Abstract: A random access method for a terminal with the processor and the memory to access a low earth orbit satellite network formed by multiple low earth orbit satellites (LEO SAT) includes: the stage where a Deep Reinforcement Learning (DRL) algorithm is applied for a pre-set time to decide which one between the first and the second actions should be performed at every access cycle, and to perform the random access to the low earth orbit satellite network based on the above decision while learning it; and the stage where, according to the learning result of the DRL algorithm performed for above pre-set time, it decides which of the first and the second actions should be chosen when attempting to access the low earth orbit satellite network at a new access cycle and then to perform the random access to the low earth orbit satellite network according to the above choice.

Abstract: Disclosed herein are a time synchronization method and apparatus for a low-orbit satellite cluster. The time synchronization method for a low-orbit satellite cluster includes: receiving time information from N participating satellites directly connected; calculating a reference time using time information based on a reliability of each of the N participating satellites; performing time synchronization using the reference time and then recording a synchronization history; and generating a new block using the synchronization history.

Abstract: A random access method for a terminal with the processor and the memory to access a low earth orbit satellite network formed by multiple low earth orbit satellites (LE0 SAT) includes: the stage where a Deep Reinforcement Learning (DRL) algorithm is applied for a pre-set time to decide which one between the first and the second actions should be performed at every access cycle, and to perform the random access to the low earth orbit satellite network based on the above decision while learning it; and the stage where, according to the learning result of the DRL algorithm performed for above pre-set time, it decides which of the first and the second actions should be chosen when attempting to access the low earth orbit satellite network at a new access cycle and then to perform the random access to the low earth orbit satellite network according to the above choice.

Abstract: Disclosed is an apparatus based on wireless optical communication, which may include: a light source outputting light; an optical circulator outputting the light in at least one direction; a collimator converting and outputting the light output through the optical circulator into a parallel beam; an optical regulator reflecting the light converted into the parallel beam, and transferring the reflected light to an external apparatus, and receiving the reflected light from the external apparatus, the reflected light being light output by reversely reflecting the light by the external apparatus; an optical detector converting the reflected light into an electric signal to generate an optical signal; and a controller analyzing the optical signal and acquiring an intensity of the reflected light, and calculating central coordinate information of the external apparatus based on the intensity value of the reflected light.

Abstract: Disclosed is a phase noise mitigation method using a MIMO system in which each antenna has an independent oscillator. The phase noise mitigation method includes: receiving a transmission signal transmitted from a transmitting antenna, through a receiving antenna and an oscillator; estimating multiple parameters for a phase noise of a transmission terminal and a phase noise of a receiving terminal on the basis of a result of mathematical modeling of signals transmitted and received through the MIMO system in which each antenna has an independent oscillator; and mitigating phase noises of the transmission terminal and the receiving terminal which are estimated from the received signal.

Abstract: The present disclosure relates to a pre-5th-generation (5G) or 5G communication system to be provided for supporting higher data rates beyond 4th-generation (4G) communication system such as a long term evolution (LTE). A method for selecting a radio frequency beam by a receiving apparatus in a wireless communication system supporting a beamforming scheme includes determining a number of reference signal intervals in which a reference signal is transmitted based on a number of transmitting apparatuses, estimating full channel information by repetitively performing a partial channel estimating based on the number of reference signal intervals, and selecting a reception RF beam and a transmission RF beam for each of the transmitting apparatuses based on the full channel information.

Abstract: A frequency assignment method in a communication system is provided. The method includes transmitting, by a base station, a pilot signal to the plurality of terminals; receiving, by the base station, channel information and a Signal to Interference Ratio (SIR) from the plurality of terminals as feedback information; determining, by the base station, a number of subcarriers to be used for interference alignment and a terminal to which interference alignment is to be applied, using the feedback information; selecting, by the base station, a frequency set to be used for interference alignment among preset frequency sets for interference alignment, and generating a transmit precoding matrix using a maximum of Degrees of Freedom (DoF) that can be obtained for each frequency; and transmitting, by the base station, an index of the selected frequency set to the determined terminal using the generated transmit precoding matrix.

