Realization of 2-D OCDMA network using EDW code

The attraction towards two-dimensional optical code division multiple access (2D-OCDMA) systems has increased due to its potential in enhancing the performance of optical access networks and producing optical code-based signals. 2D-OCDMA network systems enable better bit-error-ratio (BER) performance as well as increase the number of supportable users in the optical network. Time-spreading wavelength-hopping is one of the many techniques that has been proposed for 2D-OCDMA. In this paper, we present the simulative study of a 2D-OCDMA system. The developed time-spreading, wavelength-hopping network utilizes enhanced double weight (EDW) code which has enhanced properties such as a cross-correlation value of 1 and has a simple encoder/decoder design. The output BER was satisfactory at above 10^?9 at data rate of 1.25 Gbps for 20 km distance with the ITU-T G.652 standard single mode optical fiber for 3 users.     

New design of spectral amplitude coding in OCDMA with zero cross-correlation

A zero cross-correlation (ZCC) code is proposed to reduce the impact of system impairment and multiple access interference (MAI) in spectral amplitude coding optical code division multiple access (SAC-OCDMA) system. Bit-error-rate (BER) performance is derived taking into account the effect of some noises. The key to an effective OCDMA system is the choice of efficient address codes with good or almost zero correlation properties for encoding the source. The use of ZCC code can eradicate phase induced intensity noise (PIIN) which will contribute to better BER. Thus, we demonstrate, theoretically, the performance of optical ZCC code. It is shown that optical ZCC code can accommodate more users simultaneously for the typical error rate of optical communication system of 10⁻⁹. The result indicates that the established system not only preserves the capability of suppressing MAI, but also improves bit-error-rate performance as compared to the conventional coders.     

Performance improvement of spectral amplitude coding-optical code division multiple access systems using NAND detection with enhanced double weight code

The bit-error rate (BER) performance of the spectral amplitude coding-optical code division multiple access (SACOCDMA) system has been investigated by using NAND subtraction detection technique with enhanced double weight (EDW) code. The EDW code is the enhanced version of double weight (DW) code family where the code weight is any odd number and greater than one with ideal cross-correlation. In order to evaluate the performance of the system, we used mathematical analysis extensively along with the simulation experiment. The evaluation results obtained using the NAND subtraction detection technique was compared with those obtained using the complementary detection technique for the same number of active users. The comparison results revealed that the BER performance of the system using NAND subtraction detection technique has greatly been improved as compared to the complementary technique.     

A new code construction with zero cross correlation based on BIBD

This paper presents a newly constructed zero cross correlation code (ZCC) which is based on BIBD (balanced incomplete block design) code. The ZCC (C, w) code is a family of binary sequences of length C and constant Hamming-weight w. Such codes find applications in spectral amplitude-coding optical code division multiple access (SAC-OCDMA). The constructing ZCC codes have a size of C ? N ÿ w + 1, where N is the number of users and C is any prime number. The proposed construction method is not complicated compared to the existing ones.     

New technique for construction of a zero cross correlation code

This paper proposes a new technique for constructing zero cross correlation codes (ZCC). In the existing techniques, especially for weight w more than one, the weight is always fixed to the maximum number of users (i.e. the code size). To overcome this difficulty, an efficient design is presented. The code design procedure can be easily used to construct variable length and non-constant weight w. A comparison has been established between existing ZCC optical codes and the novel ZCC classes.     

A novel non-coherent spectral OCDMA system using one-dimensional expanded Hybrid codes for two-code keying

We propose leveraging one-dimensional expanded Hybrid codes (1-D E-Hybrid codes) for two-code keying (TCK) in spectral amplitude coding (SAC) optical code division multiple access (OCDMA) networks. Compared with the existing work, the proposed system can utilize all codes and provide a larger code size to support more simultaneous users. The numerical results demonstrate that the 1-D E-Hybrid codes for TCK outperform the existing 1-D approaches in terms of bit error rate (BER), and the data transmission rate can achieve 2.5 Gbps.     

A New Algorithm for Development of Dynamic Cyclic Shift Code for Spectral Amplitude Coding Optical Code Division Multiple Access Systems

Abstract

This article presents a new code—the dynamic cyclic shift code—for spectral amplitude coding–optical code division multiple access systems. One of the important properties of the dynamic cyclic shift code is that the number of users can be increased without increasing the weight value. System performance was evaluated by using both theoretical analysis as well as the simulation experiment. The analysis results show that the proposed dynamic cyclic shift code can support more users in spectral amplitude coding–optical code division multiple access systems compared to spectral amplitude coding–optical code division multiple access codes. It was ascertained by performance evaluation that the dynamic cyclic shift code possesses ideal properties for use in spectral amplitude coding–optical code division multiple access systems.     

