Comb Adaptation for Interlaced FDM DMRS Orthogonality
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Solution Overview
Problem
Current LTE systems face challenges in maintaining DMRS port orthogonality for higher-order MU-MIMO in uplink communications, especially with the deployment of massive antennas, and the application of Interleaved Frequency Division Multiplex (IFDM) DMRS is limited by sequence length and orthogonality issues in small RB allocations.
Innovation Solution
The proposed solution involves dynamically assigning different comb values for each slot in a subframe and using inter-subframe comb hopping to increase DMRS port orthogonality, combined with time domain OCCs, to support multiple UEs with partially overlapping bandwidth allocations, and introducing new DMRS sequence designs for improved orthogonality and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If IFDM DMRS is used with traditional comb structures, then frequency domain multiplexing is achieved, but orthogonality is lost in small RB allocations due to sequence length limitations
Solution Approach 1:
The patent applies dynamics by making the comb value configurable and changeable across different slots and UEs. The network can dynamically assign different comb values (0, 1, 2, or 3) to different UEs and slots, allowing the system to adapt to varying RB allocation sizes and maintain orthogonality under different conditions rather than using a fixed comb structure
Solution Approach 2:
The patent changes the parameter of comb value from a fixed traditional value to a configurable parameter that can take values 0, 1, 2, or 3. This parameter change enables the DMRS sequence to maintain adequate length and orthogonality even in small RB allocations, resolving the contradiction between maintaining orthogonality and supporting small RB allocations
2Ease of operation
If the same comb value is used for all slots, then configuration simplicity is maintained, but interference randomization is insufficient leading to poor system performance
Solution Approach 1:
The patent implements periodic action through inter-slot comb hopping where the comb value changes periodically across slots according to a hopping pattern. This periodic change randomizes interference across different slots while maintaining a relatively simple configuration framework, balancing ease of operation with improved system performance
Solution Approach 2:
The system transitions from a static comb value assignment to a dynamic comb hopping mechanism where comb values change across slots based on configurable hopping patterns. This dynamic approach improves interference randomization and system performance while maintaining configuration simplicity through standardized hopping patterns
3Reliability
If comb hopping is introduced to improve interference randomization, then system performance improves, but DMRS sequence design complexity increases
Solution Approach 1:
The patent manages sequence design complexity by systematically varying DMRS parameters including comb values, cyclic shifts, and orthogonal cover codes according to defined hopping patterns. This structured parameter variation achieves improved interference randomization while keeping the sequence design methodology systematic and manageable rather than arbitrary and complex
Data Source
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AI summary
Comb adaptation for interlaced frequency division multiplex (IFDM) demodulation reference signals (DMRS) is discussed. Transmission configuration for DMRS may be assigned to UEs with a coded combination of cyclic shift, orthogonal cover code, OCC, and a comb value. Some assigned combinations provide for a different comb value to be used for the different slots in the same subframe. Further aspects provide additional interference randomization through comb shifting, using inter-subframe hopping functions.