Ahmed E. Morra

Performance Analysis of Both Shot- and Thermal-Noise Limited MultiPulse PPM Receivers in Gamma–Gamma Atmospheric Channels

The performance of free-space optical (FSO) communication systems adopting multipulse PPM (MPPM) techniques is investigated taking into account the effects of both the atmospheric turbulence and receiver noise. The atmospheric turbulence is modeled by a gamma-gamma distribution, which is suitable for both weak and strong turbulence. As for the receiver noise, both shot- and thermal-noise limited scenarios are considered. For the shot-noise limited system, both exact and approximate expressions of the average symbol-error rate (SER) of the system are obtained. For the thermal-noise limited system, a closed form for the upper bound of the average system SER, based on the Meijer G function, is obtained. Then, we validate it using Monte Carlo simulation results. Furthermore, we study the effects of changing the atmospheric conditions, operational wavelengths, and number of time slots on the average system performance. In addition, we compare the performance of the aforementioned system with that of the traditional PPM technique, in a gamma-gamma channel, under same constraints on the average energy per bit, transmission data rate, and bandwidth.

Performance analysis of free-space optics systems adopting multi-pulse PPM techniques in gamma-gamma channels for thermal noise limited systems

Atmospheric turbulence has a strong effect on the performance of the terrestrial free space optics system and there are many statistical models that are used to describe the atmospheric turbulence but gamma-gamma is shown to be the most suitable model in both weak and strong turbulence. In this paper, we adopt gamma-gamma model and use the characteristics of Meijer G function to get a closed form expression for the average symbol error rate of multi-pulse PPM under gamma-gamma fading channel. Next, we use our derived form to study the effect of atmospheric conditions, operating wavelength and modulation level on the system performance.

Performance evaluation of hybrid DPSK-MPPM techniques in long-haul optical transmission

The performance of DBPSK-MPPM technique is evaluated in long-haul transmission using GN-model. The BER expression is extended to address fiber nonlinearity. Results show that fiber nonlinearity effects are more significant in DBPSK-MPPM than traditional ones.

Chaotic DPSK-MPPM modulation technique for a physically secure and highly robust optical communication system

In this paper, we present a novel chaotic hybrid DPSK-MPPM modulation technique which is ultimately secure, spectrally efficient, and highly detection-sensitive. The position and phase information are perturbed by two variables of 2D chaotic map. The BER performance of the proposed scheme is then evaluated numerically and compared with that of the CPPM.

Encoding M classical bits in the arrival time of dense-coded photons

We present a scheme to encode M extra classical bits to a dense-coded pair of photons. By tuning the delay of an entangled pair of photons to one of 2M time-bins and then applying one of the quantum dense coding protocols, a receiver equipped with a synchronized clock of reference is able to decode M bits (via classical time-bin encoding) + 2 bits (via quantum dense coding). This protocol, yet simple, does not dispense several special features of the used programmable delay apparatus to maintain the coherence of the two-photon state. While this type of time-domain encoding may be thought to be ideally of boundless photonic capacity (by increasing the number of available time-bins), errors due to the environmental noise and the imperfect devices and channel evolve with the number of time-bins.

An exact expression for symbol-error rate of multipulse PPM technique in free-space optics with gamma-gamma channels

Atmospheric turbulence, also called scintillation, is one of the major challenges that face free space optics (FSO) communications. In this paper, we derive both exact and approximate expressions for the average symbol-error rate (SER) of free-space optics systems adopting multipulse PPM (MPPM) technique in gamma-gamma channels. Our expressions are then verified by getting the same results using lognormal and exponential channel expressions where lognormal and exponential distributions are valid only for weak and strong turbulence, respectively. As the computation of the exact expression is time consuming, we get an approximate expression based on Gauss-Laguerre quadrature. Both expressions produce almost the same results. Finally, we make a comparison between the average SER performance of MPPM and PPM assuming equal average energy per bit and equal data rate. We found that the performance of MPPM is better than that of PPM in case of weak turbulence but at strong turbulence both MPPM and PPM have nearly the same performance.