Fiber-optic Code-division Multiple-access Systems Research Articles

On The Performance of The Effects of Temperature Variation in Ultrafast Incoherent Fiber-Optic CDMA Systems With SOA-Based Tunable Dispersion Compensator

Recent studies show that temperature variation in ultrafast incoherent fiber-optic code-division multiple-access (FO-CDMA) systems using picosecond multiwavelength codes is a realistic problem even though dispersion-compensating fiber is utilized. The phenomenon creates distortions in auto- and cross-correlation functions and then worsens system performance. A physical-layer mitigation approach has been reported by using a recently demonstrated semiconductor-optical-amplifier-based tunable dispersion compensator to fully recover the auto-correlation peaks. Applying the concept of “chip granularity” to account for the effects of temperature variation to the cross-correlation functions, this paper formulates a new performance-analytical model for such FO-CDMA systems. The model also supports adjustable quality-of-services through code weight control.

Performance analysis of fiber-optic BPPM CDMA systems with single parity-check product codes

The application of a family of single parity-check (SPC) product codes in the fiber-optic code-division multiple-access (CDMA) systems with binary pulse position modulation (BPPM) is considered in this paper. We evaluate the bit-error probabilities of the coded systems, taking into account the photodetector noise, thermal noise, and the multiple-access interference. In this paper, the performance of the employed coding schemes over a binary-input output-symmetric channel is analyzed, based on the density evolution approach. The validity of the analytically obtained bit-error rates (BERs) over binary symmetric channels (BSCs) for each of the decoding iterations is verified by the system simulation. It is then shown that the application of these coding schemes in the optical BPPM-CDMA communication system, which can be modeled as a BSC, significantly improves the system performance. Particularly, for a certain BER (less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> ) and bandwidth, the coded systems not only permit a higher number (more than twice) of active users, compared with the uncoded systems, but also can operate at higher channel bit rate (up to four times) with more than 10% energy saving. Furthermore, by increasing the number of code dimensions, less power (less than 40%) is required to achieve the desired performance

Significantly enhanced fiber optic code-division multiple-access system using a novel optical decoder with an AND-gate logic element

We propose a novel optical decoder for a fiber-optic code-division multiple-access communication system. In particular, we discuss a means of reducing the effective multiple-access interference signal by inserting an optical hard limiter (optical thyristor). The optical decoder employs an AND gate logic element (AGLE) composed of a 1×M splitter, optical delay lines, an M×1 combiner, and the optical hard limiter. It is found that the AGLE suppresses the interference signal, so that the autocorrelation sidelobe and the cross-correlation peaks can be fully eliminated for any two users.

The Impact of Dispersion Penalty and Device Losses on the Performance of Fiber-optic CDMA Systems

Fiber-optic code division multiple access (FO-CDMA) system configuration is introduced. The device losses of active fiber connector, optical encoder/decoder, star coupler, transmission media, power penalty induced by fiber dispersion and the chirp effect of laser source are analyzed. Theoretical analysis of system bit error rate (BER) is achieved. Numerical results show that, dispersion power penalty makes system BER decline. The chirp effect of laser source can compensate for the dispersion power penalty for short transmission distance. For a FO-CDMA system with 20 active users, optical orthogonal code with weight 4 is users' address codes, and the distance between transmitter and receiver is 30 km, if BER is 10 -9 , then the transmitted power requires 4.4 dBm for normal single mode fiber (SMF) and 0.7 dBm for dispersion shift fiber (DSF). The system total loss is 44.9 dB for normal SMF and 41.2 dB for DSF.

Internally channel-coded framed time-hopping fiber-optic CDMA communications

Due to the low cardinality of optical orthogonal codes (OOCs) with a correlation value of 1, the capability of an internal channel-coding scheme cannot be applied effectively for an increasing number of simultaneous users in a typical fiber-optic code division multiple-access (FO-CDMA) system. In this paper, we consider applying the internal channel-coding scheme to the framed time-hopping (FTH) FO-CDMA system. Due to the extremely high cardinality of the spreading sequence in FTH FO-CDMA, the technique highlights the ability of the internal channel-coding scheme to increase the effective number of users in an FO-CDMA system. For the FTH FO-CDMA system, we only consider a Poisson noise-limited channel and do not take into account the physical fiber-optic channel impairments. Our simulation and analytical results show that, due to the large cardinality of spreading codes, the capability of the internal channel-coding technique to increase the maximum number of simultaneous users becomes more obvious in the FTH FO-CDMA system.

