Dynamic Sequence Offset for LTE-A Reference Signal Orthogonality
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Solution Overview
Problem
In LTE-A CoMP scenarios, especially in HetNet environments, the limited number of usable signal sequences for UEs in one cell leads to interference and deterioration of channel estimation accuracy for DMRS and SRS, as different UEs use different sequence groups, causing orthogonality issues and interference.
Innovation Solution
A terminal apparatus and base station system that dynamically allocates sequence numbers with varying offsets based on a common hopping pattern within one cell cluster but different across clusters, ensuring non-overlapping and continuously varying sequence numbers to enhance the number of usable signal sequences without increasing interference-related accuracy deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If different sequence groups are allocated to different UEs in one cell, then orthogonality between UEs is improved, but the number of usable signal sequences is limited and interference increases
Solution Approach 1:
The patent applies dynamics by making the sequence group allocation dynamic rather than static. The determining section selects sequence groups based on time-varying parameters including subframe number, slot number, and UE-specific parameters. This dynamic allocation allows the system to provide different sequence groups to different UEs at different times, effectively increasing the number of usable signal sequences while maintaining orthogonality and reducing interference.
Solution Approach 2:
The patent introduces additional dimensions for sequence group differentiation by incorporating multiple parameters: subframe number, slot number, UE identifier, and cell identifier. This multi-dimensional approach allows the system to generate a much larger space of distinguishable sequence groups from a limited base set, effectively solving the contradiction between limited sequence availability and the need for multiple orthogonal sequences.
2Object-affected harmful factors
If sequence group hopping is implemented, then interference uniformity is improved, but sequence number overlap between cells increases causing accuracy deterioration
Solution Approach 1:
The patent applies preliminary anti-action by having the determining section proactively check whether the selected sequence group number overlaps with sequence group numbers used by other cells before finalizing the allocation. This preemptive interference checking and avoidance mechanism prevents accuracy deterioration while maintaining the benefits of sequence group hopping for interference uniformity.
Solution Approach 2:
The system implements feedback by monitoring sequence group number overlaps between cells and adjusting allocations accordingly. The determining section uses information about other cells' sequence group usage to make informed allocation decisions, ensuring that sequence groups are assigned in a way that avoids overlap and maintains channel estimation accuracy while still achieving interference uniformity through hopping.
3Measurement precision
If cell-specific sequence offsets are allocated, then orthogonality between cells is improved, but the number of distinguishable sequence groups decreases
Solution Approach 1:
The patent compensates for the reduction in distinguishable sequence groups caused by cell-specific offsets by introducing additional time-varying dimensions. By incorporating subframe number and slot number into the sequence group determination, the system creates many more distinguishable sequence groups over time, effectively offsetting the limitation imposed by cell-specific sequence offsets while maintaining inter-cell orthogonality.
Solution Approach 2:
The system uses dynamic time-varying parameters (subframe number, slot number) to generate additional differentiation between sequence groups. This dynamic approach allows the system to maintain inter-cell orthogonality through cell-specific offsets while simultaneously providing a large number of distinguishable sequence groups through time-varying allocations.
Data Source
AI summary
A terminal device is equipped with: a sequence determination unit that determines a sequence number with a different pattern than the assignment pattern for the sequence number assigned to the cell in which the host device resides; a reference signal generation unit that generates a reference signal for a sequence group corresponding to the sequence number that has been determined; and a wireless transmission unit that transmits the reference signal that has been generated to a base station. The sequence determination unit employs a configuration whereby, with the sequence number assigned to the cell in which the host device resides as a cell-specific sequence number, a dynamic offset which periodically changes over time and for which the same value is not consecutive is added to the cell-specific sequence number, thereby determining a sequence number which never overlaps with the cell-specific sequence number.