Co-existing/Cooperating Multicell Massive MIMO and Cell-Free Massive MIMO Deployments: Heuristic Designs and Performance Analysis

TL;DR

To take into account the effect of the proposed cooperation scenarios on the fronthaul links, this paper provides a fronthaul-aware heuristic association algorithm between users and network elements, which allows the fulfillment of the front-haul requirement on each link.

Abstract

Cell-free massive MIMO (CF-mMIMO) systems represent a deeply investigated evolution from the conventional multicell co-located massive MIMO (MC-mMIMO) network deployments. Anticipating a gradual integration of CF-mMIMO systems alongside pre-existing MC-mMIMO network elements, this paper considers a scenario where both deployments coexist, in order to serve a large number of users using a shared set of frequencies. The investigation explores the impact of this co-existence on the network's downlink performance, considering various degrees of mutual cooperation, precoder selection, and power control strategies. Moreover, to take into account the effect of the proposed cooperation scenarios on the fronthaul links, this paper also provides a fronthaul-aware heuristic association algorithm between users and network elements, which allows the fulfillment of the front-haul requirement on each link. The research is finally completed by extensive simulations, shedding light on the performance outcomes associated with the various levels of cooperation and several solutions delineated in the paper.

Figures (10)

• Figure 1: The simulated network deployment. The performance results that will be reported will refer only to the three cells with bolder edges. The remaining surrounding cells are considered to avoid border effects and take into account the extra-cell interference.
• Figure 2: Flowchart of the precoding design and user association considering limited-capacity fronthaul constraints.
• Figure 3: Array gain versus $\theta_{k,\ell}$, the angle between the $k$-th user and the $\ell$-th BS.
• Figure 4: CDF of the rate per user in the four considered scenarios with FPA with $\alpha=-0.5$, MMSE beamfoming at the BSs and APs and 5 users per sector, i.e., $K=180$. Continuous lines represent uniform APs placement in the cells and dashed lines represent cell-edge APs placement.
• Figure 5: CDF of the rate per user in the HORIZONTAL-Coop and FULL-Coop scenarios with FPA with $\alpha=-0.5$, 5 users per sector, i.e., $K=180$, and uniform APs distribution. Comparison between the beamforming techniques at the APs and BSs.