Return-to-zero Research Articles

Performance comparison of different intensity modulation formats for FSO systems

Abstract Intensity modulation (IM) formats are the legacy formats which are continuing to act as modulation formats of interest in fiber optic communication systems and optical networks. The IM formats have become formats of interest in free space optic communication (FSO) systems due to its simple generation and detection principle, thus making FSO system economical and easier to handle/operate under adverse and random characteristics of atmospheric channel. This paper compares the performance of different IM formats (with memory and without memory or memoryless). The IM formats considered here are non return to zero (NRZ), return to zero (RZ), carrier suppressed RZ (CSRZ), vestigial side band CSRZ (VSB-CSRZ), duobinary RZ (DRZ) and modified duobinary RZ (MDRZ). The comparative analysis investigates the effect of launch power and length of FSO channel at different data rates of 10 Gb/s and 40 Gb/s for single channel FSO system, with the help of simulations. The results discussed, depicts that VSB-CSRZ outperforms other modulation formats at 10 Gb/s and duobinary format has shown lesser degradation in system performance when bit rate increases from 10 Gb/s to 40 Gb/s.

Models and methods for RZ-signals distinction in non-Gaussian noise for information-measurement systems

Abstract Polynomial Decision Rules (DR) for the problems of discrete RZ (Return-to-Zero) signal distinction in asymmetric-excess non-Gaussian noise are proposed. A new approach is proposed, which is based on the use of a modified moment quality criterion of statistical hypothesis testing and the application of higher-order statistics to describe the characteristics of non-Gaussian noise. Simulation of the DR with different parameters of the signal and noise was carried out. It is shown that taking into account the coefficients of skewness and kurtosis of the non-Gaussian noise the efficiency of signal distinction increases with non-linear processing DR compared to known results, which are optimal for the Gaussian noise model. The conducted studies demonstrate a reduction in false decisions in the processing of RZ signals when considering the coefficients of skewness and kurtosis of non-Gaussian noise. Such an increase in efficiency can exceed twofold, depending on the noise parameters. It is shown that the efficiency of the proposed approach is much higher for small SNR (Signal-to-Noise Ratio) values, for example, less than 1.

Design and performance of WDM system for high-speed optical communication on different modulation formats

Abstract In this paper, the performance analysis of the WDM (wavelength division multiplexing) system on the optical fiber transmission link is proposed. High data transmission is possible by implementing a WDM optical communication system using different modulation formats. Firstly, the WDM optical communication system is designed on an Optiwave simulation tool and distortion in the optical fiber by “eye pattern analysis” is analyzed. Secondly, the optical SNR of the proposed WDM optical communication system is studied. Further, the bit-error rate (BER) plot is studied and optimization techniques are applied to enhance the proposed system for long-haul communication. Furthermore, the BER plots are analyzed by varying the length of the fiber and applying different coding techniques like NRZ (non-return zero), RZ (return to zero), QAM (quadrature amplitude modulation) etc. using the Optiwave simulation tool. The results obtained in the Optiwave simulation tool are validated by theoretical implementation in the MATLAB tool.

Analysis of inter-satellite optical wireless communication systems for enhanced data transmission in satellite constellations

This research focuses on the comprehensive performance analysis of inter-satellite optical wireless communication (IsOWC) systems, specifically tailored for high data rate applications in Earth observation satellites. The research employs OptiSystem 21.0 simulation software to model and analyze the IsOWC systems. The simulation scenario is set in a low Earth orbit (LEO) constellation, typical for Earth observation satellites. Various system parameters are systematically varied to assess their impact on performance. Modulation types, such as non-return-to-zero (NRZ) and return-to-zero (RZ) are analyzed for their influence on the quality (Q) factor. The study further explores the effects of different wavelengths, antenna apertures, transmitter output powers, and link distances on the IsOWC system performance. This research provides valuable insights into optimizing IsOWC systems for Earth observation satellites, contributing to the advancement of communication technologies in satellite networks. The research shows that the NRZ modulation consistently outperforms RZ modulation in terms of maximum Q factor and minimum BER across different antenna apertures and power levels. Additionally, shorter wavelengths exhibit improved performance, while larger antenna apertures contribute to enhanced signal quality. The relationship between transmitter power and data rate is also investigated, demonstrating the potential for achieving higher data rates with increased transmitter power. The findings guide the selection of parameters to achieve optimal performance, ensuring efficient data transfer and meeting the demands of contemporary Earth observation missions. This study provides conclusive evidence that the 1350 nm wavelength outperforms the 1550 nm wavelength in reliable and high-data-rate optical wireless communications, offering higher received power, superior signal quality, and lower bit error rates. This makes it a preferred choice for systems in challenging space environments and could enhance future satellite communication architectures.

