Upstream Interference Elimination in RFoG Optical Networks
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Solution Overview
Problem
Radio Frequency over Glass (RFoG) systems face upstream interference issues due to optical beat interference (OBI) when multiple transmitters send signals on closely spaced wavelengths, impacting return path performance and bandwidth utilization, particularly in multiple-dwelling unit (MDU) applications with bonded upstream channels.
Innovation Solution
Implementing a scheduler-based approach that prevents simultaneous transmission of interfering upstream devices by scheduling only one device to send data at a time, and transmitting digital baseband data without RF modulation through the optical network, eliminating the need for modulation and demodulation at the headend.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple upstream devices transmit data simultaneously on closely spaced wavelengths, then bandwidth utilization increases, but optical beat interference occurs degrading return path performance
Solution Approach 1:
The system performs preliminary wavelength assignment and transmission scheduling to prevent simultaneous transmissions on closely spaced wavelengths. The headend assigns specific wavelengths to upstream devices and schedules transmission slots in advance, ensuring that only one device transmits on each wavelength at any given time, thereby preventing optical beat interference before it occurs.
Solution Approach 2:
The system dynamically adjusts transmission parameters including wavelength selection and transmission timing based on network conditions. The headend monitors the optical network and dynamically reassigns wavelengths or modifies transmission schedules to avoid interference scenarios while maximizing bandwidth utilization, making the system adaptive to changing conditions.
2Adaptability or versatility
If RF modulation is used for upstream transmission, then signal compatibility with existing HFC equipment is maintained, but system complexity increases due to required modulation and demodulation
Solution Approach 1:
The invention extracts and removes the RF modulation step from the upstream transmission path. By transmitting digital baseband signals directly over the optical network without RF modulation, the system eliminates the need for modulators at upstream devices and demodulators at the headend, significantly reducing system complexity while maintaining compatibility through direct digital signal processing.
Solution Approach 2:
The invention substitutes the electrical RF modulation mechanism with direct optical transmission of digital baseband signals. Instead of using electrical modulators to impose RF signals onto optical carriers, the system transmits digital signals directly through optical transceivers, replacing complex electrical modulation mechanics with simpler optical domain transmission.
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 solution reduces OBI, enhances upstream bandwidth, and simplifies the transmission process by eliminating the need for separate optical network units (ONUs), thereby improving the overall return path performance and capacity in RFoG networks.
Implementation Method 1
an optical transceiver coupled to the user device to send the digital baseband signal to a headend through an optical network
Data Source
AI summary
Particular embodiments provide a method for delivering data in the upstream direction without the need for upstream radio frequency (RF) modulation. For example, in some embodiments, an optical network may reach to a gateway associated with a user device. The gateway may receive digital baseband data from the user device in the upstream direction. The gateway can then send the digital baseband data through the optical network without modulating the digital baseband signal via radio frequency. At the headend, because no modulation is performed in the upstream direction, there is no need for de-modulation in the headend. In one embodiment, a scheduler-based approach is used to avoid instances of optical beat interference in the upstream direction as only one upstream device that may interfere with other devices may be able to send data at one time.