Uplink Code Sequence Selection for MTC Interference Reduction
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Solution Overview
Problem
In LTE-A communication systems, sharing a multiple-subframe spreading code between a base station and a terminal is challenging without increasing overhead, particularly in MTC coverage enhancement modes where repetition transmission is used, leading to reduced spectral efficiency and increased interference.
Innovation Solution
A communication method and device that utilize existing DCI fields to indicate a multiple-subframe spreading code by reusing the fields for cyclic shift and orthogonal code used for DMRS, allowing the base station to share the code with the terminal without adding new overhead, ensuring flexible uplink scheduling and reducing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a multiple-subframe spreading code is shared between base station and terminal, then spectral efficiency is maintained and interference is reduced, but overhead increases due to additional signaling requirements
Solution Approach 1:
The patent applies universality by making the existing DCI fields (cyclic shift field and orthogonal code field) serve dual purposes: their traditional function for DMRS configuration and the additional function of indicating the multiple-subframe spreading code. This allows the spreading code to be signaled without requiring new dedicated fields, thus maintaining spectral efficiency while avoiding overhead increase.
Solution Approach 2:
The patent merges the indication of the multiple-subframe spreading code with the existing DCI fields for cyclic shift and orthogonal code. By combining multiple functions into existing signaling structures, the patent achieves code sharing between base station and terminal without adding separate signaling overhead.
2Reliability
If repetition transmission is used in MTC coverage enhancement modes, then coverage is improved, but spectral efficiency is reduced and interference increases
Solution Approach 1:
The patent segments the uplink transmission across multiple subframes using repetition, where each subframe contains a portion of the repeated transmission. By applying code spreading across these segmented subframes, the patent maintains coverage enhancement while managing spectral efficiency through orthogonal code multiplication.
Solution Approach 2:
The patent changes the parameter of the uplink signal by multiplying it with orthogonal codes across multiple subframes. This parameter change (code multiplication) enables the system to maintain reliability through repetition while controlling spectral efficiency and interference through orthogonal code properties.
3Object-generated harmful factors
If different cyclic shifts and orthogonal codes are applied to DMRS among terminals, then interference between DMRS is reduced, but device complexity increases
Solution Approach 1:
The patent applies universality by using the same DCI fields (cyclic shift field and orthogonal code field) to serve both DMRS configuration and multiple-subframe spreading code indication. This unified approach reduces device complexity by eliminating the need for separate code management mechanisms while still achieving interference reduction through orthogonal code application.
Data Source
AI summary
A base station selects, from among a plurality of code sequences orthogonal to one another, one code sequence by which an uplink signal including a demodulation reference signal repeated in a plurality of subframes is multiplied and transmits, to a terminal for which transmission of the repeated uplink signal is configured, information indicating the selected code sequence by using a field for indicating a cyclic shift and an orthogonal sequence used for the demodulation reference signal. A terminal receives information indicating one of a plurality of code sequences orthogonal to one another using a field for indicating a cyclic shift and an orthogonal sequence used for a demodulation reference signal and multiplies an uplink signal including the demodulation reference signal repeated in a plurality of subframes by the code sequence indicated by the information.