Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1998-06-11
2001-06-26
Chin, Stephen (Department: 2734)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S262000, C341S094000
Reexamination Certificate
active
06252911
ABSTRACT:
This application relates generally to modems and, in particular, to a trellis shaping method for PCM modems.
BACKGROUND OF THE INVENTION
One of the problems in PCM (56K) modems is that the filters at the line cards and the transformers present in the analog portion of the telephone line put a null at DC frequency in the overall response of the channel. The filters at the line card also suppress frequency components around and near the Nyquist frequency (4 kHz for telephone lines). However, the problem is more severe at the DC and low frequencies as the transformers also exhibit non-linearity at such frequencies. These conditions make frequencies near DC and 4 kHz unusable for PCM modems. It is thus necessary to modify the spectrum of the output of the modems to match the channel.
Several proposals have been submitted to date to the TR-30.1 and ITU-T standard committee to modify the output spectrum. One promising submission by Motorola uses a convolutional code. See, Vedat Eyaboglu, “More on Convolutional Spectral Shaping,” presented at the V.pcm Rapporteur Meeting, La Jolla, Calif., May, 5-7 , 1997, incorporated herein by reference. The code is generated through the use of a Viterbi decoder. The proposal uses a convolutional code with a very simple trellis.
SUMMARY OF THE INVENTION
The invention provides an approach using a more complicated trellis. Experimental results using the novel approach show better performance may be obtained by using properly designed convolutional code. A general structure for use with PCM modems is provided.
REFERENCES:
patent: 4527279 (1985-07-01), Yasuda et al.
patent: 4578800 (1986-03-01), Yasuda et al.
patent: 5073940 (1991-12-01), Zinser et al.
patent: 5263051 (1993-11-01), Eyuboglu
patent: 5289501 (1994-02-01), Seshadri et al.
patent: 5321725 (1994-06-01), Paik et al.
patent: 5388124 (1995-02-01), Laroia et al.
patent: 5418531 (1995-05-01), Laroia
patent: 5428646 (1995-06-01), Eyuboglu
patent: 5446758 (1995-08-01), Eyuboglu
patent: 5455839 (1995-10-01), Eyuboglu
patent: 5488633 (1996-01-01), Laroia
patent: 5511081 (1996-04-01), Hagenauer
patent: 5535228 (1996-07-01), Dong et al.
patent: 5673291 (1997-09-01), Dent
patent: 5710790 (1998-01-01), Herzberg et al.
Ali Murtaza
Gatherer Alan
Brady III Wade James
Chin Stephen
Franz Warren L.
Jiang Lenny
Telecky , Jr. Frederick J.
LandOfFree
Trellis shaping for PCM modems does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Trellis shaping for PCM modems, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Trellis shaping for PCM modems will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2537730