Multiple-length extended carrier-hopping prime codes for optical CDMA systems supporting multirate multimedia services

Extended carrier-hopping prime codes (ECHPCs) with ideal correlation properties (i.e., zero autocorrelation sidelobes and cross-correlation values of at most 1) and significantly expanded cardinality were recently constructed for wavelength-hopping time-spreading optical code division multiple access (O-CDMA). To support multimedia services with different bit-rate requirements, a new family of multiple-length constant-weight ECHPCs with ideal correlation properties is constructed algebraically in this paper. The performance of these new codes in an O-CDMA multimedia system is analyzed. Contrary to conventional single-length codes, our study shows that the performance of these multiple-length codes improves as the code length decreases, thus supporting prioritization in O-CDMA.     

Multiple-wavelength optical orthogonal codes under prime-sequence permutations for optical CDMA

A new family of two-dimensional (2-D) wavelength-hopping time-spreading codes, which employs wavelength hopping algebraically under prime-sequence permutations on top of time-spreading optical orthogonal codes, is studied and analyzed. Different from other 2-D codes, our new codes allow the number of wavelengths and code length to be chosen independently and, at the same time, the code cardinality is a quadratic function of the number of wavelengths without sacrificing the maximum cross-correlation value (i.e., still at most one). They are particularly suitable for high bit-rate optical code-division multiple-access systems with broadband mode-locked lasers, in which the number of time slots is very limited, and system capacity can only be grown by increasing the number of wavelengths, rather than code length. Finally, a novel wavelength-aware detector for wavelength-hopping time-spreading codes is discussed and shown to provide improved code performance.     

New construction of multiwavelength optical orthogonal codes

We investigate multiwavelength optical orthogonal codes (MWOOCs) for optical code-division multiple access. Particularly, we present a new construction method for (mn,/spl lambda/+2,/spl lambda/) MWOOCs with the number of available wavelengths m, codeword length n, and constant Hamming weight /spl lambda/+2 that have autocorrelation and cross-correlation values not exceeding /spl lambda/. In the proposed scheme, there is no constraint on the relationship between the number of available wavelengths and the codeword length, and it is also possible to use an arbitrary /spl lambda/. We show that the constructed code is optimal, especially for /spl lambda/=1. Finally, we analyze the bit error rate of the new code and compare it with that of other optical codes.     

Wavelength-time codes with maximum cross-correlation function of two for multicode-keying optical CDMA

In this paper, a new family of wavelength-time codes with expanded code cardinality and the maximum cross-correlation function of 2 (i.e., /spl lambda//sub c/=2) is constructed and analyzed. One application of the large code cardinality of our /spl lambda//sub c/=2 codes is multicode-keying wavelength-time optical code division multiple access (O-CDMA), in which each user is allocated with multiple code matrices, instead of just one code matrix in the conventional ON-OFF keying (OOK) O-CDMA. System throughput is increased because a lower baud rate O-CDMA system can be used to support higher bit-rate transmission since each code matrix is used to represent a "symbol" of several data bits. User code confidentiality is improved because of symbol transmission. The performances of two multicode-keying O-CDMA schemes with the new /spl lambda//sub c/=2 wavelength-time codes are also analyzed. The results in this paper show that there is a tradeoff between the performance and the number of code matrices per user.     

Performance Analysis of Variable-Weight Multilength Optical Codes for Wavelength–Time O-CDMA Multimedia Systems

To support multimedia services with different discrete bit-rate requirements, families of multilength optical codes, such as the carrier-hopping prime code (CHPC), extended CHPC, and multiwavelength optical orthogonal code, were recently constructed for wavelength-time optical code-division multiple-access (O-CDMA). In this paper, the performances of these multilength optical codes in a multimedia O-CDMA system with a variable-weight operation are analyzed. Our study shows that short-length codes generate stronger interference than long-length codes. This supports services prioritization in O-CDMA. Our study also shows that code weight is a more important factor than code length in determining code performance.     

Performance Analysis of Variable-Weight, Multilength Optical Codes for Wavelength-Time O-CDMA Multimedia Systems

To support multimedia services with different discrete bit-rate requirements, families of multilength optical codes, such as the carrier-hopping prime code (CHPC), extended CHPC, and multiwavelength optical orthogonal code, were recently constructed for wavelength-time optical code-division multiple-access (O-CDMA). In this paper, the performance of these multilength optical codes in a multimedia O-CDMA system with a variable-weight operation are analyzed. Our study shows that short-length codes generate stronger interference than long-length codes. This supports services prioritization in O-CDMA. Our study also shows that code weight is a more important factor than code length in determining code performance (i.e., quality of service).      

