Sidelobe Suppression in OFDM Systems via Active Interference Cancellation
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Solution Overview
Problem
Existing OFDM communications systems face challenges in sidelobe suppression, particularly when transmitters perform baseband operations like adding a cyclic prefix and using transmit time-windowing, as previous techniques are limited in their application and do not effectively optimize the signal spectrum.
Innovation Solution
The method involves generating active interference cancellation (AIC) sub-carrier data based on the information to be transmitted, which is then used to create an OFDM symbol that includes both information and AIC sub-carriers. This symbol undergoes baseband processing, including cyclic prefix addition and time-domain filtering, to reduce out-of-band emissions by optimizing the signal spectrum beyond its original constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If guard bands are used to prevent signal leakage, then interference to adjacent channels is reduced, but signal leakage still occurs and out-of-band emissions are not sufficiently suppressed
Solution Approach 1:
The patent applies preliminary anti-action by calculating and applying cancellation carrier values before transmission to preemptively counteract the sidelobe effects. The cancellation carriers are computed based on the expected interference pattern and subtracted from the original signal, creating a pre-compensated signal that inherently suppresses out-of-band emissions without requiring post-transmission correction or wider guard bands.
2Ease of manufacture
If simple sinc function is used for interference calculation, then computation is simplified, but the technique is not applicable to systems with cyclic prefix and transmit time-windowing
Solution Approach 1:
The patent changes the fundamental parameters of the interference calculation model to account for cyclic prefix and time-windowing effects. Instead of using a simple sinc function, the patent derives cancellation carrier values that incorporate the actual pulse shaping function and cyclic prefix characteristics of the OFDM system, making the technique adaptable to real-world implementations while maintaining computational feasibility through efficient algorithms.
3Object-affected harmful factors
If tone-nulling is applied to control interference level, then narrowband communications are protected, but sidelobes are not effectively suppressed
Solution Approach 1:
The patent introduces cancellation carriers as an intermediary element that mediates between the data carriers and the surrounding spectrum. These cancellation carriers are specifically designed to cancel the sidelobe components without affecting the data transmission, acting as a buffer that absorbs and neutralizes the interference energy before it can impact adjacent channels or narrowband communications.
Data Source
AI summary
A system and method for sidelobe suppression in OFDM communications systems is provided. A method for transmitting an information symbol having a plurality of information sub-carriers and a plurality of active interference cancellation (AIC) sub-carriers includes generating AIC sub-carrier data based on the information to be transmitted, populating the plurality of information sub-carriers with the information, populating the plurality of AIC sub-carriers with the AIC sub-carrier data, applying baseband processing to the information symbol, thereby producing a processed symbol, and transmitting the processed symbol.