Exact Multiple Access Analysis for Pulsed DS-UWB Systems with Episodic Transmission in Flat Nakagami Fading

Exact bit error probabilities (BEP) are derived in closed form for pulsed binary direct sequence ultra-wideband (DS-UWB) multiple access systems in flat Nakagami fading channel. The characteristic function (CF) method is adopted where an exact expression of the CF is obtained through a straight forward method. The method is simple and good for any arbitrary pulse shape. The results from exact analysis are then compared with those obtained from the standard Gaussian approximation (SGA), for which also a new expression is given for the error probability. It is shown that the shape of the CF depends considerably both on chip length and chip-duty and can be different even for the same processing gain (PG), since different combinations of the parameters may result into the same PG. In such a case, the BEP for a PG, however, though remains unchanged in a highly faded channel, may vary substantially in lightly faded channel. Irrespective of the chip length and chip-duty, the SGA is found quite accurate for highly faded channel, which, however, becomes extremely optimistic for low duty systems in lightly faded channels.