  Unified performance analysis is carried out for amplify-and-forward (AF)
multiple-input-multiple-output (MIMO) beamforming (BF) two-way relay networks
in Rayleigh fading with five different relaying protocols including two novel
protocols for better performance. As a result, a novel closed-form sum-bit
error rate (BER) expression is presented in a unified expression for all
protocols. A new closed-form high signal-to-noise-ratio (SNR) performance is
also obtained in a single expression, and an analytical high-SNR gap expression
between the five protocols is provided. We compare the performance of the five
relaying protocols with respect to sum-BER with appropriately normalized rate
and power, and show that the proposed protocol with four time slots outperforms
other protocols when transmit powers from two sources are sufficiently
different, and the one with three time slots dominates other protocols when
multiple relay antennas are used, at high-SNR.
