  For MIMO two-way relay channel, this paper proposes a novel scheme,
VBLAST-PNC, to transform the two superimposed packets received by the relay to
their network coding form. Different from traditional schemes, which tries to
detect each packet before network coding them, VBLAST-PNC detects the summation
of the two packets before network coding. In particular, after firstly
detecting the second layer signal in 2-by-2 MIMO system with VBLAST, we only
cancel part of the detected signal, rather than canceling all the components,
from the first layer. Then we directly map the obtained signal, summation of
the first layer and the second layer, to their network coding form. With such
partial interference cancellation, the error propagation effect is mitigated
and the performance is thus improved as shown in simulations.