A fiber-wireless integration approach in WDM-PON architecture, boosted with polarization multiplexing and optical frequency comb source

Abstract The paper discusses an optical frequency comb source (OMCG)-enabled hybrid single mode fiber (SMF) and free space optical (FSO) communication system (fiber-wireless) delivering a total capacity of 96 Gbps by incorporating polarization division multiplexing (PDM) in passive optical network (PON) architecture. For the accomplishment of PDM, three diverse states of polarization (SOPs) are explored such as 00, 450, and 900. Performance investigation of proposed system is conducted for assessing Q factor and BER by exploring the different modulation formats in proposed system such as modified duo-binary return to zero (MDRZ), return to zero (RZ), compressed spectrum RZ (CSRZ), and non-RZ (NRZ). Results revealed that presented design can cover 30 km SMF + 3.4 km FSO range by incorporating MDRZ due to its spectral efficient and dispersion tolerant properties.

Analyzing the phase and amplitude noise of RZ, NRZ and RF DACs

This article considers a multi-mode RF DACs phase and amplitude noise for non-return-to-zero (NRZ), return-to-zero (RZ), and mix/RF reconstruction waveforms under the assumption that two switch pairs (or two channels) in each current switch cells are alternately active in every clock cycle, Analysis shows that each channel of multimode DAC is completely characterized with RZ mode, and all other modes can be derived from this mode, in particular NRZ mode is not a complete analog of conventional DAC performance when reconstruction pulse duration and period are equal. When determining phase and amplitude noise of multi-mode RF DAC, one should keep in mind the phase shift between two switch pairs output pulses spectral components in NRZ and RF modes. This phase shift depends upon DAC mode (NRZ or RF) and output oscillation frequency. As consequence an analysis indicates that the 3 dB improvement of 1/F phase noise can be achieved in 1st Nyquist zone when using NRZ mode, the same in 2nd Nyquist zone with RF mode if amplitude noise of DAC switch pairs is negligible. The independence of 1/F noise from clock frequency has simple physical interpretation. As correlation period of 1/F noise is significantly greater than output oscillation period, the delay of this oscillation caused by phase fluctuations in DAC is the same for any mode, and analysis of noise spectral density for conventional DAC can be extended to multi-mode RF DACs.

Optimization method of refracturing timing for old shale gas wells

Based on the elastic theory of porous media, embedded discrete fracture model and finite volume method, and considering the micro-seepage mechanism of shale gas, a fully coupled seepage-geomechanical model suitable for fractured shale gas reservoirs is established, the optimization method of refracturing timing is proposed, and the influencing factors of refracturing timing are analyzed based on the data from shale gas well in Fuling of Sichuan Basin. The results show that due to the depletion of formation pressure, the percentage of the maximum horizontal principal stress reversal area in the total area increases and then decreases with time. The closer the area is to the hydraulic fracture, the shorter the time for the peak of the stress reversal area percentage curve to appear, and the shorter the time for the final zero return (to the initial state). The optimum time of refracturing is affected by matrix permeability, initial stress difference and natural fracture approach angle. The larger the matrix permeability and initial stress difference is, the shorter the time for stress reversal area percentage curve to reach peak and return to the initial state, and the earlier the time to take refracturing measures. The larger the natural fracture approach angle is, the more difficult it is for stress reversal to occur near the fracture, and the earlier the optimum refracturing time is. The more likely the stress reversal occurs at the far end of the artificial fracture, the later the optimal time of refracturing is. Reservoirs with low matrix permeability have a rapid decrease in single well productivity. To ensure economic efficiency, measures such as shut-in or gas injection can be taken to restore the stress, and refracturing can be implemented in advance.

Frequency Analysis of Pulse-Width Modulation on All-Digital Transmitters

This work investigates the frequency spectrum in the modulator and up-conversion outputs of a generic all-digital transmitter architecture. Considering the modulator is implemented as a pulse-width modulation (PWM), it is verified that this up-conversion process introduces a series of impulses resembling the spectrum of a unipolar return-to-zero (RZ) waveform in addition to the PWM impulses. Simulations show the minimum bit resolution of PWM signals where the impulses introduced are almost unnoticed, thus their influence is not distinguished from random background noise. An all-digital transmitter is designed on a field-programmable gate array to verify it experimentally. Experimental results show that reducing power from PWM harmonics leads to a power increase in the RZ harmonics, and vice-versa. These harmonic’s power present an energy trade-off relation, a novelty demonstrated in this paper. Finally, but not least, it is observed that filtering the carrier wave out causes a considerable amount of power to be lost.

