This letter presents a K-band high power amplifier (HPA) monolithic microwave integrated circuit (MMIC) for satellite communications. In pulsed condition, a peak output power is larger than 45 dBm in 17.5 ~ 20.5 GHz, with an power added efficiency (PAE) and gain up to 29 % and 22 dB.

This paper describes the structure and applications of a delay tolerant network (DTN) to be operated using a DTN payload (DTNPL) mounted on the Korea pathfinder lunar orbiter (KPLO), which was launched in August 2022. DTN is a communication technology to support reliable communication even in space where communication is frequently disrupted. ETRI has researched a core technologies of DTN, and developed DTNPL as a space testbed. With the DTNPL, we plan to test various applications of DTN such as message exchange, file transfer, and video streaming between the lunar orbiter and the Earth.

This paper presents a multibeam reflector antenna fed by array elements for GEO flexible satellites. The reflector structure is designed within the constraints of satellite mounting. The array feed network with shared elements have close beam spacing, compact volume and light weight. A feed component assembled with a horn and a polarizer is also designed. The antenna composed of a reflector and feed components with optimal feed excitations forms four beams on the Korean Peninsula and surrounding marine areas for universal service.

UAS (Unmanned Aerial Systems) are now drawing a lot of attention from academic and research fields as well as the general public. The UAS is expected to provide many promising applications such as intelligent transportation system, disaster management, search and rescue, public safety, smart delivery, wild species monitoring, and wireless service area extension. More specifically, as a part of the wireless service extension, we deal with the information dissemination and collection using a UAV in this paper. In this application, because the UAV communicates with each CH (Cluster Head) to collect data from sensor nodes or to disseminate information to the sensor nodes, well-behaved and qualified nodes should be elected as CHs and their integrity should be preserved. Even though a UAV makes the information dissemination and collection process efficient in a WSN, we can make the UAV help the election of new CHs to mitigate the threat of compromised CHs. To this aim, we first propose a UAV-aided CH election framework where a UAV delivers the critical information collected from sensors to the sink, and the sink reselects a set of well-behaved and qualified CHs considering the information. Then, we classify the existing security-driven CH election schemes into several categories and explain the principle of each category and its representative schemes. For each representative scheme, we also explain how to adapt it into the UAV-aided CH election framework. Next, we identify some desirable security properties that a CH election scheme should provide and reveal the security level that each representative scheme reaches for the desirable security properties. Next, we compare communication and computation overhead of the security-driven CH election schemes in terms of the big O notation. In conclusion, we reveal what we have learned from this survey work and provide a future work item.

As many-to-one traffic patterns prevail in data center networks, TCP flows often suffer from severe unfairness in sharing bottleneck bandwidth, which is known as the TCP outcast problem. The cause of the TCP outcast problem is the bursty packet losses by a drop-tail queue that triggers TCP timeouts and leads to decreasing the congestion window. This paper proposes TCPRand, a transport layer solution to TCP outcast. The main idea of TCPRand is the randomization of TCP payload size, which breaks synchronized packet arrivals between flows from different input ports. We investigate how TCPRand reduces consecutive packet drops and demonstrate various benefits of TCPRand with extensive experiments and ns-3 simulation. Our evaluation results show that TCPRand guarantees the superior enhancement of TCP fairness with negligible overheads in all of our test cases.