Spectral Amplitude Coding Research Articles

Performance analysis of MDM-OCDMA free space optical system using shift ZCC codes

Abstract Free space optical communication is promising wireless technology which saves cost, saves time, has high security and acts as backend, backhaul system. Optical code division multiplexing based on spectral amplitude coding is a potential method to support many users with high data speeds. Optical code division multiplexing reliant spectral amplitude coded zero cross-correlation free space optical communication is proposed in this work incorporating shift zero cross-correlation codes. Mode Division Multiplexing is used to lower the cost of the system and to minimize the interferences. With the realization of the proposed system, the capacity of 100 Gbps is accomplished supporting 10 different users. Different atmospheric turbulences are also analyzed over FSO to investigate their effects on BER.

Performance Analysis of Spectral Amplitude Coding Methods in Fiber Optical Communication System

Performance Analysis of Spectral Amplitude Coding Methods in Fiber Optical Communication System

Operating Characteristic Curves of Optical Packet-Switching Using Optical Code-Division Multiplexing for Label Switching

In this paper, the operating characteristic curves (OCCs) of optical code-division multiplexing (OCDM) technology for label switching of an optical packet-switching (OPS) network was evaluated. A node structure for processing the packets, with spectral-amplitude-coding (SAC) labels, considering a balanced detector and an optical switch, was developed and modeled. The effects of decoding noises on the performance of both M-sequence and stuffed quadratic congruence (SQC) labeling systems were addressed. Hypothesis testing was applied to the decoder to investigate the results of label recognition. The null and alternative hypotheses were, respectively, defined as a decoder receiving the matching and mismatching labels. Due to the noise effects, the decoder output may not reflect the label status correctly. Type I error occurs when the null hypothesis is true while accepting the alternative one. Type II error occurs when the alternative hypothesis is true while accepting the null one. Analytic equations of both errors were given, considering a desired packet that was missed and an undesired packet shown in a switched path. The trade-off between these two errors, regarding the decoder threshold, was demonstrated in operating characteristic curves (OCCs). A better OCC could be found when a packet had more labeled payload bits, or when the utilized label code had a lower auto-to-cross-correlation ratio.

New Zero Cross-Correlation Codes Based on Zech Method’s for OCDMA Systems

A new structure code for Spectral Amplitude Coding Optical Code Division Multiple Access (SAC–OCDMA) system with zero cross-correlation (ZCC) is presented in this paper. The principle idea of this method is based on the use of Zech logarithms in the construction of the code sequences to ensure orthogonality and compare their performances with previously reported codes. The maximum cross-correlation of this code is zero signifying that Multi-Access Interference (MAI) and Phase-Induced intensity noise (PIIN) effects are eliminated thus the system performances are improved. The BER simulation results against the total number of active users show a significant improvement in the performance of the proposed code over preceding reported codes. The system can accommodate more than 90 simultaneous users compared to other codes at a bit error rate of 10^(-9). Furthermore, the construction method offers good flexibility in the choice of the number of users, the weight, and the code length.

Development of New Spectral Amplitude Coding OCDMA Code by Using Polarization Encoding Technique

OCDMA is an optical access technology that has a lot of potential because it can be asynchronously accessed and provides a higher level of security. The authors presented a new DW family code, a flexible double weight (FDW) code, and a novel polarization encoding approach in this paper. The new code is applicable to both odd- and even-weighted codes. The novel polarization encoding approach may be used for numerous wavelengths that overlap. Based on analytic principles, a comparison of two widely used spectrum amplitude-coding SAC-based OCDMA codes, notably modified frequency hopping (MFH), Hadamard, and the double weight (DW) code family. The comparison was based on observing the bit error rate (BER) in each situation. The DW code has a fixed weight of two. The FDW code was introduced to reduce phase-induced intensity noise and multiple access interference (MAI) in transmission networks. FDW codes are versions of the DW code family with weights larger than two. The FDW code outperforms the Hadamard, MFH, DW, modified double weight (MDW), and enhanced double weight (EDW) algorithms. FDW has the capacity to support up to 220 concurrent users. With the new polarization encoding technology, the FDW code can travel up to 60 km at a bit rate of 2.5 Gb/s and 40 km for a 10 Gb/s bit rate.

