MU-MIMO Downlink DM-RS Port Allocation for Better Channel Estimation
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Solution Overview
Problem
Current channel estimation methods in MU-MIMO systems face interference and performance trade-offs due to pilot-on-pilot arrangements, particularly for partially loaded DM-RS ports, compromising channel estimation quality.
Innovation Solution
Implement a method for dynamic DM-RS port allocation based on scheduling information, incorporating Partial Port Occupancy Information (P-Poi) and Hybrid ARQ processes to enhance channel estimation quality without compromising other ports, using scheduling aware UE port mapping and CDM spreading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If reference signals for different users or layers occupy the same time-frequency resources (pilot-on-pilot arrangement), then resource utilization is improved, but interference between pilots increases and channel estimation quality deteriorates
Solution Approach 1:
The reference signal resources are segmented into different CDM groups, where each group uses orthogonal cover codes to separate users or layers. This segmentation allows multiple users to share time-frequency resources while maintaining orthogonality within each CDM group, thus improving resource utilization without sacrificing channel estimation quality.
Solution Approach 2:
Different CDM groups are assigned with different orthogonal cover codes, creating local orthogonality within each group. This local quality approach ensures that while resources are shared globally, each local CDM group maintains interference-free channel estimation through code division multiplexing.
2Measurement precision
If orthogonal cover codes are used to separate users or ports in MU-MIMO, then channel estimation quality is improved, but the number of supported users or layers is limited by the total number of available DM-RS ports
Solution Approach 1:
The patent extends the orthogonality dimension from single CDM group to multiple CDM groups. By introducing the CDM group dimension, the system can support more users or layers than the number of ports in a single CDM group, as each CDM group can be independently configured with orthogonal cover codes.
Solution Approach 2:
The DM-RS port structure is designed to be universal across multiple CDM groups, where each port can be configured to belong to different CDM groups based on scheduling requirements. This multi-functionality allows the same port to serve different users in different CDM groups, increasing system flexibility and user capacity.
3Device complexity
If the channel estimate is assumed to be constant across the time-frequency grid spanned by the CDM group, then processing complexity is reduced, but performance trade-offs occur in MU-MIMO scenarios
Solution Approach 1:
The time-frequency grid is segmented into multiple CDM groups, each with its own channel estimation process. This segmentation allows the system to maintain the simple assumption of constant channel estimate within each small CDM group, while achieving better overall performance through multiple independent estimation regions that can be combined.
Data Source
AI summary
A system and method for enabling downlink signal transmission in a Multiple-Input Multiple-Output (MU-MIMO) system is provided. The method comprises of creating a scheduling information based on MU-MIMO Scheduling of a plurality of User equipments (UES), multiplexing the plurality of UES paired based on the scheduling decisions across time, frequency and code, inputting transport blocks of each UE pushed on to a Downlink shared channel (DLSCH), performing bit processing of each of the CRC encoded UEs, inputting Code-rate (MCS) for data modulation mapping on a post bit processed data, assigning DM-RS ports to the UE based on allocated MCS and number of antenna ports from a scheduling information structure, adding, a Partial Port Occupancy information (P-Poi) for each UE along with the scheduler information structure required for demodulation at UE and enabling optimal channel estimation at UE by adding new DM-RS port combinations using reserved fields in the DCI messaging.