Duobinary Research Articles

Dual Polarization DQPSK ROF System with Duo Binary Precoding and Hybrid Amplification for Effective Hybrid SMF FSO Transmission Medium

This article demonstrates the utilization of a hybrid amplification technique on the transmission part of the proposed hybrid medium transmission system which includes both using Single Mode Fiber (SMF) with 60 km and Free Space Optic (FSO) with a range between 5 km and 25 km. It has included four weather situations with an investigation of the FSO medium-based system performance. The system uses 64 channels based on Dual Polarization-Differential Quadratic Phase Shift Keying (DP-DQPSK) Dense Wavelength Division Multiplexing (DWDM) for the Radio over Fiber (RoF) system using the Duo Binary coding scheme to improve the system efficiency in general and the cross-talk in particular. The investigations will include using the hybrid amplifiers of Erbium Doped Fiber Amplifier (EDFA) and Optical Amplifier (OA) for transmission. The analysis results show that using the hybrid amplification could improve the transmission to reach 25 km for light air case, meanwhile, for light haze, it could reach up to 20 km. Moderate haze could improve transmission efficiency for a distance of 7 km. Finally, for moderate rain situations, the transmission could be further improved to cover a distance of up to 5 km.

A Low BER DB-PAM4 Adaptive Equalizer for Large Channel Loss in Wireline Receivers

A high-speed serial interface is the core IP of a high-performance computer, data center and interconnection network; its bandwidth and bit error performance restrict the development of the system. With the evolution of high-speed serial interface line rates from 56 G to 112 G in high-end information systems, their bit errors increase sharply, limiting system performance. In order to solve the high-bit-error problem of the 112 Gb/s high-speed serial interface, this paper proposes a low-error Duo-binary PAM4 (DB-PAM) receive equalization technology. This technology utilizes the Duo-binary (DB) signal in which the channel and the transceiving equalizer work together to realize the low-error reception of the 112 Gb/s signal in the high-attenuation channel. To solve the problem of difficulty in generating high-speed DB-PAM4 signals and the complex adjustment of equalization parameters, this paper proposes a two-step progressive equalization technique. In the first step, the technology transmits not-return-to-zero (NRZ) signals at the transmitter (TX) and generates a Duo-binary (DB) signal path at the receiver using the least mean square error (LMS) algorithm. In the second step, the technology sends a precode-PAM4 (pre-PAM4) signal at TX; at the receiving end, the adaptive equalization algorithm is used to adjust the DSP equalization parameters to generate the optimal equalization parameters of the DB-PAM4 signal. This paper uses Cadence’s AMS simulation platform to verify the receive equalizer of DB-PAM4. Simulation results show: when a 112 Gb/s pre-PAM4 signal passes through the 35 dB@28 GHz channel, the receiver (RX) utilizes the adaptive equalizer to generate a 112 Gb/s DB-PAM4 signal, and the receiver bit error rate (BER) is less than 3e-9.

Performance Improvement Using DCSRZ at 10 GHz OCDMA Transmission Link

In this paper, a method based upon combination of duo-binary (DB) and carrier suppressed return-to-zero (CSRZ) format has been proposed that has significantly improved the performance of optical code division multiple access (OCDMA) system by means of two dimensional (2D) codes based on two parameters; wavelength and time. The various investigations divulge that highest Q2 (dB) of minimum and maximum value [18,23]; [14,17]; [9,12] and [1,6] has been obtained at a power variation of -10 to 20 dBm f or DCRZ, DB, CSRZ and RZ modulation formats respectively for a communication distance of 80 kilometers. It has also been identified that maximum OSNR of [37-29] dB is obtained by using DCSRZ modulation format for the same distance. The maximum opening of eye for DCSRZ format has further proved its robustness to suppress the channel impairments at a high-power level of 20 dBm for 10 GHz optical CDMA systems.

