System and method employing two hop spread spectrum signal transmissions between small earth stations via a satellite and a large earth station and structure and method for synchronizing such transmissions

• US 4,532,635 A
• Filed: 08/19/1983
• Issued: 07/30/1985
• Est. Priority Date: 08/19/1983
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: RCA Corporation (General Electric Company)
• Inventors: Mangulis, Visvaldis
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US06/524,542
• Time in Patent Office: 711 Days
• Field of Search: 375/1, 375/107, 375/109, 375/115, 375/3, 375/4, 455/12, 455/13, 343/7 PL, 343/353, 343/358, 370/104, 370/107
• US Class Current: 375/141
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]

Abstract

In a data communication system including a plurality of small earth stations (SES), a satellite, and a master earth station (MES), a method of transmitting signal transmissions, each consisting of a series of bit representing pseudo random sequences (PRS), each consisting of N time synchronous chips between the SESs. The steps of the method include generating at selected SESs a stream of PRS signals having bit and chip rates B_SES and C_SES and having pause periods that occur periodically in the stream of PRS signals, transmitting the PRS signals via the satellite to the MES as a single composite signal, B_SES, determining if each B_SES, C_SES and the pause periods of all of the PRS signals from the SESs are in common phase synchronization with each other as they arrive at the MES, generating an error correction code (ECC) which defines the amount and direction of phase deviation of any of B_SES, C_SES or pause periods from common phase synchronization, transmitting the composite signal from the MES to the SESs with common periodic pause periods therein and with the ECC signal contained in such common pause periods, and correcting the phase of B_SES, C_SES, and the pause period of each PRS_SES at the SESs so that they are phase synchronized with each other at the MES.

Claims

1. A communication system comprising:

a satellite;

a master earth station (MES);

a plurality of small earth stations (SES) each comprising first means including a signal transmission means for generating signal transmissions addressed and transmittable to a selectable other SES via the satellite, the MES, and then the satellite again;

said satellite comprising first signal processing means responsive to said signal transmissions from said SESs to retransmit said signal transmissions to said MES;

said signal transmissions consisting of a stream of bits representing orthogonal pseudo random sequence (PRS) signals (PRS_SES) which in turn consist of chips arranged in predetermined and identifiable patterns and with periodic pause periods in said streams of PRS signals and with bit, chip and pause period occurrence rates B_SES, C_SES, and P_SES, respectively, being synchronized with each other as they arrive at the MES;

said MES comprising means responsive to said signal transmissions from said satellite to amplify and retransmit said signal transmissions as a composite signal with a common pause period to said satellite;

said satellite comprising second signal processing means responsive to said signal transmissions from said MES to retransmit said signal transmissions to said SESs;

said MES comprising logic to compare the phases of the B_SES, the C_SES, and the P_SES of all of the PRS_SES signals and to generate error correction command (ECC) signals defining the deviation of the phase of any of said B_SES, said C_SES, or said P_SES from common synchronization as they arrive at said MES; and

said MES and said SESs further comprising cooperative means responsive to said ECC signals to maintain synchronism between the bit and chip rates of said PRS_SES signals as they arrive at said MES.

2. In a data communication system including a plurality of small earth stations (SES), a satellite, and a master earth station (MES), a method of transmitting signal transmissions each consisting of a series of time synchronous orthogonal pseudo random sequence (PRS) signals, each in turn consisting of N time synchronous chips arranged in a predetermined pattern, from a first SES to a second SES and comprising the steps of:

generating a stream of PRS signals consisting of bits and chips of bit and chip rates B_SES and C_SES at selected ones of said SESs and having pause periods occurring periodically in said stream of PRS signals;

transmitting said PRS signals to said satellite and then from said satellite to said MES as a single composite signal with B_SES and C_SES and the pause periods all synchronized;

determining if each B_SES, C_SES and the pause periods of all of said PRS signals from said SESs are in common phase synchronization with each other at the time of arrival thereof at said MES;

generating an error correction code (ECC) defining the amount and direction of phase error with respect to said common phase synchronization of any of said B_SES, C_SES or pause periods;

transmitting said composite signal from said MES to said SESs with common periodic pause periods therein and with said ECC signal contained in one or more of said common pause periods; and

correcting the phase of the B_SES, C_SES, and pause period of each PRS_SES at said SESs so that they are all in phase synchronization with each other at the time of arrival thereof at said MES.

