Ghafour Amouzad Mahdiraji

Abstract: A unified and comprehensive study on the small-signal intensity and frequency modulation characteristics of a fiber Bragg grating Fabry-Perot (FBG-FP) laser are numerically investigated. The effect of injection current, temperature, external optical feedback (OFB), nonlinear gain compression factor, fiber grating (FG) parameters and spontaneous emission factor on modulation response characteristics are presented. The rate equations of the laser model are presented in the form that the effect of temperature (T) and external optical feedback (OFB) are included. The temperature dependence (TD) of laser response is calculated according to the TD of laser cavity parameters instead of directly using the well-known Parkove equation. It is shown that the optimum external fiber length (L-ext) is 3.1 cm and the optimum range of working temperature for FGFP laser is within +/- 2 degrees C from the FBG reference temperature (T-o). Also, the antireflection (AR) coating reflectivity and the linewidth enhancement factor have no significant effect on the modulation spectra. It is also show that modulation response is extremely sensitive to the OFB level, high injection current and gain compression factor. The study indicates clearly that good dynamic characteristic can be obtained by system parameters optimization. (C) 2012 Elsevier Ltd. All rights reserved.

Abstract: A comprehensive study on the phase noise characteristics of a single-mode fiber grating Fabry–Perot (FGFP) laser was conducted numerically. Adding to previous studies, the effects of external optical feedback (OFB), external cavity length, temperature, injection current, cavity volume, nonlinear gain compression factor and fiber grating parameters on phase noise characteristics are presented. The temperature dependence (TD) of phase noise was calculated according to the TD of laser parameters and not by the well-known Parkove equation. The frequency spectra of FGFP laser phase noise were calculated by using a Fourier transform. Results show that the TD of the phase noise in FGFP lasers is smaller than that for distributed feedback lasers. The shortest external cavity length that provides the minimum phase noise is found to be around 3.1 cm. In addition, the relaxation oscillation frequency shifts towards more than 6 GHz, which provides larger flat frequency range. Furthermore, phase noise can be eliminated either by increasing the injection current or the OFB level.

Abstract: Demultiplexing concept of Duty-Cycle Division Multiplexing (DCDM) technique is tested in the back-to-back connection and after transmission over copper wire and optical fiber. Three different lengths of copper wire are tested with the total loss of 3.3, 6.6, and 9.9 dB respectively. Even though the sampling points and threshold values were not dynamic, the demultiplexing process for the case of back-to-back, and after transmission over the links with 3.3, and 6.6 dB losses, was successful without experiencing any errors. This can be witnessed when the recovered data is compared against the transmitted bits. However, the errors are recorded in the link with 9.9 dB losses, which was mainly due to the non-optimized sampling points and threshold values. In experiment over 60 km Standard Single Mode Fiber, successful transmission was demonstrated. The receiver sensitivity is calculated off-line by using bit error rate analysis. These results confirm the validity of DCDM demultiplexer structure including the sampling process and the data recovery rules.

Abstract: A set of nonlinear rate equations that can describe an external cavity laser with any arbitrary external optical feedback (OFB) level are derived. A comprehensive study on the relative intensity noise (RIN) characteristics of a fiber grating Fabry-Perot is performed numerically. In this paper, fiber Bragg grating (FBG) is used as a wavelength lasing selective element to control the external OFB level, thereby control the RIN. In addition to the external OFB level, the effect of other external cavity parameters such as temperature, injection current, cavity volume, gain compression factor, and FBG parameters on RIN characteristics is investigated. The temperature dependence (TD) of RIN is calculated according to TD of laser parameters instead of well-known Parkove relationship. Results show that by optimization, the peak value of the RIN can be reduced down to around -150 dB/Hz. The optimum and the shortest external cavity length that provides the minimum RIN is found to be around 3.1 cm. In addition, by optimization, the relaxation oscillation frequency of RIN spectra is shifted toward around 5.6 GHz.

