CSI-RS Transmission in 2D Planar Array MIMO Systems
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Solution Overview
Problem
In massive MIMO systems with two-dimensional planar array antennas, existing technologies face challenges in efficiently transmitting Channel State Information Reference Signals (CSI-RS) using limited downlink radio resources, necessitating innovative methods for channel estimation and optimal selection of Spatial Multiplexing (SM) and Space Division Multiple Access (SDMA) techniques.
Innovation Solution
The proposed solution defines Space Resource Blocks (SRBs) based on high spatial correlation between channels, transmits CSI-RS in vertical dimension elements corresponding to selected horizontal elements, and adapts SRB size and position dynamically, while optimizing SM and SDMA techniques to maximize capacity gain by limiting transmission ranks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CSI-RS is transmitted for all space elements in two-dimensional space, then channel estimation accuracy is improved, but downlink resource consumption increases
Solution Approach 1:
The patent segments the two-dimensional space elements into multiple one-dimensional beams in the horizontal direction. Instead of transmitting CSI-RS for all 2D space elements, it transmits CSI-RS for selected 1D beams, reducing resource consumption while maintaining estimation accuracy through beam-based segmentation
Solution Approach 2:
The transmitted CSI-RS for one-dimensional beams serves multiple purposes: it enables channel estimation for the beams themselves, provides basis for beam selection, and supports both SM and SDMA techniques through the obtained channel state information, making the limited CSI-RS transmissions multi-functional
2Productivity
If Spatial Multiplexing is used to increase data rate, then productivity is improved, but transmission rank complexity increases
Solution Approach 1:
The patent dynamically adjusts the transmission rank based on channel conditions and beam selection results. The rank is not fixed but adapts to the estimated channel state, allowing the system to optimize between SM (higher rank) and SDMA (lower rank) based on current conditions, reducing complexity while maintaining productivity
3Use of energy by moving object
If beamforming gain is increased by adding transmission antennas, then power efficiency is improved, but device complexity increases
Solution Approach 1:
The patent segments the large two-dimensional antenna array into multiple one-dimensional beams in the horizontal direction. This segmentation allows the system to achieve beamforming gain through selective beam transmission rather than utilizing all antennas simultaneously, reducing the effective complexity while maintaining power efficiency
Solution Approach 2:
Instead of using all transmission antennas for CSI-RS transmission, the patent transmits CSI-RS for only selected one-dimensional beams. This partial action approach achieves sufficient beamforming gain for power efficiency while avoiding the complexity of managing and transmitting through the entire antenna array
Data Source
AI summary
The present invention proposes a hybrid spatial multiplexing (SM) and a space division multiple access (SDMA) technique in a frequency division duplex (FDD) massive multiple-input multiple output (MIMO) system using a two-dimensional planar array antenna, which effectively transmits a channel state information reference signal (CSI-RS) for estimating a downlink two-dimensional space channel using only a limited amount of downlink radio resources, and optimally selects and performs the SM and SDMA techniques in a two-dimensional space channel. To this end, the present invention proposes a technique which defines space resource blocks (SRB) by grouping space elements (SE) having a high spatial correlation between downlink channels in the horizontal dimension and corresponding SEs thereof in the vertical dimension, and transmits CSI-RSs for estimating channels in vertical dimension SEs corresponding to one selected horizontal SE in each SRB every transmit time interval (TTI). The present invention proposes a technique wherein user equipment (UE) estimates the spatial correlation between channels of different horizontal dimension SEs belonging to the same SRB received in different TTIs and the spatial correlation between channels of horizontal dimension SEs belonging to different SRBs received in the same TTI, and feeds information for changing the size of SRB of the corresponding UE to an optimal size back to eNodeB. The present invention proposes a technique wherein the UE estimates downlink channels through CSI-RSs transmitted from each SRB, and each UE feeds an index of a preferred SRB, a rank of the corresponding SRB in the vertical dimension, and channel quality information (CQI) back to eNodeB. When each UE determines the rank, it is possible to transmit the ranks to the fullest extent in the vertical dimension and only a single rank from each SRB in the horizontal dimension.