Direct Detection OFDM Signal SSBI Cancellation
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Solution Overview
Problem
Signal-signal beat interference (SSBI) causes performance degradation in direct detection orthogonal frequency division multiplexing (OFDM) systems, leading to increased bit error rates due to its deterministic nature, which existing methods struggle to mitigate effectively without compromising spectrum efficiency or increasing computational complexity.
Innovation Solution
A method using a digital signal processor (DSP) to calculate and subtract the SSBI component from the OFDM signal by modulating each subcarrier with a symbol, thereby reducing interference and improving error performance without requiring iterative cancellations or increased hardware resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If iterative SSBI cancellation at the RX side is performed, then error performance improves, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by performing SSBI cancellation at the transmitter side before signal transmission, rather than iteratively at the receiver side. The transmitter calculates the SSBI component based on known transmitted symbols and subtracts it from the signal, eliminating the need for complex iterative processing at the receiver and reducing computational complexity while maintaining error performance
Solution Approach 2:
The patent uses copying by reconstructing the SSBI component at the transmitter using a copy of the transmitted symbol sequence. Since the transmitter knows exactly what symbols are being transmitted, it can generate an accurate copy of the expected SSBI interference and subtract it, avoiding the need for iterative estimation and cancellation at the receiver
2Reliability
If gap between dc carrier and OFDM signal is reserved or only odd subcarriers are used, then SSBI distortion is reduced, but spectrum efficiency decreases
Solution Approach 1:
The patent applies the extraction principle by isolating and removing the SSBI component from the transmitted signal. It calculates the SSBI term separately based on the known OFDM signal structure and carrier frequency, then subtracts this extracted interference component, allowing full utilization of the spectrum without gaps or unused subcarriers
Solution Approach 2:
The patent changes the parameter approach by moving from structural modifications (gaps, odd subcarriers) to a signal processing parameter approach. It modifies the transmitted signal by subtracting a calculated SSBI component with specific amplitude and phase parameters derived from the known signal structure, maintaining full spectrum utilization while reducing distortion
Data Source
AI summary
System and method embodiments are provided for improving reception of direct detection optical signals. In an embodiment, a method for optical transmission includes bit loading and power loading, with a digital signal processor (DSP), transmission bits of an orthogonal frequency-division multiplexing (OFDM) signal; calculating, with the DSP, a signal-signal beat interference (SSBI) component of the bit and power loaded OFDM signal by modulating each subcarrier with a symbol; and subtracting, with the DSP, the calculated SSBI component from the bit and power loaded OFDM signal.