Spectral Division Research Articles

Construction and performance analysis of a new SAC-OCDMA code based on Latin square matrix

In this paper a family of novel spreading code called Latin square code (LSC) is proposed for spectral amplitude coding-optical code division multiple access (SAC-OCDMA) system. The main feature of the proposed code is the zero cross-correlation which eliminates both multiple access interference (MAI) and phase induced intensity noise (PIIN). The code construction can be easily accomplished using Latin square matrix (LSM) for any weight and number of users. The simplicity in the construction code has made it a compelling candidate for future OCDMA applications. SAC-OCDMA system employing direct decoding is mathematically analyzed and then numerically simulated using Matlab and OptiSystem respectively. The results show the improvement given by the LSC code to the SAC-OCDMA system compared to the other codes such as: ZCC (zero cross-correlation) and MMS (modified multiservice) by allowing high cardinality and improving BER. Furthermore, the transmission quality, so that the BER does not exceed the value of $10^{-9}$, is ensured by the LSC code with a lower effective source power of -14.5 dBm, a bit rate of 4.6 Gb/s and a cardinality exceeding ZCC and MMS by 1.7 and 1.22 times respectively. The simulation results validate the mathematical analysis and show that the system makes it possible to increase the transmission distance without affecting QoS (quality of service)

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

Development and performance improvement of a novel zero cross-correlation code for SAC-OCDMA systems

Abstract In order to improve the performance of the Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA) system, a zero cross-correlation (ZCC) code named double weight multi-diagonal (DW-MD) is proposed with constant weight (CW) or variable weight (VW). Mathematical results illustrate that it is feasible to reduce the number of filters without sacrificing system performance by using the CW DW-MD code instead of the multi-diagonal (MD) code. And for the VW DW-MD code, the supportable number of users for lower code weight W L (3) at bit error rate (BER) of 10−3 (voice) is 43, medium code weight W M (4) at BER of 10−9 (data) is 29, and higher code weight W H (5) at BER of 10−12 (video) is 32. Finally, the analysis about the position of chips “1” is given, and the simulation setups show that the CW DW-MD code outperforms the MD code when Gaussian optical filter is used.

16QAM spectral efficiency frequency division multiplexing transmission with Tomlinson–Harashima precoding for intensity modulation and direct detection optical links

In the spectral efficient frequency division multiplexing (SEFDM) system, in order to minimize mutual interference between subcarriers, a detector should be introduced at the receiver to handle the interference, but increases the complexity of system. In this paper, we propose a simplified precoding algorithm at transmitter instead of receiver, which can first implement higher 16QAM SEFDM transmission over standard single mode fiber (SSMF). The technique is based on interference information from non-orthogonality between subcarriers and uses nonlinear matrix operations to improve system performance with low complexity. The numerical results show that the precoding scheme achieves SSMF transmission of intensity modulation and direct detection (IM/DD) 16QAM SEFDM system under the premise of achieving higher spectral efficiency, and obtains good bit error rate performance.

Sound field synthesis of arbitrary moving sources using spectral division method.

The spectral division method (SDM) is one of several sound field synthesis techniques of spatial sound reproduction. The synthesis accuracy of SDM is usually higher than that of wave field synthesis (WFS). However, existing SDM-based sound field synthesis methods are developed for virtual sources moving uniformly along a straight trajectory. This Letter proposes a 2.5-dimensional SDM driving function for arbitrary moving sources. Numerical simulations have validated the driving function. The results indicate that the synthesis error of the SDM with the proposed driving function is lower than that of WFS, especially when the virtual source is close to the secondary sources.

A configurable transmitter-receiver structure to support QoS for spectral amplitude coding-optical code division multiple access

Abstract This paper proposes a new coding scheme for spectral amplitude coding (SAC) family, known as Sigma Shift Matrix (SSM). Two techniques are proposed for the design of SSM coding scheme. The first technique combines the identity and upper shift matrices to form an SSM coding matrix named as SSMI. The second approach adapts the assembly of a single – entry, lower and upper shift matrices to compose another SSM matrix called SSMs. Combination of these matrices generates variable SSM code families, which can provide more flexibility in code weight selection and the number of users respectively. Furthermore, a modified SSM (MSSM) coding scheme is proposed through bitwise ANDing of SSMI and SSMS to further elevate performance of the proposed setup. The optimized structure of SSM coding scheme eliminates the influence of multiple access interference (MAI) and alleviate the effect of phase induced intensity noise (PIIN). Numerical results show that MSSM, SSMI and S S M S SSMS outperform the existing coding schemes in descending order and proves to be an efficient candidate for the implementation of high capacity next generation of optical communication networks.