A Monotonic Early Output Asynchronous Full Adder

This article introduces a novel asynchronous full adder that operates in an input–output mode (IOM), displaying both monotonicity and an early output characteristic. In a monotonic asynchronous circuit, the intermediate and primary outputs exhibit similar signal transitions as the primary inputs during data and spacer application. The proposed asynchronous full adder ensures monotonicity for processing data and spacer, utilizing dual-rail encoding for inputs and outputs, and corresponds to return-to-zero (RtZ) and return-to-one (RtO) handshaking. The early output feature of the proposed full adder allows the production of sum and carry outputs based on the adder inputs regardless of the carry input when the spacer is supplied. When utilized in a ripple carry adder (RCA) architecture, the proposed full adder achieves significant reductions in design metrics, such as cycle time, area, and power, compared to existing IOM asynchronous full adders. For a 32-bit RCA implementation using a 28 nm CMOS technology, the proposed full adder outperforms an existing state-of-the-art high-speed asynchronous full adder by reducing the cycle time by 10.4% and the area by 15.8% for RtZ handshaking and reduces the cycle time by 9.8% and the area by 15.8% for RtO handshaking without incurring any power penalty. Further, in terms of the power-cycle time product, which serves as a representative measure of energy, the proposed full adder yields an 11.8% reduction for RtZ handshaking and an 11.2% reduction for RtO handshaking.

Powers Correlation Analysis of Returns with a Non-stationary Zero-Process

Abstract The higher order dynamics of individual stocks is investigated. We show that classical powers correlation analysis can lead to a spurious assessment of the volatility persistence or long memory volatility effects, if the zero return probability is non-constant over time. In other words, classical tools are not able to distinguish between long-run volatility effects, such as IGARCH, and the case where the zero returns are not evenly distributed over time. As a remedy, new diagnostic tools are proposed that are robust to changes in the zero return probability. Since a time-varying zero return probability could potentially be accompanied by a non-constant unconditional variance, we also develop powers correlation analysis that is robust in such a case. In addition, the diagnostic tools we propose offer a rigorous analysis of the short-run volatility effects, while the use of the classical powers correlations lead to doubtful conclusions. Monte Carlo experiments, and the study of the absolute value correlation of daily returns taken from the Chilean financial market and the 1-min returns of Facebook stocks, suggest that the volatility effects are only short-run in many cases.

A 33-Gb/s/Pin 1.09-pJ/Bit Single-Ended PAM-3 Transceiver With Ground-Referenced Signaling and Time-Domain Decision Technique for Multi-Chip Module Memory Interfaces

A three-level pulse amplitude modulation (PAM-3) transceiver (TRX) with improved simultaneous switching output (SSO) noise and reference voltage margin was studied. PAM-3 signaling with an insertion of 3 bits in 2-unit intervals (UI) was implemented using the upper, under, and ground voltages, achieving 150% pin efficiency. The ground-referenced signaling (GRS) charge pump driver reduced SSO noise and maintained ground as the solitary return current path. Capacitive peaking and middle edge-rate boosting were implemented for transmitter (TX) equalization. With the receiver (RX), the ground level was used as a reference voltage for a single-to-differential (S2D) amplifier. PAM-3 signaling was converted to binary data using the time-domain decision technique in comparators. The decision time of comparators for data and reference voltage was compared. This technique shows the increased voltage margin, the reduced decision time, and the decreased error rate. The reduced decision time improved the performance of the PAM-3 decision feedback equalizer (DFE). A clock disabled the circuit, and a low-power return-to-zero (RZ) to non-RZ (NRZ) converter was configured for the proposed comparator output cases. The prototype TRX was fabricated in a 28-nm complementary metal–oxide silicon (CMOS) process with a surface area of 0.006 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{2}$</tex-math> </inline-formula> . The total power efficiency was recorded as 1.09 pJ/b at 33 Gb/s/pin. Through the flame retardant-4 (FR-4) 20-mm printed circuit board (PCB) channel and coaxial cable, a bit error rate (BER) of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-12}$</tex-math> </inline-formula> was measured.

