Abstract: Methods and apparatus for detecting the presence of a particular signal among all the channels of interest in a cellular or similar type system are disclosed. A first method detects CDPD signals, and a second method detects DQPSK signals used in digital control channels in accordance with the IS-136 standard. These methods include the steps of sampling a received signal in at least one channel to obtain a predetermined number of samples for the at least one channel; computing an error value for each sample; determining a minimum error value; determining a ratio of the minimum error value to a reference value; and making a decision as to whether the received signal is the prescribed signal on the basis of at least the ratio, wherein the decision is made by comparing the ratio to a threshold value.

Abstract: The present invention provides a frequency tracking and compensation system and methods for minimizing the frequency offset between remote and local units of a communications system. The system of the present invention resides in the local unit and comprises a downconverter, a digital transceiver, a processor, a reference oscillator and a frequency synthesizer. The downconverter mixes a signal received from the remote unit with a local oscillator (LO) signal generated by the frequency synthesizer. The frequency of the LO signal is based on the frequency of a reference signal generated by the reference oscillator. The system of the present invention utilizes the digital transceiver to determine a frequency offset of the received signal without comparing the received signal to the reference signal. The processor then utilizes the frequency offset to adjust the frequency of the reference signal.

Abstract: A unique word detector for use in detecting a unique word received by a demodulator in one of a plurality of windows offset in time is provided. The unique word detector includes a correlator for receiving successive sequences of binary data related to one of the windows. The correlator compares each of the successive sequences with the unique word to generate a measure of correlation between the sequences of binary data and the unique word. The unique word detector also includes a window detector interfaced with the correlator for comparing each of the measures of correlation to a predetermined threshold to determine whether the unique word has been received. A method of detecting the unique word in one of the windows is also provided.

Abstract: A programmable digital modulator and methods of modulating digital data for transmission by a communication system according to operating parameters selected for various applications are provided. A two-chip system is utilized by a preferred embodiment of the invention. One chip comprises a PROM for storing impulse response data which would result from filtering the data to be transmitted. The second chip comprises a data interface for accepting input data, an address generator for generating an address of the PROM where the impulse response data is stored which corresponds to the data input to the chip and for causing the PROM to output the impulse response data stored at the address generated, and a data modulator for modulating a carrier signal with the impulse response data provided by the PROM.