  In this paper, we study the sensitivity and robustness of Space Shift Keying
(SSK) modulation to imperfect channel knowledge at the receiver. Unlike the
common widespread belief, we show that SSK modulation is more robust to
imperfect channel knowledge than other state-of-the-art transmission
technologies, and only few training pilots are needed to get reliable enough
channel estimates for data detection. More precisely, we focus our attention on
the so-called Time-Orthogonal-Signal-Design (TOSD-) SSK modulation scheme,
which is an improved version of SSK modulation offering transmit-diversity
gains, and provide the following contributions: i) we develop a closed-form
analytical framework to compute the Average Bit Error Probability (ABEP) of a
mismatched detector for TOSD-SSK modulation, which can be used for arbitrary
transmit-antenna, receive-antenna, channel fading, and training pilots; ii) we
perform a comparative study of the performance of TOSD-SSK modulation and the
Alamouti code under the same imperfect channel knowledge, and show that
TOSD-SSK modulation is more robust to channel estimation errors; iii) we point
out that only few pilot pulses are required to get performance very close to
the perfect channel knowledge lower-bound; and iv) we verify that transmit- and
receive-diversity gains of TOSD-SSK modulation are preserved even for a
mismatched receiver.
