Phase-Domain Equalization for PSK Demodulator ISI Mitigation
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Solution Overview
Problem
Current wireless communication devices face significant challenges in mitigating intersymbol interference (ISI) in phase modulated signals due to transmitter or receiver impairments, frequency selective channel responses, and carrier frequency offsets, which degrade the performance of multilevel phase coded demodulators and increase the complexity and cost of receiver designs.
Innovation Solution
A nonlinear adaptive phase domain equalization mechanism is employed, operating on phase domain signals (r, θ) rather than classical Cartesian quadrature components (I, Q), which simplifies the equalization process and reduces ISI, allowing for lower IC area and power filtering schemes and mitigating demodulator impairments such as carrier frequency offset and timing phase errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a less complex filter is used in the receiver, then device complexity and cost are reduced, but intersymbol interference (ISI) increases
Solution Approach 1:
The patent introduces a phase domain equalizer as an intermediary component that operates on the phase of the received signal. This equalizer compensates for ISI caused by simple filtering by adjusting the phase of received symbols based on feedback from symbol decisions, thereby mitigating the harmful effects of using less complex filters
Solution Approach 2:
The invention changes the domain in which equalization is performed - transitioning from Cartesian (I,Q) domain to polar (phase, magnitude) domain. By operating in the phase domain, the equalizer can more effectively compensate for ISI with reduced complexity, as phase adjustments directly counteract the phase distortions introduced by simple filtering
2Measurement precision
If frequency offset correction is applied, then demodulation accuracy is improved, but device complexity increases
Solution Approach 1:
The patent combines frequency offset correction and phase equalization into a single phase domain equalizer. By merging these functions, the system achieves frequency offset compensation without requiring separate complex correction circuits, as the phase equalizer naturally handles both phase distortion and frequency offset effects through its adaptive phase adjustment mechanism
3Reliability
If complex equalization is applied to mitigate ISI, then communication reliability is improved, but device complexity and power consumption increase
Solution Approach 1:
The phase domain equalizer serves as an intermediary that simplifies the equalization process by operating directly on the phase of received symbols rather than manipulating complex I,Q components. This intermediate phase domain representation enables effective ISI mitigation with reduced computational complexity and lower power consumption
Solution Approach 2:
The invention changes the operational domain from Cartesian coordinates (I,Q) to polar coordinates (phase, magnitude). This parameter transformation simplifies the equalization mathematics and reduces computational requirements, as phase equalization involves simpler trigonometric operations compared to complex arithmetic in the Cartesian domain
Data Source
AI summary
A novel and useful apparatus for and method of nonlinear adaptive phase domain equalization for multilevel phase coded demodulators. The invention improves the immunity of phase-modulated signals (PSK) to intersymbol interference (ISI) such as caused by transmitter or receiver impairments, frequency selective channel response filtering, timing offset or carrier frequency offset. The invention uses phase domain signals (r, θ) rather than the classical Cartesian quadrature components (I, Q) and employs a nonlinear adaptive equalizer on the phase domain signal. This results in significantly improved ISI performance which simplifies the design of a digital receiver.