Abstract: Provided is a circuit that has a simple circuit configuration and can detect zero values in a 1-bit digital signal irrespective of a recording medium such as SACD. DSD data forming the 1-bit digital signal are successively sent to a shift register (1) whose number of stages corresponds to the number of bits of an idle pattern such as “101010101” which appears when assuming a zero value. For example, the shift register (1) is an 8-bit shift register. An adder (2) sums up the values at each stages of the shift register (1). A zero decision circuit (4) produces an output indicating decision of zero if the sum value is half of the number of bits. A counter (5) keeps counting while the output indicating zero decision is being delivered. If the count value of the counter exceeds a given value, the counter produces an output indicating detection of a zero value.

Abstract: A speaker system that detects what type of audio signal is supplied to it and automatically adjusts to reproduce sound from either an analog audio input signal or a digital audio input signal. The speaker system has one or more converters to convert each form of digital audio into analog audio, a detection means to detect whether an analog audio input signal or one of the possible digital audio signals is present and a multiplexer to switch between either the analog audio input signal or one of the outputs of the digital audio converters. Amplifier and speaker drivers are shown for completeness.

Abstract: A baseband detector includes a complex differential detector, a constellation point computer, and a phase shift keying (PSK) decoder. The complex differential detector outputs complex values in response to digitized samples derived from a received baseband signal. The PSK decoder generates decoded bits representing information symbols by determining in minimum distance between the complex values and plural constellation points provided by the constellation point computer. The constellation point computer can adaptively generate the constellation points based on a training sequence of information symbols and their corresponding complex valued outputs from the complex differential detector. The baseband detector can be used for frequency shifting keying (FSK) and differential phase shift keying (DPSK) demodulation in direct conversion receivers (DCRs).

Abstract: A differential latch includes a sample transistor section, a hold transistor section, a 1st gating circuit and a 2nd gating circuit. The sample transistor section is operably coupled to sample, when coupled to a supply voltage (e.g., VDD and VSS) a differential input signal. The hold transistor section is operably coupled to latch, when coupled to the supply voltage, the sampled differential input to produce a latched differential signal. The 1st gating circuit is operable to couple the sampled transistor section to the supply voltage in accordance with a 1st clocking logic operation and a 2nd clocking logic operation. The 2nd gating circuit is operable to couple the hold transistor section to the supply voltage in accordance with a 3rd clocking logic operation and a 4th clocking logic operation.

Abstract: A receiver is equipped with a demodulation circuit for taking a signal indicating broadcast contents of an analog broadcast out of the first and second intermediate-frequency signals, and for taking a signal indicating broadcast contents of a digital broadcast out of the first and second intermediate-frequency signals. Frequencies of local oscillation signals are made to be a first frequency within a frequency band of the digital broadcast adjacent to a frequency band of the analog broadcast received by the receiver at a time of receiving the analog broadcast, and the frequencies of the local oscillation signals are made to be a second frequency equal to the carrier frequency of the analog broadcast adjacent to the frequency band of the digital broadcast received by the receiver at a time of receiving the digital broadcast.

Abstract: A radio circuit that includes a radio front-end for receiving a radio signal and converting the radio signal to a first intermediate frequency signal and a second intermediate frequency signal. The radio circuit also includes an analog back-end having a plurality of inputs for receiving the first intermediate frequency signal and for processing the first intermediate frequency signal in response to digital signals. Also included is a digital back-end having a plurality of inputs for receiving the second intermediate frequency signal and for processing the second intermediate frequency signal in response to the digital signals.

Abstract: A digital GMSK filter for use for frequency modulation of a carrier signal in a GMSK transmission system is described. The GMSK filter uses a large number of individual current sources, whose current values are individually weighted. The current sources are driven via a control logic module using a shift register with a thermometer code, such that this results in a total current with a Gaussian characteristic, which is converted across a resistor to a voltage and drives a voltage controlled oscillator (VCO). The filter provides exact implementation of the sample values, virtually without any quantization error, and requires only a small chip area for its implementation.

Abstract: A transmitter (100) includes a fractional N synthesizer, a baseband digital modulation stage coupled to the fractional N synthesizer in a first modulation mode, and a baseband I/Q modulation stage also coupled to the fractional N synthesizer and reusing the fractional N synthesizer in a second modulation mode. A method (300) of operating a transmitter includes transmitting a first signal from a transmitter using the fractional N synthesizer and the baseband digital modulation stage to modulate the first signal according to a first wireless protocol. The method (300) also includes transmitting a second signal from the transmitter using the baseband I/Q modulation stage and the fractional N synthesizer to modulate the second signal according to a second wireless protocol.

