  Full-duplex (FD) radio has been introduced for bidirectional communications
on the same temporal and spectral resources so as to maximize spectral
efficiency. In this paper, motivated by the recent advances in FD radios, we
provide a foundation for hybrid-duplex heterogeneous networks (HDHNs), composed
of multi-tier networks with a mixture of access points (APs), operating either
in bidirectional FD mode or downlink half-duplex (HD) mode. Specifically, we
characterize the net- work interference from FD-mode cells, and derive the HDHN
throughput by accounting for AP spatial density, self-interference cancellation
(IC) capability, and transmission power of APs and users. By quantifying the
HDHN throughput, we present the effect of network parameters and the self-IC
capability on the HDHN throughput, and show the superiority of FD mode for
larger AP densities (i.e., larger network interference and shorter
communication distance) or higher self-IC capability. Furthermore, our results
show operating all APs in FD or HD achieves higher throughput compared to the
mixture of two mode APs in each tier network, and introducing hybrid-duplex for
different tier networks improves the heterogenous network throughput.
