Outage analysis and finite SNR diversity-multiplexing tradeoff of hybrid-duplex systems for aeronautical communications

In this work, the advantages of joint detection (JD) in a hybrid-duplex unmanned aerial vehicle (UAV) communication system (HBD-UCS) are investigated as a step towards addressing spectrum scarcity in UAV communications. Through extensive outage probability and finite signal-to-noise-ratio (SNR) diversity gain analysis, we showed that the performance of joint detection (JD) is independent of the strength and the data rate of the inter-UAV interference signal. On the contrary, the successive interference cancellation (SIC) detector requires the data rate of the interfering UAV to be less than the ground station before meaningful performance can be seen. At the system level, it is observed that the half-duplex UAV communication system outperforms the HBD-UCS with JD at moderate and high SNR regimes, as the latter is constrained by self-interference at the full-duplex ground station. Lastly, we investigated the multiplexing gain region and showed that the joint detector offers higher diversity gain over a wide range of multiplexing gains over the interference ignorant (II) and the SIC detector.

With the growing popularity of unmanned aerial vehicles (UAVs), spectrum management is a pressing issue, particularly for multi-UAV systems. To this end, a hybrid-duplex (HBD) UAV communication system (UCS) consisting of a fullduplex (FD) enabled ground station (GS), and legacy halfduplex (HD) UAVs is proposed in this paper. To model the fading and shadowing environment commonly encountered in UAV communications, a mix of Rician and Rician shadowed fading is assumed. In particular, novel power series approximations of the Rician shadowed fading power probability density function (PDF), and cumulative distribution function (CDF) are presented, along with closed-form outage probability expressions.Performance analysis shows that the proposed HBD-UCS exhibits lower outage probability than the HD-UCS when shadowing is encountered at low signal-to-noise ratios (SNRs). Also, inter-UAV interference has a stronger influence on outage probability decay at low SNR regimes, with lower inter-UAV interference corresponding to a sharper decline in outage probability.

In this work, the outage probability of an unmanned aerial vehicle (UAV) network with hybrid-duplex (HBD) UAV communications is investigated in a stochastic geometry framework. We demonstrate that the HBD UAV communication system (HBD-UCS) can concurrently support more UAVs while achieving higher reliability than the half-duplex (HD) UCS (HD-UCS). Specifically, at low transmit power regimes, it is shown that the HBD-UCS attains lower uplink and downlink outage probability than an HD-UCS, even as the UAV operating altitude is increased.

A hybrid-duplex (HBD) UAV communication system (UCS), i.e., HBD-UCS, to improve spectrum utilization is investigated in this work. By considering the combined effect of fading and shadowing, a comprehensive outage probability analysis of the HBD-UCS under various inter-UAV interference and shadowing scenarios over Rician shadowed fading channels is conducted. It is demonstrated that the ground station (GS) in full-duplex (FD) mode operates at lower outage probability than in half-duplex (HD) mode. Furthermore, the joint detector is shown to achieve lower outage probability than the interference ignorant (II) detector and HD-UCS, even when severe shadowing is encountered. As such, utilizing joint detectors in an HBD-UCS enables multi-UAV networks to achieve high reliability when operating in urban environments. INDEX TERMS Unmanned aerial vehicle, spectrum efficiency, half-duplex, full-duplex, hybrid-duplex, outage probability, rician, shadowing. A. MOTIVATION AND RELATED LITERATURE Although utilitarian, multi-UAV networks are mired with its own set of challenges that must be addressed. Of particular importance is the lack of available spectrum for UAV communications [5], [6]. Despite the allocation of parts of The associate editor coordinating the review of this manuscript and approving it for publication was Jiayi Zhang. the L-band and C-band for UAV control and non-payload communications (CNPC) by the International Telecommunications Union (ITU) [5], spectrum scarcity is still a challenge. In particular, many other existing systems, e.g., aeronautical communication systems, are also operating on both the L-band and C-band [5]-[7]. In this aspect, a hybrid-duplex (HBD) UAV communication system (UCS), i.e., HBD-UCS, can be a direct solution address spectrum scarcity in UAV communications. The HBD paradigm enables UAVs with existing half-duplex (HD) communication systems, i.e., HD-UCS to simultaneously operate on the same spectrum with full-duplex (FD) ground stations (GSs), effectively doubling spectrum efficiency. However, the simultaneous transmission and reception of signals results in self-interference (SI) at the FD-enabled GS, which can be mitigated via passive or active SI mitigation architectures [8], [9]. The former entails introducing path loss and shadowing, e.g., through antenna placements, while the latter involves canceling SI in the analog or digital domain [9]. Even after SI mitigation, residual SI can still remain due to non-ideal FD transceiver impairments, such as carrier phase noise and imperfect

In this paper, a hybrid-duplex control and nonpayload communication (HBD-CNPC) system is proposed to address spectrum scarcity in unmanned aerial vehicle (UAV) communications. By considering the effects of fading and inter-UAV interference, an outage analysis of the proposed system is conducted. It is shown that the successive interference cancellation (SIC) detector achieves lower outage probability than the interference ignorant (II) detector when the desired signal experiences more severe fading than the interfering signal. It is also demonstrated that the HBD-CNPC system achieves better reliability with longer transmission rage and lower transmission requirements over half-duplex (HD) CNPC systems.

Air traffic growth is expected to rise sharply in the near future, causing a swell in data communication demands on the congested aeronautical spectrum which cannot be met with existing aeronautical communication systems. To this end, a hybrid-duplex (HBD) aeronautical communications system consisting of a full-duplex (FD) enabled ground station, and legacy half-duplex (HD) air-stations is proposed as a direct solution to boost spectral efficiency. In particular, the system level outage probabilities and transmission power requirements of the proposed HBD and HD aeronautical communication systems are analyzed. Performance analysis shows that the proposed HBD system can attain better outage performance in the en route scenario. The proposed HBD system is also able to support an equivalent data rate as an HD system with lower transmit power and signal-to-interference-plus-noise-ratio (SINR) requirements and longer transmission range when inter-aircraft interference and residual self-interference is kept sufficiently low.

To address spectrum scarcity in unmanned aerial vehicle (UAV) communications, non-orthogonal multiple access (NOMA) aided multi-UAV communications in full-duplex (FD) heterogeneous networks (HetNets) is investigated in this paper. Specifically, an ergodic capacity analysis of NOMA-aided multi-UAV communications in FD-HetNets is conducted through a moment generating function (MGF) approach within a stochastic geometry framework. By employing the MGF approach to evaluate ergodic capacity, exact expressions that are simpler to evaluate are obtained. When compared against half-duplex HetNets, i.e., HD-HetNets, FD-HetNets with effective interference management enable higher ergodic capacity to be obtained by the macro base station and UAVs. Furthermore, we show that it is possible for NOMA-aided multi-UAV communications in FD-HetNets to achieve higher ergodic sum capacity and ergodic capacity gains than HD-HetNets while supporting more UAVs at low altitude due to a stronger desired signal. Even with lower levels of self-interference (SI) suppression and strong phase noise, NOMA-aided multi-UAV communications in FD-HetNets is still able to achieve higher ergodic sum capacity over HD-HetNets. Therefore, the attractiveness of NOMA-aided multi-UAV communications in FD-HetNets is highlighted as a promising solution towards improving spectrum utilization in UAV communications.