In this paper, non-orthogonal multiple access (NOMA) is investigated as a potential solution to address spectrum scarcity in unmanned aerial vehicle (UAV) communications. In particular, the ergodic capacity of uplink (UL) NOMA is characterized within a stochastic geometry framework for a multi-UAV network comprising a ground station (GS) and multiple UAVs. Our analysis reveals that UL NOMA enables fairness, in terms of ergodic capacity, to be achieved in the multi-UAV network. When compared against conventional UL orthogonal multiple access (OMA), we show that the ergodic capacity and ergodic sum capacity is higher for the proposed UL NOMA transmissions. Thus, the proposed scheme enables higher throughput to be achieved in multi-UAV networks while simultaneously improving spectrum efficiency.

The impact of cellular interference on uplink unmanned aerial vehicle (UAV) communications is analyzed in this paper for a multi-UAV network. Specifically, the outage probability and finite signal-to-noise ratio (SNR) diversity gain of the multi-UAV network is characterized in the presence of interference from uplink UAVs and cellular base stations. We demonstrate that the operational altitude of the multi-UAV network determines the severity of cellular interference across low-to-high transmit power regimes. In particular, UAVs operating at higher altitudes are less affected by cellular interference, with higher finite SNR diversity gains and lower outage probability floors observed. Thus, interference mitigation techniques may have to be considered when multi-UAV networks are operating at low altitudes in areas with cellular networks.

In this paper, we demonstrate the necessity of robust cellular interference cancellation when co-locating uplink (UL) unmanned aerial vehicle (UAV) communications with cellular networks. Through a stochastic geometry based evaluation framework, we show through bit error rate (BER) and ergodic capacity analysis that multi-user interference (MUI) is the main limiting factor in UL UAV communications after cellular interference cancellation. It is also observed that high altitudes and weak residual cellular interference corresponds to lower BER. In contrast, low altitudes and weak residual cellular interference results in higher ergodic capacity. Hence, advanced interference cancellation techniques should be considered to suppress the presence of strong MUI in the multi-UAV network.

Unmanned aerial vehicles (UAVs) are set to feature heavily in upcoming fifth generation (5G) networks. Yet, the adoption of multi-UAV networks means that spectrum scarcity in UAV communications is an issue in need of urgent solutions. Towards this end, downlink non-orthogonal multiple access (NOMA) is investigated in this paper for multi-UAV networks to improve spectrum utilization. Using the bivariate Rician shadowed fading model, closed-form expressions for the joint probability density function (PDF), marginal cumulative distribution functions (CDFs), and outage probability expressions are derived. Under a stochastic geometry framework for downlink NOMA at the UAVs, an outage probability analysis of the multi-UAV network is conducted, where it is shown that downlink NOMA attains lower outage probability than orthogonal multiple access (OMA). Furthermore, it is shown that NOMA is less susceptible to shadowing than OMA.

As unmanned aerial vehicles (UAVs) are expected to play a significant role in fifth generation (5G) networks, addressing spectrum scarcity in UAV communications remains a pressing issue. In this regard, the feasibility of full-duplex non-orthogonal multiple access (FD-NOMA) UAV communications to improve spectrum utilization is investigated in this paper. Specifically, closed-form outage probability expressions are presented for FD-NOMA, half-duplex non-orthogonal multiple access (HD-NOMA), and half-duplex orthogonal multiple access (HD-OMA) schemes over Rician shadowed fading channels. Extensive analysis revealed that the bottleneck of performance in FD-NOMA is at the downlink UAVs. Also, FD-NOMA exhibits lower outage probability at the ground station (GS) and downlink UAVs than HD-NOMA and HD-OMA under low transmit power regimes. At high transmit power regimes, FD-NOMA is limited by residual SI and inter-UAV interference at the downlink UAVs and FD-GS, respectively. The impact of shadowing is also shown to affect the reliability of FD-NOMA and HD-OMA at the downlink UAVs.

