Synchronizing system for spread spectrum transmissions between small earth stations by satellite via an intermediate hop to a large earth station

• US 4,617,674 A
• Filed: 07/14/1983
• Issued: 10/14/1986
• Est. Priority Date: 07/14/1983
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: RCA Corporation
• Inventors: Schiff, Leonard N., Mangulis, Visvaldis
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Glenny, Raymond C.
• Application Number:
  US06/513,737
• Time in Patent Office: 1,188 Days
• Field of Search: 375/1, 375/34, 375/58, 375/107, 375/108, 375/109, 375/111, 375/114, 375/118, 455/12, 455/51, 370/103, 370/104, 343/7.5
• US Class Current: 375/141
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]

Abstract

A communication system comprising a satellite, a master earth station (MES), and a plurality of small earth stations (SESs) provides signal transmissions addressed and transmittable to a selectable other SES via the satellite, the MES, and then the satellite again. The signal transmissions consist of bit representing pseudo random sequence (PRS) signals PRS_SES which in turn consist of chips arranged in predetermined and identifiable patterns and with the bit and chip occurrence rates C_SES and B_SES of each SES being synchronized with each other as they arrive at the MES. The satellite responds to the signal transmissions from the SESs to retransmit the signal transmissions to the MES, which in turn responds to the signal transmissions from the satellite to amplify and retransmit such signal transmissions back to the satellite again. The satellite again responds to the signal transmissions from the MES to retransmit them to the SESs. The MES and SESs further include apparatus to maintain synchronism between the chip and bit rates of the PRS_SES signals as they arrive at the MES.

Claims

1. In a data transmission system comprising a plurality of small earth stations (SES), a master earth station (MES), and a satellite, a system for transmitting data from a first SES to said MES via said satellite in a first transmission hop and then from said MES to a second SES via said satellite in a second transmission hop and comprising:

a transmitter and a receiver at said first and second SESs for transmitting and receiving a string of time synchronous pseudo random sequence (PRS) signals (PRS_SES) with periodic data pauses therein and with each PRS signal being uniquely coded to each SES, and with each PRS signal representing a data bit of chip rate C and having a bit rate B;

comparing means at said MES for comparing C and B of each PRS signal received from each SES with the chip and bit rate C_M and B_M of a PRS signal transmitted from the MES and received back from the satellite by the MES to generate an error correction command (ECC) signal which defines the instantaneous amount and direction of phase difference between the C and the B of the PRS generated by each SES and C_M and B_M, respectively; and

means for transmitting said ECC signal to said first SES during the pause period of the PRS signal generated by said second SES;

said first SES comprising logic responsive to said ECC signal transmitted from said MES to correct the phase of C and B of the PRS signal generated at said first SES to be synchronized with C_M and B_M at the time of arrival of C, B, C_M, and B_M at the MES.

2. A transmission system as in claim 1 in which each SES comprises means for generating a train of M=N-X data bits at a bit rate equal to N bits per second followed by a pause period of X data bit periods where M>

>

X; and

in which said MES further comprises;

means for detecting the pause period in each PRS_SES ; and

means for inserting said ECC signal into the pause period of said PRS signal generated by said second SES for subsequent transmission to said first SES; and

in which said first SES comprises logic for detection of said ECC signal transmitted in the pause period of the PRS transmission from said second SES via the MES and the satellite and the decoding of the ECC signal contained therein to correct the phase of the chip and bit rates C_A and B_A of said first SES.

3. A communication network comprising:

a satellite;

a master earth station (MES);

a plurality of small earth stations (SES) each comprising logic for generating and transmitting in a first transmission hop to said MES via said satellite a stream of pseudo random sequence (PRS) signals PRS_SES having a repetition rate B_SES and each consisting of a plurality of chips occurring at a chip rate C_SES, and arranged in patterns unique to said each SES, and with each PRS signal representing a bit and further with said streams of PRS signals each having periodic pause periods therein consisting of a predetermined number of bit periods for receiving and carrying error correction command (ECC) signals;

said MES comprising;

means for generating, transmitting and then receiving back from said satellite a PRS signal PRS_M having a chip and bit clock rate C_M and B_M, respectively;

said MES further comprising means for receiving said PRS signals (PRS_SES) and for generating an ECC signal in response to the phase difference between C_M and the C_SES of each SES and the phase difference between B_M and the B_SES of each SES indicating the amount and direction of such phase differences;

said MES further comprising logic for detecting and identifying the occurrence of the periodic pause period of each SES and for inserting in such pause periods the ECC signal required for the SES to which the transmissions from said each SES are addressed; and

each of said SESs being responsive to an ECC addressed thereto to correct the phases of the C_SES and the B_SES of the PRS_SES unique thereto so that said C_SES and said B_SES are synchronized with C_M and B_M, as returned from the satellite, at the MES.

