OCDMA System Research Articles

A Novel Embedded Pilot-Aided OCDM System Over Time-Varying Channels

A Novel Embedded Pilot-Aided OCDM System Over Time-Varying Channels

An Iterative Channel Estimation Algorithm Based on OMP for OCDM Systems

An Iterative Channel Estimation Algorithm Based on OMP for OCDM Systems

A Novel Delay-Doppler-Based Channel Estimation Method in Doubly-Dispersive OCDM Systems

A Novel Delay-Doppler-Based Channel Estimation Method in Doubly-Dispersive OCDM Systems

Performance investigation of 1.5 Tb/s optical hybrid 2D-OCDMA/OFDM system using direct spectral detection based on successive weight encoding algorithm

In order to raise the performance of optical communication systems, it is imperative mainly to increase the number of available users while decreasing the bit error rate (BER) in the required spectral width. This can be challenging in optical multiplexing systems including incoherent optical code division multiplexing (OCDMA). In this respect, an interesting two-dimensional hybrid spectral/spatial OCDMA system using orthogonal frequency division multiplexing (OFDM) technology based on successive weight (SW) coding has been investigated. Using the zero cross-correlation (ZCC) feature, the novel approach declined the effect of phase-induced intensity noise (PIIN), and multi-user interference (MUI) at the receiver has been fully eradicated. When compared to systems with Modified Double Weight (MDW), Flexible Cross Correlation (FCC), and two-dimensional hybrid Flexible Cross-Correlation - Modified Double Weight 2D-MDW/FCC codes, numerical findings demonstrate that our proposed system is more efficient, increasing the number of simultaneous users to 350, and achieving a higher overall transfer rate towards 1.5 Tb/s under the required optical communication conditions.

Ispitivanje nulte unakrsne korelacije fleksivilne promenljive težine (FVWZCC) za primenu u različitim medijima

Introduction/purpose: In this paper, we propose a novel code construction method with the zero cross-correlation property, the Flexible Variable Weight Zero Cross-Correlation (FVWZCC). This method is simple and flexible, using different code weights to support different classes of users according to their transmission distance and the quality of services they require (data, audio, and video) in OCDMA systems. The use of higher code weights enables the support of higher-priority application networks, such as long-haul reach networks. The ZCC code structure does not have overlapping of bit '1' and can efficiently eliminates the MAI interference between users and PIIN noise, thus enhancing the system overall performance. Methods: The shifting element position and the concatenation matrix process of the three basic matrices denoted as the Right vector, the basic matrix, and the Left vector were used for the construction of the proposed FVWZCC code. The mathematical analysis and simulations with Matlab and Optisystem software were used to evaluate the performance of the proposed FVWZCC method in SAC-OCDMA systems using the direct detection. Results: The results show a significant improvement in the presented code compared to other existing codes in terms of simplicity, flexibility, and cost implementation. The method uses either constant or variable weight with the Zero cross-correlation property. For a maximum acceptable BER of 10~9 , the simulation results of the SAC-OCDMA system using direct detection under OptiSystem software show better performance of the proposed code with four users of weight 6 at 10 Gb/s. Moreover, it can support up to 60 users simultaneously and reach a fibre distance of about 67 km. Consequently, the proposed FVWZCC code can be applied to support different Quality of Service (QOS) requirements with low cost and low complexity with a direct detection receiver. Conclusion: The findings of this study highlight the need for the FVWZCC code to support end-user QoS requirements. The new approach to code construction offers low-cost implementation, simplicity, and flexibility.

