Multiclass optical orthogonal codes for multiservice optical CDMA networks

Optical code division multiple access (CDMA)-based networks are an interesting alternative to support various traffic types of multimedia applications with highly variable performance targets. Generally, multilength codes are designed to support multirate services, while the multiweight codes are designed to support differentiated quality of service (QoS) for multimedia applications. However, existing optical orthogonal codes (OOCs) are limited to single class or multiclass with restricted weight and length properties. Therefore, there exists a lack of flexibility in the existing OOCs to support arbitrary rate and QoS. This paper presents a proposal of generation procedure and performance analysis of joint multiweight multilength strict OOCs. The approach used in this paper is to apply a methodology strongly relying on developed analytical theory that is supported by computer optimization, because it has turned out that it is mathematically intractable to construct unconstraint joint multilength multiweight OOCs using pure algebraic techniques. The generated code set fulfills the conditions of strictly OOCs, namely, the maximum nonzero shift autocorrelation and the maximum cross correlation constraints of one. The mark position difference (MPD) approach is used to generate in a flexible way the multiclass code set. The MPD results in the simple evaluation of multiclass code set cardinality. Furthermore, the multiple-access interference (MAI) in a multiclass OOC system is evaluated by modeling the interference per class as a Poisson distribution to simplify performance evaluation with acceptable accuracy.     

Two-dimensional optical orthogonal codes for fiber-optic CDMA networks

Several constructions of two-dimensional (2-D) codes have been proposed to overcome the drawbacks of nonlinear effects in large spread sequences of one-dimensional (1-D) unipolar codes in fiber-optic code-division multiple-access (FO-CDMA) networks. Wavelength-time (W/T) encoding of the 2-D codes is practical in FO-CDMA networks. W/T codes reported so far can be classified mainly into two types: 1) hybrid codes, where one type of sequence is crossed with another to improve the cardinality and correlation properties and 2) conversion of 1-D sequences to 2-D codes to reduce the "timelike" property. This paper describes the basic principles of a new family of wavelength/time multiple-pulses-per-row (W/T MPR) codes, for incoherent FO-CDMA networks, which have good cardinality, spectral efficiency, and minimal cross correlation values. In addition, an expression for the upper bound on the cardinality of W/T MPR codes is derived. Another feature of the W/T MPR codes is that the aspect ratio can be varied by a tradeoff between wavelength and temporal lengths. The correlation properties of W/T MPR codes are verified by simulation using Matlab. For given wavelength /spl times/ time dimensions, various W/T codes, whose cardinalities are known, are compared, and it is shown that the W/T MPR family of codes have better cardinality and spectral efficiency than the other W/T codes. Performance analysis of the W/T MPR codes and their limiting cases is carried out for various parameter variations such as the dimensions of wavelength, time, and weight of the code.     

Design of multilength optical orthogonal codes for optical CDMA multimedia networks

To simultaneously support multimedia services with different signaling rates and quality-of-service requirements in optical code division multiple access (CDMA) networks, a new class of multilength, constant-weight optical orthogonal codes (OOCs) with good correlation properties is constructed algebraically in this paper. The performance of these new OOCs in an optical CDMA system with double-media services is analyzed. In contrast to conventional CDMA, our study shows that the performance of these multilength OOCs worsens as the code length increases, allowing prioritization in optical CDMA. Finally, an application of these multilength OOCs to integrate different types of multimedia services is briefly discussed.     

Novel combinatorial constructions of optical orthogonal codes for incoherent optical CDMA systems

Three novel classes of optical orthogonal codes (OOCs) based on combinatorial designs are proposed. They are applicable to both synchronous and asynchronous incoherent optical code-division multiple access (OCDMA) and compatible with spectral-amplitude-coding (SAC), fast frequency hopping, and time-spreading schemes. Simplicity of construction, larger codeword families, and larger flexibility in cross-correlation control make the proposed OOC families interesting candidates for future OCDMA applications. A novel balanced SAC receiver for multiuser interference cancellation that can handle unequal in-phase cross correlation of OOC is also proposed. The upper bound on the bit-error rate as a function of the number of users in SAC schemes is given for all proposed OOC classes.     

