Abstract: The present invention relates to a method of calculating a log-likelihood ratio and a method of detecting a transmission signal. According to the present invention, when a transmission symbol candidate vector is detected on the basis of a received signal, a threshold value and an ML metric of each transmission symbol candidate vector are calculated and the ML metric that is larger than the threshold value is updated by the threshold value. Further, a log-likelihood ratio of the transmission signal bit is calculated using the updated ML metric and the threshold value, and a transmission signal is detected using the log-likelihood ratio.

Abstract: The present invention relates to an apparatus and method of compensating for a frequency offset in an orthogonal frequency division multiple access system that is capable of efficiently estimating and compensating for the frequency offset. A receiver of the orthogonal frequency division multiple access system can individually estimate a fractional frequency offset and an integer frequency offset by using a downlink preamble signal. Further, the receiver can compensate for the frequency offset by adding the integer frequency offset once after completely compensating for the fractional frequency offset. Therefore, it is possible to efficiently compensate for the frequency offset.

Abstract: The present invention relates to an apparatus and method of acquiring initial synchronization of a terminal in a mobile communication system. According to an exemplary embodiment of the present invention, one or more auto-correlation values of a preamble constituting a signal that is received from a base station are calculated. Averages of the calculated auto-correlation values according to samples are calculated, and then a peak value is detected among the calculated values. Then, a cell search is performed on the basis of the detected peak value, and a peak value from the result of the cell search is regularized. Then, the regularized peak value is compared with a predetermined reference value such that it is checked whether synchronization of a signal that has been searched is accurate or not.

Abstract: A terminal of a communication system includes a power amplifier, an open-loop power controller, a gain controller, a modulator, and a digital/analog converter. The power amplifier amplifies transmission power of a transmission signal. The open-loop power controller measures a received signal strength to control the transmission power, and increases a gain of the power amplifier according to the received signal strength. The gain controller sets a power concentration gain and applies the power concentration gain to the transmission signal when the gain of the power amplifier is maximized. The modulator modulates the transmission signal. The digital/analog converter converts an input signal to an analog signal. The gain controller applies the power concentration gain to the trans mission signal modulated by the modulator, and transmits the power concentration gain to the digital/analog converter.

Abstract: An apparatus for demodulating signals received from a plurality of base stations including a serving base station and a neighbor base station determines start timings of a serving cell signal transmitted from the serving base station and neighbor cell signals transmitted from the neighbor base stations, and verifies whether or not the neighbor cell signals that are earlier than the serving cell signal are provided on the basis of the determined start timings. Next, the apparatus selects a section where the reception energy of the symbol has the maximum level among symbols corresponding to signals of frames corresponding to the signals, respectively, as a demodulation section, and demodulates a multicast signal including the received signals on the basis of the selected demodulation section.

Abstract: The present invention relates to a transmitter of an OFDMA system capable of controlling a gain for variation of subchannel allocation, and a method thereof. The transmitter includes a subchannel number determining unit, a modulator, a digital/analogue converter, and a gain controller controlling the gain. The subchannel number determining unit determines the number of subchannels in use according to communication environments, and the modulator modulates transmission data with reference to the number of subchannels determined by the subchannel number determining unit and outputs the modulated transmission data. The digital/analogue converter converts the transmission data into analogue data and transmits the converted analogue data through a transmit antenna. The gain controller controls gains of the transmission data according to gain values corresponding to the number of subchannels.

Abstract: Disclosed is a method and apparatus for composing a received symbol signal modulated with a bit reflected Gray code into bit information. According to an embodiment of the present invention, a positive integer of the received symbol signal having bits is assigned according to the Gray mapping rule, and a sign is determined. A value that is indicative of an arrangement of the bits constituting the received symbol signal is calculated. A boundary value in at least one bit group consisting of the bits constituting the received symbol signal is acquired, and a difference from an absolute value of the received symbol signal is calculated. The received symbol signal is converted into information per bit using a value of the received symbol signal based on the positive integer and the determined sign, the value that is indicative of the bit arrangement, and the difference from the absolute value.