Simulative Analysis of Robustness of Various Modulation Formats for Optical CDMA using 2D Codes for Different Encoders at 10Gbps

This paper reports the simulative analysis of NRZ, RZ, carrier-suppressed RZ (CSRZ) and duo-binary (DB) modulation formats for optical code division multiple access (OCDMA) system for two different types of encoders at 10 Gbps. The investigations reveal that highest Q2(dB) of the order of 16.5;14.5;6.2 and 3.8 has been obtained when we use combination of optical filters and time delay components as optical encoders in OCDMA system for CSRZ, DB, RZ and NRZ formats respectively. It is also observed that for fiber Bragg grating (FBG’s) as optical encoders, Q2 (dB) of the order of 17.7;11.8;7 and 4 is achieved in case of DB, CSRZ, RZ and NRZ formats respectively. CSRZ and duo-binary formats have shown the robustness over other formats for OCDMA system using filter, time delay components and fiber Bragg gratings (FBGs) as optical encoders respectively. The maximum eye opening in case of these formats further proved their efficiency.

Comparative Analysis of DCF based Dispersion Compensation Techniques in Optical Fiber Communication Link using Different Input Transmitter Conditions at 10 Gbps

In this paper, Dispersion Compensating Fiber (DCF) based various dispersion compensating techniques (pre, post and symmetrical) with different modulation format like Non Return to Zero(NRZ), Return to Zero(RZ), Carrier Suppressed Return to Zero(CSRZ) and Duo Binary(DB) along with PN, FCC and Walsh code input sequences are implemented. Simulation and analysis of these implemented techniques were done at 10 Gbps bit rate and input laser power ranging from 1 mW to 10 mW at transmission distance of 240 km using BER Analyzer in Optisystem 17.0 software. Comparison between different techniques was done in terms of Q factor and BER versus input CW laser power for different modulations and input sequences. From the analysis, it is concluded that when Walsh code as user defined input sequence are used for all the implementation, it gives higher value of Q factor and lower value of Bit Error Rate as compared to PN and FCC codes for most of the input CW laser power.

Palliation of Four-Wave Mixing in Optical Fibers Using Improved DSP Receiver

A long haul optical communication system (LHOCS) is one of the key resources to fulfill the higher capacity requirements in future communication networks. To launch LHOCS, the system mainly faces high order nonlinear effects. The four-wave mixing (FWM) is one of the major nonlinear effects, which limits the transmission distance. Therefore, in this paper, an advanced duo-binary (DB) modulation scheme-based system is evaluated by employing an improved digital signal processing (IDSP) approach at the receiver side to suppress the FWM effect. In addition, an analytical analysis is also performed for the proposed system. To observe the difference between the IDSP and conventional digital signal processing (DSP), the various performance metrics such as bit error rate (BER), Q-factor, and optical signal-to-noise ratio (OSNR) parameters are evaluated. Variable channel spacing along with polarization mode dispersion (PMD) are analyzed at several ranges of input powers and fiber lengths. The analytical and simulation-based calculations exhibit the effectiveness of the proposed model and hence, FWM effect are compensated to achieve 500 km optical fiber propagation range with a BER below 10−6.

Transmission Beyond 200 Gbit/s With IM/DD System for Campus and Intra-Datacenter Network Applications

Intensity modulation and direct detection (IM/DD) with pulse amplitude modulation (PAM) is a cost-effective option for intra- and inter-data center (DC) applications. Due to current demand on DC data traffic, transmission rates beyond 200 Gbit/s/ $\lambda $ are desirable. However, employing commercially available lower bandwidth components introduces severe inter-symbol interference (ISI). In addition, to achieving high-speed data rates, digital signal processing (DSP) schemes like Tomlinson-Harashima precoding (THP) and decision feedback equalizer (DFE) can increase tolerance against ISI. In this letter, we show an experimental comparison of PAM-4, PAM-6 and PAM-8 modulation formats with and without THP on the transmitter-side and Volterra nonlinear equalizer (VNLE) on the receiver-side. We provide also results with and without duobinary (DB) encoding on the transmitter side and DFE on the receiver side. The experiment is conducted using an O-band electro-absorption modulated laser over transmission distances up to 20 km.

