Uplink Reference Signal Precoding in MIMO Systems

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Solution Overview

Problem

In MIMO communication systems, frequent transmission of sounding reference signals for uplink channel state measurement leads to resource reservation challenges and increased interference, especially with a large number of users and antennas, and reciprocity-based precoding fails to estimate channel quality and interference state at user equipment.

Innovation Solution

Implementing a base station and user equipment configuration that allows for uplink reference signal transmission in an uplink shared channel during an uplink subframe, enabling accurate uplink channel estimation and downlink precoding based on uplink channel state, while also allowing user equipment to feed back channel quality information to the base station.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If sounding reference signals are transmitted frequently for uplink channel state measurement, then channel state estimation accuracy is improved, but resource reservation becomes difficult and interference increases

Engineering Contradiction:

Improvechannel state estimation accuracyVSAvoidresource consumption

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent makes the uplink shared channel serve dual purposes: transmitting user data and transmitting reference signals for channel state measurement. By allowing reference signals to be embedded within the uplink shared channel resources, the system achieves channel estimation without requiring separate dedicated reference signal resources, thus resolving the resource consumption issue while maintaining measurement accuracy

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent combines the data transmission function and reference signal transmission function into a single uplink shared channel. Instead of separating these functions into different channels or resource blocks, the reference signals are multiplexed within the uplink shared channel, merging resource usage and eliminating the need for additional resource reservation

Inventive Principle:

Principle #5Merging (Combining)

2Productivity

If the number of users and antennas increases for sophisticated MIMO techniques, then communication capacity is improved, but resource reservation for sounding reference signals becomes more difficult

Engineering Contradiction:

Improvecommunication capacityVSAvoidresource consumption

Core Design Contradiction:

ProductivityVSQuantity of substance

Solution Approach 1:

The uplink shared channel is designed to serve multiple users and support multiple antenna ports simultaneously through multi-user MIMO. The same uplink shared channel resources are shared among multiple users and antenna configurations, allowing the system to scale communication capacity without proportionally increasing reference signal resource consumption

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent changes the parameters of the uplink shared channel to accommodate reference signal transmission. By adjusting the resource allocation, modulation scheme, and coding parameters of the uplink shared channel, the system can efficiently transmit both data and reference signals, supporting increased numbers of users and antennas without linearly increasing resource consumption

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If reciprocity based precoding is used to avoid feedback channel resources, then resource reservation is improved, but channel quality and interference state estimation at user equipment cannot be obtained

Engineering Contradiction:

Improveresource consumptionVSAvoidchannel quality information

Core Design Contradiction:

Quantity of substanceVSLoss of information

Solution Approach 1:

The patent implements a feedback mechanism where user equipment measures the downlink channel quality and interference state using received reference signals, then feeds back this channel state information to the base station. This feedback enables the base station to obtain accurate channel quality and interference state information at user equipment, complementing the reciprocity-based precoding approach and resolving the information loss issue

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces channel state information as an intermediary that bridges the gap between reciprocity-based precoding limitations and the need for accurate channel quality estimation. The channel state information, derived from uplink measurements and fed back to the base station, serves as a mediator that provides the missing channel quality and interference state data without requiring additional dedicated feedback channel resources

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11212794B2Base station and user equipment

Publication Date: 2021.12.28 NTT DOCOMO INC

AI summary

In one aspect, a user equipment is disclosed including a control unit configured to precode an uplink reference signal based on a downlink reference signal, and a transmission unit configured to transmit the precoded uplink reference signal. In another aspect, a transmission method is disclosed including precoding an uplink reference signal based on a downlink reference signal, and transmitting the precoded uplink reference signal.