DMRS Precoding Matrix Segmentation for LTE Channel Estimation
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Solution Overview
Problem
In LTE systems, the precoding matrix ratio for data RE to UE-specific RS EPRE violates the 0 dB specification, impacting channel estimation performance, especially when DMRS power is lower.
Innovation Solution
A two-layer DMRS-based transmission scheme is proposed, where the precoding matrix on data RE is represented as A×B, with A being the precoding matrix for UE-specific RS and B as the co-phasing cycling matrix, ensuring a 0 dB ratio of PDSCH EPRE to DMRS EPRE, thereby improving channel estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the precoding matrix on data RE is different from the precoding matrix on reference signal RE, then the spectral efficiency is improved, but the channel estimation performance deteriorates
Solution Approach 1:
The precoding matrix is segmented into two parts: a common precoding matrix W applied to both reference signals and data, and a separate co-phasing cycling matrix Ui applied only to data REs. This segmentation allows the reference signal to maintain a simple precoding structure for accurate channel estimation, while the data REs can utilize the full precoding matrix for spectral efficiency.
Solution Approach 2:
The co-phasing cycling matrix Ui acts as an intermediary that transforms the reference signal precoding matrix into the data RE precoding matrix. This intermediary allows the UE to derive the data precoding from the reference signal precoding through a known transformation relationship, maintaining channel estimation accuracy while enabling spectral efficiency.
2Object-generated harmful factors
If the DMRS power is reduced, then the interference is reduced, but the channel estimation performance deteriorates
Solution Approach 1:
The power of the DMRS is dynamically adjusted based on the transmission mode and precoding configuration. By changing the DMRS power parameter according to the actual transmission conditions, the system can reduce interference when DMRS power is high while ensuring sufficient power for accurate channel estimation when needed.
Data Source
AI summary
A method of two-layer (Rank=2) demodulation reference signal (DMRS) based transmission scheme is proposed. The precoding matrix on a data RE can be represented as A×B. The precoding matrix on the UE-specific reference signal DMRS is A. Matrix B is the co-phasing cycling matrix. By applying the proposed co-phasing cycling matrix B for Rank=2 DMRS-based transmission scheme, the ratio of PDSCH EPRE to DMRS EPRE is equal to 0 dB, as required by the LTE specification. Further, when the DMRS power follows the precoding matrix A, UE channel estimation performance is improved.