4,277 research outputs found
Optimization and Analysis of Wireless Powered Multi-antenna Cooperative Systems
In this paper, we consider a three-node cooperative wireless powered
communication system consisting of a multi-antenna hybrid access point (H-AP)
and a single-antenna relay and a single-antenna user. The energy constrained
relay and user first harvest energy in the downlink and then the relay assists
the user using the harvested power for information transmission in the uplink.
The optimal energy beamforming vector and the time split between harvest and
cooperation are investigated. To reduce the computational complexity,
suboptimal designs are also studied, where closed-form expressions are derived
for the energy beamforming vector and the time split. For comparison purposes,
we also present a detailed performance analysis in terms of the achievable
outage probability and the average throughput of an intuitive energy
beamforming scheme, where the H-AP directs all the energy towards the user. The
findings of the paper suggest that implementing multiple antennas at the H-AP
can significantly improve the system performance, and the closed-form
suboptimal energy beamforming vector and time split yields near optimal
performance. Also, for the intuitive beamforming scheme, a diversity order of
(N+1)/2 can be achieved, where N is the number of antennas at the H-AP
Secure Communication with a Wireless-Powered Friendly Jammer
In this paper, we propose to use a wireless-powered friendly jammer to enable
secure communication between a source node and destination node, in the
presence of an eavesdropper. We consider a two-phase communication protocol
with fixed-rate transmission. In the first phase, wireless power transfer is
conducted from the source to the jammer. In the second phase, the source
transmits the information-bearing signal under the protection of a jamming
signal sent by the jammer using the harvested energy in the first phase. We
analytically characterize the long-time behavior of the proposed protocol and
derive a closed-form expression for the throughput. We further optimize the
rate parameters for maximizing the throughput subject to a secrecy outage
probability constraint. Our analytical results show that the throughput
performance differs significantly between the single-antenna jammer case and
the multi-antenna jammer case. For instance, as the source transmit power
increases, the throughput quickly reaches an upper bound with single-antenna
jammer, while the throughput grows unbounded with multi-antenna jammer. Our
numerical results also validate the derived analytical results.Comment: accepted for publication in IEEE Transactions on Wireless
Communication
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