OFDM Interleaving for Phase Noise Tolerance in DFT-S Systems
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Solution Overview
Problem
DFT-S OFDM systems face increased phase noise tolerance issues due to sub-banding, which degrades laser linewidth tolerance and affects overall system performance, particularly in long-haul optical communication links.
Innovation Solution
The implementation of differential precoding at the transmitter and multi-symbol differential detection (MSDD) phase recovery at the receiver, combined with non-redundant interleaving, to mitigate phase noise by assigning temporally successive symbols to adjacent spectral sub-bands, effectively canceling out common phase noise and improving laser phase noise tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sub-banding is applied in DFT-S OFDM systems, then spectral efficiency is improved, but phase noise tolerance deteriorates
Solution Approach 1:
The system divides the frequency spectrum into multiple sub-bands and processes symbols in each sub-band independently. This segmentation allows phase noise to be managed locally in each sub-band while maintaining overall spectral efficiency. The sub-bands are processed through separate DFT operations and interleaved at the output, enabling both high spectral efficiency and improved phase noise tolerance.
Solution Approach 2:
The invention introduces a temporal dimension to frequency-domain processing by interleaving symbols from different sub-bands in the time domain. This dimensional transformation allows phase noise that would otherwise affect all sub-bands simultaneously to be distributed and managed across different time slots, improving overall phase noise tolerance while preserving spectral efficiency.
2Reliability
If differential precoding and MSDD are implemented, then phase noise tolerance is improved, but device complexity increases
Solution Approach 1:
The differential precoding and MSDD algorithms utilize the received signal itself as the reference for phase estimation. By using the signal's own properties (autocorrelation and autocross-correlation functions) rather than external reference signals, the system achieves phase noise tolerance without requiring additional complex reference signal generation or external synchronization mechanisms.
Solution Approach 2:
The MSDD algorithm performs multiple functions simultaneously: it estimates carrier phase, recovers frequency offset, and equalizes channel effects all within a single processing operation. This multi-functionality reduces the need for separate dedicated algorithms for each function, thereby managing computational complexity while achieving robust phase noise tolerance.
3Object-affected harmful factors
If non-redundant interleaving is applied, then phase noise is reduced, but computational overhead increases
Solution Approach 1:
The interleaving operation is performed at the transmitter before the signal enters the channel, and the corresponding de-interleaving is performed at the receiver. This preliminary action at the transmitter allows the receiver to simply reverse the permutation without needing to perform complex phase noise estimation and correction operations, reducing the computational burden at the receiver while still achieving phase noise reduction.
Data Source
AI summary
An orthogonal frequency division multiplexing (OFDM) transmitter that includes an encoder, an interleaver, a symbol processor; and a transmission module; wherein the encoder is configured to encode a superframe to provide an encoded superframe; wherein the encoded superframe comprises a sequence of encoded frames; wherein the interleaver is configured to allocate multiple frequency sub-bands to each encoded frame of the encoded superframe by assigning adjacent frequency sub-bands to successive symbols of each encoded frame; wherein the symbol processor is configured to generate, for each encoded frame and according to the assignment of the multiple frequency sub-bands, an intermediate set of symbols; and wherein the transmission module is configured to transmit simultaneously, for each encoded frame, OFDM symbols that represents the intermediate set of symbols.