An optimal power allocation(OPA)scheme is proposed to solve the power resource waste problem between source and relay nodes for a cooperative communications system with single decode-and-forward relay over double Nakagami-m fading which is caused by equal power allocation(EPA). The proposed scheme bases on minimizing symbol-error-ratio(SER). First
the asymptotic SER is analyzed and then simplified in the so called typical condition. Then
the power allocation problem is formulated as a typical convex optimization problem with the SER as the objective function and the restriction of the sum power as the constrain condition. The Lagrange method is used to solve the optimization problem to obtain the close-form of the optimal power allocation in the so called typical condition. Simulations and comparisons with EPA show that in a big rang OPA can obtain the signal to noise ratio(SNR)gain about 1dB over some channel condition
and that the gain is consistent with the theoretical SNR gain.
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