Modified Quadratic Congruence Research Articles

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.

A hybrid next-generation passive optical network and visible light communication for future hospital applications

The advancement in the latest healthcare technologies have shown a growing interest in 10/10 Gbps per channel hybrid next generation passive optical network (NG-PON) and visible light communication (VLC) networks to achieve the aim of future hospital applications. This paper investigates the use of hybrid time and wavelength division multiplexing PON (TWDM-PON), wavelength division multiplexing optical code division multiple access PON (WDM-OCDMA PON) using zero cross-correlation (ZCC) code and VLC for the hospitals scenario. The proposed bidirectional system is investigated for four TWDM, six WDM-OCDMA and three VLC information channels in terms of variable fiber length, bit rate, different OCDMA codes and multi-hospital systems. It is investigated that upstream channels performs better than downstream channels and provides the successful 10/10 Gbps hybrid system over 50 km fiber and 10 m VLC link serving 53 users in single hospital system. It also provides the high eye-height, optical signal to noise ratio (OSNR) and received power. Moreover, the performance of the proposed system can be further enhanced by using modified quadratic congruence (MQC) code and high transmission power. Also the comparative analysis with existing systems show the superiority of the hybrid NG-PON/VLC system using fiber/wireless links over the conventional radio access networks in healthcare applications.

Performance analysis of high speed backward compatible TWDM-PON with hybrid WDM–OCDMA PON using different OCDMA codes

In this paper, a backward compatible bidirectional 160/40 Gbps time and wavelength division multiplexing-passive optical network with hybrid wavelength division multiplexing optical code division multiple access PON (WDM–OCDMA PON) has been proposed. Six OCDMA codes have been used to enhance the security and users’ ability to access shared bandwidth of an optical network. In this “pay-as-you-grow” supported system, the fiber impairment effects have been effectively reduced. The performance of the proposed system has been analyzed for variable input power (4–19 dBm) and transmission distance (10–70 km) supporting 120 active users under the influence of fiber nonlinearities, attenuation, dispersion and noise. Based on the numerical calculations, the proposed system using modified quadratic congruence (MQC) code is shown to provide better performance compared to multi diagonal, hadamard, zero cross-correlation (ZCC), shift ZCC and flexible cross-correlation codes. To validate the numerical analysis, the simulation of the proposed system at 160/40 Gbps data rate for 70 km downstream and greater than 70 km upstream fiber link transmission at 10−9 BER limit for 68 active users have been successfully demonstrated. Also, it has been shown that MQC code provides optimum results at 10 dBm input power over 55 km distance and supports more than 120 active users with high gain of − 1.97 dB and low noise figure of 2 dB. Further, the comparative performance of the proposed system with the previous latest works in literature reveals a superior performance of the system.

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.

An Efficient Method to Reduce an MAI’s Effect in Spectral Amplitude Coding OCDMA Network

Multiple access interference (MAI) in spectral-amplitude coding, optical code division multiple access (SAC-OCDMA) scheme hardly limits the system performance. This problem increases proportionally with the amount of concurrent users. In addition, phase induces intensity noise (PIIN) coming from the spontaneous emission process of light source is extra impairment leads to system drop needs to be tackled too. Towards overcome the specified problems, vector combinatorial (VC) codes which based on grouping of certain vectors is proposed. Any positive integer number can be used in both weighs and user parameters in code building procedure, these technique nominees our code to be a potential reliable applicant for future optical communication schemes. Such flexibility is an exceptional property for VC compared to SAC-OCDMA counterparts’ codes. Compared with the systems employing Hadamard, Modified Frequency Hopping (MFH), Modified Quadratic-Congruence (MQC), and Modified Double Weight (MDW), numerical results show that, the VC is effective to reduce the power of MAI and PIIN. It has been exposed that, performance can be superior significantly when VC is used.

An Efficient Method to Reduce an MAI’s Effect in Spectral Amplitude Coding OCDMA Network

Multiple access interference (MAI) in spectral-amplitude coding, optical code division multiple access (SAC-OCDMA) scheme hardly limits the system performance. This problem increases proportionally with the amount of concurrent users. In addition, phase induces intensity noise (PIIN) coming from the spontaneous emission process of light source is extra impairment leads to system drop needs to be tackled too. Towards overcome the specified problems, vector combinatorial (VC) codes which based on grouping of certain vectors is proposed. Any positive integer number can be used in both weighs and user parameters in code building procedure, these technique nominees our code to be a potential reliable applicant for future optical communication schemes. Such flexibility is an exceptional property for VC compared to SAC-OCDMA counterparts’ codes. Compared with the systems employing Hadamard, Modified Frequency Hopping (MFH), Modified Quadratic-Congruence (MQC), and Modified Double Weight (MDW), numerical results show that, the VC is effective to reduce the power of MAI and PIIN. It has been exposed that, performance can be superior significantly when VC is used.

