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Assignee3Com Corporation
InventorsCarl H. Alelyunas, Scott A. Lery, Vladimir Parizhsky
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The present invention provides a method of generating a signal that may be used to determine the characteristic response of a communication channel that utilizes the public Digital Telephone Network (DTN). The channel includes the DTN, which may have Network Digital Attenuators (NDA) and/or Robbed Bit Signalling (RBS), and a Digital-to-Analog Converter (DAC), (also known as a codec), as well as the analog characteristics of the local loop, typically a twisted pair of copper wires. The present invention provides a method and apparatus to determine the optimal sampling instant of the received data stream. The present invention provides a probing signal that is well-suited for use in determining the channel's response to a known sequence of PCM codes used as data symbols. This is especially useful in so-called PCM modulation schemes that utilize the DTN, where knowledge of network and DAC distortion predicates the selection of available PCM codes used to represent data. This information is also useful when the data receiver, or PCM modem, makes determinations of which codes were actually sent.
A method of probing a communication channel between a digital data source and an analog subscriber connected to a digital telephone network by an analog loop comprising the steps of:
A code generator for generating a probing signal for transmission over a communication channel between a digital data source and an analog subscriber connected to a digital telephone network by an analog loop, wherein said probing signal consists of a sequence of PCM codewords, said codeword sequence corresponding to analog voltages having a plurality of positive and negative values with regions of zero values therebetween, said regions comprising a centrally located region of intervening zero values and a plurality of lateral regions of intervening zero values, and wherein said sequence of PCM codewords is generated from at least one PCM codeword magnitude and a kernel sequence having elements selected from the group of +1, -1 and 0 by inserting said at least one PCM codeword magnitude in signed accordance with the elements +1 and -1 of the kernel sequence.
Dependencies are inferred from the claim text.