摘要:
A low level initial acquisition signal consisting of a continuous wave signal portion followed by a phase-modulated signal portion is transmitted via a satellite to a receiving station. The received CW signal is converted by a voltage-controlled variable frequency local oscillator to an intermediate frequency signal which is fed to a narrow passband filter. The local oscillator frequency is linearly swept, and the maximum signal passing through the filter during one sweep is detected. The local oscillator is then locked at the local frequency which produced the maximum signal, thereby effecting frequency acquisition. Next, the phase-modulated signal portion is multiplied by a phase-modulated signal output from a variable phase local signal generator. The phase of the local generator is also swept, and the maximum phase correlation signal passing through the band pass filter is again detected, and the phase of the generator output is corrected by the phase shift which produced the maximum phase correlation signal. This phase shift is used as a basis for determining the proper timing for acquisition of the correct time slot in the TDMA frame at the satellite for a transmitted data burst. The acquisition is confirmed by comparing the maximum phase correlation signal obtained during phase sweeping with the signal level obtained after the phase of the generator has been locked.
摘要:
An equalizer corrects cross-polarization distortion which occurs between two series of digital signals which are transmitted on individually associated ones of two mutually orthogonal cross-polarized waves. The distortion is corrected when a circuit discriminates between the two series of digital signals and gives an output signal which represents a value judgment as to the amount of distortion which has occurred. The output signal serves as an address for selecting one of many memory element circuits, each element circuit having a predetermined value stored therein. The value stored in the selected memory element circuit is subtracted from one series of the digital signals. The idea is that, during transmission, something (e.g., raindrops) transfers energy from one to the other of the cross-polarized waves. The equalizer circuit passes judgment as to how much energy has been transferred, and then subtracts that amount of energy in order to return to the original signal. The circuit also corrects for rotation of the two mutual orthogonal waves about their common axis.
摘要:
To provide an orthogonal frequency division multiplex modem circuit which can multiplex signals, whose bit rates and QoS are different from one another, and can transmit the signals via one OFDM line. A serial/parallel converter converts input signals into a complex parallel signal respectively, and a sub carrier and a modulation system are assigned every communication channel. A randomizer changes the alignment sequence of the signal, a discrete inverse Fourier transformer processes the signal, a parallel/serial converter converts the signal into a serial signal, and a transmitter performs the orthogonal modulation of the signal to output the signal from an antenna. A receiver performs orthogonal demodulation of the signal received with an antenna, a serial/parallel converter converts the signal into a parallel signal, and a discrete Fourier transformer processes the parallel signal. In addition, a de-randomizer restores the alignment sequence of the subcarriers into the original condition, and a parallel/serial converter decodes and outputs the signal.
摘要:
A cellular system according to an exemplary aspect of the present invention is a cellular system in which a plurality of frequency carriers are available for communication between a base station and a mobile station, including: a first measurement unit for measuring a rate of time that interference power of a frequency carrier in uplink is more than a pre-determined threshold; a carrier availability/unavailability determining unit for putting the frequency carrier into an unavailable state if the time rate is more than a first threshold and putting the frequency carrier into an available state if the time rate is less than a second threshold; and a communication unit for using the frequency carrier in an available state for the communication between the base station and the mobile station.
摘要:
To provide an orthogonal frequency division multiplex modem circuit which can multiplex signals, whose bit rates and QoS are different from one another, and can transmit the signals via one OFDM line. A serial/parallel converter converts input signals into a complex parallel signal respectively, and a sub carrier and a modulation system are assigned every communication channel. A randomizer changes the alignment sequence of the signal, a discrete inverse Fourier transformer processes the signal, a parallel/serial converter converts the signal into a serial signal, and a transmitter performs the orthogonal modulation of the signal to output the signal from an antenna. A receiver performs orthogonal demodulation of the signal received with an antenna, a serial/parallel converter converts the signal into a parallel signal, and a discrete Fourier transformer processes the parallel signal. In addition, a de-randomizer restores the alignment sequence of the subcarriers into the original condition, and a parallel/serial converter decodes and outputs the signal.
