M-ary orthogonal keying system
DCFirst Claim
1. A method for modulating information bits over a radio frequency communication channel, comprising:
- grouping a number of information bits,based on the grouping, choosing one of M modified orthogonal codes that are produced by modifying an orthogonal code with a complementary code, andmodulating, with a modulator, the phase of a complex carrier signal in accordance with the chosen modified orthogonal code,wherein the complementary code is determined according to the expression;
c={ei(Φ
1+Φ
2+Φ
3+Φ
4), ei(Φ
1+Φ
3+Φ
4), ei(Φ
1+Φ
2+Φ
4), −
ei(Φ
1+Φ
4), ei(Φ
1+Φ
2+Φ
3), ei(Φ
1+Φ
3), −
ei(Φ
1+Φ
2), eiΦ
1},where Φ
i correspond to phase angles of code bits.
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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.
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Citations
32 Claims
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1. A method for modulating information bits over a radio frequency communication channel, comprising:
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grouping a number of information bits, based on the grouping, choosing one of M modified orthogonal codes that are produced by modifying an orthogonal code with a complementary code, and modulating, with a modulator, the phase of a complex carrier signal in accordance with the chosen modified orthogonal code, wherein the complementary code is determined according to the expression;
c={ei(Φ
1+Φ
2+Φ
3+Φ
4), ei(Φ
1+Φ
3+Φ
4), ei(Φ
1+Φ
2+Φ
4), −
ei(Φ
1+Φ
4), ei(Φ
1+Φ
2+Φ
3), ei(Φ
1+Φ
3), −
ei(Φ
1+Φ
2), eiΦ
1},where Φ
i correspond to phase angles of code bits.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method for demodulating, with a demodulator, a received signal that conveys information bits over a radio frequency communication channel, comprising the steps of:
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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, andselecting one of the M symbols in the code set based upon the correlating step, wherein the complementary code used to modify the orthogonal code set is determined according to the expression;
c={ei(Φ
1+Φ
2+Φ
3+Φ
4), ei(Φ
1+Φ
3+Φ
4), ei(Φ
1+Φ
2+Φ
4), −
ei(Φ
1+Φ
4), ei(Φ
1+Φ
2+Φ
3), ei(Φ
1+Φ
3), −
ei(Φ
1+Φ
2), eiΦ
1},where Φ
i correspond to phase angles of code bits.- View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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Specification