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- Bengtsson, Erik L, et al.
(författare)
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A Case Study on the Influence of Multiple Users on the Effective Channel in a Massive MIMO System
- 2019
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Ingår i: IEEE Wireless Communications Letters. - 2162-2337. ; , s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the importance of weak clusters when modeling a wireless massive MIMO channel. We do this by studying the influence of densely spaced terminals and the number of base-station antennas for a zero-forcing precoded massive MIMO system. In particular, we focus on the influence on the correlation and imbalance between the signals at the terminal antennas, the effective channel-gain, the eigenvalue distributions and the number of clusters.The study is based on measured radio-channels from terminal prototypes with integrated antennas connected to a massive MIMO testbed.We further evaluate the advantage of using block-diagonalized zero-forcing compared to conventional zero-forcing in a massive MIMO system. Unexpectedly, terminals with low antenna envelope correlation coefficient may benefit significantly from block-diagonal zero-forcing in a massive MIMO system.The main conclusion is that weaker clusters are important when modeling multi-user scenarios.
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| 2. |
- Sanchez, Juan, et al.
(författare)
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Optimal, Low-Complexity Beamforming for Discrete Phase Reconfigurable Intelligent Surfaces
- 2021
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Ingår i: 2021 IEEE Global Communications Conference, GLOBECOM 2021 - Proceedings. - 9781728181042
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Konferensbidrag (refereegranskat)abstract
- Reflective reconfigurable intelligent surface (RIS) technology is regarded as an innovative, cost- and power-effective solution that aims at influencing the wireless channel through controlled scattering. The technology can be realized by using metamaterials and/or resonant elements that scatter electromagnetic waves with a configurable phase shift. Most of the previous work on beamforming techniques for RIS assumes ideal hardware and, thus, continuous phase shifts. However, hardware constraints limit the phase shift resolution, manifested into the amount of discrete phase shifts that can be configured into each RIS element. This paper aims to offer a discrete phase shift beamforming algorithm for reflective RISs that targets minimization of the quantization error resulting from discretization of continuous phase shifts. The beamforming solution proves to be optimal under perfect channel knowledge for any discrete set of uniformly distributed phase shifts. The required complexity to find the optimal beamforming vector for our approach is found to be linear with the number of RIS elements, the minimum needed to obtain optimal results. Simulated behavior is validated by measurements, showing robustness against angle misalignments and distance variations.
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