US2007177689A1PendingUtilityA1
Method and apparatus for sub sample-per-symbol demodulator for a spectrally efficient waveform with an lpi feature
Est. expiryMar 17, 2023(expired)· nominal 20-yr term from priority
H04L 27/2003H04L 25/03834
51
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Claims
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.
Claims
exact text as granted — not AI-modified1 . 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.
2 . The apparatus according to claim 1 , wherein the information symbols are binary.
3 . (canceled)
4 . The apparatus according to claim 1 , wherein the peak-to-average power ratio of the waveform is unity.
5 . The apparatus according to claim 1 , wherein the waveform is a constant envelope waveform.
6 . (canceled)
7 . 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.
8 . The method according to claim 7 , wherein the waveform is defined by:
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 α k are the information symbols. T s is the symbol rate.
9 . The method according to claim 7 , wherein the communications signal is reconstructed by Trellis decoding of accumulating excess phase Φ(t,α).
10 . The method according to claim 7 , wherein the information symbols are M-ary alphabet symbols.
11 . The method according to claim 7 , wherein the information symbols are binary.
12 . The method according to claim 7 , wherein the step of selecting is based on maximum sampling rate and spectral limitations of a receiver.
13 . The method according to claim 7 , wherein the peak-to-average ratio of the waveform is unity.
14 . The method according to claim 7 , wherein the waveform is a constant envelope waveform.
15 . The method according to claim 8 , where the phase pulse shape is
q
(
t
)
=
∫
-
∞
t
g
(
τ
)
ⅆ
τ
and
g
(
τ
)
is selected from the group of: LRC, TRM, LSRC, GMSK, LREC, and Gaussian pulse shapes.
16 . The method according to claim 7 , wherein the symbol rate is greater than 2*B symbols/sec, where B is bandwidth.
17 . 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.
18 . The method according to claim 17 , comprising the step of reconstructing the waveform from the samples.
19 . The method according to claim 18 , wherein the waveform is reconstructed by interpolation.
20 - 22 . (canceled)
23 . The method according to claim 17 , wherein the peak-to-average ratio of the waveform is unity.
24 . The method according to claim 17 , where in the waveform is a constant envelope waveform.
25 . (canceled)
26 . 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 α k are the information symbols. T s is the symbol rate.
27 . The communication system of claim 26 , wherein the information symbols are M-ary alphabet symbols.
28 . The communication system of claim 26 , wherein the phase pulse shape is
q
(
t
)
=
∫
-
∞
t
g
(
τ
)
ⅆ
τ
and
g
(
τ
)
is selected from the group of: LRC, TRM, LSRC, GMSK, LREC, and Gaussian pulse shapes.
29 . The communication system according to claim 26 , wherein the high symbol rate is greater than 2*B symbols/sec, where B is bandwidth.
30 . 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.
31 . 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.
32 . The method according to claim 31 , further comprising the steps of:
receiving the communication signal at the one of the at least one remote stations; sampling the communication signal at the maximum conversion rate to obtain signal samples; reconstructing the waveform from the signal samples to obtain a reconstructed waveform; and, demodulating the reconstructed waveform to extract the information symbols.
33 . The method according to claim 31 , wherein the information symbols are M-ary alphabet symbols.
34 . The method according to claim 33 , wherein the information symbols are binary.
35 . The method according to claim 31 , wherein the waveform is a partial response continuous phase modulated waveform defined by:
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 α k are the information symbols. T s is the symbol rate.
36 . The method according to claim 35 , where h limits the spectrum.
37 . The method according to claim 31 , comprising the steps of:
informing the base station the maximum conversion rate and spectrum limitation of the others of the at least one remote stations; selecting the minimum conversion rates from the maximum conversion rates of the at least one remote stations as the maximum conversion rate; selecting the narrowest spectrum limitation of the spectrum limitations of the at least one spectrum limitation as the spectrum limitation on which to base phase pulse shape selection; and, transmitting the communication signal with the selected pulse shape parameters to each of the at least one remote stations.
38 . The method according to claim 35 , wherein the phase pulse shape is
q
(
t
)
=
∫
-
∞
t
g
(
τ
)
ⅆ
τ
and
g
(
τ
)
is selected from the group of: LRC, TRM, LSRC, GMSK, LREC, and Gaussian pulse shapes.
39 . The method according to claim 31 , wherein the symbol rate is greater than 2*B symbols/sec, where B is bandwidth.
40 . 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.
41 . The method of claim 40 wherein the PRCPM waveform has a low modulation index.
42 . The method of claim 40 wherein the PRCPM waveform has a low bandwidth-time product.
43 . The method of claim 40 wherein the PRCPM waveform has a low modulation index and a low bandwidth-time product.
44 . 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.
45 . The method of claim 44 wherein the PRCPM waveform has a low modulation index.
46 . The method of claim 44 wherein the PRCPM waveform has a low bandwidth-time product.
47 . The method of claim 44 wherein the PRCPM waveform has a low modulation index and a low bandwidth-time product.
48 . 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.
49 . The system of claim 48 wherein said PRCPM waveform has a low modulation index.
50 . The system of claim 48 wherein said PRCPM waveform has a low bandwidth-time-product.
51 . The system of claim 48 wherein said PRCPM waveform has a low modulation index and a low bandwidth-time product.
52 . 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.Join the waitlist — get patent alerts
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