Multimode digital modem

• US 6,055,268 A
• Filed: 06/20/1996
• Issued: 04/25/2000
• Est. Priority Date: 05/09/1996
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Lu, Xiaolin, Wu, Song, Schurr, Paul E., Gatherer, Alan, Polley, Michael O., Shaver, Donald P., Frantz, Gene A., Weiner, Douglas B., Mannering, Dennis G., Riley, Terence J., Timm, William C., Garcia, Domingo G., Chen, Walter Y.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): GHAYOUR, MOHAMMAD H
• Application Number:
  US08/667,267
• Time in Patent Office: 1,405 Days
• Field of Search: 375/229, 375/231, 375/295, 375/296, 455/68, 455/69
• US Class Current: 375/229
• 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 1/0016 involving special memory structures, e.g. look-up tables
• CPC Class Codes: H04L 1/0023 characterised by the signalling
• 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 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• 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
• CPC Class Codes: Y02D 30/50 in wire-line communication networks, e.g. low power modes or reduced link rate

Abstract

A modem communication system with receiving and transmission paths includes a direct equalizer system having an adaptive filter (1532) in the transmission path to compensate for frequency distortion of the communication channel. The transmitter filter coefficients are adapted by a filter coefficient calculator (1528), under control of a data detector (1526) which detects incoming data in the receiving path. A switch (1534) is controlled by status of a transmit output data buffer to multiplex either the training sequence or output data into the transmission path. When the buffer is idle, the training sequence generator (1540) is linked to a digital-to-analog (D/A) converter (1536) and line driver (1538). The receiving path includes an isolation switch (1520), a receiver amplifier (1522) and a slicer (1524). The receiver correlates the received training sequence with a known training sequence and updates the equalizer filter coefficients using an adaptation algorithm, such as a least mean squared algorithm. A first embodiment utilizes a high speed digital programmable filter (1532). Another embodiment utilizes a data buffer (1533) which is periodically filled with data filtered by a digital signal processor (DSP).

Claims

1. A data rate negotiation process for a pair of modems which comprises the steps of:

(a) providing a subscriber station having a first modem;

(b) providing a central station having a second modem;

(c) transmitting a signal from said first modem to said second modem requesting a first data transmission rate;

(d) transmitting a signal from said second modem to said first modem either accepting or rejecting said first data transmission rate;

(e) responsive to rejection of the requested first data transmission rate, repeatedly repeating steps (c) and (d) with a continually different requested transmission rate until said second modem accepts a said requested data transmission rate; and

(f) then commencing non-rate negotiation communication between said first and second modems at the accepted negotiated rate;

wherein rate adjustment is based upon a data rate table associated with each of said first and second modems indicating available data rates for respective modem, and further based upon at least one of line conditions between said first and second modems, backbone network accessibility, computational capabilities of the modems, and application requirements.

2. The process of claim 1 wherein the adjustment of the data rate comprises adjustment of the number of bits represented by each symbol.

3. The process of claim 1 wherein said subscriber station and said central station are each capable of communication at a plurality of data rates, said subscriber station and said central station being provided with additional hardware and at least one of said subscriber station and said central station being provided with software, at least one of said subscriber station and said central station adjusting request for a transmission rate to conform to the capabilities of additional hardware and software, if present.

4. The process of claim 2 wherein said subscriber station and said central station are each capable of communication at a plurality of data rates, said subscriber station and said central station being provided with additional hardware and at least one of said subscriber station and said central station being provided with software, at least one of said subscriber station and said central station adjusting request for a transmission rate to conform to the capabilities of additional hardware and software, if present.