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Channel Image Save and Restore for Modem Training Time Reduction

IP.com Disclosure Number: IPCOM000009606D
Publication Date: 2002-Sep-04
Document File: 4 page(s) / 107K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that uses the full resources of a modem receiver to identify a channel which the receiver has compensated for. The disclosed method defines a way to reduce connection delay on connections which have been previously “learned” without loss of performance once connected. Benefits include saving resources and code space.

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Channel Image Save and Restore for Modem Training
Time Reduction

Disclosed is a method  that uses the full resources of a modem receiver to identify a channel which the receiver has compensated for. The disclosed method defines a way to reduce connection delay on connections which have been previously “learned” without loss of performance once connected. Benefits include saving resources and code space.

Background

When two modems connect to each other over the PSTN they can, according to various International Telecommunications Union specifications, use time during connection establishment to allow their adaptive filters to “train” or “learn” the channel characteristics to achieve optimal performance (see Figure 1). This learning process typically consists of updating vectors with new values based on an informed trial-and-error algorithm, such as Least Mean Squared (LMS), and can take thousands of iterations to achieve a useful level of performance. This training time represents much of the connection delay between dialing up the Internet Service Provider and actually logging in.

General Description

Figure 2 shows a block diagram of a typical modem transmitter/receiver pair. The transmitter modulates TX Customer Data onto a signal, which is sent to the telephone line (TX Line Signal) and drives an echo canceller. The receiver accepts the impaired RX Line Signal from the Local Loop, subtracts the local Transmitter echo by adding in the Echo Canceler output, and then compensates for channel impairments via the Gain Compensation and Equalizer functions. The correct received symbol is detected in the Slicer, is decoded and descrambled, then sent to the user as RX Customer Data.  These receiver functions rely on dedicated Data RAM to adapt t...