Performance Analysis of Modulation Formats for Next Generation RoF Systems

Radio over fiber (RoF) has found to be one of the most effective communication techniques. It has the tendency to incorporate both optical fiber and free space radio paths. In this research article, importance, benefits, and applications of RoF system are discussed in detail for futuristic networks. The performance of RoF system is visualized by modulating the data with the RF signal having same frequency at both transmitter and receiver ends. Initially, the performance is checked using non-return to zero (NRZ) format and later compared with duobinary (DB) and carrier suppressed return to zero (CSRZ). Various simulations are performed which directly affect the system performance. Important parameters such as RoF link distance, data rate, transmitter power, amplifier gain, and RF signal frequency are tested. The operation is carried out at 1550 nm wavelength and 30 GHz RF frequency. System is optimized to receive the transmitted waveforms successfully. Simulations are performed in Optisystem 17.0 and MATLAB. For the analysis, the results are plotted using Q-factor and BER values.

Performance enhancement of ultra-dense WDM over FSO hybrid optical link by incorporating MIMO technique

Abstract Free-space optical (FSO) communication is a wireless optical data transmission technology with a high data transmission rate. It has received much attention in recent years as it is cost-effective and has license free operation. It is line of sight free-space communication technique where optical signal severely degraded from atmospheric losses especially due to weather conditions; hence it restricts the link range and data carrying capacity. Therefore, a 16-channel ultra-dense wavelength division multiplexing–free space optics (UWDM–FSO) system each having each 10 Gb/s data rate is proposed to enhance the capacity and performance of FSO system. To authenticate the performance of the proposed system, investigation for different modulation formats such as nonreturn to zero (NRZ), return to zero (RZ), carrier suppressed return to zero (CSRZ) and duo binary (DB) are reported. Further, to reduce the atmospheric interference, multiple input multiple output (MIMO) technique is integrated into the proposed system. The outcomes of MIMO–UWDM–FSO link revealed a significant improvement in the bit error rate (BER), eye diagram and Q-factor, under different weather conditions. It is also observed that NRZ modulation formats perform better than RZ, CSRZ and DB formats.

Performance Analysis of Duobinary and CSRZ Modulation Based Polarization Interleaving for High-Speed WDM-FSO Transmission System

Abstract In this paper, the bit error rate (BER) performance of Duobinary (DB) is compared with carrier-suppressed return-to-zero (CSRZ) based polarization interleaving (PI) schemes for high-speed transmission system. The system is integrated with wavelength-division multiplexing (WDM) scheme and PI scheme for free space optical communications (FSO). The simulation results show that DB offers betters BER performance compared to CSRZ in high-speed WDM-FSO-PI system.

Performance Evaluation of OOK, DPSK and Duo-binary Modulation Format based Mixed-Line-Rate (MLR) Optical Network

With the steady increase in the heterogeneous Internet traffic, the optical wavelength division multiplexed (WDM) networks based on a mixed line rate (MLR) strategy have emerged as an efficient-solution. Also, with the migration from the legacy to the higher line rate(s), the advanced modulation format(s) (MF) is/are required. However, use of appropriate MF(s) for the higher line rate(s) still remains an open problem. In this article, we compare the performance of an On-Off Keying (OOK), Differential Phase Shift Keying (DPSK) and Duo-binary (DB) MF based MLR network in the presence of various physical layer impairment(s) (PLIs) for which, we propose a mathematical model based on various MFs. As a novelty, we validate the proposed theoretical model’s results by comparing them with the results obtained through simulations from OptSim, which has not been conducted in any existing study(s) thus far. Our simulation results show that the DB MF is perfectly suitable for high spectral-efficient MLR systems owing to its high resistance to various PLIs.

