Method for selecting baud rates for a rate adaptive digital...

Details Method for selecting baud rates for a rate adaptive digital... Method for selecting baud rates for a rate adaptive digital...

Filed on

1998-04-08

Date issued

2001-06-12

Examiner

Cangialosi, Salvatore (Department: 2661)

Patent Class

Multiplex communications

SubClass

Communication techniques for information carried in plural...

SubSubClass

Adaptive

Other Related Categories

C370S465000, C375S222000

Type

Reexamination Certificate

Status

active

Patent number

06246694

Description

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates to rate adaptive digital subscriber line modems.
BACKGROUND OF THE INVENTION
Different transmission throughputs or baud rates have been proposed for Rate Adaptive Digital Subscriber Line (RADSL). K. Sistanizadeh, J. Waldhuter, H. Suyderhoud, and M. Sorbara,
Recommendation on Symbol Rates, Constellations, and Spectral Placement and Shaping for the CAP/QAM Spec
., Joint T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-134, Mar. 5, 1997; H. Samueli, R. Joshi, M. Darveau, and R. Carsten,
Draft PMD Specification for Rate
-
Adaptive ADSL
(
RADSL
), Broadcom T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-013, Jan. 22-23, 1997. H. Samueli, R. Joshi, M. Darveau, and R. Carsten,
Draft PMD Specification for Rate
-
adaptive ADSL
(
RADSL
), Broadcom T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-013, Jan. 22-23, 1997. There was a concern that the currently proposed throughput step size was too big. R. A. McDonald, “
Transceiver Rate Adaptation Step Sizes
,” Pacific Bell Telesis Technologies Laboratory T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-019, Jan. 22-23, 1997.
The relationship between baud rates and a fixed system clock is first explored.
Baud Rates Derived from A Fixed Master Clock
Baud rates ƒ
B
i
are usually derived from a fixed common clock frequency ƒ
clock
according to
ƒ
B
i
=ƒ
clock
/m
i
where m is an integer. A shift register of n bits, where Max(m
i
)<2
n
, is necessary to derive the baud rate from the master clock.
For the proposed baud rates from Globspan Table 1, we have ƒ
clock
=114.24 MHz, m
1
=840, m
2
=336, m
3
=168, m
4
=140, m
5
=120, m
6
=105. K. Sistanizadeh, J. Waldhuter, H. Suyderhoud, and M. Sorbara,
Recommendation on Symbol Rates, Constellations, and Spectral Placement and Shaping for the CAP/QAM Spec
., Joint T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-134, Mar. 5, 1997.
TABLE 1
Proposed Baud Rates from GlobSpan
Up
Downstream
Baud Rate
136
340
680
816
952
1088
For the proposed baud rates from Broadcom
In Table 2, we have ƒ
clock
=2.016 MHz, m
1
=24, m
2
=16, m
3
=8, m
4
=4, m
5
=3, m
6
=2. H. Samueli, R. Joshi, M. Darveau, and R. Carsten,
Draft PMD Specification for Rate
-
Adaptive ADSL
(
RADSL
), Broadcom T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-013, Jan. 22-23, 1997
TABLE 2
Proposed Baud Rates from Broadcom
Up
Downstream
Baud Rate
84
126
252
504
672
1008
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a variable throughput step size depending on the baud rate used in conjunction with use of a fractional bit constellation. An optimal baud rate and constellation size identification procedure is identified that may be used in an initialization process. Optimal baud rates have been examined for different length twisted pair telephone loops and optimal baud rates have been found to be about 200 KHz apart for loops with an 1 kft length difference. It has also been found that by employing a set of baud rates with 200 KHz steps, it is possible to maintain a performance within 0.5 dB of an optimal performance. A representation set of baud rates are provided for RADSL.
A method of operating a CAP-RADSL system, is provided that determines a finite set of baud rates for a CAP-RADSL system based on a performance criterion, and selects one of the baud rates based on operating environment, including channel conditions and network synchronization requirements.


REFERENCES:
patent: 5987069 (1999-11-01), Furukawa et al.
patent: 6167095 (2000-12-01), Furukawa et al.

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