Abstract
Low-complexity beamformer design with practical constraints is an attractive research area for hybrid analog/digital systems in mm-wave massive multiple-input multiple-output (MIMO). This paper investigates interference-aware pre-beamformer (analog beamformer) design for joint spatial division and multiplexing (JSDM) which is a user-grouping based two-stage beamforming method. Single-carrier frequency domain equalization (SC-FDE) is employed in uplink frequency-selective channels. First, unconstrained slowly changing statistical analog beamformer of each group, namely, generalized eigenbeamformer (GEB) which has strong interference suppression capability is designed by maximizing the mutual information in reduced dimension. Then, constant-modulus constrained approximations of unconstrained beamformer are obtained by utilizing alternating minimization algorithms for fully connected arrays and fixed subarrays. In addition, a dynamic subarray algorithm is proposed where the connections between radio frequency (RF) chains and antennas are changed with changing channel statistics. Convergence of the proposed alternating minimization-based algorithms is provided along with their complexity analysis. It is observed that the additional complexity of proposed algorithms is insignificant for the overall system design. Although most of the interference is suppressed with the help of proposed constrained beamformers, there may be some residual interference after analog beamforming stage. Thus, minimum mean square error (MMSE) criterion based iterative block decision feedback equalization (IB-DFE) method, which takes the residual interference in reduced dimension into account, is promoted for digital beamforming stage. Simulation results verify the superiority of the proposed interference-aware constrained design over existing approaches in terms of beampattern, spectral efficiency, outage capacity, bit-error rate (BER), and channel estimation accuracy.
Highlights
M ASSIVE multiple-input multiple-output (MIMO) at mm-wave bands is the frontier technology for generation wireless communication systems due to the availability of vast spectrum [1], [2]
We aim to find a near-optimal unconstrained analog beamformer, which results in a linear transformation, that preserves the mutual information in reduced dimension
We proposed an interference-aware two-stage beamforming framework, for Joint spatial division and multiplexing (JSDM), where interference is considered in both analog and digital beamforming stages
Summary
M ASSIVE multiple-input multiple-output (MIMO) at mm-wave bands is the frontier technology for generation wireless communication systems due to the availability of vast spectrum [1], [2]. Hybrid analog/digital structure is an efficient approach for these systems as it has lower hardware complexity and energy consumption compared to fully digital beamforming and mm-wave bands exhibit joint angle-delay sparsity [3]. Researchers have been working on low-complexity beamformer design for hybrid systems. Joint spatial division and multiplexing (JSDM) is a user-grouping based two-stage beamforming method where analog beamformers are designed by using slowly. User-grouping reduces signal processing complexity since digital processing of each group becomes independent from each other. Only instantaneous intra-group channels in reduced dimension need to be learned which reduces channel estimation overhead. We adopt JSDM framework in frequency-selective channels where we employ single-carrier frequency domain equalization (SC-FDE) for uplink transmission
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
