Research On Transmission Strategy Of Two-Way Relay Networks Based On A PS Receiver

Two-way relaying has shown higher spectrum efficiency and longer range coverage of the network due to full use of the time slot resources.These advantages have triggered substantial research interest in two-way relay networks(TWRNs).In TWRNs,the energyconstrained relay node helps the two source nodes to exchange their information while exhausting its own battery.Since the wireless radio frequency(RF)signals can carry the information and the energy at the same time,simultaneous wireless information and power transfer technology is introduced into TWRNs.The energy-constrained relay node harvests energy from the ambient RF signals to prolong the lifetime of the energy-constrained TWRN.This thesis investigates a TWRN based on a power splitting(PS)receiver.An optimization problem of the transmission power allocation and the signal PS ratio(s)is explored to bring more flexibility for the network design and the lower network outage probability.Contrary to the existing static symmetric PS strategy,a dynamic symmetric PS strategy is proposed.In this strategy,the symmetric PS ratio is adjusted dynamically according to the instantaneous channel state information(CSI),achieving a balance of the power of the retransmitted signal and the harvested energy.There is no extra CSI overhead as the CSI is utilized when calculating the amplification factor.In consideration of the asymmetric characteristic of the instantaneous CSI in the TWRN,we further propose a dynamic asymmetric PS strategy.For these two strategies,an optimization problem of the PS ratio(s)is formulated to minimize the network outage probability.As this optimization problem is non-convex,an equivalent problem of maximizing the minimum signal to noise ratio(SNR)is discussed and an efficient Dinkelbach-based iterative algorithm is given.Simulation results show that the optimal PS ratio(s)can be obtained in two or three iterations,and the proposed strategies outperform the existing static symmetric PS strategy in the sense of the network outage performance.Building on the above strategies,allocating the power of the two source nodes reasonably can further improve the network outage performance by exploiting the instantaneous CSI of the relay feedback.In a dynamic transmission strategy,a joint optimization problem of the power and the PS ratio(s)is analyzed to minimize the network outage probability with a constraint on the total power of the two source nodes.To be specific,firstly,we establish an optimization problem in order to minimize the network outage probability;secondly,we transform it into an equivalent nonlinear fractional programming problem in order to maximize the SNR of one of the two links;finally,the optimal power of the two source nodes and PS ratio(s)are jointly solved by the dimension reduction and a two-step iterative algorithm based on Dinkelbach's method and alternate repeat.Simulation results corroborates the quick convergence of the iterative algorithm,and shows that the multi-dimensional dynamic transmission strategy that combines the power of the two source nodes and the PS ratio(s)can get more network outage performance gains in comparison to the strategy with the optimization of only the PS ratio(s).