EP0806852A2
Expired / Lapsed
EP
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A multimode digital modem
Assignee: Texas Instruments Inc
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Filing: 1997-05-06
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Granted: —
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Expires: 2017-05-06
Abstract
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. A new synchronization startup procedure for CAP based MDSL modems is provided. The handshake protocol and receiver algorithm allow reliable modem synchronization over severely amplitude distorted channels such as standard telephone twisted-pair wire. the algorithm makes use of a short length sequence to train a synchronizing equalizer at the receiver. After training to this sequence, a matched filter or correlator is used to detect the inverted sync sequence. The detection of the inverted sequence signals the start of the normal reference training o the CAP demodulation equalizers. The MDSL line connection management process provides a simple, efficient, and flexible interface to mange the line connection between MDSL-C (MDSL in Central Office site) and MDSL-R (MDSL in resident site) in the telecommunication Wide Area Networking environment. An internal state machine in an MDSL modem records and monitors the line status and notifies the state change to the other MDSL and also the host processor. The protocol used for exchanging line connection management messages is a simplified Link Control Protocol (LCP) for MDSL. <IMAGE>
Inventors
- 👤 William C. Timm
- 👤 Walter Y. Chen
- 👤 Gene A. Frantz
- 👤 Domingo G. Garcia
- 👤 Xiaolin Lu
- 👤 Dennis G. Mannering
- 👤 Michael O. Polley
- 👤 Terence J. Riley
- 👤 Donald P. Shaver
- 👤 Song S. Wu
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-24 08:03
CPC Classifications
H; H04; H04L; H04L1/00; H04L1/0001; H04L1/0023; H04L1/0002; H04L1/0003; H04L1/0009; H04L1/0015; H04L1/0016; H04L25/00; H04L25/02; H04L25/03; H04L25/03006; H04L25/03343; H04L25/38; H04L25/40; H04L25/49; H04L25/4917; H04L25/4919; H04L25/4921; H04L27/00; H04L27/26; H04L27/2601; H04L27/2647; H04L27/2655; H04L27/2668; H04L27/2673; H04L27/2675; H04L5/00; H04L5/14; H04L5/1438; H04M; H04M11/00; H04M11/06; H04M11/062; H04L1/004; H04L1/0056; H04L1/0059; H04L1/12; H04L1/16; H04L2025/0335; H04L2025/03375; H04L2025/03414; H04L2025/03592; H04L2025/03598; H04L2025/03611; Y; Y02; Y02D; Y02D30/00; Y02D30/50
Claims Analysis
Total Claims: 30
Claim 1
Independent Claim
41 words
A communications system, comprising: circuitry for providing communication signals, a node connected to said circuitry for point to multipoint communications, a wireless network unit for receiving said multipoint communications and providing said communications to respective end users using dedicated communications channels.
Claim 2
Dependent Claim
63 words
A local multipoint distribution system, comprising: a wireless distribution node; a plurality of wireless network units, each of said units in wireless communication with said node; and wherein each of said units includes connections to a plurality of twisted pair telephone lines, each of said connections at a point on the corresponding twisted pair between a telephone central office and a telephone customer.
Claim 3
Dependent Claim
21 words
The system of claim 2, wherein: said wireless distribution node is coupled to a telephone central office by optical fiber connection.
Claim 4
Dependent Claim
44 words
The system of claim 2, wherein: each of said units includes a modem operable at frequencies higher than voice band; and at least two of said twisted pairs couples at a telephone customer end to a modem operable at frequencies higher than voice band.
Claim 5
Dependent Claim
123 words
A direct equalization communications system, comprising: a switch connected to a transmission path for multiplexing received data and training data, an amplifier connected to said switch, a slicer connected to said amplifier, a received data detection circuit connected to said slicer, a filter coefficient calculation circuit connected to said slicer and a training sequence providing circuit, a programmable filter circuit connected to said filter calculation circuit for equalizing data to be transmitted, a dual port switch having one port connected to said programmable filter circuit and having a second port connected to a circuit for providing a training sequence, a D/A circuit connected to said dual port switch, and a line driver connected to said D/A circuit, said switch and said transmission path.
Claim 6
Dependent Claim
22 words
The system of claim 5 further comprising, a data buffer circuit connected between said programmable filter circuit and said dual port switch.
Claim 7
Dependent Claim
41 words
An equalizer system for symmetrical channel communication, comprising: a receiver; a channel distortion compensation filter coefficient calculator coupled to said receiver; and a transmitter including a programmable filter coupled to said calculator, said programmable filter with coefficients controlled by said calculator.
Claim 8
Dependent Claim
17 words
The system of claim 7, wherein: said calculator and said transmitter are coupled to training sequence sources.
Claim 9
Independent Claim
48 words
A method for demodulating a received DSL modem signal, comprising the steps of: bandpass filtering said received signal, and downsampling said received signal from a first higher frequency band to create an image of said signal in a second lower frequency band in order to demodulate said signal.
