Modulation system for spread spectrum CDMA communiction
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United States of America Patent
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Sep 16, 1997
Grant Date -
N/A
app pub date -
Jun 6, 1995
filing date -
Nov 24, 1992
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Abstract
The OCDMA waveform of the present invention uses bi-phase PN modulation (BPSK PN chip modulation) in conjunction with MPSK or MQASK data modulation (QPSK data modulation is one preferred embodiment) to increase bandwidth efficiency. The number of orthogonal users that can be placed on a single carrier is equal to, at most, the length of the orthogonal binary sequence. The Radamacher-Walsh (RW) sequence chip rate must be 4.sup.n times the symbol rate (where n is a positive integer) since the symbol transitions must be synchronized to the RW period to guarantee orthogonality of the multiple users when data transitions are present. The symbol rate for QPSK modulation is one-half that for BPSK modulation. As a result, twice as many orthogonal functions are available for a given clock rate for QPSK as for BPSK modulation. That is, an OCDMA system with QPSK data can support twice as many users in a given bandwidth as an OCDMA system with BPSK data.
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