OFDM Preamble Quadratic Modulation for Low PAPR

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Solution Overview

Problem

Conventional OFDM systems face challenges in reducing Peak-to-Average Power Ratio (PAPR) effectively, especially when the number of subcarriers changes, leading to increased Bit Error Rate (BER) and Adjacent Channel Interference (ACI), and require complex preprocessing techniques that are inefficient or degrade performance with higher order modulation schemes.

Innovation Solution

A novel low PAPR preamble with a typical PAPR of 2.6 dB is introduced, which is independent of the number of subcarriers, utilizing quadratic modulation and evenly spaced subcarriers for channel sounding, and is easily implemented using IFFT/FFT circuits, improving signal-to-noise ratio (SNR) and reducing processing power.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional OFDM systems use multiple subcarriers for transmission, then data rate and spectral efficiency are improved, but Peak-to-Average Power Ratio (PAPR) increases leading to clipping and increased Bit Error Rate (BER)

Engineering Contradiction:

Improvedata rateVSAvoidBit Error Rate

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies quadratic phase rotation to the subcarriers, transforming the phase parameters of the OFDM signal. This parameter change in the frequency domain corresponds to time-domain signal shaping that reduces PAPR while maintaining data transmission integrity, thereby resolving the contradiction between high data rate and low BER

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If Power Amplifier operates at high power to improve transmit efficiency, then power consumption is reduced, but signal clipping occurs increasing in-band noise and out-of-band noise

Engineering Contradiction:

Improvepower efficiencyVSAvoidclipping noise

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

The patent applies quadratic phase rotation preprocessing to the OFDM signal before amplification. This preliminary action shapes the time-domain signal envelope to have reduced peak values, allowing the Power Amplifier to operate more efficiently without causing signal clipping, thus reducing harmful noise while maintaining power efficiency

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If conventional preambles are designed for fixed number of subcarriers, then channel estimation accuracy is improved, but system adaptability to varying subcarrier configurations deteriorates

Engineering Contradiction:

Improvechannel estimation accuracyVSAvoidsubcarrier configuration flexibility

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent designs a universal preamble structure with quadratic phase rotation that functions effectively across different subcarrier configurations. The quadratic phase pattern maintains consistent correlation properties regardless of the number of subcarriers, enabling the same preamble design to achieve accurate channel estimation in various system configurations

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Device complexity

If nonlinear signal distortion techniques are used to reduce PAPR, then implementation complexity is reduced, but performance degrades with higher order modulation schemes

Engineering Contradiction:

ImprovePAPR reduction complexityVSAvoidmodulation performance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent replaces nonlinear signal distortion techniques with quadratic phase rotation in the frequency domain. This substitution maintains implementation simplicity while avoiding the performance degradation associated with nonlinear distortion methods, particularly for higher order modulation schemes where Euclidean distance between symbols is smaller

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS8189697B2Orthogonal frequency division multiplexing (OFDM) communications device and method that incorporates low PAPR preamble and receiver channel estimate circuit

Publication Date: 2012.05.29 SMARTSKY NETWORKS LLC

AI summary

A communications device includes a demapping and demodulation circuit that demaps and demodulates an OFDM communications signal as modulated subcarriers carrying communications data and modulated subcarriers carrying a training sequence forming a preamble that includes a long sync sequence for channel and frequency offset estimation having a extended guard interval (GI). The OFDM subcarriers carrying the training sequence have a quadratic modulation to produce a low peak-to-average power (PAPR) preamble with PAPR of approximately 2.6 decibels (dB). A channel estimate circuit is positioned to receive signals after processing within a FFT circuit and subcarrier demapper circuit and estimates the channel characteristics of the communications channel based on splitting the extended guard interval from the long sync sequence and processing into values that represent the low PAPR preamble as plus or minus one (+/−1) values in a real or imaginary component as adds and subtracts.