Numerical Method for Constructing Fixed Right Shift (FRS) Code for SAC-OCDMA Systems

In optical code division multiple access (OCDMA) systems, multiple access interference (MAI) problem which amplifies with the number of users actively involving in the network robustly bound the performance of such network. In this paper an algorithm to generate binary code sequences based on spectral amplitude coding (SAC) technique for CDMA under optical communication systems environment named fixed right shifting (FRS) is proposed. This algorithm is built with minimum cross correlation (MCC) using some type of Jordan matrices with straightforward algebraic methods. By using the code weight W and the number of users N, various sets of binary code sequences for the possibilities of even and odd combination are constructed. Furthermore, this algorithm allows users with different code sequences to transmit data with minimum likelihood of interference. Simulation results show our technique for an agreeable bit error rate (BER) of 10-12 can support a higher number of users in deterministic and stochastic methods compared to reported techniques such Modified Quadratic Congruence (MQC) and Modified Frequency Hopping (MFH).

A Review on Successive Interference Cancellation-Based Optical PPM-CDMA Signaling

AbstractThis paper presents a comprehensive review of successive interference cancellation (SIC) scheme using pulse position modulation (PPM) for optical code division multiple access (OCDMA) systems. SIC scheme focuses on high-intensity signal, which will be selected after all users were detected, and then it will be subtracted from the overall received signal, hence, generating a new received signal. This process continues till all users eliminated one by one have been detected. It is shown that the random location of the sequences due to PPM encoding can reduce the probability of concentrated buildup of the pulse overlap in any one-slot time, and support SIC to easily remove the effect of the strongest signal at each stage of the cancellation process. The system bit error rate (BER) performance with modified quadratic congruence (MQC) codes used as signature sequence has been investigated. A detailed theoretical analysis of proposed system taking into account the impact of imperfect interference cancellation, the loss produced from the splitting during encoding and decoding, the channel loss and multiple access interference is presented. Results show that under average effective power constraint optical CDMA system using SIC scheme with

A new two dimensional spectral/spatial multi-diagonal code for noncoherent optical code division multiple access (OCDMA) systems

A new two dimensional codes family, namely two dimensional multi-diagonal (2D-MD) codes, is proposed for spectral/spatial non-coherent OCDMA systems based on the one dimensional MD code. Since the MD code has the property of zero cross correlation, the proposed 2D-MD code also has this property. So that, the multi-access interference (MAI) is fully eliminated and the phase induced intensity noise (PIIN) is suppressed with the proposed code. Code performance is analyzed in terms of bit error rate (BER) while considering the effect of shot noise, PIIN, and thermal noise. The performance of the proposed code is compared with the related MD, modified quadratic congruence (MQC), two dimensional perfect difference (2D-PD) and two dimensional diluted perfect difference (2D-DPD) codes. The analytical and the simulation results reveal that the proposed 2D-MD code outperforms the other codes. Moreover, a large number of simultaneous users can be accommodated at low BER and high data rate.

In-band Bidirectional Optical Network Based on OCDMA Technique

Bidirectional optical network based on direct detection optical code division multiple access (OCDMA) technique is implemented. In this architecture, in-band was used for up/downstream transmission data encoded by modified quadratic congruence (MQC) codes at channel spacing 12.5 GHz (i.e., 0.1 nm), and simultaneously transmitted since they are at different wavelengths. The results of the system with optimum parameters show low error rate transmission at 1 Gbit/s data rate and minimum receiver sensitivity −24 dBm which make the high performance is achievable. The results have indicated that bidirectional optical CDMA technique capable to support local area networks as an application for fiber to the home (FTTH).

