  In this work a novel dual-hop relay-assisted hybrid Free Space Optical /
Radio Frequency (FSO / RF) communication system is presented. In this system,
RF signal is transmitted from two antennas, and then forwarded by a single
antenna relay through FSO channel. This is the first time that performance of
using Alamouti Coding (AC) or Antenna Selection (AS) at the transmitter of a
hybrid FSO / RF system is investigated. FSO link has Gamma-Gamma atmospheric
turbulence, and in order to get closer to the actual results, the effect of
pointing error is also considered. For the first time closed-form expressions
are derived for Bit Error Rate (BER) and Outage Probability of the proposed
system and validated through MATLAB simulations. Results indicate that in this
structure, there is slight performance difference between AC and AS schemes.
Hence due to more complexity, power consumption and latency of AC, AS is
recommended. Dual-hop, hybrid FSO / RF system significantly improves
performance and reliability of the system, and is particularly suitable for
long-range applications that direct RF communication between source and
destination is not possible. Considering these advantages this structure is
particularly suitable for mobile communications which has power and processing
limitations.
