Polar Transmitter IQ Trajectory Shifting for Bandwidth Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Polar transmitters face challenges in reducing phase and amplitude modulation bandwidth, particularly for wideband wireless standards like 3G WCDMA, due to limited modulation range and high frequency deviations, leading to increased phase noise and error vector magnitude (EVM) degradation.
Innovation Solution
A fully digital bandwidth reduction mechanism that modifies zero-crossing trajectories in the IQ domain to reduce phase modulation bandwidth, using a zero crossing detector and offset vector generator to shift the trajectory away from the origin, thereby reducing the phase modulation bandwidth while maintaining EVM and phase noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If polar modulation is used for wideband wireless standards like 3G WCDMA, then the transmitter can support wideband communication, but the phase modulation bandwidth increases significantly due to high frequency deviations
Solution Approach 1:
The patent segments the frequency deviation signal into multiple components and processes them through different paths. Specifically, it separates the large frequency deviation component (handled by frequency hopping) from the smaller residual frequency deviation (handled by phase modulation), allowing each path to operate within optimized bandwidth constraints
Solution Approach 2:
The patent introduces frequency hopping as an intermediary mechanism that handles the bulk of frequency translation, thereby reducing the burden on the phase modulator. This intermediary approach allows the system to achieve wideband communication while keeping the phase modulation bandwidth manageable
2Reliability
If the modulation range is limited to reduce bandwidth, then phase noise is reduced, but the frequency modulation range becomes insufficient for wideband standards
Solution Approach 1:
The frequency modulation function is segmented between frequency hopping (handling large frequency shifts) and phase modulation (handling fine frequency adjustments). This segmentation allows the phase modulator to operate with limited range and lower phase noise, while the overall system achieves wide frequency coverage through frequency hopping
Solution Approach 2:
The patent adds the time dimension to frequency modulation by using frequency hopping sequences. Instead of requiring a wide instantaneous frequency range, the system achieves wideband coverage by switching between different frequency channels over time, thereby reducing the required phase modulation bandwidth at any given moment
3Measurement precision
If the sampling rate is increased to reduce quantization noise, then the dynamic range improves, but the bandwidth requirements increase further
Solution Approach 1:
The signal processing is segmented into multiple stages with different sampling rates. Frequency hopping operates at a lower sampling rate handling coarse frequency adjustments, while phase modulation operates at a higher sampling rate for fine adjustments. This segmentation allows quantization noise reduction without uniformly increasing the sampling rate across the entire system
Solution Approach 2:
The patent changes the sampling rate parameter dynamically based on the modulation path. The frequency hopping path uses a lower sampling rate while the phase modulation path uses a higher sampling rate, optimizing the trade-off between quantization noise and bandwidth requirements for each specific function
Data Source
AI summary
A novel and useful apparatus for and method of reducing phase and amplitude modulation bandwidth in polar transmitters. The bandwidth reduction mechanism of the present invention effectively reduces the phase modulation bandwidth of the polar modulation performed in the transmitter by modifying the zero-crossing trajectories in the IQ domain. This significantly reduces the phase modulation bandwidth while still meeting the output spectrum and error vector magnitude (EVM) requirements of the particular modern wideband wireless standard, such as 3G WCDMA, etc. The mechanism detects a zero crossing or a near zero crossing within a predetermined threshold of the origin and an offset vector is generated that when added to the input TX IQ data, shifts the trajectory to avoid the origin thus reducing the resultant polar modulation amplitude and phase bandwidth.