130 research outputs found
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
Resource Allocation for Secure Gaussian Parallel Relay Channels with Finite-Length Coding and Discrete Constellations
We investigate the transmission of a secret message from Alice to Bob in the
presence of an eavesdropper (Eve) and many of decode-and-forward relay nodes.
Each link comprises a set of parallel channels, modeling for example an
orthogonal frequency division multiplexing transmission. We consider the impact
of discrete constellations and finite-length coding, defining an achievable
secrecy rate under a constraint on the equivocation rate at Eve. Then we
propose a power and channel allocation algorithm that maximizes the achievable
secrecy rate by resorting to two coupled Gale-Shapley algorithms for stable
matching problem. We consider the scenarios of both full and partial channel
state information at Alice. In the latter case, we only guarantee an outage
secrecy rate, i.e., the rate of a message that remains secret with a given
probability. Numerical results are provided for Rayleigh fading channels in
terms of average outage secrecy rate, showing that practical schemes achieve a
performance quite close to that of ideal ones
Subcarrier Pairing as Channel Gain Tailoring: Joint Resource Allocation for Relay-Assisted Secure OFDMA with Untrusted Users
Joint resource allocation involving optimization of subcarrier allocation,
subcarrier pairing (SCP), and power allocation in a cooperative secure
orthogonal frequency division multiple access (OFDMA) communication system with
untrusted users is considered. Both amplify and forward (AF), and decode and
forward (DF) modes of operations are considered with individual power budget
constraints for source and relay. After finding optimal subcarrier allocation
for an AF relayed system, we prove the joint power allocation as a generalized
convex problem, and solve it optimally. Compared to the conventional channel
gain matching view, the optimal SCP is emphasized as a novel concept of channel
gain tailoring. We prove that the optimal SCP pairs subcarriers such that the
variance among the effective channel gains is minimized. For a DF relayed
system, we show that depending on the power budgets of source and relay, SCP
can either be in a subordinate role where it improves the energy efficiency, or
in a main role where it improves the spectral efficiency of the system. In an
AF relayed system we confirm that SCP plays a crucial role, and improves the
spectral efficiency of the system. The channel gain tailoring property of SCP,
various roles of SCP in improving the spectral and the energy efficiency of a
cooperative communication system are validated with the help of simulation
results
Resource Allocation in OFDM-Based Cognitive Two-Way Relay Networks
Cognitive radio (CR), nowadays, is considered as one of the most promising techniques which introduce the flexible usage of radio spectrum and improve the spectral efficiency by enabling unlicensed users to exploit the licensed spectrum in an opportunistic manner. Moreover, the two-way relay communication has attracted a great attention as it introduces a relaying scheme with a bidirectional transmission to exchange information between two nodes. This strategy assumed to improve the overall capacity, since less time slots are needed than the one-way strategy, besides extending the radio coverage range of networks. Another common technique that improves the bandwidth efficiency and spectrum utilization is the orthogonal frequency division multiplexing (OFDM) technique which exhibits a distinctive efficiency in mitigating inter-symbol interference (ISI) and combating frequency selective fading. Therefore, two-way relay CR communication among OFDM terminals can take advantage of these three techniques to boost up the capacity together with the networks quality. In this thesis, an OFDM-based amplify and forward (AF), cognitive two-way multiple-relay network is considered where two transceiver nodes exchange information via relay nodes. The full transmission happens in two time slots. In the first time slot, multiple access phase (MA), the transceiver nodes send their signals to the relay nodes while in the second time slot, broadcast phase (BC), the relay nodes broadcast the received signals to the transceivers. In this dissertation, the problem to jointly optimize the network resources is considered. The first is the transmission power of transceivers and relay nodes to ensure suitable allocated power for best signals transmission besides ensuring no harmful interference is caused to the primary system. The other important resource to be optimized is the subcarrier pairing where the first and second time slots subcarriers have to be matched such that the subcarriers with the best conditions is reserved. The final tuned resource, in this work, is the relay selection where the relay node that assures the best transition of the received signal is selected. The dual decomposition technique is applied to get the optimal resource allocation. Moreover, suboptimal algorithms are proposed to perform the resource allocation reducing, significantly, the computational complexity compared with the optimal solution with small performance degradation. Finally, simulation results of the suggested AF OFDM cognitive relaying network are shown to compare the performance gain of the different algorithms which reveals that the proposed suboptimal algorithm achieves good performance with much less computational complexity than the optimal one
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