Design Implementation and Performance Analysis of M-QAM and PAM-n Signalling Schemes

Abstract: Two circuits have been simulated in the Optisystem 20 software. One circuit has M-QAM and the other has PAM-n. Both the circuits have been compared on the basis of Bits per symbol, signal power,Noise power, etc. The total power and noise power havebeen calculated in the electrical power meter visualizer.In both the circuits, PRBS generator is used to generate the sequence of the bits. In M-QAM,return to zero pulse generator is used and in PAM-n notreturn to zero pulse generator is used. The full width pulse is also known as NRZ (not return to zero) and halfwidth pulse is also known as RZ (return to zero). The main objective of the simulation is to get perfect Eye diagram in the Eye Diagram Anaylzer. The parametriccomparison of different types of QAM have also be doneon the basis of number of samples, sequence length, samples per bit and output power in dBm andcomparison is done by state of art. In the final result, itwill be concluded that M-QAM performs much better than the PAM-n as it is capable of transferring higher data rates. The different types of M-QAM and PAM-n eye diagrams have been plotted like 16-QAM, 64-QAMand PAM-3.

Design of OMCG based high capacity hybrid passive optical network (PON) and FSO system employing three SOPs/λ

Abstract This paper presents a cost effective optical multi-carrier generation (OMCG) based 96 Gbps hybrid passive optical network (PON) and free space optical (FSO) communication system. Polarization division multiplexing (PDM) using three different state of polarizations (SOPs) such as 0°, 45° and 90° has been realized and incorporated in the system for tripling the capacity of the proposed hybrid single mode fiber (SMF) and FSO system. Non-return-to-zero (NRZ) modulation format is considered for the cost comparison analysis between conventional PON system, existing PON + FSO system and proposed NRZ modulated three SOPs enabled hybrid PON + FSO system. Results revealed that proposed system provide 24 % cost reduction than conventional PONs and 0.64 % cost reduction as compared to exiting hybrid SMF + FSO PON. Further, effects of different modulation formats such as return-to-zero (RZ), AND compressed spectrum RZ (CSRZ) are investigated in terms of log bit error rate (BER) at different SMF link lengths and fixed FSO range. Our demonstrated hybrid SMF + FSO system can successfully cover the 25 km SMF distance and 3.4 km FSO link range using NRZ showing BER 10−20, RZ 10−6 and CSRZ 10−21.

Simultaneous multichannel RZ to NRZ format conversion for LP01 and LP11 using a few-mode fiber Bragg grating.

We propose a novel format conversion scheme, which can implement multichannel format conversion from return-to-zero (RZ) to non-return-to-zero (NRZ) for both LP01 and LP11 simultaneously by designing a few-mode fiber Bragg grating (FM-FBG) with comb spectra. To achieve filtering for all channels of the two modes, the FM-FBG response spectra of LP11 is designed to shift with that of LP01 by the WDM-MDM channel spacing. This approach is realized by carefully selecting the specifications of the few-mode fiber (FMF) to fulfill the requirements of the effective refractive index difference between LP01 and LP11. Each single-channel outline of the FM-FBG response spectra is designed according to the algebraic difference between the RZ and NRZ spectra. Numerical results show that both LP01 and LP11 channels with 300-GHz-spaced RZ signals at 40 Gbit/s can be converted into NRZ signals simultaneously, and the converted NRZ signals have high Q-factor and their eye diagrams are clean and open.

A Bipolar 3-Level High-Voltage Pulser for Highly Integrated Ultrasound Imaging Systems

This paper presents a design solution for a bipolar return to zero (RZ) 3-level high-voltage TX pulser for high performance portable ultrasound medical imaging systems. Designed to be integrated in the front end of a PMUT probe composed by a 64-channel array working in the 1-10 MHz frequency range, the pulser is compact and power efficient as it employs minimum number of power transistors while ensuring high transmitting linearity because of the implementation of the RZ state. The circuit presents programmable features such as variable delays and rise/fall times to be controlled independently through a digital interface and it dissipates only 4.5 mW to bias the PMUT in RX state while achieving a small Req (2.24 Y). Transistor level and post-layout simulations performed in a BCD-SOI 0.16-lm technology are reported to demonstrate the effectiveness of the approach.

