Modem initialization process for line code and rate selection in DSL data communication

• US 5,987,061 A
• Filed: 10/31/1996
• Issued: 11/16/1999
• Est. Priority Date: 05/09/1996
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Chen, Walter Y.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): GHAYOUR, MOHAMMAD H
• Application Number:
  US08/741,776
• Time in Patent Office: 1,111 Days
• Field of Search: 375/222, 375/231, 370/278, 379/100.05
• US Class Current: 375/222
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 2025/03611 Iterative algorithms
• CPC Class Codes: H04L 25/03 Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 25/4921 using quadrature encoding, e.g. carrierless amplitude-phase coding
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 27/2656 Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 5/1438 Negotiation of transmission parameters prior to communication modified according to link quality H04L1/0001
• CPC Class Codes: H04M 11/06 Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data

Abstract

A modem that operates selectively in the voice-band frequency band and at higher frequency bands is provided. This modem supports multiple line codes, like DMT and CAP. The modem uses a Digital Signal Processor (DSP), so that different existing ADSL line codes, such as Discrete MultiTone (DMT) and Carrierless AM/PM (CAP), can be implemented on the same hardware platform. The modem negotiates in real-time, for a desired line transmission rate to accommodate line condition and service-cost requirement. The line code and rate negotiation process may be implemented at the beginning of each communication session through the exchange of tones between the modems. A four-step MDSL modem initialization process is provided for line code and rate compatibility.

Claims

1. A method for modem initialization in a data communication system having central office and subscriber modems respectively connected to opposite ends of a twisted pair telephone subscriber loop transmission channel of a switched telephone network, comprising the steps of:

(i) the subscriber modem sending first spaced tones whose frequencies are in an upstream frequency band above voice band to characterize the channel for the upstream frequency band and indicate line code capability of the subscriber modem, and

(ii) the central office modem sending second spaced tones whose frequencies are in a downstream frequency band above voice band to to characterize the channel for the downstream frequency band and indicate line code capability of the central office modem.