Xiaofei Di

Simultaneous Wireless Information and Power Transfer in Cooperative Relay Networks With Rateless Codes

This paper investigates the simultaneous wireless information and power transfer (SWIPT) in cooperative relay networks, where a relay harvests energy from the radio frequency (RF) signals transmitted by a source and then uses the harvested energy to assist the information transmission from the source to its destination. Both source and relay transmissions use rateless codes (RCs), which allow the destination to employ any of the two information receiving strategies, i.e., the mutual information accumulation (IA) and the energy accumulation (EA). The SWIPT-enabled relay employs three different SWIPT receiver architectures, the ideal receiver, and two practical receivers (i.e., the power splitting (PS) receiver and the time switch (TS) receiver). Accordingly, three relaying protocols, namely, the ideal protocol, PS protocol, and TS protocol, are presented. To explore the system performance limits with these three protocols, optimization problems are formulated to maximize their achievable information rates. For the ideal protocol, explicit expressions of the optimal solutions are derived. For the PS protocol, a linear-search algorithm is designed to solve the nonconvex problems. For the TS protocol, two solving methods are presented. Numerical experiments are carried out to validate our analysis and algorithms, which show that, with the same SWIPT receiver, the IA-based system outperforms the EA-based system, whereas with the same information receiving strategy, the PS protocol outperforms the TS protocol. Moreover, compared with nonrateless-coded systems, the proposed protocols exhibit considerable performance gains. Moreover, the effects of the relay position on system performance are also discussed, which provides insights on SWIPT-enabled relay systems.

Outage Performance of Space-Time Network Coding With Overhearing AF Relays

This letter investigates the outage performance of overhearing amplify-and-forward (AF) cooperative relaying system, where multiple sources transmit information symbols to a destination through multiple helping overhearing AF relays with space-time network coding (STNC) employed. First, by introducing the overhearing among the relays of STNC, a new transmission protocol, i.e., the STNC-based cooperative relaying with overhearing AF relays (STNC-OHAF), is presented. Then, the instantaneous end-to-end SNR expression of STNC-OHAF is analyzed. Based on this, an explicit expression of the outage probability for STNC-OHAF over independent but not necessarily identically distributed (i.n.i.d) Rayleigh fading channels is theoretically derived and the ability of STNC-OHAF to achieve full diversity order is proved. Numerical results validate our theoretical analysis and show that by introducing overhearing among relays, the outage performance of the STNC-based AF relaying system can be greatly improved. Besides, it is also shown that there is a trade-off between the normalized sum efficient system transmission rate and the number of sources.

Optimal Resource Allocation in Wireless Powered Communication Networks With User Cooperation

This paper investigates the optimal resource allocation in wireless powered communication network with user cooperation, where two single-antenna users first harvest energy from the signals transmitted by a multi-antenna hybrid access point (H-AP) and then cooperatively send information to the H-AP using their harvested energy. To explore the system information transmission performance limit, an optimization problem is formulated to maximize the weighted sum-rate (WSR) by jointly optimizing energy beamforming vector, time assignment, and power allocation. Besides, another optimization problem is also formulated to minimize the total transmission time for given amount of data required to be transmitted at the two sources. Because both problems are non-convex, we first transform them to be convex by using proper variable substitutions and then apply semi-definite relaxation to solve them. We theoretically prove that our proposed methods guarantee the global optimum of both problems. Simulation results show that system WSR and transmission time can be significantly enhanced by using energy beamforming and user cooperation. It is observed that when the total amount of information of two users is fixed, with the increase of the information amount of the user relatively farther away from the H-AP, the transmission time of the user cooperation scheme decreases while that of the direct transmission increases. Besides, the effects of user position on the system performances are also discussed, which provides some useful insights.

Power splitting based SWIPT in network-coded two-way networks with data rate fairness: an information-theoretic perspective

This paper investigates the simultaneous wireless information and power transfer (SWIPT) for network-coded two-way relay network from an information-theoretic perspective, where two sources exchange information via an SWIPT-aware energy harvesting (EH)relay. We present a power splitting (PS)-based two-way relaying (PS-TWR) protocol by employing the PS receiver architecture. To explore the system sum rate limit with data rate fairness, an optimization problem under total power constraint is formulated. Then, some explicit solutions are derived for the problem. Numerical results show that due to the path loss effect on energy transfer, with the same total available power, PS-TWR losses some system performance compared with traditional non-EH two-way relaying, where at relatively low and relatively high signal-to-noise ratio (SNR), the performance loss is relatively small. Another observations is that, in relatively high SNR regime, PS-TWR out-performs time switching-based two-way re-laying (TS-TWR) while in relatively low SNR regime TS-TWR outperforms PS-TWR. It is also shown that with individual available power at the two sources, PS-TWR outperforms TS-TWR in both relatively low and high SNR regimes.

Cooperative multi-relay transmission for high-speed railway mobile communication system with fountain codes

This paper presents a cooperative transmission scheme for cooperative multi-relay high-speed railway mobile communication system, where fountain codes and mutual information accumulation (IA) method are adopted. The spreading codes are used to separate and detect the signal with interference from multiple relays, and the signal detection process and information receiving strategy at the destination are designed. Then we analyze the performance of the system in terms of the transmission rate, where the probability density function of the transmission rate of IA is derived, as well as the corresponding average transmission rate. For comparison, the traditional energy accumulation (EA) based receiving scheme is also analyzed. Results show when spreading codes are not orthogonal, if the signal to noise ratio (SNR) is relatively low, the performance of IA-based information receiving method is worse than that of EA-based one, and if SNR is relatively high, the performance of IA-based information receiving method is superior to that of EA-based one.