SLM based Circular (6, 2) mapping scheme with improved SER performance for PAPR reduction in OCDM without side information

Abstract Like OFDM, OCDM signal also suffers from high PAPR. SLM is an attractive PAPR reduction method but it needs to transmit the information regarding phase sequence i.e. SI to the receiver, which results in reduction in SE and data rate. Various SLM based SI free and SI embedding schemes are available in the literature. In this paper, different possible quaternary to 8-QAM mapping schemes for SI free SLM based PAPR reduction in OCDM system are discussed. Moreover, a new mapping scheme to eliminate the SI requirement has also been presented in this manuscript for SLM based PAPR reduction in OCDM system. Proposed Circular (6, 2) mapping scheme doesn’t require SI at the receiving end which results in increase in SE and data rate as compared to standard SLM technique. Random sequence with phase factors {1, −1} is used to generate the phase sequences for the proposed mapping scheme. Also, the analytical expression for SER of Circular (6, 2) mapping scheme over AWGN channel is derived. We have also evaluated the mathematical expression for SER of other possible quaternary to 8-QAM mapping schemes. Computer simulation using MATLAB are also carried out to investigate the performance of all these mapping schemes in terms of PAPR reduction performance as well as SER performance over AWGN and multipath Rayleigh fading channel. Proposed scheme achieves the same PAPR reduction and improved SER performance w.r.t. other six schemes taken into consideration.

Development of OCDMA system in spectral/temporal/spatial domain for non-mapping/MS/MD codes

Development of OCDMA system in spectral/temporal/spatial domain for non-mapping/MS/MD codes

Concentric triangular mapping with iterative substitution method for PAPR reduction in OCDM system without SI

Abstract OCDM, a new MCM scheme, has been proposed in the literature. Like widely used OFDM, OCDM also has a drawback of high PAPR. PAPR reduction schemes like SLM and PTS require information about phase factors i.e. SI used at the transmitting end for PAPR reduction for recovery of original data signal at the receiver. Transmission and recovery of SI is always a concern. In this paper a new CTM-IS method has been proposed for PAPR reduction of OCDM signal without SI. Main objective of the proposed scheme is to improve the error performance of SI free SLM and PTS based schemes without any degradation in PAPR reduction. PAPR performance and SER performance, over AWGN as well as multipath Rayleigh fading channels, of OCDM signal with proposed CTM-IS scheme is evaluated. Analytical expression for SER of the proposed CTM-IS scheme over AWGN channel is also derived. The computational complexity of the proposed CTM-IS scheme is also presented. Performance of the proposed CTM-IS scheme is compared with the existing MSM combined with SLM (MSM-SLM), CCM combined with SLM (CCM-SLM) and OM combined with SLM (OM-SLM) schemes. The proposed CTM-IS scheme has demonstrated to offer a theoretical power gain of about 3.01 dB, 2.55 dB, and 14.23 dB over MSM-SLM, CCM-SLM and OM-SLM schemes, respectively. Proposed CTM-IS scheme provides better SER performance with respect to MSM-SLM, CCM-SLM and OM-SLM without any loss in the PAPR performance. Moreover, computational complexity of CTM-IS scheme is less than that of MSM-SLM and CCM-SLM schemes.

Novel technique to cancel MAI for OCDMA system

Abstract Code division multiple access in optical domain has a potential in next-generation long-haul transmission systems. However, multiple user interference is a snag in functioning of system employing OCDMA. A detailed analysis of multiple access interference (MAI) which causes a severe degradation in the system performance is done in this paper. An optimum MAI cancellation scheme has been proposed. This cancellation scheme depends not only on using the excellent correlation property of the double padded modified prime codes (DPMPC) as spreading sequence but also on employing minimum shift keying (MSK). The performance of the proposed cancellation scheme is compared with the existing techniques of FSK-OCDMA and PPM-OCDMA cancellation techniques. MSK-OCDMA cancellation technique achieves the lowest bit error rate of 10−20. It is also efficient in power. It achieves lowest bit error rate at same number of mean photon number when compared to the existing techniques. The investigations reveal that MSK-OCDMA cancellation technique outperforms FSK-OCDMA and PPM-OCDMA cancellation schemes.

Comparative analysis of two address codes in a fiber-optic SA OCDMA system with FWM

Comparative analysis of two address codes in a fiber-optic SA OCDMA system with FWM

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.

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

Performance evaluation of a 160-Gbit/s OCDMA-FSO system via Laguerre-Gaussian beams under weather conditions

For capacity enhancement of free space optics (FSO) communication, a new model based on using four Laguerre-Gaussian (LG) beams, each carries four different users use optical code division multiplexing (OCDMA) techniques, is proposed. Additionally, the permutation vector (PV) codes that have zero cross correlation with direct detection (DD) technique are assigned to the OCDMA system. Each user carries 10 Gbps information data, so the overall capacity is 4 LG beams × 4 users (OCDMA) × 10 Gbps = 160 Gbps. Furthermore, the proposed model is simulated under the effects of different attenuations caused by different weather conditions and the performance is studied. The conducted results reveal successful transmission of 13 km under clear air (CA), 1.75 km under heavy haze (HH), 1.1 km under heavy rain (HR), and 0.9 km under heavy fog (HF) with an overall system capacity of 160 Gbps. These results were obtained with an acceptable log bit error rate (BER) less than −9 and quality (Q)-factor nearly 6.

Research and Simulation of OCDM Switch Layer Based on 2D WDM-Optical Code Switching Structure

Optical Communication is widely used in military and civilian backbone network communication, but due to the limitation of “electronic bottleneck”, the ability of network nodes to process information and optical layer data transmission capacity is seriously mismatched, which directly causes optical cross connectors in optical nodes. The number of ports carried has skyrocketed. In order to improve the processing speed of network nodes, this paper studies the four-layer multi-granularity switching system of optical fiber, wavelength band, wavelength, and optical code, and finally builds a complete OCDMA system through simulation software, simulates multi-user simulation, and successfully realizes The encoding and decoding process is analyzed, and the performance simulation and analysis of the core switching module of the four-layer multi-layer optical switching system-OCDM switching module are carried out, and the feasibility and superiority of the selected system are verified.

Investigation of inline optical amplifiers in 2-D time-wavelength OCDMA systems

This paper introduces the first mathematical investigation on utilizing a single inline optical amplifier in the 2-D time-spreading wavelength-hopping (TW) code division multiple access (OCDMA) system. The study adopts a non-ideal erbium-doped fiber amplifier (EDFA), where the optical gain depends on the input power of the amplifier. Three en/decoders representing different loss levels are examined. In addition, the paper highlights the significance of the power budget in the amplified TW systems to ensure the accomplishment of two concurrent conditions. First, the total input power from all users to the inline amplifier should fall within the amplifier input power range to gain sufficient amplification. Hence, the transmitted chip power from users is the key contributor. The second condition is the ordinary case where the desired received power should meet the required bit error rate (BER). The number of central splitter/combiner ports (Nsys) is an additional important system parameter, representing the upper bound of the available number of simultaneous users (K). The analysis supported by the Optisystem simulation results shows that the best location for the inline amplifier is close to the central system’s combiner. The results also reveal that, for low-user system capacities, employing a single inline optical amplifier in the 2-D TW OCDMA system is effective for the low-loss TW en/decoders but with increased code weights (w). For an 8-user system (i.e., Nsys = 8), transmitted chip power of 15 dBm, and EDFA amplification gain of 28 dB, the system can support the full-user capacity (at a BER ≤ 10-9) when w = 29. On the contrary, the performance of the higher system capacities sustains only a particular number of simultaneous users, accommodating up to 60 % of the full-user capacity when Nsys = 16.

Performance analysis of optical spectral amplitude CDMA system unipolar codes with double weight construction design

Abstract Optical Codes Division Multiple Access is a multiplexing approach in which the transmitter a distinguishable optical code is assigned to each user in the communication channel. OCDMA is designed for radio frequency (RF) communication systems and it is a variation of the CDMA system. Subsequently, to develop all OCDMA communication systems, the success of CDMA in wireless networks, as well as the full benefits of fibre optics, such as good security, extremely high bandwidth, low attenuation, and long-haul transmission. In this research Spectral Amplitude Coding-Optical Code Division Multiple Access is proposed. Initially, Modified Double Weight and Zero Cross-Correlation (MDW-ZCC) is proposed in this research to construct the code design of SAC-OCDMA, it produces the best possible autocorrelation and cross-correlation values. Subsequently, a combined Single Photodiode (SPD) and Direct detection technique is introduced to decode the transmitter information and it reduces the noise. Accordingly, a Gaussian approximation technique is presented to estimate the Bit error rate from the eye diagram of BER and Q-factor. Accordingly, the proposed method is simulated using Python software. The performance metrics are Q-factor, and bit error rate and the proposed method is compared with the existing Three-Dimensional Single Weight Zero Cross-Correlation (3D-SWZCC) Code, Two Dimensional Spectral/Spatial Cyclic Shift (2D-SSCS), and Permutation Matrix Zero Cross-Correlation (PM-ZCC) Code. Subsequently, these results exhibit that the proposed method produces the best performance than the other methods and it estimates the BER. Consequently, future work is based on the study of 3D codes with m-sequence code in the spectral/time/spatial OCDMA domain. The approach has elegantly integrated the design of an encoder and a decoder, allowing the system to efficiently create code in 3D bipolar mode, respectively.

