Method and apparatus for constant envelope demodulation
Certain aspects of the present disclosure relate to a method for demodulating CPM modulated signals transmitted in a wired or wireless communication system using a linear modulation model consisting of a linear superposition of time pulses modulated using pseudo-PSK pulses.
1. A method for communication, comprising:
receiving a signal modulated with non-linear continuous phase modulation;
demodulating the received signal using a linear superposition of time-shifted pulses modulated with symbols from a continuously rotated differential pseudo Phase Shift Keying (PSK) constellation; and
de-mapping the demodulated signal into data bits from pseudo-PSK symbols or rotated pseudo-PSK symbols.
2. The method of claim 1 , wherein continuous phase modulation comprises at 2-CPM, 4-CPM, filtered rotated differential pseudo-BPSK (πh 2 -DPBPSK) modulation, or rotated generalized differential pseudo-QPSK (πh 4 -GDPQPSK) modulation.
3. The method of claim 1 , wherein the non-linear continuous phase modulation is filtered πh 2 -DPBPSK modulation that comprises mapping each binary bit of a data stream into one of two constant-amplitude constellation points, differentially encoding the mapped data stream, continuously rotating the differentially encoded and mapped data stream by a constant phase of πh 2 , wherein π is Pi and h 2 is a modulation index, and filtering the continuously rotated differentially encoded and mapped data stream to produce a quasi-constant envelope signal.
4. The method of claim 3 , wherein the πh 2 -DPBPSK modulation-employs symbol-level continuous rotation, wherein each n th symbol is rotated by nπh 2 , where n is an integer-valued index.
5. The method of claim 1 , wherein non-linear continuous phase modulation is πh 4 -GDPQPSK modulation that comprises generating even complex symbols and odd complex symbols, wherein generating the even complex symbols comprises mapping bit pairs of a data stream into a constellation of four constant-amplitude points, differentially encoding the mapped data stream, continuously rotating the differentially encoded and mapped data stream by a constant phase of πh 4 , wherein π is Pi, and h 4 is a modulation index, and wherein the odd symbols are generated by correcting even symbols using a correction term computed from data bit pairs and the modulation index h 4 .
6. The method of claim 5 wherein the πh 4 -GDPQPSK modulation employs symbol-level continuous rotation, wherein each n th symbol is rotated by nπh 4 , where n is an integer-valued index.
7. The method of claim 1 wherein the received signal comprises a linear superposition of time-shifted pulses modulated with symbols from a rotated differential pseudo-PSK constellation of the form:
∑
n
c
(
n
)
h
(
t
-
nT
)
,
where T denotes symbol duration, h(t) is a filtered multipath channel pulse, and {c(n)} is a set of rotated differential pseudo-BPSK mapped symbols obtained from a binary data stream {a(n)} using differential pseudo-BPSK mapping, wherein each bit a(n) of the binary data stream is mapped into one of two constant-amplitude constellation points, differentially encoded, and continuously rotated.
8. The method of claim 7 , wherein continuously rotating the differentially encoded and mapped symbols, comprises rotating each n th differentially encoded and mapped symbol by nπh 2 where n is an integer-valued index, π is Pi, and h 2 is a modulation index.
9. The method of claim 1 , wherein the received signal comprises a linear superposition of time-shifted pulses modulated with symbols from a rotated differential pseudo-PSK constellation of the form:
∑
n
c
(
n
)
h
(
t
-
nT
-
T
/
2
)
,
where T denotes symbol duration, h(t) is a filtered multipath channel pulse, and {c(n)} is a set of rotated generalized differential pseudo-QPSK mapped symbols obtained from a binary data stream {a(n)} using generalized differential pseudo-QPSK mapping, wherein even symbols {c(2n)} are generated by mapping each pair of bits a(2n) and a(2n+1) of the binary data stream into one of four constant-amplitude constellation points, differentially encoding the mapped symbols, and continuously rotating the differentially encoded and mapped symbols, and wherein odd symbols {c(2n+1)} are generated by correcting the even symbols {c(2n)} by a correction term computed from the pair of bits a(2n) and a(2n+1) and a modulation index h 4 .
10. The method of claim 9 , wherein continuously rotating the differentially encoded and mapped symbols comprises rotating each n th differentially encoded and mapped symbol by nπh 4 , where n is an integer-valued index, π is Pi, and h 4 is a modulation index.
11. The method of claim 1 , wherein the signal is modulated, with 2-CPM modulation with a modulation index h 2 =1/2, and demodulating the received signal comprises modeling the signal as a linear superposition of pulses modulated with rotated differential BPSK symbols.
12. The method of claim 1 , wherein the signal is modulated with 4=CPM modulation with a modulation index h 4 =1/4, and demodulating the received signal comprises modeling the signal as a linear superposition of pulses modulated with rotated differential QPSK symbols.
13. The method of claim 1 , further comprising continuously de-rotating the received signal before demodulating the signal, wherein the n th symbol is de-rotated by nπh, where n is an integer-valued index, π is Pi, and h is a modulation index.
14. The method of claim 1 , wherein the de-mapper is configured for performing generalized differential pseudo-QPSK or rotated generalized differential pseudo-QPSK de-mapping.
15. The method of claim 1 , wherein the de-mapper is configured for performing differential pseudo-BPSK or rotated differential pseudo-BPSK de-mapping.
16. An apparatus configured to perform the method of claim 1 .
17. An apparatus for communication comprising:
a receiver for receiving a signal modulated with non-linear continuous phase modulation;
a demodulating means for demodulating the received signal using a linear superposition of time-shifted pulses modulated with symbols from a continuously rotated differential pseudo Phase Shift Key (PSK) constellation; and
a de-mapper for de-mapping the demodulated signal into data bits from pseudo-PSK symbols or rotated pseudo-PSK symbols.
18. An apparatus for communication comprising:
a receiver for receiving a signal modulated with non-linear continuous phase modulation; and
a demodulator employing a linear superposition of time-shifted pulses modulated with symbols from a continuously rotated differential pseudo Phase Shift Key (PSK) constellation;
and a de-mapper for de-mapping the demodulated signal into data bits from pseudo-PSK symbols or rotated pseudo-PSK symbols.
19. The apparatus of claim 18 , wherein the de-mapper is configured for performing generalized differential pseudo-QPSK or rotated generalized differential pseudo-QPSK de-mapping.
20. The apparatus of claim 18 , wherein the de-mapper is configured for performing differential pseudo-BPSK or rotated differential pseudo-BPSK de-mapping.
21. The apparatus of claim 18 , wherein the receiver comprises a de-rotator for de-rotating the received signal prior to demodulation, wherein an n th symbol is de-rotated by nπh, where n is an integer-valued index, π is Pi, and h is a modulation index.