  In this paper a novel multi-hop relay-assisted hybrid Free Space Optical /
Radio Frequency (FSO / RF) communication system is presented, in which a mobile
user is connected to the Base Station via a multi-hop relay-assisted hybrid FSO
/ RF link with receive diversity. In this structure, received signal at each
relay is demodulated and forwarded. This is the first time that in a multi-hop
hybrid FSO / RF system, receive diversity is used. Bit Error Rate (BER) and
Outage Probability (P_out) are investigated as system performance criteria. New
exact and asymptotic expressions are derived for these criteria, and MATLAB
simulations are provided to verify the obtained results. For the first time
impact of number of receive antennas and number of relays on the performance of
such a structure is investigated. Results indicate that proposed structure has
low dependence on number of receive antennas; therefore, in the proposed
structure use of single receive antenna has the same performance as the
multi-antenna, while low complexity and power consumption. The proposed
structure shows independent performance at moderate and strong atmospheric
turbulence regimes. Hence, it does not require adaptive processing to match
itself according to atmospheric turbulence condition, therefore is cost
effective and particularly suitable for urban areas that encounter frequent
changes in atmospheric turbulence.

Signal Processing