Direct-sequence spread-spectrum communication system with asynchronous despreading

• US 5,243,622 A
• Filed: 08/02/1991
• Issued: 09/07/1993
• Est. Priority Date: 08/02/1991
• Status: Expired due to Term

• Current Assignee: Retro Reflective Optics
• Original Assignee: General Dynamics Corporation
• Inventors: Fischer, Jeffrey M., Lux, Paul A.
• Primary Examiner(s): CANGIALOSI, SALVATORE A
• Application Number:
  US07/739,524
• Time in Patent Office: 767 Days
• Field of Search: 375/1, 380/33, 380/34
• US Class Current: 375/147
• CPC Class Codes: H04B 1/70718 with asynchronous demodulation, i.e. not requiring code synchronisation

Abstract

A direct-sequence spread-spectrum communication system having a receiver that despreads a received signal that has been modulated with a pseudonoise code generated by a linear feedback shift register. The receiver despreads the received signal by multiplying it with a limited number of delayed replicas of the received signal. Despreading is thus performed without need for a locally generated pseudonoise code or a synchronizing clock.

Claims

1. A communication system receiver for despreading a direct-sequence spread-spectrum signal having a predetermined chip interval and center carrier frequency, said spread-spectrum signal being modulated with an information signal and being spread by a linear feedback shift register having a plurality of taps, said receiver comprising:

a plurality of delay means, the number of said delay means being equal to the number of said taps, each said delay means for delaying said spread-spectrum signal and to produce a delayed replica; and

multiplication means for multiplying said spread-spectrum signal with each said delayed replica and to produce a despread signal.

2. The communication system receiver described in claim 1 wherein:

each said delay means delays said spread-spectrum signal by a unique integral number of delay units.

3. The communication system receiver described in claim 2 wherein:

each said delay unit is substantially equal to said chip interval.

4. The communication system receiver described in claim 3 wherein:

each said delay unit is equal to an odd number of cycles of said center carrier frequency.

5. The communication system receiver described in claim 1 wherein said multiplication means comprises:

a plurality of multipliers, each corresponding to only one of said delay means.

6. The communication system receiver described in claim 5 further comprising:

antenna means for receiving said spread-spectrum signal and to produce a received spread-spectrum signal;

amplifier means for amplifying said received spread-spectrum signal and to produce an amplified spread-spectrum signal; and

demodulation means for recovering said information signal from said despread signal.

7. A method for despreading a direct sequence spread-spectrum signal having a predetermined chip interval and center carrier frequency, said spread-spectrum signal being modulated with an information signal and being spread by a linear feedback shift register having a plurality of taps, comprising:

forming a plurality of delayed replicas of said spread-spectrum signal, the number being equal to the number of said taps, each delayed by a unique amount of time; and

multiplying said spread-spectrum signal with each said delayed replica.