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This paper investigates secure communication from a wireless-powered transmitter to a desired receiver with multiple eavesdroppers in the wireless powered communication networks (WPCNs). Considering the non-linear energy harvesting (EH) model, we propose a secure two-phase communication protocol with the help of a hybrid base station (HBS). First, in the power transfer (PT) phase, the HBS transfers wireless power to the transmitter. Then in the subsequent secure information transmission (SIT) phase, the transmitter sends the secret information using the energy harvested in the PT, under the protection of artificial noise (AN) generated by the HBS. First, based on this communication protocol, we maximize the secrecy throughput with perfect channel information state (CSI) under the transmit power constraint at the HBS. The secrecy throughput maximization (STM) problem is non-convex, and hence we reformulate it by exploiting the primal decomposition method (PDM) to obtain tractable forms. The PDM-based transmit scheme (PDM-TS) is proposed for the STM. In addition, considering the imperfect CSI of wiretap channel, we further design the robust transmit scheme for the worst-case secrecy throughput maximization (wSTM) problem. Since the wSTM shows high non-convexity, we extend the PDM by combining it with the Sprocedure, and the PDM-based robust transmit scheme (PDM-RTS) is proposed for the wSTM. Finally, the numerical simulations are provided to show the effectiveness of the proposed transmit schemes.INDEX TERMS Wireless powered communication networks (WPCNs), non-linear energy harvesting (EH) model, physical layer security (PLS), secrecy throughput, robust beamforming.

The aim of the present study was to investigate the impact of squamous and/or glandular differentiation on the recurrence and progression in patients with nonmuscle invasive urothelial carcinoma of bladder (NMIUCB) following transurethral resection (TURBT). A total of 869 patients with NMIUCB who had been treated with TURBT at The Second Hospital of Tianjin Medical University (Tianjin, China) between January 2006 and January 2011 were retrospectively selected for the present analysis. Associations among squamous and/or glandular differentiation with other clinical and pathological features were assessed by the χ2 test. Recurrence-free survival (RFS) and progression-free survival (PFS) curves were estimated using the Kaplan-Meier method. Univariate and multivariate analyses were performed through a Cox's proportional hazards regression model. Among the 869 patients, 232 (26.7%) patients had squamous and/or glandular differentiation. High grade tumors were more common in patients with squamous and/or glandular differentiation compared with those with pure urothelial carcinoma of bladder (P<0.001). Associations between age (P=0.115), sex (P=0.184), tumor size (P=0.223), tumor multiplicity (P=0.108), pathological tumor stage (P=0.909) and squamous and/or glandular differentiation were not observed to be statistically significant. There was a significant tendency towards higher recurrence rate and shorter RFS time in patients with squamous and/or glandular differentiation. However, no statistically significant differences were observed in progression rate and PFS between the two groups. The multivariate Cox regression analysis, identified squamous and/or glandular differentiation as an independent prognostic predictor of recurrence (hazard ratio =1.46, 95% confidence interval=1.10–1.92, P=0.008). In the present study, the presence of squamous and/or glandular differentiation was associated with a higher recurrence rate and shorter RFS time in patients with NMIUCB. Squamous and/or glandular differentiation is therefore an independent prognostic predictor of recurrence.