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This paper proposes a large-scale wireless powered communication network (WPCN), which consists of a hybrid access point (H-AP) and numerous nodes. The H-AP broadcasts energy to all nodes, and the nodes harvest the energy and then use the harvested energy to transmit information. For the large-scale WPCN, we also propose a novel hybrid multiple access protocol, termed hybrid multiple access-based dual harvest-then-transmit. The proposed protocol utilizes both time division multiple access (TDMA) and carrier-sense multiple access (CSMA), in order to deal with various traffic patterns and transmission reliability of different applications in large-scale networks. We consider a dual wireless energy transfer (WET) at the H-AP. The main WET is performed in TDMA and the other WET is performed at space holes in CSMA, to increase the channel utilization and harvested energy. For the considerations, we study the sumthroughput maximization in the large-scale WPCN based on hybrid multiple access-based dual harvest-then-transmit. Simulation results show that the proposed protocol outperforms the conventional protocol in large-scale WPCN.

The communication paradigms for Delay/Disruption Tolerant Networks (DTN) have been modeled after email. Supporting email over DTN in a backwards compatible manner in a heterogeneous environment has yet to be fully defined. In the Simple Mail Transfer Protocol (SMTP) based on TCP/IP used in the existing terrestrial Internet, the protocol works through multiple interactions between the sender’s mail server and the receiver’s mail server. However, in the space Internet environment, since the contact times are limited, reliability cannot be guaranteed for the interaction between the server and the client used in the existing SMTP. Therefore, this paper proposes a novel mail transfer protocol, DTN-SMTP for space Internet over DTN. To minimize the interaction of the existing SMTP, it relies on one-way transmission and optionally performs retransmission mechanisms. Finally, we have built and configured two DTN nodes to implement DTN-SMTP. Also, we have confirmed the mail’s reception and the file attachment from the external mail client with minimized interactions between the SMTP messages.

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