Design and comparative analysis of Inter Satellite-Optical Wireless Communication (IS-OWC) for Return to Zero (RZ) and Non-Return to Zero (NRZ) modulation formats through channel diversity technique

Design and comparative analysis of Inter Satellite-Optical Wireless Communication (IS-OWC) for Return to Zero (RZ) and Non-Return to Zero (NRZ) modulation formats through channel diversity technique

COMPARING DISPERSION COMPENSATION METHODS FOR 120 GB/S OPTICAL TRANSMISSION: PRE, POST, AND SYMMETRICAL SCHEMES

One of the major factors that limit the performance of an optical fiber communication system isdispersion. In order to get a high transmission range with high data rates, techniques must be in place to compensate for the dispersion caused by fiber nonlinearity. Dispersion Compensating Fiber (DCF) and Fiber Bragg Grating (FBG) are the trending dispersion compensation techniques in optical fiber communication. The use of DCF and FBG as a method of dispersion compensation can notably enhance the overall performance of the system. Broadening is a function of distance as well as the Dispersion parameter (D). The dispersion parameter is given in ps/nm/km and changes from fiber to fiber and also is a function of wavelength. In this paper, we investigate pre-, post-, and symmetrical compensating schemes in three different compensating models: DCF, FBG, and DCF cascaded to FBG. The system performance was evaluated in terms of Q-factor and Bit Error Rate (BER) for one optical channel communication system at 120 Gbps Return to Zero (RZ) signal launched over Single-Mode Fiber (SMF) of 100 km by using OptiSystem 7.0 software.

Receiver sensitivity of type-I return-to-zero signals having finite extinction ratios.

In this two-part paper, we develop expressions describing the receiver sensitivity of return-to-zero (RZ) signals having finite extinction ratios (ERs) and arbitrary duty cycles. Between the two known ways of modeling RZ signals, this work focuses on the RZ signal composed of strong and weak pulses, which represent marks and spaces, respectively (hereinafter referred to as Type I). Using our derived expressions, we show that the receiver sensitivity of a Type-I RZ signal is independent of the duty cycle if the system performance is limited by signal-dependent noise. Otherwise, there exists an optimum duty cycle for receiver sensitivity. We also quantitatively discuss the varying impact of finite ER on the receiver sensitivity for different duty cycles. We present the experimental results supporting our theoretical analysis.

Design and comparative analysis of Inter Satellite - optical wireless communication (IS-OWC) for Return to Zero (RZ) &amp; Non-Return to Zero (NRZ) Modulation formats Through channel diversity

IS-OWC (Inter Satellite Optical Wireless Communication) is a novel method of establishing interconnection between two satellites. Inter-satellite Optical Wireless Communication is concerned with the use of lasers instead of traditional radio and microwave systems for wireless optical communication. When compared to a single channel, the channel diversity strategy produces better results. The IS-OWC device uses a diversity technique in which several signal paths are available, allowing the Q-factor and signal intensity to be extended or increased over a large distance. In this paper, the Q-factor and the Bit Error Rate (BER) are analyzed with diverse modulation formats like Return to Zero (RZ) and Non-Return to Zero (NRZ) using the channel diversity technique.

Gerchberg-Saxton Based FIR Filter for Electronic Dispersion Compensation in IM/DD Transmission Part II: Experimental Demonstration and Analysis

In this article, the first experimental demonstration of a non-iterative electronic dispersion compensation (EDC) solution implemented at the transmitter using a finite impulse response (FIR) filter optimized with the Gerchberg-Saxton (GS) algorithm, is presented, for intensity-modulation and direct-detection (IM/DD) systems. The theoretical framework and preliminary simulations have been presented in Part I of this work. Here, the performance is compared between the GS FIR filter and the iterative GS algorithm in 56-Gb/s on-off keying (OOK) transmissions over 80-km single mode fiber (SMF) with a post feed-forward equalizer (FFE) for combating residual inter-symbol interference. Furthermore, the influence of the pulse shape (raised cosine or rectangular) and modulation format (return-to-zero (RZ) or non-return-to-zero (NRZ)) on the measured bit error ratio (BER) is investigated, while changing the number of FIR taps, post-FFE taps, and post-FFE samples-per-symbol. It is shown that within the range of the target digital extinction ratios (DERs) for which the original iterative GS algorithm offers benefit, both analytical and numerical methods for calculating the optimum FIR taps, outlined in Part I, produce similar BER performance as predicted. Hence, the former method is extended, here, through a non-recursive frequency response formula, which offers insight into the action of the GS filter with different pulse shaping and enables the derivation of the explicit GS impulse response. It is also shown that rectangular RZ exploits the full benefit of GS filtering through a uniform spectrum, achieving BER < 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> , with a 641-tap <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> /2-spaced pre-EDC FIR filter and a 3-tap adaptive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> -spaced post-FFE.