Abstract
Massive Multiple-Input Multiple-Output (MIMO) is one of the key techniques in 5th generation wireless systems (5G) due to its potential ability to improve spectral efficiency. Most of the existing works on massive MIMO only consider Time Division Duplex (TDD) operation that relies on channel reciprocity between uplink and downlink channels. For Frequency Division Duplex (FDD) systems, with continued efforts, some downlink multiuser MIMO scheme was recently proposed in order to enable “massive MIMO” gains and simplified system operations with limited number of radio frequency (RF) chains in FDD system. However these schemes, such as Joint Spatial Division and Multiplexing (JSDM) scheme and hybrid precoding scheme, only focus on multiuser transmission in spatial domain. Different from most of the existing works, this paper proposes Joint Spatial and Power Multiplexing (JSPM) scheme in FDD systems. It extends existing FDD schemes from spatial division and multiplexing to joint spatial and power domain to achieve more multiplexing gain. The user grouping and scheduling scheme of JSPM is studied and the asymptotic expression for the sum capacity is derived as well. Finally, simulations are conducted to illustrate the effectiveness of the proposed scheme.
Highlights
With increasing popularity of smart phones, pads, and tablet computers, mobile data traffic is experiencing unprecedented growth
Since the amount of time-frequency resources needed for downlink reference signals is proportional to the number of antennas and the amount of uplink channel state information (CSI) feedback resources is proportional to the number of active users, a massive Multiple-Input Multiple-Output (MIMO) system may require up to tens of times more resources than a conventional system
In order to achieve more multiplexing gain in the MU-MIMO stage, the power domain is introduced in spatial multiplexing transmission scheme and the joint spatial and power multiplexing (JSPM) scheme for massive MIMO system is proposed in this paper
Summary
With increasing popularity of smart phones, pads, and tablet computers, mobile data traffic is experiencing unprecedented growth. The prebeamforming matrix is chosen in order to minimize the interference across different spatial groups, and the MU-MIMO precoding matrix takes care of the multiuser interference within each group Both of these beamforming stages achieve multiplexing gain in spatial domain. In order to achieve more multiplexing gain in the MU-MIMO stage, the power domain is introduced in spatial multiplexing transmission scheme and the joint spatial and power multiplexing (JSPM) scheme for massive MIMO system is proposed in this paper. The proposed scheme relaxes the full channel knowledge to achieve the spatial multiplexing gain by using the channel second order statistics, and applies multiuser power allocation transmission at BS side and successive interference canceller (SIC) on UE side to achieve the power-domain user multiplexing gain.
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