OFDM Transmitter Segmentation for Robust Signalling

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

In Orthogonal Frequency Division Multiplexing (OFDM) systems, increasing the number of sub-carriers for improved spectral efficiency can lead to reduced robustness in data recovery, especially in challenging radio environments, due to increased Doppler frequency shifts and multipath propagation, requiring a higher signal-to-noise ratio for reliable bit error rates.

Innovation Solution

A transmitter structure that uses a mix of OFDM symbols with different numbers of sub-carriers, where a preamble OFDM symbol with fewer sub-carriers is used for signalling data and a second type with more sub-carriers for payload data, with a guard interval selected based on the longest possible guard interval of the payload OFDM symbols, to enhance the likelihood of detecting and recovering signalling data before payload data.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the number of sub-carriers is increased to improve spectral efficiency, then spectral efficiency is improved, but robustness in data recovery deteriorates due to increased Doppler frequency shifts and multipath propagation

Engineering Contradiction:

Improvespectral efficiencyVSAvoidrobustness in data recovery

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The transmission is segmented into different OFDM symbol types: a first type with fewer sub-carriers for signalling data and a second type with more sub-carriers for payload data. This segmentation allows each segment to be optimized for its specific function, resolving the contradiction between spectral efficiency and robustness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different parts of the transmission have different qualities: the first OFDM symbol type has fewer sub-carriers providing higher robustness for critical signalling data, while the second OFDM symbol type has more sub-carriers providing higher spectral efficiency for payload data. Each part is locally optimized for its specific requirement.

Inventive Principle:

Principle #3Local quality

2Duration of action of stationary object

If the number of sub-carriers is increased to increase OFDM symbol duration, then the ability to cope with multipath propagation is improved, but demodulation difficulty increases due to reduced separation between sub-carriers

Engineering Contradiction:

ImproveOFDM symbol durationVSAvoiddemodulation difficulty

Core Design Contradiction:

Duration of action of stationary objectVSDifficulty of detecting and measuring

Solution Approach 1:

The system segments OFDM symbols into two types with different durations and sub-carrier configurations. The first type has longer duration with fewer sub-carriers for robust signalling, while the second type has shorter duration with more sub-carriers for efficient payload transmission, resolving the contradiction between duration and demodulation difficulty.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system changes parameters (number of sub-carriers and guard interval duration) depending on the data type being transmitted. For signalling data, it uses fewer sub-carriers with longer guard intervals; for payload data, it uses more sub-carriers with appropriate guard intervals, optimizing both demodulation ease and spectral efficiency.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If a guard interval is minimized as a fraction of OFDM symbol duration to increase spectral efficiency, then spectral efficiency is improved, but the ability to absorb multipath echoes is reduced

Engineering Contradiction:

Improvespectral efficiencyVSAvoidmultipath echo absorption

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The transmission is segmented into first and second OFDM symbol types with different guard interval fractions. The first type uses a larger guard interval fraction to absorb multipath echoes for robust signalling data, while the second type uses a minimized guard interval fraction for high spectral efficiency payload data.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different guard interval qualities are applied locally to different data types: the first OFDM symbol type has a larger guard interval providing strong multipath protection for signalling data, while the second OFDM symbol type has a minimized guard interval providing high spectral efficiency for payload data.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS11394592B2Transmitter and method of transmitting and receiver and method of detecting OFDM signals

Publication Date: 2022.07.19 SATURN LICENSING LLC

AI summary

A transmitter transmits payload data using Orthogonal Frequency Division Multiplexed (OFDM) symbols. The first OFDM symbol is a first type having a number of sub-carriers which is less than or equal to the number of sub-carriers of the one or more second OFDM symbols of a second type and a guard interval for the first OFDM symbol is selected in dependence upon the longest possible guard interval of the second OFDM symbol. Accordingly an OFDM communications system can be formed in which data is transmitted using a frame structure in which a guard interval is adapted to allow a mix of different types of OFDM symbols.