Analog Least Mean Square Loop for Self-Interference Cancellation: A Practical Perspective.

Area of Science:

• Electrical Engineering
• Telecommunications
• Signal Processing

Background:

• Self-interference (SI) is a major obstacle to practical in-band full-duplex (IBFD) communication.
• Analog multi-tap adaptive filters effectively mitigate SI by addressing nonlinear components and noise.
• The Analog Least Mean Square (ALMS) loop offers a simple, purely analog solution for SI cancellation.

Purpose of the Study:

• To propose and implement a practical structure for the ALMS loop.
• To evaluate the SI cancellation performance of an implemented ALMS loop prototype in an IBFD system.
• To analyze the impact of system parameters on ALMS loop performance.

Main Methods:

• Implementation of a two-tap ALMS loop using off-the-shelf components for a 2.4 GHz IBFD system.
• Experimental evaluation in single-carrier signaling IBFD systems with 20 MHz and 50 MHz bandwidths.
• Analysis of the effect of pulse shaping filter's roll-off factor and testing with multicarrier signaling.

Main Results:

• Achieved 39 dB and 33 dB of SI cancellation in the radio frequency domain for 20 MHz and 50 MHz bandwidths, respectively.
• Demonstrated that the ALMS loop's performance is consistent across single-carrier and multicarrier signaling.
• Confirmed the impact of the pulse shaping filter's roll-off factor on SI cancellation levels.

Conclusions:

• The implemented ALMS loop prototype effectively cancels self-interference in IBFD systems.
• The experimental results validate theoretical analyses of ALMS loop behavior.
• The proposed practical ALMS loop structure is suitable for real-world IBFD applications.