摘要:
In a spread spectrum device including a serial to parallel converter (14) for converting a serial information signal (10) into a parallel signal of n bits, where n represents an integer not smaller than two, an information modulator (20) carries out information modulation on m bits among the n bits of the parallel signal and produces a modulated information signal, where m represents a positive integer smaller than n. A selective spreading code producing circuit (21, 22) has spectrum spreading codes which are equal in number to 2.sup.(n-m) and are different from one another. The selective spreading code producing circuit selectively produces, as a selected spreading code, one of the spectrum spreading codes that is specified by remaining (n-m) bits among the n bits of the parallel signal. A spectrum spreading circuit (23) carries out spectrum spreading on the modulated information signal on the basis of the selected spreading code and produces a spectrum spread signal (13). The spectrum spread signal may be transmitted by a radio portion (18) as a radio information signal (11).
摘要:
In a spread spectrum device including a serial to parallel converter (14) for converting a serial information signal (10) into a parallel signal of n bits, where n represents an integer not smaller than two, an information modulator (20) carries out information modulation on m bits among the n bits of the parallel signal and produces a modulated information signal, where m represents a positive integer smaller than n. A selective spreading code producing circuit (21, 22) has spectrum spreading codes which are equal in number to 2.sup.(n-m) and are different from one another. The selective spreading code producing circuit selectively produces, as a selected spreading code, one of the spectrum spreading codes that is specified by remaining (n-m) bits among the n bits of the parallel signal. A spectrum spreading circuit (23) carries out spectrum spreading on the modulated information signal on the basis of the selected spreading code and produces a spectrum spread signal (13). The spectrum spread signal may be transmitted by a radio portion (18) as a radio information signal (11).
摘要:
To provide an orthogonal frequency division multiplex modem circuit which can multiplex signals, whose bit rates and QoS are different from one another, and can transmit the signals via one OFDM line. A serial/parallel converter converts input signals into a complex parallel signal respectively, and a sub carrier and a modulation system are assigned every communication channel. A randomizer changes the alignment sequence of the signal, a discrete inverse Fourier transformer processes the signal, a parallel/serial converter converts the signal into a serial signal, and a transmitter performs the orthogonal modulation of the signal to output the signal from an antenna. A receiver performs orthogonal demodulation of the signal received with an antenna, a serial/parallel converter converts the signal into a parallel signal, and a discrete Fourier transformer processes the parallel signal. In addition, a de-randomizer restores the alignment sequence of the subcarriers into the original condition, and a parallel/serial converter decodes and outputs the signal.
摘要:
A system is provided for efficiently utilizing a transmission capacity without complicated processing by using a hierarchical code comprised of a plurality of layers having different error correcting capabilities. In a transmitter, an encoding unit encodes an image in accordance with a hierarchical coding scheme to generate a plurality of layer data. An error correcting code addition unit performs error correction coding on each of at least one layer data including the lowermost layer data in accordance with an error correction coding scheme which gives higher error correcting capabilities to a lower layer than a higher layer. A transmission unit transmits each of the layer data and error correcting codes onto a transmission path. A receiver corrects possible errors introduced on the transmission path into the layer data received from the transmitter in accordance with the error correction coding scheme, and decodes layer data received in a quality available for decoding to restore the image.
摘要:
In a transmission side, a k-bit parallel signal is divided into n signals, which are respectively encoded and then phase-shifted so as to causing a mutual phase difference of &pgr;/2n. Spectrum spreading is performed on the phase-shifted encoded signals which are combined together to produce a transmission digital signal. In a receiving side, reverse spreading is performed on a receiving signal to produce reverse-spread signals, which are given the phase difference to cancel the phase shift of the transmission side, and then decoded. Thus, the original k-bit parallel signal is reproduced in the receiving side.