Digital modulation method with controlled envelope variation
Patent 5633893 Issued on May 27, 1997. Estimated Expiration Date: 
September 29, 2014. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
September 29, 2014. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent References 3747024 Minimum shift keying communication system Correlated signal processor Waveform shaping apparatus Digital data modulator and digital-to-analog converter Method for transmitting digital data by means of continuous phase modulation Digital premodulation filter Modem for RF subscriber telephone system Digitally implemented modulators Phase accumulation continuous phase modulator InventorsApplicationNo. 313599 filed on 09/29/1994US Classes:375/297, Power amplifier332/100, FREQUENCY SHIFT KEYING MODULATOR OR MINIMUM SHIFT KEYING MODULATOR332/124, Nonlinearity reduction or compensation375/272, Frequency shift keying375/275, More than two frequencies375/278, Antinoise or distortion375/303, Frequency shift keying375/340, Particular pulse demodulator or detector375/348, Intersymbol interference455/44, With stated modulation index455/110, Angle modulation708/319TransversalExaminersPrimary: Chin, StephenAssistant: Le, Amanda T. Attorney, Agent or FirmInternational ClassH04K 001/02AbstractContinuous phase modulated (CPM) signals, such as quaternary CPFSK signals, are filtered to limit their bandwidth while simultaneously minimizing the amount of amplitude modulation and intersymbol interference introduced by this filtering process. By designing a modulation filter such as a finite impulse response (FIR) filter to add only a nominal, controlled amount of amplitude modulation, high efficiency, nonlinear power amplifiers may be employed to transmit the filtered CPFSK signals. Although the filter adds a small amount of amplitude modulation and intersymbol interference, digital signal processor-based receivers satisfactorily demodulate this type of signal using sequence estimation algorithms such as the Viterbi algorithm. Thus, the filtering of CPM signals permits narrowing of the transmitted signal spectrum while managing the intersymbol interference resulting from the controlled amount of amplitude modulation added by filtering. Narrowed bandwidth along with high efficiency, nonlinear power amplifiers make the present invention particularly well suited to narrowband mobile radio communications.Other References
Field of SearchMaximum likelihood decoder or viterbi decoderAngle modulation Frequency shift keying Combined with phase shift keying More than two frequencies Antinoise or distortion Antinoise or distortion Antinoise or distortion (includes predistortion) Power amplifier Quadrature amplitude modulation Angle modulation Frequency shift keying Angle modulation Frequency shift keying Particular pulse demodulator or detector Maximum likelihood decoder or viterbi decoder Intersymbol interference Plural signal paths in receiver By filtering (e.g., digital) FREQUENCY SHIFT KEYING MODULATOR OR MINIMUM SHIFT KEYING MODULATOR PHASE SHIFT KEYING MODULATOR OR QUADRATURE AMPLITUDE MODULATOR FREQUENCY MODULATOR Including amplitude modulation Including stabilization or alternatively distortion, noise or other interference prevention, reduction, or compensation Nonlinearity reduction or compensation PHASE MODULATOR Percent modulation control or automatic amplitude control of carrier or modulating signal MODULATION CONVERTER HAVING PRE-MODULATED INPUT (E.G., FM TO AM) Frequency or phase modulation With modification of frequencies of analog signal passed (e.g., pre-emphasis and de-emphasis) With stated modulation index Angle modulation | |
