Abstract: An orthogonal frequency division multiplex (OFDM) modulation apparatus which can transmit just one of single side bands by a simple circuit and an OFDM demodulation apparatus superior in the ratio of the signal power to noise power ratio, wherein a serial/parallel converter converts the input signal from the serial to parallel format, inputs the results to the 1 to N-1 stage of an inverse discrete Fourier transformation (IDFT) circuit, and inputs a fixed value to the other stages (0 stage and N stage to 2N-1 stage). The IDFT circuit is a 2N input IDFT circuit which performs IDFT processing on the input signal converted to the parallel format by the serial/parallel converter and inputs the real number portion of the transformation result to a parallel/serial converter and the imaginary number portion to a parallel/serial converter. The imaginary number portion of the output signal of the IDFT circuit becomes the Hilbert transformation of the real number portion.

Abstract: A system and method for providing service in an aircraft having a plurality of passenger seats. The system of the invention includes a plurality of attendant call lights each serving a different one of the passenger seats, a plurality of reading lights each serving a different one of the passenger seats, a plurality of switch units each for controlling one of the attendant call lights and one of the reading lights, and a plurality of terminal units each provided at a different one of the passenger seats. Each terminal unit has an atttendant call key, a reading light key, and an address generator, and is capable of generating a request signal including an address in response to operation of the attendant call key or the reading light key. The inventive system also includes a head end apparatus capable of generating a control signal for controlling one of the attendant call lights or reading lights in response to each request signal.