MIMO-OFDM Null-Space Projection for Low-PAPR Transmission

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Solution Overview

Problem

Existing Convex Reduction of Amplitude (CRAM) schemes for MIMO systems suffer from degraded performance due to imperfect channel knowledge, especially in codebook-based systems, leading to increased Peak-to-Average Power Ratio (PAPR) and throughput impact, particularly with fast-moving UEs and channel aging.

Innovation Solution

A CRAM-based Crest Factor Reduction (CFR) scheme that uses projection matrices based on static or semi-static information, such as antenna array null space, physical deployment of cells, and historical channel information, to project clipping energy into a null space, reducing PAPR while minimizing downlink throughput impact and intercell interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If CRAM-based PAPR reduction schemes use dynamic channel knowledge for projection matrices, then PAPR reduction effectiveness is improved, but processing complexity and channel knowledge requirements increase

Engineering Contradiction:

ImprovePAPR reduction effectivenessVSAvoidprocessing complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent pre-computes and stores array null space projection matrices based on static antenna array characteristics before actual transmission. This preliminary action eliminates the need for real-time computation of projection matrices during operation, significantly reducing processing complexity while maintaining PAPR reduction effectiveness through the use of pre-established null space projections.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent extracts and utilizes only the essential geometric characteristics of the antenna array (array null spaces) to construct projection matrices, separating this static structural information from dynamic channel knowledge. This extraction allows the system to achieve PAPR reduction using only array geometry without requiring complex real-time channel state information.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If CRAM schemes use channel-based projection matrices, then clipping energy is hidden in channel null space, but performance degrades with imperfect channel knowledge

Engineering Contradiction:

Improveperformance reliabilityVSAvoidchannel knowledge accuracy

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

Instead of projecting clipping energy into channel null spaces as in conventional CRAM schemes, the patent inverts the approach by projecting into array null spaces based on antenna array geometry. This inversion eliminates dependency on channel knowledge accuracy while maintaining the fundamental CRAM mechanism of hiding clipping energy in null spaces, thereby improving reliability under imperfect channel conditions.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent introduces array null spaces as an intermediary between the transmitter and channel conditions. By using array geometry-derived null spaces as a mediator, the system achieves PAPR reduction without direct reliance on channel state information, buffering against the effects of imperfect channel knowledge.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If projection matrices are updated frequently for accurate channel tracking, then PAPR reduction accuracy is improved, but power consumption and processing load increase

Engineering Contradiction:

ImprovePAPR reduction accuracyVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent performs the computationally intensive task of computing and storing array null space projection matrices in advance, based on static antenna array characteristics. This preliminary computation eliminates the need for frequent updates during operation, maintaining PAPR reduction accuracy while dramatically reducing power consumption and processing load during actual transmission.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent creates a distinction between static array geometry (used for pre-computing projection matrices) and dynamic transmission conditions. By fixing the projection matrices based on static array characteristics rather than dynamically updating them with channel conditions, the system achieves energy efficiency while maintaining sufficient accuracy through the time-invariant nature of array null spaces.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS12634186B2Systems and methods related to a null-space for a MIMO transmitter system

Publication Date: 2026.05.19 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Systems and methods are disclosed herein for a Convex Reduction of Amplitude (CRAM) based processing scheme for a Multiple Input Multiple Output (MIMO) Orthogonal Division Multiplexing (OFDM) transmitter system. In one embodiment, a method performed by a processing system for a MIMO OFDM transmitter system comprises precoding frequency-domain input signals to provide frequency-domain precoded signals for multiple subcarriers. The method further comprises processing the frequency-domain precoded signals in accordance with a CRAM-based processing scheme to provide time-domain precoded signals for respective transmit branches of the MIMO OFDM transmitter system. The CRAM-based processing scheme uses projection matrices for the subcarriers, respectively, to project clipping energy into a null space of the MIMO OFDM transmitter system. Further, the projection matrices are a function of static or semi-static information that defines the null space of the MIMO OFDM transmitter system.