Absolute polar duty cycle division multiplexing: an economical and spectral efficient multiplexing technique

A new multiplexing technique based on duty cycle division is proposed, under the name: Absolute Polar Duty Cycle Division Multiplexing (APDCDM). The new technique allows for more efficient use of time slots as well as the spectrum, taking the advantage of both the conventional TDM and FDM. The basic properties based on theoretical analysis as well as simulation studies have been done to evaluate the performance of this technique based on the signal energy and symbol error rate (SER). In this paper the performance of Absolute Polar Duty Cycle Division Multiplexing is compared with multilevel M-ary as well as with the time division multiplexing (TDM) techniques. The simulation has been set for wireless transmission based on free space propagation model with adaptive white Gaussian noise (AWGN). PSK and QAM are used as modulation schemes to evaluate these techniques against data rates and number of users. The study shows that by increasing the number of users, the energy per bit in APDCDM has better performance than that of TDM technique. The simulation result correspond with the theoretical study shows that Absolute Polar Duty Cycle Division Multiplexing (APDCDM), has better SER than TDM

Absolute Polar Duty Cycle Division Multiplexing (APDCDM); technique for wireless communications

A new multiplexing and demultiplexing technique for wireless communications which is called Absolute Polar Duty Cycle Division Multiplexing (APDCDM) is presented in this paper. APDCDM can become an alternative multiplexing technique in wireless communications. The new technique allows for better error detection, correction, clock recovery and more efficient use of time slots as well as spectrum. The principle of the APDCDM technique has been discussed in this paper based on theoretical analysis as well as simulation studies. The performance comparison is made against time division multiplexing technique (TDM). The simulation has been set for wireless transmission, based on free space propagation model with adaptive white Gaussian noise (AWGN); QAM is used as modulation scheme to evaluate this technique against data rate and number of users. The simulation result correspond with the theoretical study show that APDCDM has better performance than TDM for supporting higher number of multiplexing users and bit rate

A fuzzy expert system for classification of short duration voltage disturbances

One of the important aspects in power quality assessment is automated detection and classification of power quality disturbances which requires the use of artificial intelligent techniques. This paper presents the application of fuzzy expert system for classification of short duration voltage disturbances which include voltage sag, swell and interruption. To obtain unique features of the voltage disturbances, fast Fourier transform analysis and root mean square averaging technique are utilized so as to determine the disturbance parameters such as duration, maximum and minimum rms voltage magnitudes. Based on these parameters, a fuzzy-expert system has been developed to set the fuzzy rules incorporating five inputs and three outputs. The system is designed for detecting and classifying the three types of short duration voltage disturbances, so as to determine whether the disturbance is instantaneous, momentary and non sag, swell and interruption. To verify the accuracy of the proposed system, it has been tested with recorded voltage disturbances obtained from monitoring. Tests results showed that the developed fuzzy�expert system gives a correct classification rate of 98.4

Comparison of selected digital modulation schemes (OOK, PPM and DPIM) for wireless optical communications

In this article, three digital modulation schemes popular in optical wireless communication systems (OOK, PPM and DPIM) are compared based on bandwidth requirement, power efficiency, transmits-ion capacity and biterror probability. In OOK, the bandwidth requirement is roughly equivalent to the data rate (Rb). PPM achieves higher average power efficiency than OOK at the expense of an increased bandwidth ( 4) compared to OOK. Besides, the use of PPM imposes more system complexity compared to OOK since both slot- and symbol-level synchronizati-ons, critical to system performance, are required at the receiver. Unlike PPM, DPIM does not require symbol synchronization since each symbol is initiated with a pulse. Furthermore, DPIM displays a higher transmiss-ion capacity by eliminating all the unused time slots from within each symbol. In terms of BER, 4-DPIM displays a performance in between that of OOK and PPM. It is concluded that DPIM is the most efficient scheme in terms of transmission capacity and band-width requirements. When it comes to power and error performance, PPM is the best among the three schemes

Improving the performance of electrical duty-cycle division multiplexing with optimum signal level spacing

Performance optimization of 3 x 10 Gbps conventional electrical-duty-cycle division multiplexing (C-E-DCDM) technique is investigated. It is shown that controlling signal level spacing can optimize its performance. Two level spacing optimization techniques, one in electrical domain and another in optical domain are examined. In general, performance of the C-E-DCDM is improved significantly using both approaches. The results show by optimization, an improvement of around 5.5 dB can be achieved for the C-E-DCDM in terms of receiver sensitivity and optical signal-to-noise ratio using both electrical and optical methods. However, chromatic dispersion tolerance in one of the optimization approaches is degraded by around 34 ps/nm for negative dispersion, while the positive dispersion tolerance improved compared to the C-E-DCDM. (C) 2011 Elsevier B.V. All rights reserved

