Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1998-07-10
2001-04-17
Chin, Stephen (Department: 2634)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S298000, C375S332000, C375S354000
Reexamination Certificate
active
06219386
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data communications, and more particularly, to a system and method for forward error correction using frameless Reed-Solomon coding.
BACKGROUND OF THE INVENTION
The field of data communications typically uses transceivers, or modems, to convey information from one location to another. Digital Subscriber Line (DSL) technology now enables transceivers to communicate rapidly large amounts of data. Transceivers communicate by modulating a baseband signal carrying digital data, converting the modulated digital data signal to an analog signal, and transmitting the analog signal over a conventional wire using techniques that are known in the art. These known techniques include mapping the information to be transmitted into a signal space constellation and slicing the received constellation to recover the transmitted information. The constellation can include both analog and digital information or only digital information.
In the above mentioned communications environment, it is possible that some of the transmitted information could be lost or corrupted. In that event, it is desirable to have a means for error detection and correction. Forward error correction is one well known method of achieving error detection and correction. Error correction codes can be, for example, block codes, cyclic codes, convolutional codes and Viterbi codes.
Reed-Solomon (RS) coding is a widely used cyclic, block coding scheme, particularly suited to demanding applications such as terrestrial broadcasting of digital television, deep space communications, compact disk storage, and data communications over terrestrial lines. RS codes are multi-level codes where the code words are constructed from symbols from a Galios (finite) Field. The code words have the property that is 2 t parity symbols are added to each data word to form a code word, then the code can find and correct up to any t lost symbols. Conventional RS coding requires the use of in-band framing bytes added to the code in order to insure alignment of the RS frame. One of the drawbacks of the aforementioned technique is that the use of in-band framing is wasteful of bandwidth and requires additional circuitry.
Thus, it would be desirable to develop a system in which RS forward error correction may be employed without the need of transmitting additional framing bytes.
SUMMARY OF THE INVENTION
The present invention provides an improvement to Reed-Solomon (RS) coding by allowing a transceiver to send and receive RS encoded frames without the need to send additional framing bytes. This is accomplished by providing a system for data communications comprising a Reed-Solomon (RS) encoder and a counter configured to enable the RS encoder to encode data without the use of framing bits. This task is accomplished by counting a number of timing (or baud) cycles from the end of a pre-existing time stamp and then starting the RS encoder and decoder. The time stamp can be, for example, a Tomlinson exchange frame as is known in the art of data communications, However, any method of determining a suitable place to begin counting the baud cycles can be used to practice the concept of the invention.
For example, a full bandwidth pattern of all ones can be sent, thus signaling the receiver to synchronize on that fill bandwidth pattern and begin RS encoding/decoding. Also included is a mapper designed to map the data into a signal space constellation and a transmitter designed to transmit the signal space constellation.
The system also includes a receiver designed to receive the signal space constellation and a Viterbi decoder and demapper designed to recover the data from the signal space constellation. A Reed-Solomon (RS) decoder configured to decode the data without the use of framing bits by using a counter similar to that described with respect to the encoder is also included. Similarly, the counter is configured to enable the RS decoder to decode the data without the use of framing bits by counting a number of timing cycles from the pre-existing time stamp prior to starting the decoder. Optionally a scrambler and descrambler can be included in order to supply data in a scrambled format. The present invention also enables the devices equipped therewith to maintain synchronization in the event of a signal interruption by employing an equalizer in the receiver, the equalizer designed to cooperate with the counter.
The present invention can also be conceptualized as a method for data communications comprising the steps of supplying data to a Reed-Solomon (RS) encoder and counting a number of timing cycles prior to engaging the RS encoder in order to encode the data without the use of framing bits. The signal is then mapped into a signal space constellation and transmitted over a communication channel. At a receiver, the signal space constellation is received and demapped in order to recover the original data. Prior to engaging a RS decoder a number of timing cycles are counted in order to enable the RS decoder to decode the data without the use of framing bits.
The invention has numerous advantages, a few of which are delineated hereafter, as merely examples.
An advantage of the present invention is that it eliminates the need to send additional framing bytes with the Reed-Solomon frame, thus conserving system resources.
Another advantage of the present invention is that the need for frame synchronizing circuitry in data mode is eliminated.
Another advantage of the present invention is that it is simple in design, reliable in operation, and its design lends itself to economical mass production in modems.
REFERENCES:
patent: 5363408 (1994-11-01), Paik et al.
patent: 5511096 (1996-04-01), Huang et al.
patent: 5583889 (1996-12-01), Citta et al.
patent: 5659578 (1997-08-01), Alamouti et al.
patent: 5835165 (1998-11-01), Keate et al.
Amrany Daniel
Chen Xian-Ying
Langberg Ehud
Scholtz William
Chin Stephen
Deppe Betsy L.
Globespan, Inc.
Thomas Kayden Horstemeyer & Risley
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