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

On constructions for optimal two-dimensional optical orthogonal codes

Two-dimensional optical orthogonal codes (2-D OOCs) are of current practical interest in fiber-optic code-division multiple-access networks as they enable optical communication at lower chip rate to overcome the drawbacks of nonlinear effects in large spreading sequences of one-dimensional codes. A 2-D OOC is said to be optimal if its cardinality is the largest possible. In this paper, we develop some constructions for optimal 2-D OOCs using combinatorial design theory. As an application, these constructions are used to construct an infinite family of new optimal 2-D OOCs with auto-correlation 1 and cross-correlation 1.

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.

Analysis of the higher order signals in fiber optic code-division multiple access networks using series coupler access encoder and series coupler access decoder

Fiber optic code-division multiple access (FO-CDMA) networks using optical series coupler access encoders (SCAEs) and series coupler access decoders (SCADs) are analyzed considering the higher order signals of the optical matched filter. By mathematically interpreting the inevitable interference effect of the higher order signals up to the third order, we found that the performance of the FO-CDMA networks could be seriously degraded due to the sidelobe peaks increased by the higher order signals. We also found that the interference signal intensities increase according to the increase of coupling coefficient (?). Compared with the conventional analysis without considering the higher order signals, the peak-to-sidelobe ratio considering the higher order signals is degraded, for example, by 3.75 dB for N(coupler number) = 5, ? = 0.5, and the code length of 341.

New fiber-optic ATM switching networks using optical code-division multiple access for broadband communication applications

We design new fiber-optic asynchronous-transfer-mode (ATM) networks which are based on incoherent optical code-division multiple access (CDMA). To eliminate the throughput bottleneck, optical signal processing is used in the proposed switching network to guarantee a high processing speed which is required by incoherent optical CDMA. This in turn can support real-time broadband communication services. Because strict optical orthogonal codes (OOCs) are employed, both cross-correlation and autocorrelation constraints are strictly limited to be "1" for variable-bitrate (VBR) and constant-bit-rate (CBR) data communications. In the VBR case, the use of strict OOCs can guarantee a lower bit error rate than using conventional OOCs. Moreover, the proposed ATM switching network can efficiently support CBR and VBR communications (e.g. HDTV and video conferencing with the MPEG-2 standard), with no increase of system bandwidth and no change of optical CDMA encoder/decoder. Simple theory and code construction of strict OOCs are presented. Moreover, error correction codes are used in fiber-optic CDMA networks to improve the system performance.

Novel spatial spread spectrum based fiber optic CDMA networks for image transmission

Novel code division multiple access (CDMA) fiber optic networks based on spatial frequency spread spectrum for image transmissions are proposed. Two key technologies are the parallel fiber optic transmission of spatially encoded images and parallel access to image data through optical spatial encoding and decoding. The temporal signature sequences used in conventional time-domain CDMA are replaced by two-dimensional (2-D) signature patterns to encode and decode binary image pixels. This enables the fully parallel access and transmission of images. The fundamental rules and methodology to construct optical orthogonal signature patterns (OOSP) are presented. Furthermore, it is shown that the all-optical implementation of the proposed system is feasible by utilizing optically addressable spatial light modulators in both the spatial encoder and the decoder along with multicore fibers as the parallel image transmission medium. The predicted overall throughput can reach 10 Tb/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>