Shifted carrier-hopping prime codes for multicode keying in wavelength-time O-CDMA

In this paper, we study the use of shifted carrier-hopping prime codes (CHPC) for multicode keying in wavelength-time optical code-division multiple-access (O-CDMA) systems. By using the code's good properties of zero autocorrelation sidelobes and cross-correlation functions of at most one, each user is assigned M=2/sup m/ shifted copies of its own code matrix to represent m data bits per symbol with minimal interference. The advantages of our scheme are that: 1) a lower baud rate O-CDMA system can now support a higher bit rate; 2) no network synchronization is required; 3) no M-fold increase in code cardinality is needed, as compared with standard M-code keying; 4) the numbers of optical encoders and decoders can be reduced from M to one per user, a major hardware cost savings; and 5) user code confidentiality is enhanced, as compared with the transmission of one code matrix for each data-bit one in conventional "on-off keying" O-CDMA schemes. Finally, our performance analysis shows that there is a tradeoff between the error probability and the choice of M.     

Construction and performance analysis of 2-D variable-length variable-weight optical orthogonal codes

In this paper, a new generation algorithm of a two-dimensional variable-length and variable-weight optical orthogonal codes (2-D VLVWOOCs) is proposed. By analysis of the BER performance for the corresponding optical code division multiple access (OCDMA) system, it is shown that the users with different codewords have significant differences in performance. Users with heavier-weight address matrices always outperform those with lighter-weight address matrices, and shorter-length and longer-length matrices support high bit-rate and low bit-rate in OCDMA applications, respectively. Therefore, heavier-weight shorter-length matrices can accommodate high bit-rate and high-quality of services (QoS) (e.g., real-time video), and lighter-weight longer-length matrices can achieve low bit-rate and low-QoS (e.g., voice). The system performance becomes worse as the users concentrate on one type of service. Especially, a surge of the number of users with shorter-length matrices has particularly impact on system performance. Thus, the 2-D VLVWOOCs can be used to provide many different types of services with different rate-levels and different levels of QoS, and simultaneously make better use of bandwidth resources in optical networks.

Optimizing spectral efficiency in multiwavelength optical CDMA system

Prime codes are excellent candidates for use in multiwavelength optical code-division multiple-access (O-CDMA) systems. We show that in an O-CDMA system using two-dimensional single-pulse-per-row codes, a single choice of the number of wavelength channels can. accommodate different numbers of users with maximal spectral efficiency. The optimum single-user-detection spectral efficiency of the system can be reached using AND detection. A fixed-hardware network can readily be adapted in response to changes in the number of users and traffic load.     

Comparison of diverse optical CDMA codes using a normalized throughput metric

A new method of comparing optical CDMA codes of different families, sizes and weights is described. We outline why the traditional performance metric of bit-error rate versus number of simultaneous users is lacking and propose a new performance measure - the peak throughput normalized with respect to the size of the code. This new metric is used to show that optical-orthogonal codes (OOCs) with a weight of 4 perform best at low offered loads while OOCs with weight 5 should be used at higher offered loads. By applying the technique across different families of codes, we demonstrate that multi-wavelength OOCs (MWOOCs) perform better than both OOCs (by a factor of approximately 1.25) and asymmetric prime-hop codes (by a factor of approximately 3.5), over a wide range of offered loads.     

Frequency-hopping codes for multimedia services in mobiletelecommunications

In this paper, “multilength” frequency-hopping (FH) codes are constructed by modifying the generalized prime codes (GPCs). The new codes have asymptotically optimal cardinality as well as zero autocorrelation sidelobes and cross-correlation functions of no greater than one. They are suitable for the integration of multimedia services (e.g., data, voice, image, and video) with different quality-of-service (QoS) requirements and signaling rates in future telecommunication systems, such as third-generation cellular mobile radio systems, where rate and service quality are dynamically matched to users' needs through the assignment of different-length FH patterns. The use of the new codes in multirate multimedia systems with FH code-division multiple access (FH-CDMA) is illustrated. Providing frequency and time diversities, the applications of the GPCs to an FH time-division multiple-access (FH-TDMA) and FH/time-hopping TDMA (FH/TH-TDMA) system are also discussed. Finally, the use of the codes in optical CDMA systems as multiwavelength optical orthogonal codes is studied     

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.     

