Optical Code-division Multiple-access Communication Research Articles

Importance Sampling Over Monte Carlo Technique to Estimate Wireless Infrared On-Chip Communication

Optical code division multiple access (OCDMA) represents the development of optical communication. The advantages of OCDMA such as, asynchronous multiuser communication transmission, flexibility, ample bandwidth and scalability; have made this technique a better candidate to be proposed for next generation network on chip. In this paper, performance of on-chip OCDMA communication system is analyzed. Analytical techniques for estimating the performance of optical communication systems are difficult, complicated and no complete analytical treatment of the problem has been obtained before. Simulation techniques such as Monte Carlo (MC) are used to obtain reasonable estimates of these systems performance. For optical communications, Monte Carlo require excessively large sample sizes which makes it cumbersome in terms of physical resources, and are not practical for estimating very low values of error probabilities. Modified Monte-Carlo (Importance sampling/IS) method was used to reduce the number of simulation tests for estimating error probabilities for optical communications systems by modifying the probability density function of the on-chip noise process. Simulation results are presented and assessed in term of bit error rate (BER), showing the contribution of IS relatively to MC.

New Optical Codes Based on Construction of Parity Check Matrix of LDPC Codes

Abstract In this paper, new spectral optical codes based on the construction parity check matrix of LDPC codes were designed and implemented in an optical code-division multiple access communication system. Two types optical family codes can be obtained with respectively a cross correlation of λ c = 0 {\lambda _c} = 0 and λ c = 1 {\lambda _c} = 1 . In each case, the codes can either be decoded using the direct detection or the balanced detection. Performance was evaluated by referring to the Q factor, the bit error rate and the eye pattern diagrams using Optisystem 9.0.

Two-Stage Code Acquisition in Wireless Optical CDMA Communications Using Optical Orthogonal Codes

In this paper, we analyze the performance of code acquisition system in atmospheric optical code division multiple access (OCDMA) communications using optical orthogonal codes. Memory introduced by temporal correlation of optical fading process precludes us from using the Markov chain model for a code acquisition analysis. By considering this issue, we discuss how to extend the applicability of the Markov chain model to the atmospheric OCDMA communications. We analyze and compare the performance of correlator and chip level detector (CLD) structures in the acquisition system. In our analysis, we consider the effects of free space optical channel impairments, multiple access interference, and receiver thermal noise in the context of semi-classical photon-counting approach. Furthermore, we evaluate the performance of various two stage schemes that utilize different combinations of active correlator, matched filter, and CLD in search and verification stages, and we find the optimum acquisition scheme among them. Numerical results show significant improvement in reducing the acquisition time and required power for synchronization using our optimum scheme in the wireless OCDMA communications.

Fourier information optics for the ultrafast time domain

Ultrafast photonic signal processing based on Fourier optics principles offers exciting possibilities to go beyond the processing speeds of electronics technologies for applications in high-speed fiber communications and ultrawideband wireless. I review our recent work on processing of ultrafast optical signals via conversion between time, space, and optical frequency (Fourier) domains. Specific topics include optical arbitrary waveform generation, application of optical pulse shaping technologies for wavelength-parallel compensation of fiber transmission impairments and for experimental studies of optical code-division multiple-access communications, and application of photonic methods for precompensation of dispersion effects in wireless transmission of radio-frequency signals over ultrawideband antenna links.

BER analysis of coherent optical CDMA communication systems with transfer function matrix

We analyze the bit error rate (BER) of coherent optical code-division multiple-access (CDMA) communication systems with a transfer function matrix (TFM). The coherent optical CDMA is a promising system for an access network due to its advantages of asynchronous transmission, information security, multiple-access capability. TFM is defined as the Fourier transform of the impulse response of an optical fiber, which interconnects each CDMA system. TFM has parameters such as the state of polarization (SOP), phase difference, power distribution between two orthogonal modes over an optical frequency range. We first analyze the statistic of a received signal via an optical fiber with TFM, and then apply the statistic to the BER analysis. The analytical results show that BER increases with the bandwidth of a signal, and that selecting a proper center frequency leads to the BER reduction.

Monotonicity of Likelihood Ratio of MAP Correlation Detection for OCDMA Communication

In this paper, the monotonicity of the likelihood ratio used in the optimal correlation detection is established for optical code division multiple-access (OCDMA). The monotonicity property not only guarantees the optimality of the detection, it also enables us to calculate the bit-error-rate bounds for OCDMA in the presence of uncertain a priori probabilities.

