Abstract
As a promising technology in the next generation mobile network, millimeter-wave (mmWave) communication can mitigate the spectrum crunch of improving the network capacity by exploiting the large underutilized spectrum bands of the mmWave frequencies. The hybrid (analog/digital) beamforming of multi-data streams are widely used to further the spectrum efficiency of mmWave relay system when faced with the complex environment or long distance communication. This paper investigates the hybrid beamforming scheme for the decode-and-forward (DF) mmWave massive multiple-input multiple-output (MIMO) relay system with mixed structure and full-connected structure. We optimize hybrid beamforming of relay system by maximizing the sum rate of the overall system as an objective function. To reduce the computational complexity, we reformulate the original problem as two single-hop mmWave MIMO sum-rate maximization subproblems. Then, the piecewise successive approximation method is proposed based on the criterion which jointly designs the analog and digital beamforming stages by trying to avoid the loss of information at each stage. The hybrid beamforming of the two subproblems can be solved by the proposed scheme united with the idea of successive interference cancelation (SIC), the baseband block diagonalization (BD) scheme, and waterfilling power allocation method. Finally, simulation results confirm that the proposed optimal method can achieve good performance in hybrid beamforming design of relay system with both mixed and full-connected structures.
Highlights
In order to meet the great requirements of wireless communication, mmWave communication has recently gained considerable interest in both academia and industry as a promising candidate in the future cellular network [1], [2]
We propose an effective hybrid beamforming design scheme to fill the theoretical gap for the mixed structure in mmWave massive MU-multiple-input multipleoutput (MIMO) relay system
To solve the intractable optimal hybrid beamforming design problem for the relay system with the mixed and full-connected structures, the piecewise successive approximation method was proposed based on the criterion which jointly designs the analog and digital beamforming stages by trying to avoid the loss of information at each stage
Summary
In order to meet the great requirements of wireless communication, mmWave communication has recently gained considerable interest in both academia and industry as a promising candidate in the future cellular network [1], [2]. We propose an effective hybrid beamforming design scheme to fill the theoretical gap for the mixed structure in mmWave massive MU-MIMO relay system. For the mixed structure, the major problems in maximizing the sum rate of the overall system includes ten optimal elements involving power allocation to be solved, and the block-diagonal (BD) and constant-modulus constraints in the analog beamforming design caused by the characteristics of phase shifter and sub-connected structure. To solve the sum-rate maximization subproblem from the source to the relay decoding, we propose the piecewise successive approximation method based on the criterion which jointly designs the analog and digital beamforming stages by trying to avoid the loss of information at each stage. A denotes the operation of getting the angle of each entry in matrix A; Dl×l and Cm×n describe a real diagonal matrix of dimension l × l and a complex matrix of dimension m × n, respectively. tr {·} and Re (·) denote trace and real part of the matrix, respectively
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