Uplink DMRS Comb Structure for Multi-UE Multiplexing
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Solution Overview
Problem
In LTE systems, the multiplexing ratio of uplink physical resources is limited when multiple UEs share PUSCH frequency-domain resources, as traditional DMRS configurations do not provide enough orthogonal signals to efficiently multiplex uplink physical resources, especially when PUSCH resources overlap incompletely.
Innovation Solution
A method and apparatus for transmitting uplink DMRSs, where the UE determines an optimal DMRS format based on frequency-domain resources, using a comb structure with specified intervals between subcarriers, and selects appropriate cyclic shifts and orthogonal cover codes to ensure orthogonality and increase the multiplexing ratio, even when PUSCH resources overlap incompletely.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional DMRS configurations are used, then the system maintains simplicity in DMRS structure, but the multiplexing ratio of uplink physical resources is limited when multiple UEs share PUSCH frequency-domain resources
Solution Approach 1:
The patent segments the frequency-domain resources by introducing a comb structure where DMRS subcarriers are distributed at regular intervals (e.g., every 2nd or 4th subcarrier). This segmentation allows multiple UEs to be multiplexed by assigning different comb patterns (comb-0, comb-1, comb-2, comb-3) to different UEs, thereby increasing the multiplexing ratio without significantly complicating the overall DMRS configuration
Solution Approach 2:
The patent introduces an additional dimension for DMRS differentiation by combining comb-based frequency-domain spacing with cyclic shifts and orthogonal cover codes. This multi-dimensional approach (comb index + cyclic shift + OCC) enables more UEs to be multiplexed on the same time-frequency resources while maintaining orthogonality, effectively resolving the contradiction between multiplexing capacity and configuration complexity
2Quantity of substance
If DMRS configurations are increased to support more UEs, then the multiplexing ratio improves, but the complexity of DMRS configuration and management increases
Solution Approach 1:
The patent creates a universal DMRS framework where a single comb-based configuration can serve multiple UEs simultaneously. The comb structure with configurable spacing and multiple cyclic shifts provides a multi-functional solution that can adapt to different numbers of UEs and different resource allocation scenarios, increasing the quantity of orthogonal DMRS signals without proportionally increasing configuration complexity
Solution Approach 2:
The patent enables dynamic parameter changes in DMRS configuration, including comb spacing (2 or 4), comb index (0-3), and cyclic shift values. These parameter changes allow the system to flexibly adjust the number of orthogonal DMRS signals available based on the actual number of UEs requiring uplink resources, thereby increasing multiplexing capacity while keeping the configuration manageable through standardized parameter sets
3Productivity
If PUSCH frequency-domain resources are allocated to multiple UEs, then resource utilization improves, but orthogonality of DMRSs cannot be ensured when resources overlap incompletely
Solution Approach 1:
The comb structure segments the frequency spectrum into distinct patterns where DMRS subcarriers are placed at regular intervals. When multiple UEs are allocated overlapping PUSCH resources, different comb patterns (e.g., comb-0 vs comb-1) ensure that their DMRS subcarriers do not collide, maintaining orthogonality even when PUSCH resources overlap incompletely. This segmentation approach enables both high resource utilization and reliable DMRS orthogonality
Solution Approach 2:
The comb structure acts as an intermediary mechanism that mediates between multiple UEs sharing the same time-frequency resources. By introducing comb indexing as an intermediate layer of resource differentiation, the system ensures that even when PUSCH allocations overlap, the DMRS signals remain orthogonal through the comb pattern assignment, thereby maintaining reliability while enabling high resource utilization
Data Source
AI summary
A method and an apparatus for transmitting uplink demodulation reference signals (DMRSs) is provided. The method includes a user equipment (UE) determines an uplink DMRS format for demodulating a physical uplink shared channel (PUSCH) according to frequency-domain resources occupied by the PUSCH, in which the uplink DMRS format includes a comb occupied by a PUSCH DMRS sequence. The comb is subcarriers having specified intervals occupied by demodulation reference signals, and the specified intervals between the occupied subcarriers are same. For the DMRSs using the comb format, subcarriers with specific intervals are used for channel estimation, and values of the channel estimation are used for data demodulation. The UE transmits uplink information and the demodulation reference signals on physical resources using the uplink DMRS format. The present disclosure can improve the multiplexing ratio of uplink physical resources in a multi-UE scenario.