Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1998-09-11
2002-02-05
Chin, Stephen (Department: 2734)
Pulse or digital communications
Transceivers
Modems
C375S228000, C370S252000
Reexamination Certificate
active
06345071
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to digital modem that supports fast retrain based on communication profiles.
DESCRIPTION OF THE RELATED ART
Many personal computer systems (PC's) are sold with, or have the ability to add, a communication device such as a digital or analog modem or the like that enables communication with an external network via telephone wires from the home. The most common external network is the Internet, although other networks including broadband networks, public networks and wide area network (WANs) are contemplated. For simplicity, all such external or broadband networks are referred to herein as WANs. Dial-up modem technology is relatively easy to install and comfortable for the end user to use and currently operates up to a common data rate of approximately 56K bits per second (bps). The 56K bps dial-up modem solution provides a significant increase in speed as compared to a 14.4K bps modem, but does not provide a significant speed advantage as compared to a 28.8K bps modem. The actual modem speed achieved is directly proportional to the quality of the channel characteristics of the voice band signal in a given home location. At the present time, none of the Internet Service Providers (ISP) are guaranteeing the actual rate for the end user.
One significant problem with analog modems are that they interfere with or otherwise cannot be used simultaneously with standard telephones operating according to the Plain Old Telephone Service (POTS) or Message Telecommunications Services (MTS) and other voice band services. The home user is forced to install an entirely separate telephone line in order to have simultaneous access to a WAN while maintaining standard telephone service. An entirely separate and independent phone line is relatively costly and inconvenient.
In spite of advances in dial-up technology, the explosive popularity of the Internet has caused consumers to become frustrated by the relatively slow speed of their connection using analog modems. The Integrated Services Digital Network (ISDN) service has been used at some home sites and small businesses and offers somewhat higher speed access. However, access charges for ISDN are still high for the average consumer and it is not available everywhere. Also, each customer's loop must first be qualified in order to be connected. Digital Subscriber Loop (DSL) technology, particularly the asymmetrical DSL (ADSL), is beginning to emerge as the technology of choice to provide broadband access to consumers. A digital class of modems supporting ADSL provides significantly higher speed than either analog modems or ISDN devices. Furthermore, ADSL does not require a different type of transmission media such as an ISDN line or the like. Traditionally, however, ADSL required a second phone wire to be installed within the home that required a truck roll and possibly a POTS splitter to be installed at the demarcation point at the home.
The LAN and broadband access issues are also applicable to the small office environment. Small offices commonly include an entirely separate telephone network, a separate LAN network and a separate WAN or broadband connection through a separate physical medium connection such as an ISDN line or the like.
One issue with using ADSL and POTS on the same transmission media is that each phone handset changes the line quality and communication characteristics of the transmission media, such as the characteristic impedance, when on or off hook. Such change in the communication characteristics of the transmission media effects ADSL operation, such as the signal quality, divergence of equalizers, echo cancelers, carrier and timing recovery and other digital signal processing (DSP) algorithms, etc.
It is desired to use existing phone lines and to further provide broadband access without the requirement of a local POTS splitter or separate phone lines. It is further desired to use standard telephone services on the same transmission medium such as a standard phone line without interfering with ADSL communications.
SUMMARY OF THE INVENTION
A digital modem that supports fast retrain based on communication profiles according to the present invention includes a memory that stores a plurality of communication profiles. The modem also includes communication logic that sends and receives information via a transmission medium and that operates according to any one of the plurality of communication profiles, and monitor logic that continuously monitors communication by the communication logic on the transmission medium according to any one of the plurality of communication profiles and that provides a signal change indication if the communication characteristics change by at least a predetermined amount. The modem further includes fast retrain logic that selects another one of the communication profiles stored in the memory in response to the signal change indication, that retrains the communication logic to operate according to the selected communication profile and that cooperates with the communication logic to transmit a fast retrain indication via the transmission medium.
In the embodiments illustrated, the digital modem is an ADSL modem that operates according to the Discrete MultiTone (DMT) modulation method using a plurality of upstream and downstream tones, where each tone is within one of a plurality of sub-channels or sub-frequencies of the transmission medium bandwidth. The ADSL modem may operate at a home location without requiring a POTS splitter. The ADSL modem, otherwise referred to as the Remote ADSL Termination Unit (ATU-R), communicates with a Central Office ADSL Termination Unit (ATU-C) located at the central office of the telephone company. Because a POTS splitter is not present, the digital modem operates on the same phone lines or transmission medium as one or more standard telephones operating according to POTS. In this manner, POTS signaling and on/off hook transitions of the telephones change the communication characteristics of the phone lines and affect ADSL communications. The signal quality is compromised so that the same data rate may not be maintained. However, communication may be continued at a lower data rate according to a different profile. The digital modem includes the fast retrain logic to automatically switch between communication profiles to resume communications very quickly.
The digital modem may include measuring logic that cooperates with the communication logic to measure the communication characteristics of the transmission medium and that generates and stores a corresponding communication profile in the memory. In at least one embodiment, each of the communication profiles are measured and stored in this manner. Upon initialization of the modem, the measuring logic is employed to measure the initial signal line quality, which typically reflects the optimal conditions of the phone lines while all of the telephones are on-hook. During operation, the monitoring logic detects a disturbance of the communications, such as when any one or more of the phones transition to off-hook. If the communication profile is no longer valid where the communication logic is unable to sustain communications, and if the fast retrain logic determines that none of the profiles stored in the memory are valid for the given status of the transmission medium, then the measuring logic is again invoked to measure the communication characteristics and generate a new communication profile. The new profile is stored in the memory and sent to the other modem via the transmission medium. Both modems retrain according to the new communication profile. Operation continues in this manner for any number or up to a maximum number of profiles.
The monitoring logic also detects when a disturbance is removed and the communication characteristics improve. If so, the monitoring logic indicates to the fast retrain logic, which finds a better communication profile and quickly retrains the communication logic according to the better communication profile. Also, once all
Akin Gump Strauss Hauer & Feld & LLP
Chin Stephen
Compaq Computer Corporation
Jiang Lenny
LandOfFree
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