Layer-to-DMRS Port Mapping for MIMO Systems
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Solution Overview
Problem
Current layer-to-demodulation reference signal port mapping in LTE-A is inefficient, leading to increased DMRS overhead, incompatibility with Rel-9 and Rel-10 UEs, and limited support for retransmissions, especially at rank=2, where two codewords are mapped to different CDM groups, resulting in higher resource element/PRB usage and restricted single-codeword transmission.
Innovation Solution
A method and apparatus for layer-to-demodulation reference signal port mapping that assigns data streams to DMRS ports based on the rank of MIMO downlink transmission, allowing two layers to be mapped to the same DMRS CDM group during double-codeword transmission and retransmission, and optimizing port allocation across different ranks to maintain compatibility with existing systems while reducing DMRS overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two codewords are mapped to different CDM groups at rank=2, then codeword transmission flexibility is improved, but DMRS overhead increases and resource element/PRB usage increases
Solution Approach 1:
The patent merges the CDM group assignments for two codewords at rank=2 by mapping both codewords to the same CDM group (first CDM group). This is achieved by assigning layers corresponding to different codewords to the same CDM group, thereby reducing DMRS overhead while maintaining the ability to transmit multiple codewords simultaneously through spatial multiplexing.
Solution Approach 2:
The patent introduces dynamic CDM group assignment based on transmission mode and rank. The mapping strategy changes depending on whether single-codeword or double-codeword transmission is used, and whether rank=2 or higher. This dynamic adaptation allows the system to optimize between overhead reduction and transmission flexibility in different operating conditions.
2Device complexity
If layer-to-port mapping is simplified for rank=1, then mapping complexity is reduced, but compatibility with Rel-9 and Rel-10 UEs is worsened
Solution Approach 1:
The patent applies different mapping strategies for different transmission scenarios. For rank=1, a simplified mapping to first CDM group is used. For rank=2 and higher, the mapping adapts based on codeword transmission mode. This local differentiation maintains simplicity where appropriate while ensuring compatibility where needed.
Solution Approach 2:
The patent creates a universal mapping framework that works across multiple release versions (Rel-8, Rel-9, Rel-10) and multiple transmission modes (single-codeword, double-codeword, initial transmission, retransmission). The same framework adapts its behavior based on transmission parameters, ensuring broad compatibility without requiring separate mapping schemes for each scenario.
3Adaptability or versatility
If DMRS ports are allocated for all 8 layers, then spatial multiplexing capability is improved, but DMRS overhead increases
Solution Approach 1:
The patent applies partial action by not always allocating DMRS ports for all 8 layers. Instead, it dynamically allocates DMRS ports based on the actual number of layers being transmitted and the transmission mode. For example, at rank=2 with double-codeword transmission, only the first CDM group is used, effectively using fewer DMRS resources than the maximum 8 ports, thereby reducing overhead while maintaining the capability for spatial multiplexing when needed.
Data Source
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AI summary
A demodulation reference symbol port mapping method is disclosed. The method includes: a base station communicates with a User Equipment (UE), and allocates corresponding data stream to the UE according to the attribution of the UE; the base station maps the corresponding data stream from a layer to a corresponding demodulation reference symbol port; the base station transmits the corresponding data stream to the UE via demodulation reference symbol port. By restricting the demodulation reference symbol port mapping solution of rank=1 to rank=8 and the demodulation reference symbol port mapping solution when the retransmission occurs, the technical solution enables the demodulation reference symbol port mapping solution to compatible with the present system and to keep lower overhead of the demodulation reference symbol.