Implementation of Shared Laser–LED Sources in a Free Space Optics (FSO) Network under Environmental Impact

This paper is devoted to evaluating the combined coherent and incoherent sources (CCIS) technique for different applications in the optical domain and future optical code division multiple access (OCDMA) networks. Spectral amplitude coding (SAC) has gained significant attention in optical processing systems due to its increased capabilities in dealing with multiple-access interference (MAI) efficiently. Fixed right shift (FRS) is adopted as a signature code in this study. Furthermore, performance analysis is studied in terms of bit error rate (BER) for the system using CCIS in both the free space optics (FSO) and sky mesh network using an aerial altitude platform system (AAPS). Simulation results confirmed that a CCIS design significantly improves system performance with moderate cost. An acceptable BER value of 10−9 at 1.25 Gbps data rate and 60 km, 38 km, and 6 km distances for the laser, CCIS, and LED sources, respectively, can be supported. In particular, at Q-factor ~4.5, the FSO ranges under low haze, moderate haze, and heavy haze are, respectively, 3.7 km, 2.5 km, and 1.5 km. The reason is that a CCIS design causes an increase in the effective transmitted power. It can be summarized that a CCIS design can provide reliable solutions and an affordable cost for future optical fiber and wireless network applications.

Construction and performance analysis of variable weight zero cross correlation Latin square code for spectral amplitude coding OCDMA systems

Construction and performance analysis of variable weight zero cross correlation Latin square code for spectral amplitude coding OCDMA systems

Multiservice transmissions in optical code-division multiple access networks of spectral amplitude coding based on hypothesis testing and multiple chip decoding

I propose a multiservice scheme in optical code-division multiple access (OCDMA) networks by adapting hypothesis testing to a receiver design of multiple chip decoding. Each transmitted bit of a single user is divided into several time-domain chips carrying an identical spectral amplitude coding (SAC) signature. Multiservice transmissions are achieved by assigning the users with different chip numbers based on the user classes. Hypothesis testing is employed to derive the required chip number supporting the desired bit-error rate (BER) performance. Numerical results have shown that efficient BER classifications are achieved among distinctive classes for multiple conditions of user numbers and power levels. The proposed multiservice scheme can be transparently applied to SAC-OCDMA systems with existing optical codes and various user class numbers.

Implicit Label Number for Optical Packets in Label Switching Networks Based on Spectral Amplitude Coding and OCDM Path

This paper presents an implicit labeling scheme where stacked spectral-amplitude-coding (SAC) labels are inscribed in multiple payload bits in the packet front. Reliable label recognition in optical packet switching (OPS) is achieved by analyzing the overall decoding results of all labeled bits instead of considering each labeled signal individually. The concept of hypothesis testing is employed to determine the optimal labeled bit number. A decision rule of correct switching is designed based on the photocurrent mean of the decoded label stacks. Considering the noise factors shown in the decoding process, the desired label number has been analyzed under different conditions of code types, label power, and the level of significance. Simulation results provide good suggestions for the tradeoff between the system insensitivity to noise effects and the transmission redundancy of carrying repetitive label information in an optical packet.

Cardinality Enhancement of SAC-OCDMA Systems Using New Diagonal Double Weight Code

Optical code division multiple access (OCDMA) provides another dimension to multiple access systems, in which each user is assigned a unique code. This allows each subscriber to simultaneously access the medium without any contention. However, simultaneous access of multiple users introduce multiple access interference (MAI) which primarily deteriorates the performance of OCDMA systems. This paper proposes a new code called diagonal double weight (DDW) code to elevate the performance and cardinality of spectral amplitude coding (SAC) OCDMA systems. Performance of our proposed code is evaluated using comprehensive analytical analysis followed by simulation analysis. Examination of bit error rate shows that DDW code along with single photodiode detection technique provides efficient performance, with added benefits of simplified design, large cardinality and ease of implementation.

Phase Carrier approach based on Optical Code Division Multiple Access Networks

A technique for optical code-division multiple-access (OCDMA) spectral amplitude coding is proposed and analyzed. The proposed approach is based on combining both OCDMA systems over a phase carrier. Compared with conventional OCDMA systems, this approach exhibits numerous advantages such as simplicity in the system design and cost efficiency. The phase shift based on phase modulation is adopted in the proposed system, and the orthogonal function based on the random diagonal code is applied. The proposed scheme is considered cost-effective because only one laser source is used; which minimizes interference for access network passive optical network applications and improves the system performance of bit-error rate (BER 10-12).

Optical fiber sensor network integrating SAC-OCDMA and cladding modified optical fiber sensors coated with nanomaterial

Three modified single mode optical fiber ammonia sensors coated with nanocomposite of polyaniline/graphite nanofiber (PANI/GNF) are integrated with optical code division multiple access utilizing spectral amplitude coding (SAC-OCDMA) optical fiber sensors network. The sensors are modified using both etching and tapering processes. A thin layer of PANI/GNF is spared on the etched–tapered SMF sensors. The sensors based on the evanescent wave absorption are investigated by measuring the output optical power in the C-band wavelength range (1535–1560 nm) at room temperature. SAC-OCDMA using Khazani Syed (KS) code is deployed as it has the capability to remove multiple access interference (MAI) and it is cost effective. The performance of the developed optical fiber sensor network based on star topology is investigated remotely over 3 km using Erbium doped fiber amplifier for NH3 sensing in terms of received optical power, crosstalk, and optical signal-to-noise ratio (OSNR). OSNR is observed to vary with fiber diameter and NH3 concentration level. The smaller tapering diameter and higher NH3 concentrations generate lower OSNR at the output of the related decoder. The measured OSNR for the developed optical fiber sensor network was 22 and 18.45 dB when sensors implied in the network exposed to 0.125% and 1% NH3 concentrations, respectively.

