Abstract: A method is disclosed for performing a discrete cosine transform on a transform input value wherein the discrete cosine transform has a plurality of predetermined transform coefficients. A number N.sub.1 of shift operations is determined independently of the transform input value in order to provide a set of N.sub.1 of shift operations. A number N.sub.2 of add operations is determined independently of the transform input value in order to provide a set of N.sub.2 add operations. The transform input value is operated upon only by the N.sub.1 shift operations and the N.sub.2 add operations to provide a discrete cosine transform output value without any multiplication. This method may be applied to both forward and inverse discrete cosine transforms. The transform coefficients are simplified coefficients which are provided by truncating and modifying prior art transform coefficients.

Abstract: An improved method of doppler searching in a digital GPS receiver is described. According to the principles of the present invention, an N-point fourier transform is performed on samples of a down converted GPS signal representing the entire range of Doppler-shifted GPS carrier frequencies. The magnitude of the square of each of the output samples is calculated to produce N power quantities, corresponding to N search frequencies. The power quantities for each of the N search frequencies are then summed to produce N quantities proportional to average power. The maximum of the N-power quantities indicates the presence of the corresponding GPS signal.

Abstract: A digital FM demodulator is described. According to the principles of the present invention, a digital FM signal is demodulated by processing sampled input vectors of a quadrature FM digital signal centered approximately zero frequency. The sampled quadrature input vectors are quantized to lie within a predetermined magnitude range. The quantized vectors are coupled to a phase accumulator which generates a current coarse phase value related to input vectors of the quadrature FM signal. The output of the phase accumulator is also coupled to a vector rotation means which rotates the input vector to a predetermined quadrant to determine a fine phase value based on said rotated input signal vector. The fine and coarse values are then summed and output as a composite phase value, and digitally filtered by subtracting the value of the previous composite phase angle sample from the value of the current composite phase angle sample to produce a demodulated message sample.

Abstract: A dispatch trunked radio system which provides duplex or simplex telephone interconnect communications to subscriber units is described. The system allows duplex capable trunked system subscriber units to establish a full duplex communication link with conventional land based telephone interconnect service in accordance with a method which unifies the operation of the trunked system subscriber units, a plurality of trunked system repeaters, a trunked system central control unit, and a telephone interconnect control unit. The method of the present invention also provides improved trunked system performance by allowing simultaneous transmission and reception of channel controlling information.

Abstract: A method and means for improving the frequency resolution in a digital oscillator is described. According to the principles of the present invention, a digital oscillator may be comprised of a frequency latch, a phase accumulator, and a ROM based waveform generator. Improved frequency resolution is achieved in the digital oscillator, without increasing ROM size by quantizing the summed output of a dither generator and the phase accumulator before sending the resultant multi-bit signal to a ROM. The contents of the ROM are sequentially addressed with the resultant multi-bit signal. The output of the ROMs comprise digital words corresponding to a desired waveform envelope.

Abstract: A method and means for quadrature amplitude modulation is described. The improved QAM modulator circuit utilizes a small read only memory to hold multiple versions of a signal constellation resulting in the elimination of hardware modulator circuits. In addition, the described device can be potentially any modulation scheme on an input signal which is sampled in time by modifying the contents of said ROM.

Abstract: A system and method for use in a network of the type including a bus which carries a plurality of digital, multiple bit time divided channels of information including audio information provides for the decoding of digital audio within one of the channels to analog audio signals, the coding of analog audio to digital audio and the placing of the digital audio onto the bus within one of the channels, and the generation of internal or localized analog tones in an improved and efficient manner. A decoding means is provided for converting a digital multiple bit word to analog form. A control means which includes tone generating means adapted for providing digital multiple bit tone words controls a select means which selectively couples the decoding means to the bus to enable decoding of the digital audio or to the tone generating means for providing the analog tones in response to digital data received from the bus within a preselected channel.

Abstract: A system for radio-telephone communication between a user at a remote location and the commercial telephone system or between two users at remote locations comprises a fixed terminal that is connected by wire lines or the like to the commercial telephone system and a plurality of portable radio units. The terminal is equipped for duplex operation on a plurality of channels, each of which uses separate frequency bands for transmitting and receiving. Each of the portable units is a simplex transceiver adapted to receive on each of the frequencies of transmission from the terminal and to broadcast on each of the frequencies received by the terminal. The terminal places a channel acquisition tone on an unused channel that is the next to be used. The terminal calls portable unit by shifting channel acquisition tone to another channel and broadcasting an identifier to the portable unit.

Abstract: A hybrid filter comprising a plurality of removably mountable resonator modules, each constructed of nmicrostrip, and mounted parallel to each other and perpendicular to the substrate so as to isolate the resonators for single mode operation; the inter-resonator coupling is provided by adjustable capacitor coupling gaps on the host substrate.