Abstract-We consider the topological interference management problem for a downlink hexagonal cellular network, where the channel state information at the transmitters is limited to just the network topology. Recent work by Jafar showed that if interference is limited to only near the cell boundary, then, an aligned frequency reuse pattern achieves the optimal value of 6/7 degrees of freedom (DoF) per cell, as opposed to the conventional frequency reuse baseline of 1/3 DoF per cell. We generalize the setting to include interference from multiple layers of adjacent cells and characterize how the gains of the optimal solution over basic frequency reuse diminish with increasing number of interference layers. Next, we focus on single-layer interference and explore the sensitivity of the idealized assumptions behind the connectivity model of Jafar, which achieves higher DoF but only at the cost of a higher effective noise floor than the baseline, and under idealized placements of users. A modified connectivity model that operates at a comparable noise-floor to the baseline is then studied, and its DoF are shown to be bounded above by 6/11 and below by 1/2. Through numerical simulations, we compare the solutions that achieve 6/7, 1/2, and 1/3 DoF per cell and find that, while both the 6/7 and the 1/2 DoF solutions beat the baseline 1/3 figure, between them, the 1/2 DoF aligned frequency reuse pattern is more robust for small cell networks particularly for random users' distribution on the cell boundaries.Index Terms-Hexagonal cellular network, degree of freedom, aligned frequency reuse, topological interference management.

Abstract. Heterogeneous cellular networks, due to its multi-tier topological structure, provide significant improvements in terms of increased data rates and cell coverage. However, there are important intra-tier and inter-tier interference management problem to be solved. In this paper, we model a two-tier uplink heterogeneous network, which include a macrocell and K overlaid femtocells. Meanwhile we constitute a heterogeneous configuration that each femto BS is equipped with two antennas and the macro BS is equipped with 2 2antennas. We proved that the sum-DoF outer bound of the network is 2 4 4 K K A , and the DoF outer bound for the femtocell and macrocell is 2 4 K A K A and 4 A K A respectively. Moreover, we present the achievable scheme, which is based on interference alignment. The simulation results show that the sum rate of the whole HetNet increases as the number of macro BS's antennas increases.

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This paper analyzed the development course, present situation and trend of traditional satellite communication system which can provide internet broadband access and emerging satellite internet constellation. Considering the unique advantages of the geostationary earth orbit (GEO) and low earth orbit (LEO) satellite system and our country's national conditions, the concept of GEO-LEO hybrid satellite internet constellation is put forward, which provides the construction suggestions for our country's development of satellite internet constellation.

The land-sea-air-space integrated information network is capable of providing globally accessible, safe, and reliable information services for land-, sea-, space-, and air-based users; it is an important infrastructure for China to maintain independence in the field and to become a cyberpower. This study uses literature research and expert consultation as the main research methods to summarize the development requirements of the land-sea-air-space integrated information network. After a detailed study on typical domestic and foreign systems, the major weaknesses of China's land-sea-air-space integrated information network are summarized. Moreover, an integrated information network architecture and development routes are proposed. Specifically, we suggest that China should focus on the deep integration in terms of network architecture, technical system, and application services; integrate the communication, navigation, and remote sensing systems; promote technical independence and industrial upgrade of space-based networks; and strengthen its system security protection capabilities.