Intensity Modulation And Direct Detection Research Articles

Advanced nonlinearity equalizer with TC-NL-MLSE for transmitting beyond 200-Gb/s PAM-8 in IM/DD systems.

The severe band-limited effect resulted from the low-cost optical transceiver increases the channel memory length and the number of taps of the equalizers. Besides, the interaction of fiber dispersion and square-law detection introduce nonlinear distortions in intensity modulation and direct-detection (IM/DD) transmission systems. The serious band-limited effect and nonlinear distortions degrade the transmission performance and bring challenges to current equalizers for low-complexity implementation. In this paper, we propose a trellis-compression nonlinear maximum likelihood sequence estimation (TC-NL-MLSE) algorithm to compensate the linear and nonlinear distortions with lower complexity. In the TC-NL-MLSE, we introduce a polynomial nonlinear filter (PNLF) to partly compensate both the linear distortions and nonlinear distortions. Then, we establish a look-up-table (LUT) to calculate the nonlinear branch metric (BM). To simplify the calculation, two or three levels with the highest probabilities are selected according to decision thresholds for each symbol to compress the state-trellis graph (STG). This significantly reduces computational complexity on BM calculations especially for high-order modulations. We conduct experiments to transmit beyond the 200-Gb/s PAM-8 signal over 2-km standard single mode fiber (SSMF) at C-band. The TC-NL-MLSE outperforms the reduced-state MLSE with PNLF, and can reach the 7%-overhead hard-decision forward error correction threshold. Moreover, the TC-NL-MLSE reduces the complexity by 97% compared with standard LUT-MLSE, limiting the multipliers around 100 at the expense of only 0.2-dB receiver sensitivity penalty.

High-speed PAM4 transmission using directly modulated laser and artificial neural network nonlinear equaliser

Due to its simplicity, low-cost and small footprint, intensity modulation and direct detection (IM/DD) using directly modulated lasers (DMLs) remains the most widely-adopted optical transmission scheme for short-reach applications. However, when the data rate increases to 100 Gb/s and beyond, the DML nonlinearity and fibre chromatic dispersion become major factors that limit system performance. In this paper, we show that artificial neural networks (ANNs) are an effective nonlinear equaliser for enhancing the transmission performance of high-speed IM/DD systems using DML. More specifically, for 56 Gbaud PAM-4 transmission system, a low-complexity ANN equaliser with only 1 hidden layer and 10 neurons can increase the receiver sensitivity at KP-4 FEC limit in comparison with FFE-15 by approximately 1 dB at dispersion of −60 ps/nm and ＋20 ps/nm. In addition, we also show that ANN equaliser outperforms the commonly used Volterra equaliser for 56 Gbaud PAM-4 transmissions.

Comparison of low-complexity sparse and weight-sharing nonlinear equalizers for C-band 100-Gbit/s DSB PAM-4 transmission over 60-km SSMF.

To cope with the nonlinear distortions and the chromatic dispersion (CD) induced power fading in double-side band (DSB) intensity modulation and direct detection (IM/DD) transmission systems, high-performance Volterra nonlinear equalizers (VNLEs) including Volterra feed-forward equalizer (VFFE) and Volterra decision-feedback equalizer (VDFE) are widely applied. However, the conventional VNLEs have high computational complexity, especially for longer memory lengths. In this paper, based on sparse and weight-sharing strategies for significant kernel reduction, we propose four low-complexity NLEs including a sparse diagonally pruned VDFE (S-DP-VDFE), a sparse diagonally pruned absolute-term DFE (S-DP-ATDFE), a weight-sharing DP-VDFE (WS-DP-VDFE), and a weight-sharing DP-ATDFE (WS-DP-ATDFE), and present a comprehensive comparison among them in terms of computational complexity and bit error ratio (BER) performance in a C-band 100-Gbit/s PAM-4 transmission system over 60-km standard single-mode fiber (SSMF). The experimental results show that the proposed S-DP-VDFE and WS-DP-VDFE not only exhibit comparable performance with the conventional DP-VDFE but also reduce the complexity by 54.5% and 45.9%, respectively. While the proposed S-DP-ATDFE and WS-DP-ATDFE yield lower complexity at the expense of a slight performance degradation. Compared with the proposed S-DP-VDFE, S-DP-ATDFE, and WS-DP-VDFE, the proposed WS-DP-ATDFE with the lowest number of real-valued multiplications of 45 achieves up to 90.9%, 81.6%, and 95.8% complexity reduction, respectively, at the 7% hard-decision forward error correction (HD-FEC) BER limit of 3.8 × 10-3. The proposed low-complexity WS-DP-ATDFE shows great potential in low-cost and high-performance IM/DD optical transmission systems.

