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US 5,523,726 AGranted
Digital quadriphase-shift keying modulator
AssigneeWestinghouse Electric Corp.
InventorsBrian W. Kroeger, Roy Stehlik
Life of this patent
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Abstract
A digital quadriphase-shift keying modulator is described which generates a modulated intermediate carrier frequency (IF) based on a desired number of samples for each input information bit. The design includes a ROM (or RAM) look-up table which stores digitized waveforms. The inphase and quadrature components of a complex baseband signal are translated to an IF at a multiple of the sampling rate simply by alternating the inphase and quadrature samples and alternating signs. The real IF output is produced by summing the inphase and quadrature signals.
Claims30
A method of modulating binary data sequences, each having a plurality of symbols occurring at a symbol frequency, to an intermediate carrier frequency, and a ROM having a plurality of stored digital waveforms including a plurality of digitized samples and corresponding to one of a plurality of outputs of a filter in response to a plurality of combinations of symbol inputs having a predetermined span of symbols, said method comprising the steps of:
- inputting, in parallel, first and second data sequences at the symbol frequency;
- multiplexing an M number of symbols from each sequence at a sample frequency, the sample frequency being the intermediate carrier frequency divided by four to produce a multiplexed train of successive groups of the M number of symbols, in parallel, from first and second data sequences;
- inverting every other pair of successive groups of the multiplexed train to form successive first portions of an address from successive inverted and non-inverted groups of the multiplexed train;
- forming successive second portions of the address in accordance with a position of one of the groups in the inverted and non-inverted groups of the multiplexed train;
- outputting from the ROM contents of a storage location corresponding a combination of the first and second portions of the address, so that for each parallel input from the first and second data sequences, a number of digital samples, corresponding to the sample frequency, are read out from the ROM at the intermediate carrier frequency;
- and
- converting the ROM outputs to an analog signal at the intermediate carrier frequency.
4 more elements
A modulator for modulating data sequences, each having a plurality of symbols occurring at a symbol frequency, to a carrier frequency, and a ROM having a plurality of stored digital waveforms including a plurality of digitized samples and corresponding to one of a plurality of outputs of a filter in response to a plurality of combinations of symbol inputs having a predetermined span of symbols, said digital modulator comprising:
- serial to parallel input means for serially inputting, in parallel, first and second data sequences at the symbol frequency and outputting, in parallel, an M number of symbols from both trains;
- a multiplexer for multiplexing the M number of symbols from each data sequence at a sample frequency, the sample frequency being an intermediate carrier frequency divided by four to produce a multiplexed train of successive groups of the M number of symbols, in parallel, from first and second data sequences;
- an inverter for inverting every other pair of successive groups of the multiplexed train to form successive first portions of an address from successive inverted and non-inverted groups of the multiplexed train;
- counting means for determining a position of one of the groups in the inverted and non-inverted groups of the multiplexed train corresponding to the first portion of the address;
- address forming means forming successive second portions of the address from the position of the one of the groups in the inverted and non-inverted groups of the multiplexed train corresponding to the first portion of the address;
- a ROM for outputting contents of a storage location corresponding to a combination of the first and second portions of the address, so that for each parallel input from the first and second data sequences, a number of digital samples, corresponding to the sample frequency, are read out from the ROM at the intermediate carrier frequency;
- a digital-to-analog converter for converting the ROM outputs to an analog signal at the intermediate carrier frequency;
- and
- an up-converter for converting the analog signal to a carrier frequency.
