Performance of Network-Assisted Full-Duplex for Cell-Free Massive MIMO

Abstract

Network assisted full-duplex (NAFD) is a spatial-division duplex technique for future wireless networks with cellfree massive multiple-input multiple-output (CF massive MIMO) network, where a large number of remote antenna units (RAUs), either using half-duplex or full-duplex, jointly support truly flexible duplex including time-division duplex, frequency-division duplex and full duplex on demand of uplink and downlink traffic by using network MIMO methods. With NAFD, bi-directional data rates of the wireless network could be increased and end-to-end delay could be reduced. In this paper, the spectral efficiency of NAFD communications in CF massive MIMO network with imperfect channel state information (CSI) is investigated under spatial correlated channels. Based on large dimensional random matrix theory, the deterministic equivalents for the uplink sum-rate with minimum-mean-square-error (MMSE) receiver as well as the downlink sum-rate with zero-forcing (ZF) and regularized zero-forcing (RZF) beamforming are derived. Numerical results show that under various environmental settings, the deterministic equivalents are accurate in both a large-scale system and system with a finite number of antennas. It is also shown that with the downlink-touplink interference cancellation, the uplink spectral efficiency of CF massive MIMO with NAFD could be improved.The spectral efficiencies of NAFD with different duplex configurations such as in-band full-duplex, and half-duplex are compared. With the same total numbers of transmit and receive antennas, NAFD with half-duplex RAUs offers a higher spectral efficiency. To alleviate the uplink-to-downlink interference, a novel genetic algorithm based user scheduling strategy (GAS) is proposed. Simulation results show that the achievable downlink sum-rate by using the GAS is greatly improved compared to that by using the random user scheduling. Index TermsNetwork-assisted full-duplex, cell-free massive MIMO, full-duplex, spectral efficiency, deterministic equivalent, scheduling Recently, a novel concept called cell-free (CF) massive multiple-input multiple-output (MIMO) was proposed to overcome the inter-cell interference by innovating the cellular architecture [18], [19]. Compared to small-cell network, CF massive MIMO potentially has a large spectral efficiency [19]. From the point of view of baseband transmission, the performance gain of CF massive MIMO comes from the joint processing of a large number of geographically distributed RAUs [20]. Our recent prototyping system in large-scale distributed MIMO has demonstrated that the data rate of 10Gbps could be achieved by a 128x128 large-scale distributed MIMO (or CF massive MIMO) with 100MHz bandwidth [21]. Different from the existing works, in this paper, we propose a network-assisted full duplex (NAFD) to unify the flexible duplex, hybrid-duplex, full-duplex, and other duplex methods [7], [14], [15], [22] under the CF massive MIMO network, and solve the CLI problem to achieve truly flexible duplex, which is essential in the 5G NR [...

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