{ m il. tan.dao, fran./III11!: , svettana .girs. eli.mherh.lIhlem mm }@mdh .se Ah.\,troct-Rt'Ccntly, eommunicutinn u sin ~unm anned a erial w hich's (UAVs)as relay nodes ha s beenco nsideredb eneficial fur a num ber uf application s. !\Ion -mer, non-orthogonal multipl ea ccess (l"O:\IA) with users bein ga ssigned differ ent sig nal power lewis whil e s h a ri n~the Slime tim e-frequency domain has been found effectivet oe nhance spectrumu tilizationli nd providep redictable access1 0 th ec hannel. Thus, inIh is paper \\'1,' co nsider a n VAVc omm unlcatkm system with NOMA and pmpn se aso lution tn lind the optimal valu es for the user's power allocatiun cneffieientx WACs) needed to achieve the requ ired levels nf communicatiunreli ahility. We present a closed-term expression fur the "AC nf each user and alsu propose an a l~u r i t h m for ttndtng theop timal altitude ofth e UAV required to satisfy the ralmes sc ondition fora ll users. "'inally, we provid e numerical e xamples and compareth e results for three types of communteauon environment s.

In this paper, we evaluate the overall outage probability (OOP) of pairwise Non-orthogonal Multiple Access (NOMA) for both uplink and downlink. We also propose a dynamic decoding order (DDO) together with a fixed pairwise power allocation (FPPA) scheme, in which the optimal decoding order is decided based on the instantaneous channel gains, and thereafter, a pair of power levels is assigned in accordance with the selected decoding order. Exact closed-form expressions of the OOPs for both uplink and downlink pairwise NOMA considering all proposed decoding orders over Nakagami-m fading are derived. Further, we find the optimal fixed power levels for different power allocation strategies so that the OOPs are minimized. Moreover, we investigate the influence of the distances between the source nodes and the access point (AP), the target transfer rates and the path-loss exponents on the OOPs for all cases of decoding orders. In addition, we benchmark our proposed DDO against other decoding orders in terms of the OOP. The results show that assigning optimal fixed power levels which takes the instantaneous decoding order into account not only improves the communication reliability, but also reduces the complexity and computational load at the AP.

No abstract

Low latency and on demand resource availability enable fog computing to host industrial applications in a cloud like manner. One industrial domain which stands to benefit from the advantages of fog computing is robotics. However, the challenges in developing and implementing a fog-based robotic system are manifold. To illustrate this, in this paper we discuss a system involving robots and robot cells at a factory level, and then highlight the main building blocks necessary for achieving such functionality in a fog-based system. Further, we elaborate on the challenges in implementing such an architecture, with emphasis on resource virtualization, memory interference management, real-time communication and the system scalability, dependability and safety. We then discuss the challenges from a system perspective where all these aspects are interrelated.

In this paper, an uplink pairwise Non-Orthogonal Multiple Access (NOMA) scenario using a mobile access point (AP) or an unmanned aerial vehicle in the presence of a jamming attack is considered. To mitigate the influence of the jamming attack, a joint power allocation and AP placement design is proposed. Accordingly, closed-form expressions of the overall outage probability (OOP) and the individual outage probability (IOP) considering imperfect channel state information for each of the source nodes the AP serves, are derived over Nakagami-m fading channels using dynamic decoding order and fixed pairwise power allocation. We conduct an investigation of the effect of different parameters such as power allocation, source node placements, AP placement, target rates, and jammer location on the OOP and the IOP performance. By adapting the power allocation and the AP placement to the jamming attack, the communication reliability can be increased significantly compared to neglecting the presence of the jammer or treating the jammer as noise. Since the malicious jammer and the AP have conflicting interests in terms of communication reliability, we formulate a non-cooperative game for the two players considering their positions and the power allocation of the NOMA nodes as their strategies and the OOP as utility function. We propose using hybrid simulated annealing -greedy algorithms to address the joint power allocation and AP placement problem for the cases of both a fixed and a mobile jammer. Finally, the Nash equilibrium points are obtained and then the UAV goes directly to this position and keeps staying there to save power consumption.