Multi-bit AD Converter for RoF Signal Accuracy
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Solution Overview
Problem
In wireless access systems using Radio over Fiber (RoF) technology, the Analog to Digital (AD) converters struggle to accurately convert pulse width modulation signals due to varying rising and falling edges, leading to inaccurate digital signal representation of analog uplink signals.
Innovation Solution
The system includes a centralized control station and an access point connected through an optical network, with a modulation unit performing pulse width modulation, an optical signal conversion unit, an electrical signal conversion unit, a filter unit, a digital signal conversion unit that converts signals to two or more bits, and a signal processing unit, enabling accurate digital representation of analog uplink signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 1-bit AD converter is used to convert the analog modulation signal to a digital signal, then the device complexity is reduced, but the measurement precision deteriorates because the converter cannot accurately represent the varying pulse edges
Solution Approach 1:
The patent changes the bit resolution parameter of the AD converter from 1 bit to multiple bits (e.g., 8 bits or more). This parameter change enables the converter to accurately represent the varying signal levels of the analog modulation signal, including the varying rising and falling edges of the pulse width modulation waveform, thereby resolving the measurement precision issue while maintaining reasonable device complexity
Solution Approach 2:
The patent applies preliminary filtering action by inserting a low-pass filter between the AD converter and the digital signal processing unit. This filter removes high-frequency components and noise from the analog modulation signal before conversion, preventing aliasing and improving the accuracy of the digital representation without requiring a more complex converter
2Productivity
If the sampling period is extended to reduce processing speed requirements, then the productivity is improved, but the measurement precision deteriorates because the varying pulse edges may be missed between sampling points
Solution Approach 1:
The patent changes the quantization precision parameter of the AD converter to multiple bits, which allows for more accurate representation of the analog signal at each sampling point. This enables the system to use longer sampling periods (lower sampling rates) while maintaining measurement precision, as each sampled value contains more information about the signal level
Solution Approach 2:
The patent implements digital signal processing with feedback mechanisms that analyze the converted digital signal and can adjust sampling timing or apply interpolation techniques to ensure accurate capture of pulse edges even with extended sampling periods
3Adaptability or versatility
If pulse width modulation is used to transmit the analog uplink signal through the optical network, then the adaptability is improved for optical transmission, but the measurement precision deteriorates because the varying pulse edges cannot be accurately captured by periodic sampling
Solution Approach 1:
The patent changes the AD converter resolution from 1-bit to multi-bit, which fundamentally alters the measurement capability. This allows the system to accurately capture the varying pulse edges of the PWM signal regardless of their timing, enabling precise reconstruction of the original analog uplink signal while maintaining compatibility with optical PWM transmission
Solution Approach 2:
The patent introduces a low-pass filter as an intermediary component between the AD converter and the digital signal processing unit. This filter mediates the signal by removing high-frequency PWM carrier components and noise, allowing the multi-bit AD converter to accurately capture the envelope information of the PWM signal without being affected by the rapid pulse edge variations
Data Source
AI summary
A wireless access system includes: a centralized control station; and an access point. The access point performs a pulse width modulation process on an analog uplink signal, thereby to generate an analog modulation signal; and converts the analog modulation signal to an optical uplink signal. The centralized control station converts the optical uplink signal to an electrical uplink signal; performs, on the electrical uplink signal, a filtering process for extracting an analog extraction signal including a signal component corresponding to the analog uplink signal; and converts the analog extraction signal to a digital uplink signal representing a signal level of the analog extraction signal by two or more bits.