Abstract: Disclosed is an OFDM (orthogonal frequency division multiplexing) wireless communication system operable on a frequency selective channel, and a channel compensation method. An IDFT (inverse discrete Fourier transform) unit of a transmitter includes first through third N-point IDFT units, and performs IDFT on a binary information signal twice. A DFT (discrete Fourier transform) unit of a receiver includes first through third N-point DFT units, a channel predictor and interpolator, and a channel compensator, and performs DFT on the signal received from the transmitter twice.

Abstract: Disclosed is an OFDM (orthogonal frequency division multiplexing) wireless communication system operable on a frequency selective channel, and a channel compensation method. An IDFT (inverse discrete Fourier transform) unit of a transmitter includes first through third N-point IDFT units, and performs IDFT on a binary information signal twice. A DFT (discrete Fourier transform) unit of a receiver includes first through third N-point DFT units, a channel predictor and interpolator, and a channel compensator, and performs DFT on the signal received from the transmitter twice.

Abstract: Disclosed is an OFDM (orthogonal frequency division multiplexing) wireless communication system operable on a frequency selective channel, and a channel compensation method. An IDFT (inverse discrete Fourier transform) unit of a transmitter includes first through third N-point IDFT units, and performs IDFT on a binary information signal twice. A DFT (discrete Fourier transform) unit of a receiver includes first through third N-point DFT units, a channel predictor and interpolator, and a channel compensator, and performs DFT on the signal received from the transmitter twice.

Abstract: The present invention relates to a bidirectional message transmission system and method. The system performs first authentication on a first user based on user ID information provided by a first user terminal connected to the wired Internet, and performs second authentication in cooperation with a first portable terminal having a wireless telephone number provided by the first user terminal. The message provided by the first user terminal having undergone the first and second authentication is transmitted to at least two second users' terminals. The second users' terminals include a wireless terminal and a wired terminal. Therefore, the bidirectional communication service for concurrently transmitting the message to at least two other terminals is allowable based on stable and reliable authentication.

Abstract: A system for providing a bi-directional communication service is provided. The system includes a client terminal and a bi-directional communication service providing/managing server. The client terminal sends a short message after passing a user authentication and receives a short message from outside. The bi-directional communication service providing/managing server transmits the short message sent by the client terminal simultaneously to at least two other party client terminals after a user authentication process, or transmits a short message received from another party client terminal to the client terminal after a user authentication process.

Abstract: Disclosed is an OFDM (orthogonal frequency division multiplexing) wireless communication system operable on a frequency selective channel, and a channel compensation method. An IDFT (inverse discrete Fourier transform) unit of a transmitter includes first through third N-point IDFT units, and performs IDFT on a binary information signal twice. A DFT (discrete Fourier transform) unit of a receiver includes first through third N-point DFT units, a channel predictor and interpolator, and a channel compensator, and performs DFT on the signal received from the transmitter twice.