Nec Corporation

Nippon Electric Co., Ltd.

Nippon Electronics Co., Ltd.

Junji Namiki

Yukitsuna Furuya

Makoto Shibutani

Toshihito Kanai

Kazutomo Kobayashi

Yoshio Matsuo

Katsumi Emura

Fumio Akashi

Kojiro Watanabe

A cellular mobile communication system in which each of one or more cells is provided with a base radio station, and mobile terminals communicate with the base radio stations. Base radio stations (21, 22 and 23) are connected to a central base station (100) by optical fibers. The central base station is connected to a mobile switching center (50). Each of the base radio stations is provided with an O/E converter (201) and E/O converter (207). The O/E converter converts a optical signal containing speech signals and a call connection control signal into RF signals. The E/O converter (207) converts RF signals, received from a mobile terminal (11) via an antenna (204), into optical signals and transmits the optical signals to the central base station. The central base station comprises O/E converters (301-303) for converting optical signals from each base radio station into RF signals; receivers (401-403) for demodulating these RF signals; transmitters (406-408) for converting speech signals and a call connection control signal from the mobile switching center into RF signals; and E/O converters (304-306) for converting these RF signals into optical signals and transmitting the optical signals to a base radio station.

Mobile communication system

In a multipoint communication system, first polling signals are sequentially and respectively transmitted to terminal stations on a broadcast channel from a central station, asking a request for reservation without waiting for a reply from the terminal stations. A reservation signal is transmitted on a multiple access channel from a terminal station requesting the reservation to the central station in response to the first polling signal addressed to it. A second polling signal is then transmitted on the broadcast channel in response to the reservation signal and the multiple access channel is reserved for a period of time variable in accordance with the reservation signal. A data signal is transmitted from the terminal station requesting the reservation on the reserved multiple access channel in response to the second polling signal.

Multipoint communication system having polling and reservation schemes

A digital microwave radio repeater using the same carrier frequency for the transmitter and the receiver carriers for improving the frequency utilization efficiency. The transmitter-to-receiver interference signal is cancelled by producing an estimated-interference signal of the interference signal from the digital baseband signal by the use of a transversal filter and by subtracting the estimated-interference signal from the received signal. The estimated-interference signal is also produced by frequency shifting a digital modulated signal in the transmitter. The transmitter carrier frequency is locked to the receiver carrier frequency by the use of a phase-locking technique, so that the interference signal is reduced.

One frequency repeater for a digital microwave radio system with

A telecommunication system includes an earth-to-satellite-to earth link over which transmission is made on a time division basis. Each earth station assembles data to be transmitted in bursts during time period assigned to such earth station. The time position has a variable length which corresponds to the amount of data that is to be sent. The time positions are shifted to immediately follow each other with no idle and unused time space in or between adjoining time positions. Thus, each time frame is adaptively changed to fit the instantaneous communications traffic needs.

TDMA communications apparatus having adaptive burst duration

A space diversity system for transmitting digital microwaves is disclosed. Each of two antennas receives a direct wave and an interference wave. The output phase of one of the two antennas is controlled to combine an output thereof with that of the other antenna, so that the interference waves cancel each other and a vector sum of the direct waves is produced as a combined output. Even if the two antenna inputs are so much alike, the combined output level and thereby the signal-to-noise ratio is prevented from being lowered whereby error in identification is eliminated.

Space diversity system

An interference cancellation type space diversity system transmits digital microwaves in a sure and stable manner. Signals coming in through two spaced antennas are combined together into a single input signal and the composite signal is processed by a demodulator into a baseband signal which is identical with a transmitted signal. The demodulated baseband signal is processed by a frequency/amplitude characteristic detector network, which comprises a correlation circuit and an identification circuit, thereby controlling output phases of the antennas.

Interference cancellation type space diversity system

A cross-polarization crosstalk canceller is equipped to receive two polarized waves which are orthogonally crossing each other. The cross-polarization interference is eliminated by multiplying the signal received on one side by a compensating coefficient and adding the resulting product to the signal received on the other side. A discrimination error represents the difference between the reception signal after compensation and the identified value thereof. An adder and a subtractor supplies the sum and the difference between the real part and the imaginary part of the discrimination error. A discriminator detects equality between the absolute values of the real part and the imaginary part of the signal received on the interfering polarized wave side and supplies a control signal depending on the quadrant to which the signal belongs. A switch combines and varies a combination of the signs of the outputs of the adder and subtractor in response to the control signal supplied by the discriminator. A low-pass filter smooths the output of the switching in order to give the compensation coefficient.

