Non-Orthogonal DMRS Sequence Grouping for Uplink Collision Reduction
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Solution Overview
Problem
Current wireless communication systems face challenges in supporting a large number of user equipments (UEs) due to the requirement for a large number of demodulation reference signal (DMRS) sequences, which is not feasible with limited time and frequency resources, especially in non-orthogonal multiple access (NOMA) systems.
Innovation Solution
The proposed solution involves grouping DMRS sequences based on cross correlation, cubic metric, or peak-to-average power ratio (PAPR), allowing for joint channel estimation and power control to minimize traffic collisions and enhance system capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large number of DMRS sequences are used to support a large number of UEs, then the system capacity increases, but the complexity of sequence management and resource allocation increases significantly
Solution Approach 1:
The patent segments the large set of DMRS sequences into multiple groups based on cross-correlation properties. Each group contains sequences with similar characteristics, allowing the system to manage sequences in smaller, organized subsets rather than handling all sequences individually, thereby reducing management complexity while maintaining support for many UEs
Solution Approach 2:
The patent changes the parameter of sequence selection by grouping sequences according to their cross-correlation values, cubic metric, or PAPR characteristics. This parameter-based grouping allows efficient identification and selection of appropriate sequences for different UE scenarios, reducing the computational burden of sequence management
2Reliability
If orthogonal DMRS sequences are used for multiple UEs, then interference between UEs is minimized, but the number of available sequences is limited by time and frequency resources
Solution Approach 1:
The patent introduces a new dimension for sequence differentiation by utilizing non-orthogonal sequences with controlled cross-correlation properties. Instead of relying solely on orthogonal sequences in the traditional time-frequency domain, the system exploits the cross-correlation domain as an additional dimension, enabling more sequences to be supported within the same resource constraints
Solution Approach 2:
The patent creates composite sequence structures by combining base sequences with different cyclic shifts and grouping them based on multiple criteria (cross-correlation, cubic metric, PAPR). This composite approach allows the system to generate a larger effective number of sequences from a limited set of base sequences, overcoming the resource limitations
3Productivity
If non-orthogonal DMRS sequences are used to increase the number of supported UEs, then the system capacity increases, but the channel estimation accuracy deteriorates due to higher cross-correlation
Solution Approach 1:
The patent applies local quality by ensuring that within each group of non-orthogonal sequences, the cross-correlation properties are controlled and optimized. By grouping sequences with similar cross-correlation characteristics, the system maintains acceptable channel estimation accuracy locally within each group while allowing global system capacity to increase through the use of multiple groups
4Reliability
If DMRS sequences are grouped based on cross-correlation, then the probability of traffic collisions is reduced, but the computational complexity of sequence grouping increases
Solution Approach 1:
The patent performs preliminary action by pre-grouping DMRS sequences based on their cross-correlation properties, cubic metric, or PAPR characteristics before actual UE transmission. This pre-computation and organization of sequences into groups reduces the real-time computational burden during operation and minimizes traffic collisions by ensuring sequences are already optimized for their intended usage scenarios
Data Source
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AI summary
Aspects of the present disclosure provide techniques for grouping demodulation reference signal (DMRS) sequences for uplink transmission without grant based on one or more of cross correlation of sequences, the cubic metric or peak-to-average power ratio (PAPR). In accordance with this technique, the power control for transmissions of DMRS can also be exploited to enhance sequence grouping. Features of the present disclosure may prepare a composite sequence that is generated by concatenating two base sequences. In this instance, the base station may provide UEs with a pool of base sequences. For transmission of DMRS, the UEs may select two base sequences that may be transmitted in two consecutive slots or two DMRS symbols in a slot. By allowing the UE to select two base sequences, the network may reduce the probability of a collision that may occur when two UEs select the same base sequence.