Optical Carrier Frequency Arrangement for Bidirectional PON Interference
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Solution Overview
Problem
Point to multipoint communication networks face challenges in achieving high data rates in both downstream and upstream directions while maintaining reasonable costs, due to complex time management and lower data rates associated with burst mode transmission.
Innovation Solution
A method for transmitting optical downstream and upstream signals via a single optical fiber, where an optical OLT carrier signal is generated with a carrier frequency between sub-carrier frequencies of downstream signals, and upstream signals are associated with received downstream signals, using single sideband modulation to reduce interference and enhance spectral and power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If time diversity multiplex (TDM) and burst mode transmission are used, then bidirectional communication is achieved, but data rates are reduced and time management becomes complex
Solution Approach 1:
The patent employs periodic time slots for upstream burst mode transmissions, where each ONU is assigned specific time windows to transmit data to the OLT. This periodic structure simplifies time management by creating predictable, repeating patterns rather than requiring complex dynamic scheduling, while maintaining high data rates through efficient utilization of each time slot.
Solution Approach 2:
The downstream bandwidth is segmented into multiple frequency channels using WDM, with each channel carrying independent data streams. The upstream transmission is segmented into burst mode packets assigned to specific time slots. This segmentation allows parallel transmission of multiple signals simultaneously, increasing overall data rate while simplifying management through structured organization.
2Ease of manufacture
If a single optical fiber is used for bidirectional transmission, then cost is reduced, but signal interference between upstream and downstream signals occurs
Solution Approach 1:
The patent transitions from time-domain separation to frequency-domain separation by implementing WDM. Downstream signals are transmitted on specific wavelength channels while upstream signals use different wavelength channels. This dimensional shift from time to frequency allows simultaneous bidirectional transmission without interference, maintaining cost-effectiveness of single-fiber deployment.
Solution Approach 2:
Optical filters act as intermediaries to separate downstream and upstream signals based on their different wavelength channels. The filters selectively pass desired wavelength ranges while blocking others, preventing signal interference and enabling clean separation of bidirectional traffic on the same physical fiber medium.
3Use of energy by moving object
If carrier power is minimized, then power efficiency is improved, but signal detection becomes more difficult
Solution Approach 1:
The patent replaces direct electrical detection with coherent optical detection. The receiver uses a local oscillator laser to mix with the incoming weak signal, converting optical power variations into electrical signals through the photodetector. This substitution enables detection of low-power signals by leveraging the high sensitivity of coherent optical mixing rather than relying on direct electrical signal strength.
Solution Approach 2:
The system implements carrier recovery and synchronization mechanisms where the receiver continuously adjusts its local oscillator frequency and phase based on feedback from the received signal. This feedback loop maintains optimal detection conditions even when carrier power is minimized, ensuring reliable signal detection while maintaining power efficiency.
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 enables bidirectional data transmission with high data rates and reduced costs by minimizing carrier power and optimizing signal processing, ensuring efficient data transmission without interference between downstream and upstream signals.
Implementation Method 1
an optical modulator modulates a plurality of QPSK modulated microwave subcarrier signals onto an optical carrier signal
Implementation Method 2
an optical detector detects the modulated subcarrier from the optical carrier signal to produce a detected subcarrier signal
Data Source
Figure 1~5
Figure 2
Figure 3
AI summary
Bidirectional data signals are exchanged between a central unit (OLT) and a plurality of network terminals (ONU1 - ONU10). The optical carrier frequencies of the downstream and upstream signals are chosen that reflections do not interfere with the selected signal at the optical network unit and not with the received upstream signals at the central unit. The optical network units select their associated downstream signal and generate an associated upstream signal.