Abstract: A system for transmitting digitized samples of analog signals while concealing unrecoverable digitized samples of analog signals to maintain a level of fidelity in reproducing the analog signals. The digitized samples of the analog signals are burst transmitted such that the probability of interference with the transmission and thus corruption of the digitized samples of the analog signals is minimized. The digitized samples are received without synchronizing a receiving clock with a transmitting clock to capture the digitized samples of the analog signals. The digitized samples are converted from various sampling rates to digitized samples of the analog signals having a rate. Any large groups of digitized samples that are in error or corrupted in transmission are softly muted to avoid annoying clicks. Any long term difference between a transmit clock and a receive clock is tracked and the digitized samples are interpolated or decimated to eliminate any underrun or overrun of the digitized samples.

Abstract: An interface, e.g., a modem-like interface for converting a digital information signal into an analog signal for use within an analog television studio infrastructure. Namely, the present invention employs a novel modulator that conveys compressed video data into analog video lines by creating an analog “video” signal that contains video gray-scale levels which correspond to digital data values, instead of containing an image.

Abstract: The present invention provides an improved apparatus and method for detecting a reverse carrier signal. The present invention utilizes a peak detector/envelope filter for determining the peak level of the reverse analog waveform. The peak level is compared to a threshold level during a predetermined time period to determine the presence of a valid reverse carrier signal. Once determined, an enable signal is provided to an electronics device that allows further transmission of the reverse signals.

Abstract: A radio-frequency apparatus includes an integrated circuit. The integrated circuit includes receiver analog circuitry, receiver digital circuitry, a digital-to-analog converter, and a signal selector. The receiver analog circuitry receives radio-frequency signals, and provides a first digital signal. The receiver digital circuitry receives the first digital signal, and provides a second digital signal. The digital-to-analog converter converts the second digital signal into a first analog signal. The signal selector receives the second digital signal and the first analog signal, and selectively provides one of the second digital signal and the first analog signal as an output signal of the integrated circuit.

Abstract: The present invention provides an improved apparatus and method for detecting a reverse carrier signal. The present invention utilizes a peak detector/envelope filter for determining the peak level of the reverse analog waveform. The peak level is compared to a threshold level during a predetermined time period to determine the presence of a valid reverse carrier signal. Once determined, an enable signal is provided to an electronics device that allows further transmission of the reverse signals.

Abstract: The digital signal is provided to the digital-to-analog upconverter (40) such as through digital signal processing circuitry (70). A sample rate signal and a divided sample rate signal are provided by divider chain (96) using the clock input (44). The divided sample rate signal is used to drive the decode circuit (88). The digital outputs of the decoder circuit (88) is combined with the sample rate signal in a mixer (52) which in turn generates a digitally upconverted signal which drives a plurality of switches combined together to form the analog output (46).

Abstract: Line drivers are provided that are suitable for driving communication cables (e.g., in Data Over Cable Service Interface Specification (DOCSIS) certified systems) without the need for output drivers and their size, power-consumption, noise and signal-distortion penalities. These line drivers directly couple switched current mirrors to a transformer's input winding to simultaneously provide currents in response to a differential input signal and a digital command signal and drive the load impedance to thereby realize a corresponding signal gain.

Abstract: The invention is a method and transmission system which transmits an analog composite signal, including carriers which are respectively modulated with different digital data signal.

Abstract: An apparatus for converting a digital input signal to an analog signal for transmission. The input signal can include more than one carrier signal. A plurality of delta-sigma modulation loop circuits are connected in an increasing order of operating frequency so as to reduce a word length of the input signal. A tuning circuit adjusts the signal frequency to a transmitting frequency for conversion to analog by a digital-to-analog converter. A first loop circuit is implemented using CMOS gates, and a second loop circuit and the tuning circuit are implemented using indium phosphide gates. The apparatus allows a high-resolution, wide-band RF multiple-carrier signal to be re-quantized to a lower-resolution signal while an acceptable signal-to-noise ratio is maintained.

