Recently, the use of multi-rotor (MR) unmanned aerial vehicles (UAVs) has emerged as a promising solution for establishing flexible free-space optical (FSO) communication links. We address in this paper accurate channel modeling to assess the benefits of MR UAV-based deployment for such links. In particular, in the absence of active tracking subsystems, we derive statistical models for ground-to-UAV, UAV-to-UAV, and UAV-to-ground links over both Gamma-Gamma and lognormal atmospheric turbulence models. Unlike previous works on this topic, our proposed model considers the joint effect of atmospheric turbulence along with position and angle-of-arrival fluctuations. The high accuracy of the proposed analytical models is verified by comparing numerically solved and Monte-Carlo simulation results in terms of link outage probability. We further discuss the impact of different transmitter/receiver parameters and their optimization in view of maximizing the link availability.

Ubiquitous networks provide roaming service for mobile nodes enabling them to use the services extended by their home networks in a foreign network. A mutual authentication scheme between the roamed mobile node and the foreign network is needed to be performed through the home network. Various authentication schemes have been developed for such networks, but most of them failed to achieve security in parallel to computational efficiency. Recently, Shin et al. and Wen et al. separately proposed two efficient authentication schemes for roaming service in ubiquitous networks. Both argued their schemes to satisfy all the security requirements for such systems. However, in this paper, we show that Shin et al.'s scheme is susceptible to: (i) user traceability; (ii) user impersonation; (iii) service provider impersonation attacks; and (iv) session key disclosure. Furthermore, we show that Wen et al.'s scheme is also insecure against: (i) session key disclosure; and (ii) known session key attacks. To conquer the security problems, we propose an improved authentication scheme with anonymity for consumer roaming in ubiquitous networks. The proposed scheme not only improved the security but also retained a lower computational cost as compared with existing schemes. We prove the security of proposed scheme in random oracle model. of 20Step 1: MN ! FA: M 1 D ¹M V 1 ; M V 2 ; M V 3 º MN inputs his identity ID MN and password P W MN . MN then computes h.ID M jjh.P W MN // and checks if the result and A MN stored in his mobile device are of 20 4 Mobile node chooses its identity ID MN , password P W MN , and a random number d . Further, MN computes f D h.ID MN kP W MN kd /. Finally, MN sends ID MN and f to the HA by using some secure channel. HA computes K MN D h.ID MN jjx/˚f using secret x. Further, HA pledges a counter ct r MN D 0 for MN and forms a record .ID MN ; ct r MN / in his database. HA then engraves the smart card (SC MN ) with K MN , ct r MN , h.:/, and n. HA issues the smart card (SC MN ) to MN. After obtaining the smart card (SC MN ), MN computes f D h.ID MN˚P W MN˚d / and writes f on SC MN . Finally, the SC MN contains ¹ct r MN ; K MN ; f ; n; d , h.:/º. Login and authentication phaseThe procedure for login and authentication is outlined in Figure 3; the same is illustrated as follows: (1) MN ! FA W M 1 . MN inserts his smart card (SC MN ) in the reader and enters his identity ID MN and password P W MN . SC MN computes f 0 D h.ID MN˚P W MN˚d / and then verifies whether f 0 D f or not. If f 0 ¤ f , the login phase terminates immediately. Otherwise, SC MN computes K MN D K MN˚h .ID MN kP W MN kd /. Then SC MN generates random n MN and computes ct r MN D ct r MN C 1 and V 1 D .ID MN jj K MN jjn MN jjct r MN jjID FA / 2 modn. Finally, MN sends the M 1 D .V 1 ; ct r MN ; ID HA / to FA.Figure 3. Wen et al.'s scheme [38]. Proposition 5 (Secure key establishment)The improved scheme provides secure key establishment. ProofAfter completion of the protocol, the MN, FA, and HA will establish a common session key SK FA D SK MN ...

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We introduce and discuss new accelerated algorithms for linear discriminant analysis (LDA) in unimodal multiclass Gaussian data. These algorithms use a variable step size, optimally computed in each iteration using (i) the steepest descent, (ii) conjugate direction, and (iii) Newton-Raphson methods in order to accelerate the convergence of the algorithm. Current adaptive methods based on the gradient descent optimization technique use a fixed or a monotonically decreasing step size in each iteration, which results in a slow convergence rate. Furthermore, the convergence of these algorithms depends on appropriate choices of the step sizes. The new algorithms have the advantage of automatic optimal selection of the step size using the current data samples. Based on the new adaptive algorithms, we present self-organizing neural networks for adaptive computation of −1/2 and use them in cascaded form with a PCA network for LDA. Experimental results demonstrate fast convergence and robustness of the new algorithms and justify their advantages for on-line pattern recognition applications with stationary and non-stationary multidimensional input data.

Assuming imperfect channel estimation, we propose an improved detector for ultra wideband (UWB) systems employing multiband orthogonal frequency-division multiplexing (MB-OFDM). By adopting a Bayesian approach involving the statistics of the channel estimation errors, we formulate an improved maximum-likelihood (ML) detection metric taking into account the characteristics of the channel estimates. As a first step, we propose a modified iterative detector based on maximum a posteriori which reduces the impact of channel uncertainty on the decoder performance, by an appropriate use of this metric. The results are compared to those obtained by using a detector based on a mismatched ML metric, which uses the channel estimate as if it was the perfect channel. In a second step, we calculate the information rates achieved by both the improved and mismatched ML detectors, in terms of achievable outage rates. These outage rates are compared to those provided by a theoretical (not practical) decoder defined as the best decoder in the presence of channel estimation errors. Numerical results over both uncorrelated Rayleigh fading channels and realistic UWB channels show that the improved detector provides significant gains in terms of bit error rate and achievable outage rates, compared to the classically-used mismatched approach, without any increase in the receiver complexity.

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