4,144 research outputs found
Optimizing cooperative cognitive radio networks with opportunistic access
Optimal resource allocation for cooperative cognitive radio networks with opportunistic access to the licensed spectrum is studied. Resource allocation is based on minimizing the symbol error rate at the receiver. Both the cases of all-participate relaying and selective relaying are considered. The objective function is derived and the constraints are detailed for both scenarios. It is then shown that the objective functions and the constraints are nonlinear and nonconvex functions of the parameters of interest, that is, source and relay powers, symbol time, and sensing time. Therefore, it is difficult to obtain closed-form solutions for the optimal resource allocation. The optimization problem is then solved using numerical techniques. Numerical results show that the all-participate system provides better performance than its selection counterpart, at the cost of greater resources
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
Power Allocation Based on SEP Minimization in Two-Hop Decode-and-Forward Relay Networks
The problem of optimal power allocation among the relays in a two-hop
decode-and-forward cooperative relay network with independent Rayleigh fading
channels is considered. It is assumed that only the relays that decode the
source message correctly contribute in data transmission. Moreover, only the
knowledge of statistical channel state information is available. A new simple
closed-form expression for the average symbol error probability is derived.
Based on this expression, a new power allocation method that minimizes the
average symbol error probability and takes into account the constraints on the
total average power of all the relay nodes and maximum instant power of each
relay node is developed. The corresponding optimization problem is shown to be
a convex problem that can be solved using interior point methods. However, an
approximate closed-form solution is obtained and shown to be practically more
appealing due to significant complexity reduction. The accuracy of the
approximation is discussed. Moreover, the so obtained closed-form solution
gives additional insights into the optimal power allocation problem. Simulation
results confirm the improved performance of the proposed power allocation
scheme as compared to other schemes.Comment: 27 pages, 5 figures, submitted to the IEEE Trans. Signal Processing
in Feb. 201
Relaying Strategies for Wireless-Powered MIMO Relay Networks
This paper investigates relaying schemes in an amplify-and-forward
multiple-input multiple-output relay network, where an energy-constrained relay
harvests wireless power from the source information flow and can be further
aided by an energy flow (EF) in the form of a wireless power transfer at the
destination. However, the joint optimization of the relay matrix and the source
precoder for the energy-flow-assisted (EFA) and the non-EFA (NEFA) schemes is
intractable. The original rate maximization problem is transformed into an
equivalent weighted mean square error minimization problem and optimized
iteratively, where the global optimum of the nonconvex source precoder
subproblem is achieved by semidefinite relaxation and rank reduction. The
iterative algorithm finally converges. Then, the simplified EFA and NEFA
schemes are proposed based on channel diagonalization, such that the matrices
optimizations can be simplified to power optimizations. Closed-form solutions
can be achieved. Simulation results reveal that the EFA schemes can outperform
the NEFA schemes. Additionally, deploying more antennas at the relay increases
the dimension of the signal space at the relay. Exploiting the additional
dimension, the EF leakage in the information detecting block can be nearly
separated from the information signal, such that the EF leakage can be
amplified with a small coefficient.Comment: Submitted for possible journal publicatio
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