Performance comparison of multiwavelength CDMA and WDMA+CDMA forfiber-optic networks

A “multiwavelength” scheme has been proposed to support large numbers of subscribers and simultaneous users in optical code-division multiple-access (CDMA) networks without using very large bandwidth expansion or the need of complicated and not-yet-feasible optical processing. In this paper, multiwavelength optical orthogonal codes (MWOOCs), which consist of two-dimensional codewords (or matrices) with every pulse of a codeword encoded in a distinct wavelength, are constructed for this scheme. MWOOCs have larger cardinality than the one-dimensional codes used in the hybrid wavelength-division multiple-access (WDMA) and CDMA scheme. With the same hardware configuration, our analysis shows that the multiwavelength scheme, in general, performs better than the hybrid scheme, particularly when the traffic load is heavy. However, if a central controller (i.e., under the best scenario) is used to uniformly distribute all available wavelengths to simultaneous users in the hybrid scheme, both schemes have comparable performance for a medium traffic load and the hybrid scheme can theoretically achieve error-free transmission when the load is light. In addition, using multiple wavelengths, the requirements of fiber ribbons and multiple stars in temporal/spatial optical CDMA networks are eliminated     

The role of optical CDMA in access networks

We investigate the possible role of optical CDMA (O-CDMA) in future access networks. We begin with a short review of the O-CDMA technique for those unfamiliar with the technology. Next, we investigate in detail those characteristics of O-CDMA that make it an attractive technology for application in metro access networks: fairness, flexibility, simplified network control and management, service differentiation, and increased security. Although O-CDMA has many favorable attributes, it also has several actual or perceived drawbacks. We discuss the technical, economic, and perception barriers that may have limited the widescale deployment of O-CDMA access networks. We try to determine which of these drawbacks may be surmountable in the near future and which may be true "showstoppers"     

System performance comparison of optical CDMA and WDMA in a broadcast local area network

The performance of optical code-division multiple-access (CDMA) systems with wavelength-hopping/time-spreading codes is compared to that of a wavelength-division multiple-access (WDMA) system. The multiple-access techniques are applied in a time-slotted broadcast local area network. The utilization, defined as the throughput per unit of time-domain bandwidth expansion, and packet delay are used as metrics of performance. When more than seven wavelengths are available, optical CDMA systems using asymmetric prime-hop codes and all-optical signal processing are shown to have higher peak utilization and lower corresponding delay than a WDMA system with the same number of wavelengths. When the encoders/decoders operate at the chip rate, the utilization of optical CDMA exceeds that of WDMA at high offered loads; however, the peak utilization of the WDMA system is still superior.     

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.     

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.     

Two-dimensional spatial signature patterns

An optical orthogonal signature pattern code (OOSPC) is a collection of (0,1) two-dimensional (2-D) patterns with good correlation properties (i.e., high autocorrelation peaks with low sidelobes, and low cross-correlation functions). Such codes find applications, for example, to parallelly transmit and access images in “multicore-fiber” code-division multiple-access (CDMA) networks. Up to now all work on OOSPCs has been based on an assumption that at most one pulse per column or one pulse per row and column is allowed in each two-dimensional pattern. However, this restriction may not be required in such multiple-access networks if timing information can be extracted from other means, rather than from the autocorrelation function. A new class of OOSPCs is constructed without the restriction. The relationships between two-dimensional binary discrete auto- and cross-correlation arrays and their corresponding “sets” for OOSPCs are first developed. In addition, new bounds on the size of this special class of OOSPCs are derived. Afterwards, four algebraic techniques for constructing these new codes are investigated. Among these constructions, some of them achieve the upper bounds with equality and are thus optimal. Finally, the codes generated from some constructions satisfy the restriction of at most one pulse per row or column and hence can be used in applications requiring, for example, frequency-hopping patterns     

Extended carrier-hopping prime codes for wavelength-time optical code-division multiple access

A two-dimensional wavelength-hopping time-spreading coding scheme has been recently studied for optical code-division multiple access, owing to maturity in fiber-Bragg grating (FBG) and arrayed-waveguide grating (AWG) technologies. Most of the optical codes designed for the scheme were based on an assumption, which may not be true in high data-rate systems, that the number of chips is higher than the number of available wavelengths. To provide a flexible code design without the assumption, this paper studies and analyzes a new family of carrier-hopping prime codes with expanded cardinality and ideal correlation properties. Flexible implementation of programmable AWG- and FBG-based coding hardware by using the wavelength-shift property of the codes is discussed.     

OCDMA系统中一种新的多倍长光垂直码

提出了一种新的容量大、相关性好的多倍长、多波长二维光正交码（2D MW-OOC），基于多倍长一维光正交码（1DOOC）构造了MW-OOC。对同时使用具有2种码长的MW-OOC的光码分多址（OCD-MA）系统性能分析表明，使用该MW-OOC的系统性能良好，明显好于同样码长下的多倍长1-DOOC；使用短码序列的信号误码率性能好于使用长码序列信号的误码率性能。这些特征能充分发挥OCDMA系统大容量的技术优势，满足将来大容量多媒体OcDMA网络系统对同时传输的不同信号所需传输质量不同的需求。