Abstract: An improved transmitter capable of achieving high linearity with minimal power dissipation is disclosed, comprising a digital phase splitter and an output stage. The digital phase splitter includes a positive phase digital-to-analog converter (DAC) for converting the positive phase portion of a set of input digital data into an analog signal, and a negative phase DAC for converting the negative phase portion of the set of input digital data into another analog signal. The analog signals from the phase splitter are passed to the output stage for transmission onto a transmission medium. The transmitter may be operated in low power dissipation mode. Because the phases of the input digital signal are split in the digital domain prior to the output stage, the output stage experiences minimal crossover distortion. Consequently, the transmitter is able to minimize power dissipation without suffering from poor linearity performance.

Abstract: A digital audio signal processing and distribution sub-assembly unit, plug compatible or integratable with single user digital radios, for audio channels and simultaneous re-transmission to multiple user headsetss. The sub-assembly will enable multiple users to select individual channels for listening, via audio headsets, from satellite digital radio broadcasts, which will encompass up to 100 channels of music and talk show programming. Headsets will have either direct wire connections to the digital radio receiver (via a jack connection), or infra-red (IR) links or RF links, which can allow the user to roam significant distances from the radio without the encumbrance of a wire link. The unit will function in automobiles or in homes, with auto usage eventually implemented with interior wiring with access jacks for the headsets built into doors and dashboards.

Abstract: A converter or a resampler used in a digital communication system converts a first digital signal representing an analog signal into a second digital signal representing the same analog signal. The converter includes a converter filter and a timing circuit. The timing circuit provides a first clock generated from a second clock, and a phase control signal for controlling the conversion of the converter filter. The timing circuit is preferably a numerical controlled oscillator (NCO) and includes an accumulator for generating the first clock from the second clock and a phase offset, and a phase calculator which receives the phase offset to generate a phase control signal. The phase control signal includes a plurality of phase weighting signals, a plurality of control signals, and an interpolation signal. The first digital signal is selectively convoluted with the phase weighting signals, which is controlled by the control signals.

Abstract: A dual-mode radiotelephone capable of operation in analog or digital modes. According to exemplary embodiments, a digital signal processor receives a speech signal to be transmitted in the digital or analog mode and generates In-phase (I) and Quadrature (Q) modulating signals. The I and Q signals are supplied to a quadrature modulator for generating a digitally modulated signal and are supplied to an analog modulator for generating an analog modulated signal.

Abstract: A method of estimating SNR for a plurality of carriers modulated with digital information, wherein the digital information includes data baud and training baud, comprising the steps of: receiving the plurality of carriers; determining a first SNR for the data baud; determining a second SNR for the training baud; comparing at least one of the first and second SNRs to predetermined selection criteria; and selecting one of the first and said second SNRs based on the comparison step. In the preferred embodiment, the carriers are processed to produce an equalizer output for each of the carriers, and the equalizer output is processed to produce a symbol decision for each of the carriers. The equalizer output is subtracted from the symbol decision when a data baud is received to produce a first difference value, and the first difference value is squared to produce a first signal to noise estimate.

Abstract: A differential line driver includes first, second, third and fourth cascode transistors connected in parallel, wherein drains of the first and third transistors are connected to a negative output of the differential line driver, and wherein drains of the second and fourth transistors are connected to a positive output of the differential line driver. First, second, third and fourth switching transistors are connected in series with corresponding first, second, third and fourth cascode transistors and driven by a data signal. First and second compound transistors inputting a class AB operation signal at their gates, wherein the first compound transistor is connected to sources of the first and second switching transistors, and wherein the second compound transistor is connected to sources of the third and fourth switching transistors.

Abstract: A system for combining AM and FM transmissions. In-band, on-channel, FM Digital Audio Broadcast (IBOC FM-DAB) allows simultaneous transmission of DAB and FM over existing FM allocations without interfering with conventional analog FM signals. The utility of existing FM spectrum allocations is therefore enhanced.

Abstract: A technique is described for reliably determining whether a direct digital connection exists between a transmitting server modem and a receiving client modem. Such a determination is an essential part of the training procedure for modems that conform to ITU-T Recommendation V.90 but is also applicable to other data communications configurations and equipment. In some configurations in accordance with the present invention, segments of a modem training signal, L1L2, are used to make the determination.