Design and analysis of three-dimensional m-sequence bipolar OCDMA spectral amplitude code

This paper has been focused to utilize the m-sequence (matrix) code in spectral/time/spatial OCDMA domain in a bipolar mode (Three Dimensional modes). The scheme has elegantly incorporated the design of an encoder and decoder such that the system efficiently generates the code in three-dimensional bipolar mode. The decoder design is such that it effectively suppresses the multiple user interference (MUI) of three-dimensional code. System analyses are carried for defining the BER performance variation with users acceptability and received power. The observed results demonstrate that the cardinality of m- matrix three-dimensional bipolar code is larger than the existing 3D Pascal code, 2D-MDW, 3D-PDC, 2D-PDC, 1D-CWH and 1D-MS codes. The received power in proposed system is − 5.8 dBm lesser than the 3D Pascal Code at 10–18 BER and the users in system more than 210% can be accomplished as compared to 3D Pascal code.

Performance Analysis of Bipolar Optical Code Division Multiple Access with Dual Electro-Optical Modulator Scheme for Free-Space Optical Communication

In this study, the performance of bipolar optical code division multiple access (OCDMA) with dual electro-optical modulator (EOM) scheme for multi-user scenario was tested and analyzed with OptiSystem version 10. The performance measurement was implemented for free-space optical (FSO) communication and includes the common noises in optical communication. Two different channels were used in the measurement, i.e., additive white Gaussian noise (AWGN) and fading channel. Two extreme weather conditions, strong rain and storm, were considered in the simulation. The performance between three spectral amplitude coding (SAC) codes, i.e., Modified M-Sequence code, Walsh-Hadamard code, and random diagonal (RD) code were measured and compared. The simulation results indicate that Modified M-Sequence code had the highest BER while RD code achieved the lowest BER in the short-range and Walsh-Hadamard code got the lowest BER for the medium-range of FSO, both for AWGN only and AWGN with fading channel. In strong turbulence condition, the performance of all codes become comparable after 500 m of FSO range. Modified M-Sequence suffered the lowest performance degradation while RD code endured the highest performance deterioration in all-weather condition. The results show that Modified M-Sequence can be applied for medium to long-range FSO.

Nonlinear Effect and MAI Impact on SAC-OCDMA System Based on 2D Multi-Diagonal Code and Laser Array

A new architecture for Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system based on two Dimensional Multi Diagonal (2D-MD) codes named 2D-MD SAC-OCDMA and utilizing a laser optical source is proposed for Long-Reach Passive Optical Network (LR-PON). In this work, a computer simulator tool is used, for the first time, as a SAC-OCDMA simulation set-up utilizing the unique combination of a coherent laser array and 2D-MD codes. In addition, the system performance is addressed numerically by taking into account Multiple Access Interference (MAI), optical coherent source noise, first, second and third order fiber dispersion, nonlinear effects and photo-detector noise. Simulation results indicate that for a single user (i.e., without considering MAI), the system can operate at a maximum bit rate of 55 Gb/s over 250 km of Single Mode Fiber (SMF), with a Bit Error Rate (BER) below 10−9 (Q-limit = 15.5 dB), when only first order fiber dispersion is considered. However, including the effects of second and third order fiber dispersion as frequency domain parameters, results in a reduction of the maximum bit rate to 40 Gb/s, while maintaining a Q-factor above the Q-limit under the same transmission distance. Furthermore, we demonstrate that the proposed architecture extends the SMF transmission reach up to 600 km and 480 km, when considering linear and nonlinear effects, respectively. Finally, we show that our proposed 2D-MD SAC-OCDMA system outperforms existing solutions presented in the literature for LR-PON configuration, in terms of both aggregate bit rate and transmission reach.

