Base Station DL-CSI Feedback Reduction in Asymmetrical TDD Systems
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Solution Overview
Problem
In 4G TDD communication systems with asymmetrical DL and UL bandwidths, reciprocity between DL-CSI and UL-CSI is not secured, leading to decreased system throughput and transmission rates due to the inability to perform effective DL closed-loop control without feedback.
Innovation Solution
A base station apparatus and terminal apparatus configuration that estimates UL-CSI through channel sounding in overlapping bands and interpolates DL-CSI in non-overlapping bands for closed-loop control, reducing the need for feedback and enhancing system throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If TDD scheme uses asymmetrical DL and UL bandwidths to meet 4G requirements, then system capacity and adaptability are improved, but reciprocity between DL-CSI and UL-CSI cannot be secured, causing loss of closed-loop control capability
Solution Approach 1:
The patent segments the bandwidth into overlapping and non-overlapping parts between DL and UL channels. In the overlapping part, channel reciprocity is utilized for closed-loop control, while in the non-overlapping part, open-loop control is used. This segmentation allows the system to maintain reciprocity where possible while accommodating asymmetrical bandwidth requirements.
Solution Approach 2:
The patent applies different control strategies to different parts of the bandwidth: closed-loop control is applied locally in the overlapping frequency region where reciprocity exists, while open-loop control is applied in the non-overlapping region. This local differentiation optimizes performance in each region according to its specific characteristics.
2Reliability
If TDD scheme uses symmetrical DL and UL channels to secure channel reciprocity, then closed-loop control performance is improved, but bandwidth flexibility and system capacity are reduced
Solution Approach 1:
The patent divides the channel into overlapping and non-overlapping segments, allowing symmetrical treatment (closed-loop control) in the overlapping segment where reciprocity is beneficial, while permitting asymmetrical treatment (open-loop control) in the non-overlapping segment to maintain bandwidth flexibility.
Solution Approach 2:
The patent creates a hybrid control mechanism that can operate in both closed-loop mode (when reciprocity is available) and open-loop mode (when bandwidth flexibility is needed). This multi-functional approach allows the system to adapt its control strategy based on the specific bandwidth allocation requirements.
3Productivity
If UL channel sounding is used to estimate DL-CSI in symmetrical TDD, then feedback overhead is reduced and throughput is improved, but this method fails in asymmetrical TDD due to lack of reciprocity
Solution Approach 1:
The patent segments the channel estimation process: in the overlapping frequency region, UL channel sounding is used to estimate DL-CSI (maintaining the efficient feedback-free approach), while in the non-overlapping region, DL channel state information is obtained through traditional feedback methods, ensuring accuracy where reciprocity cannot be assumed.
Solution Approach 2:
Different channel estimation strategies are applied to different frequency regions: efficient UL-based estimation is used locally in the overlapping region where reciprocity holds, while conventional DL feedback-based estimation is used in the non-overlapping region where asymmetry prevents reciprocity from being valid.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables improved system throughput and transmission rates in TDD radio communication systems with asymmetrical DL and UL channels while minimizing feedback information.
Implementation Method 1
the base station apparatus performs UL channel sounding using a UL pilot from the UE, based on the channel reciprocity between DL and UL, to estimate UL-CSI
Data Source
AI summary
Provided is a base station device capable of reducing a DL-CSI feedback amount in a TDD type radio communication system in which a DL bandwidth is different from a UL bandwidth. In this device, a demultiplexing unit (133) separates an UL pilot, a DL-CQI, and a DL-CSI fed back from a plurality of UEs as communication partners; a channel estimation unit (134) performs channel sounding by using a UL pilot from a UE in which a DL channel and a UL channel are allocated by overlapping a part of the bandwidth so as to obtain UL-CSI; a control DL-CSI acquisition unit (135) performs interpolation of DL-CSI by using the DL-CSI of some RB contained in the bandwidth where the DL channel and the UL channel fed back from the UE are not overlapped; and a DL close loop control unit (104) combines the estimated UL-CSI and the interpolated DL-CSI so as to use them as DL-CSI for controlling the DL close loop.