Abstract: A power efficient and reduced electromagnetic interference (EMI) emissions transmitter for unshielded twisted pair (UTP) data communication applications. Transmit data is interpolated by N and processed by a digital filter to obtain the pulse shape required by the particular communication application. The digital filter output data is converted to a current-mode analog waveform by a digital-to-analog converter (DAC). The digital filter is integrated with the DAC binary decoder in a memory device such as a ROM with time multiplexed output. When implemented in such manner, the logical implementation and memory replaces digital filtering circuits, DAC decoding logic circuit and re-synchronization logic circuits that are conventionally implemented in hardware. Thus, the hardware functionality of these circuits is rendered into arithmetic form and implemented in a memory device.

Abstract: An RF receiver operates to receive broadcast RF signals that include at least one of an analog portion and a digital portion. The RF receiver performs processing of the analog portion and/or the digital portion to generate a digital path signal. The RF receiver performs further processing of the analog portion to generate a first audio signal. A digital modulation processing system may be electrically connected with the RF receiver. The digital modulation processing system may receive and process the digital path signal to generate a second audio signal. The RF receiver may selectively utilize at least one of the first audio signal and the second audio signal to generate an audio output.

Abstract: A method of demodulation and equalization is used to process an amplitude modulated compatible digital broadcasting signal including an amplitude modulated radio frequency signal having a first carrier modulated by an analog program signal in a first frequency spectrum, a plurality of digitally modulated carrier signals positioned within a bandwidth which encompasses the first frequency spectrum, a first group of the digitally modulated carrier signals including complementary carrier signals and lying within the first frequency spectrum, and second and third groups of the digitally modulated carrier signals including non-complementary carrier signals and lying outside of the first frequency spectrum.

Abstract: A system and method for converting an analog voltage signal to a digital representation at high speeds, known as an analog to digital converter (A/D converter), is provided. The invention teaches an N-bit A/D converter, made by N superconducting, preferably HTC, transmission lines. The N lines are arranged adjacently and in parallel with each other. On each line 2N-1 JJs are imbedded in series. The JJs form a matrix over the configuration of the N superconducting transmission lines in such a manner that across the lines the JJs give N digit binary numbers, while in the length direction these N digit binary numbers fall in numerical order. A scanning electron beam is made to impinge on this arrangement. The beam is scanned across the lines at a high frequency, while it is deflected by the applied voltage signal along the direction of the lines. The beam generates a voltage step on any one of the N lines on condition of hitting any one of the JJs.

Abstract: A method and system is presented for coordinating the transmission of supplemental digital data to accompany broadcast data, and in particular, analog radio broadcasts, among a plurality of broadcasters. The supplemental digital data may provide information about the particular broadcast data being transmitted (i.e. cut data) or may be supplemental to such data (i.e. news, weather and traffic data). The supplemental digital data to be presented is sorted based on particular algorithms which may take into account broadcaster-specified criteria such as target audience, time of day, type of broadcast data presented, and the like. The supplemental digital data may be audio data, visual data, or audio-visual data for presentation with the broadcast data. The supplemental digital data may further be advertisement data. The advertisement data may be sold by the broadcasters or the party coordinating the IBOC transmission of the supplemental digital data.

Abstract: A portable radio telephone handset includes the capability of operating as a data transfer terminal as well as an analog cellular telephone subscriber station. Two modes of operation are available in the handset, an analog cellular communication mode and a Cellular Digital Packet Data (CDPD) mode. A paging function for incoming analog cellular communication is carried out on a CDPD channel. The handset distinguishes between paging signals identifying CDPD mode communications and paging signals identifying analog cellular communications. The handset automatically preempts CDPD communications in favor of analog cellular communications such as those carried out in an AMPS configuration.

Abstract: A power efficient and reduced electromagnetic interference (EMI) emissions transmitter for unshielded twisted pair (UTP) data communication applications. Transmit data is interpolated by N and processed by a digital filter to obtain the pulse shape required by the particular communication application. The digital filter output data is converted to a current-mode analog waveform by a digital-to-analog converter (DAC). The digital filter is integrated with the DAC binary decoder in a memory device such as a ROM with time multiplexed output. When implemented in such manner, the logical implementation and memory replaces digital filtering circuits, DAC decoding logic circuit and re-synchronization logic circuits that are conventionally implemented in hardware. Thus, the hardware functionality of these circuits is rendered into arithmetic form and implemented in a memory device.

