Patent ID: 7428273

Claim:
A preamble detector for QPSK, comprising: an input for receiving digitized input I and Q samples, wherein said input I and Q samples represent a reconstructed base band form of QPSK modulation; a carrier derotation means for aligning said incoming signal phases with I and Q axes; sign means for producing a ‘1’ if said I and Q samples are greater than or equal to 0, or a ‘0’ if said samples are less than 0; sample delay means for providing chains of N-sample delays to yield one symbol-length delay for both I and Q; a differential decoder for combining a current symbol state with a prior symbol state to yield a differentially decoded symbol value; a multiplexer for alternating between a least-significant and a most-significant bit of said differentially decoded symbol values; and a preamble shift register containing a serial-sequential representation of a received data stream.