Improved Rates and Coding for the MIMO Two-Way Relay Channel

Abstract—The Gaussian multiple-input multiple-output two-way relay channel is considered. By applying linear pre- and post-processing, the channel matrices are transformed into triangular form having equal diagonals. Over the obtained triangular chan-nels, dirty-paper coding is applied, yielding parallel symmetric scalar two-way relay channels; thus, reducing the coding task to that of coding over the scalar symmetric two-way relay channel. Any existing coding technique can then be readily applied over these resulting channels. This technique allows to obtain new achievable rates in the symmetric case. Index Terms—Physical-layer network coding, network capac-ity, multiple-access channel, structured codes, MIMO chan-nels, two-way relay channel, compress-and-forward, decode-and-forward, joint matrix decomposition, successive interference cancellation, dirty-paper coding I