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This paper investigated the multiple unmanned aerial vehicle (UAV) relays' assisted network in the Internet of Things (IoT) systems enhanced with energy harvesting in order to overcome the largescale fading between source and sink as well as achieve the green cooperative communications, where time switch (TS) and power splitting (PS) strategies were typically applied for UAV relays to implement energy harvesting transmission, which was also selected via signal to noise ratio (SNR) maximization criterion so that the terminal node can obtain the optimal signal. Meanwhile, it was worth noting that the terminal node may be disturbed by aggregated interference caused by dense network signaling interaction in the future 5G/B5G systems. Therefore, after TS and PS protocols designing and utilizing, the closed-form expressions of outage probability and bit error rate (BER) for UAV relay assisted IoT systems suffered from aggregated interference were derived in detail. In addition, the throughput and delay limited state of UAV relay assisted transmission were also analyzed thoroughly. The derivations and analysis results showed that the proposed multi-parameter joint optimization of transmitting power, scaling factor, and UAV relay selection could effectively improve the system throughput and reduce the system outage probability and BER. The simulation experiments verified the effectiveness of the proposed schemes and the correctness of theoretical analysis. INDEX TERMS Unmanned aerial vehicles (UAV), relay assisted, IoT, energy harvesting, protocol design, aggregate interference.

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In this paper, an overhearing protocol is proposed for two-way cooperative multi-antenna relaying systems, where the relays equipped with multiple antennas collaborate to relay signals between the base station (BS) and two user equipments (UEs). In the proposed overhearing protocol, the UE in the uplink transmission phase transmits only in the first time slot, i.e., it remains silent in the second time slot, whereas the previous overhearing protocol assumes the UE transmitting also in the second time slot. Therefore, the proposed overhearing protocol is more power-efficient. The precoding matrix at each cooperative relay is optimized in the sense of minimizing the weighted mean squared error (WMSE). Simulation results show that the proposed scheme shows not only lower MSE but also higher achievable sum-rate than existing cooperative relaying schemes.Index Terms-Overhearing, multi-antenna relay, cooperative relays, asymmetric multi-user channel I. INTRODUCTIONTwo-way relaying [1], [2] improves the spectral efficiency of the one-way relaying protocol [3], [4] by employing twoway relays which simultaneously receive from or transmit to both of the base station (BS) and user equipment (UE). Our focus is amplify-and-forward (AF) relaying which is more preferable in practical systems, compared to decodeand-forward (DF) or compress-and-forward relaying, due to its easier implementation [5], [6]. It is observed from the conventional two-way relaying protocol that the terminal as the transmitter in one directional transmission must be the same terminal as the receiver in another directional transmission. Nevertheless, this strict requirement is typically not satisfied in many cellular communication scenarios, which constrains the applications of the two-way conventional relaying protocol in many practical systems. For example, one user has the uplink traffic yet another user has the downlink traffic, indicating

The conventional two-way relaying (TWR) protocol requires that the transmitter (receiver) in one direction must be the receiver (transmitter) in the other direction, an limitation precluding the application of the TWR for sophisticated realworld wireless networks. In this paper, we study a more general multi-cell system consisting of a downlink (DL) traffic in one cell and an uplink (UL) traffic in an adjacent cell, with a multi-antenna relay located in the cell-edge and shared by both cells. For the coexistence of DL and UL transmissions, we propose to exploit the overheard signals from the adjacent cell (commonly known as the inter-cell interference) to improve the quality of signal reception in both cells. To reduce the power consumption to suit for green networks, we design the optimum relay precoder to minimize the total power at the relay, yet satisfying the rate constraints for both the DL and UL traffics. The original precoder design is a non-convex problem which is difficult to solve. To make the problem tractable, we transform the non-convex problem to an equivalent quadratically constrained quadratic program, which is then solved by the semidefinite relaxation technique. Finally, simulations validate the effectiveness of our proposed protocol together with the optimized relay precoder.Index Terms-Overhearing protocol design, dual-hop channel, multi-cell, minimum mean squared error (MMSE).