3-Dimensional PAM-8 modulation for 200 Gbps/lambda optical systems

Abstract We propose a novel 8-level multidimensional intensity modulation scheme with the goal of achieving transmission rates higher than 200 Gbps when using only commercially available components. The generation of this modulation scheme is explained here and it is shown to increase the noise tolerance when compared with the 8-level pulse amplitude modulation (PAM-8), at the expense of spectral efficiency. We show that the proposed 3-dimensional (3D) modulation provides the same relative minimum distance gain for both non-duobinary (non-DB) and duobinary (DB) signaling. Gains ranging from 1 dB and up to 1.9 dB are shown in simulations for bit-error rates (BER) equal to or below 4x10−3, when comparing with the classic PAM-8. We demonstrate experimentally that 3D PAM-8 lowers the BER by up to 10 times for non-DB transmissions and by up to 3 times for DB transmissions. The proposed multidimensional modulation increases the maximum achievable bit rate from 205 Gbps (with PAM-8) up to roughly 240 Gbps, enabling 200 Gbps net rate single-lambda transmissions for next generation intra- and inter-datacenter optical transmission systems.

Adaptive Transmit-Side Equalization for Serial Electrical Interconnects at 100 Gb/s Using Duobinary

The ever-increasing demand for more efficient data communication calls for new, advanced techniques for high speed serial communication. Although newly developed systems are setting records, off-line determination of the optimal equalizer settings is often needed. Well-known adaptive algorithms are mainly applied for receive-side equalization. However, transmit-side equalization is desirable for its reduced linearity requirements. In this paper, an adaptive sign–sign least mean square equalizer algorithm is developed applicable for an analog transmit-side feed-forward equalizer (FFE) capable of transforming non-return-to-zero modulation to duobinary (DB) modulation at the output of the channel. In addition to the derivation of the update strategy, extra algorithms are developed to cope with the difficult transmit–receive synchronization. Using an analog six tap bit-spaced equalizer, the algorithm is capable of optimizing DB communication of 100Gb/s over 1.5-m Twin-Ax cable. Both simulations and experimental results are presented to prove the capabilities of the algorithm demonstrating automated determination of FFE parameters, such that error-free communication is obtained (BER $ using PRBS9).

Investigation of Influence of Mixed Configurations on Performance of WDM-PON

This paper aims at assessing of implementation of the concept of mixed systems in wavelength-division-multiplexing passive optical networks (WDM-PONs). At the first stage, the authors evaluate performance of two equal-channel transmission systems with non-return-to-zero (NRZ) and duobinary (DB) coding in terms of Q-factor, minimal channel spacing and supported data rate. At the second stage, two configurations of mixed transmission systems are proposed. The system with unequal channel spacing and multiple modulation formats (MMFs) as well as the system with mixed line rates (MLRs) and MMFs are investigated. The obtained results reveal that the impact of implementation of both systems is positive and concept of mixed transmission system can be considered as a potential solution for the increase of spectral efficiency (SE) of WDM-PON transmission system.DOI: http://dx.doi.org/10.5755/j01.eie.23.2.18003

On Some Homomorphic Extensions of Duo Binary Systems

This paper explores the following problem: Let \(A=(A,+,\cdot)\) and \(E=(E,+,\cdot)\) be duo binary systems. Let \(S=(S,+,\cdot)\) be a subsystem of \(A\). Under what conditions can a homomorphism \(p:S\to E\) be extended to a homomorphism \(P:A\to E\) and how?

Performance evaluations of hybrid modulation with different optical labels over PDQ in high bit-rate OLS network systems

Two orthogonal modulation optical label switching(OLS) schemes, which are based on payload of polarization multiplexing-differential quadrature phase shift keying(POLMUX-DQPSK or PDQ) modulated with identifications of duobinary (DB) label and pulse position modulation(PPM) label, are researched in high bit-rate OLS network. The BER performance of hybrid modulation with payload and label signals are discussed and evaluated in theory and simulation. The theoretical BER expressions of PDQ, PDQ-DB and PDQ-PPM are given with analysis method of hybrid modulation encoding in different the bit-rate ratios of payload and label. Theoretical derivation results are shown that the payload of hybrid modulation has a certain gain of receiver sensitivity than payload without label. The sizes of payload BER gain obtained from hybrid modulation are related to the different types of label. The simulation results are consistent with that of theoretical conclusions. The extinction ratio (ER) conflicting between hybrid encoding of intensity and phase types can be compromised and optimized in OLS system of hybrid modulation. The BER analysis method of hybrid modulation encoding in OLS system can be applied to other n-ary hybrid modulation or combination modulation systems.