Cardinality enhancement of spectral/spatial modified double weight code optical code division multi-access system by PIIN suppression

A new two-dimensional (2-D) optical code division multiple access (OCDMA) scheme to increase the achievable system capacity is proposed. The code exhibits good cross-correlation property time and wavelength shift. Performances are analyzed on code size and correlation properties affecting two important system parameters, bit error rate (BER) as a function of cardinality generated and optical power transmission requirement. The proposed system can effectively suppress phase-induced intensity noise (PIIN) and has multi-access interference (MAI) cancellation property. Results in a good agreement indicate that 2-D modified double weight (MDW) offers 163.7% and 336.2% larger cardinality compare to 2-D perfect difference code (PDC) and 2-D modified quadratic congruence (MQC) code. By increasing spatial code (N) and keeps similar code length system performance can be further optimized. 2-D MDW (M=45, N=18) accommodates 252.2% and 18.3% cardinality increment and low effective transmitted power (Psr) at −17.9dBm, compare to 2-D MDW (M=247, N=3) and (M=84, N=9) at 10−9 BER error floor. The architecture of the spectral/spatial MDW OCDMA system with property of MAI cancellation is presented.

Spectral efficiency analysis of bipolar spectral-amplitude coding optical code-division multiple-access systems using different one-dimensional codes

In this study, the spectral efficiency (SE) of bipolar spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems operating with incoherent sources is analysed. The analytical expressions of the model were derived to assess the performance of SAC-OCDMA systems, taking into account the intensity noise as the primary source of noise. Four different SAC codes were used to evaluate and compare the SE against the number of active users and code length for a bit-error rate (BER) of 10−11. The investigated codes are Hadamard, modified quadratic congruence (MQC), balanced incomplete block design (BIBD) and zero cross-correlation (ZCC). Our analytical results revealed that ZCC code has the ability to support more users at a high data rate up to 2.5 Gbps and offers significant SE enhancement in bipolar SAC-OCDMA system over other SAC codes under investigation. In addition, bipolar encoding improves the SE compared with unipolar technique, for example bipolar ZCC has 7.7-dB SE advantage than unipolar ZCC. Furthermore, when BER requirement of the system decreases, the SE can be increased.

Improved BER based on intensity noise alleviation using developed detection technique for incoherent SAC-OCDMA systems

The major drawback of incoherent spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems is their inherent intensity noise originating due to the incoherency of the broadband light sources. In this paper, we propose a developed detection technique named the modified-AND subtraction detection for incoherent SAC-OCDMA systems. This detection technique is based upon decreasing the received signal strength during the decoding process by dividing the spectrum of the utilized code sequence. The proposed technique is capable of mitigating the intensity noise effect, as well as suppressing the multiple-access interference impact. Based on modified quadratic congruence (MQC) code, the analytical results reveal that the modified-AND detection offer best bit-error rate (BER) performance and enables MQC code to support higher transmission rate up to 1.25 Gb/s compared to conventional AND detection. Furthermore, we ascertained that the proposed technique enhances the system performance using a simulation experiment.

Modified-AND Subtraction Detection Technique Based on Weight-Division for SAC-OCDMA Systems

In this paper, we investigate the use of the modified-AND subtraction detection to assuage the intensity noise in spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems. This detection approach is based upon reducing the received power to the decoders by dividing the weight of the utilised code sequence. The proposed technique has the ability to suppress the influence of multiple-access interference (MAI), in addition to alleviate the intensity noise effect. We simulate the system performance of the proposed detection technique using OptiSystem software Version 9.0. The software considered the entire practical impacts in the system, such as nonlinear effect, dispersion, and attenuation in the fiber. The simulation results based on the modified quadratic congruence (MQC) code show that the modified-AND subtraction detection offer best bit-error rate (BER) performance compared to traditional AND subtraction detection.

Investigation of in-band transmission of both spectral amplitude coding/optical code division multiple-access and wavelength division multiplexing signals

The transmission of both optical code division multiple-access (OCDMA) and wavelength division multiplexing (WDM) users on the same band is investigated. Code pulses of spectral amplitude coding (SAC)/optical code division multiple-access (CDMA) are overlaid onto a multichannel WDM system. Notch filters are utilized in order to suppress the WDM interference signals for detection of optical broadband CDMA signals. Modified quadratic congruence (MQC) codes are used as the sig- nature codes for the SAC/OCDMA system. The proposed system is sim- ulated and its performance in terms of both the bit-error rate and Q-factor are determined. In addition, eavesdropper probability of error-free code detection is evaluated. Our results are compared to traditional nonhybrid systems. It is concluded that the proposed hybrid scheme still achieves acceptable performance. In addition, it provides enhanced data confiden- tiality as compared to the scheme with SAC/OCDMA only. It is also shown that the performance of the proposed system is limited by the interference of the WDM signals. Furthermore, the simulation illustrates the trade- off between the performance and confidentiality for authorized users.

