  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.
