Performance of Cell-Free Systems with Channel Reciprocity Errors

Abstract

Cell-free systems are characterized by the absence of a cell-based spatial subdivision. In these systems a large number of access points may serve each user, which contribute to improve signal transmission conditions. In this context, it is important to obtain equations that describe the behavior of the system, as a function of its main parameters. Such equations become more complete when more effects are taken into account. One of these effects is the loss of channel reciprocity due to radiofrequency (RF) mismatch. This paper proposes the introduction of a multiplicative model for the reciprocity errors resulting from RF mismatch in all devices of a cell-free model. Additionally, it also proposes the use of different levels of mismatch for each device. The main contribution of this work is an analytical expression for the downlink achievable rates in the presence of multiplicative reciprocity errors due to RF mismatch. Based on it, one can compute the approximate value of the achievable rates. The analytical expression is used in scenarios with and without line-of-sight. It is shown that the analytical expression is very close when there is line-of-sight, as it provides achievable rate values closer to that obtained by using Monte Carlo simulation.