  In this paper, we consider a full-duplex (FD) space shift keying (SSK)
communication system, where information exchange between two users is assisted
only by a reconfigurable intelligent surface (RIS). In particular, the impact
of loop interference (LI) between the transmit and receive antennas as well as
residual self-interference (SI) from the RIS is considered. Based on the
maximum likelihood detector, we derive the conditional pairwise error
probability and the numerical integration expression for the unconditional
pairwise error probability (UPEP). Since it is difficult to find a closed-form
solution, we perform accurate estimation by the Gauss-Chebyshev quadrature
(GCQ) method. To gain more useful insights, we derive an expression for UPEP in
the high signal-to-noise ratio region and further give the average bit error
probability (ABEP) expression. Monte Carlo simulations were performed to
validate the derived results. It is found that SI and LI have severe impacts on
system performance. Fortunately, these two disturbances can be well
counteracted by increasing the number of RIS units.