Abstract: A comprehensive study on the small-signal intensity modulation (IM) characteristics of a fiber grating Fabry-Perot (FGFP) laser is numerically investigated. The effect of external optical feedback (OFB), temperature, injection current, cavity volume, nonlinear gain compression factor, and fiber grating (FG) parameters on IM characteristics are presented. The temperature dependence (TD) of IM is calculated according to the TD of laser cavity parameters instead ;of using the well-known Parkove relationship. It has been shown that the optimum external fiber length (L-ext) is 3.1 cm. The optimum range of working temperature for FGFP laser is between 23 to 27 degrees C. We also show that by increasing the laser injection current from 10 to 60 mA, the IM peak amplitude decreased from 6.3 to 0.2 dB and the relaxation-oscillation frequency (ROF) is shifted from 1.2 GHz towards higher frequency of 5.48 GHz. In addition, the AR coating reflectivity and gain compression factor have no significant effect on the IM. The study indicates that a stable operation and excellent modulation characteristic can be obtained after optimization process.

Abstract: 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.

Abstract: 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 %.

Abstract: In this paper, turn-on time delay characteristics of a fiber grating Fabry-Perot (FGFP) laser are numerically investigated by considering all the carrier recombination rate (CRR) R(N) coefficients (nonradiative, A(nr); radiative, B; and Auger coefficient, C). The results show that the turn-on time delay significantly reduces by increasing the injection current (I-inj) and/or the initial value of carrier density (N-i). Meanwhile, the turn-on time delay increases by increasing the CRR coefficients. However, its effect can be minimized by increasing I-inj and/or N-i. In addition, the turn-on time delay can be reduced by increasing the external optical feedback (OFB) level. Moreover, it is shown that the optimum external-cavity length (L-ext) is 3.1 cm. Furthermore, an antireflection (AR) coating reflectivity value of 1 X 10(-2) is sufficient for the laser to operate at good turn-on time delay and low fabrication complexity. The obtained results can provide an important idea for the practical fabrication of the FGFP laser used in the dense wavelength-division multiplexing (DWDM) systems and optical access networks.

Abstract: Self-phase modulation (SPM) effect on performance of 40 Gbit/s (3 × 13.33 Gbit/s) optical duty-cycle division multiplexing (O-DCDM) over 400 km (5 × 80 km) standard single mode fiber (SSMF) based on three different dispersion compensation schemes is investigated by simulation. The result shows that the SPM effect is very strong in dispersion pre-compensation compared to post-compensation. Further reduction in SPM effect is observed by combination of pre- and post-compensation with the optimum pre-compensation value of around 215 ps/nm. The simulation is performed at different launched power into dispersion compensation fiber (DCF). The range between -6 to -8 dBm is observed as the optimum power for all dispersion compensation schemes. The highest SPM threshold is observed when dispersion pre- and post-compensation are used together, which is around +6.7 dBm. In addition, the optimum range of launched power into SSMF for different transmission distances from 80 km to 1280 km is also presented.

Abstract: A multiplexing technique, which is based on duty-cycle division, is proposed. The channel multiplexing and demultiplexing are performed electrically at the single user bitrate, which is very economic. In a three-user system (3 x 10 Gb/s), the simulation results show that the best receiver sensitivity value achieved is -30.1 dBm with an optical signal-to-noise ratio (OSNR) of 22.3 dB, while the chromatic dispersion tolerance ranges from 192 to 280 ps/nm. Migration from 30 to 120 Gb/s is achieved with the penalty of 6.4 and 5.2 dB in the receiver sensitivity and OSNR, respectively, for the worst user. (C) 2009 Elsevier Ltd. All rights reserved.

Abstract: We modeled and analyzed a method to improve receiver sensitivity of the Absolute Polar Duty Cycle Division Multiplexing (AP-DCDM) transmission system by using Dual-Drive Mach–Zehnder-Modulator (DD-MZM). It is found that by optimizing the bias voltage in DD-MZM, the sensitivity of the AP-DCDM can be improved. The optimizations lead towards the larger eye opening. As opposed to the previous work, in terms of receiver sensitivity and dispersion tolerance, similar performance for all channels was achieved. In comparison to the previously reported AP-DCDM system, this work resulted in almost 3.6 dB improvement of the receiver sensitivity, came together with acceptable chromatic dispersion tolerance.

