Pulse or digital communications – Pulse width modulation
Reexamination Certificate
1998-11-24
2001-06-12
Pham, Chi (Department: 2631)
Pulse or digital communications
Pulse width modulation
C375S316000, C375S286000
Reexamination Certificate
active
06246718
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of decoding digital data for transmission over a medium. More specifically, the present invention relates to the decoding of a bit sequence transmittal over Plain Old Telephone Service (POTS) wiring.
BACKGROUND
Local Area Network (LAN) standards and products have not significantly penetrated the home computing market for a number of reasons, including the lack of perceived need and the required installation of special cabling, which is difficult within a residential household. As multiple personal computers (PCs) are becoming increasingly common within households, the notion of implementing a LAN within a residential environment is gaining in popularity. Specifically, the ability to share information between multiple PCs, and to share resources such as printers and modems, is becoming increasingly attractive to home computer users. In particular, the ability to achieve shared, high-speed Internet access by a number of computers within a household is becoming important as multiple users within a residence may wish simultaneously to access the Internet.
One economical method of creating a LAN within a residential household proposes using the existing telephone wiring within the residence (POTS wiring) as the medium over which the LAN is implemented. Such wiring typically comprises unshielded, twisted-pair (UTP) telephone cable and may comprise either Category 1 or Category 2 cable, as defined by the EIA/TIA 568 specification. The use of such residential telephone wiring poses a number of problems in that the transmission of data signals must occur over an arbitrary, unterminated wiring system, with unknown electrical characteristics. This results in impedance mismatches. The lack of termination also contributes to the persistent reflection of signals and unpredictable peaks and valleys in frequency response within a band of interest. The power splitting effect of star configurations, which are commonly found in residential wiring, attenuate the levels of signal features whose duration is short compared to the propagation delay of the wire branches.
A LAN implemented over residential telephone wiring may also be required to coexist with the POTS service, and to be FCC part 68 compliant, which dictates the use of signals with no frequency components below 270 kHz and transport levels below 178 mV.
SUMMARY OF THE INVENTION
According to the invention, there is provided a method of decoding a symbol having a time duration indicative of a bit sequence, the time duration be determined by first and second delimiters. The decoding method commences when the first delimiter is detected, whereafter a timer is initiated. Detection of the second delimiter is prevented for a predetermined blanking interval so as to prevent detection of reflections resulting from the propagation of the first delimiter over the carrier medium. The second delimiter is then detected after expiration of the blanking interval. In one embodiment, at least one bit of the bit sequence may be decoded utilizing the polarity of the second delimiter.
The invention extends to a decoder that implements the above methodology.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows.
REFERENCES:
patent: 5790495 (1998-08-01), Kimura et al.
patent: 5856980 (1999-01-01), Doyle
patent: 5930303 (1999-07-01), Walker
patent: 6064697 (2000-05-01), Yoshikawa
Graham Martin H.
Webber, Jr. Harold H.
Bayard Emmanuel
Blakely & Sokoloff, Taylor & Zafman
Pham Chi
Tut Systems, Inc.
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