Abstract: A method and apparatus capable of restricting the resending operation are disclosed, in which the resending operation is controlled by determining the conditions of the input signal from a movable transmitting end, based on the guard interval period set in the signal to be resent, thereby resending only a valid transmission signal. Once an input signal is supplied from the movable transmitting end to the resending apparatus, a guard information detector determines whether the input signal is to be resent or not, based on the degree of correlation of the guard interval period, and controls the operation of a voltage-controlled amplifier, thereby resending only a valid transmission signal. This determination is made based on the degree of correlation between a signal converted from the input signal and the guard interval period of the signal delayed from the converted signal.

Abstract: A communication method in an orthogonal frequency division multiplexing modulation communication system includes a transmission apparatus in which a frequency bandwidth of a signal modulated in accordance with an orthogonal frequency division multiplexing modulation system is changed and the modulated signal is transmitted and a receiving apparatus in which the modulated signal is received and a frequency bandwidth for demodulation of the received signal is changed to follow the change of the frequency bandwidth of the modulated signal.

Abstract: A transmitting system wherein a transmission signal composed of main data and a TMCC signal having a SYNC pattern indicating the header portion and a bit pattern indicating setting information of the main data is transmitted and received. In the transmitting apparatus, the reference timing for starting the input data scramble process is rendered to coincide substantially with the modulation timing for modulating the scrambled data and generating the main data, and the modulation timing is rendered to coincide substantially with the timing for generating the TMCC signal thereby to generate the TMCC signal. From the transmission signal, the receiving apparatus demodulates the main data, extracts the SYNC pattern indicating the header portion from the TMCC signal and inversely scrambles the main data based on the extracted SYNC pattern.

Abstract: A digital signal communication system includes a transmission circuit or a receiving circuit for digitally transmitting two types of signals by orthogonal modulation. The transmission circuit includes an orthogonal modulator and a nonrecursive digital low-pass filter having the same frequency characteristic as a predetermined frequency characteristic of the output signal of the orthogonal modulator. The receiving circuit includes an orthogonal demodulator and a nonrecursive digital low-pass filter having the same frequency characteristic as a predetermined frequency characteristic of the output signal of the orthogonal demodulator. The total number of taps required for determining the frequency characteristic of the nonrecursive digital low-pass filter is set to H, and the series of tap coefficients is set as C1, C2, C3, . . . , CH, where H is an arbitrary positive integer of not less than 2.

Abstract: A data transmitting apparatus in which in an antenna switching of the data transmitting apparatus, a sudden change of transmission path characteristics is prevented and a state where an automatic equalizing function on the reception side can follow can be held. The apparatus has a processing circuit for gradually switching antennas of the data transmitting apparatus with respect to the time and for continuously switching one antenna from the rated level to the 0 level and for continuously switching the other antenna from the 0 level to the rated level. The apparatus operates so as to always keep the optimum constellation state in which the automatic equalizing process follows.

Abstract: A bi-directional digital transmission method, and system, for sending and receiving digital transmission signals having a frame configuration modulated by an orthogonal frequency division multiplex modulation scheme. A first sending unit in a first transmission station converts first continuous data to a up-direction intermittent transmission signal, and sends it from a first antenna via a first switchover unit. The up-direction intermittent transmission signal is received by a second antenna of a second transmission station, and supplied to a second receiving unit of the second transmission station via a second switchover unit of the second transmission station. The second receiving unit determines whether receiving operation of the up-direction intermittent transmission signal has been established, and if so, restores the original first continuous data.

Abstract: A data transmission apparatus of an orthogonal frequency multiplex modulation system wherein data is transmitted using a plurality of carriers which are in a mutually orthogonal relationship with one another. The apparatus includes a transmitter which previously inserts a group of predetermined synchronization symbols into an OFDM modulated transmission signal every fixed period and a receiver which demodulates a received OFDM modulated transmission signal to a baseband OFDM signal. In the receiver, an absolute value of an A/D converted digital signal is taken and the signal is bandwidth-limited to a predetermined band width. Then, it is decided whether an amplitude of the signal is larger than or smaller than a predetermined value and a decision result thereof is produced. A null section in the synchronization symbol group is detected on the basis of the decision result and a start point of another synchronization symbol subsequent to the null section is further detected.

Abstract: An orthogonal frequency division multiplex (OFDM) modulator of such a system as to add guard intervals to a temporal waveform generated by modulating an input data train into a large number of (sub)carriers, conducting quadrature modulation, and outputting an OFDM signal.

