  One of the main problems in mobile communication systems is the degradation
of Radio Frequency (RF) connection when mobile user is far from base station.
One way to solve this problem is to increase the transmitter power, but the
mobile transmitter is not able to supply much power. Another way is to use a
relay; among relay schemes, amplify and forward is better for long range
communications. Amplify and forward relay is not affordable in terms of power
consumption and performance, because it consumes a lot of power inefficiently
and enhances the noise. Therefore, in other cases, except in the case of long
range links, other relay protocols, such as decode and forward, as well as
demodulate and forward, are preferable. In this paper, a novel multi-hop hybrid
Free Space Optical (FSO) / RF link is presented; it is made up of two main
parts. The first part establishes the connection between the mobile user and
source base station, and the second part establishes the connection between the
source and the destination base stations. In the first part, a mobile user
wants to connect to the source base station via a long range link; therefore, a
fixed gain amplify and forward relay with multiple receive antennas is used for
communication establishment. In the second part, the source and the destination
base stations are connected via a multi-hop hybrid parallel FSO / RF link with
demodulate and forward relaying. Considering the FSO link in Gamma-Gamma
atmospheric turbulence with the effect of pointing error in moderate to strong
regime and the Negative Exponential atmospheric turbulence in saturate regime,
and the RF link in Rayleigh fading, new closed form exact and asymptotic
expressions are derived for the Outage Probability and Bit Error Rate of the
proposed structure. Derived expressions are verified with MATLAB simulations.