Evaluation of coherent homodyne and heterodyne optical CDMA structures

This paper evaluates the coherent optical code-division multiple-access (OCDMA) techniques and examines the overall system performance in terms of signal-to-noise ratio (SNR) penalty as a function of simultaneous users accommodated to maintain an appropriate value of the bit-error rate (BER) for homodyne and heterodyne detections. As spreading codes, the proposed structures are utilizing a recently introduced prime code family hereby referred to as double-padded modified prime code (DPMPC). As a coherent modulation, binary phase-shift keying (BPSK) format is deployed. In homodyne detection, two different phase modulations are studied including either an external phase-modulator or injection-locking methods. The phase limitation and the performance for two methods plus multiple-access interferences (MAI) and receiver noise in a shot-noise limited regime are investigated. In heterodyne detection, BER analysis of the system based on only external phase modulator is examined. It is found that by maintaining BER = 10⁻⁹, this system can accommodate an increased number of simultaneous users to compare with systems which employ conventional bipolar codes.     

A novel 2D-OCDMA system with dynamic optimum decision threshold by estimating the number of active users

A novel two dimensional optical code division multiple access (2D-OCDMA) system with dynamic optimum decision threshold by estimating the number of active users is proposed. The bit-error rates (BER) of the system is analyzed. By using one wavelength as the estimator of the number of active users, which is not assigned to any address code, the number of active users can be obtained. The dynamic optimum decision threshold can be obtained according to the multiple user interference (MUI), which can be obtained by cross-correlation characteristics between address codes and the number of active users.     

A novel encoder/decoder design scheme utilizing differential detection in OCDMA systems

In this paper, we report the use of differential detection in optical code-division multiple access (OCDMA) systems which use encoders and decoders based on unbalanced codes and utilize bipolar modulation/differential detection to demonstrate a significant improvement in system performance. Differential detection has been reported earlier also requiring a large number of one-chips in the code for (balanced codes) or with unbalanced codes with very long temporal dimensions requiring a large number of delay elements (either the delay lines in the ladder-type structures or the gratings in the multiple fiber gratings) making the encoder/decoder structures. We use single pulse per row codes to design our system and carry out the simulations for showing the results. The improved BER performance is achieved that can be traded for increasing the number of codes. Using optical simulation tool, the OCDMA system has been simulated for four users. The results of this system utilizing differential detection and another system that uses the same coding scheme but employing direct detection, for the same number of interfering users, are shown for comparison. The BER and the power penalty plots are shown for the two systems. Also, it is shown that performance degradation occurs due to the linear and non-linear effects of the fiber medium. The BER worsens more rapidly with link length for direct detection case, whereas for differential detection with an initial improvement of 8 dB, the increase in BER is insignificantly small for a link length of 500 km.     

Performance analysis of quantum access network using code division multiple access model

A quantum access network has been implemented by frequency division multiple access and time division multiple access, while code division multiple access is limited for its difficulty to realize the orthogonality of the code. Recently,the chaotic phase shifters were proposed to guarantee the orthogonality by different chaotic signals and spread the spectral content of the quantum states. In this letter, we propose to implement the code division multiple access quantum network by using chaotic phase shifters and synchronization. Due to the orthogonality of the different chaotic phase shifter, every pair of users can faithfully transmit quantum information through a common channel and have little crosstalk between different users. Meanwhile, the broadband spectra of chaotic signals efficiently help the quantum states to defend against channel loss and noise.     

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 (P_sr) at −17.9 dBm, 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.     

Performance analysis and improvement of spectrally amplitude encoded/decoded OCDMA system

This paper describes a performance analysis of an incoherent optical code-division multiple-access scheme based on wavelength/time (W/T) codes. The system supports 16 users operating at 2.5Gb/s/user while maintaining bit-error rate (BER) < 10⁻¹¹ for the correctly decoded signal. It has been observed that there are two major problems giving rise to performance degradation of the system in terms of number of users and type of code.In this paper we have studied the optical simulator Encoding/Decoding for different lengths & gain in terms of Quality factor (Q) and Bit Error Rate (BER) performance. The system supports 16 users while maintaining bit-error rate (BER) < 10⁻¹¹ for the correctly decoded signal. Our aim is to design and simulate a Tree Network Topology Optical Code Division Multiple Access System for large number of users using wavelength–time code and to analyze the performance of the system based on BER and Eye Diagram under the influence of number of simultaneous users with different received powers.     

Design and implementation of 2-dimensional wavelength/time codes for OCDMA

In this paper, two-dimensional (2D) wavelength/time codes are designed and implemented. The 2D codes are constructed by a technique based on folding of Golomb rulers. The performance evaluation of OCDMA system based on wavelength/time code has been analyzed by measuring the values of bit error rates and eye diagrams for different number of active users. It is shown that eye opening decreases and BER increases with increase in number of active users. It is also shown that BER further increases with increase in number of active users when number of decoders increases on receiver side. Hence, it is concluded that multiple access interference (MAI) is the dominant source of BER and there is graceful degradation in system performance when number of simultaneously active users increases. The received optical power is also measured at different transmission distance. It has been observed that received optical power decreases with increase in length of fiber due to attenuation.     

