Topological Pilot Assignment in Large-Scale Distributed MIMO Networks

TL;DR

This paper addresses the pilot assignment challenge in large-scale distributed MIMO networks by modeling the problem as a topological interference management task, proposing solutions for known and unknown connectivity patterns, and evaluating their efficiency.

Contribution

It introduces a topological pilot assignment framework for distributed MIMO, formulating it as low-rank matrix completion and maximum weight matching problems, with efficient algorithms for each case.

Findings

Algorithms perform well in cell-free massive MIMO scenarios.

Proposed methods effectively handle known and unknown connectivity patterns.

Efficient solutions improve pilot assignment in large-scale distributed MIMO networks.

Abstract

We consider the pilot assignment problem in large-scale distributed multi-input multi-output (MIMO) networks, where a large number of remote radio head (RRH) antennas are randomly distributed in a wide area, and jointly serve a relatively smaller number of users (UE) coherently. By artificially imposing topological structures on the UE-RRH connectivity, we model the network by a partially-connected interference network, so that the pilot assignment problem can be cast as a topological interference management problem with multiple groupcast messages. Building upon such connection, we formulate the topological pilot assignment (TPA) problem in two different ways with respect to whether or not the to-be-estimated channel connectivity pattern is known a priori. When it is known, we formulate the TPA problem as a low-rank matrix completion problem that can be solved by a simple alternating projection algorithm. Otherwise, we formulate it as a sequential maximum weight induced matching problem that can be solved by either a mixed integer linear program or a simple yet efficient greedy algorithm. With respect to two different formulations of the TPA problem, we evaluate the efficiency of the proposed algorithms under the cell-free massive MIMO setting.