Capacity of BICM using (Bi-)orthogonal signal constellations in the wideband regime

Bit-interleaved coded modulation (BICM) using (bi-)orthogonal signals is especially well suited for applications operating in the power-limited regime and require a very low-complexity transmitter and receiver design, such as, e.g., impulse-radio ultra-wideband transmission systems. In this paper, we analyze the capacity of BICM using (bi-)orthogonal signals with coherent and noncoherent detection for the case of lognormal fading and put particular focus on the power-limited or so-called wideband regime. We give analytical expressions for the ratio of energy per bit and 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.