In practice, the coherence time of the channels
between relays and users can be small, so it is highly preferred
if we can obtain a feasible solution with acceptable total
transmission power in a limited number of iterations. This
can be done by periodically solving an extra set of optimization
problems during the operation of Algorithm 1. Suppose
that { ˆQB,i, ˆQR,i} is the local solution at relay i after some
iterations, and that