In conventional half-duplex (HD) wireless communications systems, bidirectional communications between a pair of nodes is achieved with eitherfrequency division duplexing (FDD) or time division duplexing (TDD).The former technique employs different frequency bands for the uplink(UL) and downlink (DL), whereas, in the latter technique, a single channel is shared in the time domain for both UL and DL. Such techniqueshowever may not be suitable to fulfil the envisioned requirements of nextgeneration wireless systems. Historically, simultaneous transmission andreception in wireless communications was deemed infeasible in practicedue to the so called self-interference (SI), which is the interference generated by the transmitter of a radio on its own receiver. Recent developments in SI cancellation techniques have led to the practical realizationof FD radios. FD technology has a number of attractive features, forexample, it can potentially double (theoretically) the ergodic capacity,reduce the feedback delay, decrease the end-to-end delay, improve thenetwork secrecy and increase the efficiency of network protocols.Motivated by these developments,first in this study, a two-tier heterogeneous cellular networks (HCNs) wherein the first tier comprises half-duplex (HD) macro base stations (BSs) and the second tier consists of FD small cells. Advocating for the use of small cells as a strong candidate to deploy FD technology, for its low-powered nature and ease of deployment. The study is conducted through a stochastic geometry approach, we characterize and derive the closed-form expressions for the outage probability and the rate coverage.Furthermore, we move up the layers of the protocol stack and presentan energy-effcient medium access control (MAC) protocol for distributedfull-duplex (FD) wireless network, termed as Energy-FDM. The key aspects of the Energy-FDM include energy-effciency, co-existence of distinct types of FD links, throughput improvement, and backward comparability with conventional half-duplex (HD) nodes.Finally, we present a cross-layer aided routing protocol, termed asX-FDR, for multi-hop FD wireless networks. X-FDR exploits a Physical(PHY) layer model capturing imperfection of SI cancellation. At themedium access control (MAC) layer, X-FDR adopts an optimized MACprotocol which implements a power control mechanism without creatingthe hidden terminal problem. X-FDR exploits the unique characteristicsof FD technology at the network layer to construct energy-efficient andlow latency routes in the network.
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