Emerging OCDMA communication systems and data networks [Invited

Feature Issue on Optical Code Division Multiple AccessI present an in-depth review of the trends and the directions taken by researchers worldwide in optical code-division multiple-access (OCDMA) systems. I highlight those trends and features that I believe are essential to the successful introduction of various OCDMA techniques in communication systems and data networks in the near future. In particular I begin by giving a comprehensive review of the construction of optical orthogonal codes (OOCs). Specifically I discuss the recently developed algorithms that are based on matrix algebra, which simplify and enhance the efficiencies of algorithms in OOC generation. In communication systems studies I first focus on and discuss various OCDMA techniques, such as incoherent and coherent OCDMA. A comprehensive discussion takes place on all important aspects of each OCDMA technique. In particular, I elaborate on enabling technologies that are needed prior to full scale consideration of OCDMA in communication systems. For incoherent OCDMA the technique is categorized into two distinguished techniques, namely, 1D and 2D OCDMA. For each technique I discuss the various receiver structures proposed to date. In particular I discuss a recently introduced powerful receiver structure based on optical AND logic gate elements. Based on this receiver structure I conclude that in many practical applications, OOCs with a cross-correlation value λ equal to 2 or 3, which have a much larger cardinality compared to OOCs with λ=1, perform much better. Many fundamental issues, including architectural consideration of multiple amplifiers, various acquisition algorithms, and advanced signaling methods, such as pulse position modulation, are discussed. For coherent OCDMA or spectrally encoded ultrashort light pulse OCDMA, I begin by having an in-depth discussion on the key and enabling technologies that are essential in the successful implementation of this very important and extremely powerful technique. In particular on the encoder-decoder side I present discussions on various key device technologies such as virtually imaged pulsed array, fiber Bragg gratings, and arrayed waveguide gratings. On the receiver side I elaborate on various nonlinear detection schemes used in such OCDMA networks. I will present an analytical framework on the above nonlinear detection schemes and discuss their pros and cons. I extend the discussion to various data networks. In particular I will discuss applications such as wireless OCDMA LAN, free-space OCDMA, fiber-to-the-home, and other code-division-multiple-access-based packet communication networks using label addressing and processing techniques to indicate the directions and the applications for which OCDMA systems are considered. It is believed that in the not so distant future OCDMA, once fully developed and matured, will be an inseparable part of advanced optical communication systems and networks, due to its various desirable features and functionalities.

Permuted M-matrices for the reduction of phase-induced intensity noise in optical CDMA network

Two codeword families and the corresponding encoder/decoder schemes are present for spatial/frequency optical code-division multiple-access communications. These 2-D codewords have multiple weights per row and can be encoded/decoded via compact hardware. With the proposed decoding mechanism, the intended user will reject interfering users and multiple-access interference is fully eliminated. In addition, the power of the same wavelength contributed by all interfering codewords is split and detected by distinct photodiodes in the decoder. Thus the performance degradation due to the beat noise arising in the photodetecting process is improved, as compared with the traditional 1-D coding scheme, and a larger number of active users is supported under a given bit-error rate.

Optimality of chip-level detection for OCDMA

This paper derives the optimal chip error rate (CER) of the chip-level detection for optical code division multiple-access communication (OCDMA). By introducing two auxiliary functions and exploring their properties, it is shown for the first time that when the detection is based on the photon counts, the optimal CER can be achieved uniquely by thresholding the receiving photon counts at each chip with a threshold of one. Simulation studies verify the theoretical analysis.

Optimality of the Users Strength in Optical PPM-CDMA Channels

An upper bound on the users strength in direct-detection optical code-division multiple-access communication systems, which employ pulse-position modulation techniques, is developed. This upper bound is consistent with the lower bound derived previously, as long as the transmitted information per photon is less than some positive threshold. The concept of users strength was introduced by the author in a previous paper, where it provides a measure to the maximum number of simultaneous users that can communicate simultaneously with arbitrary small probability of error.

Evaluation of new codes for spectral-amplitude-coding optical code-division multiple-access communication systems

New classes of codes, namely extended modified prime sequence codes (EMPSC) and difference codes, both having an ideal in-phase cross-correlation (IPCC) value of one, are suggested for spectral-amplitude-coding optical code-division multiple-access communication systems. The general structure of the system is discussed with simpler encoder and decoder architectures based on fiber Bragg gratings. Since the influence of multiuser interference can be completely removed due to ideal IPCC, the performance analyses of the proposed codes have been carried out by incorporating the effects of phase-induced intensity noise (PIIN), shot noise, and thermal noise at the receiver, employing Gaussian approximation. Assuming typical system parameters, evaluation results show that with an increase in code weight, the maximum number of accommodative users in the system can be increased as well as significant improvements in bit error probability for a given number of active users. For the same code weight, the difference codes can support a greater number of simultaneous users than the other. It is found that the effects of PIIN dominate compared to shot noise and thermal noise at large powers, whereas the effects of PIIN and shot noise are highly reduced at low powers, so that thermal noise becomes a more influential limitation factor. In comparison with earlier codes, the error performance of EMPSC is similar to that of modified quadratic congruence codes, while difference codes resemble those codes developed based on Steiner systems.

Cyclotomic Optical Orthogonal Codes of Composite Lengths

Optical orthogonal codes (OOCs) have applications in optical code-division multiple-access communications systems and other wideband code-division multiple environments. They can also be used to construct protocol sequences for multiuser collision channel without feedback, and constant-weight codes for error detection and correction. We have given a cyclotomic construction of several classes of (2/sup m/-1,w,2) OOCs recently. The purpose of this paper is to present five classes of (q-1,w,2) OOCs, and thus five classes of binary constant-weight cyclic codes, where q is a power of an odd prime.

