Before revision:   The solution for optimizing power allocation  is also provided  . Numerical results are provided to demonstrate substantial performance gain of the jointly optimal solution over some suboptimal alternatives.
After revision:  It follows that the channel pairing problem in joint optimization can be again decomposed into independent pairing problems at each relay based on sorted channel gains. The solution for optimizing power allocation is also provided . Numerical results are provided to demonstrate substantial performance gain of the jointly optimal solution over some suboptimal alternatives.