OFDM-TDMA Echo Cancellation for Spectrum Utilization

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Solution Overview

Problem

In OFDM-TDMA two-way communication systems, the time division duplex method leads to low spectrum utilization and increased overheads due to separate timeslots for uplink and downlink communications, causing interference from echo OFDM signals.

Innovation Solution

A method for echo cancellation in the digital signal frequency domain, where the phase difference and channel transfer function of the echo path are used to generate an echo cancellation signal, which is then subtracted from received signals to cancel the echo OFDM signal, allowing simultaneous uplink and downlink communications in the same timeslot.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If time division duplex method is used for two-way communication, then uplink and downlink scheduling is simplified, but spectrum utilization deteriorates and scheduling overheads increase

Engineering Contradiction:

Improvescheduling complexityVSAvoidspectrum utilization

Core Design Contradiction:

Device complexityVSQuantity of substance

Solution Approach 1:

The patent merges uplink and downlink communications into the same timeslot by combining OFDM technology with TDMA, allowing simultaneous bidirectional communication on overlapping frequency spectra through echo cancellation, thereby improving spectrum utilization while maintaining scheduling simplicity

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the frequency domain parameters by allowing spectrum overlap between uplink and downlink signals, using phase difference and channel transfer function adjustments to enable simultaneous transmission on the same frequency resources

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If separate timeslots are allocated for uplink and downlink, then interference management is simplified, but spectrum utilization deteriorates

Engineering Contradiction:

Improveinterference managementVSAvoidspectrum utilization

Core Design Contradiction:

Object-affected harmful factorsVSQuantity of substance

Solution Approach 1:

The patent converts the harmful echo OFDM signal into a beneficial component by using it to generate an echo cancellation signal that actively suppresses interference, allowing spectrum overlap while managing interference through digital signal processing

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Quantity of substance

If echo cancellation is implemented in frequency domain, then spectrum utilization improves, but device complexity increases

Engineering Contradiction:

Improvespectrum utilizationVSAvoidsignal processing complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The patent replaces traditional time-domain echo cancellation mechanisms with frequency-domain processing, using phase difference and channel transfer function calculations to generate cancellation signals, thereby achieving better spectrum utilization through digital signal processing

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentEP3145146B1Processing method and communications device based on OFDM-TDMA two-way service

Publication Date: 2018.01.03 HUAWEI TECH CO LTD

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AI summary

The present invention provides a processing method based on an OFDM-TDMA two-way service and a communications device. The method includes: assigning timeslots in a TDMA frame structure to multiple users in a TDMA manner, so that each user has a different timeslot, and each timeslot of the users is simultaneously used for uplink and downlink communication; simultaneously sending a local-end OFDM signal and receiving a remote-end OFDM signal in each timeslot of the users; and cancelling, in an OSD manner, interference caused by an echo OFDM signal, which is produced according to the local-end OFDM signal, to the remote-end OFDM signal, where a spectrum of the echo OFDM signal and a spectrum of the remote-end OFDM signal overlap.