Energy Efficiency of User-Centric, Cell-Free Massive MIMO-OFDM with Instantaneous CSI

Abstract

In the user-centric, cell-free, massive multi-input, multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) system, a large number of deployed access points (APs) serve user equipment (UEs) simultaneously, using the same time–frequency resources, and the system is able to ensure fairness between each user; moreover, it is robust against fading caused by multi-path propagation. Existing studies assume that cell-free, massive MIMO is channel-hardened, the same as centralized massive MIMO, and these studies address power allocation and energy efficiency optimization based on the statistics information of each channel. In cell-free, massive MIMO systems, especially APs with only one antenna, the channel statistics information is not a complete substitute for the instantaneous channel state information (CSI) obtained via channel estimation. In this paper, we propose that energy efficiency is optimized by power allocation with instantaneous CSI in the user-centric, cell-free, massive MIMO-OFDM system, and we consider the effect of CSI exchanging between APs and the central processing unit. In addition, we design different resource block allocation schemes, so that user-centric, cell-free, massive MIMO-OFDM can support enhanced mobile broadband (eMBB) for high-speed communication and massive machine communication (mMTC) for massive device communication. The numerical results verify that the proposed energy efficiency optimization scheme, based on instantaneous CSI, outperforms the one with statistical information in both scenarios.

Performance of Spatially Diverse URLLC and eMBB Traffic in Cell Free Massive MIMO Environments

“…We assume a Cf-maMIMO-OFDM system as in [10]. In downlink (DL), the N sc = 2400 subcarriers are divided into multiple resource blocks (RB), allocated to UEs such that In the time domain, according to the massive MIMO operation, the subcarriers and time samples are grouped to fit the coherence interval (CI), which consists of a number of subcarriers and time samples where the channel response can be approximated as constant and flat-fading.…”

“…For the URLLC case, we assume that multiple UEs can be scheduled for transmission in the same coherence interval, as the size of URLLC packets is much smaller than that of eMBB. Theoretically, assuming that each RB serves k URLLC UEs, the Cf-maMIMO-OFDM system can support a total of kN sc /12 URLLC UEs transmitting simultaneously [10]. We formalize the RB allocation scheme described above by assuming that the URLLC utilizes a fraction δ B of the coherence bandwidth B c and a fraction of the downlink transmission time, as explained in Sec.…”

DCC: CF-MIMO- A new Dynamic Cooperation Cluster Driven Cell-Free Massive MIMO Architecture Network for Future Networks

“…In [16] In this article, the authors provides a comprehensive survey of Cell free massive MIMO systems.…”