  In this paper, we address the problem of target detection in passive
multiple-input-multiple-output (MIMO) radar networks. A generalized likelihood
ratio test is derived, assuming prior knowledge of the signal format used in
the non-cooperative transmit stations. We consider scenarios in which the
unknown transmitted signal uses either a linear digital modulation scheme or
the Orthogonal Frequency-Division Multiplexing (OFDM) modulation scheme. These
digital modulation schemes are used in popular standards including
Code-Division Multiple Access (CDMA), Digital Video Broadcasting-Terrestrial
(DVB-T) and Long Term Evaluation (LTE). The performance of the generalized
likelihood ratio test in the known signal format case is often significantly
more favorable when compared to the case that does not exploit this
information. Further, the performance improves with increasing number of
samples per symbol and, for a sufficiently large number of samples per symbol,
the performance closely approximates that of an active radar with a known
transmitted signal.
