Optical OFDMA Ranging Sequence Design for Upstream Synchronization
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Solution Overview
Problem
Optical communication networks, particularly those using the OFDMA scheme, face challenges in upstream signal synchronization due to multiple access interference, symbol timing offset, carrier frequency offset, and intersymbol interference, which degrade signal quality and orthogonality between subcarriers.
Innovation Solution
The optical communication network employs a ranging procedure where each optical network unit generates a ranging sequence comprising a constant amplitude zero auto-correlation sequence multiplied by a pseudo noise sequence, allowing the receiving unit to synchronize upstream signals and maintain orthogonality between subcarriers through correlation operations and ranging response adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ranging procedures are used in OFDMA networks, then upstream signals can be transmitted, but signal quality degrades due to multiple access interference, symbol timing offset, carrier frequency offset, and intersymbol interference
Solution Approach 1:
The patent applies preliminary action by performing ranging detection and synchronization operations before main data transmission begins. The receiving unit executes correlation operations with stored ranging sequences to determine timing and frequency offsets in advance, allowing the transmitting unit to adjust its parameters before actual data communication starts, thereby preventing signal quality degradation during the main transmission phase
Solution Approach 2:
The patent implements feedback through the ranging response mechanism where the receiving unit sends back synchronization information to the transmitting unit based on the correlation results. This feedback loop allows the transmitting unit to adjust its timing and frequency parameters according to the actual channel conditions, continuously improving signal quality by compensating for multiple access interference, symbol timing offset, carrier frequency offset, and intersymbol interference
2Measurement precision
If ranging sequences are stored in the receiving unit for correlation operations, then upstream signals can be synchronized, but device complexity increases
Solution Approach 1:
The patent applies copying by having the receiving unit store copies of the ranging sequences that are generated by the transmitting unit. Instead of implementing complex real-time generation and analysis, the receiving unit simply stores reference copies of the ranging sequences and performs correlation operations with received signals, significantly reducing device complexity while maintaining high synchronization accuracy through the correlation detection mechanism
Data Source
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AI summary
The invention relates to an optical OFDMA communication network, comprising: • - a plurality of optical network units (ONUs 2a-2n), wherein each one of the ONUs (2a-2n) is configured to generate a ranging sequence (20b - 20n) for upstream synchronization of the ONUs (2a-2n); • - a receiving unit (5) for receiving signals of the ONUs (2a-2n), the receiving unit (5) being also configured to receive the ranging sequences (20b - 20n) of the ONUs (2a-2n), • - wherein the receiving unit (5) comprises a correlator unit (61) in which a plurality of ranging sequences (611) is stored, • - and wherein the receiving unit (5) is configured to perform a ranging detection operation including performing a correlation operation with a plurality of the received ranging sequences (20b - 20n) using at least one of the stored ranging sequences (611) and to transmit a ranging response to the ONUs (2a-2n) depending on the result of the correlation operation. The ranging sequence consists in a four time repeated CAZAC sequence, multiplied by a ONU specific PN sequence and by a frequency shift.