Blind start-up of a dual mode CAP-QAM receiver

Details Blind start-up of a dual mode CAP-QAM receiver Blind start-up of a dual mode CAP-QAM receiver

1998-07-02

2001-06-26

Le, Amanda T. (Department: 2734)

Pulse or digital communications

Equalizers

Automatic

C375S233000, C375S350000, C708S323000

Reexamination Certificate

active

06252903

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Related subject matter is disclosed in the co-pending, commonly assigned, U.S. Patent application of L. M. Garth, entitled “Automatic Constellation Phase Recovery in Blind Start-Up Of A Dual Mode CAP-QAM Receiver,”.
FIELD OF THE INVENTION
The present invention relates to communications equipment, and, more particularly, to the use of blind equalization in a receiver.
BACKGROUND OF THE INVENTION
Carrierless amplitude modulation/phase modulation (CAP) is a bandwidth-efficient two-dimensional passband line code. (Additional information on a CAP communications system can be found in J. J. Werner, “Tutorial on Carrierless AM/PM-Part I-Fundamentals and Digital CAP Transmitter,”
Contribution to ANSI X
3
T
9.5
TP/PMD Working Group,
Minneapolis, Jun. 23, 1992.) CAP is closely related to the more familiar quadrature amplitude modulation (QAM) transmission scheme. In voiceband modems, QAM has been used for over 25 years, while CAP has been used for over 15 years. However, CAP is simpler to implement digitally. Illustrative prior art transceiver structures for the QAM and CAP transmission schemes are shown in
FIGS. 1 and 2
, respectively. Both
FIGS. 1 and 2
illustrate two-dimensional encoding where a complex symbol, A
n
, is applied to the transmitter portion (where A
n
=a
n
+jb
n
), and a recovered complex symbol, Â
n
, is provided by the receiver portion, where Â
n
=â
n
+j{circumflex over (b)}
n
. With respect to other notation used in these FIGS., g(t) (e.g., see
FIG. 1
) is an impulse response of a baseband shaping filter, e
in
(t) and e
qu
(t) are equalizers for the in-phase and quadrature components, respectively, and p(t) and {tilde over (p)}(t) are impulse responses of a shaping filter which form a Hilbert pair (e.g., see FIG.
2
).
As can be observed from
FIG. 1
, the conventional QAM transceiver structure requires a modulator
1
and a demodulator
2
at the transmitter and receiver, respectively. In contrast, the CAP transceiver of
FIG. 2
does not require a modulator and a demodulator. Generally speaking, the CAP system of
FIG. 2
is not compatible with the QAM system of
FIG. 1
, but provides the same theoretical performance as QAM and is simpler to implement digitally than QAM. Indeed, the CAP structure of
FIG. 2
can be modified into a simpler QAM-only transceiver, which is shown in FIG.
3
.
Currently, some broadband access applications, such as VDSL (Very high rate Digital Subscriber Line), may require either a CAP receiver or a QAM receiver. Some in the art have proposed simply putting both the CAP receiver and the QAM receiver into one receiver—in effect having a dual structure receiver with a CAP section (having its own equalizer) and a separate QAM section (with its own equalizer). To further complicate matters, this dual structure receiver may require the use of blind equalization techniques in both the QAM section and the CAP section. In this case, there is no training signal for the dual structure receiver to use to identify the type of modulation. As such, the dual structure receiver must first independently converge both the equalizer in the QAM section and the equalizer in the CAP section, and then make a decision as to the type of modulation—all of which may cause significant timing overhead.
SUMMARY OF THE INVENTION
We have developed a receiver that has a dual mode of operation—a CAP mode and a QAM mode-yet only requires a single equalizer structure for both the CAP mode of operation and the QAM mode of operation during blind start-up.
In an embodiment of the invention, a receiver comprises an adaptive filter. The same blind equalization updating algorithm is used independent of the type of received signal. The blind equalization updating algorithm incorporates a constant R, whose value is a function of the type of received signal, e.g., a QAM signal or a CAP signal. The type of received signal is determined as a function of the in-phase component of the mean-squared error, E[e
2
n
]. As such, this receiver can be started blindly without knowing whether the received signal is a QAM signal or a CAP signal.


REFERENCES:
patent: 5673293 (1997-09-01), Scarpa et al.
patent: 5799037 (1998-08-01), Strolle et al.
patent: 5930309 (1999-07-01), Knutson et al.
Yang, J. and Werner, J.J., The Multimodulus Blind Equalization Algorithms, Processings of DSP97, Santorini, Greece, 1997.
Benvenuto, N. and Goeddel, T. W. “Classification of Voiceband Data Signal Using the Constellation Magnitude”, IEEE Trans. Commun., vol. 43, No. 11, pp. 2759-2770, 1995.

Affiliated with

Also associated with

Rating

Blind start-up of a dual mode CAP-QAM receiver does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Blind start-up of a dual mode CAP-QAM receiver, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Blind start-up of a dual mode CAP-QAM receiver will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2532789