6 more elements
A digital quadriphase-shift keying modulator, comprising:
- a counter responsive to a clock signal for outputting successive pluralities of bits which represent successive values of the counter;
- a first serial-to-parallel converter for receiving a plurality of first symbols in serial fashion and outputting a predetermined number of the plurality of first symbols in parallel fashion in response to a first bit of one of the successive pluralities of bits output by the counter;
- a second serial-to-parallel converter for receiving a plurality of second symbols in serial fashion and outputting a predetermined number of the plurality of second symbols in parallel fashion in response to the first bit of the successive pluralities of bits output by the counter;
- a multiplexer for selecting between the output of the first serial-to-parallel converter and the output of the second serial-to-parallel converter in response to a second bit of the successive pluralities of bits output by the counter;
- sign changing means for changing a sign of the output selected by the selecting means in response to a third bit of the successive pluralities of bits output by the counter;
- and
- a memory for storing a plurality of digital samples of a waveform and outputting one of the plurality of digital samples in response to an address, wherein the address includes the output of the counter and the output of the multiplexer.
4 more elements
A method for communicating with a satellite comprising the steps of:
- receiving first signals from the satellite in the form of first modulated signals;
- demodulating the first modulated signals to produce first demodulated signals;
- outputting the first demodulated signals;
- generating first and second data sequences, each having a plurality of symbols occurring at a symbol frequency to be transmitted;
- modulating the first and second data sequences for transmission to a carrier frequency, utilizing a ROM having a plurality of stored digital waveforms including a plurality of digitized samples and corresponding to one of a plurality of outputs of a filter in response to a plurality of combinations of symbol inputs having a predetermined span of symbols, said modulating comprising the substeps of:
- inputting, in parallel, first and second data sequences at the symbol frequency;
- multiplexing an M number of symbols from each train at a sample frequency, the sample frequency being an intermediate carrier frequency divided by four to produce a multiplexed train of successive groups of the M number of symbols, in parallel, from first and second data sequences;
- inverting every other pair of successive groups of the multiplexed train to form successive first portions of an address from successive inverted and non-inverted groups of the multiplexed train;
- forming successive second portions of the address in accordance with a position of one of the groups in the inverted and non-inverted groups of the multiplexed train;
- outputting from the ROM contents of a storage location corresponding a combination of the first and second portions of the address, so that for each parallel input from the first and second data sequences, a number of digital samples, corresponding to the sample frequency, are read out from the ROM at the intermediate carrier frequency;
- and
- converting the ROM outputs to an analog signal at the intermediate carrier frequency;
- up-converting the analog signal to the carrier frequency;
- and
- transmitting the up-converted signal to the satellite.
12 more elements
A mobile terminal unit for receiving from, and transmitting to, a satellite comprising;
- receiving means for receiving signals from the satellite;
- demodulating means for demodulating the received signals;
- modulating means for modulating first and second data sequences, each data sequence having a plurality of symbols occurring at a symbol frequency, to an intermediate carrier frequency, said modulating means comprising:
- a ROM having a plurality of stored digital waveforms including a plurality of digitized samples and corresponding to one of a plurality of outputs of a filter in response to a plurality of combinations of symbol inputs having a predetermined span of symbols;
- serial to parallel input means for serially inputting, in parallel, first and second data sequences at the symbol frequency and outputting, in parallel, an M number of symbols from both trains;
- a multiplexer for multiplexing the M number of symbols from each train at a sample frequency, the sample frequency being the intermediate carrier frequency divided by four to produce a multiplexed train of successive groups of the M number of symbols, in parallel, from first and second data sequences;
- an inverter for inverting every other pair of successive groups of the multiplexed train to form successive first portions of an address from successive inverted and non-inverted groups of the multiplexed train;
- counting means for determining a position of one of the groups in the inverted and non-inverted groups of the multiplexed train corresponding to the first portion of the address;
- address forming means forming successive second portions of the address from the position of the one of the groups in the inverted and non-inverted groups of the multiplexed train corresponding to the first portion of the address;
- a ROM for outputting contents of a storage location corresponding to a combination of the first and second portions of the address, so that for each parallel input from the first and second data sequences, a number of digital samples, corresponding to the sample frequency, are read out from the ROM at the intermediate carrier frequency;
- and
- a digital-to-analog converter for converting the ROM outputs to an analog signal at the intermediate carrier frequency;
- and
- an up-converter for converting the modulated first and second pulse trains to a carrier frequency.
11 more elements
Dependencies are inferred from the claim text.