Claim 10
Independent Claim
64 words
A method for modulating a DSL modem signal, comprising the steps of; providing said signal, upsampling said signal in a first lower frequency band to generate an image of said signal in a second higher frequency band, and bandpass filtering to select said image of said signal in said second higher frequency band in order to transmit said signal at said higher frequency band.
Claim 11
Independent Claim
39 words
A method for processing signals with a modem, comprising the steps of: employing a DMT line code in said modem, and variably scaling data in at least one computation stage of a multistage transform for said DMT line code.
Claim 12
Dependent Claim
23 words
A modem, comprising: a digital signal processor employing a multistage computational transformation using variably scaled data in at least one of said stages.
Claim 13
Dependent Claim
11 words
A multimode modem, comprising: a voice-band modem, and a DSL modem.
Claim 14
Dependent Claim
22 words
A multimode modem, comprising: a voice-band modem, and a DSL modem, wherein said DSL modem is capable of selecting a line code.
Claim 15
Dependent Claim
39 words
A modem, comprising: a DSP, an A/D and D/A circuit connected to said DSP, a VB analog front end connected to said A/D and D/A circuit; and a CAP analog front end connected to said A/D and D/A circuit.
Claim 16
Dependent Claim
47 words
A multi-link mode modem, comprising: a single link associated with a leased line; multiple links associated with a leased line; at least a single link associated with a switched line with soft dial; and at least a single link associated with a switched line with hard dial.
Claim 17
Dependent Claim
39 words
A link connection management process for a modem, comprising the steps of: link connection establishment; link disconnection establishment; link status monitoring; link status change notification to the host processor; and link configuration, link connection/disconnection messaging between said two modems.
Claim 18
Independent Claim
37 words
A method of identifying a modem, comprising the steps of : providing a telephone number for the line to which said modem is connected; and adding one digit post-fix to said telephone number to identify said modem.
Claim 19
Dependent Claim
36 words
A rate negotiation process for a modem, comprising the step of adjusting the throughput based upon: line conditions between said modem and a second modem; backbone network accessibility; computational capabilities of said modem; and application requirements.
Claim 20
Independent Claim
28 words
A method for selecting a rate used by a pair of DSL modems, comprising the steps of: interoperable modes that enable communication among a range of price/performance modems.
Claim 21
Dependent Claim
50 words
A rate negotiation process for a modem, comprising the steps of: adjusting the bandwidth used in a line and adjusting the number of bits represented by each symbol based upon: line conditions between said modem and a second modem; backbone network accessibility; computational capabilities of said modem; and application requirements.
Claim 22
Dependent Claim
45 words
A modem channel map message, comprising: a channel map header indicating the total channel capacity and available channel capacity; current channel allocation represented by 0 or more channel entries; channel change request represented by 1 or more channel entries flagged by their most significant bits.
Claim 23
Independent Claim
87 words
A method of data link layer rate negotiation of a modem, comprising the steps of: said modem sends an channel map change request message and waits for reply; the associated modem checks the channel map change request and send out one of the following possible messages in reply: a channel change request acknowledgment message to confirm the channel map change; a channel map change reject message to reject the channel map change; and a channel map change negative acknowledgment message to start a channel map change re-negotiation.
Claim 24
Independent Claim
35 words
A method for initial synchronization of a CAP or QAM based modem, comprising the steps of: a startup handshake between said modem and a second modem including a plurality of segments of known symbol sequences.
Claim 25
Independent Claim
41 words
A method for modem initialization, comprising the steps of: first spaced tones whose frequencies are above the voice band to characterize the channel; and second spaced tones in the same frequency range to determine modem capabilities and exchange user preference information.
Claim 26
Dependent Claim
34 words
A rate negotiation process for a modem, comprising the steps of: a physical transmission throughput maximization procedure; a frame and time slot assignment procedure; a software and hardware interface; and a status transition algorithm.
Claim 27
Independent Claim
84 words
A method for DMT modem initial synchronization, comprising the steps of: a training sequence for probing the length of channel impulse response including repetitive data blocks with the block polarity alternating periodically; deriving residual channel inter-symbol interference and frame boundary by subtracting the previously received data block from the current received data block; time domain equalizer training by using said training sequence and said residual channel inter-symbol interference to update equalizer coefficients; and frame synchronization by using said training sequence and said frame boundary.
Claim 28
Dependent Claim
33 words
A video conferencing system comprising: a system where video is transmitted using a modem which uses frequencies above the voice-band, and audio is transmitted in the voice band on the same subscriber line.
Claim 29
Independent Claim
88 words
A method for interfacing modem hardware with a host operating system comprising the steps of: calling a defined set host interface functions for command/control; calling a defined set of host interface functions for link connection management; calling a defined set of host interface functions for data sending/receiving; and calling a defined set of host interface functions for synchronization between voice-band audio and above voice-band video; and calling a defined set of host interface functions to use the voice-band as control channel and above voice-band for the data channel.
Claim 30
Independent Claim
34 words
A method of establishing a new mode of modem capability for a multi-mode modem comprising the steps of: receiving software using an available modem mode to upgrade modem capability to support an additional mode.
References Cited (Backward Citations)
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