Improvement of the bit error rate of a non-coherent OCDMA system for FTTH network applications

In this paper, an optical code division multiple access (OCDMA) system was analysed to improve the bit error rate (BER) performance at 10 Gbps. The improvements to this system were based on a modified double weight code and a NAND subtraction technique and aimed to support the large number of active users in the fibre-to-the-home network. The system performance was investigated through extensive theoretical and numerical simulation analyses. The theoretical and simulation results revealed that the new detection technique exhibits improved BER performance compared to conventional techniques, such as complimentary subtraction techniques. The system performance was characterised by the signal-to-noise ratio, the bit error rate (BER), and various transmit powers ( $P_{sr} - 10$  dBm). The results show that the proposed system, which is based on a new detection technique, can achieve the optimal BER with a high number of users and maintains the error floor transmission rate $(\le 10^{-9})$ .     

Construction of zero cross correlation code using a type of anti-diagonal-identity-column block matrices

This paper presents a new method for constructing zero cross correlation code with the help of anti-diagonal type-identity-column block matrices. The advantages of this code are easy code construction, existence for every natural number and acceptable code lengths. The numerical comparison shows that the newly constructed code is better code length and it supports more users than other Optical Spectrum Code Division Multiple Access (OSCDMA) codes.     

Performance of concatenated codes over an APD-based optical system with estimated channel-state information

In this paper, we investigate the efficiency of serially concatenated codes using a BCH (32400, 32208) inner code and an LDPC (64800, 32400) outer code over a free-space optical communication (FSOC) system with APD detectors. Based on the experimental optical signals recorded from a FSO (free-space optical) link with the distance z = 11.8 km, the bit error rate (BER) performance of the concatenated codes is evaluated from the aspect of simulation under weak turbulence conditions (for which the scintillation index σ _I ² = 0.18) and strong turbulence conditions (for which σ _I ² = 1.49). The results indicate that the fade level P _T can be set much lower for the FSOC system using the concatenated codes, leading to shorter fade length and interleavers in smaller size. The concatenated codes are shown to even outperform the (4, 1, 7) convolutional code in both cases. In addition, we analyze the BER performance of these concatenated codes on the basis of pilot-aided channel estimation with different numbers of pilot symbols.     

Cardinality enrichment of flexible cross correlation (FCC) code for SAC-OCDMA system by alleviation interference scheme (AIS)

In this paper, we propose an alleviation interference scheme (AIS) for spectral amplitude coding (SAC) – optical code division multiple access (OCDMA) coding system approaches. The AIS SAC-OCDMA systems is demonstrated by utilizing the new flexible cross correlation (FCC) code. The FCC code has advantages, such as flexibility in-phase cross-correlation at any given number of users and weights, as well as effectively reduces the impacts of phase-induced intensity noise (PIIN) and has the multiple-access interference (MAI) cancelation property. The results indicated good performance whereas the FCC (W = 4, K = 150) AIS SAC-OCDMA coding system offers 66%, 172%, 650% and 900% percentage of cardinality enrichments as a contrast to DCS (W = 4, K = 90), MDW (W = 4, K = 55), MFH (W = 4, K = 20) and Hadamard (W = 8, K = 15) codes, respectively. Finally, the FCC AIS SAC-OCDMA coding system has low effective receive power Psr = −21 dBm which is expected to be more significant for future SAC-OCDMA coding systems without requiring any amplification at the receiving plant.     

Design of double-weight code for synchronous OCDMA systems with power control

Double-weight optical code division multiple access(OCDMA) systems are proposed for studying differentiated quality-of-service transmission. Based on quadratic congruence code(QCC), we construct a one-dimensional double-weight code family, which can be well utilized in incoherent synchronous double-weight OCDMA networks. By introducing algebraic transformation to code sequences of QCC in level 1, we obtain multiple double-weight codes with cross-correlation 1. Under the same-bit-power assumption, the performance of low-weight codes can be significantly improved and is always superior to that of high-weight codes in double-weight OCDMA systems with power control. This property is contrary to previous conclusions under the same-chip-power assumption.     

A new family of two-dimensional triple-codeweight asymmetric optical orthogonal code for OCDMA networks

A new generation algorithm of two-dimensional triple-codeweight asymmetric optical orthogonal codes for optical code division multiple access （OCDMA） networks is proposed. The code cardinality is obtained and the error-probability performance for corresponding OCDMA system is analyzed. The codes with two constraints （i.e., auto- and cross-correlation properties） being unequal are taken into account. On the premise of fixed system resources, the code of the error-probability performance, it is shown cardinality can be significantly improved. By analysis that the codes with different parameters have different performances. Therefore, this type of codes can be applied to support diverse quality of service （QoS） and satisfy the quality requirement of different multimedia or distinct users, and simultaneously make the better use of bandwidth resources in oDtical networks.