Low-Cost Broadband RF Front-End Design for Enhanced Isolation in In-Band Full Duplex Radio

Abstract

Future radios face the challenge of delivering faster data rates while efficiently utilizing the limited and regulated electromagnetic spectrum. In this context, broadband spectrum access in-band full-duplex (IBFD) operation using a simultaneous transmit and receive (STAR) radio architecture is attractive. These radios' features are not only enhancing throughput but also improving multi-user access. However, in designing STAR radios, it is necessary to suppress self-interference (SI) from the transmitted and received signals. The challenge of suppressing this interference becomes even more severe for wideband operation due to the dynamic and time-varying nature of wireless channels. In fact, the SI leakage at the receiver can be up to 10 billion (109) times greater in magnitude than the intended signal power. This necessitates a multi-stage cancellation approach. To address this, we propose a custom-designed and cost-effective multi-stage SI cancellation strategy. The first two stages incorporate passive components to achieve high isolation across a wide bandwidth. Our innovative RF-SIC (self-interference cancellation) filter, combined with a multi-antenna setup, provides > 60 dB of isolation in the analog domain across a contiguous 1 GHz bandwidth from 2–3 GHz. Past STAR radios delivered up to 500 MHz bandwidths. Therefore, this is the first paper to present a RF-SIC filter that works across 1 GHz. The paper is focused on the RF-SIC filter using a microstrip fabrication process. Also, in contrast to past FIR filters, the proposed one doesn't employ discrete components. Instead, it uses the impedance and delay of the shunt section as control parameters.