A New Construction for Optimal Optical Orthogonal Codes

The study of optical orthogonal code has been motivated by an application in fiber-optic code division multiple access (FO-CDMA) systems. An optical orthogonal code is a family of binary (0, 1) sequences with good correlation property, as a preferred address code, generally used in non-coherent FO-CDMA systems. Construction for optical orthogonal code (OOC) is closely related to cyclic difference family (CDF). In this paper, we state the fundamental relationship between (v, k, 1) OOC and (v, k, 1) CDF. Based on this relationship, an approach of constructing (v, k, 1) OOC from finite field is suggested. With the assistance design of computer, some results are obtained. By making use of these results, we obtained some optimal (v, k, 1) optical orthogonal codes (OOC's) for k = 4, 5 and 6, here, v is a prime number.

Soft-input decoder for decoding of internally channel coded fiber-optic CDMA communication systems

We propose using a soft-input decoder for the decoding of internally convolutional coded Poisson noise-dominated fiber-optic code-division multiple-access (CDMA) communication systems using optical orthogonal codes. We first compute the coded symbol log-likelihoods at the output of the Poisson noise-dominated channel, which is then used by a soft-input maximum-likelihood decoder, for a fiber-optic CDMA system assuming both on-off keying and binary pulse position modulation schemes. Furthermore, we develop a discrete soft-output channel model for a Poisson noise-dominated channel, with which we evaluate the upper bound on the bit error probability of the internally coded Poisson noise-dominated fiber-optic CDMA system using a soft-input decoder. It is shown that the soft-input decoder significantly outperforms the hard-input decoder. Furthermore, the performance of the soft-input decoder is also evaluated in the presence of different values of dark current.

Temporal/spatial fiber-optic CDMA systems with post- and pre-optical amplification

We present a thorough analysis based on photon-counting techniques on temporal/spatial fiber-optic code-division multiple-access systems incorporating both post- and pre-optical amplifiers. In this analysis, we consider the effect of shot noise, thermal noise, and source extinction on system bit-error rate. Our results can be used to estimate the maximum tolerable amount of quantum fluctuations in the received signal.

Multistage decoding for internally bandwidth efficient coded Poisson fiber-optic CDMA communication systems

We consider the structure and performance of a multistage decoding scheme for an internally bandwidth efficient convolutionally coded Poisson fiber-optic code division multiple access (CDMA) communication system. The decoder is implemented electronically in several stages in which in each stage, the interfering users' coded bit decisions obtained in the previous stage is applied for computing the likelihood of the coded symbols of the desired user. The first stage is a soft-input Viterbi decoder for the internally coded scheme, in which the soft-input coded symbol likelihood values are computed by considering the multiuser interference as a noise signal. The likelihood of coded symbol computed in each stage is then entered into the convolutional decoder for the next bit decisions. The convolutional codes that are used for demonstrating the performance of the multistage decoder are super orthogonal codes (SOCs). We derive the bit error rates (BERs) of the proposed decoder for internally coded Poisson fiber-optic CDMA systems using optical orthogonal codes (OOCs) along with both ON-OFF keying (OOK) and binary pulse position modulation (BPPM) schemes. Our numerical results indicate that the proposed decoding scheme substantially outperforms the single-stage soft-input Viterbi decoder. We also derive the upper bound on the probability of error of a decoder for the known interference case, which is the ultimate performance of a multiuser decoder, and compare the result with that of the soft-input Viterbi decoder.

Optical orthogonal code acquisition in fiber-optic CDMA systems via the simple serial-search method

We analyze, for the first time, the performance of a serial-search algorithm for optical code-division multiple access (CDMA) systems using optical orthogonal codes (OOC). For our analysis, we use advance photon-counting methods and we consider the effect of shot noise and dark current and multi-access interference (MAI). We introduce a new method for modeling the effect of MAI, then we use two approaches to consider this effect on the performance of the synchronization system. For the first approach, we consider the average effect of interference in our analysis, while for the second approach two specific forms of interference are taken into account where one form represents a heavily localized interference pattern and the other shows a uniformly distributed one. The effects of different parameters of the system including system threshold, number of active users in the network, and mean number of photons in each optical pulse on the performance of the synchronization system are evaluated and discussed.