Error-Controlled Iterative Algorithms for Digital Linearization of IMDD-Based Optical Fibre Transmission Systems

In intensity-modulation and direct-detection (IMDD) single-mode fibre (SMF) transmission systems, the nonlinear operation of square-law detection causes signal-signal beating interference (SSBI) that considerably limits the signal transmission capacity versus reach performance of the systems. To address this challenge, an error-controlled iterative algorithm (ECIA) with extra decision thresholds is proposed to digitally linearize the IMDD transmission systems. In the ECIA, instead of amplitude errors used in previously reported algorithms, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{Q}}}^{ - 2}$</tex-math></inline-formula> factor is utilized as an objective function, along with the proposed stochastic gradient descent (SGD) optimization of the thresholds for symbol decision. The thresholds can be adaptively adjusted to reduce decision errors during iterations. To improve the algorithm's adaptivity to various system operation conditions, new constraints are also introduced including maximum step size and/or sign of threshold variation. By making use of the identified optimum key parameters of the ECIA, numerical investigations are conducted of the effectiveness of the proposed scheme in supporting 100 Gb/s 4-level pulse amplitude modulation (PAM4) transmissions over 80 km standard SMFs. Results show that compared with the previously reported decision-directed data-aided iterative algorithm (DD-DIA), the ECIA significantly reduces the power/optical signal-to-noise ratio (OSNR) penalty, required minimum number of iterations (convergence rate) and improves the wavelength drift tolerance. For the ECIA, an OSNR penalty of ≤3.8 dB (10% overhead) and a minimum iteration count of 50 are observed for up to 400 km SMF transmissions, showing its robustness to accumulated dispersions of long fibres. More importantly, a pilot-free operation (0% overhead) is also feasible at a cost of a slightly increased OSNR penalty of ≤0.5 dB.

Real-Time GB-OFDM Signal Generation/ Reception Using Image Spectra and Undersampling for IMDD System

We proposed and experimentally demonstrated a low-complexity generation and reception scheme for guard-band orthogonal frequency-division multiplexing (GB-OFDM) in intensity-modulation and direct-detection (IMDD) transmission systems. The image spectra that arise in the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> Nyquist zone from a digital-to-analog converter (DAC) operating in radio-frequency mode is exploited to efficiently generate GB-OFDM signal. In the receiver, the analog-to-digital converter (ADC) undersampling technique is applied to recover the baseband OFDM signal. The sampling rate of DAC/ADC is reduced and no electrical mixer and oscillators are required for up/down-conversions. Moreover, the same digital signal processing algorithms as the baseband OFDM can be applied to the proposed GB-OFDM. The proposed GB-OFDM scheme is experimentally investigated in a real-time short-reach IMDD system. The results exhibit that the receiver sensitivity in terms of the received optical power of the proposed real-time 16/64QAM-encoded GB-OFDM system over 50 km standard single-mode fiber can be improved by 7.5/3.5 dB at the bit error rate of 3.8e-3, compared to the baseband OFDM.

