Wing C. Kwong

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.

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.

Experimental demonstration and scalability analysis of a four-node 102-Gchip/s fast frequency-hopping time-spreading optical CDMA network

We present experimental and simulation results from a 102-Gchips/s incoherent wavelength-hopping time-spreading optical code-division multiple-access testbed, utilizing four 50-GHz ITU grid wavelengths. Error-free operation of four users is obtained with an effective power penalty /spl sim/0.5 dB. Simulation studies show scalability to >10 users with an effective power penalty of /spl sim/4 dB. The simulation study of the impact of asynchronous access on the performance allows for a complete network design from an engineering viewpoint.

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.

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).

2/sup n/ prime-sequence codes and coding architecture for optical code-division multiple-access

Recent study shows that optical code-division multiple-access (CDMA) networks cannot be evaluated or designed by only considering the performance (i.e., correlation properties) of the optical pseudo-orthogonal codes selected. The structures of optical encoders and decoders are another important factors to consider and are needed to coordinate with the selected optical codes as much as possible. A special family of 2/sup n/ codes, so-called 2/sup n/ prime-sequence codes, is constructed. A general theorem on the cardinality of the new codes is provided. The properties and performance of the codes are also studied. Since these codes pose the algebraic properties of both prime-sequence and 2/sup n/ codes, new optical encoding and decoding structures are designed to optimize the system parameters (e.g., power budget and cost) of these optical CDMA networks. This new configuration is particularly attractive for ultrafast optical processing and waveguide implementation for tile future high-capacity, low-loss, all-optical CDMA networks.

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.

Determination of FWM products in unequal-spaced-channel WDM lightwave systems

Recently, unequal-spaced channel-allocation techniques have been studied and analyzed to reduce four-wave-mixing (FWM) crosstalk in high-capacity, long-haul wavelength-division multiplexing (WDM) transmission systems. It will be helpful to system designers if there exists a fast tool to measure the strength of FWM crosstalk in such WDM systems. In this paper, we develop two algorithms, using frequency difference triangles and frequency difference squares, that can determine the total numbers of FWM signals falling onto the operating band and each channel, respectively, of unequal-spaced WDM systems. By knowing these two numbers, one can adjust the system parameters, such as minimum channel spacing, in order to keep a good balance on the adverse effects of FWM crosstalk and interchannel interference, or avoid the assignment of channels at locations with the most severe crosstalk.

Ultrafast all-optical code-division multiple-access (CDMA) fiber-optic networks

Abstract With the advanced development of fiber-optics, the large bandwidth-expansion required by spread spectrum code-division multiple-access (CDMA) can now be accomodated by using a fiber-optic channel for transmission and incoherent optical signal processing for code generation and correlation. Optical synchronous CDMA (S/CDMA), a synchronous transmission format, is introduced and compared with optical (asynchronous) CDMA. Using modified prime sequence codes, S/CDMA is shown to accomodate a larger number of subscribers and more simultaneous users than CDMA. A two-user experiment demonstrating the feasibility of optical S/CDMA is performed at 10 Mbit/s (500 Mchip/s), using optical signal processing. (A chip is a bit-representation component; please see Section 2.) An environment in which S/CDMA would be particularly suited is also discussed. In addition, recent research shows that the feasibility of optical CDMA is also determined by the architecture of the optical encoders/decoders. The coding architecture affects, for example, the amount of power loss and length of optical delays associated with code sequence generation and correlation, which, in turn, affect the power budget, size, and cost of an optical CDMA system. Therefore, a new, modified 2 n coding architecture is proposed and compared with prime and 2 n coding architectures. Study shows that the modified 2 n architecture performs the best and is particularly suitable for ultrafast all-optical processing and waveguides implementation for the future all-optical CDMA networks. A 100 Mbit/s optical CDMA experiment in free space demonstrating the feasibility of the modified 2 n coding architecture, using a serial combination of 50/50 beam splitters and retroreflectors, at 10 Tchip/s (i.e., 100,000 chip/bit) with 100 fs laser pulses is also reported.

Performance analysis of extended carrier-hopping prime codes for optical CDMA

A new class of two-dimensional (2-D) carrier-hopping prime codes with very good correlation properties and significantly expanded cardinality was recently constructed for wavelength-hopping time-spreading optical code-division multiple access (CDMA). In this paper, the performance of the new codes is analyzed and compared to a carrier-grouping scheme of the original carrier-hopping prime codes. In addition, the traditional chip-synchronous assumption used in the performance analysis of optical CDMA is removed, for the first time, for 2-D optical codes with cross-correlation functions of at most one, showing improvement and better accuracy in error probabilities.