Abstract: According to the present invention, an analog-mode discharge characteristic storage area (21a) and a digital-mode discharge characteristic storage area (21b) store threshold data of remaining battery display in an incoming-call standby status in an analog mode and that in a digital mode, respectively. A remaining battery determination means (20a) determines a remaining battery level corresponding to a selected communication mode based on both a voltage of detected by a voltage detection circuit (32) and data stored in the analog-mode discharge characteristic storage area (21a) or the digital-mode discharge characteristic storage area (21b). A remaining battery display control means (20b) causes the remaining battery to be displayed on an LCD display of a control unit (22) in accordance with a determination result of the remaining battery determination means (20a).

Abstract: An enhanced radio graphic data system comprises an FM receiver, RDS demodulator and decoder, display, microprocessor and memory. The system incorporates a protocol enhancement of RDS involving the redefinition of several bits within the B-block. An accompanying arrangement utilizes data in the C- and D-Blocks to create message streams containing the text data to be presented along with associated formatting instructions.

Abstract: A method is provided for identifying a training baud in a digital audio broadcasting signal. The method includes the steps of receiving a plurality of carrier signals modulated by a plurality of data baud, wherein the data baud include normal baud and training baud. The data baud received on the carriers are compared with predetermined data signals to produce a plurality of difference signals. The difference signals are then used to produce a plurality of distance signals, which are combined to produce group distance signals. One of the group distance signals is selected and used to determine if the data baud corresponding to the selected group distance signal is a training baud or a normal baud. This determination is performed by storing successive selected group distance signals until at least one training baud has been received, and using the stored group distance signals to determine normal/training synchronization.

Abstract: A method 1100 and apparatus 1200 utilizing unbalanced modulation for providing users in a communication system with different amounts of effective communication energy according to their individual communication environments. A user's communication energy needs are determined based on conditions such as weather, signal-to-noise ratio, and cell location. Signals destined for a user are modulated according to the determined needs of the user. A signal destined for a user operating in a relatively friendly communication environment is modulated with less effective energy than a signal destined for a user operating in a relatively hostile communication environment.

Abstract: A radio receiver is adapted to receive radio signals in at least two frequency bands, in which the radio signals are modulated by information signals. The radio receiver includes a device for down-converting a received radio signal to an intermediate frequency signal by using a local oscillator, and a demodulating device for recovering the information signals from the intermediate frequency signal. The frequency of the local oscillator is selected so that the frequencies of at least one of the frequency bands are above the frequency of the local oscillator, and the frequencies of at least one of the frequency bands are below the frequency of the local oscillator.

Abstract: A circuit is disclosed for sampling analog signals at a rate which is a rational, non-integer fraction of a clock frequency. The analog signal is sampled at non-equidistant sampling points, with the distances between successive points forming a jitter sequence. The jitter sequence is pre-calculated and stored in a memory within the circuit, reducing processing requirements in use.

Abstract: Control information is processed in synchronism with audio and video data according to a protocol such as RTP (Real-time Transfer Protocol). In one embodiment, a payload handler receives incoming data packets and forwards them to either a data control filter or an audio packet handler. The data control filter determines whether the data payload contains video data or control information and forwards video data to a video data packet handler and data control information to a data handler. The data control information can include an action identifier field (e.g., containing a “display” command) and a data object field (e.g., identifying a file location in a memory) so that the data control filter can display the identified file with the presentation of the other video and audio data.

Abstract: An apparatus for digitally processing signals within wireless communications basestations which includes a channel pooling signal processor and a digital signal processor. The channel pooling signal processor includes a plurality of computation units typically realized in a heterogeneous multiprocessing architecture, a test interface for testing the function of the plurality of the computation units, a general-purpose microprocessor for managing the dataflow into and out of the channel pooling signal processor as well as effecting the control and configuration of the computation units, and an interconnect mechanism for connecting the plurality of computation units to the input, output, test interface, and the general-purpose microprocessor.

Abstract: Various systems and methods providing high speed decoding, enhanced power reduction and clock domain partitioning for a multi-pair gigabit Ethernet transceiver are disclosed. ISI compensation is partitioned into two stages; a first stage compensates ISI components induced by characteristics of a transmitter's partial response pulse shaping filter in a demodulator, a second stage compensates ISI components induced by characteristics of a multi-pair transmission channel in a Viterbi decoder. High speed decoding is accomplished by reducing the DFE depth by providing an input signal from a multiple decision feedback equalizer to the Viterbi based on a tail value and a subset of coefficient values received from a unit depth decision-feedback equalizer. Power reduction is accomplished by adaptively truncating active taps in the NEXT, FEXT and echo cancellation filters, or by disabling decoder circuitry portions, as channel response characteristics allow.

