Programmable time invariant coherent spread symbol correlator
First Claim
1. A signal processing apparatus comprising:
- a plurality N of first means for correlating a first signal with a second signal and generating an output representative of the correlation between said first and second signals;
second means for applying said first signal in parallel to each of said first means; and
third means for continuously applying said second signal to each respective one of said first means at a time that is offset relative to the time of application of said second signal to any other respective one of said first means.
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Abstract
An hybrid array correlator is configured of a cascaded array of individually identical correlator cells, through which a preselectable reference symbol sequence, identifiable with a symbol to be acquired, is successively clocked, from cell to cell and then recirculated back to the beginning or first cell of the array. The physical span of the correlator covers one complete symbol time, with each cell imparting a one-half chip delay to the reference spreading sequence as it is clocked through the correlator. Yet, because of the recirculation of the reference spreading sequence from the last cell back to the first cell, the electrical span of the correlator is effectively infinite or time invariant. An incoming unknown symbol sequence capable of being acquired is applied in parallel to all the cells of the correlator array. Regardless of the time of arrival or phase of this incoming spreading sequence, in one of the cells of the correlator, the reference spreading sequence will have a phase that is effectively aligned with that of the incoming signal and, assuming that the incoming symbol sequence is associated with that matched filter, this particular correlator cell will produce a strong correlation output at the completion of the duration of the symbol span, thereby indicating that the symbol has been detected.
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Citations
20 Claims
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1. A signal processing apparatus comprising:
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a plurality N of first means for correlating a first signal with a second signal and generating an output representative of the correlation between said first and second signals; second means for applying said first signal in parallel to each of said first means; and third means for continuously applying said second signal to each respective one of said first means at a time that is offset relative to the time of application of said second signal to any other respective one of said first means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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9. A signal processing apparatus according to claim 8, wherein each of said first means includes means for producing first and second correlation outputs A(t) and B(t) defined in accordance with the relationships:
- ##EQU1## where Ts is the symbol time span of said first signal.
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10. A signal processing apparatus according to claim 9, wherein each of said first means comprises a plurality of switches, each of which has a control input selectively coupled to receive, as said second signal, a delayed version of one of the signals Si(t), Si(t), Sq(t), Sq(t), a signal input selectively coupled to receive, as said first signal, one of the signals I(t), I(t), Q(t), Q(t), and an output, the outputs of said switches being selectively combined and coupled to integrator means for producing said outputs A(t) and B(t).
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11. A signal processing apparatus according to claim 10, wherein each of said switches is formed of a field effect transistor, one of the source and drain of which corresponds to its signal input, the other of the source and drain of which corresponds to its output, and the gate electrode of which corresponds to its control input.
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12. An apparatus for encoding and transmitting coherent communication signals comprising:
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first means for receiving information signals and encoding said information signals into respective groups of intermediate signals which have maximized and equalized energy spacing with respect to one another; second means, coupled to said first means, for generating for each of said groups of intermediate signals a coherent plurality of symbols in the form of respective spreading sequences and including means for controllably varying the spreading sequences by way of which the respective symbols are formed, so that for successive prescribed time intervals each symbol is formed of a respectively different sequence; and third means, coupled to said second means, for modulating an output carrier by spreading sequences of said symbols. - View Dependent Claims (13, 14)
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15. A communication system comprising:
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at a transmitting station; first means for receiving information signals and encoding said information signals into respective coherent groups of intermediate signals which have maximized and equalized energy distance with respect to each other; second means, coupled to said first means, for generating for each of said groups of intermediate signals a plurality of symbols in the form of respective spreading sequences and including means for controllably varying the spreading sequences by way of which the respective symbols are formed, so that for successive prescribed time intervals each symbol is formed of a respectively difference sequence; and third means, coupled to said second means, for modulating an output carrier by the spreading sequences of said symbols and causing said carrier to be transmitted to a receiving station; at a receiving station; fourth means, for demodulating a received signal to obtain said respective spreading sequences; fifth means, coupled to said fourth means, for correlating said obtained spreading sequences with respective ones of a set of reference spreading sequences defining the symbols capable of being transmitted; and sixth means, coupled to said fifth means, for deriving, from the correlated outputs of said fifth means, respective coherent groups of said intermediate signals and recovering therefrom said information signals. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification