Digital Modulation System Using Modified Orthogonal Codes To Reduce Autocorrelation
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Accused Products
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.
37 Citations
31 Claims
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1-11. -11. (canceled)
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12. An M-ary orthogonal keying (MOK) modulator comprising:
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a serial-to-parallel converter configured to generate data symbols based on received input data bits; a first modulator configured to (i) receive a first n bits of each data symbol and (ii) select a corresponding length q orthogonal code modified by a complementary code based on the n bits; a second modulator configured to (i) receive a subsequent m bits of each data symbol and (ii) select a corresponding length r orthogonal code modified by the complementary code based on the m bits; a first logic device configured to, if a first subsequent bit of the data symbol is a first predefined value, change polarity of the modified length q orthogonal code generated by the first modulator; a second logic device configured to, if a second subsequent bit of the data symbol is a second predefined value, change polarity of the modified length r orthogonal code generated by the second modulator; a first mixer configured to modulate the modified length q orthogonal code with a carrier frequency; a second mixer configured to modulate the modified length r orthogonal code with the carrier frequency shifted by 90 degrees; wherein the modulated modified length q orthogonal code and the modulated modified length r orthogonal code are combined and transmitted. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. An M-ary orthogonal keying (MOK) demodulator comprising:
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a first mixer configured to demodulate an In-Phase (I) component of a received signal; a second mixer configured to demodulate a Quadrature (Q) component of a received signal; a first low pass filter configure to filter the I component of the received signal and a second low pass filter configured to filter the Q component of the received signal; a first correlator configured to correlate the I component of the received signal against a code set of M modified orthogonal codes, M>
1, the code set being produced by modifying an orthogonal code with a complementary code;a second correlator configured to correlate the Q component of the received signal against the code set of M modified orthogonal codes, wherein the first correlator and the second correlator are configured to correlate the received signal to the modified orthogonal code in the code set that produces the highest correlation magnitudes; and a decoder to decode the modified orthogonal codes into corresponding data bits. - View Dependent Claims (27, 28, 29, 30, 31)
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Specification