Improve cardinality with two-dimensional unipolar (optical) orthogonal codes for multiple access interference

Abstract Optical code division multiple access (OCDMA) is one of the promising technologies to be implemented using all-optical networks. The OCDMA system performance is substantially determined by the particular encoding codes. Due to the different transmitter and receiver design considerations, selecting the right code family and code dimension is critical. In this research, 2D codes based on permutation vectors’ (PV) codes are presented to overcome the Multiple Access Interference (MAI) problem and system complexity. Consequently, the research work focused on two-dimensional unipolar codes to mitigate the probability error and cardinality of the optical CDMA system. A fast wavelength-hopping/time-spreading (FWHTS) is introduced as an encoding technique. The FWHTS is used for code construction design, and it achieves cardinality in upper bound theory without sacrificing good auto-and-cross correlation properties. Accordingly, hybrid codes with serial elimination interference receivers are presented to estimate the error probability of 2D optical codes. The proposed method is simulated using Python software. The performance metrics are flexibility, bit rate, minimum temporal length, computational complexity, cardinality and wavelength. The proposed method is compared with the existing 2D balanced incomplete block design (BIBD) technique and multidiagonal (MD) codes. The performance of the proposed method is approximately 4% higher than these existing methods. Subsequently, in the future work, a SAC-OCDMA code construction design shall be presented and the decoding techniques can be introduced, which can reduce the receiver noise and other phase intensity induced noise, respectively.

Contribution of OFDM modulation to improve the performance of non-coherent OCDMA system based on a new variable weight zero cross correlation code

Contribution of OFDM modulation to improve the performance of non-coherent OCDMA system based on a new variable weight zero cross correlation code

Development of multi diagonal based OCDMA system for free space optical communication system

The performance of FSO communication link is subject to numerous atmospheric factors in wireless communication like fog, rainfall, and haze which leads to deteriorate the performance of a system in term of BER and power at the receiver side. Due to numerous advantages of OCDMA over other access techniques, it allows various users to access a channel simultaneously without intervention with the other user. It has the ability to provide security, large number of users, privacy, reduce interference from multiple users and operate asynchronously. So, in this paper, Multi-Diagonal codes along with the fiber brags grating filters for Spectral amplitude coded OCDMA technique is developed for FSO system and performance analysis is performed in terms of BER and received power.

Reduction of Complexity Design of SAC OCDMA Systems by Utilizing Diagonal Permutation Shift (DPS) Codes with Single Photodiode (SPD) Detection Technique

In this paper, a diagonal permutation code is presented for spectral amplitude coding optical code division multiple access (SAC-OCDMA) employing a single photodiode (SPD) detection technique. It is characterized by practical code length and ideal in-phase cross correlation (CC) that results in multiple access interference (MAI) suppression. A diagonal permutation shift (DPS) code can be constructed using both prime codes and some matrix operations. In addition, it can be easily implemented as it exists for prime numbers P, which limits the addressing probability of codes to P2. Fiber Bragg gratings (FBGs) are used for code encoding and decoding. Simulation analysis that calibrates with BER, Q-factor, and eye diagram proves that DPS code using SPD technique is able to maintain error free transmission compared to the complementary detection scheme (CDS) technique. It is reported that a reduction of fiber Bragg grating (FBG) sets by 41.6% was achieved for SPD over CDS techniques.