Digital equalization method and apparatus
First Claim
1. A digital equalizer for use with a spread spectrum communications system, said digital equalizer comprising:
- data input means for receiving an input signal comprising a correlated output signal corresponding to a complex I and Q-channel digital signal that has a data phase associated with a non-dispersive channel and a random phase associated with a dispersive channel;
time delay means for delaying the input signal to produce a time delayed input signal;
demodulation means for determining the data phase contained in the input signalfirst combining means for combining the time delayed input signal with the data phase of the input signal to produce an estimated matched filter signal;
accumulating means for computing an accumulated estimated matched filter signal;
second combining means for combining the correlated output signal with the accumulated matched filter signal to eliminated the random phase contained in the correlated output signal;
integrating means for integrating the correlated output signal to increase the signal to noise ration thereof and for providing a time equalized signal.
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Accused Products
Abstract
A digital equalizer and equalization method for a spread spectrum communication link that has a dispersive channel and other systems that process signals having a sufficient degree of redundancy in time and/or phase. No training signal is required, except for an initialization bit sequence. The receiver incorporating the equalizer uses correlation over a bit time between a received signal, that includes data modulation, and a locally generated spreading signal that does not. The output of the correlator is a set of complex digital samples (I and Q-channel) taken at the spreading sequence bit rate. In the absence of multipath dispersion, there is perfect cross-correlation function, and hence only one large sample per transmitted data symbol. With multipath dispersion, the received energy is spread over two or more samples of the correlation. The equalizer combines the signal energy contained in the multiple output samples, converting the concatenation of the channel and equalizer into an equivalent nondispersive channel. The equalizer uses the output of its demodulator function to convert the data bearing signals into a known signal structure, which is used to determine the (unknown) channel impulse response. The equalizer employs optimum filtering of the individual correlation samples averaged over many bit times, to determine a set of multiplicative weights that time and phase align the samples so that they are coherently added. The equalizer improves the effective signal to noise ratio to a point that is close to the theoretical nondispersive channel without increasing signal power or reducing data rate.
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Citations
15 Claims
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1. A digital equalizer for use with a spread spectrum communications system, said digital equalizer comprising:
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data input means for receiving an input signal comprising a correlated output signal corresponding to a complex I and Q-channel digital signal that has a data phase associated with a non-dispersive channel and a random phase associated with a dispersive channel; time delay means for delaying the input signal to produce a time delayed input signal; demodulation means for determining the data phase contained in the input signal first combining means for combining the time delayed input signal with the data phase of the input signal to produce an estimated matched filter signal; accumulating means for computing an accumulated estimated matched filter signal; second combining means for combining the correlated output signal with the accumulated matched filter signal to eliminated the random phase contained in the correlated output signal; integrating means for integrating the correlated output signal to increase the signal to noise ration thereof and for providing a time equalized signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of digitally equalizing a data symbol transmitted using a spread spectrum communications system, said method comprising the steps of:
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processing the data symbol to determine its phase; time-delaying the data symbol; combining the phase with the time-delayed data symbol to strip the phase from time-delayed symbol; accumulating the combined signal to produce a matched filter signal; combining the matched filter signal with the non time-delayed data symbol to produce a combined signal; and integrating the combined signal to produce an equalized signal. - View Dependent Claims (11, 12, 13, 14, 15)
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Specification