Adaptive Interpolation for Polar RF Transmitter Signals
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Solution Overview
Problem
Current interpolation methods in polar RF transmitters face challenges such as high computational expense and signal distortion due to high frequency spectral components when IQ trajectories approach the origin of the IQ plane, and existing methods either require costly IQ-to-polar conversion at high clock rates or introduce error vector magnitude (EVM) with radius constraints.
Innovation Solution
An adaptive interpolation method is proposed that dynamically selects between polar interpolation and mapped linear interpolation based on the position of IQ trajectories relative to the origin, using a selection metric to choose the appropriate interpolation method and generate interpolated polar samples at a higher sampling rate, thereby reducing computational load and signal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polar interpolation is used, then spectral requirements are met, but high frequency spectral components cause signal distortion when IQ trajectories approach the origin
Solution Approach 1:
The patent applies different interpolation methods based on the local position of IQ trajectories. When the trajectory is far from the origin, polar interpolation is used to meet spectral requirements. When the trajectory approaches the origin, mapped linear interpolation is used to avoid high frequency spectral components and signal distortion. This local adaptation resolves the contradiction between spectral requirements and signal distortion.
Solution Approach 2:
The patent dynamically selects between polar interpolation and mapped linear interpolation based on the real-time position of IQ trajectories relative to the origin. The selection metric continuously monitors the trajectory position and switches interpolation methods accordingly, making the system adaptive to changing conditions and resolving the contradiction between spectral requirements and signal distortion.
2Productivity
If IQ-to-polar conversion is performed at high clock rates, then interpolated polar samples are generated, but computational expense increases
Solution Approach 1:
Instead of always performing computationally expensive IQ-to-polar conversion at high clock rates, the patent applies mapped linear interpolation for trajectories near the origin, which avoids the need for expensive conversion operations. This partial application of the simpler method reduces overall computational expense while still generating the required interpolated polar samples.
Solution Approach 2:
The patent changes the interpolation method parameter based on the trajectory position parameter. When the trajectory position indicates proximity to the origin, the system switches from polar interpolation to mapped linear interpolation, changing the operational parameter to reduce computational expense while maintaining productivity.
3Productivity
If radius constraints are applied, then interpolation is performed, but error vector magnitude increases
Solution Approach 1:
The patent applies different interpolation approaches based on the local position of IQ trajectories. For trajectories far from the origin, polar interpolation with radius constraints is used. For trajectories near the origin, mapped linear interpolation is used to avoid EVM degradation. This local differentiation resolves the contradiction between interpolation productivity and EVM precision.
Solution Approach 2:
The patent dynamically adjusts the interpolation method based on real-time trajectory position monitoring. The selection metric continuously evaluates whether radius constraints would cause EVM degradation, and switches interpolation methods accordingly, making the system adaptive and resolving the contradiction between productivity and precision.
Data Source
AI summary
An apparatus for interpolation of polar signals in RF transmitters is disclosed. The apparatus comprises an estimation circuit configured to receive an input in-phase (I) quadrature (Q) signal comprising a plurality of input IQ samples having a first sampling rate associated therewith, and determine a selection metric value indicative of a position of an IQ trajectory associated with one or more input IQ samples of the input IQ signal. The apparatus further comprises a selection circuit configured to receive the input IQ signal and the selection metric value; and adaptively provide the input IQ signal to a first interpolation circuit that implements a first interpolation method or to a second interpolation circuit that implements a second, different interpolation method, for generating interpolated polar samples at a second, different sampling rate, from the input IQ signal, based on the selection metric value.