Abstract: Disclosed is a phase noise mitigation method using a MIMO system in which each antenna has an independent oscillator. The phase noise mitigation method includes: receiving a transmission signal transmitted from a transmitting antenna, through a receiving antenna and an oscillator; estimating multiple parameters for a phase noise of a transmission terminal and a phase noise of a receiving terminal on the basis of a result of mathematical modeling of signals transmitted and received through the MIMO system in which each antenna has an independent oscillator; and mitigating phase noises of the transmission terminal and the receiving terminal which are estimated from the received signal.

Abstract: The present disclosure relates to a pre-5th-generation (5G) or 5G communication system to be provided for supporting higher data rates beyond 4th-generation (4G) communication system such as a long term evolution (LTE). A method for selecting a radio frequency beam by a receiving apparatus in a wireless communication system supporting a beamforming scheme includes determining a number of reference signal intervals in which a reference signal is transmitted based on a number of transmitting apparatuses, estimating full channel information by repetitively performing a partial channel estimating based on the number of reference signal intervals, and selecting a reception RF beam and a transmission RF beam for each of the transmitting apparatuses based on the full channel information.

Abstract: Disclosed is a method for removing signal interference in a MIMO-based interference removing apparatus including transmitting a reference signal to at least one receiver; if channel information is estimated by the receiver, receiving the estimated channel information from the receiver as a feedback signal; and producing transmission pre-coding matrix, beam forming matrix, and weighted matrix using the received channel information. Further, the method includes transmitting information containing the transmission pre-coding matrix, the beam forming matrix, and the weighted matrix by including them in a pilot signal to the receiver, and the MIMO-based interference removing apparatus comprises at least one transmitter.

Abstract: A method comprising: determining, by a transmitter, a fixed number of effective IAI channels; estimating, by a receiver, channel information H through information provided from the transmitter; sharing, by a receiver, the channel information among a plurality of receivers that are belonging to a same BSS (Basic Service Set); calculating effective IAI channel information q and decoding vector u using the channel information; feeding back the calculated effective IAI channel information q and decoding vector u to the transmitter; and calculating, by the transmitter, a transmitting precoding vector, after sharing the fed-back effective IAI channel information q and decoding vector u, and the channel information H among a plurality of other transmitters.

Abstract: A method and an apparatus for transmitting and receiving a signal using interference alignment in a multi-cellular network are provided. The method includes determining a total number Sj of effective Inter-Cell Interference (ICI) channels of a j-th cell, determining a number tj,i of effective ICI channels caused by each of other Base Stations (BSs) and a number nj,i(s) of ICI channels aligned to each effective ICI channel, acquiring information about a channel matrix between users of the j-th cell and each BS, determining effective ICI channels reaching from the other BSs to users of the j-th cell and a receive beamforming matrix by reference to tj,i, nj,i(s) and information about the channel matrix, transmitting feedback information indicating the channel matrix and the receive beamforming matrix to the BS of the j-th cell, and receiving a signal from the BS of the j-th cell using the determined receive beamforming matrix.

Abstract: Disclosed is a method for removing signal interference in a MIMO-based interference removing apparatus including transmitting a reference signal to at least one receiver; if channel information is estimated by the receiver, receiving the estimated channel information from the receiver as a feedback signal; and producing transmission pre-coding matrix, beam forming matrix, and weighted matrix using the received channel information. Further, the method includes transmitting information containing the transmission pre-coding matrix, the beam forming matrix, and the weighted matrix by including them in a pilot signal to the receiver, and the MIMO-based interference removing apparatus comprises at least one transmitter.