Abstract: A terminal demodulation apparatus previously stores a received frame signal in a memory before inputting the same into a fast Fourier transform (FFT) unit, performs a demodulation to necessary information read from the corresponding memory, and has a separate data subcarrier memory and pilot subcarrier memory, and uses the signal demodulation method mixed with a subcarrier allocation method so as to easily demodulate various subcarrier allocation methods.

Abstract: The present invention relates to a demodulating device and method in an orthogonal frequency division multiple access (OFDMA) communication system. A demodulating device according to an exemplary embodiment of the invention uses only one demodulator, one slot buffer, and one channel decoder to demodulate a plurality of data bursts included in one frame. In addition, in order to reduce a memory size required to demodulate a plurality of data bursts, a memory is managed in the units of sub-channels, instead of classifying memory cells so as to correspond to the data bursts. According to the demodulating device, it is possible to simplify a hardware structure and to reduce a memory size required to demodulate data bursts. As a result, it is possible to reduce manufacturing costs and decrease the number of signal lines of a channel decoder required for an interface.

Abstract: The present invention relates to an automatic gain control apparatus and method in a mobile communication system. According to the automatic gain control apparatus of an embodiment of the invention, when downlink signals include both directional beam signals and beam signals traveling in all directions due to the antenna system, different reception gain reference values are used according to whether downlink signals including only the beam signals traveling in all directions are received or downlink signals including the directional beam signals are received, thereby controlling the gain of the received signal. When the downlink signals including the directional beam signals are received, the automatic gain control apparatus can appropriately control the gain of the received signal on the basis of the directional beam signals to prevent saturation of the received signal.

Abstract: A receiving apparatus of a mobile terminal receiving a signal in a synchronous OFDM system under a multi-cell environment, including a demodulation start controller performing frame synchronization and cell search using a received signal and outputting information on a demodulation start point and a to-be-demodulated neighbor cell; a FFT unit converting a time-domain signal into a frequency-domain signal; a scramble code generator generating scramble codes for the to-be-demodulated neighbor cell from the demodulation start controller and the current cell; a correlator multiplying a signal from the FFT unit and scramble codes from the scramble code generator and outputting correlation signals; demodulators provided corresponding to a current cell and a maximum number of neighbor cells to be demodulated, and demodulating the correlation signals; and a decoder decoding signals from the demodulators and restoring original information transmitted from the corresponding cell.

Abstract: The present invention provides a method for designing operation schedules of a fast Fourier transform (FFT) and a multiple input multiple output orthogonal frequency division multiplexing modem (MIMO-OFDM modem) thereof. According to the present invention, an operation speed of an FFT operator is set up, a receiving symbol is arranged in an OFDM symbol duration in an FFT after receiving the symbol, a transmitting symbol is arranged in an OFDM symbol duration in the FFT schedule before transmitting the symbol, a transmitting/receiving symbol which has the same timing is inserted into an idle symbol duration of the FFT schedule, an FFT schedule which is good to be deleted is deleted, and symbols of the deleted FFT schedule are re-arranged in order to not have an error occur in transmitting/receiving timing.

Abstract: Disclosed is an automatic gain control device in an orthogonal frequency division multiplexing system. A variable gain amplifier controls a gain of an input signal; an energy calculator calculates an energy of the input signal; a truncator accumulates the calculated energies, finds an average thereof, and generates a DC offset of the input signal; a subtracter subtracts a predefined reference value from the DC offset, and outputs a signal; and an RC filter feeds the value output by the subtracter back to the variable gain amplifier so that the value output by the subtracter may be used for an automatic gain control. The predefined reference value given to be 4.Ov is a reference power generated based on a saturation to RMS ratio for minimizing the bit error rate of the orthogonal frequency division multiplexing system.