Abstract: The performance of 5 × 10 Gb/s on-off-keying (OOK) modulation format over DCDM system is reported. The aggregate bit rate of 50 Gb/s is achieved with only 120 GHz spectral width. The clock and data recovery is realized at 10 GHz clock rate, which is very economic and efficient. The worst receiver sensitivity of –16.3 dBm, optical signal-to-noise ratio (OSNR) of 36 dB and chromatic dispersion tolerance of ±32 ps/nm are achieved. For the best channel, the receiver sensitivity, OSNR and chromatic dispersion tolerance are –26.5 dBm, 26.2 dB and ±69 ps/nm respectively.

Abstract: An improved estimation of bit-error-rate (BER) for electrically multiplexed duty-cycle division multiplexing (E-DCDM), which is based on the probability of error, is presented. Performance of 3 x 10 Gbit/s E-DCDM is investigated in terms of optical signal-to-noise ratio (OSNR) and dispersion tolerance. This technique requires 29.4 dB OSNR and can tolerate +/- 96 ps/nm chromatic dispersion for the worst user.

Abstract: 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.

Abstract: The performance of ASK over DCDM for up to seven channels is reported. The aggregate bit rate of 70 Gb/s is achieved with only 160-GHz modulation bandwidth. The clock and data recovery are realized at 10-GHz clock rate, which is very economic and efficient. At 7 × 10 Gb/s, the worst receiver sensitivity of−10 dBm, OSNR of 41.5 dB and chromatic dispersion tolerance of ±17 ps/nm are achieved. Whereas, for the best channel, the receiver sensitivity,OSNR, and chromatic dispersion tolerance are −23.5dBm, 29dB, and ±36 ps/nm, respectively.

Abstract: The performance of absolute polar duty cycle division multiplexing (AP-DCDM) over wavelength division multiplexing (WDM) system is presented based on the simulation results. The AP-DCDM signal has narrower bandwidth than conventional time division multiplexing (TDM) signal, which makes its implementation in WDM system advantageous. In this paper, characteristics of AP-DCDM and TDM signals in WDM system are compared at the speed of 40 Gbit/s per channel, for the minimum allowed channel spacing and the chromatic dispersion tolerance. The results clearly show that AP-DCDM performs significantly better than TDM. By using AP-DCDM, 1.28 Tbit/s (32 x 40 Gbit/s) was successfully transmitted over 320 km standard single mode fiber. Spectral efficiency of 0.64 b/s/Hz was achieved by using 10 Gbit/s transmitters and receivers without polarization multiplexing.

Abstract: We propose and investigate a technique to reduce the spectral width as well as increase the tolerance to chromatic dispersion (CD) using improved return-to-zero (RZ) on-off-keying (OOK) over absolute polar duty cycle division multiplexing (AP-DCDM) technique. The proposed channel multiplexing and demultiplexing are performed electrically using only one modulator for n number of users, which is very economical. It is demonstrated that the spectral width occupied by 30 Gb/s RZ-OOK without AP-DCDM measured at 220 dB from the peak power is around 105 GHz whereas, this value can be reduced to around 64 GHz for 30 Gb/s RZ-OOK over AP-DCDM. This amount of saving in the spectral width is a significant achievement, which leads to better tolerance to CD. Its tolerance to CD is in the range of +/- 109 and +/- 155ps/nm, for the worst and the best users, respectively. These values are higher than that of 30 Gb/s conventional RZ-OOK, which is around +/- 86.5 ps/nm. At 120 Gb/s RZ-OOK over AP-DCDM ( the worst user) has pre-amplified receiver sensitivity and optical signal to noise ratio (OSNR) of 222.5 dBm and 28.57 dB, respectively.

