Apparatus for synchronizing spread spectrum transmissions from small earth stations used for satellite transmission

• US 4,587,661 A
• Filed: 03/04/1983
• Issued: 05/06/1986
• Est. Priority Date: 03/04/1983
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: RCA Corporation
• Inventors: Schiff, Leonard N.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Chin, Stephen
• Application Number:
  US06/472,256
• Time in Patent Office: 1,159 Days
• Field of Search: 375/1, 375/115, 375/106, 375/109, 370/104, 370/107, 343/5 PN, 455/12, 371/42, 371/47
• US Class Current: 375/141
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A low-power, spread spectrum synchronized communication system employing a satellite which continuously and iteratively re-transmits a PRS signal PRS_m from a master earth station having a chip rate C_m and a bit rate B_m and comprising a plurality of ground stations each including a transmitter for transmitting a first PRS signal (PRS_G) unique thereto and having a first chip rate C_G and a first bit rate B_G and a receiver for receiving and identifying PRS_G after being returned by the satellite as PRS_Gr with a chip rate C_Gr and a bit rate B_Gr. Also provided is a phase difference detector responsive to C_m and C_Gr to periodically produce a signal representative of the change of phase difference thereof and a frequency changing circuit responsive to such signal to change the chip rate C_Gr by an amount which will cause the phase of C_Gr to approach the phase of C_m at a given rate.

Claims

1. A communication system, employing a satellite which continuously and interatively re-transmits a pseudo-random sequence signal PRS_m having a chip rate C_m and a bit rate B_m, said system comprising:

a plurality of ground stations each having a transmitter and a receiver;

means for transmitting a first pseudo-random sequence signal PRS_G having a first chip rate C_G and a first bit rate B_G from at least one ground station to said satellite;

means at said at least one ground station for receiving and identifying PRS_G after being returned by said satellite as PRS_Gr with a chip rate C_Gr ;

means at said at least one ground station for receiving and identifying PRS_m ;

means responsive to the phase difference between C_m and C_Gr to produce a signal value representative thereof every time period τ

; and

means responsive to said signal value to change the chip rate C_Gr by an amount which will cause the phase of C_Gr to approach the phase of C_m at a rate which will approximate the phase of C_m at the end of the next time period τ

.

2. A communication system employing a satellite which continuously and iteratively re-transmits a pseudo-random sequence signal having a chip rate C_m and a bite rate B_m, said system comprising:

a plurality of ground stations each comprising;

means for transmitting a first pseudo-random sequence signal PRS_G unique thereto and have a first chip rate C_G and a first bit rate B_C and for receiving and identifying PRS_G after being returned by said satellite as PRS_Gr with a chip rate C_Gr and a bit rate B_Gr ;

means responsive to C_m and C_Gr to periodically produce a signal representative of the phase difference therebetween; and

means responsive to said signal to change the phase of C_G in a direction which will cause the phase of C_Gr to approach the phase of C_m.

3. A receiver in a communications system employing a satellite for receiving and retransmitting pseudo random sequence (PRS) signals from said receiver and having logic for iteratively transmitting master PRS signal PRS_m having a chip rate C_m and a bit rate B_m, said receiver comprising:

means for transmitting a first PRS signal PRS_G having a first chip rate C_G and a first bit rate B_G ;

means for receiving and identifying PRS_G after being returned by said satellite as PRS_Gr having a chip rate C_Gr and a bit rate B_Gr ;

means for receiving and identifying PRS_m ;

means responsive to C_Gr and C_m to produce a signal representative of the phase difference therebetween every time period τ

;

means responsive to successive phase differences between C_Gr and C_m to determine the frequency difference between C_Gr and C_m ; and

means responsive to said frequency difference to change the chip rate C_Gr by an amount which will cause the phase of C_Gr to change by an amount which will cause the phase of C_Gr to approach the phase of C_m at a given rate.

4. In a commmunication system employing at least one ground station and a satellite having a transponder for receiving and re-transmitting pseudo random sequence (PRS) signals transmitted from said at least one ground station, and logic for iteratively transmitting a master PRS signal PRS_m having a chip rate C_m and a bit rate B_m, a method for synchronizing the chip and bit rate of the PRS_m and the PRS signal retransmitted at said satellite and comprising the steps of:

transmitting from said at least one ground station a first PRS signal PRS_G having a first chip rate C_G and a first bit rate B_G ;

receiving and identifying PRS_G after being returned by said satellite as PRS_Gr with a chip rate C_Gr and a bit rate B_Gr ;

receiving and identifying PRS_m at said at least one ground station;

comparing the phases of C_m and C_Gr to produce a signal representative of the difference therebetween every time period τ

; and

changing the chip rate C_Gr in response to said signal by an amount and in a direction which will cause the phase of C_Gr to appraoch the phase of C_m.

5. A commmuncation system as in claim 4 in which the step of comparing the phases of C_m and C_Gr comprises the steps of:

comparing C_m and C_Gr every time period τ

to periodically produce a signal representative of the phase difference thereof; and

computing the frequency difference between C_Gr and C_m by comparing the differences between successive phase differences of C_Gr and C_m.