A hybrid-duplex aeronautical communication system (HBD-ACS) consisting of a full-duplex-enabled ground station (GS) and two half-duplex (HD) air stations (ASs) is proposed as a direct solution to the spectrum crunch faced by the aviation industry. The closed-form outage probability and finite signal-to-noise ratio (SNR) diversity gain expressions in aeronautical communications over Rician fading channels are derived for a successive interference cancellation (SIC) detector. Similar expressions are also presented for an interference ignorant (II) detector and the HD-equivalent modes at GS and ASs. Through the outage and finite SNR diversity gain analysis conducted at the nodes, and system level, residual self-interference (SI) and inter-AS interference are found to be the primary limiting factors in the proposed HBD-ACS. Further investigations revealed that the II and SIC detectors in the proposed HBD-ACS are suitable for the weak and strong interference scenarios, respectively. When compared with the HD-ACS, the proposed HBD-ACS achieves a lower outage probability and higher diversity gains at higher multiplexing gains when operating at low SNRs. The finite SNR analysis also showed the possibility of the proposed HBD-ACS being able to attain interference-free diversity gains through proper management of the residual SI. Hence, the proposed HBD-ACS is more reliable and can provide a better throughput compared with the existing HD-ACS at low-to-moderate SNRs.

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 full-duplex (FD) enabled ground station (GS), and legacy half-duplex (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.

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.

The demand for high data rate communication is continuously increasing. To address this, studies on bit error rate improvements, cooperative diversity and transmit diversity have been topics of interest. In this paper, a novel Quad State- Paired QPSK (QS-PQPSK) modulation scheme is proposed. The proposed technique is simulated and compared with other main PSK-based modulation schemes. Preliminary simulation results show that in the presence of only Additive White Gaussian Noise (AWGN), QS-PQPSK performs better than 8-PSK in terms of symbol error rate and effective throughput. In a Rayleigh flat fading channel with AWGN, QS-PQPSK outperforms 8-PSK in terms of bit and symbol error rates and effective throughput. The performance of the proposed method also surpasses the other main PSK-based methods in most cases. This highlights the proposed QS-PQPSK technique as a viable spectrally efficient modulation technique for high data rate applications.

An enormous influx of wireless services and devices coupled with inefficient usage of electromagnetic spectrum has led to an apparent scarcity of usable radio bandwidth. Cognitive radio is leading the trend for increasing the spectrum efficiency by utilising the vacancy in the radio spectrum created by absence of the licensed primary user. This paradigm shift can only take place if the means to detect the primary user are well established so that an ecosystem can be created where both primary and secondary users can co-exist without interfering with each other. In this study the authors propose a two-stage detection mechanism which gives an improved performance over conventional single-stage detectors yet optimises the usage of the second stage, thereby reducing the sensing time as compared to conventional two-stage spectrum sensing algorithms. A hardware implementation of the algorithm has also been done to quantify the area and power consumption values. By utilising the second-stage optimally, the algorithm presented in this study helps in reducing the sensing time by 86% as compared with the conventional two-stage detector. By not activating the second stage at high SNRs, the proposed algorithm saves 0.915 W of dynamic power out of a total of 1.09 W, thus effectively reducing the dynamic power consumption by 84%.

Spectrum sensing techniques for Cognitive radios have led to the emergence of a wide variety of analytical methods to detect the presence of a primary user. Though each technique has its own advantages, the disadvantages associated with them makes a standalone implementation of the technique unviable for practical use. A two stage detector for spectrum sensing can be used to mitigate the disadvantages of a single stage detection technique and synergize the advantages offered by the individual methods. However, a two stage analysis increases the time taken to sense the spectrum and arrive at a conclusive result. In this paper, we propose an algorithm which can be used to minimize the time taken by a two stage detector. Simulation results have been used to show that the proposed algorithm leads to a large savings in time as compared to an existing two stage detection algorithm. The savings in time increases as spectrum utilization of the band under consideration becomes more sparse.

This work describes a novel multi-signaling protocol architecture of a VoIP end point in an IP packet network. The endpoint is a single channel IP phone or gateway, but can handle H.323, SIP or MGCP calls simultaneously to/from different end points. The other endpoints could be using any of the signaling protocols. The endpoint is registered to a media gateway controller, SIP server and a H.323 gatekeeper, possibly with the same number. The details of the design including the state machines of the different call control modules are described. The advantage of such architecture is reduced delay in call setup between two endpoints that otherwise use different signaling protocols. The architecture has been implemented and verified on one of the company's IP phone chip, which has an ARM7 and a DSF core. An example of a simple handling of a second call from a different protocol endpoint, when the first call is in progress, has also been given.