  We propose to control handoffs (HOs) in user-centric cell-free massive MIMO
networks through a partially observable Markov decision process (POMDP) with
the state space representing the discrete versions of the large-scale fading
(LSF) and the action space representing the association decisions of the user
with the access points. Our proposed formulation accounts for the temporal
evolution and the partial observability of the channel states. This allows us
to consider future rewards when performing HO decisions, and hence obtain a
robust HO policy. To alleviate the high complexity of solving our POMDP, we
follow a divide-and-conquer approach by breaking down the POMDP formulation
into sub-problems, each solved individually. Then, the policy and the candidate
cluster of access points for the best solved sub-problem is used to perform HOs
within a specific time horizon. We control the number of HOs by determining
when to use the HO policy. Our simulation results show that our proposed
solution reduces HOs by 47% compared to time-triggered LSF-based HOs and by 70%
compared to data rate threshold-triggered LSF-based HOs. This amount can be
further reduced through increasing the time horizon of the POMDP.