Cross-polarization crosstalk canceller

A digital transmission system is provided based on a cross-polarization band-sharing technique using a conventional antenna system which does not have a sufficient cross-polarization discrimination. An interference elimination circuit receives two mutually orthogonal cross-polarized waves and restores to at least one of the received cross-polarized signals, a baseband signal which is free of cross-polarization interference attributable to orthogonal cross-polarization crosstalk components. This circuit includes an orthogonal cross-polarization, crosstalk component adder having a weighting circuit for multiplying an interference component of the received orthogonal cross-polarized signals by a compensation coefficient. A compensating adder adds the output of the weighting circuit to a desired one of the received cross-polarized signals. An error detector detects the difference between a transmitted signal and the desired one of said received signals on the basis of the output of said cross-polarization crosstalk component adder. An oscillator generates cyclic infinitesimal signals which a correlator uses for detecting any correlation between the output of the oscillator and the output of the error detector. An integrator integrates the output of said correlator. A control unit adds the output of the integrator to the output of the oscillator and supplies the resulting sum as the compensation coefficient for the weighting circuit of the orthogonal cross-polarization component adder.

Cross-polarization crosstalk elimination circuit

The invention eliminates an FM interference from a digital signal when the interference occurs because the FM and digital signals are transmitted over adjacent routes and sharing a common frequency band. An error detector finds a difference between a detected baseband digital signal and an assumed transmission code, which is taken from the baseband signal. The detector produces a first error signal responsive thereto. A phase synchronizing circuit produces an output signal synchronized with the first error signal. A coefficient circuit multiplies the output of the synchronizing circuit by a complex coefficient which is then subtracted from the baseband signal. A second error detector produces a second error signal responsive to the difference between the output of the subtractor and a discriminated transmission code. Responsive thereto to a control circuit varies the complex coefficient to produce an output which is the original baseband signal, free of the FM interference.

Digital signal receiver with FM interference elimination capability

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.

Digital equalizer for a cross-polarization receiver

The invention is used in a receiver for a communication system, which transmits periodically occurring digital signals over a pair of orthogonally related polarized waves. Horizontal signals from one of the orthogonal waves are applied to a first input terminal of an equalizer in the receiver. Vertical signals from the other of the orthogonal waves are applied to a second input terminal. An individually associated, cascaded plurality of delay circuits is coupled to each of the input terminals. The delay in each of the delay circuits is equal to the time spacing between the occurring signals. Therefore, a plurality of the recurring digital signals appear simultaneously at the outputs of each of the delay circuits. A variable attenuator, individually associated with the output of each delay circuit, is adjusted to pass an incremental signal responsive to each of the occurring signals appearing simultaneously at the outputs of the delay circuits. These incremental signals are added to produce a first full signal when all of the digital signals received at one of the input terminals appear simultaneously at the outputs of the delay circuits associated therewith. The adder also adds the incremental signals to produce a second full signal when all of the digital signals received at the other of the input terminals appear simultaneously at the outputs of the delay circuits associated therewith. The polarity of the second full signal is opposite to the polarity of the first full signal. Therefore, the second full signal is subtracted from that part of the first full signal which appears simultaneously with the second full signal. This subtracted signal is the interference in the first signal which occurs responsive to the second signal. Therefore, only the signal applied to one input terminal appears at the output of the adder.

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.

Initial acquisition signal detection system for TDMA satellite

A phase synchronizer for a reference carrier signal reproduced in a receiver for a combined amplitude and phase modulated signal comprises a window specifier for specifying windows for preselected ones of true signal points of which the demodulated signal is selectively representative. The phase synchronizer includes a demodulator for producing complex signals representative of coarse signal points so long as the reproduced carrier signal has a phase error which falls within the windows. Differences between the true points and the coarse points falling within the windows are calculated and summed up to produce a control signal for reducing the phase error substantially to zero.

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Tokyo, Japan

Junji Namiki