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To coexist with existing legacy wireless systems, the transmit power spectral density of ultrawideband (UWB) impulse radio systems is limited. The coverage range of UWB systems is then confined to within a few meters. Dual-hop relaying or multiple-input-multiple-output (MIMO) technology is one possible way of achieving greater UWB system coverage. This paper presents the design of dual-hop UWB MIMO relay systems (in which a source, relay, and destination have multiple antennas) according to the availability of channel state information (CSI) and their performance analysis over a UWB multipath fading channel. In particular, the decouple-and-forward and decode-and-forward relay systems are proposed when partial CSI is only available at the receiver side. On the other hand, with partial CSI being available at the transmitter side, we propose the amplify-and-forward and detect-and-forward relay systems. The exact formulas for the outage probabilities of those systems are derived. Furthermore, we evaluate, in closed form, the amount of fading and bit error rate expressions under sufficiently high signal-to-noise ratio and verify them through comparison with the simulation results. The effect of spatial correlation on the performance of our proposed systems is also studied. Numerical examples of the results provide valuable insights into the design of UWB MIMO relay systems.