In this paper, we propose a Time Interleave (TI)-Ultra Wideband (UWB)-Impulse Radio (IR) system where Nf monocycle pulses per information symbol are transmitted not continuously but discontinuously through the time interleaver to get more time diversity. Moreover, we compare the diversity gains of the UWB-IR systems on block fading channels with the fading block size q: the UWB-IR system with a single transmit antenna, the Space Time (ST)-UWB-IR system with Nt transmit antennas, and the TI-UWB-IR system with a single transmit antenna. Simulation results show that when the fading block size q = 1, the diversity gains of all the systems are same. When q is larger than or equal to 2 (q 2) and when both the number of transmit antennas Nt of the ST-UWB-IR system and the time interleaver size NTI of the TI-UWB-IR system are larger than or equal to q (Nt, NTI q), we show the following; both the ST-UWB-IR system and the TI-UWB-IR system achieve the same diversity gain that is constant regardless of Nt and NTI. On the other hand, when q 2 and when Nt and NTI < q, we show the following; when Nt = NTI, the ST-UWB-IR system and the TI-UWB-IR system get the same diversity gain; when Nt > NTI, the diversity gain of the ST-UWB-IR system is larger than that of the TI-UWB-IR system; and vice when Nt > NTI.

In this letter, we compare a Multiple-Input Single-Output (MISO)-Ultra WideBand (UWB)- Impulse Radio (IR) system and a Single-Input Single-Output (SISO)-UWB-IR system at high transmission rates. We evaluate the Bit Error Rate (BER) of the two systems with some RAKE receivers under heavy multipath environments. From the results of our computer simulation, we show that the SISO-UWB-IR system with Minimum Mean Square Error (MMSE)-RAKE receiver is a good candidate to achieve high transmission rates.