Uplink Precoder Selection via Downlink Reference Signals
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Solution Overview
Problem
Existing wireless communication systems, particularly in LTE and NR, face challenges in efficiently determining uplink precoders due to the lack of effective methods for utilizing downlink and uplink channel reciprocity.
Innovation Solution
Techniques are developed to use downlink reference signals for uplink precoder determination and uplink reference signals for downlink precoder determination when channel reciprocity exists, enabling UEs and base stations to selectively transmit signals or measurement reports based on indications and identify appropriate precoders for precoding communications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional methods are used to determine uplink precoders without leveraging channel reciprocity, then the system can operate with simpler procedures, but the precoder determination efficiency is low and communication quality is not optimized
Solution Approach 1:
The system performs preliminary channel state estimation using downlink reference signals (CSI-RS) before uplink precoder determination is needed. By measuring the downlink channel characteristics in advance and exploiting channel reciprocity, the UE can determine the uplink precoder without requiring separate uplink channel measurements, thus improving efficiency while maintaining manageable system complexity
Solution Approach 2:
The patent introduces downlink reference signals as an intermediary mechanism to indirectly obtain uplink channel information. Instead of directly measuring the uplink channel, the system uses the downlink reference signals to estimate the channel state, which serves as a mediator between the downlink transmission and the uplink precoder determination, enabling efficient precoder selection without additional complexity
2Reliability
If downlink reference signals are used to determine uplink precoders by exploiting channel reciprocity, then precoder determination efficiency is improved and communication quality is enhanced, but the system requires additional signaling and measurement procedures
Solution Approach 1:
The downlink reference signals serve multiple functions: they are used for downlink channel estimation, downlink precoder determination, and also for uplink precoder determination through channel reciprocity. This multi-functionality allows the system to improve communication quality and reliability without proportionally increasing complexity, as the same reference signals contribute to multiple optimization objectives
3Loss of time
If channel reciprocity is exploited for precoder determination, then the need for separate uplink reference signals is reduced, but the system must accurately estimate and manage channel state information
Solution Approach 1:
The system implements feedback mechanisms where the UE measures downlink reference signals, determines channel state information, and uses this information to select appropriate precoders for uplink transmissions. This feedback loop allows continuous optimization of channel state estimation accuracy while reducing the time required for precoder determination by leveraging the already-measured downlink channel characteristics
Data Source
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AI summary
Certain aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may receive an indication of whether to use uplink reference signals or downlink reference signals for uplink precoder determination. The UE may selectively transmit a plurality of uplink reference signals or one or more measurement reports based at least in part on the indication, wherein the one or more measurement reports are determined based at least in part on measuring a plurality of downlink reference signals. The UE may receive an indication of a precoder, of a plurality of precoders, to be used to precode an uplink communication, wherein the precoder is identified based at least in part on the plurality of uplink reference signals or the one or more measurement reports. The UE may precode the uplink communication using the precoder. Numerous other aspects are provided.