Abstract: Provided is an iterative residual frequency and phase compensation apparatus for an OFDM system and a method thereof. The apparatus includes: a first classifying unit for classifying symbol sequences by each subcarrier wave; a soft-decision calculating unit for calculating a soft-decision value of a data symbol using a soft-decision reliability obtained from iterative decoding performed by the iterative decoder; a classifying unit for classifying the soft-decision values by a carrier wave; a frequency estimating unit for estimating a residual frequency error of each carrier wave using the soft-decision value; a phase estimating unit for estimating an average residual phase error using the soft-decision value; a frequency and phase compensating unit for compensating frequencies and phases for input symbols of each carrier wave using the estimated frequency error and the estimated phase error; and a buffer for temporally storing the compensated symbols to provide it to the first classifying unit.

Abstract: Provided is a soft-output demodulation apparatus and method having a relatively low complexity and capable of acquiring a channel reliability value to be inputted to an iterative decoder, in a digital communication system.

Abstract: Provided is a method for adaptive transmit power allocation in a multiuser OFDM system. The method includes: a) obtaining a channel gain for a predetermined bit period for each user at a predetermined time, and allocating all of available sub carriers to a user farthest separated among a plurality of users having a good channel gain; b) comparing a channel gain of the user allocated with the subcarrier at the step a) with an initial threshold value; c) allocating a transmit power uniformly to each of the sub carries allocated at the step a) using an Equal-power allocation algorithm if the channel gain is larger than the initial threshold value at the step b); and d) allocating a transmit power to each of the sub carriers allocated at the step a) using a water-filling power allocation algorithm if the channel gain is smaller than the initial threshold value at the step b).

Abstract: Provided is a call admission control method for use in a packet based communication system, which can secure a handoff and a quality of service (QoS) by discriminating a new call and a handoff call and borrowing a shared bandwidth, a reserved bandwidth, and a bandwidth of other service according to kinds of services and their characteristics.

Abstract: Provided is a device for shaping a flat-topped element pattern using a circular polarization microstrip patch. The device includes: a microstrip patch feeding unit for generating circularly polarized signals of a basic mode; a circular waveguide for guiding the circular polarized signals and generating signals of high-order modes; and a pattern shaping unit for shaping FTEP through an electromagnetic mutual coupling between the signals of the high-order modes generated from the pattern shaping unit.

Abstract: Provided is an antenna control apparatus for controlling an antenna mounted on a stratospheric platform of the stratospheric communication system. The apparatus includes a plurality of location signal receivers, each receiver being positioned at each of predefined different points of the stratospheric platform and receiving a location signal for the stratospheric platform, a calculating circuit for calculating an adjustable displacement for the antenna, and an antenna driver for adjusting a direction of the antenna. The calculating circuit calculates a location and attitude of the stratospheric platform based on the location signals, and then computes the adjustable displacement using the location and attitude information. This invention can reduce power consumption in the stratospheric platform and recovery time of directional point of the beam.

Abstract: A fast LUT predistortion apparatus and method for compensating nonlinear distortion of the high power amplifier HPA is disclosed. The apparatus includes a predistortion unit for predistorting an input complex digital signal based on a look up table LUT implementation and outputting a predistorted complex signal; and a power amplifier for amplifying the predistorted signal and outputting an amplified complex signal.

Abstract: A hexagonal array structure of a dielectric rod for shaping a flat-topped element pattern (FTEP) is provided. The hexagonal structure of dielectric rods forming a flat-topped element pattern (FTEP) includes: a center element for forming a unit radiation pattern of the FTEP through an electromagnetic wave mutual coupling by receiving a polarization signal of a basic mode; a plurality of first ring elements arranged at vertexes of a regular hexagon based on the center element for forming the unit radiation pattern by electromagnetic wave mutual coupling with the center element and an electromagnetic wave; and a circular waveguide array supporting unit for supporting the center element and the plurality of first ring elements.

Abstract: Provided is a device for shaping a flat-topped element pattern using a circular polarization microstrip patch. The device includes: a microstrip patch feeding unit for generating circularly polarized signals of a basic mode; a circular waveguide for guiding the circular polarized signals and generating signals of high-order modes; and a pattern shaping unit for shaping FTEP through an electromagnetic mutual coupling between the signals of the high-order modes generated from the pattern shaping unit.

Abstract: Provided is an antenna control apparatus for controlling an antenna mounted on a stratospheric platform of the stratospheric communication system. The apparatus includes a plurality of location signal receivers, each receiver being positioned at each of predefined different points of the stratospheric platform and receiving a location signal for the stratospheric platform, a calculating circuit for calculating an adjustable displacement for the antenna, and an antenna driver for adjusting a direction of the antenna. The calculating circuit calculates a location and attitude of the stratospheric platform based on the location signals, and then computes the adjustable displacement using the location and attitude information. This invention can reduce power consumption in the stratospheric platform and recovery time of directional point of the beam.

Abstract: A hexagonal array structure of a dielectric rod for shaping a flat-topped element pattern (FTEP) is provided. The hexagonal structure of dielectric rods forming a flat-topped element pattern (FTEP) includes: a center element for forming a unit radiation pattern of the FTEP through an electromagnetic wave mutual coupling by receiving a polarization signal of a basic mode; a plurality of first ring elements arranged at vertexes of a regular hexagon based on the center element for forming the unit radiation pattern by electromagnetic wave mutual coupling with the center element and an electromagnetic wave; and a circular waveguide array supporting unit for supporting the center element and the plurality of first ring elements.

Abstract: A fast LUT predistortion apparatus and method for compensating nonlinear distortion of the high power amplifier HPA is disclosed. The apparatus includes a predistortion unit for predistorting an input complex digital signal based on a look up table LUT implementation and outputting a predistorted complex signal; and a power amplifier for amplifying the predistorted signal and outputting an amplified complex signal.