Method and system providing unified DPSK-PSK signalling for CDMA-based satellite communications

• US 6,072,770 A
• Filed: 03/04/1997
• Issued: 06/06/2000
• Est. Priority Date: 03/04/1997
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Ho, Jin-Meng, Sharma, Ramautar
• Primary Examiner(s): Hsu, Alpus H.
• Assistant Examiner(s): Previl, Daniel
• Application Number:
  US08/808,777
• Time in Patent Office: 1,190 Days
• Field of Search: 370/315, 370/320, 370/323, 370/316, 370/209, 370/208, 370/204, 370/335, 370/342, 370/441, 375/200, 375/206, 375/208
• US Class Current: 370/209
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: H04L 27/2071 in which the data are represented by the carrier phase, e.g. systems with differential coding
• CPC Class Codes: H04L 27/2332 using a non-coherent carrier

Abstract

A method and a system for multi-user communications in a CDMA-based satellite network. An uplink RF signal containing a coded user message that has been differentially phase encoded and spread using a Walsh function and a pseudo-random number (PN) sequence for the uplink, is received by a satellite receiver. The received uplink RF signal is non-coherently quadrature demodulated and then despread using the uplink PN sequence and Walsh function. The differential phase signal carrying the coded user message is regenerated onboard the satellite by phase comparison and switched to a selected downlink transmitter. The quadrature components of the differential phase signal are then respread using a Walsh function and a PN sequence for the downlink, followed by quadrature modulation for transmission to a terrestrial receiver. The received downlink RF signal is coherently quadrature demodulated and despread using the PN sequence and Walsh function for the downlink. The downlink carrier phase originated from the uplink differential phase is regenerated from the despread quadrature baseband components and, hence, the coded user message is detected and decoded.

Claims

1. A method for signaling in a CDMA-based satellite communications network, comprising the steps of:

receiving an RF signal over an uplink, the RF signal containing a coded user message that has been differentially phase encoded, and spread using two code sequences associated with the uplink;

non-coherently quadrature demodulating the RF signal into quadrature baseband components;

despreading the quadrature baseband components using the two code sequences associated with the uplink;

phase comparing consecutive blocks of the despread quadrature baseband components for regenerating the differential phase signal carrying the coded user message;

switching the regenerated differential phase signal to a selected downlink transmitter;

respreading the quadrature baseband components of the differential phase signal using two code sequences associated with a downlink; and

impressing the respread quadrature baseband components of the differential phase signal onto quadrature components of a downlink carrier to form a downlink RF signal.

2. The method according to claim 1, further comprising the step of transmitting the downlink RF signal.

3. The method according to claim 1, wherein the RF signal received over the uplink is received at a satellite and the downlink RF signal is transmitted from a satellite transmitter.

4. The method according to claim 1, wherein the two code sequences associated with the uplink include a user Walsh function and a beam pseudo-random number sequence for the uplink;

and

wherein the two code sequences associated with the downlink include a user Walsh function and a beam pseudo-random number sequence for the downlink.

5. The method according to claim 1, further comprising the steps of:

grouping coded user message bits into successive groups at an uplink transmitter;

generating a differential phase for each message bit group by mapping each message bit group on to a predetermined PSK constellation;

generating an absolute phase for each message bit group by adding the differential phase for a current message bit group to an absolute phase for a message bit group that is preceding the current message bit group;

phase modulating an uplink carrier using the absolute phase signal to form an RF signal;

spreading the RF signal using the two code sequences associated with the uplink; and

transmitting the spread RF signal on the uplink.

6. The method according to claim 5, wherein the uplink RF signal is transmitted from a terrestrially-based transmitter and received at a satellite receiver.

7. The method according to claim 5, wherein the two code sequences associated with the uplink include a user Walsh function and a beam pseudo-random number sequence for the uplink.

8. The method according to claim 1, further comprising the steps of:

receiving the downlink RF signal, the downlink RF signal containing the user message that has been regenerated, respread and impressed onto quadrature components of the downlink RF signal;

coherently quadrature demodulating the downlink RF signal into quadrature baseband components;

despreading the quadrature baseband components using the two code sequences associated with the downlink;

evaluating a downlink carrier phase from the despread quadrature baseband components; and

recovering the user message.

9. The method according to claim 8, wherein the downlink RF signal is transmitted from a satellite transmitter and received at a terrestrially-based receiver.

10. The method according to claim 8, wherein the two code sequences associated with the downlink include a user Walsh function and a beam pseudo-random number sequence for the downlink.

11. A method for signalling in a CDMA-based satellite network, comprising the steps of:

grouping coded user message bits into successive groups at an uplink transmitter;

generating a differential phase for each message bit group by mapping each message bit group on to a predetermined PSK constellation;

generating an absolute phase for each message bit group by adding the differential phase for a current message bit group to an absolute phase for a message bit group preceding the current message bit group;

phase modulating an uplink carrier using the current absolute phase to form an RF signal;

spreading the RF signal using two code sequences associated with the uplink; and

transmitting the spread RF signal on the uplink.

12. The method according to claim 11, wherein the uplink RF signal is transmitted from a terrestrially-based transmitter and received at a satellite receiver.

13. The method according to claim 11, wherein the two code sequences associated with the uplink include a user Walsh function and a beam pseudo-random number sequence for the uplink.

14. A method for signalling in a CDMA-based satellite network, comprising the steps of:

receiving a phase shift keyed downlink RF signal, the downlink RF signal containing a user message that has been regenerated from a differentially phase shift keyed uplink RF signal, respread and impressed onto quadrature components of the downlink RF signal;

coherently quadrature demodulating the downlink RF signal into quadrature baseband components;

despreading the quadrature baseband components using two code sequences associated with the downlink;

evaluating a downlink carrier phase from the despread quadrature baseband components; and

recovering the user message.

