English

Zero Cross-Correlation (ZCC) code stands out amongst the most helpful codes in Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA) system because of its features like zero cross-correlation and high auto-correlation. However, for long-range communication, as the number of user’s increases, the performance of the system is degraded. In this paper, we made an effort to enhance the performance of SAC-OCDMA system using Dense Wavelength Division Multiplexing (DWDM). SAC-OCDMA is an inseparable part of the global optical communication systems. It provides high speed, high bit-rate, security and high bandwidth for advanced services in different networks. Therefore, the hybrid DWDM and SAC-OCDMA system makes it believable to create other codes like multi diagonal (MD) and random diagonal (RD). Our results show that the number of users increases ten times by using a combination of 20-channel DWDM and SAC-OCDMA ZCC code system at a bit-rate of 10 Gbps for 60 Kms.

In this study, the authors proposed a new approach to evaluate the system performance of spectral amplitude codingoptical code division multiple access (SAC-OCDMA) systems. The system performance is evaluated based on a new code called the dynamic cyclic shift (DCS) code. The bit-error-rate (BER) performance of the DCS code on high-speed SAC-OCDMA systems has been analysed and reported in this study. The most remarkable trait of the newly developed DCS code is that the cross-correlation is variable between 1 and 0, and the phase induced intensity noise is low. In order to evaluate the performance of the DCS code in high-speed SAC-OCDMA system, the mathematical analysis has been extensively derived along with the simulation analysis at 10 Gbit/s, which is carried out by using 'Optisys TM ver.9 simulation software from Optiwave'. The results obtained for the DCS code were compared with those obtained from different coding schemes [e.g. random diagonal code and modified quadratic congruence code] for the same number of interfering users. It has been observed that the DCS code of BER equal to 10 -11 can support high data rate (5 Gbit/s) at 60 km transmission link.

We compare the spectral efficiency of unipolar and bipolar encoding for spectral-amplitude coding optical code-division multiple access (SAC-OCDMA) systems operating with incoherent sources considering the intensity noise as the primary noise source. For both encoding techniques, the spectral efficiency of four SAC codes such as Hadamard, modified quadratic congruence (MQC), balanced incomplete block design (BIBD) and zero cross-correlation (ZCC) is evaluated and compared as a function of the number of users and code length for a BER= 10−10. Analytical derived equations and results verified that ZCC code can support high number of users and leads to the best achievable spectral efficiency than other SAC codes considered. Furthermore, bipolar encoding improves the spectral efficiency as compared to unipolar technique, e.g., bipolar ZCC has 7.7 dB spectral efficiency advantage than unipolar ZCC.

Hybrid Subcarrier Multiplexing (SCM) incorporating spectral amplitude coding optical code division multiple access (SAC-OCDMA) technology was investigated both mathematically and by simulation. The hybrid SCM/SAC-OCDMA system combined two schemes in such as a way that the resulting hybrid system is robust against the Multi- Access Interference (MAI) and much enhanced the channel data rate. In this paper, we describe the improved performance of the hybrid SCM/SAC-OCDMA system based on the use of spectral amplitude coding to suppress impairments and to improve the overall system improve the overall sensitivity of system performance at a BER of 10-9. As a result, the proposed system based on Multi-Diagonal (MD) code shows better performance in comparison to the conventional code that employs the SAC-OCDMA system. We also evaluate the different design parameters under the maximum number of subcarriers (18 subcarriers in each optical channel) multiplexed for integrating OCDMA technology onto the existing fiber-wireless infrastructure at 155 M bit/s data rate for different fiber lengths. Further, a BER of 4.4 × 10-10 was achieved based on the proposed system for 45 km at 1.21 GHz. Key words: Subcarrier multiplexing (SCM), spectral amplitude coding optical code division multiple access (SAC-OCDMA), multi diagonal (MD) code.

Performance comparison of indoor visible light communication (VLC) system with spectral amplitude coding-optical code division multiple access (SAC-OCDMA) techniques using Khazani-Syed (KS) code is examined. Bit error rate (BER) of three different codes was investigated in terms of background optical noise interference in the system. The result shows that KS code offers a slightly better performance under the influence of ambient light noise interference with a lower code length, a few number of filters and lower BER.

Integrated microwave power distribution network : E. W. Aslaksen, IEEE Trans.ED-15, September (1968), p. 678

In this paper, the Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) is investigated in Free Space Optics (FSO) using Zero Cross Correlation (ZCC) codes to evaluate its performance limits in terms of link range. The system is analyzed under clear, haze, moderate fog and dense fog weather conditions. This system has been evaluated numerically and by simulation analysis by maintaining the transmitted power at 10 dBm, for safety reason, according to International Telecommunication Union (ITU) and minimum acceptable BER of10{10}–9. The simulation results shown that the present system can transmit 622 Mbps/1 Gbps up to maximum link range of 1450 m/1100 m and 61 m/54 m under clear and dense fog conditions, respectively.

A new code construction with zero cross correlation based on BIBD

Zero Cross-Correlation (ZCC) code is a binary sequences with good auto- and cross correlation properties, i.e., the cross correlation between any two sequences remains zero throughout. In this paper, we evaluate the performance of ZCC based on Balanced Incomplete Block Design (BIBD) for Spectral Amplitude Coding Optical Code Division Multiple Access (SACOCDMA) system using direct detection. BER better than 10-9 at 622Mbps is obtained for five simultaneous users.

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.

