Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1998-06-11
2001-03-13
Chin, Stephen (Department: 2734)
Pulse or digital communications
Transceivers
Modems
C370S287000
Reexamination Certificate
active
06201830
ABSTRACT:
BACKGROUND OF THE INVENTION
Asymmetric digital subscriber line (ADSL) modems transmit high rate digital data over existing twisted pair telephone lines to connect residential customers to digital networks. Discrete multi-tone (DMT) is a multicarrier modulation technique used in xDSL systems for transmitting high speed data in the presence of significant inter-symbol interference. ADSL and DMT concepts are described in U.S. Pat. Nos. 5,408,260 and 5,533,008, and therein cited references, all of which are incorporated by reference herein. ADSL is well-suited for applications in which the data rate needed in both directions is not the same. Such an application is Internet access.
The Internet is gaining wide-spread use for both homes and offices. Most Internet applications use high speed transfer rates in the downstream direction from the central office (CO) to the remote unit (RU), and lower bit rates in the upstream direction from RU to CO. The transmission is full duplex; the transmit and receive happen simultaneously. Once the connection is established, it is desirable to maintain the connection even during idle periods.
For Internet applications, downstream data transmission rates at any given time depend upon current customer data download requests. This usually does not happen continuously (non-interrupt) during the connection.
FIG. 1
shows the transmit portion of one ADSL modem connected through a channel to the receive portion of another modem. In this system both valid and idle data are treated the same—both forms of data pass through the entire encoding and decoding operations: crc, mux, synch, etc. Because idle data transmission conveys no information, many of the encoding and decoding operations could be eliminated with no decrease in data throughput. However, some form of filler data that does not require modulation/demodulation must be put in its place and a method of controlling system state transitions must be implemented.
SUMMARY OF THE INVENTION
Two methods for reducing computational requirements during idle transmission in digital subscriber line (DSL) modems are presented. Both methods reduce processing power during idle transmission Modulation computations in the transmitter are replaced with low-complexity pseudo-noise (PN) generation techniques that produce an idle signal that is spectrally compatible with xDSL systems. The PN signal is modified to convey the pilot tone information. The phase of the pilot tone is modulated (rotated by 180 degrees) in the transmitter to indicate idle/valid status of the current
ext frame to the remote receiver. After detection of idle status at the receiver, most of the demodulation computations are avoided.
These methods are important because during idle times in an xDSL communication link they alleviate the heavy computational burden associated with transmission of valid data. The greater percentage of time that an xDSL connection is in the idle state, the greater the computational savings. In xDSL systems, many modems are co-located in the telephone company central office where the Internet service provider establishes a connection between the modems to the backbone data network, thus connecting the residential customers to the network. Although many modems may be connected at once, not all are transmitting valid data. Therefore, the method presented provides a mechanism for reducing the required computations, allowing computing resources to be shared among connections using statistical multiplexing.
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Chellali Adam M.
Gatherer Alan
Polley Michael O.
Brady III Wade James
Chin Stephen
Franz Warren L.
Jiang Lenny
Telecky , Jr. Frederick J.
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