Terabit Optical Wireless-Fiber Communication With Kramer-Kronig Receiver—Part II

A high speed optical wireless-fiber solution was proposed in part I of this research with applications such as network backhaul and data center links. The proposed system is based on the utilization of state-of-the-art modulation and multiplexing techniques in optical fiber and optical wireless communications, including multicore fibers (MCFs) and coherent detection based on Kramer-Kronig (KK) receivers. In this letter, we analyze the performance of the proposed system and compare it with an intensity modulation and direct detection (IM/DD) system. Superior performance of the KK receiver is shown for various modulation formats and optical amplification schemes. We also consider the eye-safety constraint for the optical power as a practical design factor. It is demonstrated that the position of optical amplifiers affects the multiplexing gain and achievable data rate when eye-safety constraint is imposed. Further important challenges for the practical deployment of the system are discussed.

Performance Assessments of Joint Linear and Nonlinear Pre-Equalization Schemes in Next Generation IM/DD PON

Nonlinear distortions in passive optical network (PON) systems degrade signal transmission performance. Joint linear and nonlinear pre-equalizers based on the Volterra series, memory polynomials and artificial neural networks (ANNs) are utilized to mitigate linear and nonlinear impairments. Centralized pre-equalization at the transmitter side of the optical line terminal (OLT) keeps the receiver side digital signal processing (DSP) at the optical network unit (ONU) simple. In this study, performance assessments of these three different pre-equalization schemes in intensity modulation and direct detection (IM/DD)-based 25-GBaud PON systems were evaluated. The joint linear and nonlinear pre-equalization schemes were based on the weight coefficients and the model obtained by channel estimation on the receiver side. We studied and compared the performance of three pre-equalization methods under various implementation conditions, such as received optical power (ROP), number of equalizer taps, and semiconductor optical amplifier (SOA) current. Besides, we studied the equalization performance under different modulation orders, which were applied for data rate optimization to support different power budgets, being the potential solutions for future PON systems with various fiber-reach and split-ratio distributions. As a proof-of-concept, the equalization performance of the 25-Gbaud signals modulated with non-return-to-zero (NRZ), four-level pulse amplitude modulation (PAM-4) and PAM-8 formats, corresponding to 25-, 50-, and 75-Gbps data rates, respectively, were tested. Both numerical simulations and experimental demonstrations were conducted to assess the performance of different pre-equalization schemes. With ANN pre-equalization, more than 4dB improvement in power budget was achieved for 25-GBaud PAM4 and PAM8 signals after 20 km fiber transmission. ANN-based pre-equalizer performed better than ANN-based post-equalizer even when the received signals were in low SNR. The power budgets of the 25-Gbaud NRZ, PAM4 and PAM8 signals after 20 km fiber transmission were 36.2 dB, 29.5 dB and 18 dB, respectively.

Augmented space signal detection method for IM/DD optical communication systems

The demand for high-speed data transmission has increased rapidly in data centers, leading to advanced optical communication technology innovation. At high modulation speed, severe linear and nonlinear signal distortions degrade the link performance. In order to increase the transmission capacity, a robust signal detection method based on quadratic discrimination in augmented space (QDAS) is proposed for high-speed intensity modulation and direct detection (IM/DD) optical communication systems. By projecting along the feature vector initially obtained by the objective function following the generalized Rayleigh quotient, signals with different features can be separated in augmented space. Subsequently, decision optimization is achieved through a quadratic discriminant model. Experimental verification is performed based on the 120 Gbps PAM8-modulated vertical-cavity surface-emitting laser (VCSEL) multimode fiber (MMF) optical link (100 m). The results show that, compared with the traditional Volterra nonlinear equalizer (VNLE), the proposed QDAS detection method shows improved and robust bit error ratio (BER) performance with the same complexity.

Mitigating end-to-end nonlinearity in LED-based VLC transceivers via an optical intensity feedback.

