BER performance analysis of FSO using hybrid-SIM technique with APD receiver over weak and strong turbulence channels

In this paper, a hybrid-subcarrier-intensity-modulation (hybrid-SIM) technique for the performance improvement of free-space-optical (FSO) communication system has been proposed. Subsequently, for further error performance improvement, avalanche photodiode (APD) based receiver is used in the proposed system. The system performance is analyzed at various atmospheric turbulence levels over weak and strong turbulence channels. The bit error rate (BER) is theoretically derived using Gauss–Hermite approximation and Meijer-G function and it is simulated in the MATLAB environment. The simulation result shows that the BER performance of hybrid-SIM is better than BPSK-SIM technique irrespective of the channel types and also the significant BER performance improvement is observed by APD receiver.

Influence of environmental factors onto reproductive characteristics of Daphnia galeata from Lake Baikal

The influence of various factors onto the reproductive characteristics of the cladoceran Daphnia galeata Sars, 1863 Lake Baikal was studied. With an increase in the concentration of available feed, the size of the body, average fertility, the size of the brood and the proportion of egg-bearing females increase. At high temperatures, significantly greater fecundity and the proportion of egg-bearing females were noted; other features did not change significantly with temperature increase. Under the conditions of strong turbulence, the fertility and the proportion of egg-bearing females are lower than under the conditions of low turbulence. The presence of a predator with an increase in the concentration of feed and temperature results in the decrease in the size of crustaceans and in the increase of the proportion of egg-bearing females.