Abstract: We propose a multiplexing technique that uses different Polar Return-to-Zero duty cycles to differentiate the channels for enhancing dispersion limited transmission in high speed fiber optic communications. It is demonstrated that the spectral width occupied by 30 Gb/s TDM is 120 GHz whereas, this value can be reduced to around 80 GHz and 70 GHz for 30 Gb/s TDM over 3 and 6 channels of the proposed system respectively. By increasing the number of channels at the same aggregated bitrate, the spectral width of this technique is reduced which leads to better tolerance to chromatic dispersion. Comparison against other techniques such as M-ary-RZ and M-ary-NRZ shows clear advantage of proposed technique

Abstract: An electrical multiplexing technique, namely Absolute Polar Duty Cycle Division Multiplexing (AP-DCDM) is reported for high-speed optical fiber communication systems. It is demonstrated that 40 Gb/s (4 x 10 Gb/s) AP-DCDM system shows a clear advantage over conventional 40 Gb/s RZ-OOK with 50% duty cycle in terms of dispersion tolerance and spectral efficiency. At 40 Gb/s its tolerance to chromatic dispersion (CD) is 124 ps/nm and 194 ps/nm for the worst and the best user, respectively. These values are higher than that of 40 Gb/s RZ-OOK, which is around 100 ps/nm. The spectral efficiency, receiver sensitivity and OSNR for different number of channels are discussed. Comparison against other modulation formats namely duobinary, Non-Return-to-Zero (NRZ)-OOK and RZ-Differential Quadrature Phase-Shift Keying (RZ-DQPSK) at 40 Gb/s are made. It is shown that AP-DCDM has the best receiver sensitivity (-32 dBm) and better CD tolerance (+/- 200 ps/nm) than NRZ-OOK and RZ-DQPSK. In reference to duobinary, AP-DCDM has better receiver sensitivity but worse dispersion tolerance. (C) 2009 Elsevier Inc. All rights reserved.

Abstract: We propose and investigate a technique to reduce the spectral width as well as increase the tolerance to chromatic dispersion (CD) using improved return-to-zero (RZ) on-off-keying (OOK) over absolute polar duty cycle division multiplexing (AP-DCDM) technique. The proposed channel multiplexing and demultiplexing are performed electrically using only one modulator for n number of users, which is very economical. It is demonstrated that the spectral width occupied by 30 Gb/s RZ-OOK without AP-DCDM measured at 220 dB from the peak power is around 105 GHz whereas, this value can be reduced to around 64 GHz for 30 Gb/s RZ-OOK over AP-DCDM. This amount of saving in the spectral width is a significant achievement, which leads to better tolerance to CD. Its tolerance to CD is in the range of +/- 109 and +/- 155ps/nm, for the worst and the best users, respectively. These values are higher than that of 30 Gb/s conventional RZ-OOK, which is around +/- 86.5 ps/nm. At 120 Gb/s RZ-OOK over AP-DCDM ( the worst user) has pre-amplified receiver sensitivity and optical signal to noise ratio (OSNR) of 222.5 dBm and 28.57 dB, respectively.

Abstract: A novel concepts of decision circuit and Bit-error-rate (BER) estimation method for Absolute Polar Duty Cycle Division Multiplexing (AP-DCDM) is proposed The concepts have significant differences to those used in conventional microwave communication receivers. This is due to the unique characteristics of the multilevel signal produced in AP-DCDM system. The BER estimation method is validated by simulation and compared against bit-to-bit comparison method.

Abstract: A comprehensive study on the transient response of fiber-grating Fabry–Perot (FGFP) laser is numerically conducted. Fiber Bragg grating (FBG) is used as a wavelength selective element to control the external optical feedback (OFB) level. In addition to the external OFB level, the effect of other external cavity parameters such as temperature, injection current, dc-bias level, coupling coefficient, and gain compression factor on transient response characteristics of the laser are investigated. The temperature dependence (TD) of response characteristics is calculated according to TD of laser parameters instead of well-known Pankove relationship. Results show that, by increasing the laser injection current, the relaxation oscillation’s amplitude, frequency, and damping rate are increased, while the laser turn-on time delay is reduced. In addition to the injection current and dc-bias level, the turn-on time delay can be reduced by increasing OFB reflectivity. It is shown that the optimum external fiber length ðLextÞ is 3.1 cm and the optimum range of working temperature for FGFP laser is within 2 C from the FBG reference temperature ðToÞ. Also, it is shown that antireflection (AR) coating facet reflectivity value of 1 102 is sufficient for the laser to operate at good response characteristics with low fabrication complexity.

