Multipair Two-Way Relay Network With Harvest-Then-Transmit Users: Resolving Pairwise Uplink-Downlink Coupling

Abstract

While two-way relaying is a promising way to enhance the spectral efficiency of wireless networks, the imbalance of relay-user distances may lead to excessive 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 uplinkdownlink coupling for a user. Together with the co-dependent relationship between paired users and interference among multiple user pairs, wirelessly powered two-way relay network suffers from the unique pairwise uplink-downlink coupling, and the joint uplink-downlink network design is nontrivial. To this end, for the one pair users case, we show that a global optimal solution can be obtained. For the general case of multi-pair users, based on the rank-constrained difference of convex program, a convergence guaranteed iterative algorithm with an efficient initialization is proposed. Furthermore, a lower bound to the performance of the optimal solution is derived by introducing virtual receivers at relay. Numerical results on total transmit power show that the proposed algorithm achieves a transmit power value close to the lower bound.Index Terms-Beamforming design, convex optimization, difference of convex program, multi-pair two-way relay network, rank relaxation, wireless power transfer.

Joint Communication and Motion Energy Minimization in UGV Backscatter Communication

“…Among all the vertices, the vertex m = 1 is selected as the starting point of the UGV. With the locations of all the stopping points and the IoT devices, the distances between each pair of IoT device and stopping point can be computed, and the distance-dependent path-loss model ̺ k,m = ̺ 0 · ( d k,m d0 ) −2.5 is adopted [33], where d k,m is the distance from user k to the stopping point m, and ̺ 0 = 10 −3 is the path-loss at distance d 0 = 1 m. Based on the pathloss model, channels g k,m and h k,m are generated according to CN (0, ̺ k,m ). Each point in the figures is obtained by averaging over 100 simulation runs, with independent channels and realizations of locations of vertices and users in each run.…”

Rate Optimization of Two-Way Relaying with Wireless Information and Power Transfer

“…In addition, the outage probability of the DF-TWR protocol with the PS-SWIPT and the TS-SWIPT is studied without resource allocation in cognitive radio environments [23] and with outage-optimal resource allocation in non-cognitive radio environment [25]. Some studies on the TWR with energy harvesting nodes are also observed in [14,20,22], but they are irrelevant since the SWIPT is not considered due to a different energy harvesting scenario [14] and an infrastructure relay transmitting the power is considered for the AF-TWR in [20,22].…”

“…In particular, various relaying protocols have been rebuilt to support energy harvesting devices in cooperative networks [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], where relays can be categorized into either energy harvesting nodes or energy transmission nodes. Energy harvesting relays are as low in complexity as communicating devices and harvest the energy in helping the data exchange of the devices in general [11][12][13][14][15][16][17][18][19][23][24][25][26].…”

“…Energy harvesting relays are as low in complexity as communicating devices and harvest the energy in helping the data exchange of the devices in general [11][12][13][14][15][16][17][18][19][23][24][25][26]. On the other hand, energy transmission relays are as highly complex as base stations so that the relays transfer the power and information to the communicating devices [20][21][22]; the relays even employ massive antennas to leverage the efficiency in the power and information transfer at a high cost in implementation [27,28]. This paper focuses on the former case in which there is no infrastructure relay and one of neighboring peer devices takes the role of signal relaying by spending the energy harvested by means of simultaneous wireless power and information transfer (SWIPT).…”

Wireless-Powered Communication Networks

“…Recently, researchers extended the study on SWIPT to relaying networks, in which a wireless powered relay and/or wireless powered sources were considered in a relay system [21][22][23][24]. Specifically, [22] studied a two-way relaying system with two wireless powered sources, whereas [23] investigated a two-way relaying system with a wireless powered relay.…”