Optical Code Construction Based on Enhanced Quantum Logic Gate (EQLG) Technique for Spectral Amplitude Coding Optical CDMA Systems

Spectral Amplitude Coding Optical Code Division Multiple Access (SAC–OCDMA) is an auspicious advancement in an asynchronous environments. In this paper, we have presented an effective Enhanced Quantum Logic Gate (EQLG) code for SAC–OCDMA to improve the code construction, cross-correlation and minimize the noises. The EQLG code contains unitary matrices with minimum overlaps in code spectral wavelengths of various clients. This drops the Multiple Access Interference (MAI) and furthermore EQLG code, provides high data-rate transmission in networks. The development of the proposed EQLG code is depicted in following strides as; at first build a matrix utilizing the estimation of the weight value and the number of subscribers. Based upon that, the number of rows and columns are located in the matrix. Second, each diagonal sequences are computed by using the QLG method. The execution of the recommended EQLG code will be analysed with existing SAC–OCDMA systems in response to Bit Error Rate (BER). The simulations of encoding with 10–60 users with 622 Mb/s data transmission at a BER of 10−9 have been successfully achieved.

SAC-OCDMA system performance using narrowband Bragg filter encoders and decoders

In this paper, we have studied a Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system performance using fiber Bragg gratings equivalent to very narrow filters used in the system as encoders and decoders in both the transmitter and the receiver block. The system performance depends on several variables such as: the optical power; the fiber length; the data rate and the bandwidth. Different simulations have been realized in terms of the bit error rate (BER) and the quality factor (Q) to evaluate the effect of each parameter on the system performance and also to examine the impact of number of users. The obtained results using Optisystem network show clearly that the studied SAC-OCDMA system of three users remains efficient for fiber lengths up to 25 km at a data rate of 200 Mbits/s and a FBGs bandwidth of 0.6 nm. These results are realized with an acceptable bit error rate $$BER < 10^ {-9}$$ . In addition, a SAC-OCDMA system of 9 users was also simulated to assess the effect of the number of users. The results obtained show that for a fiber length $$\hbox {L}=5$$ Km, the system remains efficient for a number of users set at 8 users, then the longer the fiber length increases the more the number of possible users decreases. For $$\hbox {L}= 35$$ Km, the number of users for whom all users obtain a good BER value is 6 users.

Detection of surface structural changes during adsorption events using two-trace two-dimensional (2T2D) correlation spectroscopy

We demonstrate a method by which a pair of spectra acquired using surface-sensitive second-order nonlinear vibrational spectroscopy, visible-infrared sum-frequency generation, can be analyzed in order to readily determine whether changes that occur as a result of varying environmental conditions results in a change in the population of surface molecules, or a structural rearrangement of the surface. This is accomplished via two-trace two-dimensional correlation analysis, a recently developed technique that uses spectral phase information to provide a level of comparison beyond what can be achieved by simple spectral subtraction or division. While surface reorientation and/or a change in the degree of ordering are often difficult to detect from spectra obtained in a single beam polarization, without detailed analysis of the lineshape, we show that such changes provide strong asynchronous cross peaks in the frequency correlation map.

Reconciling Ground Motions and Stress Drops for Induced Earthquakes in the Western Canada Sedimentary Basin

ABSTRACTA regional ground-motion prediction equation (GMPE) is defined for earthquakes in the western Canada sedimentary basin. The stress parameter model that is input to the GMPE, which controls high-frequency amplitudes, is developed based on an empirical Green’s function (EGF) study in the same region (Holmgren et al., 2019). The GMPE is developed using the generic GMPE approach of Yenier and Atkinson (2015a,b); regional parameters, including attenuation and site response, are calibrated using a database of response spectra. The ground-motion database comprises 726 records from 92 earthquakes with magnitudes 2.3–4.4, at distances to 200 km; most events are believed to be related to hydraulic fracturing. To investigate discrepancies between the values of GMPE stress parameter and EGF stress drop for individual earthquakes, stress parameters are computed for each event by fitting the GMPE to observed response spectra. There is a large scatter in the EGF versus GMPE stress estimates, even though the GMPE estimates were implicitly calibrated to equal the EGF values on average. The discrepancies can be attributed to two methodological factors. First, the EGF approach removes the site and path terms through spectral division, whereas the GMPE approach relies on an average regional model as determined from regression of the source and path attenuation. The use of an average regional model results in greater uncertainty, in particular, due to directivity effects (which are better accommodated in the EGF approach). Second, the EGF approach is performed in the Fourier domain, whereas the GMPE fitting is done in the response spectral domain. We conclude that EGF stress-drop models provide useful constraints for GMPE development, when used in combination with calibration to a ground-motion database.