Noncoherent optical CDMA system of 2-D subtracted square codes using two code keying by eliminating the multiple use interferences

We propose the new two-dimensional subtracted square (SS) codes to achieve the new family in the spectral amplitude coding (SAC) optical code division multiple access (OCDMA) networks. The proposed codes give the multiplication between the 1-D subtracted square codes and 1-D subtracted square codes to become the code sequences of the 2-D SS codes. The proposed structure using the 2-D SS codes constructs the proposed transmitter and proposed receiver to build the code sequences of the 2-D SS codes and recovered bits using the modified cross-correlation, respectively. The proposed transmitter activates the 2-D SS codes to convert the code sequences of the 2-D SS codes. The proposed receiver gets the code sequences of the 2-D SS codes to decode the recovered bits, which cancel the interferences in the powers called the multiple user interferences (MUI). The proposed receiver transfers the cross-correlation to the modified cross-correlation, which eliminates the MUI. The modified cross-correlation takes the photodiodes to suppress the phase-induced intensity noise (PIIN), simultaneously. In numerical results, the bit error rate (BER) gets the number of the simultaneous users in the proposed system using the 2-D SS codes to accomplish the all users with 84 users. And the BER takes the data transmission rate in the proposed system using the 2-D SS codes to attain the 7.1 Gbps.

Design of Bipolar Optical Code-Division Multiple-Access Techniques Using Phase Modulator for Polarization Coding in Wireless Optical Communication

In this study, a bipolar optical code-division multiple-access (Bi-OCDMA) technique based on spectral amplitude coding (SAC) was proposed by using a phase modulator to realize polarization coding through a free-space optical (FSO) channel. Various types of noise, such as amplified spontaneous emission (ASE) noise, thermal noise, and shot noise, were included in the simulation to approach the real application. The first simulation, utilizing a modified M-sequence as signature code, demonstrated that the proposed Bi-OCDMA system could be implemented in FSO communication. The proposed Bi-OCDMA scheme improves the transmission rate and power efficiency compared with the previous scheme. The structure of the proposed system alleviates multiple-access interference (MAI) with a simple and cost-effective design. The second simulation observed the performance of the proposed Bi-OCDMA for two users with several well-known SAC codes, i.e., multi-diagonal (MD) code, modified quadratic congruence (MQC) code, modified maximum length sequence (M-sequence) code, and Walsh–Hadamard code, in extreme weather conditions, both for additive white Gaussian noise (AWGN) and turbulence-induced fading channel. The simulation results indicated that the Walsh–Hadamard code has superior performance compared to other codes. The results show the MD code can be implemented in the proposed Bi-OCDMA scheme for a medium-distance FSO.

Performance and security analysis of novel ZCCRW codes in lower earth orbit based MDM-OWC incorporating hybrid modulations

Abstract Explosive data rate requirements in the satellite communication for surveillance, military services, and broadcasting have put peer pressure on the optical wireless communication (OWC) systems. Secure data transmission against eavesdropper and performance enhancement at authentic user is major concern these days. In this work, performance and security analysis of spectral amplitude codes (SAC) in mode division multiplexed (MDM) OWC have been carried out and a novel zero cross correlation resultant weight (ZCCRW) code at 100 Gbps capacity has been presented. Random diagonal (RD), Enhanced double weight (EDW), Diagonal double weight (DDW) codes have been compared through simulations and also mathematical expressions are derived under the effects of eavesdropper. Hybrid modulations have been compared to check optimal modulation with combination of Laguerre-Gaussian (LG), and HermiteGaussian (HG) modes. Results have revealed that ZCCRW code with MD-DQPSK using LG modes provide best performance and least susceptibility to eavesdropper.

Performance evaluation of 120 GB/s hybrid FSO-SACOCDMA-MDM system using newly designed ITM-Zero cross-correlation code

Since last decade, Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system has become popular since it offers security, unlimited bandwidth and eliminates multiple access interference. On the other hand, Free Space Optics (FSO) provides last-mile access at a high data rate. We have designed a new zero cross-correlation code, which is named as an identity-type matrix ZCC code. The proposed code’s performance is evaluated by designing 120 GB/s Hybrid FSO-MDM (mode division multiplexing) and SAC-OCDMA system under atmospheric turbulence using the direct detection (DD) technique. Six channels, carrying 20 GB/s data each, are transmitted over the FSO channel. Two Laguerre Gaussian modes (LG 00 and LG 01) are used in MDM. The results of the simulation show that the performance of the proposed code is better in comparison to existing codes.

Evaluation Performance of Two-Dimensional Multi-Diagonal Code Using Polarization and Wavelength of OCDMA System

In this paper, a new encoder/decoder technique has employed two orthogonal polarization states (vertical and horizontal) of a two-dimensional optical code, which combined polarization and wavelength scheme (p/w). This technique employed in order to increase the number of users in the FTTH network. In addition, Optical Fiber Systems (OFS) and Free Space Optics (FSO) scenarios were utilized with different Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) codes. The FTTH network based on incoherent SAC-OCDMA is tested by using the One and Two Dimensional Multi-Diagonal (1D-MD, 2D-MD) codes and 1D and 2D Zero Cross Correlation (ZCC) codes. The results show that the number of the total supported homes for the 2D codes is doubled as a comparison with 1D codes. As well as, the simulation results show the performance of MD code is better presented than ZCC in both OFS and FSO scenarios