DM RS Resource Randomization for SU-MIMO Interference
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Solution Overview
Problem
In wireless communication systems, particularly in LTE-Advanced, the cross-correlation properties of demodulation reference signals (DM RS) for single-user multiple input multiple output (SU-MIMO) transmissions are not effectively improved by existing methods, leading to interference issues due to constant cyclic shift separation, which is not backward compatible with Release 8 and does not account for new extensions like orthogonal cover code (OCC) and interleave frequency division multiple access (IFDMA).
Innovation Solution
The method involves storing and associating user equipment (UE) reserved DM RS resources with unique spatial layers or transmit antennas in a specific pattern across consecutive time slots, using cyclic shifts, orthogonal cover codes, and transmission combs to randomize the interference, ensuring improved signal-to-interference plus noise ratio (SINR) and channel estimation performance while maintaining backward compatibility with Release 8.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cyclic shift separation is used as the primary multiplexing scheme for DM RS in SU-MIMO, then backward compatibility with Release 8 is maintained, but cross-correlation properties of different SU-MIMO DM RS are not improved
Solution Approach 1:
The patent applies dynamics by making the cyclic shift values dynamic rather than static. The cyclic shift for DM RS is determined by a formula that incorporates slot number, subframe number, and cell ID, causing the cyclic shift to change over time. This dynamic approach maintains backward compatibility with Release 8 while improving cross-correlation properties through time-varying separation.
Solution Approach 2:
The patent changes the parameters used for cyclic shift determination. Instead of using fixed cyclic shift values, the patent introduces time-varying parameters (slot number, subframe number) and cell-specific parameters (cell ID) into the cyclic shift calculation. This parameter change resolves the contradiction by maintaining compatibility while improving cross-correlation through varied separation patterns.
2Quantity of substance
If orthogonal cover code (OCC) is used as a complementary multiplexing scheme, then the number of orthogonal reference signals is increased, but device complexity increases
Solution Approach 1:
The patent segments the reference signal resources by dividing them into different cyclic shift groups. Each group can be assigned to different spatial layers or transmit antennas, effectively increasing the number of orthogonal reference signals without requiring a completely new multiplexing scheme. This segmentation approach increases capacity while maintaining manageable complexity.
Solution Approach 2:
The patent makes the cyclic shift mechanism universal by designing it to serve multiple functions: maintaining backward compatibility, improving cross-correlation properties, and supporting multiple spatial layers. This multi-functionality allows the system to increase the number of orthogonal reference signals without adding separate complex multiplexing schemes.
3Ease of operation
If cyclic shift values are kept constant for different spatial layers, then implementation is simple, but interference between DM RS resources is not randomized
Solution Approach 1:
The patent applies dynamics by making cyclic shift values time-varying rather than constant. The cyclic shift is calculated using formulas that include slot number and subframe number, causing automatic changes over time. This dynamic approach randomizes interference between DM RS resources while maintaining implementation simplicity through formula-based calculation.
Solution Approach 2:
The patent implements periodic action by using formulas that incorporate periodic elements (slot number, subframe number) into the cyclic shift calculation. This creates periodic variations in cyclic shift values that randomize interference patterns over time while keeping the implementation simple through regular mathematical operations.
Data Source
AI summary
For an integer number R (greater than one) of demodulation reference signal DM RS resources that are reserved for SU-MIMO transmissions by a UE, there is associated in a memory a) for a first transmission instance each of the R DM RS resources with a unique one of R spatial layers or R transmit antennas, and b) for a second transmission instance each of the R DM RS resources with a different unique one of the R spatial layers or transmit antennas. The first and second transmission instances (slots or sub-frames) are consecutive. A UE transmission to a network in the first slot/sub-frame comprises each DM RS resource on the respective spatial layer or transmit antenna with which they are associated for the first slot/sub-frame, and a UE transmission to the network in the first slot/sub-frame comprises each DM RS resource on the respective spatial layer or transmit antenna with which they are associated for the second slot/sub-frame.