Outage-Optimal Power and Time Allocation for Rate-Aware Two-Way Relaying With a Decode-and-Forward Protocol

We consider a two-way relaying network, where two communicating nodes exchange their data with the help of a decode-and-forward (DF) relay. For the network, optimization of power allocation (PA) and time allocation (TA) is explored to minimize the system outage probability in supporting asymmetric data rates. We tackle the joint optimization of PA and TA with full channel state information (CSI) by dividing the problem into two convex optimization problems, which find the optimal PA in a closed form for a given TA and then find the optimal TA with the binary search method. To lower the complexity of the joint optimization, we devise suboptimal schemes, i.e., one selecting the TA value adaptively from two predetermined TA values and the other employing a single fixed TA value. We analyze the outage probabilities and asymptotic behaviors of the proposed PA-TA schemes in generalized Nakagami-m fading channels. The results show that PA optimization improves the performance for both symmetric and asymmetric rate transmissions, but TA optimization improves the performance only for the asymmetric rate transmission. In addition, the suboptimal schemes get close to the optimal scheme in the outage performance when two relay channels are asymmetric with unequal fading parameters and an asymmetric relay position.