  This paper considers a massive MIMO system under the double scattering
channels. We derive a closed-form expression of the uplink ergodic spectral
efficiency (SE) by exploiting the maximum-ratio combining technique with
imperfect channel state information. We then formulate and solve a total uplink
data power optimization problem that aims at simultaneously satisfying the
required SEs from all the users with limited power resources. We further
propose algorithms to cope with the congestion issue appearing when at least
one user is served by lower SE than requested. Numerical results illustrate the
effectiveness of our proposed power optimization. More importantly, our
proposed congestion-handling algorithms can guarantee the required SEs to many
users under congestion, even when the SE requirement is high.
