A Novel Heap-based Pilot Assignment for Full Duplex Cell-Free Massive MIMO with Zero-Forcing

This paper investigates the combined benefits of
full-duplex (FD) and cell-free massive multiple-input multipleoutput
(CF-mMIMO), where a large number of distributed
access points (APs) having FD capability simultaneously serve
numerous uplink and downlink user equipments (UEs) on the
same time-frequency resources. To enable the incorporation of
FD technology in CF-mMIMO systems, we propose a novel heapbased
pilot assignment algorithm, which not only can mitigate
the effects of pilot contamination but also reduce the involved
computational complexity. Then, we formulate a robust design
problem for spectral efficiency (SE) maximization in which the
power control and AP-UE association are jointly optimized,
resulting in a difficult mixed-integer nonconvex programming.
To solve this problem, we derive a more tractable problem
before developing a very simple iterative algorithm based on
inner approximation method with polynomial computational
complexity. Numerical results show that our proposed methods
with realistic parameters significantly outperform the existing
approaches in terms of the quality of channel estimate and SE.