  Bit-interleaved coded modulation (BICM) using (bi-)orthogonal signals is
especially well suited for the application in impulse-radio ultra-wideband
transmission systems, which typically operate in the power-limited regime and
require a very low-complexity transmitter and receiver design. In this paper we
analyze the capacity of BICM using (bi-)orthogonal signals with coherent and
noncoherent detection and put particular focus on the power-limited or wideband
regime. We give analytical expressions for the ratio energy per bit vs. noise
power spectral density in the limit of infinite bandwidth and the respective
wideband slope, and thus, are able to quantify the loss incurred by the
restriction to BICM in contrast to coded modulation. The gained theoretical
insights allow to derive design rules for impulse-radio ultra-wideband
transmission systems.
