2 research outputs found
Relay-Pair Selection in Buffer-Aided Successive Opportunistic Relaying using a Multi-Antenna Source
We study a cooperative network with a buffer-aided multi-antenna source,
multiple half-duplex (HD) buffer-aided relays and a single destination. Such a
setup could represent a cellular downlink scenario, in which the source can be
a more powerful wireless device with a buffer and multiple antennas, while a
set of intermediate less powerful devices are used as relays to reach the
destination. The main target is to recover the multiplexing loss of the network
by having the source and a relay to simultaneously transmit their information
to another relay and the destination, respectively. Successive transmissions in
such a cooperative network, however, cause inter-relay interference (IRI).
First, by assuming global channel state information (CSI), we show that the
detrimental effect of IRI can be alleviated by precoding at the source,
mitigating or even fully cancelling the interference. A cooperative relaying
policy is proposed that employs a joint precoding design and relay-pair
selection. Note that both fixed rate and adaptive rate transmissions can be
considered. For the case when channel state information is only available at
the receiver side (CSIR), we propose a relay selection policy that employs a
phase alignment technique to reduce the IRI. The performance of the two
proposed relay pair selection policies are evaluated and compared with other
state-of-the-art relaying schemes in terms of outage and throughput. The
results show that the use of a powerful source can provide considerable
performance improvements.Comment: 32 pages, 7 figures, Ad Hoc Network
Ergodic Sum Rate Analysis of UAV-Based Relay Networks with Mixed RF-FSO Channels
Unmanned aerial vehicle (UAV)-based communications is a promising new
technology that can add a wide range of new capabilities to the current network
infrastructure. Given the flexibility, cost-efficiency, and convenient use of
UAVs, they can be deployed as temporary base stations (BSs) for on-demand
situations like BS overloading or natural disasters. In this work, a UAV-based
communication system with radio frequency (RF) access links to the mobile users
(MUs) and a free-space optical (FSO) backhaul link to the ground station (GS)
is considered. In particular, the RF and FSO channels in this network depend on
the UAV's positioning and (in)stability. The relative position of the UAV with
respect to the MUs impacts the likelihood of a line-of-sight (LOS) connection
in the RF link and the instability of the hovering UAV affects the quality of
the FSO channel. Thus, taking these effects into account, we analyze the
end-to-end system performance of networks employing UAVs as buffer-aided (BA)
and non-buffer-aided (non-BA) relays in terms of the ergodic sum rate.
Simulation results validate the accuracy of the proposed analytical derivations
and reveal the benefits of buffering for compensation of the random
fluctuations caused by the UAV's instability. Our simulations also show that
the ergodic sum rate of both BA and non-BA UAV-based relays can be enhanced
considerably by optimizing the positioning of the UAV. We further study the
impact of the MU density and the weather conditions on the end-to-end system
performance