179 research outputs found
Impact of Pointing Errors on the Performance of Mixed RF/FSO Dual-Hop Transmission Systems
In this work, the performance analysis of a dual-hop relay transmission
system composed of asymmetric radio-frequency (RF)/free-space optical (FSO)
links with pointing errors is presented. More specifically, we build on the
system model presented in [1] to derive new exact closed-form expressions for
the cumulative distribution function, probability density function, moment
generating function, and moments of the end-to-end signal-to-noise ratio in
terms of the Meijer's G function. We then capitalize on these results to offer
new exact closed-form expressions for the higher-order amount of fading,
average error rate for binary and M-ary modulation schemes, and the ergodic
capacity, all in terms of Meijer's G functions. Our new analytical results were
also verified via computer-based Monte-Carlo simulation results.Comment: 6 pages, 3 figure
Multiple UAVs as relays : multi-hop single link versus multiple dual-hop links
Unmanned aerial vehicles (UAVs) have found many important applications in communications. They can serve as either aerial base stations or mobile relays to improve the quality of services. In this paper, we study the use of multiple UAVs in relaying. Considering two typical uses of multiple UAVs as relays that form either a single multi-hop link or multiple dual-hop links, we first optimize the placement the UAVs by maximizing the end-to-end signal-to-noise ratio for three useful channel models and two common relaying protocols. Based on the optimum placement, the two relaying setups are then compared in terms of outage and bit error rate. Numerical results show that the dual-hop multi-link option better than the multi-hop single link option when the air-to-ground path loss parameters depend on the UAV positions. Otherwise, the dual-hop option is only better when the source-to-destination distance small. Also, decode-and-forward UAVs provide better performances than amplify-and-forward UAVs. The investigation also reveals the effects of important system parameters on the optimum UAV positions and the relaying performances to provide useful design guidelines
Performance Analysis of Relay Selection Schemes in Multi-Hop Decode-and-Forward Networks
This paper analyses the data rate achieved by various relay selection schemes
in a single-user multi-hop relay network with decode-and-forward (DF) relaying.
While the single-user relay selection problem is well studied in the
literature, research on achievable rate maximization is limited to dual-hop
networks and multi-hop networks with a single relay per hop. We fill this
important gap by focusing on achievable rate maximization in multi-hop,
multi-relay networks. First, we consider optimal relay selection and obtain two
approximations to the achievable rate. Next, we consider three existing
sub-optimal relay selection strategies namely hop-by-hop, ad-hoc and
block-by-block relay selection and obtain exact expressions for the achievable
rate under each of these strategies. We also extend the sliding window based
relay selection to the DF relay network and derive an approximation to the
achievable rate. Further, we investigate the impact of window size in sliding
window based relay selection and show that a window size of three is sufficient
to achieve most of the possible performance gains. Finally, we extend this
analysis to a noise limited multi-user network where the number of available
relay nodes is large compared to the number of users and derive approximations
to the achievable sum-rate
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