Abstract: A method and apparatus for digitally phase modulating and frequency upconverting communication signals to an intermediate frequency, producing the IF output with only digital hardware and without the use of digital to analog converters, analog multipliers (mixers) or power combiners. A digital phase modulator provides an in-phase and a quadrature output, each of which is coupled to one input of a relatively simple multi-bit to single-bit delta-sigma data converter. The output from the converter is a pair of single-bit digital output signals. Each such single-bit output is inverted and both the inverted single-bit output and the non-inverted single-bit output of both the in-phase and the quadrature outputs are coupled to a 4:1 multiplexer. One of these four inputs is then selected by a modulo-4 counter. The modulo-4 counter is incremented at a rate that is selected based upon the desired IF frequency.

Abstract: A cellular digital packet data (CDPD) system includes a mobile data base station (MDBS) configured to interface easily with an advanced mobile phone system (AMPS). The elements of the MDBS are arranged on modules and the functionality of the MDBS is divided among the modules to facilitate flexibility, compactness and quick expansion of the MDBS. To further facilitate compactness, the MDBS includes a transceiver/modem board which uses a single chip to carry out delta-sigma modulation. In order to maintain the integrity of CDPD transmission, a channel hopping scheme is used based upon avoidance of AMPS channel use. A distinctive protocol is used to encapsulate control/query/response data for transmission throughout the CDPD system. This protocol also facilitates easy control of each MDBS throughout the system.

Abstract: A cellular digital packet data (CDPD) system includes a mobile data base station (MDBS) configured to interface easily with an advanced mobile phone system (AMPS). The elements of the MDBS are arranged on modules and the functionality of the MDBS is divided among the modules to facilitate flexibility, compactness and quick expansion of the MDBS. To further facilitate compactness, the MDBS includes a transceiver/modem board which uses a single chip to carry out delta-sigma modulation. In order to maintain the integrity of CDPD transmission, a channel hopping scheme is used based upon avoidance of AMPS channel use. A distinctive protocol is used to encapsulate control/query/response data for transmission throughout the CDPD system. This protocol also facilitates easy control of each MDBS throughout the system.

Abstract: Selectable demodulation means within a given receiver to demodulate signals potentially subjected to many different types of degradations as typically encountered in mobile communications systems, and to select the best result of provide significant performance improvement is disclosed. In accordance with the method, when an RF signal is received it is sampled and the samples are demodulated. Demodulation is performed using both coherent and non-coherent schemes with the preferred scheme selected according to the quality of performance of each demodulator. Coherent demodulation can provide better performance when the signal is subjected to significant path loss but little fading. Non-coherent demodulation can provide better performance when the signal is subjected to less path loss but significant fading. Details of the method are disclosed.

Abstract: Digital methods and apparatus for reverse link signal detection and recovery in a mobile data base station. In accordance with the method, the received signal is frequency downshifted by multiplying the received signal by inphase and quadrature components of a local carrier oscillator, and the resulting downshifted inphase and quadrature components of the signal vector is sampled and digitized at a rate of more than twice the expected bit rate. Difference vectors for digitized downshifted signal vectors one expected bit time apart are determined and examined for detection of a dotting sequence and for estimation of the carrier frequency error, which on detection of the dotting sequence, is used to initially correct the digitized downshifted signal vectors for the frequency error. Techniques for bit timing recovery, frequency error correction during data detection and detection of voice versus data, as well as other features of the invention, are disclosed.

Abstract: Open loop phase estimation methods and apparatus for coherent combining of signals on mobile channels using spatially diverse antennas are disclosed. In accordance with the method, the signals from each of two antennas are demodulated using inphase and quadrature components of a local carrier oscillator to provide RF demodulated inphase and quadrature components of the output of each antenna. These components are simultaneously sampled at a sample rate and digitized to provide the digitized components of the two signal vectors. A phase estimator vector having a phase equal to the difference in phase between the two signal vectors of each successive sample time is determined. An average phase estimator vector for a group of successive signal vectors is determined, and is used as the estimated phase difference between the signal vectors at the middle of the group of successive signal vectors to align the respective signal vectors prior to the same being combined into a single signal vector.

Abstract: Open-loop phase estimation methods and apparatus for coherent demodulation on mobile channels is disclosed. A PSK RF modulated signal is received, RF demodulated to obtain inphase and quadrature components thereof, and the inphase and quadrature components sampled and digitized periodically to provide inphase and quadrature components of the signal vector. A phase estimator strips the data contribution from each vector, leaving only a phase error measurement related to the true phase error. That phase error indication is averaged over a fixed window of time to determine an average phase estimate applicable to the signal vector at the middle of the window. Resulting one hundred eighty degree ambiguities are resolved, and then the applicable signal vector is phase corrected by the average phase estimate and result of the ambiguity resolution, with the following demodulation being responsive to the phase of the phase corrected signal vector.

Abstract: A phase-locked loop frequency modulation circuit that compensates for the inability of a phase-locked loop to pass low-frequency content of an input modulation signal, and that may be utilized with existing communication apparatus, such as a cellular telephone voice radio, for accurate data transmission without having to modify such apparatus, includes a compensation circuit for processing an input modulation signal to provide a compensation signal that is added to a loop filter output signal by processing the input modulation signal to provide the same effect as adding the input modulation signal to an integrated input modulation signal that is filtered by a filter having the same transfer function as the loop filter to provide the compensation signal.

Abstract: A decoding system capable of outputting Viterbi-decoding-algorithm-decoded data at a predetermined rate that is greater than a given rate at which coded data is processed in accordance with said algorithm to produce the decoded data. The system includes a data input bus; a data output bus; a ring of decoders, with each decoder being coupled to the input bus for receiving coded data from the input bus and coupled to the output bus for providing decoded data onto the output bus. Each of the decoders in the ring includes an input buffer, timing controller, decoding processor and output buffer. The input buffer responds to a start-input signal from a preceding decoder in the ring by buffering a block of the received coded data. The timing contoller provides a start-input signal to a succeeding decoder in the ring at such time as to cause the succeeding decoder to receive a block of coded data from the input bus that overlaps the block of coded data received from the input bus by the instant said decoder.