Universal Transmission and Combining for Ultra-Reliable MIMO Relaying

We propose a novel transmission scheme for ultra-reliable multi-hop multiple-antenna communication where relays perform only universal linear operations on the received signals. In particular, the operations are channel-oblivious, and no detection takes place in intermediate relaying nodes. The processing at each relay may be viewed as a concatenation of a dimension-reduction operation, i.e., a universal combining, and orthogonal space-time block coding, i.e., a universal transmission operation. It is demonstrated that the developed transmission-combining relaying technique guarantees reliable communication in a very strong sense: so long as all relay-to-relay links have a non-vanishing capacity, reliable communication is possible. The proposed schemes are derived by establishing a certain operational equivalence relationship between the true channel and an associated multiple-input single-output channel.