Cover Code Generation for Orthogonal Reference Signals
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Solution Overview
Problem
In wireless communication systems, particularly in 5G NR, the interference between superimposed reference signals on the same subcarrier leads to error floors in channel estimation, hindering the decoding performance due to incomplete reduction of interference by conventional cover codes.
Innovation Solution
A wireless transmitting device determines a first vector set spanning a non-full-rank subspace corresponding to a subcarrier's channel frequency response, calculates a second vector set through dot-product operations, and derives a cover code from the null space of the second vector subspace to ensure orthogonality of reference signals, allowing effective distinction by the receiving device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple reference signals are distributed to the same subcarrier in a superimposed manner to increase communication capacity, then communication capacity is improved, but interference between reference signals occurs causing the receiving device to cannot distinguish these reference signals
Solution Approach 1:
The patent introduces cover codes as intermediary elements that are multiplied with reference signals before transmission. These cover codes act as mediators that enable the receiving device to distinguish between superimposed reference signals by creating orthogonal relationships, thus resolving the interference problem while maintaining multiple reference signals on the same subcarrier
2Object-affected harmful factors
If conventional cover codes are used to reduce interference between superimposed reference signals, then some interference reduction is achieved, but error floors occur in channel estimation due to incomplete interference reduction
Solution Approach 1:
The patent changes the parameters of cover codes from conventional alternatives to specific sequences designed based on channel frequency response characteristics. By modifying the cover code sequence parameters to match the actual channel conditions, the system achieves complete interference reduction without error floors, improving channel estimation accuracy
3Device complexity
If alternative sequences are used as cover codes in 5G NR, then a simple cover code structure is provided, but such sequences cannot completely reduce interference between multiple superimposed reference signals under wireless channel influence
Solution Approach 1:
The patent performs preliminary actions by determining channel frequency responses before transmitting reference signals, and based on these responses, generates appropriate cover codes in advance. This preliminary characterization of the channel allows the system to select or generate cover codes that will effectively eliminate interference for the specific channel conditions, rather than using fixed alternative sequences
Data Source
AI summary
A method for transmitting reference signals includes: determining, by a wireless transmitting device, a first vector set used for calculating a first vector subspace that includes a channel frequency response vector corresponding to a subcarrier; calculating, by the wireless transmitting device, a second vector set including several second vectors derived from performing dot product operations to each vector in the first vector set with a conjugate vector of each vector in the first vector set; calculating, by the wireless transmitting device, a null space of a second vector subspace spanned by the second vector set and determining, by the wireless transmitting device, a cover code from the null space; and transmitting a first reference signal and a second reference signal which is a dot product of the first reference signal and the cover code on the subcarrier from the wireless transmitting device to a wireless receiving device.