  In this paper, we introduce dynamic time-frequency-division duplex (D-TFDD),
which is a novel duplexing scheme that combines time-division duplex (TDD) and
frequency-division duplex (FDD). In D-TFDD, a user receives from the base
station (BS) on the downlink in one frequency band and transmits to the BS on
the uplink in another frequency band, as in FDD. Next, the user shares its
uplink transmission (downlink reception) on the corresponding frequency band
with the uplink transmission or the downlink reception of another user in a
D-TDD fashion. Hence, in a given frequency band, the BS communicates with user
1 (U1) and user 2 (U2) in a D-TDD fashion. The proposed D-TFDD scheme does not
require inter-cell interference (ICI) knowledge and only requires channel state
information (CSI) of the local BS-U1 and BS-U2 channels. Thereby, it is
practical for implementation. The proposed D-TFDD scheme increases the
throughput region between the BS and the two users in a given frequency band,
and significantly decreases the outage probabilities on the corresponding BS-U1
and BS-U2 channels. Most importantly, the proposed D-TFDD scheme doubles the
diversity gain on both the corresponding BS-U1 and the BS-U2 channels compared
to the diversity gain of existing duplexing schemes, which results in very
large performance gains.
