Abstract
In multi-user beamforming systems, the inter-user interference are controlled by spatial filtering. Since the implementation of digital beamforming is difficult due to high hardware cost of large array system, the analog beamforming system with one phase shifter at each antenna element is considered with antenna selection scheme. However, the beamwidth is not sufficiently narrow to perfectly remove the interference due to limited size of antenna arrays. To mitigate the interference, we propose the random antenna selection system in millimeter wave channel. The random antenna selection expands the effective array size so that the beamwidth becomes narrow. We compare the beamwidth of conventional fixed antenna selection with random antenna selection and analyze the amount of interference for each selection scheme. Theoretical analysis and bit error rate simulation results indicate that the beamforming with random antenna selection can take advantage of large array.
Highlights
Millimeter wave is one of the leading candidates for the future wireless communications system thanks to the following two merits [1]
The results show that the random antenna selection gives narrower main lobes but higher side lobes than fixed antenna selection
In the case of the random antenna selection scheme, on the other hand, the interference from random direction of the grating lobes are averaged out so that other users who are located on different directions can receive their desired signals
Summary
Millimeter wave (mmWave) is one of the leading candidates for the future wireless communications system thanks to the following two merits [1]. High hardware complexity and cost make it difficult to implement MRT because it demands baseband digital signal processing (DSP) for each antenna element For this reason, analog radio frequency (RF) beamforming is considered [4]. The original purpose of ASM is to average out the signals for undesired direction by randomization, we can use the random antenna selection scheme to mitigate the inter-user interference in multi-user system which is considered in this paper. In [13, 14], the linear methods such as block diagonalization precoding and non-linear methods such as Tomlinson-Harashima precoding are introduced These techniques require a lot of RF chains to use DSP for each antenna element which results in high hardware complexity. We consider mmWave analog RF beamforming system transmitting multiple streams simultaneously with one phase shifter at each antenna element for low hardware complexity.
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