چكيده به لاتين
Free Space Optical (FSO) communication systems, have advantages of both Radio Frequency (RF) and Optical Fiber communication systems. These systems have high data rates and security, however, are heavily influenced by atmospheric turbulence and pointing error. Different effect of atmospheric turbulence on communication systems, in optical and millimeter radio frequenies is the main idea of the combination of FSO and RF systems.
In hybrid FSO / RF systems, one and two hop structures have been investigated mostly, and only few works have been investigated multi-hop structure. In this study, two novel multi-hop relay-assisted hybrid FSO / RF structure are proposed, in which a relay transmits received data from mobile users to the base station and a multi-hop relay-assisted hybrid FSO / RF link connects the source and destination Base Stations.
New closed-form expressions are derived for Symbol Error Rate (SER) and Outage Probability (P_out) of the proposed structures and are validate through the MATLAB simulations. The results indicate that the performance of proposed structures have low sensitivity to the number of users, and relays. Such that there is only 1dB SNR difference between two hop and four hop structures. The proposed structures, even at low SNRs, show favorable performance and are not sensitive to the atmospheric turbulence intensity; such that at SER=〖10〗^(-4), there is only 2dB SNR difference between moderate and saturate regimes. The proposed structures and the links between users and base station are novel and have not yet been investigated in the papers.
New Closed-form expressions are derived for Symbol Error Rate (SER) and the Outage Probability (P_out) of the proposed structures and validated through MATLAB software simulation. Results show low dependence of proposed structures on number of users, number of relays and changes in atmospheric turbulence. The difference in the performance of the first and second structures is less than the difference between the performance of the links between base station and user. For example, at SER = 〖10〗^(-4), this difference is 10dB and 15dB respectively. The offered multi-user structure shows better performance than single-user structures, proposed in papers, for example, at〖 P〗_out = 〖10〗^(-2), there is about 25dB of SNR difference between the 10 user and single user, which means significant improvement in performance of the proposed structure, relative to the previous structures. It can be seen that system performance, when the link between relay and base station is FSO, compared with when this link is parallel FSO / RF, at SER=〖10〗^(-4), there is about 23dB of SNR difference, and this shows the effect of the use of hybrid FSO/RF link.
