Design and Testbed Deployment of Frequency-Domain Equalization Full Duplex Radios

TL;DR

This work demonstrates that frequency-domain equalization (FDE) based RF self-interference cancellation can deliver wideband, high-precision cancellation for practical full-duplex radios. It develops a two-tap PCB canceller, a calibrated physical model, and a MATLAB-optimized configuration strategy, achieving up to $95\,\mathrm{dB}$ overall SIC across $20\,\mathrm{MHz}$ and a $1.87\times$ FD rate gain in real testbeds. The authors validate network-level gains across UL-DL and heterogeneous HD/FD networks, showing performance that tracks analytical predictions and depends on user SNR and FD-user count. They also release open COSMOS FD radios and a comprehensive baseband dataset to enable higher-layer protocol research, advancing the practical deployment of FDE-based FD radios in next-generation networks.

Abstract

Full-duplex (FD) wireless can significantly enhance spectrum efficiency but requires effective self-interference (SI) cancellers. RF SI cancellation (SIC) via frequency-domain equalization (FDE), where bandpass filters channelize the SI, is suited for integrated circuits (ICs). In this paper, we explore the limits and higher layer challenges associated with using such cancellers. We evaluate the performance of a custom FDE-based canceller using two testbeds; one with mobile FD radios and the other with upgraded, static FD radios in the PAWR COSMOS testbed. The latter is a lasting artifact for the research community, alongside a dataset containing baseband waveforms captured on the COSMOS FD radios, facilitating FD-related experimentation at the higher networking layers. We evaluate the performance of the FDE-based FD radios in both testbeds, with experiments showing 95 dB overall achieved SIC (52 dB from RF SIC) across 20 MHz bandwidth, and an average link-level FD rate gain of 1.87x. We also conduct experiments in (i) uplink-downlink networks with inter-user interference, and (ii) heterogeneous networks with half-duplex and FD users. The experimental FD gains in the two types of networks depend on the users' SNR values and the number of FD users, and are 1.14x-1.25x and 1.25x-1.73x, respectively, confirming previous analytical results.

Figures (22)

• Figure 1: (a) The frequency-domain equalization- (FDE-) based wideband RF canceller implemented using discrete components on a printed circuit board (PCB), (b) the implemented FDE-based mobile full-duplex (FD) radio, and (c) the mobile testbed consisting of an FD base station (BS) and 2 users mounted on carts that can operate in either half-duplex (HD) or FD mode.
• Figure 2: Integration of the FDE-based FD radios in COSMOS Sandbox 2. (a) labelled diagram of the "canceller box", showing the various system components. (b) Two out of the four canceller boxes mounted in the testbed.
• Figure 3: Block diagram of an FD radio.
• Figure 4: (a) Block diagram of an FDE-based RF canceller with $M=2$ FDE taps, and (b) illustration of amplitude and phase responses of an ideal $2^{\textrm{nd}}$-order bandpass filter (BPF) with amplitude, phase, center frequency, and quality factor (i.e., group delay) controls.
• Figure 5: Block diagram of the implemented 2 FDE taps in the PCB canceller (see Fig. \ref{['fig:fde-concept']}(a)), each of which consists of an RLC bandpass filter (BPF), an attenuator for amplitude control, and a phase shifter for phase control.