Abstract: A frequency assignment method in a communication system is provided. The method includes transmitting, by a base station, a pilot signal to the plurality of terminals; receiving, by the base station, channel information and a Signal to Interference Ratio (SIR) from the plurality of terminals as feedback information; determining, by the base station, a number of subcarriers to be used for interference alignment and a terminal to which interference alignment is to be applied, using the feedback information; selecting, by the base station, a frequency set to be used for interference alignment among preset frequency sets for interference alignment, and generating a transmit precoding matrix using a maximum of Degrees of Freedom (DoF) that can be obtained for each frequency; and transmitting, by the base station, an index of the selected frequency set to the determined terminal using the generated transmit precoding matrix.

Abstract: A method and apparatus for controlling signal transmission is provided. The method includes determining whether a signal to noise ratio (SNR) between a first base station and a signal receiving node is less than a threshold, and controlling the first base station and a second base station to cooperatively transmit a signal to the signal receiving node in response to the SNR being less than the threshold. Further, the second base station is located in an adjacent cell to a cell containing the first base station.

Abstract: A method and an apparatus for transmitting and receiving a signal in a communication system are provided. The method includes transmitting a signal to a receiver through one of the antennas, receiving an antenna switching indicator indicating to switch the transmitting antenna from the receiver, and switching the transmitting antenna according to the antenna switching indicator, and transmitting a signal to the receiver through a switched antenna.

Abstract: There are provided an apparatus and a method for reducing a peak to average power ratio (PAPR) through the recombination of an orthogonal frequency division multiplexing (OFDM) symbol. The apparatus includes an orthogonal frequency division multiplexing (OFDM) symbol transforming unit, a peak power measuring unit, and an OFDM symbol selecting unit, wherein the OFDM symbol transforming unit generates the plurality of OFDM symbols by (a) performing a process of rotating the OFDM symbol by a predetermined angle in a complex plane and performing cyclical shifting with respect to the rotated OFDM symbol and (b) repetitively performing process (a) with respect to the cyclically shifted OFDM symbol. Therefore, diversity is secured, whereby the PAPR may be reduced.

Abstract: The present invention relates to a symbol-wise beamforming apparatus and method in an OFDM communication system using multiple antennas. A weight vector calculator calculates a transmit weight vector using a signal received through the multiple antennas as an input on the basis of channel information in the time domain and covariance matrix information about interference and noise and computes a receive weight vector using the calculated transmit weight vector. At least one of the calculated transmit weight vector and receive weight vector is transmitted to a transmission apparatus through a transmitter.

Abstract: Disclosed are a beam forming method and a multiple antenna system using the same. There is provided a multiple antenna system which forms optimal beam patterns through a transmission of a training sequence between a transmitter and a receiver, each including a plurality of antennas, the multiple antenna system comprising: a transmitter selecting antennas to be activated according to a level and transmitting the training sequence to a receiver through the selected antennas; a receiver selecting the antennas to be activated according to the level and transmitting to the transmitter an index of an optimal transmission weight vector significantly reducing a cost function based on the training sequence transmitted from the transmitter, wherein the transmitter selects antennas so that the beam patterns formed by the antennas selected at a q-th level (q: the index of the level) include the beam patterns formed by the antennas selected at a q+1-th level.

Abstract: A method and an apparatus for transmitting and receiving a signal using interference alignment in a multi-cellular network are provided. The method includes determining a total number Sj of effective Inter-Cell Interference (ICI) channels of a j-th cell, determining a number tj,i of effective ICI channels caused by each of other Base Stations (BSs) and a number nj,i(s) of ICI channels aligned to each effective ICI channel, acquiring information about a channel matrix between users of the j-th cell and each BS, determining effective ICI channels reaching from the other BSs to users of the j-th cell and a receive beamforming matrix by reference to tj,i, nj,i(s) and information about the channel matrix, transmitting feedback information indicating the channel matrix and the receive beamforming matrix to the BS of the j-th cell, and receiving a signal from the BS of the j-th cell using the determined receive beamforming matrix.