Linear Precoding with DMRS Coefficients for Multi-User Interference

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Solution Overview

Problem

In wireless communications, nonlinear precoding techniques like Tomlinson-Harashima Precoding (THP) can lead to destructive interference and decreased signal power for user equipments (UEs) under low signal-to-noise ratio (SNR) conditions, especially when shared channels are used for multiple UEs, resulting in increased interference and noise.

Innovation Solution

A base station employs an enhanced precoding scheme by associating multiple antenna elements with coherent phase shifts for each port, transmitting linear combinations of data sets to UEs, and providing combination coefficients via demodulation reference signals to enable constructive interference and improved channel estimation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If nonlinear precoding techniques like Tomlinson-Harashima Precoding (THP) are used for multi-user shared channels, then spectral efficiency and multi-user support are improved, but destructive interference and decreased signal power occur under low SNR conditions

Engineering Contradiction:

Improvespectral efficiencyVSAvoidsignal power

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the precoding approach from nonlinear (THP) to linear precoding, fundamentally altering the parameter space of signal processing. This parameter change eliminates the destructive interference characteristic of nonlinear precoding while maintaining multi-user support through linear combinations of data streams, thereby resolving the contradiction between spectral efficiency and signal power reliability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of using nonlinear precoding to cancel interference (the conventional THP approach), the patent inverts the approach by using linear precoding with explicit combination coefficients that are communicated to UEs. This inversion allows the system to achieve similar multi-user separation goals without the harmful destructive interference, improving both signal power and spectral efficiency

Inventive Principle:

Principle #13The other way round (Inversion)

2Productivity

If shared channels are used to serve multiple UEs, then resource utilization is improved, but interference between UEs increases

Engineering Contradiction:

Improveresource utilizationVSAvoidinterference

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces combination coefficients as an intermediary element that mediates between the shared channel transmissions and individual UE decoding. These coefficients, communicated via DMRS, enable each UE to properly separate and decode its own data from the linear combinations transmitted on shared channels, thereby reducing interference while maintaining resource utilization efficiency

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements a feedback mechanism where the base station transmits combination coefficients to UEs via demodulation reference signals. This feedback allows UEs to adjust their decoding processes accordingly, enabling them to correctly interpret the linear combinations and eliminate interference, thus resolving the contradiction between shared channel resource utilization and inter-user interference

Inventive Principle:

Principle #23Feedback

3Reliability

If linear precoding vectors with coherent phase shifts are applied to multiple ports, then constructive interference and received signal power are improved, but device complexity increases

Engineering Contradiction:

Improvereceived signal powerVSAvoidprecoding configuration

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the precoding operation into distinct linear precoding vectors for different ports, each with well-defined phase relationships. This segmentation allows for manageable complexity in implementing coherent phase shifts while achieving constructive interference, as each segment can be independently configured and communicated to UEs through separate DMRS signals

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11689258B2Channel estimation and demodulation procedure for non-linear multi-user multiple-input multiple-output precoding

Publication Date: 2023.06.27 QUALCOMM INC

AI summary

Methods, systems, and devices for wireless communications are described. A base station may associate a first and second port with a set of antenna elements based on a first and second linear precoding vector. The base station may generate coefficients indicating a first combination and a second combination of a first data set for a first user equipment (UE) and a second data set for a second UE. The base station may apply the first and second linear precoding vectors to the first and second combinations, respectively, transmit a first demodulation reference signal (DMRS) and a second DMRS using a first comb corresponding to the first and second ports, and transmit at least a third DMRS indicating the coefficients using a second comb. The UEs may extract data from the precoded combinations by applying the coefficients and estimating channels associated with the first and second DMRS.