Sigma-Delta Modulated RF Over Fiber Filtering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for transmitting RF signals from a centralized base station to antennas in 5G networks face challenges such as significant processing requirements, difficulty in antenna synchronization, and the need for expensive high dynamic range modulators, which are exacerbated by copper loss and quantization errors.
Innovation Solution
A communication system utilizing a sigma delta modulator to convert RF signals into broadband signals with a higher signal-to-noise ratio within the frequency band of interest, allowing for optical transmission over fiber, and using power and noise matching to filter out quantization noise, enabling the use of non-linear optical transmitters and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital encapsulation of I/Q samples is used to transport RF signals over fiber, then the RF signal can be transmitted, but significant processing is required at the antenna side and synchronization of different antennas is difficult
Solution Approach 1:
The patent extracts the complex digital processing functions from the antenna side and consolidates them at the base station. By using direct RF-to-optical modulation, the antenna side is simplified to only require optical-to-electrical conversion and power amplification, removing the need for digital signal processing and synchronization mechanisms at remote locations.
Solution Approach 2:
The patent replaces the digital electronic processing system with an optical modulation system. Instead of digitally encoding and transmitting I/Q samples that require complex processing, the system directly modulates the optical carrier with the RF signal, substituting electronic-digital operations with optical-domain operations that are inherently simpler at the antenna side.
2Reliability
If Mach Zehnder modulators or direct modulation of DFB lasers are used to modulate wireless signals on an optical carrier, then the signals can be transmitted, but expensive photonic devices are required
Solution Approach 1:
The patent replaces expensive, precision photonic devices (Mach Zehnder modulators, DFB lasers) with simpler, lower-cost components. The system uses direct modulation of standard lasers combined with sigma-delta modulation and noise matching techniques, eliminating the need for costly high-dynamic-range modulators while maintaining transmission quality.
Solution Approach 2:
The patent changes the modulation approach from requiring high dynamic range analog modulation to using sigma-delta modulation with quantized levels. This parameter change allows the use of simpler devices that can handle the modulated signal, as the noise shaping and filtering techniques compensate for the reduced device performance requirements.
3Use of energy by moving object
If a lower IF frequency is used for modulation, then an upconversion stage is required at the remote antenna, but this increases the difficulty of antenna synchronization
Solution Approach 1:
The patent extracts the frequency conversion functions from the antenna side and performs all necessary modulation and frequency translation at the base station. The optical carrier is directly modulated with the RF signal at the source, eliminating the need for local oscillators and upconversion stages at remote antennas, thereby removing synchronization requirements entirely.
4Measurement precision
If sigma delta modulation is used to convert RF signals into broadband signals, then the signal to noise ratio is higher in the frequency band of interest, but quantization errors are generated that need to be filtered
Solution Approach 1:
The patent converts the harmful quantization noise into a beneficial filtering opportunity. By using noise matching between the photo-detector and output device at the specific frequency band of interest, the system allows out-of-band quantization noise to be naturally filtered out while preserving the in-band signal, turning the noise generation into a frequency-selective filtering mechanism.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances signal quality by maintaining a high signal-to-noise ratio within the frequency band of interest, reduces noise and power requirements, and supports beamforming techniques, while allowing for cost-effective and efficient transmission in 5G networks.
Implementation Method 1
a sigma delta modulator for modulating the RF signal into a broadband signal wherein the signal to noise ratio of the broadband signal is higher in the frequency band of the RF signal than outside the frequency band of the RF signal
Implementation Method 2
an optical transmitter connected with the sigma delta modulator and with an optical fiber for transmitting the broadband signal over the optical fiber
Implementation Method 3
a photo-detector configured for receiving the broadband signal from the optical fiber and converting it into an electrical signal
Implementation Method 4
a matching circuit configured for power matching and/or noise matching of the photo-detector, at the frequency band of the RF signal, with the output device
Implementation Method 5
a matching circuit configured for power matching and/or noise matching of the photo-detector, at the frequency band of the RF signal, with the output device
Data Source
Figure 1~3
Figure 4~6
Figure 7~8
AI summary
A communication system (100) for transmitting a RF signal which has a frequency band. The communication system comprises: a sigma delta modulator (110) for modulating the RF signal into a broadband signal wherein the signal to noise ratio of the broadband signal is higher in the frequency band of the RF signal than outside the frequency band of the RF signal; an optical transmitter (120) connected with the sigma delta modulator (110) and with an optical fiber (130) for transmitting the broadband signal over the optical fiber (130); a photo-detector (140) configured for receiving the broadband signal from the optical fiber (130) and converting it into an electrical signal; an output device (160) and a matching circuit (150) configured for power matching and/or noise matching of the photo-detector (140), at the frequency band of the RF signal, with the output device (160).