Abstract: An orthogonal frequency division multiplexing signal transmitted from the transmitting end to the receiving end intermittently includes a particular symbol S0 having a predetermined particular pattern in addition to a symbol Sm including data to be transmitted. At the receiving end, the variation in the receiving level and/or the variation in the frequency band of a received signal are detected and corrected on the basis of the received particular symbol S0. Since the particular symbol S0 has a particular pattern, the variation in the level and/or the variation in the frequency are strongly correlated with the variation in the receiving level and/or the variation in the frequency band of the received signal. Consequently, the variation in the receiving level and/or the variation in the frequency band of the received signal can be accurately detected from the particular symbol S0 and consequently high-precision correction can be made.

Abstract: An oscillator 1 generates a local oscillation signal. A quadrature detector 2 converts an inputted carrier band signal into an equivalent low-frequency signal on the basis of the local oscillation signal. A complex multiplier 3 performs complex multiplication of the equivalent low-frequency signal and a complex coefficient to output a detection signal. An amplitude error detecting portion 4 detects a complex amplitude error of the detection signal. A coefficient error calculating portion 5 calculates a quantity proportional to an error of the complex coefficient from the complex amplitude error and the equivalent low-frequency signal and outputs it. A filter 6 converts the output of the coefficient error detecting portion into a complex coefficient and provides it to the complex multiplier 3. A data regenerating portion 7 converts the detection signal into demodulation data and outputs it.

Abstract: A data frame which is transmitted from a transmitting station is provided with an individual response part (RS) having response bits (S1 to SN) corresponding to all stations on a network, so that the transmitting station initializes the individual response part (RS) in data transfer. Each receiving station outputs its own state to a prescribed position of the individual response part, and the transmitting station monitors the individual response part. Thus, it is possible to correctly confirm whether or not the data is normally transferred to those of the receiving stations which are to receive data.

Abstract: A position detector 1 detects the position of a display screen 4, an image memory 2 stores image information, a selector 3 selects a portion of the image information stored in the image memory 2 in accordance with the position of the display screen 4 detected by the position detector 1 and supplies the selected portion to the display screen 4, and the display screen 4 displays the selected image information. The invention is characterized in that when it is assumed that the entire image information stored in the image memory 2 is drawn in a viewing field space fixed relative to the eye, the selector 3 selects the image information to be drawn on the display screen 4 lying in the viewing field space.

Abstract: A transmitter/receiver system for converting digital information into a multi-frequency signal for transmission. A reference frequency signal is first transmitted, then a series of frequencies having information indicative of differences with the reference signal are transmitted, and a receiver discriminates differences with the reference frequency signal to decode the information.