a dual-threshold architecture where the thresholds are functions of the channel state. To remedy the channel effects, the channel state is estimated and the estimates are used to set the receiver thresholds, thereby resulting in a channel-aided scenario. Performance of the proposed optimum receiver is assessed in terms of the overall bit error rate. To assess performance, it is assumed that the turbulent channel obeys a Gamma-Gamma (GG) distribution and that the channel estimator yields an unbiased and efficient estimate of the channel state. This study shows that channel-aided reception reduces the error floor. Further, channel-aided receivers have error-floor-free signal ranges that are larger than those of the standard receivers'.