System and method for orthogonal spread spectrum sequence generation in variable data rate systems
First Claim
1. A modulation system for use in a spread spectrum communications system, said modulation system being disposed to transmit an information signal, comprising:
- means for selecting a first function from a set of functions in accordance with a selected characteristic of said information signal, said set of functions including a plurality of subsets of functions, wherein a predefined recursive relationship exists among the functions within each of said subsets, said means for selecting including means for preventing selection of more than a single function from each of said subsets, and members of said subsets are orthogonal to members of all other subsets;
means for generating a function signal representative of said first function;
means for generating a pseudorandom noise (PN) signal of a predetermined PN code; and
means for combining said function signal, said PN signal and said information signal, and for providing a resultant first modulation signal.
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Abstract
A method and system for allocating a set of orthogonal PN code sequences of variable length among user channels operative at different data rates in a spread spectrum communication system is disclosed herein. PN code sequences are constructed that provide orthogonality between users so that mutual interference will be reduced, thereby allowing higher capacity and better link performance. In an exemplary embodiment, signals are communicated between a cell-site and mobile units using direct sequence spread spectrum communication signals. Information signals communicated on the cell-to-mobile link channels are encoded, interleaved, and modulated with orthogonal covering of each information symbol. Orthogonal Walsh function codes of varying length are employed to modulate the information signals. Code assignments are made on the basis of channel data rates in a manner which results in improved utilization of the available frequency spectrum. A substantially similar modulation scheme may be employed on the mobile-to-cell link.
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Citations
25 Claims
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1. A modulation system for use in a spread spectrum communications system, said modulation system being disposed to transmit an information signal, comprising:
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means for selecting a first function from a set of functions in accordance with a selected characteristic of said information signal, said set of functions including a plurality of subsets of functions, wherein a predefined recursive relationship exists among the functions within each of said subsets, said means for selecting including means for preventing selection of more than a single function from each of said subsets, and members of said subsets are orthogonal to members of all other subsets; means for generating a function signal representative of said first function; means for generating a pseudorandom noise (PN) signal of a predetermined PN code; and means for combining said function signal, said PN signal and said information signal, and for providing a resultant first modulation signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A spread spectrum modulator for processing first and at least a second digital user information signals in preparation for respective transmission to first and second intended recipient users, comprising:
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means for selecting first and second functions from a plurality of functions in accordance with first and second data rates of said first and second information signals, respectively, said plurality of functions being divided into a plurality of subsets wherein a redefined recursive relationship exists among the functions within each of said subsets, said means for selecting including means for preventing selection of more than a single function from each of said subsets; function generator means for generating first and second Walsh function signals corresponding to said first and second functions; first combiner means for providing a first intermediate modulation signal by combining said first information signal and said first Walsh function signal, and for providing a second intermediate modulation signal by combining said second information signal and said second Walsh function signal; pseudorandom noise (PN) generator means for generating a PN signal of a predetermined code function; second combiner means for providing a first output modulation signal by combining said PN signal and said first intermediate signal, and for providing a second output modulation signal by combining said PN signal and said second intermediate signal. - View Dependent Claims (14)
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15. A signal modulation method for for use in a spread spectrum communication system within which is processed at least a first information signal, comprising the steps of:
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selecting an function from a plurality of functions in accordance with a predefined characteristic of said information signal, said set of functions including a plurality of subsets of functions wherein a predefined relationship exists among the functions within each of said subsets, said step of selecting including the step of preventing selection of more than a single function from each of said subsets; generating an function signal representative of said selected function;
generating a pseudorandom noise (PN) signal of a predetermined PN code;combining said function signal, said PN signal and said first information signal, and providing a resultant first modulation signal. - View Dependent Claims (16, 17, 18, 19)
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20. A method for processing first and second digital user information signals for respective transmission to at least first and second intended recipient users, comprising the steps of:
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selecting first and second orthogonal functions from a plurality of orthogonal functions in accordance with first and second data rates of said first and second information signals, respectively, said orthogonal functions being divided into a plurality of subsets wherein a predefined recursive relationship exists among the orthogonal functions within each of said subsets, said means for selecting including means for preventing selection of more than a single orthogonal function from each of said subsets; generating first and second Walsh function signals corresponding to said first and second orthogonal functions; providing a first intermediate modulation signal by combining said first information signal and said first Walsh function signal, and providing a second intermediate modulation signal by combining said second information signal and said second Walsh function signal; generating a pseudorandom noise (PN) signal of a predetermined code function; providing a first output modulation signal by combining said PN signal and said first intermediate signal, and providing a second output modulation signal by combining said PN signal and said second intermediate signal. - View Dependent Claims (21)
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22. A modulation system for use in a spread spectrum communication system, said modulation system being disposed to receive an information signal, comprising:
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means for selecting an orthogonal function from a set of functions in accordance with a selected characteristic of said information signal, said set of functions including a plurality of orthogonal functions divided into a plurality of subsets wherein a predefined recursive relationship exists among the orthogonal functions within each of said subsets, said means for selecting including means for preventing selection of more than a single orthogonal function from each of said subsets; means for generating an orthogonal function signal representative of said selected orthogonal function; and means for combining said orthogonal function signal and said information signal, and for providing a resultant first modulation signal. - View Dependent Claims (23, 24, 25)
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Specification