Before revision:  This separation principle significantly reduces the computational complexity in finding the jointly optimal solution. We further establish the equivalence between sorting SNRs and sorting channel gains in the jointly optimal solution , which allows simple implementation of optimal subcarrier pairing at the relays.
After revision:  This separation principle is established by observing the equivalence between sorting SNRs and sorting channel gains in the jointly optimal solution , which allows simple implementation of optimal subcarrier pairing at the relays.