This paper investigates the performance of adaptive modulation in unmanned aerial vehicles (UAVs) relay networks, in order to enhance the utilization of the spectrum resources and ensure the stability of the signal transmission, the UAV relay with the best communication link is selected to transfer the information to the target node via the decoding and forwarding protocol. on this basis, the outage probability of multiple unmanned aerial vehicles (UAVs) assisted communication is derived under independent Rayleigh fading channels. The simulation results indicate the availability of improving the performance of communication relays and communication networks and further suggest that adaptive modulation can significantly improve system performance.
KEYWORDS: Relays, Network security, Signal to noise ratio, Computer security, Picosecond phenomena, Information security, Signal processing, Physical research, Monte Carlo methods, Internet of things
Because of the openness of the wireless relay channel, the confidential information transmitted in the channel is very easy to be eavesdropped on by malicious eavesdroppers and cause information leakage. In specifically, a friendly jammer will transmit a jamming signal to confound an eavesdropper attempting to listen in on a relay transmission. For wireless relay networks using the Rayleigh fading channel model, this research proposes a physical layer security technique based on cooperative interference. In the system, we design two-time stages to realize the transmission of the source to the user. During the initial phase, the signal source transmits a composite signal to both the user and the relay. In the second phase, the confidential information is relayed and artificial noise is generated by friendly jammers to confuse eavesdroppers. Through our proposed method, we derive precise analytical expressions for the intercept probability (IP) and outage probability (OP). The correctness of the theoretical derivation is verified by numerical results and theoretical simulation.
To study the joint effects of turbulence and fog on free-space optical (FSO) communication, a joint fog-turbulence-pointing error probability model for FSO is derived based on the random fog channel, Malaga turbulence model, and pointing error model. The closed-form expressions for the average signal to noise ratio (SNR), outage probability, average bit error rate (BER), ergodic channel capacity, and moment generating function in FSO communication under intensity modulation/direct detection are derived based on the joint model. Based on the unmanned aerial vehicle (UAV) working scenario, applying these expressions, the performance analysis of the inter-UAVs optical wave communication is implemented under the conditions for different beam widths, turbulence intensity and fog density and the pointing error caused by position, orientation, and jitter deviations. The calculated results are in good agreement with the Monte Carlo simulations. The analytical results for the average BER and outage probability show that the increase in beam width can significantly degrade the BER and outage probability, for the UAVs optical communication link. The analysis for the ergodic channel capacity shows that it increases with the increase of average transmission power; however, it increases slowly with the increase of beam width. And the increase in turbulence intensity, fog density, and drone jitter will degrade the communication performance of the system. Our study lays an important theoretical foundation for the development of FSO communication and UAV communication performance improvement in joint fog and turbulent environment.
KEYWORDS: Relays, Signal to noise ratio, Chromium, Receivers, Wireless communications, Composites, Communication engineering, Cognitive modeling, Visualization, Systems modeling
In this thesis, we study the cognitive cooperative non-orthogonal multiple access network with interference power constraint in underlay mode, where a primary receiver is situated at the communication range of the secondary network. In the cognitive secondary network, the secondary originating node transmits information with the cognitive close user directly and with the cognitive remote user by the aid of multiple relays under cognitive radio constraint. Secondary originating node sends the mixed message to the cognitive close user and to multiple relays via NOMA principle. Through the signal to interference plus noise ratio between secondary originating node and multiple relays, the best relay is opted to forward the decode signal to the cognitive remote user. In order to gauge the performance of the system accurately, the exact closed form formulas for the outage probabilities of the cognitive close user and the cognitive remote user are deduced respectively over Rayleigh fading channels. Experiment results indicate that power allocation has a great influence on the performance of system for NOMA network and it is an effective way for improving the performance of cognitive cooperative NOMA network that increasing the quantity of relays.
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