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DMT SYMBOL REPETITION IN THE
PRESENCE OF IMPULSE NOISE
RELATED APPLICATION DATA
This application claims the benefit of and priority under 3 5 U.S.C. §119(e) to U.S. Patent Application No. 60/619,618, filed Oct. 15, 2004, entitled "xDSL Initialization in the Presence of Impulse Noise," which is incorporated herein by reference in its entirety. 10
BACKGROUND
1. Field of the Invention
This invention generally relates to communication sys- 15 terns. More specifically, an exemplary embodiment of this invention relates to an initialization technique for communication systems. Another exemplary embodiment relates to error detection and correction during initialization.
2. Description of Related Art 20
Communication systems often operate in environments
with impulse noise. Impulse noise is a short-term burst of
noise that is higher than the normal noise that typically exists
in the communication channel. For example, DSL systems
operate on telephone lines and experience impulse noise from 25
many external sources including telephones, AM radio, HAM
radio, other DSL services on the same line or in the same
bundle, other equipment in the home, etc. It is common prac-
tice for communication systems to use interleaving in com-
bination with Forward Error Correction (FEC) to correct the 30
errors caused by the impulse noise during user data transmis-
sion, i.e., SHOWTIME.
SUMMARY
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Standard initialization procedures in xDSL systems, such as those specified in ADSL ITU G.992 standards and VDSL ITU G.993 standards, are designed to optimize performance, such as data rate/reach, in the presence of "stationary" crosstalk or noise. Impulse noise protection is handled with 40 Interleaving/FEC during data transmission mode, known as "SHOWTIME" in ADSL and VDSL systems, but the current xDSL initialization procedures, also known as "training procedures," are not designed to operate in an environment with high levels of impulse noise. As an example, there are several 45 messages exchanged during initialization in ADSL and VDSL ITU standards that are not designed to work well in an environment with high levels of impulse noise. For example, in the ADSL2 G.992.3 standards, there are initialization messages such as R-MSG-FMT, C-MSG-FMT, R-MSG-PCB, 50 C-MSG-PCB, R-MSG1, C-MSG1, R-MSG2, C-MSG2, R-PARAMS, C-PARAMS, etc., which use modulation techniques that do not provide high levels of immunity to impulse noise. Likewise, for example, in the VDSL1 G.993.1 standards, there are initialization messages such as O-SIGNA- 55 TURE, O-UODATE, O-MSGl, 0-MSG2, O-CONTRACT, O-B&G, R-B&G, R-MSG1, R-MSG2, etc, which use modulation techniques that do not provide high levels of immunity to impulse noise. Additionally, G.994.1 (G.hs), which is used as part of the initialization procedure for most xDSL stan- 60 dards, uses modulation techniques that do not provide high levels of immunity to impulse noise. In particular, a receiver will not be able to correctly demodulate/decode the message information when only 1 DMT symbol is corrupted by impulse noise. This is especially problematic because xDSL 65 systems are generally designed to be able to pass steady-state ("SHOWTIME") data without errors in the presence of
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impulse noise by configuring a parameter called Impulse Noise Protection (INP). INP is defined in the ADSL2 and VDSL2 standards as the number of consecutive DMT symbols that, when completely corrupted by impulse noise, can 5 be completely corrected by the receiver using FEC and interleaving during SHOWTIME. For example, if INP=2, then if 2 (or less) SHOWTIME DMT symbols are corrupted by impulse noise, the interleaving and FEC coding will be configured to be able to correct all the resulting bit errors. This means that with the current initialization procedures defined in the VDSL and ADSL standards, even though the xDSL system could operate in SHOWTIME in an impulse noise environment where 2 DMT symbols are being corrupted, the transceivers would not be able to reach SHOWTIME because initialization would fail due to initialization message failure.
Accordingly, an exemplary aspect of this invention relates to an improved initialization procedure for communication systems that operate in environments with higher levels of impulse noise.
More specifically, an exemplary aspect of this invention relates to an initialization sequence where the messages exchanged during initialization are designed to operate in environments with higher levels of impulse noise.
Additional exemplary aspects of the invention relate to repeating DMT symbols within initialization messages.
Additional exemplary aspects of the invention relate to duplicating and repeating DMT symbols within initialization message(s).
Additional exemplary aspects of the invention relate to copying and repeating DMT symbols within initialization message(s).
Additional exemplary aspects of the invention relate to repeating the transmission of DMT symbols that are used to modulate initialization message information bits to correctly receive the messages in an environment with impulse noise.
Further exemplary aspects of the invention relate to using forward error correction to encode and decode initialization messages during initialization.
Aspects of the invention further relate to using forward error correction and interleaving to encode and decode initialization messages during initialization.
Still further aspects of the invention relate to using error detection techniques such as Cyclic Redundancy Checksum (CRC) on portions of an initialization message during initialization.
Additional exemplary aspects of the invention relate to using error detection techniques, such as CRC on portions of the bits in an initialization message to correctly determine which DMT symbols are corrupt.
Aspects of the invention also relate to utilizing error detection techniques, such as CRC, on portions of the bits in an initialization message to determine which bits are in error in a long message.
Aspects of the invention also relate to analyzing initialization message length to dynamically determine the type(s) of initialization message error detection and correction to be used.
Further aspects of the invention relate to using error detection techniques, such as CRC, on portions of the bits in an initialization message and message retransmission to correctly receive messages during initialization.
Additional exemplary aspects of the invention also relate to utilizing error detection techniques such as CRC on portions of the bits in any message or signal to determine which DMT symbols are corrupted by impulse noise during initialization.