Abstract: A digital signal transmission system using a digital modulation system comprising a digital signal transmitter having a first digital signal processing unit and a digital signal receiver receiving a digital signal from the transmitter, wherein the digital signal receiver comprising a second digital signal processing unit for processing the digital signal from the transmitter and outputting a digital demodulated signal and a correlation value signal, a signal converter coupled with the second digital signal processing unit and supplied the correlation value signal therefrom for generating a waveform indicating a transmission condition including a main wave in response to the correlation value signal, and a display coupled with the signal converter for displaying the waveform indicating a transmission condition in the digital transmission system.

Abstract: A data transmission apparatus using a digital modulation system wherein a transmitting side inserts a group of predetermined synchronization symbols into a transmission signal at predetermined intervals to be transmitted. A receiving side calculates an electric power value of a received transmission signal. When a no-signal period (null section) in the synchronization symbol group is to be detected and decided from a magnitude of the received signal electric power value, a threshold for reference of decision for detecting the null section is calculated on the basis of an average electric power value for a predetermined period in the received signal electric power value and the threshold calculated in accordance with the received signal level of the transmission signal is used to detect synchronization stably.

Abstract: A camera head unit generates a digital video signal, a transmission unit transmits the digital video signal from the camera head unit, and a camera control unit processes the digital video signal transmitted from the camera head unit through the transmission unit. The camera head unit includes a replacing unit for replacing the least significant bit data of the digital video signal to be transmitted from the camera head unit to the camera control unit with another signal data to thereby produce a replacement video signal which is transmitted to the transmission unit. The camera control unit includes an extraction unit for extracting the least significant bit data from the replacement video signal transmitted from the camera head unit through the transmission unit to thereby produce the above-mentioned another signal data.

Abstract: In a demodulating method of demodulating amplitude-demodulated signals in an amplitude phase shift keying system for conducting an amplitude modulation by setting signal points as information codes on a complex plane representing a signal space of transmission signals onto circumferences of two concentric circles including a first circle having a first diameter and a second circle having a second diameter smaller than the first diameter on the complex plane, there are obtained, in accordance with an amplitude value of an amplitude component of each symbol of a received amplitude-modulated signal, a first threshold value and a second threshold value having a predetermined relationship with the amplitude value.

Abstract: In a data coding method for obtaining coded data by dividing input data into different-length division blocks, the input data is divided into different-length blocks in accordance with a distortion value indicative of an error between the input data and approximate data based on the input data; variable length quantized data is obtained by quantizing the approximate data associated with the input data of each of the blocks; status data indicative of the state in which the input data is divided into the blocks is obtained; and the coded data is obtained by combining the quantized data and the status data. When the input data is divided into a plurality of blocks of unequal lengths, the amount of the coded data is determined so that it is substantially coincident with a predetermined data amount.

Abstract: An image signal compression transmission system for transmitting and receiving a compressed image signal, having a transmitter section which entropy codes digitized image data for transmission, a transmission channel through which entropy-coded codes sent from said transmitter section are transmitted, and a receiver section which decodes said entropy-coded codes received from said transmission channel and derives an original digital image signal. In the transmitter section, digital image data is entropy coded. The entropy-coded codes are transmitted to the receiver section through the transmission channel. In the receiver section, the received codes are entropy code decoded at a decoding speed corresponding to a transmission rate on the transmission channel. Coefficient codes derived by the decoding are stored into a memory at the same speed as the decoding speed.

Abstract: The transmitter section has a coder for converting an image signal into the coded data and producing the coded data at its output, a timer for producing time information which indicates a time lapse from a reference time, a first time data adding unit for adding the time information from the timer as the first time data to the coded data from the coder, a transmitter-side buffer for writing and reading the coded data with the first time data added, and a second time data adding unit for adding the time information from the timer as the second time data to the coded data read from the transmitter-side buffer, and sending the coded data to the transmission path.

Abstract: A multi-mode recording and playback system for VTR records audio signals and video signals and plays them back from audio tracks and video tracks on a magnetic tape by means of a plurality of rotating audio and video heads. A rotating drum around which a magnetic tape is wound carries therewith first to fourth rotary video heads and first and second rotary audio heads in predetermined relations with respect to angle and vertical level. In a desired mode, the audio heads write (read) audio signals in audio tracks, and the video heads write (read) video signals in video tracks, such that the centers of the audio and video tracks substantially coincide with each other.

Abstract: A duplicator in which analog signals recorded on a master or like source tape are transferred to digital discs after conversion into digital form and the digital signals thus recorded on the digital discs are then transferred to slave tapes after reconversion into analog form.