Nec Corporation

Nippon Electric Co., Ltd.

Nippon Telegraph and Telephone Public Corporation

Kouzou Kage

Ikio Yoshida

Hiroshi Watanabe

Yasuo Sato

Yoshiharu Tamura

Kazuhiro Ikeda

Shigeru Kazama

A person location system comprises radio base stations and a radio central station, all stations being connected to a public switched telephone network. The base stations respectively cover small areas, or 'microcells', in one of which is located a user station, and the central station covers an area containing all of the microcells. The central station receives a polling signal containing the user's address via the telephone network and broadcasts a copy of the polling signal. A management center is connected to the telephone network for transmitting the polling signal to the central station when a location demand arises. Each base station is responsive to the polling signal from the central station for returning field intensity data of the user station through the telephone network to the management center if the polling signal identifies the user station.

Person location system

A personal mobile communications system comprises base stations (4-1.about.4-4) located in respective zones and a paging station (8) covering an area including the zones, or cells (5-1.about.5-4). The paging station and all base stations are connected to a public switched telephone network (PSTN). When a call is originated from a PSTN user (2) to a mobile user (10), the paging station receives a call-setup request from the PSTN containing the address codes of both PSTN and mobile users, and broadcasts the call-setup signal over the covered cells. One or more base stations (4-1.about.4-3) receive the call-setup signal and, in response, broadcast an alert signal. One of the base stations (4-2) receives an off-hook signal from the alerted mobile station (10) and dials the PSTN user address code contained in the call-setup signal to the PSTN to establish a connection (15; 147.about.149; 176.about.178) between the calling and called parties (2,10).

Personal mobile communications system having central station for paging

A channel selection system for radio communication equipment which uses a control channel for interchanging control signals for connection and a plurality of data channels for interchanging data and emits an electromagnetic wave by using any one of the data channels after determining that it is idle by carrier sensing. The system rarely selects a data channel adjoining the control channel since the probability that such a data channel is registered as an idle channel is extremely low. The system, therefore, reduces the possibility of the equipment being unable to use the control channel due to the influence of power leaking from the data channel adjoining the control channel.

Channel selection system for mobile radio communication equipment

In a communication system for use in transmitting a sequence of information signals in addition to a sequence of digital voice signals subjected to adaptive delta modulation, the information signal sequence is modulated by a phase modulator (51) of the transmitter section (11a) into a phase modulated signal sequence and is combined with the digital signals by a combining circuit (15) into output signals. The phase modulated signals might be sent through an ADM decoder (36) and a switch (44) of a receiver section (12a) to a loudspeaker (45) to be reproduced together with the digital voice signals. However, such phase modulated signals are not substantially audible for listeners because the phase modulated signals scarcely comprise a low frequency component. The phase modulated signals may be binary Manchester code signals and may be either interposed in a quiescent time of the digital voice signals or placed at the end or beginning of each digital voice signal.

Signal communication capable of avoiding an audible reproduction of a

A privacy signal transmission system having a transmitter portion and a receiver portion. The transmitter portion digitizes an analog message signal and enciphers the digitized signal into a privacy signal before modulation and transmission to the receiver portion. The transmitter portion also extracts and modulates an analog error signal representative of the digitization error for transmission to the receiver portion. The receiver portion demodulates the digitized privacy signal and analog error signal, and after the privacy signal is deciphered and reconverted to an analog signal it is added to the received analog error to reconstitute the original analog message signal.

Privacy signal transmission system

A privacy code-type signal transmission system includes a transmitter having a signal sampler for producing analog samples of an analog audio signal, an analog to digital converter, a scrambler, a multi-level analog former and modulator means. The analog to digital converter converts each analog sample into a parallel n bit digital signal. The parallel n bit digital signal is scrambled by a digital scrambler to produce a second parallel n bit digital signal. The second n bit digital signal is input to a multi-level former having 2.sup.n different levels, the output of which is a 2.sup.n level analog signal which is suitably modulated for transmission to a receiver. The receiver demodulates the 2.sup.n level analog signal and with a level discriminator converts the demodulated signal to a scrambled digital signal corresponding to the scrambled digital signal produced at the transmitter. The original analog audio signal is then recovered by descrambling the digital signal and applying the descrambled digital signal to a digital to analog converter. This system eliminates any need for parallel-serial and serial-parallel converters, as well as frame sync insertion and extraction circuits necessary in conventional privacy code-type transmission systems.

Signal transmission system having encoder/decoder without frame

A noise detection circuit for a digital radio receiver comprises a sampling circuit for sampling a digital baseband signal having a noise component when an eye opening of the baseband signal is largest. A waveform generator is connected to the output of the sampling circuit for generating a waveform which is a replica of the baseband signal and free from the noise component. The waveform generator comprises a threshold comparator having decision thresholds and a waveform recovery circuit which includes a resistor, a plurality of storage capacitors of equal values and a switch responsive to the output of the threshold comparator for selectively coupling the output of the sampling circuit through the resistor to the storage capacitors. A substractor is connected to the outputs of the sampling circuit and the waveform generator for generating a signal representative of the noise component of the baseband signal. The output of the subtractor circuit can be used for various purposes including noise measurement, squelch action and automatic local oscillator frequency control.

Noise detection by sampling digital baseband signal at eye openings

An apparatus for accurately detecting a start pattern in the event of reception of a digital signal in which the start pattern is followed by an information signal. The detection of a start pattern is performed only once while a start pattern is received so that, although a pattern analogous to the start pattern may be included in a data signal, a pattern match output is prevented from responding any further despite such a pattern. Even a start pattern having an extremely great length is detected without errors.

