In this contribution, we develop a (novel) fam-ily of Multiple-Input Multiple-Output (MIMO) UWB Impulse-Radio (UWB-IR) transceivers for Orthogonal PPM-modulated (OPPM) coded transmissions over (baseband) multipath-faded MIMO channels. To by-pass expensive channel-estimation procedures, the MIMO channel pathgains are assumed to be fully unknown at the receiver. Thus, according to the UWB-IR statistical channel-models currently reported in the literature for both indoor/outdoor application scenarios, we develop and analyze three versions of the resulting noncoherent transceiver, that are optimal for Nakagami, Gaussian, and Log-normal distributed channelgains, respectively. As dictated by the Saleh-Valenzuela (SV) UWB model, the resulting noncoherent Maximum-Likelihood (ML) Decoder explicitly accounts for the Poissondistribution of the path-arrivals. Hence, after analytically evaluating the performance of the proposed noncoherent transceiver via suitable versions of the Union-Chernoff bound, we prove that the family of Space-Time OPPM (STOPPM) recently presented in the Literature is able to attain full-diversity in the considered multipath-affected application scenario. To corroborate the carried out performance analysis, we report several numerical results supporting both the medium/long coverage ranges attained by the proposed STOPPM-coded noncoherent transceiver, and its performance robustness against the degrading effects induced by Inter-Pulse-Interference (IPI), spatially-correlated multipath fading and mistiming.