Abstract: The impact of Chromatic Dispersion (CD) and NonLinear Effects (NLE) including Self-Phase Modulation (SPM) and Four-Wave Mixing (FWM), on the performance of a VariableWeight Optical Code Division Multiple Access (V W-OCDMA) system at 1.25 Gbps is analyzed by simulation. The results show that CD is the most dominant effect, which increases the users bit error rate (BER) especially for the users with higher weights. In order to investigate the performance of system in service differentiation for users with different weights, Dispersion Compensating Fiber (DCF) is used to mitigate the effect of CD caused by Single Mode Fiber (SMF). The results show that users with higher weights have better performance as expected and impact of NLE is negligible for distance up to 150 kIn, considering low launched power.

Abstract: The effect of guard band (GB) on the performance of 40 Gb/s Absolute Polar Duty Cycle Division Multiplexing (APDCDM) is investigated and reported. It is demonstrated that the spectral width occupied by 40 Gb/s AP-DCDM with GB is 100 GHz (with minimum spectral efficiency of 0.4 b/s/Hz) whereas, this value can be reduced to around 80 GHz for AP-DCDM without GB (with minimum spectral efficiency of 0.5 b/s/Hz). In addition to better spectral efficiency, this amount of saving in the spectral width leads to 60 ps/nm improvement in chromatic dispersion tolerance.

Abstract: We show the realization of 40 Gbit/s on-off-keyed system that can be recovered at 5.71 GHz clock using duty cycle division multiplexing technique with the receiver sensitivity of -22.1 dBm. ©2008 Optical Society of America.

Abstract: Experimental demonstration of Duty Cycle Division Multiplexing (DCDM) is reported which validates the potential implementation of the system in communication field. We also presented the operation of bit error rate (BER) estimation algorithm, which is specially derived for DCDM. With the increase of link attenuation, the signal amplitude decreased and the pulses are distorted. BER estimation on the received signal was performed and measured against transmission distance of 100 meter until 400 meter copper wire. It is shown that the channel with the largest duty-cycle value shows the best performance. The experimental eye diagrams at several distances are also demonstrated and compared against their back-to-back counterpart.

Abstract: Experimental demonstration of Duty Cycle Division Multiplexing (DCDM) is reported which validates the potential implementation of the system in communication field. We also presented the operation of bit error rate (BER) estimation algorithm, which is specially derived for DCDM. With the increase of link attenuation, the signal amplitude decreased and the pulses are distorted. BER estimation on the received signal was performed and measured against transmission distance of 100 meter until 400 meter copper wire. It is shown that the channel with the largest duty-cycle value shows the best performance. The experimental eye diagrams at several distances are also demonstrated and compared against their back-to-back counterpart.

Abstract: In this paper, duty cycle division multiplexing (DCDM) is proposed as an alternative multiplexing technique. It can be applied in any communication systems, although the focus in this paper is in optical fiber communications. In this paper, we examine 3 channels each operating at 10 Gbps modulation rate over a single optical carrier. The performance comparison is made against 30 Gbps RZ transmitted pulses, time domain multiplexed (TDM). The results show that at a fixed transmission power, DCDM can support longer distance than that with RZ TDM technique. Also, the results show that RZ-TDM pulses require 35.5 dB more SNR to support the same distance as that for DCDM.

Abstract: 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.

Abstract: A new multiplexing technique based on duty cycle division is proposed, thus the name Duty Cycle Division Multiplexing (DCDM). DCDM can be applied in both electrical and optical domains, for wired and wireless systems. The new technique allows for more efficient use of time slots as well as the spectrum, taking advantage of both the conventional TDM and FDM. In this paper, three channels operating at the same speed of 10 Gbps per channel are multiplexed in the electrical domain. The performance comparison is made against 3x10 Gbps TDM, and the experimental simulation results show that the DCDM system can support higher bit rate than TDM and also, it is less sensitive to the chromatic dispersion effect.

Abstract: 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.

