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Asynchronous samples data demodulation system

  • US 5,414,730 A
  • Filed: 12/21/1993
  • Issued: 05/09/1995
  • Est. Priority Date: 12/21/1993
  • Status: Expired due to Term
First Claim
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1. Apparatus for acquiring and demodulating burst of long PN coded spread spectrum signals having known data bit symbol and chip times and length but no preamble synchronizing signals, comprising:

  • analog receiver means for receiving blocks of the long burst of PN coded signals and producing a digital output representative of a plurality of data bits defined by a larger plurality of chips,correlator means N chips wide coupled to the output of said receiver means for producing a parallel partially despread block output N chips wide, where N is a small fractional part of the total number of chips in a data bit,coherent accumulating means coupled to the output of said correlator means for producing in real time once each bit symbol time Ts a plurality N of preliminary soft decision data, at least one soft decision being indicative of the proper PN replica code alignment and the encoded bit of data received during the previous bit symbol time,buffer storage mean coupled to the output of said coherent accumulation means for receiving and storing the soft decision data representative of the bursts of PN coded signals,logic selection mean coupled to the buffer storage means for selecting relevant soft decision data indicative of the best estimate of the PN replica code and the encoded data,said buffer storage means comprising means for determining the start of a burst of PN coded carrier signals, anddigital demodulation means coupled to the output of said logic selection means and to said means for determining the start of a burst of PN coded carrier signals for demodulating said soft decision data and producing a final hard best estimate data output.

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