Two-Level MIMO Precoding for Lower Feedback Overhead
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Solution Overview
Problem
Existing closed-loop MIMO (CL-MIMO) systems in LTE lack optimal power allocation among layers and rely on extensive feedback, leading to inefficiencies and increased overhead.
Innovation Solution
Implement a two-level precoding scheme where the first level is for rank adaptation and power allocation, and the second level is for unitary or non-unitary precoding, with separate feedback frequencies based on channel conditions to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If closed-loop MIMO relies on extensive feedback from the mobile terminal, then channel information can be accurately obtained, but feedback overhead increases significantly
Solution Approach 1:
The patent segments the precoding process into two independent levels: first level for rank adaptation and power allocation, second level for unitary precoding. Correspondingly, it segments the feedback into two types: long-term feedback for first level (rank and power) and short-term feedback for second level (unitary precoding). This segmentation allows each feedback component to be optimized independently, reducing overall feedback overhead while maintaining accuracy.
Solution Approach 2:
The patent implements dynamic feedback frequencies for different precoding levels based on channel conditions. The first level (rank and power allocation) uses long-term feedback with lower frequency, while the second level (unitary precoding) uses short-term feedback with higher frequency. This dynamic approach adapts feedback requirements to actual channel variations, reducing unnecessary feedback overhead.
2Device complexity
If unitary precoding is used without power allocation, then precoding complexity is reduced, but power allocation optimization is lost
Solution Approach 1:
The patent divides precoding into two sequential operations: first performing power allocation (water-filling) to determine optimal power distribution across layers, then performing unitary precoding to optimize signal directions. By separating these operations, the system achieves both power allocation optimization and unitary precoding benefits without excessive complexity.
Solution Approach 2:
The patent performs power allocation as a preliminary step before unitary precoding. The water-filling power allocation is computed first to determine optimal power distribution, then this power information is used as input for the subsequent unitary precoding operation. This preliminary action ensures that power allocation is optimized before the more complex unitary precoding is applied.
Data Source
AI summary
The present invention relates to precoding and feedback channel information in wireless communication system. A method includes receiving a first Precoding Matrix Index (PMI) and a second PMI from a terminal; mapping one or two codewords into layers; precoding symbols mapped into the layers using a first precoding matrix derived from the first PMI and a second precoding matrix derived from the second PMI; and transmitting the precoded symbols to the terminal, wherein the reception of the first PMI is less frequent than the reception of the second PMI.