Several classes of (2 m−1, w,2) optical orthogonal codes

Optical orthogonal codes have applications in optical code-division multiple access communication systems and other wide band code-division multiple environments. They can also be used to construct protocol sequences for multiuser collision channel without feedback, and constant weight codes for error detection and correction. In this paper, we construct four classes of (2 m −1, w,2) cyclotomic optical orthogonal codes, where w∈{5,9} or w⩾11 is any prime having primitive root 2, and therefore the corresponding classes of binary constant-weight cyclic codes.

Several Classes of (2m − 1, w, 2) Optical Orthogonal Codes

Abstract Optical orthogonal codes have applications in optical code-division multiple access communication systems and other wide band code-division multiple environments. They can also be used to construct protocol sequences for multiuser collision channel without feedback, and constant weight codes for error detection and correction. In this paper we construct four classes of (2 m −1, w , 2) cyclotomic optical orthogonal codes, where w _ e {5, 9, 11,13}, and therefore four classes of binary constant-weight cyclic codes.

Optical orthogonal codes: their bounds and new optimal constructions

A (v, k, /spl lambda//sub a/, /spl lambda//sub c/) optical orthogonal code (OOC) C is a family of (0, 1)-sequences of length v and weight k satisfying the following two correlation properties: (1) /spl Sigma//sub 0/spl les/t/spl les/v-1/x/sub t/x/sub t+i//spl les//spl lambda//sub a/ for any x=(x/sub 0/,x/sub 1/,/spl middot//spl middot//spl middot/,x/sub v-1/)/spl isin/C and any integer i not equivalent 0 mod v; and (2) /spl Sigma//sub 0/spl les/t/spl les/v-1/x/sub t/y/sub t+i//spl les//spl lambda//sub b/ for any x=(x/sub 0/,x/sub 1/,/spl middot//spl middot//spl middot/, x/sub v-1/) /spl isin/ C, y=(y/sub 0/,y/sub 1/,/spl middot//spl middot//spl middot/,y/sub v-1/) /spl isin/C with x/spl ne/y, and any integer i, where the subscripts are taken modulo v. The study of optical orthogonal codes is motivated by an application in optical code-division multiple-access communication systems. In this paper, upper bounds on the size of an optical orthogonal code are discussed. Several new constructions for optimal optical orthogonal codes with weight k/spl ges/4 and correlation constraints /spl lambda//sub a/=/spl lambda//sub c/=1 are described by means of optimal cyclic packings. Many new infinite series of such optimal optical orthogonal codes are thus produced.

Bit-error rate computation of optical CDMA communication systems by large deviations theory

Recently, there has been a lot of interest in using code-division multiple access (CDMA) for optical fiber communication systems. In this letter, we present a technique for estimating the bit error rate of optical CDMA communication systems employing avalanche photodiode receivers. The proposed technique, which is based on large deviations theory, is featured as a simple, accurate, and flexible method for performance evaluation of such systems.

Performance analysis of optical synchronous CDMA communication systems with PPM signaling

Direct-detection optical synchronous code-division multiple-access (CDMA) systems with M-ary pulse-position modulation (PPM) signaling are investigated. Optical orthogonal codes are used as the signature sequences of our system. A union upper bound on the bit error rate is derived taking into account the effect of the background noise, multiple-user interference, and receiver shot noise. The performance characteristics are then discussed for a variety of system parameters. Another upper bound on the probability of error is also obtained (based on Chernoff inequality). This bound is utilized to derive achievable expressions for both the maximum number of users that can communicate simultaneously with asymptotically zero error rate and the channel capacity. Our results show that under average power and bit error rate constraints, there always exists a pulse position multiplicity that permit all the subscribers to communicate simultaneously.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Constructions for optimal constant weight cyclically permutable codes and difference families

A cyclically permutable code is a binary code whose codewords are cyclically distinct and have full cyclic order. An important class of these codes are the constant weight cyclically permutable codes. In a code of this class all codewords have the same weight w. These codes have many applications, in. Eluding in optical code-division multiple-access communication systems and in constructing protocol-sequence sets for the M-active-out-of-T users collision channel without feedback. In this paper we construct optimal constant weight cyclically permutable codes with length n, weight w, and a minimum Hamming distance 2w-2. Some of these codes coincide with the well-known design called a difference family. Some of the constructions use combinatorial structures with other applications in coding.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance analysis of direct-detection optical CDMA communication systems with avalanche photodiodes

Direct-detection optical code-division multiple-access (CDMA) communication systems with avalanche photodiode (APD) photodetectors are investigated. A Chernoff upper bound, modified Chernoff upper bound, and Gaussian approximation on the probability of bit error are presented for general APDs and arbitrary

Arbitrarily tight PBE bounds for optical CDMA communications

Arbitrarily tight upper and lower bounds on the probability of bit error (PBE) for direct-detection avalanche photodiode detector (APD) based code-division multiple-access (CDMA) communication systems are presented. Previously, only the Chernoff upper bound (CB), modified Chernoff upper bound (MCB), and Gaussian approximation (GA) of the PBE have been available. The MCB is calibrated. >