Efficient algorithm for blind detection of signal constellation

Details Efficient algorithm for blind detection of signal constellation Efficient algorithm for blind detection of signal constellation

2000-07-14

2003-09-02

Vo, Don N. (Department: 2631)

Pulse or digital communications

Systems using alternating or pulsating current

Plural channels for transmission of a single pulse train

C375S264000, C375S353000

Reexamination Certificate

active

06614851

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally directed to a method to identify the constellation type of a modulated signal.
2. Background
Communication systems employ a variety of signal modulation. These include frequency independent types such as pulse amplitude modulated (PAM) signals, quadrature amplitude modulation (QAM) and phase-shift keying (PSK).
The number of discrete waveforms may be denoted as M points in the state space constellation. In PAM, the ergodic (i.e., time-dependent) signal waveform s
m
(t) may be represented by a periodic cosine function that includes a series of discrete amplitudes ranging from m=1, 2, . . . , M. For pulsed signals sent over discrete time intervals, the time t may be replaced by nT where T is the sampling period and n is a positive integer. PAM is similar to vestigial side band (VSB) used in television. The M-PAM signals may be plotted in single dimensioned signal space R (also written as R) at M discrete points along the real axis. The energy for the waveforms may be a proportional to the square of the amplitudes.
FIG. 1
shows a 4-PAM signal space diagram
10
with an axis
12
for example M=4. The data points are presented for a binary bit pair having four possible positions at points
16
a
and
16
b
on the left side of the imaginary axis and
16
c
and
16
d
on the right side in this example. Phase modulated signals, such as PSK and QAM, may be multi-dimensional belonging to signal space R
N
, where N represents the dimension superscript.
For N=2, there exist real and imaginary components for representing amplitude and phase. A distance d from the origin of a point on the two-dimensional signal grid in R
2
can be expressed in complex form as d=d
i
+jd
q
where d
i
is the in-phase or real component, d
q
is the quadrature or imaginary component and j={square root over (−1)}.
In PSK, the signal waveforms s
m
(t) have equal energy and can be plotted as being equal distant from the origin.
FIG. 2
shows an 8-PSK signal space diagram
18
for M=8 with data points
20
a
and
20
b
on the real axis
12
,
20
c
and
20
d
on the imaginary axis
14
, and
20
e
,
20
f
,
20
g
, and
20
h
at intermediate positions.
QAM may include a series of discrete amplitudes in addition to a phase component to distinguish a set of four points by the quadrant occupied.
FIG. 3
shows a 16-QAM signal space diagram
22
for M=16 with the axes
12
and
14
dividing the space into four quadrants
24
a
,
24
b
,
24
c
and
24
d
. The first quadrant
24
a
includes four points
26
a
,
26
b
,
26
c
and
26
d
. The second quadrant
24
b
includes four points
26
e
,
26
f
,
26
g
and
26
h
. The third quadrant
24
c
includes four points
26
i
,
26
j
,
26
k
and
26
l
. The fourth quadrant
24
d
includes four points
26
m
,
26
n
,
26
o
and
26
p.
For M=4, data values to be represented may range from two-digit binary numbers 00
2
, 01
2
, 10
2
, and 11
2
. For M=8, data values to be represented may range from three-digit binary numbers 000
2
, 001
2
, 010
2
, . . . , 111
2
. For M=16, data values to be represented may range from four-digit binary numbers 0000
2
, 0001
2
, 0010
2
, . . . , 1111
2
. The incoming signal to be interpreted as these data values may be received as voltages or digital numbers, with each discrete data value corresponding to a particular range of voltages.
Several communication transmission media are widely in use today, such as satellite, microwave, terrestrial, and cable systems. These transmit data at a variety of data rates. In order to convert the signals from received voltages into data, their amplitude and phase must be resolved. This task may be complicated by electronic noise from a variety of sources. A receiver configured to resolve only a select signal constellation would be unable to resolve an alternate modulation constellation. Smaller integrated chips could allow a wider variety of modulation systems to be received, if these are identified by modulation type. Accordingly, there exists a need for accurate and efficient detection of the modulation constellation type of a signal to enable multi-mode multi-standard operation of communication receivers.
SUMMARY OF THE INVENTION
A method for determining the signal constellation of a received signal establishes a moment based on each waveform, squares the moment, fourth powers the moment, divides the fourth power by the square to obtain a ratio, and compares the ratio to a threshold. If the ratio is less than threshold, the signal constellation corresponds to a first type, and if greater than the threshold, the signal constellation corresponds to a second type. The method can be generalized to a magnitude mean in place of a second moment.


REFERENCES:
patent: 5243624 (1993-09-01), Paik et al.
patent: 6167095 (2000-12-01), Furukawa et al.
patent: 6304593 (2001-10-01), Alouini et al.

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