Design and performance of spectral efficient modified new diagonal code for a spectral amplitude code-optical code division multiple access system

Our study contains performance and design of a spectral amplitude code-optical code division multiple access (SAC-OCDMA) system using proposed modified new diagonal (MND) code. The proposed MND code has advantages as very low cross-correlation value compared to other code sequences. Also the code has a short length for the higher code weight value. Furthermore, due to its enormous code property, it also introduces very low multiple access interference. Thus the MND code-based SAC-OCDMA system permits a higher number of users. The MND code construction method is also explained, which is very easy using diagonal matrices. Based on the theoretical analysis, bit error rate (BER) performance of MND code AND-subtraction scheme compare with conventional codes is better than random diagonal code, Pascal’s triangle matrix code (PTMC), and multidiagonal (MD) code, which makes it spectral efficient. It provides 5 dB lower BER compared to MD code and PTMC for 90 users. Simulation of the MND code-based system for four users with 2 Gbps data rate has been successfully demonstrated using the AND-subtraction scheme and the direct detection scheme.

Performance enhancement of multiple access 3D-OCDMA networks using a pascal triangle codes

In this paper, a novel Three Dimensional Pascal’s Triangle Zero Cross Correlation (3D-PTZCC) code is proposed for non coherent Spectral Amplitude Coding Optical Code Division Multiple Access systems with a spectral/time/spatial combination and direct detection at the level of the receiver. The proposed code is based on (1D-PTZCC) and (2D-PTZCC) codes using Pascal’s Triangle rule. Its structure can minimise the receiver complexity of 3D-Perfect/Multi Diagonal (3D-PD/MD) and 3D-Perfect Difference (3D-PD) codes. The simulation results prove that systems using the proposed code can support a high data rate, high signal power and large number of simultaneous users with less power consuming. The code can save the received power by around − 5.5 dBm and − 3.7 dBm and the system capacity can be enhanced by 4.7 and 3.85 times compared to the systems using (3D-PD/MD) and (3D-PD) codes.

Performance improvement of multi access OCDMA system based on a new zero cross correlation code

In this paper, a novel zero cross correlation (ZCC) code is proposed for spectral amplitude coding-optical code division multiple access (SAC-OCDMA) systems. The code construction method starts from the identity matrix and has several benefits summarized in both the code simplicity and flexibility. The proposed code presents also an adapted (or accepted) code length for SAC-OCDMA systems and a high SNR value that reaches respectively 3.18 and 1.84 times of the system capacity comparing to other existed codes such as modified quadratic congruence (MQC) and modified double weight (MDW) codes.

Performance of Spatial Diversity DCO-OFDM in a Weak Turbulence Underwater Visible Light Communication Channel

The performance of underwater visible light communication (UVLC) system is severely affected by absorption, scattering and turbulence. In this article, we study the performance of spectral efficient DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) in combination with the transceiver spatial diversity in turbulence channel. Based on the approximation of the weighted sum of lognormal random variables (RVs), we derived a theoretical exact bit error rate (BER) for DCO-OFDM systems with spatial diversity. The simulation results are compared with the analytical prediction, confirming the validity of the analysis. It is shown that spatial diversity can effectively reduce the turbulence-induced channel fading. The obtained results can be useful for designing, predicting, and evaluating the DCO-OFDM UVLC system in a weak oceanic turbulence condition.

A Novel Circular Flexible Multiscale Geometric Analysis Method

Image representation is an essential problem in image processing. The most effective image representation method is multiscale geometric analysis (MGA). However, the current representative MGA method has some shortcomings, such as the fixed division of the scale spectrum and the direction spectrum, which cannot achieve well the sparsest representation of the image; the lack of rotation invariance and translation invariance make it impossible to achieve better results in the application. In this paper, a new circular flexible MGA method is proposed to solve this problem. First, the McClellan method was used to design a circular flexible multiscale decomposition, which had translation invariance and rotation invariance due to the circular spectral shape. Moreover, the spectral division of the new multiscale decomposition method could be flexibly changed according to the image, rather than being fixed at π/2 in the traditional manner. Second, new linear phase directional filter banks were proposed to divide the direction flexibly, which had selectivity in any direction. Finally, the two steps above were combined to construct a new MGA method, which maintained translation invariance, low redundancy, and flexibility in both scale and direction, resulting in better frequency localization and more sparse representation. The results of our denoising experiment show that the method proposed in this paper not only achieves a perfect reconstruction, but also performs well in image denoising compared to other state-of-the-art MGA methods.

MLP With Riemannian Covariance for Motor Imagery Based EEG Analysis

Stroke is one of the leading causes of disability and incidence. For the treatment of prognosis of stroke patients, Motor imagery (MI) as a novel experimental paradigm, clinically it is effective because MI based Brain-Computer interface system can promote rehabilitation of stroke patients. There is being a hot and challenging topic to recognize multi-class motor imagery action classification accurately based on electroencephalograph (EEG) signals. In this work, we propose a novel framework named MRC-MLP. Multiple Riemannian covariance is used for EEG feature extraction. We make a multi-scale spectral division to filter EEG signals. They consist of different frequency bandwidths name sub-band. We concatenate and vectorize features extracted by Riemannian covariance on each sub-band. We design a fully connected MLP model with an improved loss function for motor imagery EEG classification. Furthermore, our proposed method MRC-MLP outperforms state-of-the-art methods and achieves approximately mean accuracy with 76%.

