  Consider media streaming in MIMO interference networks whereby multiple base
stations (BS) simultaneously deliver media to their associated users using
fixed data rates. The performance is fundamentally limited by the cross-link
interference. We propose a cache-induced opportunistic cooperative MIMO (CoMP)
for interference mitigation. By caching a portion of the media files, the BSs
opportunistically employ CoMP to transform the cross-link interference into
spatial multiplexing gain. We study a mixed-timescale optimization of MIMO
precoding and cache control to minimize the transmit power under the rate
constraint. The cache control is to create more CoMP opportunities and is
adaptive to the long-term popularity of the media files. The precoding is to
guarantee the rate requirement and is adaptive to the channel state information
and cache state at the BSs. The joint stochastic optimization problem is
decomposed into a short-term precoding and a long-term cache control problem.
We propose a precoding algorithm which converges to a stationary point of the
short-term problem. Based on this, we exploit the hidden convexity of the
long-term problem and propose a low complexity and robust solution using
stochastic subgradient. The solution has significant gains over various
baselines and does not require explicit knowledge of the media popularity.