Abstract: In this study the author has modeled and characterizes the performance of 3X10 Gbp/s Absolute Polar Duty Cycle Division (APDCDM) Multiplexing in dispersive environments at 1550 nm. APDCDM technique is examined, with comparison to nonreturn- to-zero (NRZ) and return-to-zero (RZ) Time Division Multiplexing. In this paper three channel operating at the same speed of 10 Gbps are multiplexed in electrical domain. The experimental simulation results show that the receiver sensitivity of all users in APDCDM system is similar to that of RZ- TDM and 3 dB better than NRZ-TDM. The proposed system offer reduced dispersion sensitivity; this suggests advantages for APDCDM in optical multiplexing systems. It was also showed that APDCDM can support higher bit rate than TDM and also, it is less sensitive to the chromatic dispersion effect.

Abstract: A new line encoding for duty cycle division multiplexing is proposed, under the name: Complementary unipolar Division Multiplexing (CUDCDM). 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 Complementary unipolar DCDM compared with unipolar DCDM as well as 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. The study shows that the energy per bit in complementary unipolar DCDM, unlike that of TDM technique, increases with the number of users. The simulation result shows that complementary unipolar DCDM has better SER than TDM and unipolar DCDM, even in more distances.

Abstract: In order to explore the potential of optical multilevel signaling for high speed optical fiber networks, an absolute polar duty cycle division multiplexing (AP-DCDM) is demonstrated. Three users, each with the data rate of 10 Gb/s were successfully multiplexed and transmitted over a single WDM channel, which can offer a possible transmission rate of 30 Gb/s per WDM channel. The performance of AP-DCDM technique is examined, with comparison to 30 Gb/s Time Division Multiplexing (TDM) . Back-to-back receiver sensitivity of -29.2 dBm with OSNR of 22.5 dB was achieved for the worst user, together with the chromatic dispersion tolerance ranging from 207 ps/nm to 276 ps/nm. A comparison with conventional TDM technique shows a clear advantage of the proposed AP-DCDM technique.

Abstract: A new multiplexing and demultiplexing technique based on duty cycle division is proposed, thus the name Duty Cycle Division Multiplexing (DCDM). DCDM can be applied in both electrical and optical domains. The new technique allows for more efficient use of time slots as well as the spectrum, taking advantage of both the conventional TDM and FDM. In this paper, three channels operating at the same speed of 10Gbps are multiplexed in the optical domain and demultiplexed in the electrical domain. The performance comparison is made against 30Gbps TDM, and the experimental simulation results show that the minimum sensitivity achieved is -26dBm and -25.5dBm for the two systems respectively, thus a 0.5 dB improvement.

Abstract: A new multiplexing and demultiplexing technique based on duty cycle division is proposed, thus the name Duty Cycle Division Multiplexing (DCDM). DCDM can be applied in both electrical and optical domains. The new technique allows for more efficient use of time slots as well as the spectrum, taking advantage of both the conventional TDM and FDM. In this paper, three channels operating at the same speed of 10Gbps are multiplexed in the optical domain and demultiplexed in the electrical domain. The performance comparison is made against 30Gbps TDM, and the experimental simulation results show that the minimum sensitivity achieved is -26dBm and -25.5dBm for the two systems respectively, thus a 0.5 dB improvement.

Abstract: –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.

Abstract: -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 number of users and 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.

Abstract: In this paper, fuzzy logic is applied for identifying and classifying the short duration voltage variations of 8, 32 and 128 cycles waveforms. A program is written in Matlab to determine the parameters such as duration, maximum and minimum root mean square voltages of a disturbance by using the fast Fourier transform analysis. Based on these parameters, a fuzzy inference system has been developed with five fuzzy inputs, three fuzzy outputs and 139 fuzzy rules. The inputs are the maximum and minimum voltage magnitudes in per unit and disturbance duration in seconds. On the other hand, the outputs are namely outputl, output2 and output3 in which outputl is for classifying instantaneous sag, non sag and momentary sag, output2 is for classifying instantaneous swell, non swell and momentary swell and output3 for classifying instantaneous interruption, non interruption and momentary interruption. The proposed fuzzy expert system has been tested with 1015 recorded voltage disturbances consisting of sags, swells, interruptions, transients, voltage notching and multiple disturbance waveforms. The results have proved that the developed fuzzy system has accurately identified and classified 98.42% of the tested voltage disturbances.

Abstract: 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.