Chromatic dispersion mitigation using a SEFDM-based diversity technique for IM/DD long reach optical links.

Spectral efficient frequency division multiplexing (SEFDM) can offer a higher spectral efficiency (SE) than orthogonal frequency division multiplexing (OFDM). In this work, we propose a diversity technique based on SEFDM for beyond 100-Gb/s optical intensity modulation and direct detection (IM/DD) long reach (LR) applications. We mathematically demonstrate that the self-created inter-carrier interference of SEFDM signals can be reused to achieve a diversity gain on each sub-carrier and, in turn, improve the tolerance to power fading induced by chromatic dispersion (CD) in IM/DD LR links. Based on the proposed diversity technique, we further demonstrated a 112-Gb/s SEFDM transmission over 80-km standard single-mode fiber, using only 28-GHz bandwidth and modulation format of up to 16-QAM. Experimental results show that SEFDM with the proposed diversity technique performs robust against CD effects and outperforms the conventional OFDM with adaptive bit and power loading of the same bandwidth and data rate, which validates the superiority of the proposed SEFDM in optical IM/DD LR transmissions.

Radio over fiber system based on a hybrid link for next generation of optical fiber communication

&lt;p&gt;Radio over fiber technology will play an important role in solving problems facing wireless technology. Envisaging a global village, people could transmit and receive “anytime, anywhere, and anything”. In addition, the explosive growth in internet applications such as the World Wide Web, demonstrates the tremendous increase in bandwidth and low power that the coming world of multimedia interactive applications will require from future networks. ROF technology uses multicarrier modulation like orthogonal frequency division multiplexing (OFDM), which provides an opportunity of having an increased in bandwidth together with an affordable cost and this idea has recently become a suitable topic for many research works. On the other hand, SAC-OCDMA (Spectral Amplitude Coding Optical Code Division Multiple Access) technique is able to enhance the data rate of system and increase the number of user. In this paper we introduce a ROF link using a hybrid OFDM/SAC-OCDMA technique.&lt;/p&gt;

Directional Equalization of Sparse Head-Related Transfer Function Sets for Spatial Upsampling

Acquiring decent full-spherical sets of head-related transfer functions HRTFs based on a small number of measurements is highly desirable. For spatial upsampling, HRTF interpolation in the spatially continuous spherical harmonics SH domain is a common approach. However, the number of measured HRTFs limits the assessable SH order, resulting in order-limited HRTFs when transformed to the SH domain. Thus, the SH representation of sparse HRTF sets shows restricted spatial resolution and suffers from order-limitation errors. We present a method that reduces these errors by a directional equalization prior to the SH transform. This is done by a spectral division of each HRTF with a corresponding directional rigid sphere transfer function. The processing removes direction-dependent temporal and spectral components and, therefore, significantly reduces the spatial complexity of the HRTF set, allowing for an enhanced interpolation of HRTFs at reduced SH orders. Spatial upsampling is achieved by an inverse SH transform on an arbitrary dense sampling grid. A subsequent de-equalization by a spectral multiplication with the rigid sphere transfer function recovers the energy in higher spatial orders that was not inherent in the sparse HRTF set. For evaluation, HRTFs were calculated for various limited orders from sparse datasets and compared to a reference. The results show that the proposed method clearly outperforms common SH interpolation of HRTF spectra regarding the overall spectral and temporal structure as well as modeled localization performance.

Performance Evaluation of System in Free Space Optic Utilizing Gaussian Optical Filter in Different Detection Scheme

Abstract In recent years, free space optical communication (FSO) has become a leader for its unique characteristics: large bandwidth, unlicensed spectrum, simple implementation, low power and high data rate. However, we use as a transmission medium for Spectral Amplitude Coding-Optical Code Division Multiple Access SAC OCDMA system. In this paper, we investigate the optimum received power of FSO communication system employing SAC OCDMA, by using different detection technique, such us Spectral Direct Detection SDD and Single Photodiode Detection (SPD) technique under optical Gaussian filter decoder schemes with Modified Double Weight code (MDW). In this work, the adverse effects of atmospheric channel limit the possibility of a large FSO communication, moderate turbulence and hazy weather conditions are considered. The results show that the performance of the proposed system with wavelength-division-multiplexing (WDM) multiplexer (MUX) based on Gaussian optical filter with SDP detection fares better than the system employing SDD technique.