Log-normal Atmospheric Turbulence Channels Research Articles

Block error rate of optical wireless communication systems over atmospheric turbulence channels

Block error rate performance of subcarrier intensity modulation based optical wireless communication systems is analysed over Gamma–Gamma and lognormal atmospheric turbulence channels. The analysis is applicable to non-coherent binary modulations and coherent binary phase shift keying. The special cases of K-distributed strong turbulence channel and negative exponential turbulence channel are also considered. The closed-form expressions of block error rate in the Gamma–Gamma turbulence channels are derived using a series expansion of the modified Bessel function. For the lognormal turbulence channels, the Gauss–Laguerre quadrature method can be used to estimate the block error rate accurately.

Outage Performance and Diversity Gain Analysis of Free-Space Optical Multi-hop Parallel Relaying

In this paper, we investigate the outage performance of free-space optical mesh networks, which build upon the combination of serial (multi-hop) and parallel relaying. We assume log-normal atmospheric turbulence channels and derive outage probability expressions for the multi-hop parallel relaying scheme under consideration. Our outage probability analysis demonstrates substantial performance improvements with respect to both standalone serial and parallel relaying schemes. Furthermore, we present a diversity gain analysis and quantify the achievable diversity order in terms of the number of relays and the turbulence channel parameters.

Improving the availability of terrestrial FSO links over log normal atmospheric turbulence channels using dispersive chirped Gaussian pulses

Abstract In this work, the influence of group velocity dispersion on the availability of a turbulent free space optical channel modeled with the log normal distribution is investigated. By assuming longitudinal Gaussian pulse propagation, analytical expressions for the probability of fade of such links are provided. The cases where the dispersion effect can be used in order to ameliorate the system's performance are studied and mathematical expressions for the evaluation of system's specific parameters are also derived. Moreover, various numerically evaluated results are presented.

Iterative Near Maximum-Likelihood Sequence Detection for MIMO Optical Wireless Systems

A major performance-limiting factor in terrestrial optical wireless (OW) systems is turbulence-induced fading. Exploiting the additional degrees of freedom in the spatial dimension, multiple laser transmitters combined with multiple receive apertures provide an effective solution for fading mitigation. Although multiple-input multiple-output (MIMO) OW systems have been extensively studied in recent years, most of these works are mainly limited to symbol-by-symbol decoding. MLSD exploits the temporal correlation of turbulence-induced fading and promises further performance gains. In this paper, we investigate MLSD for intensity-modulation/direct-detection MIMO OW systems over log-normal atmospheric turbulence channels. Even with a low-order modulation scheme such as OOK, which is typically used in OW systems, the complexity of MLSD might be prohibitive. We therefore present an iterative sequence detector based on the expectation-maximization (EM) algorithm. The complexity of the proposed algorithm is considerably less than a direct evaluation of the log-likelihood function, and it is independent of the channel's fading statistics. The Monte Carlo simulation results demonstrate that the EM-based algorithm outperforms the symbol-by-symbol decoder and achieves a performance, which lies within 0.3 dB of that of the optimal MLSD.