3. In a data transmission system comprising a plurality of small earth stations (SES), a master earth station (MES), and a satellite, a method of transmitting data between a first selectable SES (SES_A) and a second selectable SES (SEShd C) via said satellite and the MES, where a data bit is encoded on each of a string of orthogonal pseudo random sequence (PRS) signals at a bit rate B_SES each of said PRS signals in turn consists of W chips arranged in a predetermined pattern with a chip rate C_SES, and comprising the steps of:

generating PRS signals PRS_A and PRS_C with periodic pause periods at said first and second SESs for first hop transmissions to said MES via said satellite;

generating a PRS signal PRS_M of chip rate C_M and bit rate B_M at said MES with periodic pause periods therein followed by the transmission to and the reception back of said PRS_M signal from said satellite;

determining the phase difference between B_A, C_A, and the periodic pause periods of PRS_A and PRS_M at said MES;

generating an error correction command (ECC) signal defining the amount and direction of said phase differences;

detecting the occurrence of the pause period in all of the PRS signals originating in the SESs upon their first hop arrival at the MES from the SESs;

creating a common pause period for retransmission from the MES of the PRS signals received from the SESs and for the transmission of the PRS_M signal from the MES;

inserting said ECC signal in said common pause period;

transmitting all of the PRS signals received from the SESs and the PRS_M signal as a composite signal from the MES to said satellite as a second hop transmission;

detecting and decoding the ECC signal containing the common pause period at the SES to which the ECC signal is addressed; and

correcting the phases of B_A, C_A and the pause period of PRS_A so that they will be in synchronism with the phases of B_M, C_M, and the pause period of the returned PRS_M at the MES after PRS_A has been transmitted to the MES via said satellite.

4. A communication network comprising:

a satellite;

a master earth station (MES);

a plurality of small earth stations (SES) each comprising logic comprising only one transmitter for generating and transmitting in a first transmission hop to said MES via said satellite a stream of orthogonal pseudo random sequence (PRS) signals PRS_SES each consisting of a plurality of chips occurring at a chip rate C_SES and arranged in orthogonal 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 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 bit and chip clock rate B_M and C_M, respectively;

said MES further comprising means for receiving the PRS signals (PRS_SES) and for generating a signal in response to the phase difference between C_M and the C_SES of each SES, between B_M and the B_SES, and between the pause periods of each SES as they arrive at the MES indicating the amount and direction of such phase differences;

said MES further comprising logic for retransmitting the received PRS_SES signals as a composite signal with a common periodic pause period therein and for inserting in such common pause periods the generated ECC signal; and

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

5. 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_A to said MES via said satellite in a first transmission hop and then from said MES to a second SES_B 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 with periodic pauses P therein which are synchronous when received at said MES and with a PRS signal (PRS_SES) uniquely coded to each SES and with each PRS signal PRS_SES representing a data bit of bit rate B and having a chip rate C;

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

means for retransmitting the received PRS signals to SES_A and SES_B with the ECC signal occurring during the said common pause period of the retransmitted PRS signals;

said first SES_A comprising logic responsive to the ECC signal transmitted from said second SES_B via the satellite and said MES to correct the phases of B, C, and P of the PRS signals generated at said first SES_A to be synchronized with the phases of B_M, C_M and P_M at the time of arrival of the components of the PRS signals having rates of B, C, P, B_M, C_M, and P_M at the MES.

6. A transmission system as in claim 5 in which each SES comprises means for generating a train of M=N-X data bits at a bit rate of B of N bits 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 signal;

means for generating a common pause period for retransmission of said composite PRS signal to SES_A and SES_B ; and

means for inserting ECC signal in said common pause period for subsequent transmission to said first SES_A ; and

in which said first SES_A comprises logic for detection of the ECC signal transmitted in said common pause period of the transmission from the MES via said satellite and the decoding of the ECC signal contained therein to correct the phase of B, C, and P of the PRS of SES_A.