Single-lane 180 Gbit/s PAM-4 signal transmission over 2 km SSMF for short-reach applications.

We experimentally demonstrate the generation and transmission of a single-lane 180 Gbit/s (90GBaud) four-level pulse-amplitude modulation (PAM-4) signal in an intensity-modulation direct-detection system with a 7.5GHz 3dB bandwidth. The generated signal is transmitted over a 2km standard single-mode fiber with, to the best of our knowledge, the highest reported net data rate in the C-band: 150 Gbit/s. A net data rate of 168 Gbit/s is also reachable with 1km reach. The PAM-4 and duobinary (DB) PAM-4 modulation schemes are compared; the obtained results show that DB-PAM-4 significantly outperforms PAM-4 in the considered strong bandwidth-constrained system. Both a feed-forward equalizer and a maximum-likelihood sequence estimator are investigated for data recovery.

Investigation on Maximum Available Reach for Different Modulation Formats in WDM-PON Systems

Abstract Considering the growing demand for broadband of access networks, in the present paper we investigate various modulation formats as a way of increasing the performance of optical transmission systems. Non-return-to-zero (NRZ) on-off keying, return-to-zero (RZ) OOK, carrier suppressed RZ (CSRZ) OOK, duobinary (DB), NRZ differential phase shift keying (NRZDPSK), RZ-DPSK and CSRZ-DPSK formats are compared using the maximal achievable reach with bit error rate less than 10−9 as a criterion. Simulations are performed by using OptSim software tool. It is shown that using the transmission system without dispersion compensation the best results are shown by duobinary and CSRZ-OOK modulation formats, but with the system using dispersion compensating fiber (DCF) the longest transmission distance is achieved by RZ-DPSK modulation format. By investigating the influence of channel spacing for best-performed modulation formats, network reach decrease for transmission systems with DCF fiber has been observed due to channel crosstalk.

Comparison between Duobinary Filter and Delay-And-Add Technique of Duobinary Transmission in Fiber Optic Communication System

Binary code is a two level of bit sequence of 1 and 0. On the other side, Duobinary (DB) is a three- level code of 1, 0 and -1 levels. Using duobinary transmission instead of binary transmission, it can improve the system performance, bandwidth efficiency of output signal, average power of signal, noise and distortion ratio of output wave shapes. Duobinary encoding and decoding are used in a significant bandwidth reduction of MAC signals transmitted by high and medium power TV satellites and also used in fiber optic communication system. This paperis based on the the observationof generation performance and transmission of duobinary coding and simulation of a single channel (1550-nm) 90-km OC-192 link. In duobinary transmission, the duobinary encoding can be implemented either with a combination of a delay-and-add operation or with a duobinary filter. Duobinary filter reduces bandwidth , wavelength, noise and distortion and improves the eye diagram of the output signals than the delay-and-add circuit in duobinary transmission of optical communication system. Also in this paper circuit design, simulation and fabrication of a duobinary encoder and decoder circuit for data communication system are presented. Keywords: Duobinary transmission, Duobinary filter, Delay-and-add circuit, Optsim, Eye diagram.

High-bandwidth generation of duobinary and alternate-mark-inversion modulation formats using SOA-based signal processing

We report on the novel all-optical generation of duobinary (DB) and alternate-mark-inversion (AMI) modulation formats at 42.6 Gb/s from an input on-off keyed signal. The modulation converter consists of two semiconductor optical amplifier (SOA)-based Mach-Zehnder interferometer gates. A detailed SOA model numerically confirms the operational principles and experimental data shows successful AMI and DB conversion at 42.6 Gb/s. We also predict that the operational bandwidth can be extended beyond 40 Gb/s by utilizing a new pattern-effect suppression scheme, and demonstrate dramatic reductions in patterning up to 160 Gb/s. We show an increasing trade-off between pattern-effect reduction and mean output power with increasing bitrate.