POMDP-based Handoffs for User-Centric Cell-Free MIMO Networks

TL;DR

This paper introduces a POMDP-based approach to optimize handoff decisions in user-centric cell-free MIMO networks, significantly reducing unnecessary handoffs by considering channel state evolution and partial observability.

Contribution

It presents a novel POMDP formulation for handoff control in cell-free MIMO, with a divide-and-conquer solution to manage complexity and improve decision robustness.

Findings

Reduces handoffs by 47% compared to time-triggered methods.

Achieves 70% reduction compared to data rate threshold methods.

Further reduction possible by increasing the POMDP time horizon.

Abstract

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.