摘要:
An improved oscillator which can adjust phase and frequency of the output signal independently from each other without time delay is disclosed. The oscillator is used for instance as a clock signal generator in a TDMA satellite communication system. The oscillator (FIG. 3) comprises a fixed oscillator (13) for providing a fixed frequency signal, a quadrature hybrid circuit (14) for providing a pair of quadrature phased signals from the output of said fixed oscillator (13), a control signal generator (17) for providing a pair of quadrature phased signals which satisfy b cos (2.pi..DELTA.f.sub.D t+.DELTA..phi..sub.D) and b sin (2.pi..DELTA.f.sub.D t+.DELTA..phi..sub.D), where b is a constant, .DELTA.f.sub.D is a desired frequency change, and .DELTA..phi..sub.D is a desired phase change, a pair of mixers (15,16) for providing products of each output of the quadrature hybrid circuit (14) and each output of the control signal generator (17), and an in-phase power combiner (20) for combining the outputs of the mixers (15,16 ) to provide a controlled output signal which satisfies ab sin [2.pi.(f.sub.O +.DELTA.f.sub.D)t+(.phi..sub.O +.DELTA..phi..sub.D)], where a, f.sub.O and .phi..sub.O are constants.
摘要:
A power line communication system is provided in which the influence of the impulsive noise unexpectedly generated on a power line which is a communication medium can be reduced according to the characteristics of the impulsive noise by an existing method and power line communication can be realized without a hindrance. A transmitter is constituted by: a modulator for conveying a LIN data signal by a power line; a filter that allows a signal of a predetermined band to pass therethrough; and a sinusoidal wave outputter (sinusoidal wave in the figure). In contrast, the receiver is constituted by the sinusoidal wave outputter, the filter and a demodulator that performs demodulation. To the power line, a limiter that limits the amplitude of the propagating signal to a predetermined amplitude (reception signal amplitude) is connected.
摘要:
In an OFDM packet communication receiver, the deterioration of received signal quality is suppressed, even when carrier frequency error and/or clock frequency error exists between a transmitter and a receiver, and/or phase noise and/or thermal noise is superimposed to a received signal in a receiver.
摘要:
A method of packet transfer is provided to resolve the problem of fraudulent access to user LANs through falsified source address so that only those pre-registered terminals are permitted to transfer packets with specific data networks. Each user LAN is assigned an identifier to identify respective user LAN beforehand. Packet network stores terminal information including terminal addresses, identifiers assigned to one and more user LANs that are permitted to communicate with each packet terminal and information necessary for terminal authentication beforehand. When the packet terminal starts a communication through a base station, the packet network authenticates the packet terminal, and if it is an unauthorized terminal, the packet network informs a denial for communication to the packet terminal. If an allowance for communication is obtained by authentication, the packet terminal encrypts data to be transmitted and sends a packet to the packet network with an attachment containing the encrypted data, identifiers for the selected user LAN among one and more user LANs, the destination address and the source address. Packet network receives the packet, and while decoding the encrypted data included in the received packet, detects tampering, and if tampering is detected, the received packet is discarded, but if there is no tampering, it checks whether the identity of source address and the identifier is registered in the terminal information, and if the identity is registered, the received packet is sent to the destination address, and if the identity is not registered, the received packet is discarded.
摘要:
A power line communication system is provided in which the influence of the impulsive noise unexpectedly generated on a power line which is a communication medium can be reduced according to the characteristics of the impulsive noise by an existing method and power line communication can be realized without a hindrance. A transmitter is constituted by: a modulator for conveying a LIN data signal by a power line; a filter that allows a signal of a predetermined band to pass therethrough; and a sinusoidal wave outputter (sinusoidal wave in the figure). In contrast, the receiver is constituted by the sinusoidal wave outputter, the filter and a demodulator that performs demodulation. To the power line, a limiter that limits the amplitude of the propagating signal to a predetermined amplitude (reception signal amplitude) is connected.
