Abstract
Hybrid precoding is an attractive technique in MU-MIMO systems with significantly reduced hardware costs. However, it still requires a complex analog network to connect the RF chains and antennas. In this paper, we develop a novel hybrid precoding structure for the downlink transmission with a compact RF structure. Specifically, the proposed structure relies on domestic connections instead of global connections to link RF chains and antennas. Fixed-degree phase shifters provide candidate signals, and simple on-off switches are used to route the signal to antennas, thus RF adders are no longer required. Baseband zero forcing and block diagonalization are used to cancel interference for single-antenna and multiple-antenna users, respectively. We formulate how to design the RF precoder by optimizing the probability distribution through cross-entropy minimization which originated in machine learning. To optimize the energy efficiency, we use the fractional programming technique and exploit the Dinkelbach method-based framework to optimize the number of active antennas. Simulation results show that proposed algorithms can yield significant advantages under different configurations.
Highlights
Multiuser multiple-input multiple-output (MU-MIMO) is considered a key technology to meet the increasing traffic and critical energy efficiency demand in cellular networks [1,2]
This leads to unacceptable hardware costs as well as high energy consumption when plenty of transmit antennas are adopted in the massive MIMO scenario
The normalized millimeter wave (mmWave) downlink channel of the kth mobile stations (MSs) is modeled as the sum of all the propagation paths which is scattered in NC clusters and each cluster involves total NP paths
Summary
Multiuser multiple-input multiple-output (MU-MIMO) is considered a key technology to meet the increasing traffic and critical energy efficiency demand in cellular networks [1,2]. The analog beamformer is aimed at harvesting the array gain to improve the spectral efficiency when a digital baseband precoder is used to eliminate the inter-chain interference [8]. To reduce the hardware complexity, especially the expensive high-resolution variable-degree PSs and multiple-input RF adders, a simplified hybrid precoding structure is proposed in [22] by introducing negative signals via RF inverters. Based on this switchand-inverter (SI) based structure, an adaptive hybrid precoding algorithm is proposed by randomly generating near-optimal tests to improve spectral efficiency [23]. K=1 where SINRk is the overall signal-to-interference-plus-noise ratio of the kth MS
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