Non-symmetric Conjugate-Root Filters for Offset-QAM Interference
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Solution Overview
Problem
Conventional Offset-QAM systems in multicarrier transmission face challenges with symmetric pulse shaping filters, phase shifts between subcarriers, and increased complexity due to varying phase spaces, which complicate implementation and do not achieve full orthogonality, leading to inefficiencies in handling intercarrier and intersymbol interference.
Innovation Solution
The use of non-symmetric conjugate-root filters for pulse shaping in an Offset-QAM system, which are band-limited to two subcarriers and do not require a phase shift of ½π between subcarriers, allowing for complex-valued symbol transmission and reduced computation load in receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If symmetric pulse shaping filters are used in Offset-QAM systems, then interference mitigation is achieved, but device complexity increases due to varying phase spaces and phase shifts between subcarriers
Solution Approach 1:
The patent applies asymmetry by using non-symmetric conjugate-root filters instead of symmetric pulse shaping filters. This eliminates the need for phase shifts between subcarriers and symbols, thereby reducing the varying phase space complexity while maintaining interference mitigation capabilities through the conjugate-root filter structure.
2Reliability
If conventional Offset-QAM with symmetric filters is used, then interference is mitigated, but manufacturing precision is reduced due to inability to achieve full orthogonality
Solution Approach 1:
The patent changes the filter parameter from symmetric to non-symmetric conjugate-root filters. This parameter change enables the system to achieve full orthogonality between subcarriers and symbols while maintaining interference mitigation, thereby improving manufacturing precision in terms of orthogonality achievement.
3Reliability
If symmetric pulse shaping filters are used, then interference mitigation is achieved, but productivity is reduced due to doubled symbol rate requirement
Solution Approach 1:
By using non-symmetric conjugate-root filters, the patent enables complex-valued symbol transmission without requiring doubled symbol rates. This asymmetry approach allows the system to achieve both interference mitigation and improved productivity through more efficient data transmission.
4Productivity
If conventional Offset-QAM systems are used, then transmission is performed, but out-of-band radiation increases reducing spectral agility
Solution Approach 1:
The patent changes the filter characteristics to non-symmetric conjugate-root filters with specific band-limiting properties. This parameter change reduces out-of-band radiation while maintaining good time-frequency localization, thereby improving spectral agility and reducing harmful emissions.
Data Source
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AI summary
In an orthogonal multicarrier radio transmission system complex-valued symbols are transmitted, wherein the real part and the imaginary part of each symbol are shifted against each other by one half symbol period and wherein a non-symmetric conjugate-root filter is applied to each symbol before transmission to mitigate inter-carrier interference and intersymbol interference. Corresponding reverse steps are performed at the receiver.