This paper studies a wireless powered communication network (WPCN) where a hybrid access point (H-AP) with constant power supply coordinates wireless energy and information transmissions to distributed users without other energy sources. A "harvest-then-transmit" protocol is proposed, where users first harvest wireless energy from the H-AP in the downlink (DL) and then transmit their independent information to the H-AP in the uplink (UL) using time-division-multiple-access (TDMA). The paper focuses on maximizing the sum-throughput of all users by jointly optimizing the time allocation for DL wireless power transfer and UL information transmissions, given a total time constraint. It is shown that the sum-throughput maximization problem is convex, and closed-form expressions for the optimal time allocations are derived using convex optimization techniques. The solution reveals a "doubly near-far" phenomenon, where a far user from the H-AP, which receives less wireless energy than a nearer user in the DL, has to transmit with more power in the UL for reliable information transmission. This results in unfair rate allocation among users. To address this, a new performance metric called common-throughput is introduced, which ensures equal rates for all users regardless of their distances to the H-AP. An efficient algorithm is proposed to maximize the common-throughput. Simulation results demonstrate the effectiveness of the common-throughput approach in solving the doubly near-far problem in WPCNs. The paper also compares the sum-throughput and common-throughput approaches, showing that the common-throughput approach achieves fairer rate allocation at the cost of reduced sum-throughput. The results highlight the importance of considering fairness in WPCNs and the effectiveness of the proposed common-throughput approach in achieving this.This paper studies a wireless powered communication network (WPCN) where a hybrid access point (H-AP) with constant power supply coordinates wireless energy and information transmissions to distributed users without other energy sources. A "harvest-then-transmit" protocol is proposed, where users first harvest wireless energy from the H-AP in the downlink (DL) and then transmit their independent information to the H-AP in the uplink (UL) using time-division-multiple-access (TDMA). The paper focuses on maximizing the sum-throughput of all users by jointly optimizing the time allocation for DL wireless power transfer and UL information transmissions, given a total time constraint. It is shown that the sum-throughput maximization problem is convex, and closed-form expressions for the optimal time allocations are derived using convex optimization techniques. The solution reveals a "doubly near-far" phenomenon, where a far user from the H-AP, which receives less wireless energy than a nearer user in the DL, has to transmit with more power in the UL for reliable information transmission. This results in unfair rate allocation among users. To address this, a new performance metric called common-throughput is introduced, which ensures equal rates for all users regardless of their distances to the H-AP. An efficient algorithm is proposed to maximize the common-throughput. Simulation results demonstrate the effectiveness of the common-throughput approach in solving the doubly near-far problem in WPCNs. The paper also compares the sum-throughput and common-throughput approaches, showing that the common-throughput approach achieves fairer rate allocation at the cost of reduced sum-throughput. The results highlight the importance of considering fairness in WPCNs and the effectiveness of the proposed common-throughput approach in achieving this.