Abstract: A selective call receiver (105) for use in a selective call communication system (100) and a controller (206). The receiver (203) is for receiving and demodulating a digital signal which includes a predetermined sequence of A.times.N interleaved symbols representing a non-interleaved set of N tiers of symbols, each tier having A symbols, wherein A and N are positive integers. The controller (206) includes a deinterleaver (830) which reconstructs the non-interleaved set of N tiers of symbols from the demodulated signal, and a decoder (950) detects and corrects errors in the deinterleaved set of N tiers of symbols. The digital signal is transmitted simultaneously from two transmitters (103) having a difference frequency 1/P, and the symbols are transmitted at a rate of SPS symbols per second. The period of the difference frequency is given by P=(A.times.N)/SPS.

Abstract: A method and apparatus adaptively selects a communication strategy for communicating a message in a selective call radio communication system including a fixed portion (100) and a portable portion (101). The fixed portion (100) transmits (402) an alert signal to the portable portion (101), and awaits (404) an acknowledgment signal including a signal quality estimate from the portable portion (101). The portable portion (101) receives (602) the alert signal, and computes (604, 606) the signal quality estimate therefrom. The portable portion (101) then sends (608) the acknowledgment signal to the fixed portion (100). In response to the acknowledgment signal, the fixed portion (100) selects (407) a transmission strategy in accordance with the signal quality estimate. For compatibility, the transmission strategy requires a matching reception strategy in the portable portion (101).

Abstract: A dual mode communication receiver a receiver for receiving information transmitted in a first and second modulation format on a common channel, a first demodulator for detecting information transmitted in the first modulation format, and a second demodulator, responsive to the information detected in the first modulation format, for detecting information transmitted in the second modulation format. A power conservation circuit is also provided for selectively supplying power to the first and second demodulators for enabling the detecting of the information transmitted in the first modulation format and the second modulation format, respectively.

Abstract: An amplitude modulator circuit, having an input for receiving an input information signal and an output for providing an output signal, which is proportional to the input signal. The amplitude modulator circuit comprises at least two pass devices for amplifying the input information signal to produce the output signal and applying it to a load. The amplitude modulator circuit further comprises at least two voltage supplies for applying a plurality of supply voltages (at least some of which have different voltages) to the pass devices. The amplitude modulator circuit also includes a driver circuit having an input for receiving the input signal, and at least two driver outputs for driving the pass devices. The driver circuit activates the pass device having the lowest supply voltage that is sufficient to supply the required voltage to the load.

Abstract: A transmitter for transmitting digital information to a communication receiver employing a post detection low pass filter having a predetermined filter transfer function comprises a memory, a pulse recovery circuit, and a transmitter section. The memory stores an optimized electric pulse which is defined by the combination of an electric pulse exhibiting minimum intersymbol interference characteristics and the reciprocal transfer function of the predetermined post detection low pass filter transfer function of the communication receiver. The pulse recovery circuit recovers the optimized electric pulse from the memory, and generates a sequence of optimized electric pulses corresponding to the digital information to be transmitted. The digital information to be transmitted is then transmitted by the transmitter section.

Abstract: A paging terminal for transmitting address and variable length message signals to a plurality of remotely located acknowledge back and non-acknowledge back pagers, each having a unique address, includes an input for accepting variable length messages to be sent to a group of M pagers within the plurality of pagers, wherein M is an integer number. A controller orders the acknowledge back pager addresses for transmisison prior to the transmission of addresses for the non-acknowledge back pagers. A transmitter sequentially transmits the ordered addresses corresponding to the group of M pagers as an address batch during a first time period, and sequentially transmits the variable length messages for the group of pagers in a message batch including end of message markers delimiting an associated variable length message during a second time period subsequent to the first time period.

Abstract: A method is described for transmitting digital data with minimum splatter and for recovering the same with a conventional frequency modulated (FM) receiver to obtain data having minimum intersymbol interference. The method utilizes an optimized prototype pulse which has been predistorted to match the inverse characteristics of the post detection low pass filter in a conventional FM receiver. When the optimized electric pulse is received and processed by the post detection low pass filter of the conventional FM receiver, a pulse shape exhibiting minimal intersymbol interference is produced.

Abstract: A transmitter, with an inphase input for receiving an inphase baseband input signal, and a quadrature input for receiving a quadrature baseband input signal, comprises a modulator, coupled to the inphase and quadrature inputs, for modulating the inphase and quadrature baseband signals to provide a modulated radio-frequency signal and a linear amplifier, coupled to the modulator, for amplifying the modulated radio-frequency signal to produce an output signal. Oscillation detector means are coupled to receive the output signal, for detecting oscillation, and for producing an error signal as a result of the oscillation. The transmitter also comprises means for reducing the open loop gain of the feedback loop, disposed between the inphase and quadrature inputs and the modulator. The means for reducing the open loop gain reduces the open loop gain of the transmitter to less than one, in response to the error signal.

Abstract: A simulcast system is provided which includes a primary transmitting station surrounded by first and second rings of secondary or simulcast transmitting stations. Communication links are provided to link the primary transmitting station with the secondary stations. Respecting time delay circuits are provided in the links such that the secondary stations retransmit the information signal from the respective links at substantially the same time as the primary information signal from the primary transmitter arrives at the respective secondary transmitter.

