M-ary Orthogonal Keying System
AssigneeLSI Corporation
InventorD.J. Richard van Nee
Life of this patent
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Abstract
A digital modulation system provides enhanced multipath performance by using modified orthogonal codes with reduced autocorrelation sidelobes while maintaining the cross-correlation properties of the modified codes. For example, the modified orthogonal codes can reduce the autocorrelation level so as not to exceed one-half the length of the modified orthogonal code. In certain embodiments, an M-ary orthogonal keying (MOK) system is used which modifies orthogonal Walsh codes using a complementary code to improve the auto-correlation properties of the Walsh codes, thereby enhancing the multipath performance of the MOK system while maintaining the orthogonality and low cross-correlation characteristics of the Walsh codes.
Claims20
1-11. (canceled)
A method for modulating information bits over a radio frequency communication channel, comprising:
- allocating selected ones of a set off information bits into two or more groups of code bits,
- based on the two or more groups of code bits, choosing one of M modified orthogonal codes, each of the M modified orthogonal codes based on an orthogonal code and a complementary code combination, and
- modulating, by a transmitter, the phase of a complex carrier signal in accordance with the chosen modified orthogonal code,
- wherein the chosen one of the M modified orthogonal codes is defined according to the expression:
- c={ej(Φ1+Φ2+Φ3+Φ4), ej(Φ1+Φ3+Φ4), ej(Φ1+Φ2+Φ4), −ej(Φ1+Φ4), ej(Φ1+Φ2+Φ3), ej(Φ1+Φ3), −ej(Φ1+Φ2), ejΦ1},
- where Φi correspond to phase angles of code bits associated with the ith group of code bits.
A method for demodulating a received signal that conveys information bits over a radio frequency communication channel, comprising the steps of:
- correlating the received signal against a code set of M symbols, M>1, the code set being produced by modifying an orthogonal code with a complementary code, and
- selecting one of the M symbols in the code set based upon the correlating step,
- wherein the chosen one of the M modified orthogonal codes is defined according to the expression:
- c={ej(Φ1+Φ2+Φ3+Φ4), ej(Φ1+Φ3+Φ4), ej(Φ1+Φ2+Φ4), −ej(Φ1+Φ4), ej(Φ1+Φ2+Φ3), ej(Φ1+Φ3), −ej(Φ1+Φ2), ejΦ1},
- where Φi correspond to phase angles of code bits associated with the ith group of code bits;
- and
- associating selected ones of two or more groups of code bits with a set of the information bits.
Dependencies are inferred from the claim text.