Abstract: The present invention relates to a method for automatic gain control (AGC) before an initial synchronization of a mobile station modem in OFDM system, and an apparatus thereof.

Abstract: Provided are a transmitting apparatus and voice data transmitting and receiving methods for providing VoIP services. When a call is started and an analog signal including a voice signal is input, the transmitting apparatus divides the analog signal into a plurality of voice data packets for transmission. Here, the plurality of voice data packets are generated by sampling with different phases in the same frequency. In addition, the transmitting apparatus inserts a time indication bit that is changed every transmission period into each of the voice data packets and transmits the voice data packets, and distinguishes voice data corresponding to a current transmission period based on the time indication bit.

Abstract: Disclosed is a method of detecting signals at a receiver of a communication system with a multiple input multiple output antenna. With the signal detection method, a square of the distance between a received signal vector and a channel status-considered transmission symbol vector is calculated first, and the square of the distance is then classified into first and second components. The first component is minimized to calculate a plurality of first soft symbol estimates. A solution set of the first component is calculated on the basis of the plurality of first soft symbol estimates. The second component is minimized to calculate a plurality of second soft symbol estimates. A solution set of the second component is calculated on the basis of the plurality of second soft symbol estimates. A final solution set is calculated by doing the sum of the first component solution set and the second component solution.

Abstract: A subcarrier allocating apparatus allocating data to be transmitted to a plurality of orthogonal subcarriers in an orthogonal frequency division multiplexing (OFDM) system, the apparatus including: a logical index generator (142) generating a logical index for allocating a data subcarrier to a physical index, the logical index being included with only data subcarriers and the physical index indicating a location of a substantial subcarrier within a symbol; an intermediate index converter (144) converting the logical index into an intermediate index by performing a given operation on the generated logical index and a pilot location constant; and a physical index converter (146) converting the intermediate index into a physical index based on the number of data subcarriers on the left and right sides of a null subcarrier for insertion of a guard interval formed by the null subcarrier.

Abstract: A downlink beamforming apparatus and a transmission apparatus including the same includes a subcarrier based user identifier for dividing subcarriers according to users, a beamforming weight buffer for storing first beamforming weights for the subcarriers by each of transmitting antennas, an interpolator for outputting second beamforming weights for each transmitting antenna by interpolating the first beamforming weights, and a signal reproducer for reproducing the signal for each transmitting antenna. Subcarriers are allocated to the signal by each user; and a complex multiplier multiplies the signal for each transmitting antenna by the second beamforming weights.

Abstract: The present invention provides a method for designing operation schedules of a fast Fourier transform (FFT) and a multiple input multiple output orthogonal frequency division multiplexing modem (MIMO-OFDM modem) thereof. According to the present invention, an operation speed of an FFT operator is set up, a receiving symbol is arranged in an OFDM symbol duration in an FFT after receiving the symbol, a transmitting symbol is arranged in an OFDM symbol duration in the FFT schedule before transmitting the symbol, a transmitting/receiving symbol which has the same timing is inserted into an idle symbol duration of the FFT schedule, an FFT schedule which is good to be deleted is deleted, and symbols of the deleted FFT schedule are re-arranged in order to not have an error occur in transmitting/receiving timing.

Abstract: A tile index generation apparatus for allocating subchannels of a control channel and a diversity channel, a subchannel allocation apparatus for allocating subchannels of a diversity channel, and a subchannel allocation apparatus for allocating subchannels of an adaptive modulation coding (AMC) channel, which are used for an uplink of an orthogonal frequency division multiplexing access (OFDMA) system, are provided. With these subchannel allocation apparatuses, optimum designs for the uplink subchannel allocation in the OFDM scheme can be provided to a modulator of a subscriber station and a demodulator of a base station, and so the uplink subchannel allocation apparatus has a simple structure and an enhanced transmission speed.