While two-way relaying is a promising way to enhance the spectral efficiencyof wireless networks, the imbalance of relay-user distances may lead toexcessive wireless power at the nearby-users. To exploit the excessive power,the recently proposed harvest-then-transmit technique can be applied. However,it is well-known that harvest-then-transmit introduces uplink-downlink couplingfor a user. Together with the co-dependent relationship between paired usersand interference among multiple user pairs, wirelessly powered two-way relaynetwork suffers from the unique pairwise uplink-downlink coupling, and thejoint uplink-downlink network design is nontrivial. To this end, for the onepair users case, we show that a global optimal solution can be obtained. Forthe general case of multi-pair users, based on the rank-constrained differenceof convex program, a convergence guaranteed iterative algorithm with anefficient initialization is proposed. Furthermore, a lower bound to theperformance of the optimal solution is derived by introducing virtual receiversat relay. Numerical results on total transmit power show that the proposedalgorithm achieves a transmit power value close to the lower bound.
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