Abstract: A digital correlation receiver, having one or more filters, that uses a modified correlation waveform to undo or eliminate the effects of distortion of the received signal. A distorted information signal is applied to a multiplifer for multiplication by a correlation waveform that has been modified to eliminate the distortion present in the received information signal. The product of the information signal and the correlation waveform is then integrated and a bit decision is made at the output of the integrator. The accuracy of the bit decision is enhanced by the elimination of the effects of the signal distortion.

Abstract: A divider circuit for producing a quotient result within one cycle time is provided. The invention utilizes combinational circuitry for performing a division operation by computing a scaled reciprocal of the denominator, and multiplying the scaled output by a similarly scaled numerator. The denominator is scaled such that it falls within a predetermined range, and the reciprocal value may be looked up from a memory device such as a ROM. The output of the multiplier may also be scaled in order to produce the desired result. The resulting quotient has a controlled error over a wide range of numerator and denominator input values.

Abstract: A receiver circuit recovers the phase of the carrier of a received MSK signal so that conventional synchronous detection techniques can be employed to demodulate the received signal. A quadrature receiver circuit (204-214) processes the received MSK signal to produce in-phase and quadrature phase baseband signals. These I-channel and Q-channel baseband signals are viewed as one signal which is expressed as a complex number; the I-channel forming the real part and the Q-channel forming the imaginary part. The baseband signal is multiplied (218 and 220) by odd and even orthogonal functions (222 and 224) and then integrated (226 and 227) over odd and even numbered two bit periods, respectively. The odd orthogonal function begins and ends on odd numbered two bit periods of the received MSK signal, while the even orthogonal function begins and ends on even numbered two bit periods. The result of the integration is a single complex number for each bit of the received signal.

Abstract: A gain/phase compensation method and apparatus for a linear amplifier feedback loop in a transmitter (100). The transmitter (100) includes an input (102 or 110), alinear amplifier (143), and a modulator (142), to provide a modulator carrier-frequency output signal. The transmitter also comprises a feedback detector (154), coupled to receive the output signal and also coupled to the input. The feedback detector (120) produces a detected baseband feedback signal and applies the feedback signal to the input. The transmitter (100) of the present invention further comprises stabilizing means (118 and 130), coupled to the input (102 or 110) and to the linear amplifier (143), for reducing the open-loop gain of the linear amplifier (143) to a value lower than one for all frequencies where the feedback loop causes the phase of the baseband input signal to shift by more than 180 degrees.

Abstract: A method of demodulating a quadrature modulated signal includes first receiving the signal. The rf signal is then quadrature demodulated to produce in-phase and quadrature signals. One of these signals is filtered to produce a correction signal which is used for phase and amplitude correction. Both of the demodulated signals are again quadrature demodulated to produce the output signals. The second demodulation can be accomplished utilizing a correlation decoder. The applied correlation pulse includes a subcarrier component.

Abstract: A quadrature amplitude modulation system utilizes two subcarrier signals, each quadrature modulated with information signals which are quadrature modulated onto the RF carrier. This provides a hole in the center of frequency spectrum, permitting carrier and bit sync signals can be provided in the center area of the signal spectrum.

Abstract: A method and apparatus are provided for generating a uniquely shaped prototype digital pulse which is transmitted with minimal frequency spectrum consumption and yet a relatively high bit rate. Such uniquely shaped digital pulse is stored in a memory included in a transmitter until transmission is desired, at which time a positive of the pulse is transmitted to correspond to a first logic level or the negative of the pulse is transmitted to correspond to a second logic level.

Abstract: A processing circuit for efficiently amplifying radio frequency signals while generating minimal splatter includes a first channel having an envelope detector for generating a rectified envelope signal from a modulated radio frequency input signal provided thereto. The first channel includes a peak clipping circuit which clips portions of the rectified envelope signal having an instantaneous voltage less than a first selected threshold level. A second channel includes a symmetric clipping circuit for symmetrically clipping portions of the modulated radio frequency input signal which exceed a second voltage threshold level.

Abstract: A compatible AM stereo system including a modified quadrature modulation scheme. Two stereo modulators are described which each generate composite modulated signals including a carrier component and two phase-shifted components. The two phase-shifted components, corresponding to the left (L) and right (R) source signals, are phase shifted by equal phase angles .theta. on either side of the carrier, where .theta. is between 10.degree. and 20.degree.. A limiter is included which operates to limit the magnitude of the source signals supplied by the stereo modulator. The limiter allows each source signal to contribute up to 80% of the total modulation, as long as total modulation constraints are not exceeded due to the combined amplitudes of the two source signals. A receiver is described for demodulating the composite modulated signal.

Abstract: Radio receiver systems for recovering stereo program signals from a composite stereo signal which has been modulated with either quandrature modulation or modified quadrature modulation techniques. In one embodiment, a receiver is provided which directly recovers the program signals from the composite signal by means of product detectors, without first converting the composite signal into an IF signal. In another embodiment an IF stage is provided, but is designed to have broad bandpass characteristics. This embodiment additionally includes a phase locked loop for forcing the IF frequency into the center of the IF passband. In either case, the stereo demodulation is accomplished by product detectors which multiply the composite signal by phase reference signals. Several methods of synthesizing stable phase reference signals are shown.