Low-rate super-orthogonal channel coding for fiber-optic CDMA communication systems

In this paper, we consider using practical low-rate error correcting codes in fiber-optic code division multiple-access (CDMA) communication systems. To this end, a different method of low-rate channel coding is proposed. As opposed to the conventional coding schemes, this method does not require any further bandwidth expansion for error correction in fiber-optic CDMA communication systems. The low-rate channel codes that are used for demonstrating the capabilities of the proposed method are super-orthogonal codes. These codes are near optimal and have a relatively low complexity. We evaluate the upper bounds on the bit-error probability of the proposed coded fiber-optic CDMA system assuming both on-off keying and binary pulse position modulation schemes. It is shown that the proposed method significantly outperforms the uncoded systems for various receiver structures such as a correlator with and without hard-limiter and chip-level detector. Furthermore, the performance of the proposed coded fiber-optic CDMA system is also evaluated in the presence of different values of dark current.

Channel interference reduction using random Manchester codes for both synchronous and asynchronous fiber-optic CDMA systems

We propose the random Manchester codes (RMC) to improve the bit error probability (BEP) performance in both synchronous and asynchronous fiber-optic code-division multiple-access (CDMA) systems. The spreading sequences used in the synchronous and asynchronous systems are modified prime sequence codes and optical orthogonal codes (OOCs), respectively. Thermal noise, shot noise, and avalanche photodiode (APD) bulk and surface leakage currents are taken into consideration in the BEP analyzes. The results show that the proposed systems can support a larger number of simultaneous users than other systems with similar system complexity under the same bit-error probability constraint.

Construction and performance analysis of a new family of optical orthogonal codes for CDMA fiber-optic networks

A construction of a new family of optical orthogonal codes (OOCs) for use in code division multiple access (CDMA) fiber-optic networks is given. Previous families of OOCs are reviewed and basic requirements for successful implementation of the fiber-optic CDMA system given. The new code construction is based on Costas (1970) arrays and the codes are proved to be (/spl omega/(2p-3), /spl omega/, 1, 1), p a prime and /spl omega/*Q/spl les/p-1, where Q is the maximum number of users, OOCs. The probability of error (using the Gaussian approximation) in the multiuser system as a performance measure is calculated and compared with that of existing OOCs. The size of the code family is compared against the Johnson bound. >

Limitations on peak pulse power, pulse width, and coding mask misalignment in a fiber-optic code-division multiple-access system

The authors analyze the effects of fiber dispersion and optical nonlinearity on a code-division multiple-access (CDMA) communications system. They assume that each transmitter has a unique phase-encoding mask to scramble the pulses, and that the intended receiver has the complementary phase-decoding mask to unscramble the pulses. The necessary nonlinear pulse propagation equation is derived using a new and systematic approach. The authors then determine the minimum allowable pulse width and the maximum pulse width for the system. They next calculate the maximum optical power, which is limited by the fiber's self-phase modulation. This power is significantly larger than the minimum detectable optical power determined by the noise in the electrical receiver, so that in practice any distortion caused by the fiber's optical nonlinearity can be avoided. From their calculations estimates for all important optical parameters are provided. The deleterious effect of a slight relative misalignment between the encoding and decoding masks is also investigated. >

Emerging optical code-division multiple access communication systems

All-optical systems, which perform signal processing functions optically so that the signal conversion from optical to electrical is done only when desired, are considered. Three such schemes are discussed, namely, fiber-optic code-division multiple-access (CDMA) systems, neuromorphic CDMA systems, and ultrashort-light-pulse CDMA systems. Fiber-optic CDMA systems in which incoherent optical signal processing techniques are used to establish optical CDMA systems are first examined. In particular, a novel class of sequences for incoherent fiber-optic CDMA systems, called optical orthogonal codes, are discussed. The codes are then applied to neuromorphic optical systems, and various applications of the networks are examined. Recent experiments that demonstrate the ability to encode and decode extremely fast, femtosecond optical pulses and that suggest the possibility of ultrahigh-speed CDMA systems based on ultrashort light pulses are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Code division multiple-access techniques in optical fiber networks. II. Systems performance analysis

For pt.I see ibid., vol.37, no.8, p.824-33 (1989). In Part I a technique based on optical orthogonal codes was presented to establish a fiber-optic code-division multiple-access (FO-CDMA) communications system. The results are used to derive the bit error rate of the proposed FO-CDMA system as a function of data rate, code length, code weight, number of users, and receiver threshold. The performance characteristics for a variety of system parameters are discussed. A means of reducing the effective multiple-access interference signal by placing an optical hard-limiter at the front end of the desired optical correlator is presented. Performance calculations are shown for the FO-CDMA with an ideal optical hard-limiter, and it is shown that using an optical hard-limiter would, in general, improve system performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>