  We study the problem of managing handoffs (HOs) in user-centric cell-free
massive MIMO (UC-mMIMO) networks. Motivated by the importance of controlling
the number of HOs and by the correlation between efficient HO decisions and the
temporal evolution of the channel conditions, we formulate a partially
observable Markov decision process (POMDP) with the state space representing
the discrete versions of the large-scale fading and the action space
representing the association decisions of the user with the access points
(APs). We develop a novel algorithm that employs this model to derive a HO
policy for a mobile user based on current and future rewards. To alleviate the
high complexity of our POMDP, we follow a divide-and-conquer approach by
breaking down the POMDP formulation into sub-problems, each solved separately.
Then, the policy and the candidate pool of APs for the sub-problem that
produced the best total expected reward are used to perform HOs within a
specific time horizon. We then introduce modifications to our algorithm to
decrease the number of HOs. The results show that half of the number of HOs in
the UC-mMIMO networks can be eliminated. Namely, our novel solution can control
the number of HOs while maintaining a rate guarantee, where a 47%-70% reduction
of the cumulative number of HOs is observed in networks with a density of 125
APs per km2. Most importantly, our results show that a POMDP-based HO scheme is
promising to control HOs.
