Cyclic Shift Signaling for SU-MIMO Reference Signals
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Solution Overview
Problem
The existing LTE standard is limited in signaling cyclic shifts for reference signals, allowing only eight out of twelve possible cyclic shifts to be signaled, which is insufficient for Single User Spatial Multiplexing (SU-MIMO) schemes that require multiple reference signals, leading to increased overhead and limited data throughput.
Innovation Solution
A method for generating reference signals in SU-MIMO transmission schemes that involves selecting a cyclic shift set based on a received indicator, using at least two parameters to generate orthogonal reference signals for multiple layers, allowing for more flexible and efficient signaling of cyclic shifts, enabling the use of additional cyclic shifts beyond the limitations of the conventional LTE standard.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If a 3-bit field is used to signal the cyclic shift parameter, then the signaling overhead is reduced, but only eight out of twelve possible cyclic shifts can be signaled
Solution Approach 1:
The cyclic shift parameter signaling is segmented into two parts: a 3-bit field indicating one of four groups, and a group-specific offset value. This segmentation allows the limited 3-bit field to efficiently select a group, while each group contains multiple possible offset values, collectively enabling all twelve cyclic shifts to be signaled without increasing the basic field size.
Solution Approach 2:
The solution adds a new dimension to the cyclic shift signaling by introducing group-specific offset values. Instead of using a single flat 3-bit field to directly indicate one of eight cyclic shifts, the system creates a two-dimensional structure where the 3-bit field selects a group dimension, and within each group, additional offset values provide the second dimension, enabling access to all twelve cyclic shifts.
2Device complexity
If only eight cyclic shifts are signaled, then the signaling complexity is reduced, but Single User Spatial Multiplexing requires more reference signals
Solution Approach 1:
The reference signal generation is segmented into group selection (via 3-bit field) and offset selection (via group-specific offsets). This allows the system to maintain simple group-level signaling while providing multiple reference signal options within each group, satisfying SU-MIMO requirements without proportionally increasing overall signaling complexity.
Solution Approach 2:
The group-specific offset mechanism serves multiple functions: it enables all twelve cyclic shifts to be signaled, supports SU-MIMO spatial multiplexing schemes, and maintains compatibility with existing MU-MIMO operations. This multi-functional approach allows the same signaling structure to serve both legacy and advanced transmission modes.
3Productivity
If all twelve cyclic shifts are enabled, then data throughput is enhanced, but signaling overhead increases
Solution Approach 1:
The signaling overhead is segmented such that the constant 3-bit field handles group selection efficiently, while variable group-specific offsets are only processed when needed. This segmentation allows the system to signal all twelve cyclic shifts without requiring a full increase in the basic signaling field size, thus enhancing data throughput while controlling signaling overhead.
Solution Approach 2:
The system changes the parameter structure from a single cyclic shift indicator to a two-parameter structure (group index + group-specific offset). This parameter change allows the effective number of cyclic shifts to increase from eight to twelve while the base signaling parameter (3-bit field) remains unchanged, thereby increasing data throughput without proportional increase in signaling overhead.
Data Source
AI summary
The present disclosure relates to signalling of reference signals for Multi Input Multi Output (MIMO) transmission schemes. A method embodiment for generating reference signals for use between a mobile terminal 10 and an access node 20 in a cellular communication network 100 comprises receiving, by the mobile terminal 10, a cyclic shift set indicator; selecting, from a group of cyclic shift sets, a cyclic shift set based on the received cyclic shift set indicator, each cyclic shift set comprising at least two parameters each indicating a cyclic shift; and generating, based on at least two parameters of the selected cyclic shift set, at least two orthogonal reference signals for at least two layers of a Single User Spatial Multiplexing transmission scheme to be simultaneously transmitted. A further method embodiment comprises selecting, from a plurality of groups of cyclic shift sets, a group of cyclic shift sets based on at least one of a transmission rank, being the number of layers to be simultaneously transmitted, and a number of configured antennas of the mobile terminal 10.