Low SNR Capacity of Double-Scattering MIMO Channels with Transmitter Channel Knowledge

This paper investigates the capacity of double-scattering multiple-input multiple-output (MIMO) channels in the low signal to noise ratio (SNR) regime. We first derive analytical expressions for the two key low SNR parameters; namely, the minimum required E_b/N₀ and wideband slope, assuming statistical channel state information (CSI) at the transmitter. Based on these results, we investigate the effect of transmit, scatter, and receive correlation. For the case of the double-scattering MIMO keyhole channel, we then analyze the low SNR capacity for different levels of transmit CSI. We show that increased transmit CSI leads to a reduced minimum required E_b/N₀.