摘要:
For voltage values (observed noise sequence) in an electronic power line (communication medium) which are obtained at a predetermined interval, initial values of noise characteristics based on a statistic of the observed noise sequence itself are decided by a moment method (S301 to S307), the noise characteristics (state transition probabilities and state noise power) for maximization of the likelihood of the observed noise sequence are obtained from the initial values by MAP (Maximum A Posteriori) estimation using a Baum-Welch algorithm (S309 to S312), a state sequence is estimated from the obtained noise characteristics, and an impulsive noise at each time point is detected.
摘要:
For voltage values (observed noise sequence) in an electronic power line (communication medium) which are obtained at a predetermined interval, initial values of noise characteristics based on a statistic of the observed noise sequence itself are decided by a moment method (S301 to S307), the noise characteristics (state transition probabilities and state noise power) for maximization of the likelihood of the observed noise sequence are obtained from the initial values by MAP (Maximum A Posteriori) estimation using a Baum-Welch algorithm (S309 to S312), a state sequence is estimated from the obtained noise characteristics, and an impulsive noise at each time point is detected.
摘要:
A preamble for synchronization, or a reference timing for operation of an OFDM packet communication receiver system is detected finely even under environment of large waveform distortion due to thermal noise and/or multi-path propagation, and/or large carrier frequency offset between a transmit side and a receiver side. A correlator (1) detects a pattern of a short preamble (t1-t10) in a preamble for synchronization. An output of the correlator (1) is applied to a complex filter (7) which separates a short preamble having a predetermined repetition period from uniformly distributed noise. A scalar filter (9) integrates some period of short preambles which have distributed-delay by multi-path propagation as if a single short preamble with no delay were received for determining a reference timing. When a correlator output exceeds a predetermined threshold level a plurality of times for every repetition periods (T) of a short preamble, and an output of the correlator after time (T) from the last short preamble is decreased a predetermined ratio as compared with that of the last short preamble, it is determined that a preamble for synchronization is detected. Carrier frequency offset compensation is carried out either for each short preamble during reception of a short preamble, or based upon the last received short preamble during reception of an OFDM symbol after the last short preamble. As a preamble for synchronization is detected accurately, a guard interval of each OFDM symbol is removed accurately, or an FFT window is defined accurately, so that a demodulation is possible in spite of noise and/or interference.
摘要:
A coherent detection system for multicarrier modulation system capable of accurate channel estimation even in severe environment with high thermal noise and deep multipath fading, has been found with simple structure and small circuit size. The present coherent detection system comprises a channel estimation circuit (208) for estimating a channel attenuation of a preamble part of each subcarriers, an adaptive filter (210, 211) for smoothing estimated channel attenuation among subcarriers, a divider (213) for coherent detection of a data part by dividing a receive vector by smoothed estimated channel attenuation for each subcarriers, and a characteristic extraction circuit (209) for extracting characteristic value of each subcarriers. The adaptive filter (210, 211) is controlled depending upon characteristic value of each subcarriers measured by the characteristic extraction circuit (209). A characteristic value may be amplitude, phase rotation, vector difference, modulation system, of each subcarriers, and/or combination of those values.
摘要:
A digital communication system using superposed transmission of high and low speed digital signals capable of transmitting superposed high and low speed digital signals through an identical frequency band efficiently by increasing a simultaneously transmittable number of channels in the low speed digital signals, while achieving the practically reasonable bit error rate performances for both the high speed digital signals and the low speed digital signals. In this system, the low speed digital signals are transmitted in a form of spread spectrum signals and the high speed digital signals are cancelled out from the superposed transmission signals in obtaining the output low speed digital signals by using the phase inverted replica of the high speed digital signals to be combined with the superposed transmission signals, so that it becomes possible to increase a number of channels for the low speed digital signals, while achieving the practically reasonable bit error rate performances for both the high speed digital signals and the low speed digital signals.