OFDM Frequency Selectivity via Symbol Delay

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

OFDM networks face limitations due to the lack of frequency selectivity in channels with flat-fading, which restricts the exploitation of frequency diversity and multi-user scheduling, leading to suboptimal performance in mobile stations.

Innovation Solution

Introducing frequency selectivity by generating delayed OFDM symbols and transmitting them from multiple antennas, allowing the signal to arrive at the receiver with inherent frequency selectivity, thereby enabling frequency diversity and improved channel reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If OFDM transmission is used in flat-fading channels, then system simplicity is maintained, but frequency selectivity is lost limiting system performance

Engineering Contradiction:

Improvefrequency selectivity exploitationVSAvoidtransmission structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The transmitted signal is segmented into multiple delayed versions that are sent through different paths. By dividing the single signal into multiple time-delayed copies, the system creates artificial frequency selectivity without changing the fundamental OFDM structure, thus maintaining simplicity while gaining adaptability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a time dimension by applying delays to OFDM symbols, transforming a one-dimensional frequency-flat channel into a multi-dimensional frequency-selective channel. This adds temporal diversity to the transmission, enabling frequency selectivity exploitation without complex spatial arrangements.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If multiple delayed symbols are transmitted from multiple antennas, then frequency diversity is achieved, but transmission complexity increases

Engineering Contradiction:

Improvechannel reliabilityVSAvoidtransmission structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system pre-processes the OFDM symbols by introducing controlled delays before transmission. This preliminary action of delaying symbols creates the desired frequency selectivity and diversity effects in advance, simplifying the receiver design while improving reliability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the time-domain parameters of the transmitted symbols by introducing specific delay values. By modifying the temporal characteristics of the signal rather than its frequency content, the system achieves frequency diversity through time-domain manipulation, maintaining implementation simplicity.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If frequency selectivity is introduced through delayed symbols, then system performance is improved, but processing complexity increases

Engineering Contradiction:

Improvesystem performanceVSAvoidsignal processing complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent replaces complex frequency-domain processing with simpler time-domain delay operations. Instead of performing complex computations in the frequency domain to achieve frequency selectivity, the system uses straightforward time-domain delays, significantly reducing processing complexity while maintaining performance benefits.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS8335159B2Method and system for introducing frequency selectivity into transmissions in an orthogonal frequency division multiplexing network

Publication Date: 2012.12.18 SAMSUNG ELECTRONICS CO LTD

AI summary

A method of introducing frequency selectivity into transmissions in an orthogonal frequency division multiplexing network is provided. The method includes generating a symbol. A plurality of delayed symbols are generated based on the symbol. The delayed symbols are transmitted from multiple transmit antennas. The symbol delay values may be different for different users depending upon the users' channel characteristics.