Zengji Liu

Average BER of free-space optical systems in turbulent atmosphere with exponentiated Weibull distribution.

A computationally efficient expression is presented for evaluating the average bit error rate (BER) of an intensity-modulation and direct-detection free-space optical system with on-off keying signaling technique operating in turbulent atmosphere described by the exponentiated Weibull distribution. The presented numerical results show the effects of aperture averaging on the average BER under weak and moderate turbulence conditions, and are confirmed by Monte Carlo simulations.

Inner- and outer-scale effects on the scintillation index of an optical wave propagating through moderate-to-strong non-Kolmogorov turbulence.

By use of the generalized von Kármán spectrum model that features both inner scale and outer scale parameters for non-Kolmogorov turbulence and the extended Rytov method that incorporates a modified amplitude spatial-frequency filter function under strong-fluctuation conditions, theoretical expressions are developed for the scintillation index of a horizontally propagating plane wave and spherical wave that are valid under moderate-to-strong irradiance fluctuations. Numerical results show that the obtained expressions also compare well with previous results in weak-fluctuation regimes. Based on these general models, the impacts of finite inner and outer scales on the scintillation index of an optical wave are examined under various non-Kolmogorov fluctuation conditions.

BER Performance Analysis for M-ary PPM over Gamma-Gamma Atmospheric Turbulence Channels

Atmospheric turbulence induced fading is one of the main impairments affecting the operation of free-space optical (FSO) communication systems. In this paper, the average bit error rate (BER) of M-ary pulse position modulation (PPM) is analyzed under Gamma-Gamma fading channel. Using the characteristics of Meijer G function, Closed-form expression for average BER is derived. The investigation of how the BER performance is affected by the atmospheric conditions and other parameters such as the operational wavelength and the modulation level is made. It is shown that the influence of the turbulence on the short-wavelength is more serious than the long-wavelength. Another important result in this work is that, increasing of modulation level cannot significantly reduce the transmitted power required to achieve a desired BER in moderate-to-strong turbulence channels for M-ary PPM, which is different from the situation in the non-turbulent channel.

Formula for the average bit error rate of free-space optical systems with dual-branch equal-gain combining over gamma–gamma turbulence channels

In this Letter we propose a closed-form expression for the average bit error rate of intensity modulation/direct detection free-space optical systems employing dual-branch equal-gain combining and operating over turbulence channels. To offer a realistic error performance of the considered system we assume that both branches undergo independent but not necessarily identically distributed gamma-gamma fading. Our newly developed formula is obtained in terms of the bivariate H-Fox function, which can be readily evaluated based on its two-fold Mellin-Barnes representation. Numerically evaluated and computer simulation results are presented that verify the accuracy of the proposed mathematical analysis.

A novel wireless network architecture and its Radio frequency assignment mechanism for WLAN based on distributed antenna system using Radio over Free Space Optics

This paper presents a novel wireless network architecture using Radio over Free Space Optics (RoFSO) for wireless local area networks (WLANs). RoFSO not only transmits various kinds of radio services on optical wireless carrier, but also overcomes the defect of the unfeasibility of the optical fiber deployment. In addition, a RF assignment mechanism based on the wireless network architecture presented is proposed and studied, which can achieve efficient utilization of RF resources. The results show that the improvement in throughput performance can be obtained when the number of wireless users is increased and the location of wireless users are concentrated, and RF resources are fairly used in terms of fairness index compared with the conventional WLAN architecture.

Research on Radio Frequency Assignment Mechanism of the Distributed Antenna System Based on Radio over Free Space Optics Technology

For the problems of the unfeasibility of the optical fiber deployment and the inflexibility of the network optimization in the current Distributed Antenna System (DAS) based on Radio over Fiber (RoF) technology, this paper presents a novel wireless network architecture using Radio over Free Space Optics (RoFSO) for wireless local area networks (WLANs). RoFSO not only transmits various kinds of radio services on optical wireless carrier, but also overcomes the defect of the unfeasibility of the optical fiber deployment. In addition, a RF assignment mechanism based on the wireless network architecture presented is proposed and studied, which can achieve efficient utilization of RF resources. The results of simulation show that the improvement in throughput performance can be obtained when the number of wireless users is increased and RF resources are fairly used in terms of fairness index.

Numerical analysis of fiber optical parameter amplifier based on triangular photonic crystal fiber

Due to triangular photonic crystal fiber (PCF) high nonlinearity and low dispersion slope, using the condition that the different linear phase shift combination must satisfy the phase match, the expressions of gain and bandwidth for one-pump fiber-optic parametric amplifiers (1P-FOPA) based on PCF in the normal and abnormal dispersion regimes are derived respectively. Then, 1P-FOPAs performance comparison among PCF, dispersion-shifted fiber (DSF) and highly nonlinear fibers (HNLF) are carried out by numerical simulations. It is shown that the 1P-FOPA based on triangular PCF can provide higher peak gain over wider bandwidth. When the pump wavelength is at the zero-dispersion wavelength (ZDWL), about 108.7 nm single-pass gain bandwidth and 91.4 dB peak gain can be obtained; when in the normal dispersion regime and near zero-dispersion wavelength, not less than 46 nm single-pass gain bandwidth 77.1 nm away from pump can be achieved. Finally the influence of dispersion fluctuation is analyzed, and the result shows that the tolerance of the 1P-FOPA based on photonic crystal fiber is better.