15. The method according to claim 14, wherein the downlink RF signal is transmitted from a satellite transmitter and received at a terrestrially-based receiver.

16. The method according to claim 14, wherein the two code sequences associated with the downlink include a user Walsh function and a beam pseudo-random number sequence for the downlink.

17. A CDMA-based satellite communications system, comprising:

an RF receiver for receiving an RF signal over an uplink, the RF signal containing a coded user message that has been differentially phase encoded, and spread using two code sequences associated with the uplink;

a non-coherent quadrature demodulator for non-coherently quadrature demodulating the RF signal into quadrature baseband components;

a spread-spectrum despreader for despreading the quadrature baseband components using the two code sequences associated with the uplink;

a phase comparator for phase comparing consecutive blocks of the despread quadrature baseband components and regenerating the differential phase signal of the coded user message;

a switch for switching the regenerated differential phase signal to a selected downlink transmitter;

a spread-spectrum spreader for respreading the quadrature baseband components of the differential phase signal using two code sequences associated with a downlink; and

a quadrature modulator for modulating a downlink carrier using the respread quadrature baseband components of the differential phase signal to form a downlink RF signal.

18. The CDMA-based satellite communications system according to claim 17, further comprising a satellite transmitter for transmitting the downlink RF signal to a terrestrially-based receiver.

19. The CDMA-based satellite communications system according to claim 17, wherein the CDMA-based communications system is a satellite transceiver.

20. The CDMA-based satellite communications system according to claim 17, further comprising:

a PSK mapper for mapping coded user message bits into differential phases, the coded user message bits being grouped into blocks of message bits prior to being differentially phase mapped;

a differential phase encoder for generating a current absolute phase for each block of message bits by adding the differential phase for a current block of message bits to an absolute phase for a block of message bits preceding the current block of message bits;

a PSK modulator for phase modulating an uplink carrier using the current absolute phase to form an RF signal;

a spread-spectrum spreader for spreading the RF signal using the two code sequences associated with the uplink; and

a transmitter for transmitting the spread RF signal on the uplink.

21. The CDMA-based satellite communications system according to claim 20, wherein the RF signal for the uplink is transmitted by a terrestrially-based transmitter.

22. The CDMA-based satellite communications system according to claim 20, wherein the two code sequences associated with the uplink include a user Walsh function and a beam pseudo-random number sequence for the uplink, and

wherein the two code sequences associated with the downlink include a user Walsh function and a beam pseudo-random number sequence for the downlink.

23. The CDMA-based satellite communications system according to claim 17, further comprising:

a downlink receiver for receiving the downlink RF signal;

a coherent quadrature demodulator for coherently quadrature demodulating the downlink RF signal into quadrature baseband components;

a spread-spectrum despreader for despreading the quadrature baseband components using the two code sequences associated with the downlink;

a phase comparator for evaluating a downlink carrier phase from the despread quadrature baseband components; and

a channel decoder for detecting and decoding the coded user message.

24. The CDMA-based satellite communications system according to claim 23, wherein the downlink RF signal is received by a terrestrially-based receiver.

25. A CDMA-based satellite communications system, comprising:

a PSK mapper for mapping coded user message bits into a differential phases, the coded user message bits being grouped into blocks of message bits prior to being differentially phase mapped;

a differential phase encoder for generating a current absolute phase for each block of message bits by adding the differential phase for a current block of message bits to an absolute phase for a block of message bits preceding the current block of message bits;

a PSK modulator for phase modulating an uplink carrier using the current absolute phase to form an RF signal;

a spread-spectrum spreader for spreading the RF signal using two code sequences associated with the uplink; and

a transmitter for transmitting the spread RF signal on the uplink.

26. The CDMA-based satellite communications system according to claim 25, wherein the RF signal for the uplink is transmitted by a terrestrially-based transmitter.

27. The CDMA-based satellite communications system according to claim 25, wherein the two code sequences associated with the uplink include a user Walsh function and a beam pseudo-random number sequence for the uplink.

28. A CDMA-based satellite communications system, comprising:

a downlink receiver for receiving a downlink RF signal, the downlink signal being regenerated from a differentially phase shift keyed uplink RF signal;

a coherent quadrature demodulator for coherently quadrature demodulating the downlink RF signal into quadrature baseband components;

a spread-spectrum despreader for despreading the quadrature baseband components using two code sequence associated with the downlink;

evaluating a downlink carrier phase from the despread quadrature baseband components; and

recovering the user message.

29. The CDMA-based satellite communications system according to claim 28, wherein the downlink RF signal is received by a terrestrially-based receiver.

30. The CDMA-based satellite communications system according to claim 28, wherein the two code sequences associated with the downlink include a user Walsh function and a beam pseudo-random number sequence for the downlink.

31. A method for signaling in a CDMA-based satellite communications network, comprising steps of:

receiving a differentially phase shift keyed RF uplink signal; and

transmitting a phase shift keyed RF downlink signal, the phase shift keyed RF downlink signal being regenerated from the differentially phase shift keyed uplink RF signal.

32. A CDMA-based satellite communications system, comprising:

an RF receiver receiving a differential phase shift keyed RF uplink signal; and

a transmitter transmitting a phase shift keyed RF downlink signal, the phase shift keyed RF downlink signal being regenerated from the differentially phase shift keyed uplink RF signal.