El-Sayed A. El-Badawy

Performance analysis of an optical CDMA MAC protocol with variable-size sliding window

A media access control protocol for optical code-division multiple-access packet networks with variable length data traffic is proposed. This protocol exhibits a sliding window with variable size. A model for interference-level fluctuation and an accurate analysis for channel usage are presented. Both multiple-access interference (MAI) and photodetectors shot noise are considered. Both chip-level and correlation receivers are adopted. The system performance is evaluated using a traditional average system throughput and average delay. Finally, in order to enhance the overall performance, error control codes (ECCs) are applied. The results indicate that the performance can be enhanced to reach its peak using the ECC with an optimum number of correctable errors. Furthermore, chip-level receivers are shown to give much higher performance than that of correlation receivers. Also, it has been shown that MAI is the main source of signal degradation

Speeding-up wide-fan in domino logic using a controlled strong PMOS keeper

Wide fan in domino logic finds a variety of applications in microprocessors, digital signal processors, and dynamic memory. Specifically, there is a large number of applications that contain 8 or more transistors connected in parallel in the pull-down network (PDN) and thus the subthreshold leakage and charge sharing become severe. So, a strong PMOS keeper must be used in order to compensate for this leakage. However, the use of a strong keeper in the conventional domino circuit degrades the speed of the circuit considerably or results in an erroneous output. In this paper, a novel technique that acts to speed up the operation of wide fan in domino logic using a properly sized keeper is proposed. The keeper is controlled via a controlling CMOS circuit. Some design issues of this technique such as the effect of the charge sharing on the operation of the proposed circuit and the size of the PMOS keeper will be discussed in this paper. Simulation will be carried out for the 0.13 mum technology with VDD=1.2 V for the case of 16 NMOS transistors in the PDN. Simulation results show the better noise immunity of the proposed circuit and the larger speed, however at the cost of increasing the area.

Analysis of static/dynamic 2-D optical CDMA correlation and chip level receivers under both shot and thermal noises using array waveguide grating

The effect of both shot & thermal noises on the performance of 2-D wavelength hopping/time spreading CDMA static and dynamic systems is analyzed. Noise variance and probability of error are calculated for general systems employing asymmetric prime-hop codes (APHCs). A comparison is held between the performance of static/dynamic noisy chip level receivers, noiseless correlation receivers and noisy correlation receivers. We have proposed four new systems; dynamic 2-D transmitter, dynamic 2-D correlation receiver, static and dynamic 2-D chip level receivers. The analysis reveals that the performance of the static/dynamic chip level receiver is better than the correlation receiver. Furthermore, this paper shows that the system utilization is improved when using dynamic code allocation.

Subthreshold MOSFET transistor amplifier operation

Due to their ultra low-power consumption and the high demand of portable applications, subthreshold MOS-FET transistor operation (where the power-supply voltage is lower than the threshold voltage, VDD<Vth) took considerable interest in the last decade. However, most of the subthreshold transistor applications are in the logic circuits domain. In this paper, we will investigate the application of the MOSFET transistor in the subthreshold region as an amplifier, develop the ac small-small equivalent circuit, derive expressions for the voltage gain in a common-source configuration, and compare this amplifier with that using the MOSFET transistor operating in the superthreshold region (where VDD>Vth).

Optical CDMA protocol with selective retransmission

New protocol for optical code-division multiple access (CDMA) networks is proposed. Our proposed protocol is based on selective retransmission technique. A mathematical model is presented using a detailed state diagram. The protocol is analyzed using equilibrium point analysis (EPA), and its performance is examined using traditional throughput and average delay for several network parameters. We also compare the performance of the proposed protocol to the R/sup 3/T protocol based on go-back-n technique. Results show that a higher performance is achieved by the proposed protocol at the expense of system complexity.

Design and implementation of a 2-GHz active integrated antenna

This paper presents the design and implementation of a 2-GHz active integrated antenna module. The module comprises a microwave amplifier and a microstrip antenna array. The array comprises two microstrip patch antennas. The module is implemented using the microstrip-line technology. It gives a satisfactory performance. This module can be used in many applications such as active and semi-active seekers, satellite communication, radio altimeters, missile technology, weapon fuzing, manpack equipment, remote sensing, and biomedical radiators.

A simple 8-bit digital microcontroller implementation for chaotic sequence generation

This paper introduces a simple implementation of digital chaotic sequence generator. The implementation is based on using microcontroller ATMGA 16 to generate the chaotic map required for advanced encryption standard (AES) encryption scheme s-box and radar frequency agile control. The implemented circuit is simple, low cost and suitable for use with identification friend or foe (IFF) equipped with data encryption systems. The circuit also can changes the carrier frequency of the transmitted signal based on chaotic map, benefits a security and confidentiality to the radar waveform against Electronic Counter Measurement (ECM). The circuit generates 256 random sequences at different initial conditions and each of them has 256 sequences generated from different bifurcation parameters. The circuit is simulated under Matlab program environment and Proteus circuit simulation program. A security analysis for the implemented circuit is demonstrated. The results show the superiority of the circuit for generating the random sequences forming an efficient s-box for IFF system and radar frequency agility.

Effect of both shot and beat noises on the performance of a 2D optical CDMA correlation receiver

The effect of both shot beat noises on the performance of 2D wavelength hopping/time spreading CDMA system is analyzed. Noise variance and probability of error are calculated for a general system employing asymmetric prime-hop code (ASPHC). Comparison with a noise-free system reveals the effect of noise on performance

Improving placental blood flow in pre-eclampsia with prostaglandin A1

Prostaglandin A1 is a potent hypotensive, peripheral vasodilator, a weak oxytocic, antiplatelet aggregator. It improves the renal hemodynamics. Its effect on placental circulation was evaluated (expressed as systolic/diastolic ratio and umbilical artery resistance index) in 20 women with severe pre‐eclampsia and 10 normotensive pregnant women, by using the Doppler technique. Moreover, another 10 women with severe pre‐eclampsia received dextrose 5% as a placebo for comparative purposes. Significant improvements in both parameters studied were observed in the women with severe pre‐eclampsia. The beneficial changes differed significantly from the recorded values when using dextrose in pre‐eclampsia or prostaglandin A, in normotensive subjects. Such promising data add another important perspective to prostaglandin A, in severe pre‐eclampsia and may open up new avenues for its use in other situations with compromised placental flow.

Analysis of static idealized 1D/2D optical CDMA correlation receivers using fiber Bragg grating

The performance of 1D/2D wavelength hopping/time spreading CDMA static noiseless is analyzed. The probability of error is calculated for general systems employing asymmetric prime-hop codes (APHCs). A comparison is held between the performance of static noiseless 1D, 2D, and 1D/2D correlation receivers. We have proposed a two new systems: Static 1D/2D transmitter and Static 1D/2D correlation receiver. The analysis reveals that the performance of the static 1D/2D correlation receiver is better than both the static 1D correlation receiver and the static 2D correlation receiver.