Variable-weight optical orthogonal codes for CDMA networks withmultiple performance requirements

An optical orthogonal code (OOC) is a family of (0,1) sequences with good auto- and cross-correlation properties; they are used as a means to obtain code division multiple access (CDMA) on fiber optic networks. Previous work on OOC has assumed that the weight of each codeword is the same. We consider codes when this assumption is removed. We develop bounds on the size of such “variable-weight” OOC's and demonstrate techniques to build them. Furthermore, we provide an analysis of the performance of variable-weight OOC in a CDMA network. Varying the weight of a user's signature sequence affects that user's performance; therefore this approach is useful for CDMA fiber optic networks with multiple performance requirements     

High-performance optical CDMA system based on 2-D optical orthogonal codes

Optical code-division multiple access (OCDMA) is an interesting subject of research because of its potential to support asynchronous, bursty communications. OCDMA has been investigated for local area networks, access networks, and, more recently, as a packet label for emerging networks. Two-dimensional (2-D) OCDMA codes are preferred in current research because of the flexibility of designing the codes and their higher cardinality and spectral efficiency (SE) compared with direct sequence codes based on on-off keying and intensity modulation/direct detection, and because they lend themselves to being implemented with devices developed for wavelength-division-multiplexed (WDM) transmission (the 2-D codes typically combine wavelength and time as the two dimensions of the codes). This paper shows rigorously that 2-D wavelength/time codes have better SE than one-dimensional (1-D) CDMA/WDM combinations (of the same cardinality). Then, the paper describes a specific set of wavelength/time (W/T) codes and their implementation. These 2-D codes are high performance because they simultaneously have high cardinality (/spl Gt/10), per-user high bandwidth (>1 Gb/s), and high SE (>0.10 b/s/Hz). The physical implementation of these W/T codes is described and their performance evaluated by system simulations and measurements on an OCDMA technology demonstrator. This research shows that OCDMA implementation complexity (e.g., incorporating double hard-limiting and interference estimation) can be avoided by using a guard time in the codes and an optical hard limiter in the receiver.     

Multiple-shift code acquisition of optical orthogonal codes in optical CDMA systems

In this paper, we introduce a new and advanced algorithm, namely, multiple-shift algorithm for code acquisition in optical code-division multiple access (CDMA) systems using unipolar optical orthogonal codes (OOCs) as signature sequences. We analyze the performance of the newly proposed algorithm and obtain a bound on its performance and show its advantage in reducing the mean time of synchronization when compared with other synchronization methods. The algorithm can be used with many different receiver structures, like active or passive correlator with or without hardlimiter(s). However, in this paper, we only consider the simple active correlator structure for further discussions and analysis.     

Multiple-length multiple-wavelength optical orthogonal codes for optical CDMA systems supporting multirate multimedia services

Multiple-wavelength optical orthogonal codes (MWOOCs) with autocorrelation sidelobes and cross-correlation values of both at most one were recently proposed for wavelength-time optical code-division multiple-access (O-CDMA) systems. The codes have cardinality as a quadratic function of the number of wavelengths and find applications in high bit-rate O-CDMA systems with broadband supercontinuum lasers, in which the number of available wavelengths is larger than the number of time slots. To support multimedia services with different bit-rate and quality-of-service requirements, a new class of multiple-length constant-weight MWOOCs with autocorrelation sidelobes of zero and cross correlations of at most one is constructed algebraically in this paper. The performance of these new codes in an O-CDMA system with double-media services is analyzed. In contrary to conventional single-length codes, our study shows that the performance of these multiple-length codes improves as the code length decreases. This unique property supports "prioritization" in O-CDMA.     

On efficient code acquisition of optical orthogonal codes in optical CDMA systems

This letter presents an efficient method for optical code division multiple access (OCDMA) code acquisition based on unipolar optical orthogonal codes. We propose a two-dwell acquisition procedure and provide closed form expressions to analyze the system?s error probabilities. Our results match the Multiple Shift (MS) algorithm, recently introduced in the literature, and show that our procedure can achieve the same system performance with a lower computational complexity.     

A new modulation scheme using asymmetric erorr-correcting codesembedded in optical orthogonal codes for optical CDMA

An embedded-modulation scheme is proposed for optical code division multiple access (CDMA). In this scheme, codewords in an asymmetric error-correcting (AEC) code is embedded in a signature sequence in an optical orthogonal code (OOC) used for identification. We classify the codewords of the AEC code according to the number of "1"s in each codeword, and then derive the bit error rate (BER) of the embedded-modulation scheme. Numerical results show that although the performance has the error floor, for achieving the floor value, the embedded-modulation scheme requires less optical energy per bit than the traditional modulation scheme with the correlation and chip-level receivers. The error floor is primarily due to multiaccess interference (MAI), we furthermore apply Reed-Solomon (RS) coding to the embedded-modulation scheme. Consequently, RS coding reduces the floor value to be negligibly small     

Extended orthogonal polyphase codes for multicarrier CDMA system

The Complete Complementary (CC) codes have been able to improve the performance of multicarrier CDMA system for both downlink and uplink transmission. However, the number of users supported by CC code design is limited as its family size is relatively small. In this letter, an extension to CC codes using Zadoff-Chu sequence is proposed. The proposed codes are able to support large number of users and have perfect auto- and cross-correlation function just like CC codes.     