This Letter proposes a novel, to the best of our knowledge, intensity-modulation transmitter equipped with an optical intensity feedback (OIF) loop, which mitigates the holistic nonlinearity on both sides of intensity modulation and direct detection (IM/DD) transceivers from solely the transmitter side. In contrast to the recent effort on pre-distortion, we construct a negative feedback loop bridging the optical intensity of light-emitting diodes (LEDs) toward a sensor for nonlinearity perception to suppress the nonlinearity among all physical devices. In the meantime, we propose an analytical model for the feedback loop and an implementation scheme. The experimental results demonstrate a significant linearity improvement in the total harmonic distortion (THD) and the power gain flatness. More specifically, the average THD of the bipolar junction transistor (BJT)-based OIF transceiver is -49.4 dB (0.37%) and the minimum power gain variance is 0.0005, 0.0025% of the control group. As for the transceiver using a metal-oxide-semiconductor field-effect transistor (MOSFET), its average THD is -52.42 dB (0.25%) and the minimum power gain variance can reach 0.0026. Not only that, since the method only takes advantage of the negative feedback feature and dose not rely on any particular module, it has lower complexity and better applicability.

Performance and Complexity Analysis of Conventional and Deep Learning Equalizers for the High-Speed IMDD PON

To accommodate the exponential growth of network services in the five-generation (5G) and beyond wireless system, 50 Gb/s/λ passive optical network (PON) is developed for mobile xhaul applications. Intensity modulation and direct detection (IMDD) technology together with digital signal procession (DSP) is being considered as the promising solution for 50 Gb/s/λ PON due to its low cost, low power consumption, and compact footprint. Different DSP algorithms with varied structures are proposed for linear and nonlinear impairments compensation in the high-speed PON, while the performance and complexity analysis of these algorithms is still missing. To find the most efficient equalizers, in this paper, four conventional equalizers, including feed-forward equalizer, decision feedback equalizer (DFE), Volterra equalizer (Vol) and Volterra DFE equalizer (Vol-DFE), together with two deep learning equalizers namely fully-connected neural network, and long short-term memory equalizer are experimentally compared in a 10G optics based 50G-PON system in terms of the equalization performance, computation complexity, optimization difficulty, and generalization ability. After the evaluation of our proposed fair comparison algorithm, we consider Vol-DFE is the most efficient one considering both performance and complexity. Attributes to the strong and efficient equalization capability of Vol-DFE, C-band 50 Gb/s PAM-4 signal transmission can be supported in a 10G optics based IMDD system with a 3 dB bandwidth of 6.11 GHz, and a power budget up to 38 dB can be achieved.

Accelerating LMS-Based Equalization With Correlated Training Sequence in Bandlimited IM/DD Systems

As higher symbol rates are utilized in the intensity modulation and direct detection (IM/DD) scheme to meet the unrelenting growth of data traffic, overcoming the inter-symbol interference (ISI) induced by the limited bandwidth has become increasingly crucial. Channel equalization based on digital signal processing (DSP) is an effective solution, where least-mean squares (LMS) algorithm is adopted to adjust tap coefficients. However, the LMS algorithm usually has slow rate of convergence and requires lots of training symbols. This work proposes a novel training sequence to accelerate the LMS-based equalization. A first-order Markov chain (MC) is employed for sequence generation, which introduces correlation between samples and shapes signal spectrum. Compared with the conventional training sequence that consists of independent and identically distributed (i.i.d.) samples and has a white spectrum, the MC sequence enables faster convergence of tap coefficients and mean-squared error (MSE). Moreover, an experimental demonstration of a 43 Gbaud PAM-4 signal shows that the proposed sequence can achieve a lower pre-forward-error-correction (pre-FEC) bit error rate (BER) than that of the i.i.d. sequence with the same length. When the PAM-4 signal is transmitted over a 5-km standard single mode fiber (SSMF) with 6-dB system bandwidth of 10 GHz, more than 70% training sequence length reduction can be attained. When the fiber length is increased to 10 km and the signal suffers from severe power fading, more than 48% reduction can be achieved.

