DMRS Port Configuration Using FD-OCC for MU-MIMO Capacity
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Solution Overview
Problem
Current NR specifications limit the number of orthogonal DMRS ports to 8 or 12, which restricts simultaneous transmission layers in MU-MIMO scenarios and increases DMRS overhead, leading to capacity loss.
Innovation Solution
The proposed solution involves enhanced RRC configuration and signaling to support a doubled number of orthogonal DMRS ports through longer FD-OCCs or more cyclic shifts, allowing for increased spatial multiplexing without increasing DMRS overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of orthogonal DMRS ports is increased to support more simultaneous transmission layers in MU-MIMO, then the system capacity and number of supported UEs increase, but the DMRS overhead increases leading to capacity loss
Solution Approach 1:
The patent segments the frequency domain into multiple comb offsets (e.g., 4 comb offsets) and assigns different DMRS ports to different combs. This allows multiple orthogonal DMRS ports to share the same time-frequency resources without increasing overhead, as each port uses a distinct comb pattern. The segmentation of frequency resources enables support for more simultaneous transmission layers while maintaining efficient resource utilization.
Solution Approach 2:
The patent introduces an additional dimension for DMRS port differentiation by using multiple comb offsets in the frequency domain. Instead of allocating more separate time-frequency resources for each port, the invention utilizes the comb structure dimension, where ports are distinguished by their comb offset values. This dimensional approach allows increased port capacity without proportional increase in resource overhead.
2Loss of substance
If the number of orthogonal DMRS ports is limited to 8 or 12 as per current NR specifications, then the DMRS overhead is controlled, but the number of simultaneous transmission layers in MU-MIMO is restricted
Solution Approach 1:
The patent changes the parameter of comb offset values assigned to different DMRS ports. By configuring UEs with specific comb offset values (e.g., outOfActiveCombOffset) and applying cyclic shifts based on these offsets, the system creates additional orthogonal ports. This parameter change approach allows the network to dynamically adjust the number of orthogonal ports beyond the traditional 8 or 12 limit, enabling more simultaneous transmission layers while controlling overhead through efficient parameter utilization.
3Adaptability or versatility
If longer FD-OCCs or more cyclic shifts are used to double the number of orthogonal DMRS ports, then spatial multiplexing capability increases, but the configuration complexity increases
Solution Approach 1:
The patent implements dynamic configuration of DMRS port parameters through RRC signaling and DCI indications. The network can dynamically adjust the number of orthogonal ports, comb offsets, and cyclic shift values based on current channel conditions and traffic requirements. This dynamic approach allows the system to adapt spatial multiplexing capability to actual needs rather than being statically configured, reducing unnecessary complexity while maintaining high adaptability. The gNB can activate or deactivate specific port configurations as required.
Solution Approach 2:
The patent utilizes configurable parameters such as dmrs-UplinkConfig, outOfActiveCombOffset, and cyclicShift to flexibly control DMRS port behavior. By changing these parameters, the system can adjust the number of orthogonal ports and their mapping characteristics without fundamental architectural changes. This parameter-based control simplifies configuration management compared to hard-coded structures, allowing network operators to optimize spatial multiplexing capability through parameter adjustment rather than complex structural reconfiguration.
Data Source
AI summary
According to some embodiments, a method performed by a wireless device comprises obtaining an indication that a demodulation reference signal (DMRS) is based on frequency domain coding using a frequency domain orthogonal cover code (FD-OCC) of length greater than two and transmitting or receiving a number of DMRS based on the frequency domain coding.