Chromatic and temperature induced dispersion can both severely affect incoherent high data rate communications in optical fibre. This is certainly also true for incoherent optical code division multiple access (OCDMA) systems with multi-wavelength picosecond code carriers. Here, even a relatively small deviation from a fully dispersion compensated transmission link can strongly impact the overall system performance, the number of simultaneous users, and the system cardinality due to the recovered OCDMA auto-correlation being strongly distorted, time-skewed, and having its full width at half maximum (FWHM) value changed. It is therefore imperative to have a simple tunable means for controlling fibre chromatic or temperature induced dispersion with high sub-picosecond accuracy. To help address this issue, we have investigated experimentally and by simulations the use of a semiconductor optical amplifier (SOA) for its ability to control the chirp of the passing optical signal (OCDMA codes) and to exploit the SOA ability for dispersion management of a fibre link in an incoherent OCDMA system. Our investigation is done using a 19.5 km long fibre transmission link that is exposed to different temperatures (20 °C and 50 °C) using an environmental chamber. By placing the SOA on a transmission site and using it to manipulate the code carrier’s chirp via SOA bias adjustments, we have shown that this approach can successfully control the overall fibre link dispersion, and it can also mitigate the impact on the received OCDMA auto-correlation and its FWHM. The experimental data obtained are in a very good agreement with our simulation results.

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.

This paper presents an investigation of Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) over hybrid Fiber-to-the-x (FTTx) Free Space Optical (FSO) link under different weather conditions. FTTx and FSO are the last mile technologies that complement each other in delivering secure and high speed communication to customers’ residence or office. SAC-OCDMA is one of the potential multiplexing techniques that has become a research area of interest in optical communications and considered a promising technique for FTTx access networks. It is based on Khazani-Syed (KS) code with Spectral Direct Decoding (SDD) technique. All the components involved in the network were specified according to the available market product in order to simulate the actual environment as close as possible. The result shows that for bit error rate (BER) of 10−9, the network is able to perform with 20 km Single Mode Fiber ( SMF ) spanning from the central office (CO) and 1.48 km FSO range with transmission rate of 1.25 Gb/s during heavy rain.

Nowadays, transmitting and receiving data with high speed and a high level of security are the main demands. So, a new model of spectral amplitude coding optical code division multiple access (SAC-OCDMA) is suggested in this paper, based on a free space optical (FSO) communication system using coherent sources. Three different codes: enhanced double weight (EDW), modified double weight (MDW) and multi-diagonal (MD) codes are assigned to our proposed model with the direct detection (DD) technique. Furthermore, the model is simulated under different weather conditions including clear air (CA), light mist (LM), very light fog, and light fog (LF). The system performance is evaluated through its bit error rate (BER), Q-factor, received power, and signal to noise ratio (SNR). Moreover, classification of the information received by the three different SAC-OCDMA using three different codes (EDW, MDW, and MD) is still challenging. So, two different machine learning (ML) algorithms are used, in this study, to classify the data received using the different codes. Detecting which code is received at the receiver end is important in order to reduce code error detection. Two algorithms: K-Nearest Neighbor (KNN) and Support Vector Machine (SVM) are adopted to classify different codes used for data transmission under four different weather conditions. The ML input dataset consists of the obtained simulation results, including Q-factor, BER, and SNR. Each feature is to be normalized before using ML. The obtained results show that the performance of the proposed FSO model achieved the longest propagation range under CA weather conditions, 7 km, while the shortest is under LF, which is 0.98 km. This is due to the attenuation of fog that causes signal degradation. The FSO system that uses EDW gives the best result under different weather conditions, while the system that uses MD code gives the worst performance. Also, the highest power is achieved when the EDW code is used at 5.5 km. The EDW has a received power of − 21.58 dBm, while the received power is − 22.04 dBm and − 23.8 dBm for MDW and MD codes, respectively. As for classification between the received information coming from three different codes under different weather conditions, both algorithms, KNN and SVM, achieve promising results in most cases. They showed more than 97% of classification accuracy under CA, LM, and LF weather conditions.

Recently, free space optical (FSO) communication network has gained popularity because of its unlicensed spectrum, high data rate, low power consumption and ease of installation. Spectral amplitude coded optical code division multiple access (SAC-OCDMA) technique has become significant because of enhanced network capacity, privacy, and simultaneous use of multiple asynchronous users. However, the climatic turbulence causes signal fluctuations and degrades the quality of the received signal. Therefore, to improve the quality of the received signal in this work, SAC-OCDMA technique is integrated with orthogonal frequency division multiplexing (OFDM) technique and performance of such hybrid model is investigated. Two SAC-OCDMA codes are proposed in this work referred as triangular matrix-zero cross correlation (TM-ZCC) and pulse shifting substitution-zero cross correlation (PSS-ZCC) codes. The hybrid model uses the novel one dimensional (1D) SAC-OCDMA codes with two different types of receivers such as modified AND (M-AND), and single photodiode detection (SPD) receivers over Gamma-Gamma fading channel to evaluate the bit error rate (BER) performance of the proposed hybrid model. It is observed from the simulation results that the hybrid SAC-OCDMA-OFDM model with SPD detection receiver performs better in terms of bit error rate (BER) than that of M-AND detection receiver. Furthermore, it is also observed from the simulation results that the hybrid model based on the proposed TM-ZCC code performs better than the proposed PSS-ZCC code in terms of BER and higher FSO distance coverage. The performance of the proposed model is estimated for 20 and 30 active users simultaneously at various data rates. The TM-ZCC and PSS-ZCC codes are generated using MATLAB platform and the proposed hybrid SAC-OCDMA-OFDM model is validated using optisystem version 15 over the Gamma-Gamma fading channel.