Abstract: Base stations of a communication system belong to a sub-network, which is connected to the Internet by way of a gateway. Base stations of another communication system belong to sub-network, which is connected to the Internet by way of another gateway. A mobile terminal communicates with a server by using one of the communication systems. In this case, the mobile terminal includes mobile station network interfaces which can access to the communication systems, and is designed to switch communication systems by means of a communication system switching unit.

Abstract: A download method forms a download user network with a plurality of user terminals which are going to download the same data. The delivery server divides the data into data portions, and assigns the data portions to the respective user terminals belonging to the download user network. Then each of the user terminals downloads the assigned data portion from the delivery server. Thereafter the downloaded data portions are mutually transmitted among the user terminals within the download user network so that each of the user terminals can obtain all the data portions which constitute the data. Each of the user terminals combines the obtained data portions into the original data. Thus the data is efficiently downloaded to the plurality of user terminals.

Abstract: An adaptive receiver includes an adaptive array unit and an equalizer unit. In the adaptive array unit, receiving signals of an array antenna are demodulated, weighted by multiplying with a complex weight calculated by an adaptive arithmetic unit, and adaptively combined. In the equalizer unit, propagation path estimation values are calculated from the receiving signals by a propagation path estimating unit, weighted with the complex weight by a complex weight adjusting unit, and adaptively combined. The combined demodulation signal is divided by the combined propagation path estimation value. Thereby, not only the unwanted signal wave of low correlation but also the unwanted signal wave of high correlation can be controlled effectively using an adaptive array antenna.

Abstract: A communication device using orthogonal multiplexing carrier method for determining delay information of received radio waves. In this device, a known signal demodulator performs OFDM demodulation to output demodulated signal, and a divider performs a complex division of the demodulated signal with a data sector of known signal of a database for each sub-carrier. By the data section of the known signal, the computation result of the amount of shift can be determined for each of sub-carriers. A delay analytical calculation circuit uses the computation result of the amount of shift for sub-carriers to analyze the delayed waves. For delay analysis, ESPRIT method is used to determine delay information by means of computation result of the amount of shift for each sub-carrier.

Abstract: First, in a microcomputer of a communication terminal, data communication request is carried out. Next, a profile corresponding to contents of requested data is received from a communication control device. The microcomputer then selects one of communication systems based on the profile. The result of the selection is notified to the communication control device. Then, a transmission request signal is transmitted from the microcomputer. Thereafter, the data is received from the communication control device through the selected communication system. Thus, the download through the selected communication system is completed.

Abstract: In a gain control device for packet signal receiver, a variable gain amplifier amplifies an input signal with a gain corresponding to a control voltage applied thereto, and a power detector detects output power of the variable gain amplifier. A packet detection circuit detects a packet signal based on the detected output power. A control circuit outputs the control voltage variable with the detected output power, and the control voltage is provided for the amplifier. Thus high-speed gain control is performed immediately after the start of detection of the packet signal. When the elapsed time after the start of detection of the packet signal exceeds a predetermined time, a sample-hold circuit sample-and-holds the control voltage. This control voltage is provided for the amplifier up to the end of reception of the packet signal thereafter. Thus low-speed gain control is performed to provide stable power without distorting the signal wave.

Abstract: A radar apparatus is provided which includes a transmitter, a receiver, and a signal processor. The transmitter produces a transmit signal which is so modulated in frequency as to change with time cyclically and transmits the transmit signal as a radar wave. The receiver selectively establishes communication with one of receiving antennas and changes the communications with the receiving antennas in sequence in a cycle shorter than a cycle of a change in the frequency of the transmit signal to supply a series of signal components of input signals produced by the receiving antennas. The receiver mixes the series of signal components with a local signal having the same frequency as that of the transmit signal to produce a beat signal. The signal processor samples the beat signal to analyze frequency components thereof to determine the distance to, relative speed and azimuth of a target.

Abstract: An FM-CW radar apparatus is provided which may be employed in automotive anti-collision or radar cruise control systems. The radar apparatus transmits as a radar wave a high-frequency signal which is so modulated in frequency with a modulating signal as to vary with time in the form of a triangular wave and mixes a received signal with a local signal that is part of the transmitted signal to produce a beat signal consisting of a fundamental frequency component as a function of the distance to and relative speed of a target object. The radar apparatus also includes an amplitude modulator which modulates the amplitude of at least one of the transmitted signal, the received signal, and the local signal in accordance with the modulating signal so that the modulation index falls within a range of zero (0) to one (1). This allows harmonic components with an improved SN ratio to be extracted from the beat signal which may be used in calculating the fundamental frequency component of the beat signal.

Abstract: A frequency multiplier is constructed to input an input signal to a transistor through an input matching circuit and to output a multiplied output signal from the transistor through a reflecting type fundamental wave signal band suppressing circuit and an output matching circuit. A transmission line produces a standing wave and is disposed between the output terminal of the transistor and the input terminal of the reflecting type fundamental wave signal band suppressing circuit. Because the voltage acting on the output terminal of the transistor consequently increases, the transistor operates at a point at which the nonlinearity of its input-output characteristic is greater and the output power of the multiplied output signal increases.

Abstract: A modulation signal generating section produces a modulation signal for controlling an oscillation frequency of a voltage-controlled oscillator. The modulation signal generating section comprises a triangular wave oscillator producing a linear modulation component of a triangular waveform which varies the modulation frequency linearly, a sine wave oscillator producing a cyclic modulation component of a sine waveform which varies the modulation frequency cyclically, and a signal adder producing the modulation signal by adding the linear modulation component and the cyclic modulation component. A transmitting signal frequency modulated by the modulation signal is mixed with a received signal and produces a beat signal comprising a fundamental wave component of a beat frequency and harmonic components.

Abstract: A pseudomorphic HEMT of a structure which prevents the distribution of 2DEG in the channel layer from being concentrated near the hetero-interface relative to a doping layer and which, at the same time, enables the thickness of the channel layer to which distortion is imparted to be decreased. In an n-InAlAs/InGaAs pseudomorphic structure grown on an InP substrate 1, an InGaAs spacer layer 4 having an In composition ratio smaller than that of an InGaAs channel layer 3 is inserted in an InAlAs/InGaAs hetero-interface. The InGaAs channel layer 3 has an In composition ratio of 0.80 to exhibit a high mobility. Another InAlAs buffer layer 2, spacer layer 5 and doping layer 6 have an In composition ratio of 0.52 which is in lattice-match with the substrate, and InGaAs spacer layer 4 and cap layer 7 have an In composition ratio of 0.53 which is in lattice-match with the substrate. This constitution makes it possible to control the two-dimensional electron gas and to further increase the mobility.

Abstract: A compound semiconductor device including a semiconductor substrate having (100) plane as a crystal growth plane, a first semiconductor layer as an electron traveling layer and a second semiconductor layer for supplying electrons to the electron traveling layer. The first semiconductor layer is formed on the semiconductor substrate and has a different lattice constant from the semiconductor substrate so that a first strain is applied in the first semiconductor layer in a first strain direction. The second semiconductor layer is formed on the first semiconductor layer and has a different lattice constant from the first semiconductor layer to thereby apply a second strain to the second semiconductor layer. The second strain has a direction that is inverse to the first strain direction. In addition, the thickness of the semiconductor layer is defined so as to compensate for the first strain applied to the first semiconductor layer by the second strain applied to the second semiconductor.