  An efficient analog network coding transmission protocol is proposed in this
letter for a MIMO two way cellular network. Block signal alignment is first
proposed to null the inter-user interference for multi-antenna users, which
makes the dimensions of aligned space larger compared with the existing signal
alignment. Two algorithms are developed to jointly design the precoding
matrices at the relay and BS for outage optimization. Especially, the last
algorithm is designed to maximize the effective channel gain to the effective
noise gain ratio. The performance of this transmission protocol is also
verified by simulations.
