Abstract: A phase locked loop includes: a loop filter; a voltage controlled oscillating unit configured to output a frequency varying according to an output voltage of the loop filter; a frequency down-converting unit configured to down-convert an output frequency of the voltage controlled oscillating unit according to a band of the output frequency of the voltage controlled oscillating unit; and a frequency divider configured to divide a frequency down-converted by the frequency down-converting unit. The output frequency of the voltage controlled oscillating unit varies according to the output voltage of the loop filter and a control signal compensating the frequency down-converted by the frequency down-converting unit.

Abstract: Provided are a method and apparatus for measuring a time delay in an envelope elimination and restoration (EER) transmitter. A method of measuring a time delay in an EER transmitter includes receiving a modulated sinusoidal signal and distributing the modulated sinusoidal signal to be transmitted through transmission lines separated from each other, extracting an amplitude modulation signal and a phase modulation signal from the modulated sinusoidal signal, and detecting envelops of the amplitude and phase modulation signals and determining a difference in time between the amplitude and phase modulation signals. In the EER transmitter, to measure a time delay between input and output signals, time delays of paths of amplitude and phase modulation signals of the input signal are compared, thereby determining a difference in time between the amplitude and phase modulation signals.

Abstract: A phase locked loop includes: a loop filter; a voltage controlled oscillating unit configured to output a frequency varying according to an output voltage of the loop filter; a frequency down-converting unit configured to down-convert an output frequency of the voltage controlled oscillating unit according to a band of the output frequency of the voltage controlled oscillating unit; and a frequency divider configured to divide a frequency down-converted by the frequency down-converting unit. The output frequency of the voltage controlled oscillating unit varies according to the output voltage of the loop filter and a control signal compensating the frequency down-converted by the frequency down-converting unit.

Abstract: Provided are a forward link rain attenuation compensating apparatus using an adaptive transmission scheme in an interactive satellite communication system and a method thereof. The apparatus separates the mobile stations into clear-sky mobile stations and mobile stations in the state of rain attenuation and makes the clear-sky mobile stations receive data having a high data transmission efficiency at a high-speed while making the rain attenuation mobile stations receive the data continuously although the data transmit rate is low by making each of the two kinds of mobile stations receive data frames of a different transmission method, and provides a method therefor. The apparatus includes: a resource manager, a transmitting data format converter, a forward modulator, a backward demodulator, a receiving data format converter.

Abstract: Provided is a satellite broadcasting terminals. The satellite broadcasting terminal includes: a first antenna receiving a radio signal of a first band or a second band; a second antenna receiving a radio signal of a third band; a first stream demodulating unit demodulating a first stream signal received through the first band; a second stream demodulating unit demodulating a second stream signal received through the second band; a playing unit playing the demodulated first or second stream signal; and a gap filler receiving unit selectively providing the first stream signal to the first stream demodulating unit in response to a radio signal intensity of the third band, the first stream signal being received through the third band.

Abstract: Provided is a frequency error estimating method of a communication system. The method includes receiving a frame, and calculating a frequency error from a SOF field of the received frame.

Abstract: Provided are an apparatus and method for robust Binary Phase Shift Keying/Quadrature Phase Shift Keying (BPSK/QPSK) blind modulation classification. The apparatus includes first and second likelihood value calculators for calculating a likelihood value of a received baseband signal each for of BPSK and QPSK modulation modes. A maximum setting unit derives a maximum value of the likelihood values or ith likelihood ratios calculated by the first and second likelihood value calculators. A flag is set for the maximum value to “1” and a flag for the remaining value is set to “0”. First and second flag combining units combine the flags for the modulation modes. A modulation mode flag setting unit selects a maximum value from the flags combined by the first and second flag combining units.

Abstract: Provided are an apparatus and method for robust Binary Phase Shift Keying/Quadrature Phase Shift Keying (BPSK/QPSK) blind modulation classification against errors in a satellite communication system. The apparatus includes first and second likelihood value calculators for calculating a likelihood value of a received baseband signal each for of BPSK and QPSK modulation modes, respectively, a maximum setting unit for deriving a maximum value of the likelihood values or ith likelihood ratios calculated by the first and second likelihood value calculators and setting a flag for the maximum value to “1” and a flag for the remaining value to “0”, first and second flag combining units for combining the flags for the modulation modes, respectively, a modulation mode flag setting unit for selecting a maximum value from the flags combined by the first and second flag combining units, and a modulation classification mode deciding unit.

Abstract: Disclosed is a frequency hopping system for converting frequencies of signals into RF (radio frequency) signals, which comprises: a frequency hopper for outputting signals with temporarily varied frequencies according to a predetermined pattern; a fixed PLL (phase locked loop) unit for outputting frequency-fixed signals; a mixer for mixing the output signals of the frequency hopper and the fixed PLL unit, and outputting frequency-hopped local signals; and a modulator for receiving I and Q (in-phase and quadrature-phase) signals from a baseband device, synthesizing the I and Q signals with the frequency-hopped local signals, combining the two synthesized signals, and outputting RF signals.