MIMO Precoding PAPR Reduction via Sparse Matrix Updates

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Solution Overview

Problem

Orthogonal frequency division multiple access (OFDMA) in wireless communication networks faces high peak-to-average power ratio (PAPR) issues due to random subcarrier combinations, especially in multi-user and multiple-input, multiple-output (MIMO) scenarios, leading to poor power efficiency and increased costs, particularly in dense LTE deployments where power constraints are significant.

Innovation Solution

The solution involves selecting a subset of transmitting terminals to handle high-PAPR signals differently, with PAPR-sensitive terminals optimized for low PAPR constraints, using pre-coding, selective mapping, and PAPR-reduction symbol injection, while employing sparse matrices for partial updates to reduce computational complexity and latency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If OFDMA is used for flexible resource allocation and scheduling, then resource allocation flexibility is improved, but peak-to-average power ratio increases

Engineering Contradiction:

Improveresource allocation flexibilityVSAvoidpeak-to-average power ratio

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The patent applies Selective Mapping (SLM) which performs preliminary action by generating multiple candidate signal versions before transmission and selecting the one with lowest PAPR. This pre-processing step modifies the time-domain signal to reduce peak power while maintaining the flexible resource allocation benefits of OFDMA.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes signal parameters by applying different phase rotation sequences to generate candidate signals. By varying the phase parameters of subcarriers and selecting the optimal configuration, the system reduces PAPR while preserving resource allocation flexibility.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If MIMO precoding is applied, then system performance is improved, but PAPR performance deteriorates

Engineering Contradiction:

Improvesystem performanceVSAvoidPAPR performance

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent integrates SLM with MIMO precoding by performing preliminary signal generation and PAPR evaluation on precoded signals. The system generates multiple candidate precoded signals with different phase rotations, evaluates their PAPR characteristics, and selects the optimal candidate before transmission.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent merges SLM technique with MIMO precoding operations. By combining these two techniques, the system achieves both the spatial diversity gain from MIMO precoding and the PAPR reduction benefit from SLM, resolving the contradiction between system performance and PAPR performance.

Inventive Principle:

Principle #5Merging (Combining)

3Use of energy by moving object

If PAPR reduction techniques are applied, then power efficiency is improved, but computational complexity increases

Engineering Contradiction:

Improvepower efficiencyVSAvoidcomputational complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The patent implements partial SLM by generating and evaluating only a limited number of candidate signals (e.g., using a restricted set of phase rotation sequences) rather than exhaustively searching all possible candidates. This partial action achieves acceptable PAPR reduction while significantly reducing computational complexity compared to full SLM.

Inventive Principle:

Principle #16Partial or excessive action

4Use of energy by moving object

If PAPR reduction techniques are applied, then power efficiency is improved, but processing latency increases

Engineering Contradiction:

Improvepower efficiencyVSAvoidprocessing latency

Core Design Contradiction:

Use of energy by moving objectVSLoss of time

Solution Approach 1:

The patent uses partial SLM with a limited candidate set that can be evaluated quickly, reducing the number of IFFT operations required. This approach achieves meaningful PAPR reduction while minimizing the time penalty compared to exhaustive search methods.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS11894965B2Efficient synthesis and analysis of OFDM and MIMO-OFDM signals

Publication Date: 2024.02.06 TYBALT LLC

AI summary

A Multiple Input Multiple Output (MIMO) system in a radio access network (RAN) comprises a virtualized baseband unit, an antenna array; and a fronthaul network that connects the virtualized baseband unit to the antenna array. For a first set of antennas in the antenna array, the virtualized baseband unit generates a first MIMO matrix from channel state information (CSI); computes a sparse update matrix corresponding to an update to the first set of antennas; sums the sparse update matrix with the first MIMO matrix to produce a second MIMO matrix corresponding to a second set of antennas in the antenna array; determines which of the MIMO matrices results in a better CSI, MIMO condition number, peak-to-average-power ratio, or quality metric of spatial subchannels; and based on the determination, selects the first set of antennas or the second set of antennas to transmit or receive signals in the RAN.