EPON Clock Recovery for Synchronized TDM Transport
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Solution Overview
Problem
Current passive optical networks (PONs) face challenges in transporting frequency- and phase-synchronized TDM clocks, which are essential for cellular/mobile backhaul networks, as they are inherently asynchronous and lack guaranteed bandwidth, making it difficult to support increasing bandwidth demands while maintaining synchronization across base stations.
Innovation Solution
An Ethernet Passive Optical Network (EPON) system is developed, featuring a reference clock generating frequency- and phase-reference signals, an optical line terminal (OLT) coupled with a clock generator, and an optical network unit (ONU) with a clock recovery module, enabling the transport of synchronized clock signals over the EPON through circuit emulation techniques like PWE3 and Differential Clock Recovery (DCR).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If TDM circuits are added to increase backhaul network capacity, then bandwidth capacity is improved, but cost increases significantly
Solution Approach 1:
The patent replaces the traditional TDM circuit-based backhaul system with an Ethernet over PON system. This substitution uses packet-switched Ethernet technology instead of circuit-switched TDM, enabling higher bandwidth capacity over existing optical infrastructure without the cost of adding dedicated TDM circuits. The clock synchronization mechanism is adapted to work over the packet-switched network, maintaining TDM service requirements while leveraging the cost-effectiveness of Ethernet/PON technology.
2Ease of manufacture
If data traffic is moved to lower cost alternatives like DSL or cable modem, then cost is reduced, but base stations cannot separate voice/data traffic
Solution Approach 1:
The patent creates a universal backhaul system that handles both voice and data traffic over a single Ethernet/PON connection. The system provides multi-functionality by enabling base stations to receive both TDM voice traffic and IP data traffic through the same optical interface, eliminating the need for separate physical circuits. The clock synchronization mechanism works seamlessly with this unified approach, providing the necessary timing for voice services while accommodating high-speed data traffic.
3Quantity of substance
If EPON is used to provide higher bandwidth, then bandwidth capacity is improved, but synchronization is lost due to asynchronous nature of PON
Solution Approach 1:
The patent introduces an intermediary clock synchronization mechanism that bridges the asynchronous PON network and the synchronous TDM services. The system uses a reference clock at the OLT that generates precise timing signals, which are then distributed to ONUs through the optical network. The ONUs recover and synchronize their local clocks to this reference, acting as intermediaries that maintain TDM synchronization requirements while operating over the asynchronous Ethernet/PON infrastructure.
Solution Approach 2:
The patent implements feedback mechanisms where ONUs monitor and report their clock synchronization status to the OLT. The system uses clock recovery modules that continuously adjust local clock frequencies based on feedback from the reference clock signals received over the optical network. This closed-loop feedback ensures that synchronization is maintained despite the inherently asynchronous nature of PON, allowing the system to adapt and correct timing deviations in real-time.
Data Source
AI summary
One embodiment provides an Ethernet Passive Optical Network (EPON) system for clock transport. The system includes a reference clock configured to generate a frequency-reference signal, an optical line terminal (OLT) coupled to the reference clock, and an optical network unit (ONU). The OLT includes a clock generator configured to generate an OLT clock based on at least the frequency-reference signal. The ONU includes an optical transceiver, a clock recovery module, and a clock output mechanism. The optical transceiver is configured to transmit optical signals to and receive optical signals from the OLT. The clock-recovery module is configured to recover the frequency-reference signal from the received optical signals. The clock output mechanism is configured to output the recovered frequency-reference signal, thus facilitating transport of the frequency-reference signal over the EPON.