Start pattern detecting apparatus

An encryption/decryption system for a communication channel increases the number of values for the encryption key variable without increasing the length of a cipher feedback register. This is done by providing a selector to select one from many local and prestored keys for each frame. The transmitting end has a first storage register, a first memory, a first selector, and an encrypting circuit. The encrypting circuit combines a randomized signal with the input signal to form an encrypted signal. As cipher feedback, the first storage register provides bits of the encrypted signal as addresses to the first memory, which outputs corresponding random numbers. The first selector selects from the random number data to form the coding randomized signal fed to the encrypting circuit. The receiving end has a second storage register, a second memory, a second selector, and a digital signal decoding circuit. The second storage register stores bits of a received encrypted signal and outputs them in parallel as addresses. The second memory receives these addresses and outputs corresponding random numbers. To enable decoding, the working and stored contents of the first and second memories are identical. The second selector, operating the same way that the first operates, selects from the identical random number data to form a decoding randomized signal. The decoding circuit combines the received encrypted signal with the decoding randomized signal to reproduce the input digital signal.

Encryption/decryption system

In a receiver responsive to an input signal comprising information signals following frame synchronization signals, respectively, frame synchronization is established by a frame synchronization pulse generator (56) with reference to both of the information signals and the frame synchronization signals. A discriminator (57) discriminates between the information signals and other spurious signals by monitoring descrambled digital signals produced by a descrambler (47) in response to the information signals or by monitoring reproduced analog signals into which the descrambled digital signals are converted by a digital to analog converter (51). The monitoring is carried out within silent parts interposed between information parts of either the descrambled digital signals or the reproduced analog signals. The information signals are discriminated either by a preselected pattern inevitably appearing in the silent parts of the descrambled digital signals or by amplitudes of the silent parts of the reproduced analog signals. Alternatively, the information signals may be discriminated by detecting the autocorrelation of the reproduced analog signals.

Receiver capable of quickly establishing stable frame synchronization

An apparatus for processing a digital signal which is transmitted from a transmit station by radio equipment and contains the same repetitive information employs the principle of decision by majority. A particular signal pattern with the least error rate is determined by majority. Noncoincident bits between the determined signal pattern and each of the repeatedly received patterns are counted and, then, the number of noncoincident bits is determined on each of a predetermined number of patterns which are selected by a selector out of the repeatedly received ones. When the number is smaller than a predetermined one, the pattern is allowed for processing. That is, the signal pattern is processed by measuring the bit error rate in a transmission path with the signal pattern equivalently used as a reference.

Received signal processing apparatus

A digital signal repeater system, including means for controlling the transmitter of the system. The system is substantially immune to fading, interference and noise, and rapidly detects the reception of a digital signal. A first level detector outputs a logical 1 signal to indicate reception of a signal, in response to the level of the IF signal in the receiver. A second level detector indicates when the received signal is digital by filtering the demodulated received signal and generating a logical 1 output when the received signal has a substantial component at a predetermined clock frequency. The two logical output signals are applied to an AND gate and the output is smoothed and compared by a comparator to a reference level. The output of the comparator is used to control the transmitter. In another embodiment, a third level detection circuit determines whether the clock frequency signal has been detected for a comparatively long period of time and, if so, lowers the reference level supplied to the comparator to stabilize its output.

Digital signal repeater including means for controlling a transmitter

An interference wave detection circuit is designed so as to detect whether a beat due to the difference between two carrier wave frequencies is included or not in a received signal for a radio receiver. The detection circuit comprises circuitry for deriving a first binary signal corresponding to a level of a signal of voice frequency band obtained by demodulating the received signal and for deriving a second binary signal corresponding to a level of an envelope signal of an intermediate frequency signal from the received signal to provide a predetermined time difference between the first and second binary signals. The detection circuit further comprises a spoken message detection circuit for detecting that a carrier wave is modulated in a spoken message of the received signal, and a correlation detection circuit for detecting correlation between the first and second binary signals when the output of the spoken message detection circuit is not produced, thereby producing an interference detection signal when the correlation therebetween is detected.

Interference wave detection circuit for use in radio receiver

A squelch signal generator is responsive to a digital input signal (IN) which causes a display of an eye pattern in an oscillascope. The pattern has at least one eye at each time instant appearing at a predetermined period. A squelch threshold level (V.sub.S) is preselected outside of a predetermined one of uppermost and lowermost cross-points of at least one eye. The squelch comparator compares an input level of the input signal with the first squelch threshold level to produce a resultant signal which is representative of a first result of the comparison. The resultant signal is processed at each time instant by a processing circuit into a squelch signal when the input signal is classified into an undesired signal. An additional squelch threshold level may be preselected outside of the other of the uppermost and the lowermost cross-points.

Squelch signal generator capable of generating a squelch signal with a

An interference detector for use in determining when two carriers are producing a beat signal, comprising a low frequency automatic gain control amplifier 1' amplifying the received signal, a demodulator 5 and voice detector 6 for determining if the received signal is modulated, an amplitude detector 2 for measuring the amplitude of the amplifier output, a level measuring circuit 3 for measuring the beat component of the amplitude detector output, a comparator 4 for outputting an interference signal when the beat component exceeds a predetermined level, and a gate 7, 8 controlled by the voice detector for inhibiting the interference signal when the received signal is modulated.

Growing community of inventors

Tokyo, Japan

Kouzou Kage