Junjuan Xia

Cache Aided Decode-and-Forward Relaying Networks: From the Spatial View

We investigate cache technique from the spatial view and study its impact on the relaying networks. In particular, we consider a dual-hop relaying network, where decode-and-forward (DF) relays can assist the data transmission from the source to the destination. In addition to the traditional dual-hop relaying, we also consider the cache from the spatial view, where the source can prestore the data among the memories of the nodes around the destination. For the DF relaying networks without and with cache, we study the system performance by deriving the analytical expressions of outage probability and symbol error rate (SER). We also derive the asymptotic outage probability and SER in the high regime of transmit power, from which we find the system diversity order can be rapidly increased by using cache and the system performance can be significantly improved. Simulation and numerical results are demonstrated to verify the proposed studies and find that the system power resources can be efficiently saved by using cache technique.

Wireless powered cooperative communications with direct links over correlated channels

Abstract In this paper, we investigate the impact of correlated channels on the wireless powered cooperative networks, where the direct links between the source and destination exist and are correlated with the relaying links. In the considered system, the time switching-based relaying protocol of simultaneous wireless information and power transfer is used. In order to enhance the system performance, a better branch between the relaying link and the direct link is selected. We evaluate the system transmission performance by deriving the closed-form expression on outage probability as well as the asymptotic results for the proposed scheme, in the high regime of transmit power. Based on the theoretical analysis, we investigate the effects of the system parameters, such as channel correlation coefficient, average channel fading power, energy harvesting coefficient and slot allocation coefficient, on the system outage probability. Numerical results are provided to verify the theoretical analysis.

Subcarrier allocation based Simultaneous Wireless Information and Power Transfer algorithm in 5G cooperative OFDM communication systems

Abstract Self-sustainable communications are highly vital for large amounts of mobile terminals in the Fifth Generation (5G) communication systems. Simultaneous Wireless Information and Power Transfer (SWIPT) makes it possible that terminal transfers information while prolonging battery life by harvesting Radio Frequency (RF) energy. Though the traditional sub-carrier allocation based SWIPT algorithm in OFDM communication systems can optimize resource allocation, the receiver often cannot achieve higher information decoding rate when the channel condition of direct transmission deteriorates. In view of this situation, a sub-carrier allocation based SWIPT algorithm in 5G cooperative OFDM communication systems is proposed in this paper. The amplify-and-forward protocol is adopted by relay node which transmits information from source node to destination node by using a part of its sub-carriers. The remaining sub-carriers are used for energy harvesting. On the premise of minimum threshold of harvested energy, the sub-carrier and power allocations at relay node are optimized by establishing and solving the corresponding optimization model. Simulation results reveal that the proposed algorithm not only achieves the optimal sub-carrier and power allocations, but also improves information decoding rate with fast converging speed.

Switch-and-stay combining for energy harvesting relaying systems

Abstract In this paper, we study the switch-and-stay combining technique into the energy-harvesting relaying networks, where the relay obtains its transmit power from the source through wireless energy harvesting. The moderate shadow environments are applied, so that the data transmission from the source to the destination can go through the direct link. Although the conventional selection combining technique can exploit both the direct and relaying branches for data transmission, it has to require to know the channel parameters of both branches, and results into frequent branch switching. To solve these issues, switch-and-stay combining (SSC) is proposed into the energy-harvesting relaying networks, where the same branch keeps to be used for data transmission when it can support the transmission quality. The branch switching occurs only when the branch cannot support the transmission quality. We study the system transmission performance by deriving expression for the system analytical outage probability. We also provide the asymptotic outage probability when the transmit power is high, from which we obtain more insights on the system design, such as the system diversity order and the impact of parameters on the system performance. Simulation and numerical results are provided to validate the proposed studies in this paper.

The Precoder Design with Covariance Feedback for Simultaneous Information and Energy Transmission Systems

We consider the optimal precoder design with the assumption that the transmitter only has channel covariance information, for the multi-input multi-output (MIMO) information and energy transmission system. The objective of the system design is to maximize the average system information rate, meanwhile meeting the minimum energy requirement of the energy receiver. Following this objective, we formulate the problem as a semidefinite programming (SDP) and further transform it into a dual problem. Two methods are proposed to solve this problem: the first method decomposes the transmission covariance as a product of precoders so that the constrained optimization becomes an unconstrained one, whereas the second method derives the structure of the optimal transmission covariance analytically. Both methods are proved to be convergent and their overheads and complexity are also analyzed. The achievable rate-energy (R-E) regions for the proposed methods are presented in the simulation. Under various system settings, the superiority of the proposed methods is shown by comparing with a few existing transmission schemes.