ML-Assisted Equalization for 50-Gb/s/λ O-Band CWDM Transmission Over 100-km SMF

We propose and demonstrate a bidirectional Vanilla recurrent neural network (Vanilla-RNN) based equalization scheme for O-band coarse wavelength division multiplexed (CWDM) transmission. Based on a 4 × 50-Gb/s intensity modulation and direct detection (IM/DD) system, we demonstrate the significantly better bit error rate (BER) performance of the Vanilla-RNN scheme over the conventional decision feedback equalizer (DFE) for both Nyquist on-off keying (OOK) and Nyquist 4-ary pulse amplitude modulation (PAM4) formats. It is shown that the Vanilla-RNN equalizer is capable of compensating for both linear and nonlinear impairments induced by the transceiver and the single-mode fiber (SMF). As a result, up to 100-km and 75-km SMF transmission can be achieved for OOK and PAM4 transmission, respectively. Furthermore, through the comparison with other equalization schemes, including the linear equalizer, 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -order Volterra equalizer, and Volterra+DFE, it is demonstrated that the Vanilla-RNN equalizer achieves the best BER performance. In the meantime, it also exhibits lower implementation complexity when compared to Volterra-based schemes. Our results show that the Vanilla-RNN scheme is a viable solution for realizing simple and effective equalization. This work serves as an exploration and offers useful insights for future implementations of reach-extended O-band CWDM IM/DD systems.

Robust Frequency-Domain Timing Offset Estimation for DCO-OFDM Systems

Optical wireless communication (OWC) systems suffer inter-symbol interference (ISI) in time domain due to light emitting diode (LED)’s limited bandwidth at transmitter. As intensity modulation and direct detection (IM/DD) is used, the transmitted signals are unipolar and real-valued rather than bipolar and complex-valued as in radio frequency (RF). Thus, it is challenging to employ the RF-based timing offset estimation for OWC. Also, there is no carrier frequency offset (CFO) like in RF. It is possible to estimate timing offset in frequency domain for two reasons. First, the effect of ISI in time domain is mitigated in frequency domain with correct timing offset estimation, robust against LED’s limited bandwidth. Second, the correlation between frequency-domain signals are high, as signals are bipolar and complex-valued in frequency domain rather than unipolar and real-valued in time domain. Therefore, we propose an effective frequency-domain timing offset estimation approach for direct current biased optical-orthogonal frequency division multiplexing (DCO-OFDM) OWC systems, where a small number of pilots are applied on few DCO-OFDM subcarriers, leading to very low spectral overhead. The property of no CFO is utilized to formulate an error function, by exploring the correlation between received signals and pilots. We propose a squared error function (SEF)-based timing offset estimation approach, conducted by maximizing the ratio of two successive variances of squared errors. Simulation results show that, with a very low training overhead of 0.48%, the proposed SEF-based approach provides a bit error ratio (BER) performance close to ideal case with perfect timing offset estimation, perfect channel state information and zero-forcing (ZF) equalization.

Analysis of Scintillation Effects on Free Space Optical Communication Links in South Africa

The performance of free space optical communication (FSOC) systems is severely degraded by certain atmospheric conditions prevalent in places where they are deployed, in spite of their numerous advantages. In clear weather conditions, the random fluctuation in the atmosphere’s refractive index causes substantial scintillation losses to transmitted optical signals. It is therefore imperative to estimate the potential losses due to atmospheric turbulence in locations where FSOC links are to be deployed. This will provide the necessary fade margin for FSOC systems so that designed links withstand such atmospheric disturbances. In this paper, statistical analysis of wind speed data collected for various cities of South Africa is used for calculating the corresponding refractive index structure parameter (Cn2). These Cn2 values, as well as the zero inner scale and infinite outer scale model and finite inner and finite outer scale model, are used in computing the scintillation indices not exceeding 50%, 99%, 99.9%, and 99.99% of the time for the investigated locations. The Lognormal and Gamma–gamma distribution models are then employed for the computational analysis of the irradiance fluctuations and channel characteristics while considering the effect of pointing errors for weak and moderate to strong turbulence regimes. Finally, derived mathematical expressions for outage probabilities and bit error rate (BER) performances for FSOC links, employing various intensity modulation and direct detection (IM/DD) schemes, are presented.

