Method and apparatus for sub sample-per-symbol demodulator for a spectrally efficient waveform with an lpi feature
AssigneeHarris Corporation
InventorsEdward Beadle, John Dishman
Life of this patent
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Abstract
An apparatus and method for transmitting and receiving a communication signal includes selecting a pulse shape for a continuous phase modulated waveform, encoding specific information into the waveform to form a communication signal and transmitting the communication signal. The system receives the transmitted communication signal and samples the received signal at a specified rate, the sample rate being less than the symbol rate, enabling reconstructing the waveform and extracting encoded information at sub sample per symbol rates, thereby reducing the reliance on high speed wideband analog to digital converters (ADC) for high speed applications.
Claims50
An apparatus for processing a communication signal comprising a continuous phase modulated waveform containing information symbols of an M-ary alphabet comprising:
- an analog to digital converter;
- an interpolator for reconstructing the waveform;
- and,
- a demodulator for extracting the information symbols from the reconstructed waveform;
- wherein the ADC operates at a sample frequency at or less than the symbol rate of the communication signal.
(canceled)
(canceled)
A method for communicating information symbols with spectral efficiency comprising the steps of:
- selecting a pulse shape for a partial response continuous phase modulated waveform;
- encoding the information into the waveform to form a communication signal;
- transmitting the communication signal;
- receiving the communication signal;
- sampling the communication signal at a frequency less than the symbol rate to obtain signal samples;
- reconstructing the waveform from the signal samples;
- and,
- extracting the information encoded into the waveform.
In a method for demodulating a PRCPM waveform, containing information symbols, at a symbol rate n, wherein the waveform is converted from analog to digital in an ADC, the improvement comprising the step of sampling the waveform at a rate less than or equal to the symbol rate n.
20-22. (canceled)
(canceled)
A communication system for transmitting and receiving information symbols via a PRCPM waveform at a high symbol rate, the improvement wherein the PRCPM is:
- s
-
- (
- t
- )
- =
- 2
-
-
- E
- s
- T
- s
-
- cos
-
-
- (
- 2
-
-
- π
-
-
- f
- o
-
- t
- +
- Φ
-
-
- (
- t
- ,
- α
- )
- +
- ϕ
- 0
- )
- where Φ(t,α) is a continuous function, expressed as:
- Φ
-
-
- (
- t
- ,
- α
- )
- =
- 2
-
-
- π
-
-
- h
-
- ∑
- k
- =
- -
- ∞
- ∞
-
- α
- k
-
- q
-
- (
- t
- -
- k
-
-
- T
- s
- )
- where h is the modulation index, q(t) is the phase pulse shape and αk are the information symbols. Ts is the symbol rate.
A method of secure communication between a transmitter and a target receiver, in an environment of extraneous receivers comprising the steps of:
- encoding information symbols in a PRCPM waveform;
- transmitting, from the transmitter, the waveform at a symbol rate greater than the maximum sample rate of the extraneous receivers;
- receiving the waveform at the target receiver;
- sampling the waveform to obtain signal samples;
- and,
- reconstructing the waveform from the signal samples.
In a point to multipoint communication system comprising a base station and at least one remote station, a method of transmitting a communication signal having a waveform with information symbols from the base station to the at least one remote stations comprising the steps of:
- providing to the base station the maximum conversion rate and spectrum limitation of one or more of the at least one remote stations;
- selecting, at the base station, phase pulse shape parameters for the waveform based on the maximum conversion rate and spectrum limitations of the one or more remote stations;
- and,
- transmitting the communication signal with a symbol rate greater than the maximum conversion rate to the one or more of the at least one remote stations with the selected pulse shape parameter.
A method for communicating, from a transmitter to a receiver, a communication signal with a low probability of intercept by an unintended receiver, comprising the steps of:
- providing at the transmitter:
- an information bit stream, and
- a partial response continuous phase modulation (“PRCPM”) waveform;
- encoding the information bit stream into the PRCPM waveform to thereby form a communication signal with a low probability of intercept by the unintended receiver;
- and
- transmitting the communication signal to the receiver.
In a method for transmitting a communication signal comprising an information bit stream from a transmitter to a receiver in an environment with unintended receivers wherein the communication signal is transmitted using chip rate dithering or fast frequency hopping so as to have a low probability of intercept by at least one of the unintended receivers, the improvement comprising the steps of encoding the information bit stream into a partial response continuous phase modulation (“PRCPM”) waveform to thereby form a communication signal with a low probability of intercept by at least one of the unintended receivers and transmitting the communication signal without chip rate dithering or fast frequency hopping.
A system for communicating, from a transmitter to a receiver, a communication signal with a low probability of intercept by an unintended receiver, comprising:
- at the transmitter:
- means for providing an information bit stream, and
- means for providing a partial response continuous phase modulation (“PRCPM”) waveform;
- means for encoding the information bit stream into the PRCPM waveform to thereby form a communication signal with a low probability of intercept by an unintended receiver;
- and
- means for transmitting the communication signal to the receiver.
In a method for transmitting a communication signal comprising an information bit stream from a transmitter to a receiver in an environment with unintended receivers wherein the communication signal is transmitted using chip rate dithering or fast frequency hopping so as to have a low probability of intercept by at least one of the unintended receivers, the improvement comprising the steps of encoding the information bit stream into a waveform with partial response signaling to thereby form a communication signal with intersymbol interference and transmitting the communication signal without chip rate dithering or fast frequency hopping.
Dependencies are inferred from the claim text.