833 research outputs found
Energy Harvesting for Secure OFDMA Systems
Energy harvesting and physical-layer security in wireless networks are of
great significance. In this paper, we study the simultaneous wireless
information and power transfer (SWIPT) in downlink orthogonal
frequency-division multiple access (OFDMA) systems, where each user applies
power splitting to coordinate the energy harvesting and information decoding
processes while secrecy information requirement is guaranteed. The problem is
formulated to maximize the aggregate harvested power at the users while
satisfying secrecy rate requirements of all users by subcarrier allocation and
the optimal power splitting ratio selection. Due to the NP-hardness of the
problem, we propose an efficient iterative algorithm. The numerical results
show that the proposed method outperforms conventional methods.Comment: Accepted by WCSP 201
Subcarrier and Power Allocation in WiMAX
Worldwide Interoperability for Microwave Access (WiMAX) is one of the latest technologies for providing Broadband Wireless Access (BWA) in a metropolitan area. The use of orthogonal frequency division multiplexing (OFDM) transmissions has been proposed in WiMAX to mitigate the complications which are associated with frequency selective channels. In addition, the multiple access is achieved by using orthogonal frequency division multiple access (OFDMA) scheme which has several advantages such as flexible resource allocation, relatively simple transceivers, and high spectrum efficient. In OFDMA the controllable resources are the subcarriers and the allocated power per subband. Moreover, adaptive subcarrier and power allocation techniques have been selected to exploit the natural multiuser diversity. This leads to an improvement of the performance by assigning the proper subcarriers to the user according to their channel quality and the power is allocated based on water-filling algorithm. One simple method is to allocate subcarriers and powers equally likely between all users. It is well known that this method reduces the spectral efficiency of the system, hence, it is not preferred unless in some applications.
In order to handle the spectral efficiency problem, in this thesis we discuss three novel resources allocation algorithms for the downlink of a multiuser OFDM system and analyze the algorithm performances based on capacity and fairness measurement. Our intensive simulations validate the algorithm performances.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format
Power and Subcarrier Allocation for Physical-Layer Security in OFDMA-based Broadband Wireless Networks
Providing physical-layer security for mobile users in future broadband
wireless networks is of both theoretical and practical importance. In this
paper, we formulate an analytical framework for resource allocation in a
downlink OFDMA-based broadband network with coexistence of secure users (SU)
and normal users (NU). The SU's require secure data transmission at the
physical layer while the NU's are served with conventional best-effort data
traffic. The problem is formulated as joint power and subcarrier allocation
with the objective of maximizing average aggregate information rate of all NU's
while maintaining an average secrecy rate for each individual SU under a total
transmit power constraint for the base station. We solve this problem in an
asymptotically optimal manner using dual decomposition. Our analysis shows that
an SU becomes a candidate competing for a subcarrier only if its channel gain
on this subcarrier is the largest among all and exceeds the second largest by a
certain threshold. Furthermore, while the power allocation for NU's follows the
conventional water-filling principle, the power allocation for SU's depends on
both its own channel gain and the largest channel gain among others. We also
develop a suboptimal algorithm to reduce the computational cost. Numerical
studies are conducted to evaluate the performance of the proposed algorithms in
terms of the achievable pair of information rate for NU and secrecy rate for SU
at different power consumptions.Comment: to appear in IEEE Trans. on Information Forensics & Security, special
issue on using the physical layer for securing the next generation of
communication system
Enhancing Physical Layer Security in AF Relay Assisted Multi-Carrier Wireless Transmission
In this paper, we study the physical layer security (PLS) problem in the dual
hop orthogonal frequency division multiplexing (OFDM) based wireless
communication system. First, we consider a single user single relay system and
study a joint power optimization problem at the source and relay subject to
individual power constraint at the two nodes. The aim is to maximize the end to
end secrecy rate with optimal power allocation over different sub-carriers.
Later, we consider a more general multi-user multi-relay scenario. Under high
SNR approximation for end to end secrecy rate, an optimization problem is
formulated to jointly optimize power allocation at the BS, the relay selection,
sub-carrier assignment to users and the power loading at each of the relaying
node. The target is to maximize the overall security of the system subject to
independent power budget limits at each transmitting node and the OFDMA based
exclusive sub-carrier allocation constraints. A joint optimization solution is
obtained through duality theory. Dual decomposition allows to exploit convex
optimization techniques to find the power loading at the source and relay
nodes. Further, an optimization for power loading at relaying nodes along with
relay selection and sub carrier assignment for the fixed power allocation at
the BS is also studied. Lastly, a sub-optimal scheme that explores joint power
allocation at all transmitting nodes for the fixed subcarrier allocation and
relay assignment is investigated. Finally, simulation results are presented to
validate the performance of the proposed schemes.Comment: 10 pages, 7 figures, accepted in Transactions on Emerging
Telecommunications Technologies (ETT), formerly known as European
Transactions on Telecommunications (ETT
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