Rectangular Orthogonal Digital Filter Banks Based on Extended Gaussian Functions

Rectangular orthogonal digital filter banks (ODFBs) based on square-root-raised-cosine (SRRC) functions are widely utilised to realise flexible and elastic multi-channel aggregations for fixed and mobile networks. However, long digital filter lengths are required to minimize digital filtering-associated signal distortions. In this paper, based on the extended Gaussian function (EGF), a novel rectangular ODFB with excellent robustness against the short digital filter length-induced truncation effect is proposed. Optimum digital filter parameters of the EGF-based ODFBs are identified and verified in multi-channel hybrid OFDM-digital filter multiple access (DFMA) PONs based on intensity modulation and direct detection (IMDD). By making use of the identified optimum digital filter parameters, extensive comparisons of digital filter characteristics and corresponding multi-channel upstream PON performances are made between the EGF-based ODFBs and the SRRC-based ODFBs. It is shown that to achieve a similar aggregated upstream signal transmission capacity, the EGF-based ODFB reduces the digital filter DSP complexity by a factor of 4. For a digital filter length as short as 8, in comparison with the SRRC-based ODFB, the EGF-based ODFB introduces &gt;1.5 dB (&gt;0.8 dB) improvements in upstream receiver sensitivity for 5-bits (8-bits) DACs&#x002F;ADCs, increases the aggregated upstream signal transmission capacity by &gt;5.5&#x0025;, enlarges the ONU launch power dynamic range by &gt;2.5 dB and improves the frequency offset tolerance by a factor of &gt;1.5. In addition, the EGF-based ODFB also enhances upstream performance robustness against ONU symbol timing offsets.

Probabilistic shaping PAM8 based on Huffman coding distribution matching in optical interconnection

We propose and experimentally verify a Huffman coding distribution matching (HCDM) scheme in intensity modulation and direct-detection (IM/DD) optical interconnection applying low-density parity-check-coded (LDPC) probabilistic shaping 8-level pulse amplitude modulation (PS-PAM8). Not only superior to that of conventional PS methods in view of arithmetic distribution matching (ADM) as well as constant composition distribution matching (CCDM) with much lower computational complexity, the HCDM can also enable arbitrary symbol probability distribution (SPD) by utilizing an optimal Huffman binary tree. The binomial coefficients required for SPD can be precomputed and stored in a lookup table. The experimental results show that the HCMD PS-PAM8 shows remarkably promoted receiver power sensitivity and improved system tolerance to optical fibre nonlinear effects compared to the uniformly distributed signal with the same effective net rate.

Throughput improvement and PAPR reduction for OFDM-based VLC systems using an integrated STC-IMADJS technique

Visible light communication (VLC) is a technology that is currently being employed to achieve high data rates. Orthogonal frequency division multiplexing (OFDM) is a powerful scheme for intensity modulation and direct detection (IM-DD) that is becoming increasingly important. OFDM systems based on VLC are accomplished through the implementation of IM-DD constraints, including direct current biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), and asymmetrically clipped DC-biased (ADO-OFDM), among others. The OFDM technique based on VLC is inefficient in terms of spectral efficiency and has a high peak to average power ratio (PAPR). In this article, the symbol time compression-image adjust (STC-IMADJS) technique will be proposed for throughput maximization and PAPR reduction in the DCO-OFDM, ACO-OFDM, and ADO-OFDM systems. Furthermore, the STC technique enables the simultaneous transmission of two sub-carriers through Walsh spreading codes without inference between them. As a result, the OFDM symbol has been reduced by 50%. The IMADJS strategy reduces the high PAPR of transmitted signals by compressing large signals and expanding small signals, as long as the average power level remains constant after compression. Therefore, the proposed STC-IMADJS technique doubles the throughput as well as significantly reduces the PAPR for OFDM systems based on VLC. The simulation results are performed using Matlab-2021a for 1024 sub-carriers. As a result, the simulation results show that the proposed technique reduces the PAPR by 3.7 dB (86%), 8.16 dB (93%), and 1.81 dB (20%) for DCO-OFDM, ACO-OFDM, and ADO-OFDM systems respectively. Furthermore, the technique has a significantly lower computational complexity than conventional OFDM systems based on VLC. Finally, the measures of performance through this article are bit error rate and complementary cumulative distribution function.

