  In-band full-duplex transmission allows a relay station to theoretically
double its spectral efficiency by simultaneously receiving and transmitting in
the same frequency band, when compared to the traditional half-duplex or
out-of-band full-duplex counterpart. Consequently, the induced
self-interference suffered by the relay may reach considerable power levels,
which decreases the signal-to-interference-plus-noise ratio (SINR) in a
decode-and-forward (DF) relay, leading to a degradation of the relay
performance. This paper presents a technique to cope with the problem of
self-interference in broadband multiple-input multiple-output (MIMO) relays.
The proposed method uses a time-domain cancellation in a DF relay, where a
replica of the interfering signal is created with the help of a recursive least
squares (RLS) algorithm that estimates the interference frequency-selective
channel. Its convergence mean time is shown to be negligible by simulation
results, when compared to the length of a typical orthogonal-frequency division
multiplexing (OFDM) sequences. Moreover, the bit-error-rate (BER) and the SINR
in a OFDM transmission are evaluated, confirming that the proposed method
extends significantly the range of self-interference power to which the relay
is resilient to, when compared with other mitigation schemes.