Abstract: Current telecommunications device transmission stages require a significant number of analogue (DAC) components. The present invention provides a digital to analogue converter implementation for coupling to the digital signal processing (DSP) stage of the device and comprises a DAC and means to nullify the output of the DAC over part of the DSP data output period to produce a series of pulses corresponding to this data. The pulses are bandpass filtered to produce an analogue output signal at an intermediate frequency.

Abstract: An adaptive modulation scheme for two streams of information that have different characteristics; preferably voice and data. The voice and data are transmitted on two quadrature channels, the I and Q channels. The amount of power in the channels is adaptively varied. The voice is given all the power it needs for reliable communication over a binary phase shift keying system. The data can have higher data rates, using an M-ary amplitude modulation scheme. The data uses whatever variable amount of power is left after transmitting the voice. The data rate is changed by changing the constellation size, so that a higher bit rate is transmitted, but requiring higher power.

Abstract: The present invention provides an AM modulated wave eliminating circuit which is capable of extracting a digital modulated wave by cancelling an AM modulated wave from an AM data multiplex modulated wave.

Abstract: A radio-telephone terminal includes connection structure which connects to a radio-telephone network, a telephone handset and a data adaptation circuit arranged to be connected to a data transmission apparatus. The adaptation circuit is integrated into the terminal and can include a microprocessor arranged to manage vocal telephone communications and the data passing through the adaptation circuit.

Abstract: A method of demodulation and equalization is used to process an amplitude modulated compatible digital broadcasting signal including an amplitude modulated radio frequency signal having a first carrier modulated by an analog program signal in a first frequency spectrum, a plurality of digitally modulated carrier signals positioned within a bandwidth which encompasses the first frequency spectrum, a first group of the digitally modulated carrier signals including complementary carrier signals and lying within the first frequency spectrum, and second and third groups of the digitally modulated carrier signals including non-complementary carrier signals and lying outside of the first frequency spectrum.

Abstract: The method of quickly locating non-standard control channels in private cellular systems is accomplished in an embodiment of the present invention by determining the modulation type of a particular channel. The mobile station scans a received RF channel. The received signal is used for the evaluation of the modulation type of that channel by using matched filters designed for the specific signal of interest, and/or in another embodiment of the present invention is used for producing the spectral energy distribution of the channel revealing the type of modulation.

Abstract: An analog/digital integrated subscriber circuit includes a power supply part supplying power with respect to a subscriber line, and a signal processing part carrying out a signal processing. The power supply part is provided with a D.C./D.C. converter which controls an ON-time of a switching by detecting an output voltage and an output current supplied to the subscriber line. The D.C./D.C. converter includes a switching mechanism for switching a power supply characteristic of the power supply part to a constant current characteristic up to a maximum output voltage when supplying the power with respect to a digital subscriber line and to a constant voltage characteristic having a voltage lower than the maximum output voltage when supplying the power with respect to an analog subscriber line.

Abstract: A modem and associated method with both an RS-232 interface and a USB interface connects to a host. The modem detects which of the two interfaces is connected to the host and determines an appropriate data path. For connections to the USB interface, data is routed through a USB processor and over a serial link to the modem processor responsible for modem communications and the transfer of modem data to the POTS. The serial link between the USB processor and the modem processor is used to transfer both modem data and processor communications. A plurality of control lines are used to indicate the type of data being transferred over the serial link. For RS-232 connections, the modem data is transferred to the modem processor. Thus, one modem device may be used for either USB or RS-232 connections.

Abstract: A mobile radio communication apparatus having a communication function adaptable to both an analog mode and a digital mode is controlled by a control unit, when it receives from a radio base station a message signal representing that the digital mode is provided. When the strength of the message signal in the analog mode received by a receiving unit from the radio base station is at a predetermined level or higher, a mode of communication services is shifted into the digital mode. When the strength is lower than the predetermined level, the standby status in the analog mode is maintained. Therefore, the mode of communication services is not alternated between the analog mode and the digital mode, with the result that both an outgoing call and an incoming call can be performed successfully even in an unstable service area where a transmitted signal cannot reach the radio base station.