Equalizer with decision feedback frequency tracking and bit decoding for spread spectrum communications
A spread spectrum communications system adapted to receive simultaneous signals from multiple transmitters, separates frequency error and equalizes and decodes continuous streams of data sets from a plurality of matched filters with frequency correction and which sorts through data and successfully decodes data bits. The spread spectrum communications system includes a transmitter and a receiver. The receiver includes an RF receiver. At least one PNB matched filter receives signals from the RF receiver. A plurality of frequency shifters receives a signal from the at least one PNB matched filter. A plurality of PNA matched filters receives data from the at least one PNB matched filter and the plurality of frequency shifters. An equalizer/decoder receives signals from the plurality of PNA matched filters.
1. A spread spectrum communications system, comprising:
(A) a transmitter, said transmitter further comprising:
(1) a data source;
(2) a first mixer spreading data from said data source with a first pseudo noise source (PNA);
(3) a second mixer spreading data from said first mixer with a second pseudo noise source (PNB);
(4) an RF transmitter;
(B) a receiver, said receiver further comprising:
(1) an RF receiver;
(2) at least one PNB matched filter receiving signals from said RF receiver;
(3) a plurality of frequency shifters, receiving a signal from said at least one PNB matched filter;
(4) a plurality of PNA matched filters receiving data from said at least one PNB matched filter and said plurality of frequency shifters; and
(5) an equalizer/decoder receiving signals from said plurality of PNA matched filters.
2. A spread spectrum communications system, as recited in claim 1 , wherein said PNA pseudo noise source provides a variable length code sequence.
3. A spread spectrum communications system, as recited in claim 1 , wherein said PNB pseudo noise source provides a fixed length code sequence.
4. A spread spectrum communications system, as recited in claim 1 , wherein said first mixer/multiplier spreads said data from said data source with a variable PN code PNA.
5. A spread spectrum communications system, as recited in claim 1 , wherein said second mixer/multiplier spreads said data from said first mixer with a fixed length PN code PNB.
6. A spread spectrum communications system, as recited in claim 1 , wherein said PNB matched filter further comprises a set of coefficients correlated to said PNB pseudo noise source.
7. A spread spectrum communications system, as recited in claim 1 , wherein said plurality of frequency shifters are offset from each other by one or more degrees.
8. A spread spectrum communications system, as recited in claim 1 , wherein said PNA matched filters are correlated to said PNA pseudo noise source.
9. A spread spectrum communications system, as recited in claim 1 , wherein said PNB matched filters are correlated to said PNB pseudo noise source.
10. A spread spectrum communications system, as recited in claim 1 , wherein said equalizer/decoder selects an advantageous signal from said received signals from said plurality of PNA matched filters.
11. A spread spectrum communications system, as recited in claim 1 , wherein said equalizer/decoder performs the steps consisting of:
(A) initializing an update magnitude;
(B) forming a complex equalization point;
(C) scaling and rotating said equalization point into position;
(D) forming a decision boundary to decode bits;
(E) generating an output bit along with an error vector normalized to the origin; and
(F) updating angle and magnitude parameters for the next bit.