75 research outputs found
Secrecy Wireless Information and Power Transfer with MISO Beamforming
The dual use of radio signals for simultaneous wireless information and power
transfer (SWIPT) has recently drawn significant attention. To meet the
practical requirement that energy receivers (ERs) operate with significantly
higher received power as compared to information receivers (IRs), ERs need to
be deployed in more proximity to the transmitter than IRs. However, due to the
broadcast nature of wireless channels, one critical issue arises that the
messages sent to IRs can be eavesdropped by ERs, which possess better channels
from the transmitter. In this paper, we address this new secrecy communication
problem in a multiuser multiple-input single-output (MISO) SWIPT system where
one multi-antenna transmitter sends information and energy simultaneously to an
IR and multiple ERs, each with one single antenna. To optimally design transmit
beamforming vectors and their power allocation, two problems are investigated
with different aims: the first problem maximizes the secrecy rate for IR
subject to individual harvested energy constraints of ERs, while the second
problem maximizes the weighted sum-energy transferred to ERs subject to a
secrecy rate constraint for IR. We solve these two non-convex problems
optimally by reformulating each of them into a two-stage problem. First, by
fixing the signal-to-interference-plus-noise ratio (SINR) target for ERs (for
the first problem) or IR (for the second problem), we obtain the optimal
beamforming and power allocation solution by applying the technique of
semidefinite relaxation (SDR). Then, the original problems are solved by a
one-dimension search over the optimal SINR target for ERs or IR. Furthermore,
for each of the two studied problems, suboptimal solutions of lower complexity
are also proposed in which the information and energy beamforming vectors are
separately designed with their power allocation.Comment: accepted by IEEE Transactions on Signal Processing. Longer version of
arXiv:1306.096
Optimization techniques for reliable data communication in multi-antenna wireless systems
This thesis looks at new methods of achieving reliable data communication in wireless communication systems using different antenna transmission optimization methods. In particular, the problems of exploitation of MIMO communication channel diversity, secure downlink beamforming techniques, adaptive beamforming techniques, resource allocation methods, simultaneous power and information transfer and energy harvesting within the context
of multi-antenna wireless systems are addressed
Beamforming Techniques for Non-Orthogonal Multiple Access in 5G Cellular Networks
In this paper, we develop various beamforming techniques for downlink
transmission for multiple-input single-output (MISO) non-orthogonal multiple
access (NOMA) systems. First, a beamforming approach with perfect channel state
information (CSI) is investigated to provide the required quality of service
(QoS) for all users. Taylor series approximation and semidefinite relaxation
(SDR) techniques are employed to reformulate the original non-convex power
minimization problem to a tractable one. Further, a fairness-based beamforming
approach is proposed through a max-min formulation to maintain fairness between
users. Next, we consider a robust scheme by incorporating channel
uncertainties, where the transmit power is minimized while satisfying the
outage probability requirement at each user. Through exploiting the SDR
approach, the original non-convex problem is reformulated in a linear matrix
inequality (LMI) form to obtain the optimal solution. Numerical results
demonstrate that the robust scheme can achieve better performance compared to
the non-robust scheme in terms of the rate satisfaction ratio. Further,
simulation results confirm that NOMA consumes a little over half transmit power
needed by OMA for the same data rate requirements. Hence, NOMA has the
potential to significantly improve the system performance in terms of transmit
power consumption in future 5G networks and beyond.Comment: accepted to publish in IEEE Transactions on Vehicular Technolog
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