4. A spread-spectrum communications arrangment comprising:

a first earth station including a first spread spectrum transmitter transmitting in a first frequency band a first spread spectrum signal carrying first information encoded with a first pseudorandom code, and a first spread spectrum receiver operating in a second frequency band and responsive to a second spread-spectrum signal encoded with a second pseudorandom code for receiving information;

a second earth station including a second spread spectrum transmitter transmitting in said first frequency band a third spread-spectrum signal carrying second information encoded with a third pseudorandom code and a second spread spectrum receiver operating in said second frequency band and responsive to a fourth spread-spectrum signal encoded with a fourth pseudorandom code for receiving information;

an earth satellite including transponding means operating in said first and second frequency ranges for receiving a plurality of spread-spectrum signals in said first frequency band from earth stations, and for retransmitting said plurality of spread-spectrum signals in said second frequency band to earth stations, whereby retransmission of a plurality of spread-spectrum signals with unsynchronized bit and chip rates undesirably results in interference which reduces the utility of the system;

a master earth station including a third spread-spectrum receiver operating in said second frequency band and responsive to said first and third pseudorandom codes for receiving said first and second information, and also including a third spread-spectrum transmitter operating in said first frequency band for transmitting a fifth spread-spectrum signal in said first frequency band, the transmissions of said fifth spread-spectrum signal being encoded for retransmitting said second information with said second pseudorandom code for making said second information from said second earth station available to said first earth station, and for retransmitting said first information with said fourth pseudorandom code for making said first information from said first earth station available to said second earth station;

a master earth station fourth transmitter for transmitting to said earth satellite at said first frequency a master synchronization signal having bit and chip rates for retransmission of said master synchronization signal in said second frequency band to said first, second and master earth stations;

first synchronization error signal generating means coupled for receiving from said satellite said master synchronization signal and said first spread spectrum signal, for generating a first synchronization control signal from the instantaneous difference in chip and bit synchronization therebetween;

first earth station synchronization means responsive to said first synchronization control signal for correcting said bit and chip rates of said first spread spectrum transmitter in response to said first synchronization control signal to maintain bit and chip synchronism of said first spread spectrum signal transponded into said second frequency band in instantaneous synchronism with the bit and chip rates synchronism of said master synchronization signal in said second frequency band;

second synchronization error signal generating means coupled for receiving from said satellite said master synchronization signal and said third spread spectrum signal, for generating a second synchronization control signal from the instantaneous difference in chip and bit synchronization therebetween; and

second earth station synchronization means responsive to said second synchronization control signal for correcting said bit and chip rates of said second spread spectrum transmitter in response to said second synchronization control signal to maintain bit and chip synchronism of said second spread spectrum signal transponded into said second frequency band in instantaneous synchronism with the bit and chip rates of said master synchronization signals in said second frequency band, whereby bit and chip synchronization is maintained between said first and second spread-spectrum signals transponded into said second frequency band thereby reducing said undesirable interference, whereby if said first and second synchronization error signal generating means are located at said first and second earth station locations, respectively, additional receivers are required at said first earth station for receiving from said satellite said master synchronization signal and said first spread spectrum signal, and at said second earth station for receiving from said satellite said master synchronization signal and said third spread spectrum signal, thereby undesirably increasing the number of receivers required at each earth station, wherein the improvement lies in that;

said first and second synchronization error signal generating means are located at said master earth station whereby a single master synchronization signal receiving means is used in common and thereby reduces to one the number of receivers required for receiving said master synchronization signal, and also eliminating the need for said additional receivers required at said first earth station for receiving said first spread spectrum signal and at said second earth station for receiving said third spread spectrum signal.

5. An arrangement according to claim 4 wherein said first and second earth station synchronization means are located at said first and second earth stations, respectively, said arrangement further comprising multiplexing means whereby said first synchronization control signal is sent from said master earth station to said first earth station by multiplexing with said second information.

6. An arrangement according to claim 5 wherein said multiplexing means comprises time-division multiplexing means.