A new duty cycle based digital multiplexing technique

�A new multiplexing technique which is called duty cycle division multiplexing (DCDM) is presented in this paper. Theoretical and simulation studies have been carried out to evaluate the performance of this technique based on the signal energy and symbol error rate (SER). A wireless channel based on free space propagation model is considered for the simulation study. Two modulation schemes of PSK and QAM are used to evaluate the technique, against the data rates. Also, the performance of the multiplexing technique is compared with the conventional Time Division Multiplexing (TDM) technique as well as with the multilevel M-ary signaling. The study shows that the energy per bit in the DCDM technique, unlike that of the TDM technique increases with the number of users. The simulation results correspond with the theoretical study in which the DCDM technique has better SER than that of TDM

A novel economical duty cycle division multiplexing with electrical multiplexer and demultiplexer for optical communication systems

Duty cycle division multiplexing (DCDM) is proposed as an alternative multiplexing technique. In this technique, the channel multiplexing and demultiplexing are performed electrically. This technique allows aggregate bit rate to be recovered at the single channel bit rate, which is very economic. In this paper, we examine three channels system where each channel operates at 10 Gb/s over a single optical carrier. Performance of the system is evaluated based on back-to-back receiver sensitivity, optical signal-to-noise ratio (OSNR) and chromatic dispersion tolerance. The performance comparison is made against return-to-zero (RZ) format. The results show that, DCDM can support higher amount of chromatic dispersion than that RZ. At 3 � 40 Gb/s, a receiver sensitivity and OSNR of �16.8 dBm and 34.6 dB is respectively required for the worst DCDM channel

Collapsed optical fiber: A novel method for improving thermoluminescence response of optical fiber

A new technique is shown to provide improved thermoluminescence (TL) response from optical fibers, based on collapsing down hollow capillary optical fibers (COF) into flat fibers (FF), producing fused inner walls and consequent defects generation. Four different fused silica preform tubes are used to fabricate in-house COFs and FFs, i.e., ultra-pure (F300), relatively pure silica (PS), germanium-doped (Ge), and Ge-Boron-doped (GeB). The optical fibers are then subjected to 6 MeV electron irradiation. While the results show similar TL response from F300-COF and -FF, the TL response of PS-COF is improved by a factor of 6 by collapsing it down to a FF. By doping Ge into the F300 tube, the U response of the resultant Ge-COF shows an improvement of 3 times over that of F300-COF, while an improvement of a factor of 12 is obtained by producing a Ge-FF. In GeB preform, by collapsing the capillary fiber into a FF, an improvement in TL response of 31 times that of GeB-COF is obtained. U glow curve analysis shows an additional peak to be generated in the FFs compared to that observed in the COFs. The TL intensity value of the new peak is significantly increased in the doped FFs compared to the undoped FFs. The results suggest that defects generation occurs as a result of the fusing/collapsing technique, providing a TL response from the optical fibers that can substantially improve upon that of existing TL system sensitivities. (C) 2015 Elsevier B.V. All rights reserved

Effect of temperature and external optical feedback on intensity and phase noise characteristics in single-mode fiber grating Fabry-Perot laser

The combined effect of temperature variation and external optical feedback (OFB) on the relative intensity noise (RIN) and phase noise (FN) characteristics of fiber grating Fabry-Perot (FGFP) laser for the first time, is investigated numerically by modifying the well-known laser rate equations. The temperature dependence (TD) of RIN and FN characteristics is calculated according to TD of laser cavity parameters; not by using the well-known Pankove equation. The effect of external OFB on RIN and FN characteristics is calculated according to its effect on laser threshold carrier density. The simulation of the frequency spectra of RIN and FN are performed by fast Fourier transform (FFT). We show that FBG can be use to control the external OFB level, thereby; controlling noise level of the laser. Results show that the optimum range of working temperature for FGFP laser for low noise characteristic is within ±2 °C from the FBG reference temperature

Evaluating the optical properties of TiO2 nanofluid for a direct absorption solar collector

Recent studies specify that designated nanofluids may increase the proficiency of direct absorption solar thermal collectors. To determine the efficiency of nanofluids in solar applications, their capability to change light energy to thermal energy must be identified (i.e., the absorption spectrum of the solar material). In view of that, this study compares model predictions to spectroscopic measurements of extinction coefficients over wavelengths that are important for solar energy (200- 1100nm). In the first decade of nanofluid research, most of the focus was on measuring and modeling the fundamental thermophysical properties of nanofluids (i.e., thermal conductivity, density, viscosity, and convection coefficients). Lately, considerable focus is given to the fundamental optical properties of nanofluids. However, the effect of particle size, shape, and volume fraction of nanoparticles as well as alternation of the base fluids, which can significantly affect scattering and absorption, have not been addressed to date in the literature. In this study, the effects of size and concentration of TiO2 nanoparticles on the extinction coefficient were analyzed using the Rayleigh approach. The results show that smaller particle size (<20nm) has a nominal effect on the optical properties of nanofluids. Volume fraction is linearly proportionate to the extinction coefficient. Considering a nanoparticle size of 20nm, almost 0 transmissivity is obtained for wavelengths ranging from 200 to 300nm. However, a sudden increase of 71 in transmissivity is noted from 400nm, gradually increasing to 88 and becoming similar to that of water at 900nm. Promising results are observed for volume fractions below 0.1