Development of a new code family based on SAC-OCDMA system with large cardinality for OCDMA network

We have proposed a new Multi-Diagonal (MD) code for Spectral Amplitude – Coding Optical Code Division Multiple Access (SAC-OCDMA). Although this new MD code has many properties, one of the important properties of this code is that the cross correlation is always zero. Simplicity in code construction and flexibility in cross correlation control has made this code a compelling candidate for future OCDMA applications. The Multiple access interference (MAI) effects have been successfully and completely eliminated. Based on the theoretical analysis MD code is shown here to provide a much better performance compared to Modified Quadratic Congruence (MQC) code and Random Diagonal (RD) code. Proof-of-principle simulations of encoding with 5 and 10 users with 622 Mb/s data transmission at a BER of 10 −12 have been successfully demonstrated together with the DIRECT detection scheme.

A New Technique for Reduction the Phase Induced Intensity Noise in SAC-OCDMA Systems

A new code for reduction the phase induced intensity noise has been presented. The new code is proposed for Spectral Amplitude-Coding Optical Code Division Multiple Accesses (SAC-OCDMA). This new code family we call it Dynamic Cyclic Shift (DCS) code. The DCS code reduced the effect of Multi Access Interference (MAI) due to it is the property of variable cross correlation. We find that the performance of the DCS code is a batter than other SAC-OCDMA codes such as; Random Diagonal (RD) code, Modified Quadratic Congruence (MQC) code and Modified Frequency Hopping (MFH) code. Through the mathematical calculation and simulation analysis, for the bit-error rate of DCS code is significantly better than other SAC-OCDMA codes, the effect of Phase Induced Intensity Noise is reduced. In addition, proofof-principle simulations of 10 Gb/s for 20 km have been successfully demonstrated and achieved low BER compared to the other codes.

Performance analysis of WS-EWC coded optical CDMA networks with/without LDPC codes

One extended Welch-Costas (EWC) code family for the wavelength-division-multiplexing/spectral-amplitude coding (WDM/SAC; WS) optical code-division multiple-access (OCDMA) networks is proposed. This system has a superior performance as compared to the previous modified quadratic congruence (MQC) coded OCDMA networks. However, since the performance of such a network is unsatisfactory when the data bit rate is higher, one class of quasi-cyclic low-density parity-check (QC-LDPC) code is adopted to improve that. Simulation results show that the performance of the high-speed WS-EWC coded OCDMA network can be greatly improved by using the LDPC codes.

Code Performance Comparison in SAC-OCDMA Systems under the Impact of Group Velocity Dispersion

In this paper, three code families for spectral amplitude coding optical code division multiple access (SAC-OCDMA) systems in terms of performance are compared to each other under the impact of group velocity dispersion (GVD). The investigated code families are m-sequence, Walsh-Hadamard and modified quadratic congruence (MQC). The performance of these codes is evaluated for three types of transmission media such as single-mode fiber (SMF), dispersion shifted fiber (DSF) and nonzero dispersion shifted fiber (NZ-DSF). Results show that in each of the three transmission media m-sequence code family offers the best performance among the investigated code sets under the impact of GVD. Systems which employ m-sequence codes can achieve longer transmission length compared to those using Walsh-Hadamard and MQC codes. In addition, a chirped fiber Bragg grating (CFBG) is designed as a compensating element to compensate the impact of GVD in a SAC-OCDMA system. Employing the designed grating in the system results in a wide opening in the eye diagram as well as improved bit error rate (BER) of the system which indicate that the impact of GVD is effectively compensated.

Performance analysis of a hybrid fiber Bragg grating-based spectral-amplitude-coding/successive interference cancellation for optical CDMA systems

Successive interference cancellation (SIC) scheme is proposed as a new technique that has the potential to reduce the interference and suppress the multiple-access interference (MAI) in spectral-amplitude-coding (SAC) optical-code-division-multiple access (OCDMA) systems. The proposed receiver-based on fiber Bragg gratings (FBGs) techniques. The performance of the proposed system is theoretically analyzed, taking into account various types of noise and interference, including both multiple-access interference (MAI) and receiver noise. Analytical results show that the proposed system offers significant improvement in terms of bit error rate and system capacity (number of users). We have tested our results with both modified prime codes (MPR) and modified quadratic congruence (MQC) codes. In addition, we have compared our proposed system with the corresponding one without cancellation. It has been shown that the proposed scheme gives a substantial increase in capacity.