FBMC/OQAM Guard Interval Insertion for Intersymbol Interference Mitigation
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Solution Overview
Problem
FBMC/OQAM transmissions face challenges in mitigating intersymbol interferences, particularly when using short prototype filters, and lack cyclostationarity, which complicates equalization and increases latency.
Innovation Solution
The introduction of guard interval sequences, specifically null or known sequences, into the FBMC/OQAM signal before modulation, positioned at the end of the first half of the FBMC symbols, helps reduce intersymbol interferences and introduces cyclostationarity, facilitating low complexity equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If guard interval sequences are inserted into FBMC/OQAM signal before modulation, then intersymbol interferences are reduced and cyclostationarity is enhanced, but device complexity increases due to additional processing stages
Solution Approach 1:
The patent applies preliminary action by inserting guard interval sequences into the data stream before FBMC modulation and precoding operations. This pre-insertion ensures that guard intervals are properly positioned in the final modulated signal, reducing intersymbol interferences while maintaining systematic processing. The guard intervals are inserted at specific positions (e.g., after every 4th symbol) before subsequent processing stages transform the signal.
2Device complexity
If guard interval sequences are inserted into FBMC/OQAM signal, then equalization complexity is reduced through enhanced cyclostationarity, but transmission throughput decreases due to additional null sequences
Solution Approach 1:
The patent applies local quality by inserting guard interval sequences at specific local positions within the data stream rather than uniformly throughout. Specifically, guard intervals are inserted after every 4th FBMC symbol (or at predetermined positions), creating localized structures that enhance cyclostationarity at critical points. This selective insertion provides equalization benefits where most needed while minimizing the overall impact on throughput compared to universal insertion.
3Productivity
If FBMC symbols are overlapped after filtering, then spectral efficiency is improved, but intersymbol interferences increase due to loss of orthogonality
Solution Approach 1:
The patent applies beforehand cushioning by inserting guard interval sequences (null sequences or known sequences) between FBMC symbols before the overlapping and filtering operations. These guard intervals act as cushioning elements that prevent harmful intersymbol interference from propagating through the overlapping process. By placing these protective sequences in advance, the system maintains spectral efficiency through overlapping while cushioning against the reliability degradation that would otherwise result from lost orthogonality.
Data Source
AI summary
A method and device to modulate an FBMC/OQAM signal, the device comprising at least one QAM mapper mapping a binary stream into complex symbols, a first and a second transmission chain. Each chain comprises: a precoder transposing respective sets of symbols into frequency domain real/imaginary samples, a phase rotator applying a phase quadrature keying to said samples, an FBMC modulator to modulate the output of the phase rotator into an FBMC symbol. The device further comprises an adder of the output of the first transmission chain with a delayed output of the second transmission chain, and is configured to insert guard interval sequences into the binary stream or into the symbols processed by the precoders. A corresponding radio communication equipment, computer program and readable medium is provided.