904 research outputs found
Cellular Underwater Wireless Optical CDMA Network: Potentials and Challenges
Underwater wireless optical communications is an emerging solution to the
expanding demand for broadband links in oceans and seas. In this paper, a
cellular underwater wireless optical code division multiple-access (UW-OCDMA)
network is proposed to provide broadband links for commercial and military
applications. The optical orthogonal codes (OOC) are employed as signature
codes of underwater mobile users. Fundamental key aspects of the network such
as its backhaul architecture, its potential applications and its design
challenges are presented. In particular, the proposed network is used as
infrastructure of centralized, decentralized and relay-assisted underwater
sensor networks for high-speed real-time monitoring. Furthermore, a promising
underwater localization and positioning scheme based on this cellular network
is presented. Finally, probable design challenges such as cell edge coverage,
blockage avoidance, power control and increasing the network capacity are
addressed.Comment: 11 pages, 10 figure
Single integrated device for optical CDMA code processing in dual-code environment
We report on the design, fabrication and performance of a matching integrated optical CDMA encoder-decoder pair based on holographic Bragg reflector technology. Simultaneous encoding/decoding operation of two multiple wavelength-hopping time-spreading codes was successfully demonstrated and shown to support two error-free OCDMA links at OC-24. A double-pass scheme was employed in the devices to enable the use of longer code length
PERFORMANCE ANALYSIS OF OPTICAL CDMA SYSTEM USING VC CODE FAMILY UNDER VARIOUS OPTICAL PARAMETERS
The intent of this paper is to study the performance of spectral-amplitude coding optical code-division multiple-access (OCDMA) systems using Vector Combinatorial (VC) code under various optical parameters. This code can be constructed by an algebraic way based on Euclidian vectors for any positive integer number. One of the important properties of this code is that the maximum cross-correlation is always one which means that multi-user interference (MUI) and phase induced intensity noise are reduced. Transmitter and receiver structures based on unchirped fiber Bragg grating (FBGs) using VC code and taking into account effects of the intensity, shot and thermal noise sources is demonstrated. The impact of the fiber distance effects on bit error rate (BER) is reported using a commercial optical systems simulator, virtual photonic instrument, VPITM. The VC code is compared mathematically with reported codes which use similar techniques. We analyzed and characterized the fiber link, received power, BER and channel spacing. The performance and optimization of VC code in SAC-OCDMA system is reported. By comparing the theoretical and simulation results taken from VPITM, we have demonstrated that, for a high number of users, even if data rate is higher, the effective power source is adequate when the VC is used. Also it is found that as the channel spacing width goes from very narrow to wider, the BER decreases, best performance occurs at a spacing bandwidth between 0.8 and 1 nm. We have shown that the SAC system utilizing VC code significantly improves the performance compared with the reported codes
A NOVEL CONSTRUCTION OF VECTOR COMBINATORIAL (VC) CODE FAMILIES AND DETECTION SCHEME FOR SAC OCDMA SYSTEMS
There has been growing interests in using optical code division multiple access
(OCDMA) systems for the next generation high-speed optical fiber networks. The
advantage of spectral amplitude coding (SAC-OCDMA) over conventional OCDMA
systems is that, when using appropriate detection technique, the multiple access
interference (MAI) can totally be canceled. The motivation of this research is to
develop new code families to enhance the overall performance of optical OCDMA
systems. Four aspects are tackled in this research. Firstly, a comprehensive discussion
takes place on all important aspects of existing codes from advantages and
disadvantages point of view. Two algorithms are proposed to construct several code
families namely Vector Combinatorial (VC). Secondly, a new detection technique
based on exclusive-OR (XOR) logic is developed and compared to the reported
detection techniques. Thirdly, a software simulation for SAC OCDMA system with
the VC families using a commercial optical system, Virtual Photonic Instrument,
“VPITM TransmissionMaker 7.1” is conducted. Finally, an extensive investigation to
study and characterize the VC-OCDMA in local area network (LAN) is conducted.
For the performance analysis, the effects of phase-induced intensity noise (PIIN), shot
noise, and thermal noise are considered simultaneously. The performances of the
system compared to reported systems were characterized by referring to the signal to
noise ratio (SNR), the bit error rate (BER) and the effective power (Psr). Numerical
results show that, an acceptable BER of 10−9 was achieved by the VC codes with 120
active users while a much better performance can be achieved when the effective
received power Psr > -26 dBm. In particular, the BER can be significantly improved
when the VC optimal channel spacing width is carefully selected; best performance
occurs at a spacing bandwidth between 0.8 and 1 nm. The simulation results indicate
that VC code has a superior performance compared to other reported codes for the
same transmission quality. It is also found that for a transmitted power at 0 dBm, the
BER specified by eye diagrams patterns are 10-14 and 10-5 for VC and Modified
Quadratic Congruence (MQC) codes respectively
Pulse-power-detection analysis of incoherent O-CDMA systems under the influence of fiber temperature fluctuations
In this paper, a pulse-shift technique, which divides every time slot (or chip) into equal-width sub-chips, is used to model the effect of fiber temperature fluctuations in incoherent optical code-division multiple-access (O-CDMA) systems. With the advance in all-optical thresholding technology, power detection of ultrashort optical pulses is possible. This paper also formulates a new pulse-power-detection model for incoherent OCDMA and applies it to the analysis of the pulse-shift technique as a case study. Numerical studies and computer simulations are presented to validate the new analytical model. Our study presents a more realistic theoretical model of all-optical thresholding in incoherent O-CDMA and results in better performance than the conventional pulse-energy-detection model
Noncoherent Spatial/Spectral Optical CDMA System With Two-Dimensional Perfect Difference Codes
[[abstract]]A dynamic optical code division multiple access (DOCDMA) communication system is proposed for high-bandwidth communication systems. An implementation of the system is proposed based on a fast tunable optical filter (TOF) in each encoder and decoder. This technique actively modulates the central wavelength of a TOF according to a functional code at the transmitter during the bit period before the transmission of the data. The system is modeled and analyzed taking into account multiple access interference (MAI), thermal noise, and phase-induced intensity noise (PIIN). The performance of this system is compared to that of a spectral amplitude coding system that uses either a Hadamard code or a modified quadratic congruence (MQC) code. The results show that the proposed DOCDMA system reduces the PIIN effect on the performance of the system and improves the bit error rate (BER) performance at a large number of users. Furthermore, it is found that when the effective power is large enough, the MAI becomes the main factor that limits system performance, whereas when the effective power is relatively low, both thermal noise and PIIN become the main limiting factors with thermal noise having the main influence.[[notice]]補正完畢[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子
Using Direct-Sequenced Spread Spectrum in a Wired Local Area Network
Code division multiple access provides an ability to share channel bandwidth amongst users at the same time. Individual user performance is not degraded with the addition of more users, unlike traditional Ethernet. Using direct sequenced spread spectrum in a wired local area network, network performance is improved. For a network in overload conditions, individual station throughput is increased by nearly 212% while mean end-to-end delay was reduced by 800%. The vast improvement demonstrated by this research has the capability to extend legacy-cabling infrastructures for many years to come while easily accommodating new bandwidth intensive multimedia applications
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