Multiple-antenna capacity in the low-power regime: channel knowledge and correlation

The capacity of multiple-antenna systems in the low-power regime has gained much attention recently (Lozano, A. et al., IEEE Trans. Information Theory, vol.49, no.10, p.2527-44, 2003). When two performance metrics, namely the minimum E_b/N₀ and the wideband slope, were studied, it turned out that antenna correlation and Rician factors do not have an impact on (E_b/N₀)_min, but on the slope in bits/s/Hz/(3 dB). We analyze the impact of different types of CSI on the multiple-antenna capacity in the low-power regime. We show that (E_b/N₀)_min is reduced and the slope is increased by having channel knowledge at the transmit antenna array. The impact of spatial correlation on the two performance measures is completely characterized. Finally, the theoretical results are illustrated by numerical simulations showing the spectral efficiency over the received E_b/N₀ for various systems.