High-SNR power offset in multi-antenna Ricean channels

In the high-SNR regime, the multi-antenna mutual information behaves as an affine function of SNR|_dB, described by the multiplexing gain, which quantifies the multiplicative increase as function of the number of antennas, and the power offset (zero-order term in dB). The conventional high-SNR analysis that considers only the multiplexing gain is unable to assess the impact of channel features such as the Rician factor since, irrespective thereof, the multiplexing gain equals the minimum of the number of transmit and receive antennas. The impact of the Rician factor at high SNR can be conveniently quantified through the corresponding power offset, which this paper evaluates in closed-form.