Asymmetric Filtering for Band-Limited FDM PAPR Reduction

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Solution Overview

Problem

Current narrowband IoT communication technologies face limitations in power efficiency due to high Peak-to-Average Power Ratio (PAPR), leading to reduced coverage and throughput, especially when using multiple subcarriers, as they require significant power amplifier backoff.

Innovation Solution

The implementation of a band-limited frequency division multiplexing scheme with asymmetric filtering and cyclic extension in the frequency domain, which reduces PAPR and allows for efficient power usage without compromising spectral efficiency, enabling multi-user detection and MIMO capabilities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If multiple subcarriers are used for NB-IoT transmission, then throughput is improved, but PAPR increases leading to reduced coverage

Engineering Contradiction:

ImprovethroughputVSAvoidcoverage

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The frequency band is divided into multiple sub-bands, each handled by a separate filter with optimized characteristics. This segmentation allows each filter to operate independently with tailored parameters, reducing overall PAPR while maintaining multi-subcarrier throughput capability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different filters are designed with local quality variations - edge filters have asymmetric characteristics while central filters have symmetric characteristics. This localized optimization reduces PAPR at critical band edges while maintaining performance in central regions, enabling higher throughput without sacrificing coverage

Inventive Principle:

Principle #3Local quality

2Reliability

If power amplifier backoff is increased to reduce PAPR, then coverage is improved, but transmission power is reduced

Engineering Contradiction:

ImprovecoverageVSAvoidtransmission power

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The filter parameters (particularly Q-factor and asymmetry coefficients) are optimized to achieve the minimum required PAPR reduction. This parameter tuning allows the system to maintain adequate transmission power while achieving sufficient PAPR control for improved coverage

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If symmetric filtering is applied to all sub-bands, then implementation is simplified, but PAPR reduction is suboptimal at band edges

Engineering Contradiction:

Improvefiltering implementationVSAvoidPAPR reduction effectiveness

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Asymmetric filtering is applied specifically at band edges where PAPR reduction is most critical, while symmetric filtering is used for central sub-bands. This selective asymmetry optimizes PAPR reduction effectiveness at problematic edge regions without unnecessarily complicating the overall filtering implementation

Inventive Principle:

Principle #4Asymmetry

Data Source

PatentEP3193481B1Asymmetric filtering at edges of band consisting of overlapped sub-bands

Publication Date: 2020.03.11 HUAWEI TECH CO LTD

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AI summary

An apparatus for band-limited frequency division multiplexing for uplink transmission to a base station or access point, particularly from an IoT device, comprises a signal modulator to transmit a signal over a set of contiguous equally spaced frequency sub-carriers ranging from a lowest frequency sub-carrier via intermediate sub-carriers to a highest frequency sub-carrier. The signal modulator contains a filter to apply asymmetric filtering over the range of the frequency sub-carriers, thereby to reduce a peak-to-average power ratio of the transmitted signal.