Cyclic shifted orthogonal complementary codes for multicarrier CDMA systems

In this letter, we present a set of cyclic shifted orthogonal complementary (cyclic-OC) codes for multicarrier CDMA systems. The conventional OC codes are not adequate for the system because they are able to support only the limited number of users. By applying the proposed cyclic-OC codes for the inter-symbol interference (ISI)-free multicarrier systems, the number of users can be extended to the size of code length. We validate the effectiveness of the proposed scheme through simulations.     

Optical orthogonal codes with large crosscorrelation and their performance bound for asynchronous optical CDMA systems

Optical orthogonal codes (OOCs) are commonly used as signature codes for optical code-division multiple-access (OCDMA) communication systems. Many OOCs have been proposed and investigated. Asynchronous OCDMA systems using conventional OOCs have a very limited number of subscribers and few simultaneous users. Recently, we reported a new code family with large code size by relaxing the crosscorrelation constraint to 2. In this paper, by further loosening the crosscorrelation constraint, we adopt the random greedy algorithm to construct a code family which has larger code size and more simultaneous users. We also derive an upper bound of the number of simultaneous users for a given code length, code weight, and bit error rate. The study shows that it is possible to have codes approaching this bound.     

Multilength two-dimensional codes for optical CDMA system

A new class of multilength, constant-weight and two-dimensional multiwavelength optical orthogonal code （2D MWOOCs） with large capacity and good correlation properties is constructed based on multilength one-dimensional （1D） OOCs. The performance of these new MWOOCs in an OCDMA network with double-services is analyzed. The result shows that media with the shorter codeword performs much better than the media with longer codeword, and OCDMA system with these new multilength MWOOCs performs well. These features allow multimedia transmission of large capacity in OCDMA system.     

Multi-weight unipolar codes for multimedia spectral-amplitude-coding optical CDMA systems

A novel balanced detection scheme for multi-access interference cancellation in multimedia spectral-amplitude-coding optical code-division multiple-access system is proposed. The receiver is capable of handling both equal and unequal in-phase cross correlation of optical orthogonal codes. A novel class of constant-length variable-weight optical orthogonal codes able to support multimedia services with different quality-of-service requirements is proposed as well. The construction is based on the pairwise balanced designs, or more specifically, on an incidence structure defined on an integer sub-lattice.     

Incoherent asynchronous optical CDMA using gold codes

An approach is described for obtaining a correlation output corresponding to the difference between agreements and disagreements in incoherent optics, through the use of additional preceding and balanced detection. Calculations of the correlation spectra and of the probability of BER reveals that the proposed technique, in tandem with gold codes, can accommodate more users than previously reported systems     

A new family of 2-D optical orthogonal codes and analysis of its performance in optical CDMA access networks

A new family of two-dimensional optical orthogonal code (2-D OOC), one-coincidence frequency hop code (OCFHC)/OOC, which employs OCFHC and OOC as wavelength hopping and time-spreading patterns, respectively, is proposed in this paper. In contrary to previously constructed 2-D OOCs, OCFHC/OOC provides more choices on the number of available wavelengths and its cardinality achieves the upper bound in theory without sacrificing good auto-and-cross correlation properties, i.e., the correlation properties of the code is still ideal. Meanwhile, we utilize a new method, called effective normalized throughput, to compare the performance of diverse codes applicable to optical code division multiple access (OCDMA) systems besides conventional measure bit error rate, and the results indicate that our code performs better than obtained OCDMA codes and is truly applicable to OCDMA networks as multiaccess codes and will greatly facilitate the implementation of OCDMA access networks.     

Multiple-wavelength transmitter for WDM optical network

Optical network based on wavelength-division multiplexing (WDM) technology will be a most active research topic in the 21 st century. This paper describes a WDM multiple-wavelength transmitter and several key corresponding devices for optical network, including amplified spontaneous emission (ASE) spectrum-sliced multiple-wavelength optical source, optical add/drop multiplexer (OADM), semiconductor optical amplifier (SOA), as well as the spectrum noise suppression scheme. The new research results are reported, and the applications of these developed devices are also introduced.     

Combinatorial constructions of optical orthogonal codes for OCDMA systems

Two novel classes of optical orthogonal code (OOC) based on balanced incomplete block designs are proposed: OOC based on mutual orthogonal Latin squares/rectangles and the codes based on finite geometries. Both OOC families can be applied to synchronous and asynchronous incoherent optical CDMA, and are compatible with spectral-amplitude-coding (SAC), time-spreading encoding and fast frequency hopping schemes. Large flexibility in cross-correlation control makes those OOC families interesting candidates for applications that require a large number of users. Novel fiber Bragg grating decoding scheme for canceling the multi-user interference from SAC-signals with nonfixed in-phase cross-correlation is proposed as well.