Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1998-03-05
2001-03-06
Chin, Stephen (Department: 2734)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
Reexamination Certificate
active
06198774
ABSTRACT:
The present invention relates generally to data communications; and, in particular, to methods and apparatus for resolving ambiguities in Quadrature Amplitude Modulation (QAM) and other similarly coded data.
BACKGROUND OF THE INVENTION
In Quadrature Amplitude Modulation (QAM) techniques both amplitude and phase are used to represent the data contained within the signal. Often 8-QAM to 256-QAM systems are used in applications such as wireline communications. Data is transmitted in a QAM modulation scheme with the data contained within the amplitude and phase of the transmitted signal. In a typical system, for every n bits of data, a QAM symbol (Ik, Qk) is generated using some constellation encoder, where Ik is the kth real amplitude and Qk is the kth imaginary amplitude of the signal. In conventional systems, the signal is transmitted through a modulator which converts the signal into analog waveform for transmission through a channel to a remote location. The remote location includes a demodulator which converts the received analog waveform into a QAM constellation point, and a constellation decoder which converts the QAM constellation point back into n bits.
Usually the constellation encoder-decoder elements are designed to correct for phase ambiguities in the received QAM constellation point. See, for example, U.S. Pat. No. 5,233,630, the entirety of which is incorporated herein by reference. Overlooked, however, is the effect of spectral inversion or “mirroring” across an axis (typically, the I axis). This occurs, for example, when the signal is frequency stacked such as in cable modem system.
Thus, there is a need to design encoder-decoder elements in a constellation system that correct for spectral inversion.
SUMMARY OF THE INVENTION
The invention provides methods and apparatus to correct for spectral inversion occurring during transmission in a QAM or similar encoding system.
REFERENCES:
patent: 5974090 (1999-10-01), Hirao et al.
Brady III Wade James
Chin Stephen
Deppe Betsy L.
Franz Warren
Telecky , Jr. Frederick J.
LandOfFree
Method and apparatus for resolving spectral inversion... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for resolving spectral inversion..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for resolving spectral inversion... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2528398