Nonlinearity-aware PS-PAM-16 transmission for C-band net-300-Gbit/s/λ short-reach optical interconnects with a single DAC.

A nonlinearity-aware signal transmission scheme based on a low-complexity 3rd-order diagonally pruned absolute-term nonlinear equalizer (NLE) with weight sharing (DP-AT-NLE-WS) and rate-adaptable probabilistically shaped 16-level pulse amplitude modulation (PS-PAM-16) signal is proposed and experimentally demonstrated for C-band net-300-Gbit/s/λ short-reach optical interconnects. By replacing the multiplication operation with the absolute operation and applying weight sharing to reduce the kernel redundancy, the computational complexity of the proposed 3rd-order DP-AT-NLE-WS is reduced by >40% compared with the 3rd-order DP-Volterra NLE (DP-VNLE), DP-AT-NLE, and DP-VNLE-WS, with the achieved normalized general mutual information (NGMI) above a threshold of 0.857. Employing a commercial 32-GHz Mach-Zehnder modulator (MZM) and a single digital-to-analog converter (DAC), we demonstrate the single-lane transmission of 100-GBaud PS-PAM-16 signal using DP-AT-NLE-WS in the C band at record 370-Gbit/s line rate and 300.4-Gbit/s net rate over 1-km standard single-mode fiber (SSMF), achieving 21.2% (15.5%) capacity improvement over 100 (105)-GBaud PAM-8 transmission. To the best of our knowledge, this is the first net-300-Gbit/s intensity modulation and direct detection (IM/DD) short-reach transmission in the C band using commercially available components.

Performance analysis of serial relay orbital satellite optical communication over turbulent channels.

Optical space communication has been proven to be a reliable relay satellite transmission system. The difficulty that occurs in RF satellite communication (SatCom) can be alleviated by using free-space optical (FSO) or laser SatCom. In this work, we analyze a proposed laser downlink relay SatCom model with existing channel turbulence employing intensity modulation and direct detection (IM/DD), and amplify-and-forward (AF) technology and compare it with the optical direct link SatCom. Accounting for atmospheric attenuation and turbulence, the effect of model parameters such as zenith angle, receiver aperture radius, best number of optical ground stations (OGSs), and end-to-end operating wavelength on system performance is investigated for different OGS height scenarios. We provide exact closed-form expressions for the proposed model and optimize system performance by selecting the best number of OGSs using a selective diversity technique that can boost the system signal-to-noise (SNR) by up to 37 dB (99.9%).

Scalable Visible Light Indoor Positioning System Using RSS

This paper proposes a visible light positioning system that utilizes commercial Light-Emitting Diode (LED) lamps as transmitters and Silicon PIN photodiodes as receivers. The light signals are transmitted and received using Intensity Modulation and Direct Detection (IMDD). The lamps are modulated using On–Off Keying (OOK) with the Manchester code, and the medium access control is achieved by Time-Division Multiplexing (TDM). The position is estimated using trilateration based on the Received Signal Strength (RSS). The system’s scalability is accomplished by replicating primary localization cells composed of seven lamps and drawing on the neighborhood synchrony, exploiting the spatial multiplexing property of the light. A basic unit in the cell comprises three lamps forming a localization triangle; then, one primary localization cell shall consist of six triangles sharing lights among basic neighbor units. The cell prototype was implemented to prove the working principle of the system. Three estimation methods were used to compute the position: a deterministic approach based on least-squares regression, an Artificial Neural Network (ANN) per lamp, and an ANN for the complete system. The best per lamp estimator was the ANN, computing positions that reached an experimental accuracy of 2.5 cm under indoor conditions.