Abstract: In an upper-airspace staying type communication relay apparatus that performs an MU-MIMO radio communication with plural terminal apparatuses located in a cell, it is intended to improve the communication quality of the entire cell and enhance the system capacity, while suppressing an increase in overhead in the terminal apparatus and the communication relay apparatus even if the number of terminal apparatuses located in the cell increases.

Abstract: It is suppressed of a deterioration of a communication quality of a service link (SL), which is caused by an increase of signal attenuation in a propagation path of a feeder link (FL) between an aerial-staying type communication relay apparatus and a gateway (GW) station.

Abstract: In a mobile communication system using a mobile-type radio relay apparatus that forms a plurality of cells toward the ground or the sea while moving in an upper airspace, a deterioration in communication quality, which is caused by a Doppler shift of a reception signal due to a relative movement of a radio relay apparatus with respect to a terminal apparatus of each of a plurality of cells or a feeder station on the ground or on the sea, is suppressed. The communication system comprises a mobile-type radio relay apparatus that is disposed movably by flying in an upper airspace, forms a plurality of cells from an antenna at a predetermined altitude toward the ground or the sea, and performs a radio communication with a terminal apparatus located in each of the plurality of cells.

Abstract: A base station, a communication system and a time synchronization method between base stations are provided, which are capable of performing a time synchronization with another base station using a downlink signal of the other base station cell in which the own cell is located, without stopping transmission of the own base station even during operation.

Abstract: A base station, a communication system and a time synchronization method between base stations are provided, which are capable of performing a time synchronization with another base station using a downlink signal of the other base station cell in which the own cell is located, without stopping transmission of the own base station even during operation.

Abstract: In a mobile communication system using a mobile-type radio relay apparatus that forms a plurality of cells toward the ground or the sea while moving in an upper airspace, a deterioration in communication quality, which is caused by a Doppler shift of a reception signal due to a relative movement of a radio relay apparatus with respect to a terminal apparatus of each of a plurality of cells or a feeder station on the ground or on the sea, is suppressed. The communication system comprises a mobile-type radio relay apparatus that is disposed movably by flying in an upper airspace, forms a plurality of cells from an antenna at a predetermined altitude toward the ground or the sea, and performs a radio communication with a terminal apparatus located in each of the plurality of cells.