Fiber Bragg Grating Delay Lines for Wideband Self-Interference Cancellation

In-band full-duplex (IBFD) technology can enable future wireless systems to navigate the congested frequency spectrum by allowing them to detect users on both their current and adjacent channels. This is accomplished by incorporating techniques to sufficiently suppress each nodes self-interference, which becomes increasingly difficult when wide instantaneous bandwidths and realistic multipath environments are considered. RF cancellation is one of the key methods to mitigate this interference but has not previously been demonstrated for wideband-multipath scenarios. This article presents, for the first time, a unique analysis of fiber Bragg grating (FBG) delay lines for specific incorporation into a novel canceller architecture that can overcome these IBFD system limitations. The performance of an FBG-based prototype system with 80 taps is compared to a traditional RF canceller for a multipath interference channel with instantaneous bandwidths ranging from 10 to 1000 MHz centered at 2.5 GHz. The innovative FBG-based design was found to provide approximately 10 dB of additional cancellation for the 1000 MHz case, which demonstrates that FBGs can drastically improve cancellation performance for future IBFD systems.