Signal generator for radio navigation system

• US 4,642,647 A
• Filed: 08/29/1983
• Issued: 02/10/1987
• Est. Priority Date: 08/29/1983
• Status: Expired due to Term

• Current Assignee: Litton Systems Incorporated (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated (Northrop Grumman Corporation)
• Inventors: Knitter, Wayne L., Wu, Yi-Zen, Sturza, Mark A.
• Primary Examiner(s): Blum, Theodore M.
• Assistant Examiner(s): Issing, Gregory C.
• Application Number:
  US06/527,124
• Time in Patent Office: 1,261 Days
• Field of Search: 343/356, 343/357, 343/415, 343/414, 343/407, 343/386, 343/451, 343/5 PN, 364/443, 364/449, 375/115
• US Class Current: 342/415
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

An improved signal generator and method for radio navigation in accordance with systems of the type in which location is determined in accordance with radio fixings with respect to multiple points of reference, each of such points providing a coded transmission. Multiple coded bit sequences are stored in an adddressable read only memory. Phantom signals comprising a plurality of coded sequences are generated by addressing the memory in accordance with preselected sequences. Further, predetermined phase shifts are applied to the coded sequences to facilitate signal detection and associated computational processes.

Claims

1. A multiple code generator for use in a radio navigation system of the type wherein location is determined in accordance with multiple spatially-distributed radio frequency signal fixings, each of said signal fixings comprising a radio frequency signal of preselected coding, said code generator comprising, in combination:

a. a read only memory for storing a plurality of bit sequences, each of said sequences comprising a predetermined code of said navigation system;

b. means coupled to said read only memory for accessing preselected bit sequences;

c. means for applying a predetermined bit rate and phase shift to said sequences, said means including a counter; and

d. means for outputting said preselected bit sequences.

2. A multiple code generator as defined in claim 1 wherein said means for applying a predetermined bit rate and phase shift further includes means for presetting said counter.

3. A multiple code generator as defined in claim 2 wherein the information applied to said counter exceeds the information applied to said read only memory so that fractional code phase shifts may be attained.

4. A method for generating multiple local replica codes for use in a radio navigation system of the GPS type comprising the steps of:

a. storing a plurality of coded bit sequences in a table in a read only memory wherein each of said sequences is a pseudo-noise sequence,

b. accessing preselected bit sequences,

c. outputting said preselected bit sequences under the control of a counter and presetting said counter so that said sequences are output with predetermined phase shifts.

5. A method as defined in claim 4 including the step of arranging said counter so that the phases of said sequences can be shifted by a fraction of a bit.